Abstract:
A single-pass endocardial lead electrode adapted for implantation on or about the heart and for connection to a system for monitoring or stimulating cardiac activity including a lead body with a circumferential outer surface. The lead includes a first distal end electrode which has a first electrical conducting surface which is for positioning within the ventricle of the heart. The lead body also has a second electrode which has a second electrical conducting surface adapted for positioning within the atrium of the heart. Both of the first and the second electrodes are adapted for positioning and fixation to the wall. An active fixation element is used as part of the second electrode. The lead body also includes a curved portion which facilitates the positioning and fixing of the second electrode. 
     In another embodiment, the main lead body includes a recess into which an atrial lead body and the active fixation element attached to one end can travel from a recessed position to a position for fixation to the wall of the heart. The active fixation element which can also be moved by turning the terminal pin.

Description:
RELATED APPLICATIONS 
     This patent application is a division of Ser. No. 09/121,006, filed Jul. 22, 1998, now U.S. Pat. No. 6,152,954, issued on Nov. 28, 2000, the specification of which is hereby incorporated by reference. This patent application is also related to U.S. patent application Ser. No. 09/121,018, entitled “SINGLE PASS DEFIBRILLATION/PACING LEAD WITH PASSIVELY ATTACHED ELECTRODE FOR PACING AND SENSING” which is assigned to a common assignee and is filed on a date even herewith. The related application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of leads for correcting arrhythmias of the heart. More particularly, this invention relates to a lead having an electrode for more effective delivery of electrical charges to the heart. 
     BACKGROUND OF THE INVENTION 
     Electrodes implanted in the body for electrical cardioversion or pacing of the heart are well known. More specifically, electrodes implanted in or about the heart have been used to reverse (i.e., defibrillate or cardiovert) certain life threatening arrhythmias, or to stimulate contraction (pacing) of the heart, where electrical energy is applied to the heart via the electrodes to return the heart to normal rhythm. Electrodes have also been used to sense and deliver pacing pulses to the atrium and ventricle. The electrode in the atrium senses the electrical signals that trigger the heartbeat. The electrode detects abnormally slow (bradycardia) or abnormally fast (tachycardia) heartbeats. In response to the sensed bradycardia or tachycardia condition, a pulse generator produces pulses or signals to correct the condition. The same node used to sense the condition is also used in the process of delivering a corrective pulse or signal from the pulse generator of the pacemaker. 
     There are four main types of pulses which are delivered by a pulse generator. Two of the signals or pulses are for pacing the heart. First of all, there is a pulse for pacing the heart when it is beating too slowly. The pulses trigger the heart beat. The pulses are delivered at a rate to increase the heart rate to a desired level. The second type of pacing, called antitachycardia pacing, is used on a heart that is beating too fast. In antitachycardia pacing, the pacing pulses are delivered initially at a rate faster than the beating heart. The rate of the pulses is then slowed until the heart rate is at a desired level. The third and fourth type of pulses are used when the heart is beating too fast and the heart is fibrillating. The third type is called cardioversion. This is delivery of a relatively low energy shock, typically in the range of 0.75 to 1 joule, to the heart. The fourth type of pulse or signal is a defibrillation signal which is the delivery of a high energy shock, typically up to 34 joules, to the heart. 
     Sick sinus syndrome and symptomatic AV block constitute the major reasons for insertion of cardiac pacemakers today. Cardiac pacing may be performed by the transvenous method or by electrodes implanted directly onto the epicardium. Transvenous pacing may be temporary or permanent. In temporary transvenous pacing, an electrode lead is introduced into a peripheral vein and fluoroscopically positioned against the endocardium. The external terminals of the leads are connected to an external cardiac pacemaker which has an adjustable rate and milliamperage control. Temporary transvenous pacing is utilized (1) prior to the insertion of a permanent pacing system and (2) in situations in which the indication for pacing is judged to be reversible (drug-induced AV block or bradycardia) or possibly irreversible and progressive (AV and bundle branch blocks associated with myocardial infarction). 
     Permanent transvenous pacing is implanted under sterile surgical conditions. An electrode lead is generally positioned in the right ventricle and/or in the right atrium through a subclavian vein, and the proximal electrode terminals are attached to a pacemaker which is implanted subcutaneously. 
     Some patients require a pacing system to correct an abnormally slow heart (bradycardia condition) as well as a defibrillation system to detect when the heart starts beating abnormally fast (tachycardia condition) and to defibrillate or deliver a pulse to the heart to correct the abnormally fast heartbeat. In the past, a common practice for a patient having both of these conditions would be to provide two different leads attached to the heart. One would be implanted for delivering pacing signals to the heart to correct for the bradycardia condition. A separate lead would be implanted to sense a fast beating heart and defibrillate the heart to correct for the tachycardia condition. One lead is placed in the atrium and the other lead is placed in the ventricle. 
     Having two separate leads implanted within the heart is undesirable for many reasons. Among the many reasons are that the implantation procedure for a implanting two leads is more complex and also takes a longer time when compared to the complexity and time needed to implant a single lead. In addition, two leads may interact with one another after implantation or in vivo which can result in dislodgment of one or both of the leads. In vivo interaction may also cause abrasion of the insulative layer along the lead which can result in an electrical failure of one or both of the leads. Another problem is that as more leads are implanted in the heart, the ability to add other leads is reduced. If the patient&#39;s condition changes over time the ability to add leads is restricted. Two separate leads also increase the risk of infection and may result in additional health care costs associated with implantation and follow-up. 
     Because of these problems, a single lead having electrodes for both pacing and sensing in both chambers of the heart has been used. These leads are called single pass lead designs. Current single pass lead designs have problems. One of the more significant problems is that current single pass lead designs utilize “floating” electrodes or electrodes which are not attached to the endocardial wall of the heart. The floating electrodes lay in the blood pool or against the endocardial wall of the heart and the electrode may move slightly within the heart. The electrode positioned within the atrium of a single-pass endocardial lead generally is an electrically conductive cylindrical ring or semicylindrical ring structure, which does not allow for tissue ingrowth into the electrode. Since the location of the electrodes is not fixed with respect to the atrial wall, the electrical performance of these electrodes varies and is generally less than optimal. Both the electrical sensing capability as well as the pacing delivery capability of such electrodes are suboptimal. The pacing parameters of such a floating electrode are also suboptimal. 
     Some atrial leads have passive fixation elements that affix to the atrium over time. A problem with these leads is that the electrodes are much more likely to be displaced from the wall of the atrium than those that have an active fixation element. When the electrodes are placed far from the wall, there can be some fairly substantial effects. For example, the electrode may be unable to sense a tachycardia condition. Another example might be that signals for pacing may be ineffective. Additional power may have to be used to pace the heart thereby depleting energy from the battery of the pulse generator of the pacing system. 
     There is a real need for a single-pass endocardial pacing lead that has an electrode for active fixation to the wall of the atrium of the heart. A single-pass lead equipped with such an electrode would allow for better sensing capability and better pacing delivery to the heart. In addition, there is a need for a single-pass lead having an electrode for positioning within the atrium that allows for tissue ingrowth. Tissue ingrowth further enhances the electrical performance of the electrode. In addition, the lead and electrode is further stabilized within the heart as a result of tissue ingrowth. There is also a need for a single-pass endocardial lead which has an electrode for placing within the right atrium of the heart that accommodates eluting anti-inflammatory drugs. 
     SUMMARY OF THE INVENTION 
     A single-pass endocardial lead electrode adapted for implantation in the heart and for connection to a system for monitoring or stimulating cardiac activity includes a lead body with a circumferential outer surface. The lead includes a first distal end electrode or pair of electrodes for positioning in the ventricle and a second proximal electrode or pair of electrodes for positioning in the atrium. The second electrode or pair of electrodes are adapted for positioning and fixation to the wall of the atrium of the heart. An active fixation element is used as part of the second electrode or electrode pair. The lead body also may include a curved portion which facilitates the positioning and fixing of the second electrode or second pair of electrodes. The lead body also includes at least one recess for positioning an active fixation element within the recess. 
     In another embodiment, the recess is able to house the active fixation electrode as well as a portion of a lead body associated with the atrium (atrial lead body). By moving the terminal pin with respect to a yoke, the lead body is moved out of the recess. The atrial lead body can be a straight lead or a J-shaped lead. The type of atrial lead body used will depend on the placement of the lead within the atrium of the heart and the preference of the surgeon doing the placement. The advantage is that the active fixation electrode is placed into the recess during placement of the lead to prevent it from attaching inadvertently to the subclavian vein or other tissue while it is being inserted. 
     One of the embodiments includes the use of an active fixation electrode that can be controllably moved from a recessed position to an attachment position by rotating the terminal pin attached to the conductor coil which is attached to the body of the active fixation electrode. 
     Advantageously, the electrodes are attached to the endocardium so that the electrical signals received from the heart are better than with floating, unattached electrodes. In addition, the active fixation electrodes can be placed into a recess so that mechanisms, such as a helical hook, used to attach the electrode to the wall of the heart will not catch undesired tissue. A further advantage is that only one lead needs to be placed into the patient to do both sensing and pacing of all types. The lead can also be shaped to facilitate placement of the lead. 
     The extendable portion of the lead is mechanically isolated from the main lead body so that the helical screw or hook can turn independently of the lead body. In other words, the body of the lead does not need to be turned to affix the helical screw to the heart. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the single-pass endocardial lead for electrically stimulating the heart. 
     FIG. 2 is a cross section view of the atrial electrode of the single-pass endocardial lead showing the active attachment element in a retracted position. 
     FIG. 3 is a cross section view of the atrial electrode portion of the lead showing the active attachment element for active attachment to the atrial wall of the heart in an extended position. 
     FIG. 4 is a side view of another embodiment of a lead for active fixation attachment to the atrial wall of the heart. 
     FIG. 5 is a side view of the embodiment of the lead shown in FIG. 4 with the atrial lead body in an extended position for active attachment to the atrial wall of the heart. 
     FIG. 6 is a side view of the embodiment of the lead shown in FIG. 4 with the atrial lead body in an extended position for active attachment to the atrial wall of the heart. 
     FIG. 7 is a perspective view of another embodiment of a lead for active fixation to the wall of the heart. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     Curved Lead with Atrial Active Fixation Element 
     This invention is directed toward an active fixation element used in several types of leads. One type of lead will be described first to not only describe one embodiment of the invention but to also set forth generally the environment of the invention. After describing the first lead embodiment, the active fixation element will be detailed. Next, the other embodiments of the lead will be described. 
     FIG. 1 is a side view of one type of lead  100  for delivering electrical pulses to stimulate the heart. The lead  100  is comprised of a connector terminal  110  and a lead body  120 . The lead  100  attaches to a pulse sensor and generator  140 . The lead body has a number of electrodes in the distal end  130  which is implanted within the heart. The connector terminal  110  electrically connects the various electrodes and conductors within the lead body to a pulse sensor and generator  140 . The pulse sensor and generator  140  contains electronics to sense various pulses of the heart and also produce pulsing signals for delivery to the heart. The pulse sensor and generator  140  also contains electronics and software necessary to detect certain types of arrhythmias and to correct for them. Physicians are able to program the pulse sensor and generator to correct a particular arrhythmia that the patient may have. It should be noted that there are numerous types of connector terminals which connect to a pulse sensing and generating unit  140 . The lead terminal connector  110  provides for the electrical connection between the electrodes on the lead  100  and pulse generator  140 . The connector terminal end  110  shown is designed to international IS-1Standard ISO 5841-3(E). 
     The lead body  120  is cylindrical in shape. The lead body  120  is a tubing material formed from a polymer biocompatible for implantation, and preferably the tubing is made from a silicone rubber polymer. The silicone rubber polymer tubing contains several electrical conductors. The electrical conductors are made of a highly conductive, highly corrosion-resistant material which is formed into a helix. Several separate electrical conductors are housed within the lead body  120 . When there is more than one such electrical conductor within the lead body  120 , the lead is called a multifilar lead. The electrical conductors carry current and signals between the pulse sensor and generator  140  and the electrodes located at the distal end  130  of the lead  100 . 
     After the lead  100  has been implanted, the distal end  130  of the lead body  120  is situated within the heart. The distal end  130  of the lead body  120  includes a curved or bias portion  150  and a straight portion  160 . 
     After implantation, the curved or biased portion  150  will generally be located in the right ventricle of the heart. The straight portion  160  of this lead body will generally be located in the right atrium. The distal end  130  of the lead  100  has four electrodes. The first electrode  154  is provided at the farthest distal end of the lead for the purpose of delivering ventricular pacing therapy. The first electrode  154  is generally called the distal electrode. A second electrode  153  is located near the first or distal electrode  154  and can be used as a counter electrode for electrode  154  or as a current source for defibrillation therapy. This electrode  153  is sometimes referred to as a ventricular shocking coil. A third electrode  161  is located at a more proximal position for the purpose of delivering atrial pacing therapy. This electrode  161  is intended to be actively attached to the atrial wall of the heart. The third electrode  161  is also referred to as the proximal electrode. A fourth electrode  162  is located near the electrode  161  and can be used as a counter electrode for electrode  161  or as part of a defibrillation therapy system. The fourth electrode  162  is sometimes called the SVC shocking coil. The lead  100  may be generally described as a tachycardia or tachy lead. The shocking coils  153  and  162  are electrically conductive rings made of an alloy of platinum and iridium which is highly conductive and highly resistant to corrosion. The electrode  161  uses the active fixation element described below. The electrode  154  may include an active fixation or passive fixation portion. It should be noted that the lead shown and described above is a bipolar lead in that the positive and negative portions of a circuit are located in the lead body  100 . It should be noted that this lead may also be made a unipolar lead. In other words, one electrode of the lead body  100  can be the shocking coil and the other electrode can be the signal generator. 
     The shape of the curved portion  150  of the lead is important. The relaxed shape of the lead body  120  conforms to the shape the lead is expected to take after implantation. The distal portion of the straight portion  160  and the proximal portion of the curved portion  150  are biased to conform to the mid-portion of the atrial wall. This shape facilitates the placement of electrode  161  against the atrial wall during implantation. Furthermore, because the natural unstressed shape of the lead before implantation is approximately the same after implantation, this reduces the nominal residual stresses in the lead body. Also, this will reduce the nominal forces between the atrial wall and the point of attachment of the electrode  161  in the atrium. The shape of the middle and end portions of portion  150  conforms to the shape of the upper ventricular chamber below the tricuspid valve and ventricular septal wall. This shape will tend to cause the lead  100  to lie across the top of the ventricle in a gradual arc with the electrode  153  lying against the ventricular septum and electrode  154  resting in the ventricular apex. This lead position is advantageous because the arc shape will tend to reduce the transmitted forces between the lead fixation points at electrode  161  in the atrium and electrode  154  in the ventricle as they move relative to each other during heart rhythm. This preformed shape will ease the surgeon&#39;s task of positioning of lead  100  and, particularly, of the electrode end  130  such that less time is required and the placement procedure is less prone to error. 
     As mentioned previously, electrode  161  is designed to be attached to the wall of the atrium of the heart. FIG. 2 shows electrode  161  in a recessed position. FIG. 3 shows electrode  161  actively attached to the wall of the atrium. In this embodiment, the electrode  161  includes an active fixation screw  163  which is a helical screw. The atrial electrode  161  is configured to initially rest inside the lead body  120 , and then extend and rotate independent of the lead body  120  for atrial attachment. FIG. 2 shows the electrode  161  and the fixation screw  163  resting within the lead body. A seal  170  is shown in FIGS. 2 and 3. The seal  170  prevents body fluids from traveling into the recess in the lead body. The seal  170  is made of a biocompatible material such as silicone rubber. The seal  170  may take any appropriate shape. In this instance, the seal  170  is shaped as a permanent O-ring affixed to the recess in the lead body. This covered position of the electrode  161  and active fixation screw  163  makes the lead placement process easier since the atrial electrode  161  does not snag the vein during initial venous access and subsequent movement of the lead to the heart. The seal  170  can also be used to hold a lubricant  300  within the recess of the body of the lead. The lubricant  300  will allow the atrial electrode  161  to move from inside the recess to outside the recess with greater ease. The lubricant can be a substance such as fluorosilicone which is biocompatible. 
     FIG. 3 shows the electrode  161  extended from the lead body. The electrode  161  and active fixation screw  163  move independent of the lead body. This relative movement allows the electrode to come in contact with the atrial wall without manipulation of the lead body  120 . The electrode  161  can then be fixed by rotating the atrial electrode  161  and attached fixation screw  163 . The fixation screw  163  of the atrial electrode  161  can be advanced and retracted independent of rotation of the lead body. The active fixation screw and attached electrode are controlled from the terminal end. This is shown by turning briefly to FIGS. 4 and 5. In FIGS. 4 and 5, there is a lead housed within a recess  450  in the lead body  410 . The lead housed within the recess  450  can be moved in and out of the recess  450  by moving a terminal end  442  longitudinally with respect to the lead body  410 . As shown in FIG. 4, the lead is within a recess when the terminal end  442  is positioned even with the other terminal ends. When the terminal end is moved toward the distal end of the lead, the lead within the recess  450  is moved out of the recess  450 . As shown in FIG. 3, this additional degree of freedom allows for movement of the lead body relative to the fixed atrial electrode  161  without unscrewing (or over-screwing) the electrode from the endocardial tissue. 
     Returning to FIG. 3, as mentioned previously, the electrically conductive portion  164  which either senses electrical energy produced by the heart or delivers pacing signals to the heart is a small radius electrode. The electrode  161  has a diameter in the range of 0.024 inches to 0.050 inches. The advantage of this small radius is ease of venous access and small surface area resulting in high impedance for saving energy. Saving energy makes the battery used to power the pulse generator  140  last longer. 
     Also shown in FIGS. 2 and 3 is a multifilar coil  165  and an electrically conductive sleeve  166 . The conductive sleeve  166  has the smaller radius electrode tip  164  attached at one end of the sleeve. At the other end of the sleeve  166 , the multifilar coil  165  is attached. The multifilar coil includes at least one conductor which is used to carry electrical signals to and from the electrode tip  164 . 
     It is contemplated that slight variations in the design could be used for a particular application as required. One such variation would be the provision of steroid elution from any of the electrodes  153 ,  154 ,  161  and  162 . Steroid elution can be provided by using one or more of the steroid-releasing technologies such as sleeves or collars positioned in close proximity to the electrodes or by the use of internalized steroid-containing plugs. Steroids are generally used in order to reduce the inflammation associated with attaching an electrode to the endocardial wall of the heart. By reducing the inflammation at the time of implantation, the threshold values associated with the electrodes are usually lower when compared to threshold values associated with electrodes that did not elute a steroid over the attachment site. An example of the composition of at least one collar is dexamethasone acetate in a simple silicone medical adhesive rubber binder or a steroid-releasing plug similarly fabricated. 
     Of course, for the active fixation embodiment of this invention shown in FIGS. 1-3, various advancing and locking mechanisms can be used to manipulate the atrial electrode  161  from the proximal end of the lead during implantation. 
     Various shapes of stylets can be placed within the lead to advance and position the lead within the endocardial wall of the heart. Once positioned correctly, an active fixation element is used to secure the electrode to the wall of the heart. A locking mechanism can be employed to keep the fixation element from moving from its attached position on the heart. 
     Quad Lumen With Yoke and Active Fixation 
     FIGS. 4,  5 , and  6  show several other closely related preferred embodiments of the invention. FIG. 4 is a side view of a lead  400  which includes an active fixation element for attachment to the atrial wall of the heart. The lead  400  includes a main lead body  410 , an atrial lead body (also shown in FIGS. 5 and 6) and a ventricle lead body  420 . The main lead body  410  is attached to a yoke  430 . The yoke  430  acts as a strain reliever and also has a series of terminal pins  440 ,  442  and  444  attached to the yoke/strain reliever  430 . The terminal pins  440 ,  442  and  444  are attached to the pulse generator (not shown). The main lead body  410  is longer than as shown; a break has been put into the main lead body  410  to illustrate that the main lead body  410  is longer than that shown in FIG.  4 . The main lead body  410  includes a recess  450 . The atrial lead body (shown in FIGS. 5 and 6) fits within the recess  450  in the main lead body  410 . When the atrial lead body is housed within the recess  450 , an active fixation element on the end of the atrial lead body and associated with the proximate electrode is also housed within the recess. Advantageously, the active fixation element will not hook or snag tissue when it is housed within the recess  450 . Typically, the atrial lead body is pulled back or housed within the recess  450  when the lead  400  is being surgically implanted into the patient. Typically, the lead  400  is placed in the subclavian vein of the patient and then passed through the subclavian vein to the inner chambers of the heart. Once the lead and, more specifically, the distal electrode and the proximal electrode are within the ventricle and atrium of the heart, the various leads are removed from their respective recesses so that a surgeon can attach them to the inner wall of the heart. 
     FIG. 5 is a side view of the embodiment of a lead  400  shown in FIG.  4 . FIG. 5 has a J-shaped atrial lead body  500  which emerges from the recess  450  in the main body of the lead  410 . On the end of the atrial lead  500  is an active fixation element  510 . The active fixation element  510  typically includes a helically shaped hook for screwing into the atrium of the heart. The J-shape of the lead facilitates positioning of the end of the electrode having the active fixation element  510  to a desired position within the atrium. The J-shape eases positioning within the atrium of the heart when certain portions of the atrium are the target for connection of the active fixation element  510 . Once properly positioned, a surgeon can turn the active fixation element  510  causing it to hook the tissue in the inner wall of the heart. The atrial lead  500  is moved with respect to the recess by pushing the terminal pin from  442  forward with respect to the yoke  430 . A conductor connects the terminal pin  442  and the active fixation element  510 . By moving the terminal pin  442  inward with respect to the yoke  430 , the conductor moves with respect to the main body  410  of the lead  400 ′. This causes the atrial lead body  500  to emerge or pass through or pass out of the recess  450  in the main body  410 . The terminal pin  442  and the active fixation element attached to it move independently of the lead body  400 . Twisting the terminal pin causes the active fixation element  510  on the atrial lead  500  to turn and affix itself to the atrial wall of the heart. A locking mechanism may be provided to prevent the active fixation element  510  from “backing out” after it has been affixed to the wall. The atrial lead  500  is prestressed so that it will take the J-shape upon leaving or coming out of the recess  450 . 
     FIG. 6 is a side view of another embodiment of the lead shown in FIG.  4 . In this particular embodiment, the lead  400 ″ has a straight atrial lead  600  which comes out of the recess  450  in the main lead body  410 . The position of the atrial lead  600  is controlled by movement of the terminal pin  442  with respect to the yoke  430 . Moving the terminal pin with respect to the yoke  430  causes the atrial lead  600  to come out of the recess  450 . An active fixation element  510  is positioned on the end of the atrial lead  600 . Once the surgeon positions the atrial lead  600  and the active fixation element  510  at the end of the atrial lead in a proper position or desired position, the active fixation element  510  is used to attach the proximal electrode to the endocardial wall of the atrium. 
     FIG. 7 shows another embodiment of the invention wherein the atrial lead portion  600  does not have the ability to move in and out of a recess. Rather, the atrial lead  600  is permanently extended with respect to the lead body  410 . The active fixation element  510  on the atrial lead  600  is covered with a dissolvable coating  710 , such as mannitol. The dissolvable coating  710  remains intact during insertion of the lead  400 ″ through the subclavian vein and into the heart. The dissolvable coating  710  prevents the active fixation element  510  from catching tissue in the vein during insertion. The coating dissolves to expose active fixation element  510  and allow it to be turned into the atrial wall of the heart. In FIG. 7, the dissolvable coating  710  is depicted by a dotted line enclosure around the active fixation element  510 . Both leads have an exposed active fixation element and both are actually covered with the dissolvable coating. The terminal pin  442  is turned to rotate the active fixation element  510 . The active fixation element  510  can be turned or rotated independently of the lead body  410 . 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.