Patent Description:
Currently, angioplasty balloons are used to open calcified lesions in the wall of an artery. However, as an angioplasty balloon is inflated to expand the lesion in the vascular wall, the inflation pressure stores a tremendous amount of energy in the balloon until the calcified lesion breaks or cracks. That stored energy is then released and may stress and injure the wall of the blood vessel.

Electrohydraulic lithotripsy has been typically used for breaking calcified deposits or "stones" in the urinary or biliary track. Lithotripsy electrodes may similarly be useful for breaking calcified plaques in the wall of a vascular structure. Shock waves generated by lithotripsy electrodes may be used to selectively fracture a calcified lesion to help prevent sudden stress and injury to the vessel or valve wall when it is dilated using a balloon. It may therefore be useful to find improved ways to form shock waves in a balloon.

<CIT> discloses an apparatus including a balloon which is inflatable with liquid. It further includes a shock wave generator with the balloon that produces a shock wave.

<CIT> discloses a stone disintegrator apparatus comprising a main capacitor for receiving power from a power source, a charge circuit for charging the main capacitor, and a discharge circuit which is turned on during the discharge so as to supply a charge of the main capacitor to discharge electrodes.

The invention is described in claim <NUM>, to which reference should now be made. Additional, optional features are given in the dependent claims. Methods of treatment or surgery are not claimed.

Described herein are devices and systems that comprise one or more shock wave electrodes that may be suitable for use in angioplasty and/or valvuloplasty procedures. Generally, shock wave electrodes are provided along an axially extending elongate member (e.g., catheter) and may be attached to a source of high voltage pulses, ranging from <NUM> kV to <NUM> kV for various pulse durations. In some variations, the electrodes may be surrounded by an enclosure carrying a conductive fluid (e.g., saline). In some variations, the enclosure may comprise a balloon surrounding a portion of the elongate member and configured to be filled with a conductive fluid, where the electrodes may be enclosed within and spaced from the balloon walls.

A controller may be coupled to the first electrode pair to deliver a series of energy pulses to produce shock waves. The shock waves generated may disrupt calcified obstructions in an artery or a valve. One mechanism for shock wave formation is described below. When a high voltage is applied across a pair of electrodes located within the conductive fluid, a plasma arc may form between them, giving rise to a steam bubble in the fluid. A first shock wave may occur when the steam bubble first forms and a second shock wave may occur as the steam bubble collapses. Shock waves may be mechanically conducted through the fluid to apply mechanical force or pressure to break apart any calcified plaques on, or in, the vasculature walls.

The size, rate of expansion, and collapse of the bubble (and therefore, the magnitude, duration, and distribution of the mechanical force) may vary based on the magnitude and duration of the voltage pulse. Furthermore, the timing and size of the bubble, along with the sonic output and propagation direction of the resultant shock waves, depend at least in part on the location, geometry, size, condition, and distances between the electrodes (electrode gap distance). For example, an increase in electrode gap distance decreases the corresponding sonic output. The size and arrangement of the electrodes may also impact the types of vascular structures that may be accessed and treated by a shock wave device. Shock wave electrodes may be made of materials that can withstand high voltage levels and intense mechanical forces (e.g., about <NUM>-<NUM> psi or <NUM>-<NUM> ATM (approximately <NUM>-<NUM> MPa) in a few microseconds) that may be generated during use. For example, the electrodes may be made of stainless steel, tungsten, nickel, iron, steel, and the like.

Generally, current flowing between a pair of electrodes in a conductive fluid causes movement of metal from the positive terminal to the negative terminal, eventually depleting the positive terminal electrode of material, and may be referred to as one-sided erosion when a direction of current flow is fixed. Shock wave electrodes may experience a high rate of wear and erosion with every pulse applied due to the necessarily high current (e.g., hundreds of amps) flowing through the fluid, heat generated by the plasma arc, and mechanical shock wave forces.

The devices, systems, and methods described herein may help to reduce the rate of electrode wear to enhance electrode durability and shock wave consistency. The longevity of an electrode pair may depend on at least one of the following: polarity of a voltage pulse, length of a voltage pulse, magnitude of a voltage pulse, material properties, fluid conductivity, electrode gap distance between conductive regions of each of the electrodes in an electrode pair, and/or the surface area of the conductive region(s) of the electrodes in the pair. A longer pulse may increase the wear/erosion of an electrode pair as compared to a shorter pulse. In some variations where the electrode pair has different sized electrodes where one electrode has a smaller conductive region surface area than the other electrode, the electrode with the smaller conductive region may be more susceptible to erosion than the electrode with a larger conductive region. That is, the electrode with the smaller conductive region may erode at a greater rate than the electrode with the larger conductive region. The devices and methods described herein may help to even out the rate of erosion between the electrodes in an electrode pair, so that the electrodes erode at approximately the same rate. This may enhance the durability of the overall electrode pair, and may also facilitate uniform energy delivery to the electrode pair over a greater number of pulses.

It should be appreciated that a shock wave device generates the strongest shock waves when the electrodes are dissimilar in size where the smaller electrode has a positive polarity and the larger electrode has a negative polarity. Thus, while an electrode pair having a small, positive terminal electrode and a large, negative terminal electrode may form the strongest shock wave, this combination of size and polarity may shorten the lifetime of the electrode pair. The problem of a short lifespan may not be a simple matter of increasing electrode size since the size of a shock wave device and electrodes may be limited by the size of the vasculature through which it is advanced. However, voltage polarity switching, as described in further detail below, may facilitate electrode longevity while maintaining electrode size such that the electrode can be navigated through vasculature. Additionally or alternatively, voltage polarity switching may facilitate a reduction in electrode size with a similar electrode longevity relative to a non-polarity switching device.

Furthermore, the devices, systems, and methods described herein may facilitate the uniformity of shock wave intensity formed at different sites along a shock wave device. In some variations, a shock wave device may comprise a plurality of spaced apart electrode pairs connected in series. The shock waves generated by the electrode pairs may vary in strength even if the size and shape of the electrode pairs are the same. For instance, identical electrode pairs in series positioned <NUM> degrees apart from each other may form shock waves of varying strength from opposing sides of the device. This difference may be negligible for any single pulse. However, over a series of pulses, one side of the shock wave device may be more effective at cracking calcium deposits than the other side of the device. Voltage polarity switching, as described in further detail below, may facilitate the uniformity of shock wave intensity formed in different electrode pairs.

For example, a controller may cause current to flow through an electrode pair in a first direction for some pulses and in a second direction that is opposite to the first direction for other pulses. As an example, the direction of current flow may vary pulse to pulse or every second pulse, and is not particularly limited. It should be noted that the pulses are outputted discretely such that there is an interval of time between pulses when current does not flow through a shock wave device. The duration of the interval of time may be pre-selected according to, for example, a desired rate or frequency of shock wave generation. Furthermore, each pulse has a single direction of current flow and does not switch within the pulse. For instance, a voltage polarity switch may switch only when current is not flowing to the shock wave device (i.e., the voltage polarity switch may only occur in the interval between voltage pulses, and not during a voltage pulse).

Furthermore, the direction of current flow may vary randomly for each pulse so long as the total number of pulses maintain a predetermined current flow direction ratio. For example, for a set of <NUM> pulses being split evenly in the first direction and the second direction, the direction of current flow need not switch every pulse. As an illustrative example, <NUM> pulses in the first direction may be followed by <NUM> pulses in the second direction, then <NUM> pulses in the first direction, <NUM> pulses in the second direction, and <NUM> pulses in the first direction. Accordingly, while the total number of pulses is split evenly between the first and second direction, the number of switches in current flow does not necessarily correspond to the current flow ratio direction.

In some variations, a single pulse may be provided in the second direction with the remaining pulses in the first direction, and vice-versa. This allows the electrode pair to produce shock waves with a greater number of pulses before failure relative to an electrode pair receiving pulses with a constant polarity. Durability may thus be improved by distributing the electrode wear of the positive pulse over both electrodes.

In one variation, the current may flow in a first direction for about half of the pulses in the series and in the second, opposite direction for about the other half of the pulses in the series. In doing so, each electrode is set to be the positive terminal for about half of the pulses, thereby distributing the number of high erosion positive pulses experienced by any one of the electrodes about equally between the electrodes in the pair. The direction of current flow may be switched one or more times. In some cases, the electrode pair longevity may be about doubled relative to electrodes having a single direction of current flow, allowing more shock waves to be formed and/or the electrode pair to be formed smaller relative to electrodes having a single direction of current flow. Therefore, the shock wave devices described herein may be particularly useful in small arteries such as coronary arteries. Moreover, a shock wave device comprising a plurality of electrode pairs having pulses with current flow in both directions may facilitate the uniformity of shock wave intensity generated by the electrode pairs.

Generally described here are shock wave devices for angioplasty and/or valvuloplasty procedures. The devices and methods described here may use one or more devices or elements described in <CIT> and titled "LOW PROFILE ELECTRODES FOR AN ANGIOPLASTY SHOCK WAVE CATHETER," and/or one or more devices or elements described in <CIT> and titled "SHOCK WAVE BALLOON CATHETER WITH MULTIPLE SHOCK WAVE SOURCES,".

<FIG> is a block diagram of a controller <NUM> coupled to an electrode assembly <NUM>. Electrode assembly <NUM> may comprise a first electrode <NUM>, a second electrode <NUM>, and a third electrode <NUM>. The first electrode <NUM> may be connected to a first voltage output terminal V01 of a voltage source of the controller <NUM> by first wire <NUM>, the third electrode <NUM> may be connected to a second voltage output terminal V02 of a voltage source of the controller <NUM> by a second wire <NUM>, and the second or common electrode <NUM> may be provided in series between the first electrode <NUM> and third electrode <NUM>. Upon application of a sufficient voltage pulse, a first plasma arc may form between the first electrode <NUM> and the second electrode <NUM> (i.e., a first electrode pair), and a second plasma arc may form between the second electrode <NUM> and the third electrode <NUM> (i.e., a second electrode pair). The first and second electrode pairs are connected in series, where the second electrode <NUM> is shared between the first and second electrode pairs. Although electrode assembly <NUM> is described above as comprising three electrodes that form two electrode pairs, some variations of an electrode assembly may comprise two electrodes that form one electrode pair.

A first direction of current flow <NUM> of an energy pulse may be delivered to the electrode assembly <NUM> by a voltage source <NUM> of the controller <NUM>. The controller <NUM> may cause other pulses delivered to the electrode assembly <NUM> to have a second direction <NUM> of current flow that is the opposite direction of the first direction <NUM>. The controller <NUM> may select a direction of current flow, and thus the voltage polarity of the electrodes, for each pulse delivered to the electrode assembly <NUM>. In order to select a direction of current flow, the controller <NUM> may comprise a voltage polarity switch <NUM> to switch a polarity of the electrodes <NUM>, <NUM> between positive and negative where the electrodes <NUM>, <NUM> have opposite polarities.

In some variations, for a series of pulses, the controller may cause current to flow through the electrode pair in a first direction for some of the pulses in the series and in a second direction opposite the first direction for the remaining pulses in the series. In one variation, a first direction of current flow may be provided for at least one of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In yet another variation, a first direction of current flow may be provided for at least about a third of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In still another variation, a first direction of current flow may be provided for at least about half of the pulses.

In still other variations, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>.

It should be appreciated that these examples are non-limiting. For example, the controller may provide current delivery in a first direction for every pulse except for one pulse provided in the second direction, and vice versa. The number of pulses in each direction of current flow (e.g., ratio of current flow of first direction to second direction) may be determined based on a desired longevity of the shock wave device, shock wave uniformity, shock wave energy, and so forth. In some variations, a first direction of current flow provided for about half of the pulses may maximize the longevity of the shock wave device.

The number of transitions between current flow directions is not particularly limited. In some instances, the direction of current flow may be switched according to the ratio of pulses in the first direction to the second direction. For example, the direction of current flow may transition every pulse when there are an equal number of positive and negative pulses. However, the direction of current flow may also vary randomly for each pulse so long as the total number of pulses maintains a predetermined ratio of current flow direction. Accordingly, the direction of current flow need not switch for every pulse even if the number of pulses in each direction is equal. As another example, alternating on average the direction of current flow of the pulses may about double the durability of the smaller electrodes, and thus the lifetime of the electrode assembly. Even when the electrodes in an electrode pair are of equal size, alternating the direction of current flow so that each electrode receives about the same number of positive pulses will distribute the wear over two electrodes so as to about double the durability of the electrode pair relative to electrodes receiving a single direction of current. It should be noted that polarity switching of any number of pulses aids durability (e.g., the number of shock waves the electrode generates before electrode failure).

Moreover, shock waves output from different electrode pairs may facilitate uniformity of shock wave forces between the shock wave sites on average as polarity switching allows each electrode pair to receive the positive pulse. This allows more predictable results with a higher average shock wave strength delivered at each shock wave site. For example, <FIG> is an illustrative graph of energy delivered as a function of pulse number for a static (constant polarity) shock wave device and a switching (alternating polarity) shock wave device. In <FIG>, the electrical energy delivered by the polarity-switching shock wave device is higher on average per pulse and decays less than the energy delivered to the constant polarity device. The electrical energy delivered may be positively correlated with shock wave strength.

Next, the second electrode <NUM> illustrated in <FIG> may have a cylindrical or ring shape, similar to that depicted in <FIG> as discussed in further detail below. However, for the ease of explanation, <FIG> depict a flattened second electrode <NUM> to illustrate the different voltage polarities that may be applied to the electrode assembly <NUM>. In <FIG>, the controller <NUM> may output one or more positive pulses in a first direction <NUM> of current flow where the first wire <NUM> is coupled to a positive terminal of a voltage source <NUM> of the controller <NUM> and the first electrode <NUM>, and the second wire <NUM> is coupled to a negative terminal of a voltage source of the controller <NUM> and the third electrode <NUM>. In use, the application of the voltage pulse creates a plasma in the fluid that extends across the electrode pairs and permits conduction of the current. The current then flows from the first electrode <NUM> to second electrode <NUM>, and then to third electrode <NUM>. Plasma formation thus creates two electrode pairs connected in series. As discussed above, the positive terminal first electrode <NUM> may experience a higher rate of wear than the negative terminal third electrode <NUM> when receiving a positive pulse from the controller <NUM>.

Conversely, in <FIG>, a negative terminal first electrode <NUM> may deplete less material than the positive terminal third electrode <NUM> when receiving a negative pulse in a second direction <NUM> of current flow from a voltage source <NUM> of the controller <NUM>. In order to distribute the wear between the first electrode <NUM> and third electrode <NUM> more evenly, the controller <NUM> may cause a current to flow in a first direction <NUM> for some of the pulses (<FIG>) and in a second direction <NUM> opposite the first direction <NUM> for the other pulses (<FIG>). As a consequence, the electrode assembly <NUM> may form a greater number of shock waves with improved consistency before one or both of the smaller electrodes (<NUM>, <NUM>) are depleted and the electrode assembly <NUM> fails.

Furthermore, as shown in <FIG>, the first electrode <NUM> and the third electrode <NUM> will have opposite voltage polarities no matter the direction of current flow. Therefore, the strength of the shock waves formed by the first electrode pair and the second electrode pair will differ for every pulse. In the illustrated embodiment, the conductive region of the first electrode <NUM> and the third electrode <NUM> may be smaller than the conductive region of the second electrode <NUM>. Accordingly, the first electrode pair receiving the positive pulse <NUM> (<FIG>) may generate a stronger shock wave than the second electrode pair. Similarly, the first electrode pair receiving the negative pulse <NUM> may generate a weaker shock wave than the second electrode pair.

However, by alternating positive and negative pulses to the electrode assembly <NUM>, the average shock wave strength output by the first electrode pair and the second electrode pair may be more uniform to reduce variability. This may provide more consistent and predictable treatment by the shock wave device such that a practitioner may not need to align the shock wave device in vasculature based on differences shock wave strength between electrode pairs.

<FIG> is a block diagram of another variation of a controller <NUM> coupled to the electrode assembly <NUM>. The electrode assembly <NUM> may comprise a first electrode <NUM>, second electrode <NUM>, and a third electrode <NUM>. The first electrode <NUM> and second or common electrode <NUM> form a first electrode pair, and the third electrode <NUM> and the second electrode <NUM> form a second electrode pair. A first direction of current flow <NUM> of an energy pulse may be delivered to the electrode assembly <NUM> by a voltage source <NUM> of the controller <NUM>. The controller <NUM> may cause other pulses delivered to the electrode assembly <NUM> to have a second direction of current flow <NUM> opposite the first direction <NUM> through the electrode assembly <NUM>. The voltage polarity switch <NUM> of the controller <NUM> may select a direction of current flow, and thus the voltage polarity of the electrodes, for each pulse delivered to the electrode assembly <NUM>.

In <FIG>, the first electrode <NUM> may be connected to a first voltage output terminal V01 of a voltage source <NUM> of the controller <NUM> by first wire <NUM>, the third electrode <NUM> may be connected to a second voltage output terminal V02 of a voltage source <NUM> of the controller <NUM> by a second wire <NUM>, and the second electrode <NUM> may be connected to a third voltage output terminal V03 (ground channel) of a voltage source <NUM> of the controller <NUM> by a third wire <NUM>. In some variations, the first voltage output terminal VO1 and the second voltage output terminal VO2 may be positive channels while the third voltage output terminal VO3 may be a negative channel for some of the pulses. The controller <NUM> may also set the first voltage output terminal VO1 and the second voltage output terminal VO2 to be negative channels while the third voltage output terminal VO3 may be a positive channel for the remaining pulses.

During a high voltage pulse on the first and/or second voltage output terminals VO1, VO2, current may flow in the first direction <NUM> or the second direction <NUM> over the first wire <NUM> and/or second wire <NUM> to respective first electrode <NUM> and third electrode <NUM>. The voltage source <NUM> of controller <NUM> may apply a positive or negative pulse on output terminal VO1 such that the potential difference between the first electrode <NUM> and the second electrode <NUM> is large enough to form a plasma arc between them, generating a bubble that gives rise to a shock wave. Similarly, the voltage source of the controller <NUM> may simultaneously or sequentially apply a positive or negative energy pulse on output terminal VO2 such that the potential difference between the third electrode <NUM> and the second electrode <NUM> is large enough to form a plasma arc between them, generating a bubble that gives rise to a different shock wave. In some variations, when energy pulses are applied to output terminals V01 and V02 simultaneously, a first shock wave formed between the first electrode <NUM> and the second electrode <NUM> and a second shock wave formed between the third electrode <NUM> and the second electrode <NUM> may be formed simultaneously.

Where the first electrode <NUM> and third electrode <NUM> are located circumferentially opposite to each other (e.g., <NUM> degrees apart from each other around the circumference of the elongate member), the shock waves generated by the first and second electrodes pairs may propagate in opposite directions, extending outward from the sides of a shock wave device. The current that traverses the bubble from the first electrode <NUM> and/or the third electrode <NUM> to the second electrode <NUM> may return via third wire <NUM> to voltage output terminal VO3 (which may be a ground channel). Voltage output terminals VO1 and VO2 may be independently addressed (e.g., voltage and current may be applied to one output but not necessarily the other), or may not be independently addressed (e.g., activating one output necessarily activates the other).

In another variation, <FIG> is a block diagram of a controller <NUM> coupled to the first and second electrode assemblies <NUM>, <NUM>. The first electrode <NUM> and the first common electrode <NUM> form a first electrode pair that may generate a first shock wave, and the second electrode <NUM> and the first common electrode <NUM> form a second electrode pair that may generate a second shock wave. Likewise, the third electrode <NUM> and the second common electrode <NUM> form a third electrode pair that may generate a third shock wave, and the fourth electrode <NUM> and the second common electrode <NUM> form a fourth electrode pair that may generate a fourth shock wave.

The first, second, third, and fourth electrode pairs may be connected in a series configuration and receive a series of pulses. A first direction of current flow <NUM> of some of the pulses in the series may be delivered to the first and second electrode assemblies <NUM>, <NUM> by a voltage source <NUM> of the controller <NUM>. The controller <NUM> may cause the remaining pulses in the series that are delivered to the first and second electrode assemblies <NUM>, <NUM> to have a second direction <NUM> of current flow through the electrode assemblies <NUM>, <NUM>. A voltage polarity switch <NUM> of the controller <NUM> may select a direction of current flow, and thus the voltage polarity of the electrodes, for each pulse delivered to the electrode assemblies <NUM>, <NUM>. For instance, the voltage polarity switch <NUM> may switch a polarity of the first electrode <NUM> and fourth electrode <NUM> between positive and negative, where the first electrode <NUM> and fourth electrode <NUM> have opposite polarities.

In some variations, the number of pulses in each direction of current flow (e.g., ratio of current flow of first direction to second direction) may be determined based on a desired longevity of the shock wave device, shock wave uniformity, shock wave energy, material properties, electrode gap distance, fluid conductivity, and so forth. In some instances, the direction of current flow may be switched according to the ratio of pulses in the first direction to the second direction. In other instances, the direction of current flow may vary randomly for each pulse so long as the total number of pulses maintains a predetermined ratio of current flow direction.

Furthermore, shock waves output from the first through fourth electrode pairs may have more uniform strength on average as polarity switching allows each electrode pair to receive positive pulses. This allows more predictable results, with a greater amount of electrical energy delivered to each electrode pair, which may facilitate the generation of stronger shock waves. Thus, a shock wave device may be able to more uniformly apply mechanical forces/pressures regardless of its orientation within the vasculature.

The first and second common electrodes <NUM>, <NUM> illustrated in <FIG> may in some variations have a cylindrical or ring shape, similar to that depicted in <FIG> as discussed in further detail below. However, for the ease of explanation, <FIG> depicts flattened first and second common electrodes <NUM>, <NUM> to illustrate the different voltage polarities that may be applied to the first and second electrode assemblies <NUM>, <NUM>. A voltage source <NUM> of the controller <NUM> may output one or more pulses where the first wire <NUM> is coupled to a positive terminal VO1 of controller <NUM> and the third wire <NUM> is coupled to a negative terminal VO2 of controller <NUM>. The second electrode <NUM> may be connected to the third electrode <NUM> via a second wire <NUM> (e.g., an interconnect wire). In this configuration, the first and second electrode assemblies <NUM>, <NUM> receive a positive pulse where the first and third electrode pairs generate stronger shock waves than the second and fourth electrode pairs.

Conversely, a voltage source <NUM> of the controller <NUM> may output one or more pulses where the first wire <NUM> is coupled to a negative terminal VO1 of controller <NUM> and the third wire <NUM> is coupled to a positive terminal VO2 of controller <NUM>. In this configuration, the first and second electrode assemblies <NUM>, <NUM> receive a negative pulse where the second and fourth electrode pairs generate the stronger shock waves. Therefore, in order to distribute the wear between the electrodes of the first and second electrode assemblies <NUM>, <NUM> more evenly, the voltage polarity switch <NUM> of the controller <NUM> may cause a current to flow in a first direction for some of the pulses in a series of pulses and in a second direction opposite the first direction for the remaining pulses in the series. As a consequence, the electrode assemblies <NUM>, <NUM> may form a greater number of shock waves before one or more of the smaller inner electrodes (<NUM>, <NUM>, <NUM>, <NUM>) are depleted, as well as more uniform shock waves propagated on average from the electrode assemblies (<NUM>, <NUM>).

<FIG> is an illustrative block diagram of a variation of a shock wave system <NUM> comprising a first electrode assembly <NUM>, a second electrode assembly <NUM>, a third electrode assembly <NUM>, fourth electrode assembly <NUM>, and fifth electrode assembly <NUM>. The first electrode assembly <NUM> may comprise a first electrode 302a, second electrode 302b, and a third electrode 302c having a structure analogous to first electrode <NUM>, second electrode <NUM>, and third electrode <NUM>, respectively, as depicted in <FIG>. As denoted symbolically in <FIG>, the conductive surface areas of the first electrode 302a and third electrode 302c may be smaller relative to the conductive surface areas of the second electrode 302b. In other variations, the larger electrode 302b may comprise individual electrodes connected by, for example, an interconnect wire. The second through fifth electrode assemblies <NUM>, <NUM>, <NUM>, and <NUM> may comprise a similar configuration of electrodes as first electrode assembly <NUM>.

The first and second electrode assemblies <NUM> and <NUM> are connected in series. The fourth and fifth electrode assemblies <NUM>, <NUM> are connected in series. As shown in <FIG>, the electrode assemblies <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are switchably connected in parallel to a controller <NUM>. The controller <NUM> may comprise a voltage source <NUM> to deliver pulses to the electrode assemblies <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. A multiplexer <NUM> of the controller <NUM> may selectively activate first and second electrode assemblies <NUM> and <NUM>, third electrode assembly <NUM>, and fourth and fifth electrode assemblies <NUM> and <NUM>. The multiplexer <NUM> may be configured to selectively connect the voltage source <NUM> across the parallel electrode assembly lines individually, one at a time, or in any combination. The controller <NUM> may further comprise a voltage polarity switch <NUM> configured to provide a first direction of current flow corresponding to a first switch position <NUM> and a second direction of current flow opposite the first direction, the second direction corresponding to a second switch position <NUM>.

For example, the voltage source <NUM> outputs a predetermined voltage pulse to the voltage polarity switch <NUM>. In the switch <NUM>, a direction of current flow is selected between a first direction of current flow and a second direction opposite the first direction. The multiplexer <NUM> may receive the energy pulse in either the first direction or the second direction, and then selectively deliver a series of pulses, having the current flow direction selected by the voltage polarity switch <NUM>, to the electrode assemblies <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> as illustrated in the timing diagram of <FIG>.

<FIG> is an illustrative timing diagram of a variation of a shock wave system <NUM> for selectively coupling electrodes to a power source with a selectively delivered direction of current. For example, the controller <NUM> may activate the different sets of electrode assemblies sequentially (e.g., one at a time) at a first voltage polarity and then activate the different sets of electrode assemblies sequentially at a second voltage polarity. This reserves all of the high voltage for each shock wave source to thus form shock waves of maximum strength to be applied to the calcium deposits all along the vasculature. Reversing the polarity in the subsequent pulse for each of the electrode assemblies <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> may distribute electrode wear and shock wave strength more evenly within the electrode pairs of the electrode assemblies, thus increasing the longevity and consistency of the shock wave device. In other examples, the voltage polarity of an electrode assembly may vary pulse to pulse, every second pulse, every third pulse, and is not particularly limited. Furthermore, the voltage polarity may vary randomly. For example, for a set of <NUM> pulses being split evenly between a first voltage polarity (e.g., positive pulse) and a second voltage polarity (e.g., negative pulse), the voltage polarity need not switch every pulse. As an illustrative example, <NUM> pulses at the first voltage polarity may be followed by <NUM> pulses at the second voltage polarity, then <NUM> pulses at the first voltage polarity, <NUM> pulses at the second voltage polarity, <NUM> pulses at the first voltage polarity, and <NUM> pulses at the second voltage polarity. Accordingly, while the total number of pulses is split evenly between the first and second voltage polarities, the number of switches in polarity does not necessarily depend on the current flow ratio.

In some variations, a multiplexer may be coupled to one or more of the electrode assemblies <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, as depicted in <FIG>. For example, any of the voltage polarity switching sequences discussed herein may be incorporated with the multiplexer <NUM>. In some variations, the selection of voltage polarity may be independent of the electrode assembly selected by a multiplexer. Alternating polarity and timing may provide the dual benefits of distributing positive pulse wear over multiple electrodes and increasing rest time for the electrode assemblies.

The polarity switching and multiplexing described above may be applied to any of the shock wave devices described herein, including the illustrative variations of <FIG> as described in detail below. In one variation, a shockwave device having a plurality of electrode assemblies is described. In particular, <FIG> depicts the distal portions of a shock wave device having two electrode assemblies <NUM>, <NUM>. In particular, <FIG> depicts one variation of a shock wave device <NUM> comprising an elongate member <NUM>, a first electrode assembly <NUM> at a first location along the length of the elongate member <NUM>, a second electrode assembly <NUM> at a second location along the length of the elongate member <NUM>, and optionally, an enclosure <NUM> configured to be fillable with a conductive fluid to sealably enclose the first and second electrode assemblies <NUM>, <NUM>. In some variations, the enclosure may comprise a membrane and/or a balloon may be made of an electrically insulating material that may be non-compliant (e.g., PET, etc.), semi-compliant (e.g., PBAX, nylon, PEBA, polyethylene, etc.), and/or compliant (e.g., polyurethane, silicone, etc.). The enclosure <NUM> may enclose any number of electrode assemblies.

The shock wave device <NUM> may comprise a fluid lumen (not shown) that is in communication with a fluid source that introduces a conductive fluid into the enclosure <NUM>. A voltage source (not shown) having a first terminal <NUM> and a second terminal <NUM> may be coupled to the shock wave device <NUM>. As discussed above, the polarity of the terminals <NUM>, <NUM> may vary per pulse or in a predetermined sequence. An energy pulse may be applied to the electrode pairs <NUM>, <NUM>, thereby generating one or more shock waves that may propagate through the fluid to impinge on a calcified obstruction. Although the shock wave device <NUM> in <FIG> is depicted as having two electrode pairs <NUM>, <NUM>, it should be understood that other variations may have a different number of electrode pairs (e.g., <NUM>, <NUM>, <NUM>, <NUM> or more electrode pairs).

In some variations, the electrode assemblies <NUM>, <NUM> each may comprise two inner electrodes that are positioned circumferentially opposite each other, an insulating sheath with two openings aligned over the two inner electrodes, and an outer common electrode with two openings that are coaxially aligned with the two openings of the insulating sheath. <FIG> illustrate one variation of an electrode assembly in this configuration including two inner electrodes and an outer common electrode. Each of the electrode assemblies <NUM>, <NUM> may be configured to generate a pair of directed shock waves, where the shock waves resulting from a high voltage pulse to the first inner electrode propagate in a direction that is opposite to the direction of the shock waves resulting from a high voltage pulse to the second inner electrode. In some variations, the electrode assemblies <NUM>, <NUM> may generate shock waves that propagate outward from different locations around the circumference of elongate member <NUM>. For example, the electrode assembly <NUM> may generate shock waves that propagate from the left and right longitudinal side of the elongate member, while the electrode assembly <NUM> may generate shock waves that propagate from the top and bottom longitudinal side of the elongate member <NUM>.

In other variations, the electrode assembly <NUM> may generate a pair of shock waves that propagate outward from positions at <NUM> degrees and <NUM> degrees around the circumference of the elongate member <NUM>, while the electrode assembly <NUM> may generate a pair of shock waves that propagate outward from positions at <NUM> degrees and <NUM> degrees around the circumference of the elongate member. In still other variations, electrode assemblies <NUM>, <NUM> may each generate a pair of shock waves that propagate outward at the same locations around the circumference of the elongate member, but from different locations along the length of the elongate member. Optionally, one or more radiopaque marker bands may be provided along the length of the elongate member to allow a practitioner to identify the location and/or orientation of the shock wave device <NUM> as it is inserted through the vasculature of a patient.

It should be appreciated that shock wave devices with a plurality of electrode assemblies distributed along the length of a catheter may be suitable for use in angioplasty procedures to break up calcified plaques that may be located along a length of a vessel. Shock wave devices with a plurality of electrode assemblies along the length of a curved elongate member may be suitable for use in valvuloplasty procedures to break up calcified plaques that may be located around the circumference of a valve (e.g., at or around the leaflets of a valve). It should be noted that the circuit diagram of <FIG> and the simplified layout of <FIG> correspond electrically to <FIG> embodiment, when the electrode assemblies <NUM>, <NUM> each include two electrode pairs as shown in <FIG>.

<FIG> depict top and bottom views, respectively, of one variation of a shock wave device having an electrode assembly <NUM> that may be configured to generate shock waves in opposite directions. <FIG> is a top view of the electrode assembly <NUM> where the first inner electrode <NUM> is depicted and <FIG> is a bottom view of the electrode assembly <NUM> where the second inner electrode <NUM> is depicted. The first and second inner electrodes share a common electrode <NUM> and are located circumferentially opposite each other (i.e., <NUM> degrees apart). The first electrode <NUM> may be connected to a first voltage output terminal VO1 of a voltage source of a controller (not shown in <FIG>) by a first wire <NUM> and the second electrode <NUM> may be connected to a second voltage output terminal V02 of a voltage source of the controller by a second wire <NUM>. The first electrode <NUM> and the common electrode <NUM> form a first electrode pair that may generate a first shock wave that propagates outwards in a first shock wave direction, and the second electrode <NUM> and the common electrode <NUM> form a second electrode pair that may generate a second shock wave that propagates outwards in a second shock wave direction that is opposite to the first shock wave direction. For a positive pulse provided in a first current direction <NUM>, current flows from the first electrode pair to the second electrode pair. Likewise, for a negative pulse provided in a second current direction <NUM> opposite the first current direction <NUM>, current flows from the second electrode pair to the first electrode pair.

A difference in surface area of conductive regions within an electrode pair may be provided to generate larger shock waves. For instance, the surface area of the edges of the first electrode <NUM> and the second electrode <NUM> may serve as conductive regions, and may be the portions of the electrodes which are most likely to wear due to high energy pulses. An electrode such as the common electrode <NUM> may form two conductive regions for each of the first and second electrodes <NUM>, <NUM> having different surface areas. In some variations, a surface area of a conductive region of the first electrode <NUM> and second electrode <NUM> may be smaller in surface area relative to the common electrode <NUM>. Therefore, the longevity of the electrode assembly <NUM> may depend on the rate of depletion of the smaller electrodes <NUM>, <NUM>.

As energy pulses are applied to the electrodes pairs to form shock waves, erosion of electrode material from the inner and outer electrodes may increase a distance between the electrodes in the electrode pair until a plasma arc is no longer to likely form. At this point, the electrode pair has failed and reached the end of its lifespan. As discussed in further detail below, the degree of erosion and wear may be determined by measuring one or more of voltage drop, voltage pulse width, low voltage analogs of voltage pulse width, and/or any signals that indicate (or are correlated with) the duration of a high-voltage pulse across an electrode pair.

<FIG> depicts a perspective view of the outer common electrode <NUM>. As depicted there, first opening <NUM> may be located directly across from second opening <NUM>. The outer common electrode <NUM> may have the second opening <NUM> coaxially aligned over the second inner electrode, and the first inner electrode <NUM> may be coaxially aligned with the first opening <NUM> of the outer common electrode <NUM>. This configuration may generate a first shock wave that propagates outwards in a first direction and a second shock wave that propagates outwards in a second direction that is opposite to the first direction.

Turning back to <FIG>, the wires <NUM>, <NUM> may be electrically insulated along their length (e.g., by an insulating coating or sheath made of, for example, polyimide, PEBA, PET, FEP, PTFE, etc.) except for one or more regions where the electrically conductive core of the wire is exposed to contact a portion of the inner and/or outer electrode. The wires <NUM>, <NUM> may be made of any conductive material, for example, free oxygen copper or copper or silver.

<FIG> depict top and bottom views of one variation of a shock wave device having a first electrode assembly <NUM> and a second electrode assembly <NUM> that may be configured to generate shock waves along a length of the shock wave device. The electrode assemblies <NUM>, <NUM> may be connected in series with respect to each other such that activating a first electrode assembly <NUM> also activates a second electrode assembly <NUM>. In some variations, it may be desirable to have multiple shock wave sources without as many wires and using fewer terminals on a controller. For example, connecting two electrode assemblies in series may allow the shock wave device to simultaneously generate up to four different shock waves using just two voltage output terminals (e.g., one positive channel and one negative channel). In addition, reducing the number of wires that extend along the length of the elongate member may allow the elongate member to bend and flex more freely as it is advanced through the vasculature of a patient (e.g., may allow for a tighter turning radius).

<FIG> is a top view of the electrode assemblies <NUM>, <NUM> where the first inner electrode <NUM> and the fourth inner electrode <NUM> are depicted. <FIG> is a bottom view of the electrode assemblies <NUM>, <NUM> where the second inner electrode <NUM> and the third inner electrode <NUM> are depicted. The first and second inner electrodes <NUM>, <NUM> share a first common electrode <NUM> and are located circumferentially opposite each other (i.e., <NUM> degrees apart). The third and fourth inner electrodes <NUM>, <NUM> share a second common electrode <NUM> and are also located circumferentially opposite each other. Alternatively, the inner electrodes and electrode assemblies may be offset from each other in some other manner as described above.

The first electrode <NUM> and the first common electrode <NUM> form a first electrode pair that may generate a first shock wave that propagates outwards in a first direction, and the second electrode <NUM> and the first common electrode <NUM> form a second electrode pair that may generate a second shock wave that propagates outwards in a second direction. Likewise, the third electrode <NUM> and the second common electrode <NUM> form a third electrode pair that may generate a third shock wave that propagates outwards in a third direction, and the fourth electrode <NUM> and the second common electrode <NUM> form a fourth electrode pair that may generate a fourth shock wave that propagates outwards in a fourth direction.

The first and second electrode assemblies <NUM>, <NUM> in <FIG> may be connected in series. The first electrode <NUM> may be connected to a first voltage output terminal V01 of a voltage source of a controller (not shown in <FIG>) by a first wire <NUM>. The second electrode <NUM> may be connected to the third electrode <NUM> via a second wire <NUM> (e.g., an interconnect wire). The fourth electrode <NUM> may be connected to a second voltage output terminal V02 of the voltage source of the controller by a third wire <NUM>. Therefore, for a positive pulse provided in a first current direction <NUM>, current flows (in ascending order) from the first electrode pair to the fourth electrode pair. Likewise, for a negative pulse provided in a second current direction <NUM> opposite the first current direction <NUM>, current flows (in descending order) from the fourth electrode pair to the first electrode pair. Each of the first through fourth electrodes <NUM>, <NUM>, <NUM>, <NUM> may be smaller in size relative to the first and second common electrodes <NUM>, <NUM>. In some variations, size may refer to the total size of the electrode and/or a surface area of a conductive region of the electrode. Therefore, the longevity of the electrode assemblies <NUM>, <NUM> may depend on the rate of depletion of the smaller electrodes <NUM>, <NUM>, <NUM>, <NUM>.

Any of the shock wave devices described herein may be provided in a shock wave system suitable for use in an angioplasty or valvuloplasty procedure. A shock wave system (not shown) may include a shock wave device, catheter, a high voltage pulse generator (e.g., voltage source), and/or an enclosure configured to be fillable with a conductive fluid. The catheter may have a guide wire lumen therethrough. In some variations, the high voltage pulse generator may be a <NUM> kV to <NUM> kV pulsed power supply, for example, a <NUM> kV to <NUM> kV pulsed supply.

Generally described here are methods for forming shock waves. Any of the shock wave devices described herein may be used in an angioplasty and/or valvuloplasty procedure. The methods described here may include advancing a guide wire from an entry site on a patient (e.g., an artery in the groin area of the leg) to a target region of a vessel (e.g., a region having calcified plaques that need to be broken up. A shock wave device may comprise an axially extending elongate member with a guide wire lumen, an electrode pair comprising a first electrode and a second electrode and/or an electrode assembly provided along a length of the elongate member. The electrode pair and/or electrode assembly may be any of the electrodes described herein.

In some variations, a balloon may be collapsed over the elongate member while the device is advanced through the vasculature. In some variations, the location of the shock wave device may be determined by x-ray imaging and/or fluoroscopy. When the shock wave device reaches the target region, the balloon may be filled with a conductive fluid (e.g., saline and/or saline mixed with an image contrast agent). A series of pulses may be delivered to the first electrode pair and/or electrode assembly to create shock waves that may break up calcified plaque, for example.

In some variations, current flows through the electrode pair and/or electrode assembly in a first direction for some of the pulses in the series and in a second direction that is opposite the first direction for the remaining pulses in the series. In one variation, a first direction of current flow may be provided for at least one of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In yet another variation, a first direction of current flow may be provided for at least about a third of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In another variation, a first direction of current flow may be provided for at least about <NUM>% of the pulses. In still another variation, a first direction of current flow may be provided for at least about half of the pulses.

In still other variations, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. In another variation, the ratio of current flow of the pulses in the first direction to the second direction may be about <NUM>:<NUM>. The number of pulses in each direction of current flow (e.g., ratio of current flow of first direction to second direction) may be determined based on a desired longevity of the shock wave device, shock wave uniformity, shock wave energy, and so forth.

The number of transitions of current flow directions is not particularly limited. In some instances, the direction of current flow may be switched according to the ratio of pulses in the first direction to the second direction. In other instances, the direction of current flow may vary randomly for each pulse so long as the total number of pulses maintains a predetermined ratio of current flow direction. Accordingly, the current flow direction need not switch for every pulse even if the number of pulses in each direction is equal. Alternating on average the direction of current flow of the pulses may about double the durability of the smaller electrodes, and thus the lifetime of the electrode assembly. Even when the electrodes in an electrode pair are of equal size, alternating the direction of current flow so that each electrode receives about the same number of positive pulses will distribute the wear over two electrodes so as to about double the electrode pair durability.

Furthermore, shock waves output from different electrode pairs may have more uniform strength on average as polarity switching allows each electrode pair to receive the positive pulse. This allows more predictable shock waves with less variance in shock wave strength.

The progress of the plaque break-up may be monitored by x-ray and/or fluoroscopy. The shockwave device may be moved along the length of the vessel if the calcified region is longer than the length of the elongate member with the electrode assemblies, and/or if the calcified region is too far away from the electrode assemblies to receive the full force of the generated shock waves. For example, the shockwave device may be stepped along the length of a calcified vessel region to sequentially break up the plaque.

Voltage and current measurements may be taken at the load (in this case, the electrode assembly) to determine the condition of the shock wave device as the pulses are delivered. As discussed in further detail below, measurements including voltage drop, voltage pulse width, and current flow may be used to determine a condition/longevity of the shock wave device.

In some variations, polarity switching of the pulses may be based on the condition of the electrodes in a shock wave device. For example, the direction of current flow of pulses in a series may be determined using measurements correlated to voltage drop, such as voltage pulse width, which may be correlated to the condition of the electrodes. For instance, a first voltage pulse width across the electrode pair may be measured for a first direction of current flow and a second voltage pulse width across the electrode pair may be measured for a second direction of current flow. A difference (if any) between the first voltage pulse width and the second voltage pulse width may indicate a difference in electrode wear. In some cases, differences in the degree of electrode erosion between the electrodes in a pair may lead to a shorter lifespan of the overall shock wave device. By switching the direction of current flow based on the measured voltage pulse widths to balance the wear between the first and second electrodes, the lifetime of a shock wave device may be prolonged.

In some variations, the direction of current flow for pulses in a series (e.g., the polarity of each of the voltage pulses in a series) may be selected according to the measured voltage pulse widths. For instance, the direction of current flow may be selected such that a difference between the voltage pulse width across the electrode pair when the current flows in a first direction and the voltage pulse width when the current flows in a second direction are within a predetermined threshold. In other variations, the direction of current flow may be selected such that the voltage pulse width across the electrode pair when the current flows in a first direction is substantially equal to the voltage pulse width across the electrode pair when the current flows in a second direction. The ratio of current flow of the pulses in a first direction to a second (opposite) direction (i.e., polarity ratio) may be determined at least in part by the measured voltage pulse width. For example, if the measured voltage pulse width in the first direction of current flow (i.e., first polarity) meets or exceeds a predetermined threshold, the controller may determine that the first electrode of the electrode pair has a greater degree of erosion than the second electrode of the electrode pair. The controller may then adjust the polarity ratio so that the second direction of current flow (i.e., second polarity) is increased relative to the first direction of current flow. This may help reduce or stabilize the erosion rate of the first electrode so that the overall electrode pair may be more durable (e.g., longer lifespan) as compared to a shock wave system where the polarity is not switched and/or polarity ratio is not adjusted.

The electrode assemblies of the shock wave device may be connected in series, and may be activated simultaneously and/or sequentially, as described above. For example, a pair of electrode assemblies may be connected in series and activated simultaneously or sequentially.

Once the calcified region has been sufficiently treated, the balloon may be inflated further or deflated, and the shock wave device and guide wire may be withdrawn from the patient. Wear of the shock wave device may be evaluated through visual inspection by microscopy.

In the following examples, test results are provided for electrodes to compare electrical energy delivery to a set of electrodes receiving using a constant polarity (static device) for every pulse and alternating polarity as described above (switching device). Electrical current, voltage, energy measurements, and visual inspection as a function of pulses were taken of an <NUM> gap copper coil emitter to determine erosion, electrode integrity, and electrode lifetime.

After pulsing the devices, bright field microscopy evaluation was performed to visually inspect the wear of the electrodes. It was determined that the positive terminals in the static device had more consumed conductor than the negative terminals. The switching device had more even wear than the static device. In <FIG> and <FIG> discussed below, the shock wave devices were pulsed at <NUM> or slower with a pulse width of about <NUM>.

<FIG> is an illustrative graph of voltage drop (kV) as a function of pulse number. Voltage drop is defined as the difference between the highest and lowest voltage prior to current flow (representing voltage losses which are correlated to electrode wear). As shown in <FIG>, voltage drop increases as a function of pulse number. However, static energy delivery has a much larger rate of voltage drop compared to switching energy delivery indicating more electrode wear. <FIG> illustrates the rate of voltage drop (slope a) having a linear best fit (R). From the linear best fits, the voltage losses represented by the voltage drop (kV) increase at a much faster rate <NUM> for static energy compared to the rate <NUM> for switching energy. It should be noted that the static shock wave device fails <NUM> at about <NUM> pulses before the switching shock wave device fails at about <NUM> pulses.

Although voltage drop is plotted in <FIG>, voltage pulse width correlates strongly with voltage drop such that measurements of voltage pulse width may be used to monitor the lifetime and/or condition of a shock wave device from pulse to pulse. For example, <FIG> are illustrative graphs comparing voltage drop as a function of pulse width for a non-switching electrode assembly and a switching electrode assembly, respectively. In <FIG>, line <NUM> represents the high correlation fit between voltage drop and pulse width for a non-switching shock wave device. Similarly, line <NUM> illustrates a high correlation fit between voltage drop and pulse width for a polarity switching shock wave device. The width of each pulse (e.g., voltage, current) is defined herein as the first time and the last time the pulse reaches <NUM>% of the maximum voltage peak value. Similar to voltage drop (kV), the voltage pulse width increases as a function of pulse number and is an indicator of electrode degradation. In other words, measurement of voltage pulse width may be used as a proxy for voltage drop to monitor the condition (e.g., degradation) of an electrode pair. That is, the longer the measured voltage pulse width, the more the electrode with the positive polarity has eroded or degraded. Alternatively, measurement of an internal signal that indicates the onset and offset of a high voltage pulse across an electrode pair may be used to monitor the condition of the electrodes. For example, the internal signal may be a trigger TTL output signal of the high voltage pulse generator.

<FIG> is an illustrative graph of pulse number as a function of voltage polarity. As discussed above, <FIG> is an illustrative graph of energy delivered as a function of pulse number. Since more pulses may be provided to a switching device than a static device, the lifetime of the switching device may be about double that of the static device. In <FIG>, it is apparent that the number of pulses and the average amount of energy delivered by the switching device is significantly more than the static device due to polarity switching. For instance, the static device provides about <NUM> pulses before static device failure <NUM> while the switching device provides about <NUM> pulses before switching device failure <NUM>.

The test results indicate that switching current flow direction may increase the lifetime and energy delivered of an <NUM> gap shock wave device over a constant current flow direction <NUM> gap shock wave device. Visual inspection also shows biased wear of the electrodes when a single direction of current flow is applied compared to alternating current flow. Experimental testing has shown that the voltage pulse width is directly proportional to energy voltage drop prior to current flow. Therefore, a static device has more voltage loss compared to a switching device. The voltage pulse width may be used as a metrology tool to monitor the lifetime and/or condition of a shock wave device from pulse to pulse. Thus, switching the direction of current flow may improve the efficiency and/or consistency of shock waves output by a shock wave device.

Claim 1:
A shockwave device (<NUM>) for treating lesions in a body comprising:
an axially extending elongate member (<NUM>);
a first electrode pair (<NUM>) comprising a first electrode (<NUM>) and a second electrode (<NUM>), wherein the first electrode pair (<NUM>) is carried on the elongate member (<NUM>) and positioned within a conductive fluid; and
a controller (<NUM>) coupled to the first electrode pair (<NUM>), said controller (<NUM>) including a voltage source (<NUM>) and a polarity switch (<NUM>), said controller configured to deliver a series of individual voltage pulses to the first electrode pair such that each of the voltage pulses creates a shock wave in the conductive fluid, wherein the controller (<NUM>) causes current to flow through the first electrode pair (<NUM>) in a first direction for some of the pulses in the series and in a second direction opposite the first direction for the remaining pulses in the series through operation of the polarity switch (<NUM>) and, said controller (<NUM>) further measuring voltage or current at the first electrode pair (<NUM>) and adjusting the ratio of voltage pulses delivered in the first and second directions based on the measurement.