Source: http://www.google.com/patents/US20030229380?dq=6,788,314
Timestamp: 2014-03-13 21:10:55
Document Index: 342803783

Matched Legal Cases: ['art 16', 'art 16', 'art 16', 'art 16', 'art 16', 'art 16', 'art 16', 'art 16']

Patent US20030229380 - Heart failure therapy device and method - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsThe heart rate of a patient with conditions such as chronic heart failure, ischemia, or acute myocardial infarction is reduced by electrically stimulating the right vagus nerve of the patient. A lead is implanted with electrodes in electrical communication with tissue proximate to the vagus nerve. A...http://www.google.com/patents/US20030229380?utm_source=gb-gplus-sharePatent US20030229380 - Heart failure therapy device and methodAdvanced Patent SearchPublication numberUS20030229380 A1Publication typeApplicationApplication numberUS 10/287,254Publication dateDec 11, 2003Filing dateOct 31, 2002Priority dateOct 31, 2002Publication number10287254, 287254, US 2003/0229380 A1, US 2003/229380 A1, US 20030229380 A1, US 20030229380A1, US 2003229380 A1, US 2003229380A1, US-A1-20030229380, US-A1-2003229380, US2003/0229380A1, US2003/229380A1, US20030229380 A1, US20030229380A1, US2003229380 A1, US2003229380A1InventorsJohn Adams, Clifton AlfernessOriginal AssigneeAdams John M., Alferness Clifton A.Export CitationBiBTeX, EndNote, RefManReferenced by (44), Classifications (8), Legal Events (1) External Links: USPTO, USPTO Assignment, EspacenetHeart failure therapy device and methodUS 20030229380 A1Abstract The heart rate of a patient with conditions such as chronic heart failure, ischemia, or acute myocardial infarction is reduced by electrically stimulating the right vagus nerve of the patient. A lead is implanted with electrodes in electrical communication with tissue proximate to the vagus nerve. A stimulator in electrical communication with the electrodes delivers electrical energy that stimulates the release of acetylcholine from the vagus nerve. The amount of energy may be determined in accordance with a difference between the patient's actual heart rate and a maximum target heart rate for the patient. Delivery of energy to the lead electrodes is preferably synchronized with the detection of a P-wave. Automatic adjustment of the target heart rate may be based on current day and/or time of day information, and patient physical activity. The voltage, pulse width, or number of pulses in the stimulation may be controlled. Images(15) Claims(131)
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0038] To appreciate the present invention, it is helpful to first understand aspects of a patient's nervous system and the interaction of the nervous system with the patient's heart. The parasympathetic nervous system is a part of a patient's overall autonomic nervous system. The parasympathetic nervous system primarily contains cholinergic fibers. Stimulation of a patient's parasympathetic nervous system tends to induce secretion of acetylcholine, increase the tone and contractility of smooth muscle, and to slow the heart rate. The cholinergic nerves to the heart are the right and left vagii. [0039] The right vagus innervates the sinoatrial (SA) node, the atrial muscle, and to a much lesser degree, the atrioventricular (AV) node. The left vagus innervates the AV node, and to a lesser degree, the SA node and atrial muscle. Stimulus of the vagii nerves results in the release of acetylcholine, the amount of which is related to the magnitude of the stimulation. Acetylcholine released by a stimulated right vagus nerve is quickly taken up by the SA node and acts to increase the delay from the current heart beat to the next heart beat. Because the right vagus nerve is known to be distributed primarily in the area of the SA node, electrical stimulation of tissue surrounding the SA node results in stimulation of the right vagus nerve. The present invention takes advantage of the phenomenon that stimulation of the right vagus nerve tends to slow the rate of excitation of the SA node and thereby reduce the patient's heart rate. As used in this patent document, the terms �right vagus nerve� and �vagus nerve� refers to and includes those nerves of the patient that control the delivery of acetylcholine that is taken up by the SA node. [0040]FIG. 1A illustrates one exemplary embodiment of an implantable device 10 constructed in accordance with the present invention. In the embodiment shown, the device 10 is attached to a catheter containing an electrical lead 12 that has been implanted in a patient's heart 16. The electrical lead 12, as illustrated, has a ring electrode along the length of the lead and a tip electrode at or near the end of the lead. In particular, the electrical lead 12 has a ring electrode 18 positioned near the junction of the superior vena cava (SVC) and tip electrode 20 in the right atrium of the heart 16. [0041] The electrodes 18 and 20, as illustrated, are positioned to sense electrical signals in the atrium of the heart 16 that reflect atrial activity, which signals are relayed to the device 10 for processing by control circuitry in the device 10. The electrodes 18 and 20 are also positioned to stimulate the portion of tissue proximate to the patient's right vagus nerve and SA node. Tissue is proximate to the right vagus nerve when stimulation of the tissue results in release of acetylcholine from the vagus nerve. The acetylcholine is taken up by the SA node. [0042] Furthermore, the tip electrode 20 may include a clamp or helical screw, as shown in FIG. 1A, to better secure the electrode to the atrial tissue. As noted earlier, stimulation of the right vagus nerve, in accordance with the present invention, is designed to release acetylcholine and increase parasympathetic tone in order to slowly reduce the normal rate of excitation of the SA node. [0043] The electrodes 18 and 20 may be comprised of electrodes commonly used in cardiac sensing and pacing. However, the atrial lead 12 is different than prior art atrial pacing leads in that the spacing between the electrodes 18 and 20 may be longer than 1 to 2 cm, as is common in pacing leads. This spacing is useful in the present invention to capture a wider area of cardiac tissue, which improves the ability to ensure the right vagus nerve fibers are located in the current path between the electrodes 18 and 20. The atrial lead 12 is also different than prior art pacing leads in that the atrial lead 12 may include a relatively sharp preshaped bend between the electrodes 18 and 20. The sharp bend enables the atrial lead 12 to effectively wrap around the junction of the SVC and right atrium, and surround the tissue where the right vagus nerve and SA node are located. [0044]FIG. 1B illustrates another exemplary embodiment of implantable device 10 that includes the electrical lead 12 shown in FIG. 1A, and additionally a catheter containing an electrical lead 14 that has been implanted in a patient's heart 16. The electrical lead 14 includes a ring electrode 22 and tip electrode 24 positioned within the right ventricle of the heart 16. The ring electrode 22 and tip electrode 24 are positioned to sense electrical signals that reflect ventricular activity, which signals are relayed to the device 10 for processing by control circuitry in the device 10. The ventricular lead 14 may be constructed using a bipolar RV pacing lead which is well known in the pacing art. When plotted, the electrical signals from the atrium (sensed through lead 12) produce an atrial electrogram. The electrical signals detected in the ventricle (sensed through lead 14) produce a ventricular electrogram. [0045]FIG. 2 illustrates an example of an atrial electrogram and ventricular electrogram for a patient with a normal sinus rhythm. The peak values in the atrial electrogram reflect electrical activity that results from contraction of the atrium. This peak in atrial electrical activity is commonly referred to as a P-wave. Subsequent to contraction of the atria, electrical activity in the purkinje system causes the ventricles to contract, pushing blood into the patient's peripheral circulation system. The peak electrical activity in the ventricular electrogram in FIG. 2 is commonly referred to as an R-wave. Some embodiments of the invention detect only P-waves; other embodiments include detection of R-waves. In any event, detection of R-waves is not necessary to practice the present invention. [0046] In some implementations of the device 10, it may be advantageous to further include components that monitor the patient's blood pressure and provide the blood pressure information to the control circuitry in the device 10 that controls the operation of the device. One example of a suitable blood pressure sensor measures impedance and may be applied to the surface of the subclavian or other convenient artery. Another example of a suitable sensor is a piezoelectric device attached to an artery that generates a voltage pulse reflective of the patient's blood pressure. As the device 10 slowly lowers the normal sinus rate of the patient, the blood pressure is monitored by the control circuitry to ensure it remains within an acceptable range. For instance, the control circuitry may include a memory with programmed blood pressure limits in the form of a look up table. If the detected blood pressure drops beyond limits designated in the look up table, the control circuitry of the device 10 may be configured to produce a control signal that causes the amount of stimulation being delivered to the patient to be reduced. By lowering the amount of parasympathetic stimulation, the effect on the patient's heart rate should be reduced, thereby allowing the heart to maintain blood pressure at an acceptable level. As the patient's blood pressure stabilizes, the amount of vagal stimulation may be increased back to previous levels. [0047] As noted earlier, the ring electrode 18 and tip electrode 20 are placed in close proximity to the atrial tissue next to and surrounding the right vagus nerve and ganglionic tissue. The stimulation of the right vagus nerve in this embodiment preferably occurs during the refractory period 28 (FIG. 2) following the P-wave in the atrium. For human patients, the atrial refractory period 28 is generally considered to be about 100 ms in duration. During the refractory period 28, the cells in the atrial muscle tissue are not susceptible to direct stimulation. However, the vagus nerve fibers can be stimulated during this time to release acetylcholine that is taken up by the SA node, causing a longer delay by the SA node before initiating the next P-wave. The amount of delay to the next atrial contraction is roughly proportional to the amount of energy delivered to the right vagus nerve in the stimulus. [0048] As shown in FIG. 3, a P-wave detector 48 in the device 10 monitors the atrial electrogram for a peak value that represents the P-wave in the patient's heat. When a P-wave is detected, the P-wave detector produces a logical output 26 (FIG. 2) that marks the detection of a P-wave. In similar fashion, embodiments of the invention that include R-wave detection have an R-wave detector 40 that monitors the patient's ventricular electrogram for a peak value indicative of an R-wave. When an R-wave is detected, the R-wave detector produces a logical output 27 that marks the detection of an R-wave in the patient's heart. The construction and function of P-wave detectors and R-wave detectors are well known in the art. Further information concerning the construction of the device 10, including P-wave and R-wave detectors, is provided below in regard to FIG. 3. [0049] The amount of energy in the stimulation delivered to the patient may be controlled by varying the voltage, duration, and/or frequency of the electrical pulses providing the stimulation. A higher voltage, longer duration, or higher number of pulses, with other factors kept equal, leads to a greater amount of energy being delivered in each stimulus, thus leading to an increased time interval to the next heart beat after each stimulus. Depending on patient circumstances and placement of the electrical leads, a pulse train longer than the atrial refractory period 28 should be avoided as it may directly stimulate an atrial contraction, thus speeding the heart rate rather than slowing it. [0050]FIG. 3 is a block diagram illustrating various major components of one embodiment of the device 10 shown in FIG. 1B. As described above, the device 10 includes control circuitry that controls the operation of the device. In the embodiment shown in FIG. 3, the control circuitry of the device 10 includes processor circuitry 30 in communication with a memory 32. The memory 32, which may be formed of any type of memory components, such as RAM, ROM, flash memory etc., may include programmed instructions carried out by the processor circuitry 30. In addition to or in place of programmed instructions, the processor circuitry 30 may also operate in accordance with hardwired circuitry in or connected to the processor circuitry 30. [0051] As shown in FIG. 1B, the atrial lead 12 includes two electrodes 18 and 20 positioned near or within the right atrium of the patient. Electrical activity sensed by these electrodes is communicated via the electrical lead 12 to one or more amplifiers 42 (FIG. 3). The amplified signals are filtered in one or more filters 44, which may be used to attenuate noise and/or other signal contaminants, for example. The one or more filters 44 may also be used to emphasize portions of the signals that are of particular interest. The filtered signals are then converted from analog to digital form in an analog-to-digital (A/D) converter 46. The signal information from the A/D converter 46 is delivered to the P-wave detector 48. In FIG. 3, the P-wave detector circuitry 48 is shown integrated with the processor circuitry 30. However, in other suitable embodiments, the P-wave detector 48 may be implemented by separate circuitry in communication with the processor circuitry 30. [0052] The amplifier(s) 42, filter(s) 44 and A/D converter(s) 46 used in the device 10 may be constructed of conventional off-the-shelf components. Similarly, the amplifier(s) (as) 34, filter(s) 36, and AID converter(s) 38 (discussed below) may also be constructed of conventional components. The selection and implementation of appropriate amplifiers, filters, and A/D converters is well within the ability of one having ordinary skill in the art of implantable devices for signal processing and cardiac therapy. [0053] Electrical activity sensed by electrodes 22 and 24 in the right ventricle (FIG. 1B) are delivered to the device 10 via the ventricular lead 14. As shown in FIG. 3, the electrical signals in the ventricular lead 14 are amplified by one or more amplifiers 34 and filtered by one or more filters 36. The amplified and filtered signals are then converted from analog to digital form in an A/D converter 38. The resulting digitized signals are then delivered to an R-wave detector 40 operating within or connected to the processor circuitry 30. Embodiments of the invention that do not include a ventricular lead 14, such as the embodiment shown in FIG. 1A, may exclude the amplifier 34, filter 36, A/D converter 38, and R-wave detector 40 as shown in FIG. 3. [0054] A power source 50 in the device 10, typically a long-life battery such as a lithium battery, provides electrical power to the sensors and circuitry in the device 10. A clock 62 in communication with the processor circuitry 30 keeps track of the current date and time, for purposes explained below. The clock 62 may also provide timing information as needed to the processor circuitry 30. Conventional components for implementing the clock 62 are well known and commercially available to those having ordinary skill in the art. [0055] The device 10, as illustrated in FIG. 3, includes further components, the function and operation of which are described below in more detail. These additional components include a stimulator 52 connected to the electrodes 18 and 20 on the atrial lead 12, an activity sensor 54 that senses physical activity of the patient, counters 56 integrated within or connected to the processor circuitry 30 for monitoring the patient's heart rate and delivery of therapy to the patient, programmed settings 58 in the memory 32 that include various target values and limits used in the operation of the device 10, and lookup tables 60 in the memory 32 used primarily to set the programmed settings 58. Those of ordinary skill in the art will recognize that FIG. 3 represents only one exemplary embodiment of the device 10. Other suitable embodiments of a device constructed according to the principles of the invention may include more or fewer components than those illustrated in FIG. 3. For example, the embodiment shown in FIG. 1A may include fewer components than the embodiment in FIG. 1B. Moreover, components (such as the stimulator 52 and processor circuitry 30) shown in FIG. 3 may be integrated or kept separate, as desired. The components shown in FIG. 3 are intended to illustrate the operation of at least one preferred embodiment of the invention, and are not intended to limit the scope of the invention. The features of the invention may also be integrated into other commercially available products, such as a conventional DDDR pacemaker, an ICD, and/or a biventricular pacemaker. [0056] The device 10 delivers stimulation to the right vagus nerve to reduce the patient's heart rate. The stimulator 52, preferably controlled by the processor circuitry 30, delivers electrical pulses to the right vagus nerve via the electrodes 18 and 20 on the atrial lead 12. The stimulator 52 may be comprised of any type of circuitry capable of delivering electrical energy to the atrial lead 12. For example, the stimulator 52 may be a programmable pulse generator that receives command input from the processor circuitry 30 that directs the voltage, pulse width, and/or number of pulses to be delivered from the stimulator 52 at each stimulus cycle. Alternatively, the stimulator 52 may be an electrode driver circuitry capable of delivering an electrical signal at a specified voltage. In that circumstance, the processor circuitry 30 controls the switching (on/off) of the driver circuit, as well as the voltage, to deliver the electrical pulses in the stimulus. Other suitable constructions for delivering electrical pulses may be used. Programmable pulse generators and electrode driver circuits as noted above are well known to those of ordinary skill in the art. [0057] For embodiments of the invention configured to drive a patient's heart rate downward to a maximum target rate, the target heart rate is preferably set by a physician. FIG. 4 illustrates heart rate reduction curves that may be programmed in the device 10 by a physician, as discussed further below. The curves depicted in FIG. 4 extend over a time period of three weeks measured in days after implantation (DAI) of the device 10. In one implementation, the reduction in heart rate over time may be approximately linear, as shown by the curve 70 in FIG. 4. In this example, the patient, at Day 0, has a target heart rate of 90 beats per minute (bpm). According to curve 70, over the following three weeks, the patient's heart rate is expected to drop by approximately 5 bpm over each seven-day period, for an overall reduction of 15 bpm at the end of three weeks. The heart rate reduction may continue for additional weeks or months to reach a final desired maximum heart rate. [0058] The reduction in heart rate may also be set to follow a non-linear curve. In some circumstances, a physician may determine that a non-linear reduction will better serve the patient's health. For example, it may be determined that the patient is better served by a faster reduction in heart rate over an initial period of time, with a slower reduction of heart rate over a later period of time. See, e.g., the reduction curve 75 shown in FIG. 4. In other circumstances, it may be determined better for the patient to have a slower reduction in heart rate initially, with an increased reduction in heart rate in a later period of time. It is also contemplated that the reduction curve can be continuous (as shown) with changes in the target rate throughout each day, or it may be stepped with as few as one discrete change in target rate each day or each few days. [0059] In any event, it is anticipated that the reduction in heart rate will not be so rapid as to significantly affect the patient's sense of being. For example, as noted earlier, a reduction in heart rate that is too rapid may lead to a rapid reduction of blood pressure, resulting in patient fatigue or fainting. An implementation of the device 10 that includes blood pressure monitoring circuitry, as discussed above, may assist in maintaining the patient's blood pressure within an acceptable range. [0060] In circumstances where the patient is experiencing high blood pressure, e.g. from cardiovascular disease, a reduction in blood pressure may-be desired. In accordance with the present invention, a patient's heart rate may be reduced in a manner that results in a desired reduction of blood pressure. Provided that the patient's blood pressure remains within a medically-acceptable range, the amount of electrical stimulation delivered to the patient may be varied based on the amount of blood pressure reduction that is desired. In some embodiments, a maximum target blood pressure may be programmed in the device, much like embodiments discussed herein that use a maximum target heart rate. The difference between the patient's current blood pressure and the target blood pressure may be used to control the delivery of electrical stimulus to the patient. [0061] A physician preferably determines a final maximum target heart rate and a heart rate reduction curve for a patient after evaluating the patient's condition. The device 10 may be configured with the target rate and heart rate reduction curve information prior to or after implantation of the device 10 in the patient. If programming occurs after implantation, the programming may be accomplished via wireless communication with the device 10. The construction of appropriate RF transmitters and receivers for telemetry of data into and out of the device 10 implanted in the patient is well known. One having ordinary skill in the art may construct an appropriate transmitter and receiver for wireless programming of the device 10 using conventional components. The final target rate and heart rate reduction curve information may be stored within the lookup tables 60 shown in FIG. 3. [0062] A physician may also determine it advantageous to have the device 10 automatically adjust the target heart rate according to the physical activity of the patient. In one aspect, a device 10 constructed according to the invention may include a diurnal variation in the target rate that reflects the time in which the patient is sleeping. For example, FIG. 5 illustrates a target rate reduction curve 78 for a patient who sleeps during normal night hours. As shown in FIG. 5, during the daytime, there is no reduction of the target heart rate set in the programmed settings 58 of the device 10. Commencing at about 9:00 p.m., the target rate is lowered until it reaches a designated target rate reduction. The example in FIG. 5 shows a target rate reduction of 5 bpm, though the designated reduction of target rate may be more or less, as desired. During the normal night hours, the target heart rate is thus 5 bpm lower than it is during the day. Commencing at approximately 5:00 a.m., the target rate reduction is phased out, and the device returns to normal daytime operation with no reduction in the patient's target rate. [0063] The target rate reduction curve 78 shown in FIG. 5 is exemplary only, and does not reflect any particular limitations of the invention. For other patients, the times of day at which a reduction occurs may be different. The variation in target rate may also be more than diurnal, and include multiple times when the patient is expected to be inactive. [0064] A device 10 constructed according to the invention may also include an activity sensor 54 that monitors the patient for elevated physical activity, such as exercise. The activity sensor 54 may also respond to parameters such as blood temperature, respiratory rate, body motion, etc., as are well known in the art. See, e.g., Geddes et al., �The Exercise-Responsive Cardiac Pacemaker,� IEEE Transactions on Biomedical Engineering, 31(12) (December 1984), incorporated by reference herein. In response to detected physical activity, the target heart rate of the patient may be temporarily adjusted upward for the period of time in which the increased physical activity is detected. The increase in target heart rate may also be programmed to follow a target rate enhancement curve that permits the patient to have an adequate heart rate to sustain the physical activity while the activity is occurring. When the heightened physical activity is done, the device returns to the normal target heart rate programmed for the patient, either immediately or according to the programmed target rate enhancement curve. [0065] FIGS. 6-8 illustrate various methods by which the device 10 may set a maximum �target� heart rate for a patient during normal device operation. The method 80 shown in FIG. 6 commences at block 82 in which the device 10 is initialized. The initialization process in block 82 includes all aspects of setting up the device for normal operation, including programming the final target rate, the heart rate reduction curve, and the target rate reduction enhancement curve information in the look-up table 60 as discussed earlier. [0066] The clock 62 (FIG. 3) keeps track of current day and time information for the device 10. At block 84, the device 10 checks the current date and time information to determine the number of days it has been since the device was implanted. At block 86, the date after implantation (DAI) information is applied to the lookup table 60 to determine the target heart rate for the current day. For example, as shown in FIG. 4, the heart rate reduction curve 70 for Day 7 reflects a target rate of 85 bpm. For Day 14, the target rate is 80 bpm, etc. The determined target heart rate is returned from the lookup table 60 and is set in the programmed settings 58 (FIG. 3), as shown at block 88, to control the ongoing operation of the device 10 during that day. The method 80 returns to block 84 and repeats the entire process on a periodic basis to insure that the target heart rate set in the programmed settings 58 remains current. [0067]FIG. 7 illustrates an alternative method 90 for setting the patient's target heart rate in the programmed settings 58. The initial tasks in the method 90 are similar to those in the method 80, including initialization in block 92, checking the current date for DAI information in block 94, and looking up the target heart rate for the current day in block 96. [0068] Once the target rate is determined in block 96, the method 90 checks the current time to determine whether it is during the patient's scheduled sleep time. If, at decision block 98, the current time is during the patient's sleep time, the target rate is reduced (block 100) according to a programmed target rate reduction curve, such as the curve 78 shown in FIG. 5. At block 102, the reduced target is then set in the programmed settings 58 to control the ongoing operation of the device 10. [0069] Returning to decision block 98, if the current time is not during the patient's sleep time, the target rate determined at block 96 is set in the programmed settings 58 to control the ongoing operation of the device 10. In either case, the method 90 then returns to block 94 and repeats the process on a periodic basis to insure that the target rate set in the programmed settings 58 remains current. [0070]FIG. 8 illustrates yet another method 110 for setting the patient's target heart rate and includes additional alternative features. The initial tasks performed in the method 110 are similar to those performed in the method 80 in FIG. 6, including initialization in block 112, checking the current date for DAI information in block 114, and determining the target rate for the patient in block 116 based on the DAI information. [0071] At decision block 118, the method 110 determines whether the current time is during the patient's scheduled sleep time. If the current time is during the sleep time, the method 110 progresses to a decision block 120 where it determines whether a minimum reduction in heart rate has been achieved for the patient. For example, a physician may determine that a diurnal variation in the patient's target rate is not appropriate until the patient's heart rate has been reduced to 80 bpm. If a heart rate of 80 bpm has not yet been achieved (in this example), the method 110 progresses from decision block 120 to block 122 at which the target rate determined in block 116 is set in the programmed settings 58. If, at decision block 120, the threshold rate (here, 80 bpm) has been achieved, the device 10 reduces the patient's target rate (block 124) according to a target rate reduction curve, such as the curve 78 shown in FIG. 5. The reduced target rate is then entered into the programmed settings 58, as shown at block 122. [0072] Returning to the decision block 118, if the current time is not during the patient's sleep time, the method 110 progresses to a decision block 126 at which the device 10 determines whether the patient is experiencing heightened physical activity. If heightened physical activity is sensed, the device 10 may temporarily increase the patient's target rate (block 128) according to a target rate enhancement curve to accommodate the patient's physical activity. The increased target rate is then set in the programmed settings 58, as shown at block 122. If heightened physical activity is not sensed at block 126, the device 10 sets the target rate determined at block 116 in the programmed settings 58. [0073] In any event, after the target rate is set at block 122, the method 110 returns to block 114 and repeats the process on a periodic basis to insure that the programmed target rate remains current and reflects the diurnal variation or physical activity of the patient. [0074] Before discussing specific aspects of the amount of stimulation delivered by the device 10, it is useful to first observe the overall operation of at least one embodiment of the device 10. FIG. 9 illustrates one example of an operational method 130 for the device 10. At block 132, the device 10 undergoes initialization processes, including those processes that set up the device 10 for ongoing operation. The initialization in block 132 includes the process of setting up the target rate, as shown by the methods in FIGS. 6-8. Once the initialization processes are complete, the method 130 commences a repeated routine in which the device 10 monitors the patient's ventricular electrogram for R-waves, as indicated at block 134. The patient's heart rate can be calculated from the frequency of detected R-waves. In the embodiment shown in FIG. 9, the method 130 calculates the time interval �RI� between detected R-waves. [0075] Alternatively, the patient's heart rate can be calculated from the frequency of detected P-waves in the atrium. In that regard, the method 130 may calculate at block 134 the time interval between detected P-waves. This may be particularly useful for embodiments of the invention having a single lead in the atrium and not having a lead in a ventricle of the heart. In a normal sinus rhythm, the P-wave interval and R-wave interval are approximately the same. Accordingly, discussion of R-wave intervals herein is equally applicable to detection and use of P-wave intervals. [0076] At block 136, the device 10 uses the target heart rate set in the programmed settings 58 to determine the target time interval �TI� between R-waves. The difference between the target interval TI and the actual R-wave interval RI is calculated at block 138. [0077] To avoid skewed or erroneous information obtained for any particular R-wave interval detected in the patient, the device 10 may calculate several R-wave intervals and determine an average for the time interval RI. The device 10 may exclude specific R-wave interval calculations that reflect obvious errors in view of the average time interval RI. [0078] Once the difference between the target interval TI and the actual interval RI is calculated, the device 10 determines whether the difference is positive, as shown at decision block 140. A positive difference indicates that the patient's actual heart rate is higher than the target rate, thus indicating that stimulation of the patient's right vagus nerve in accordance with the invention is warranted. If the determined difference is not positive (thus indicating that the patient's actual heart rate is lower than the targeted rate), stimulation is not delivered. Instead, a counter (such as counter 56 shown in FIG. 3) that monitors heart beats without stimulation is incremented, as indicated at block 142. [0079] If the TI-RI difference is positive, the device 10 sets the stimulation parameters at block 144. Additional detail on the manner in which the stimulation parameters are set is provided below. Progressing to decision block 146, the method 130 determines whether a P-wave has been detected in the patient's atrial electrogram. The P-wave detection in block 146 is repeated until a P-wave is detected. At block 148, the electrical stimulation is then delivered to the patient. A counter (such as counter 56 shown in FIG. 3) that monitors heart beats with stimulation is incremented at block 150, and the method 130 returns to block 134 and is repeated. [0080] To deliver the stimulus to the right vagus nerve during the atrial refractory time 28, the stimulus is preferably synchronized with the P-wave. As noted earlier, the atrial refractory period is generally considered to be about 100 ms in duration. Therefore, the electrical stimulation of the vagus nerve should occur during a 100 ms time period commencing with or shortly after a P-wave is detected. The stimulus may be a single pulse, a burst of pulses, a steady train of pulses, etc., during the atrial refractory period. [0081] It should be noted that in implementations where the electrodes for stimulation of the right vagus nerve are placed away from the heart, such as within the right pulmonary artery or in the superior vena cava, the need to synchronize the stimulus with the P-wave diminishes. In such circumstances, there is a lesser concern of direct stimulation of the atrial muscle cells. Nevertheless, it may still be advantageous to synchronize the stimulus with the P-wave of the atrium to maintain the integrity of the stimulus and response. [0082] It should also be noted that the present invention does not require delivery of an electrical stimulus after every heart beat (when stimulation is warranted). The electrical stimulation of the right vagus nerve may be scheduled to occur every few heart beats, for example. Separating the stimuli by several heart beats may provide certain advantages. For instance, it provides the device 10 with some flexibility to increase the stimulus by reducing the number of non-stimulated heart beats between each stimulus delivery. The device 10 may also increase the number of non-stimulated heart beats between stimulus delivery as the patient's heart rate nears the target heart rate. [0083] As discussed above, the counter 56 (FIG. 3) counts the number of heart beats where a stimulus was delivered, as well as the number of heart beats without stimulus delivery. This information may be stored in the memory 32 and communicated by wireless transmission to a receiver (not shown) outside the patient for physician review. By observing the number of heart beats with and without stimulation, as well as the progress of the patient towards the target heart rate, the physician can better evaluate the efficacy of the device 10 as currently programmed. It may be that for certain patients, adjustments in the programming of the device 10 is needed to properly stimulate the patient toward the target heart rate. Nevertheless, counting the number of heart beats with and/or without vagal stimulation is optional and not necessary to practicing the present invention. [0084] The programming of the device 10 may be adjusted by the physician, or it may be done automatically by the device 10. For the latter, the device 10 is configured to provide feedback information to its control circuitry as to the patient's progress toward the target heart rate. If the device 10 observes that patient's actual heart rate is not progressing toward the target rate, the device may automatically increase the energy in each stimulus. The amount and frequency that the device 10 automatically increases the energy may be constrained by limits set in the device to ensure that the stimulation does not become excessive. [0085] The amount of effect the stimulation has on slowing a patient's heart rate is proportional to the amount of energy in the stimulation delivered to the right vagus nerve. The energy delivered in the stimulation may thus be varied to adjust the rate at which the patient's heart rate is reduced. In one aspect, a device constructed according to the present invention, such as device 10, may vary the voltage of the stimulus to vary the energy delivered by the stimulus. As shown in FIG. 10, the stimulation voltage may vary according to a curve, such as curve 160. The greater the difference between the target heart rate and the actual heart rate (or alternatively, the difference in R-wave interval), the greater the voltage of the electrical stimulus that is delivered to the patient. A maximum voltage that can be delivered to the patient may be set in the device or may be constrained by limitations of the components in the device. In the example shown in FIG. 10, a maximum voltage of 20 volts is provided. [0086] The amount of energy delivered to the patient may also be varied by delivering a number of electrical pulses to the patient. The number of pulses is varied depending on the difference between the patient's actual heart rate and the target rate. For example, as shown by the curve 164 in FIG. 11, the greater the difference in heart rate (or difference in R-wave interval), the greater the number of pulses that are delivered to the patient in each period of stimulation. Per the example shown in FIG. 11, it is anticipated that the voltage of each pulse is constant (e.g., 1-20 volts as set in the device). The pulse width of each pulse is also constant (e.g., 0.1-0.5 ms as set in the device). As the electrical stimulus is synchronized with the P-wave, the number of pulses determined by the curve 164 may be spread evenly throughout the atrial refractory period, or alternatively may be set at a frequency to all occur within a portion of the refractory period, such as the initial part of the refractory period. [0087] As to frequency, a device constructed in accordance with the present invention may implement an equation as follows: [0088] In the foregoing equation, K is a variable constant that can be increased if the actual rate exceeds the target rate and the amount of vagal stimulation is ineffective in lowering the actual rate toward the target rate. The variable constant I represents a starting frequency. [0089]FIG. 12 illustrates another example of an embodiment of the invention that varies the duration of pulses in a pulse train to vary the amount of energy delivered in the stimulus. The curve 168 shown in FIG. 12 is approximately linear and demonstrates an increase in pulse duration commensurate with the difference between the patient's actual heart rate and the patient's target rate (or difference in actual to target R-wave interval). However, linear increase in pulse duration is not necessary and in fact a non-linear increase may be warranted. For the example shown in FIG. 12, it is anticipated that the voltage and number of pulses in the stimulus remain constant, though the number of pulses may be limited by the overall duration of the patient's atrial refractory period. [0090] Because the present invention is directed to lowering the heart rate of a patient, it may be advantageous to further include circuitry for delivering pacing pulses to the patient. Unlike the present invention, a pacing pulse is designed to initiate a heart beat to maintain a desired minimum heart rate. Including pacing circuitry in the device 10 would act as a safety net in case the patient's heart rate dropped unreasonably below the set target rate for the patient. Cardiac pacing is a well-developed field of technology. The components and construction of pacing circuitry for use in the device 10 is within the ability of one of having ordinary skill in pacing art, and may use existing components of the device 10, such as the processor, pulse detection, and stimulator circuitry. For example, components of a conventional DDDR pacemaker, ICD, or biventricular pacemaker may be incorporated into the device 10 (or vice versa). [0091] While various preferred embodiments of the invention have been illustrated and described, it will be appreciated that insignificant changes can be made therein without departing from the spirit and scope of the invention. For instance, the method of operation shown in FIG. 9 is only exemplary of one embodiment of the invention. Another embodiment of the invention (e.g., as shown in FIG. 1A) may monitor a P-wave interval instead of R-wave interval as shown in block 134 of FIG. 9, and achieve the same results. Further embodiments of the invention that achieve the same advantages, including a reduction of a patient's normal sinus heart rate to allow improved perfusion through the coronary arteries, are within the ability of one having ordinary skill in the art. [0092] Other embodiments of the invention may sense the heart rate of the patient differently than described above. Rather than sensing R-waves or P-waves through leads implanted in the heart, the device 10 may include pulse detection circuitry that uses electrodes placed elsewhere in the patient's body. For instance, the pulse detection circuitry may use electrodes to sense impedance changes in an artery or may use piezoelectric sensors on an artery to sense pressure changes resulting from a cardiac pulse. See, e.g., Konrad et al., �A New Implantable Arterial Pulse Sensor for Detection of Ventricular Fibrillation,� Medical Instrumentation, 22(6):304-311 (December 1988) for an arterial pulse sensor, incorporated by reference herein. [0093] Embodiments of the invention discussed above deliver electrical stimuli based on the difference between the patient's actual heart rate and a maximum target heart rate for the patient. Nevertheless, use of a target heart rate for the patient is not necessary to practicing the present invention. Other embodiments of the invention may deliver electrical stimuli in an amount that is predetermined or is based on patient conditions, such as the frequency of cardiac contractions in the patient (i.e., heart rate). [0094] A patient's heart rate typically increases as the patient exerts increased physical work, as reflected by the upper curve 170 in FIG. 13. Embodiments of the invention that deliver a predetermined amount of electrical stimuli to the patient regardless of the patient's heart rate will reduce the patient's heart rate, as shown by the middle curve 172 in FIG. 13. However, the slope of the curve 172 is the same as the curve 170 because the amount of stimulus delivered to the patient does not vary with the heart rate resulting from the amount of physical work being performed by the patient. An embodiment of the invention of this type is also reflected by the curve 176 in FIG. 14. FIG. 14 illustrates two curves showing the amount of energy in electrical stimulus to the patient as a function of the patient's heart rate. The lower curve 176 is constant, regardless of the patient's heart rate. [0095] An embodiment of the invention that increases the amount of stimulus energy as a function of the patient's heart rate is reflected by the upper curve 178 in FIG. 14. As the patient's heart rate increases, the amount of energy delivered to the patient in each stimulus also increases. As noted earlier, the amount by which a patient's heart rate is reduced is proportional to the amount of energy delivered to the patient's vagus nerve. Accordingly, an embodiment of the invention that increases stimulus energy with the patient's heart rate will result in a heart rate that increases at a much slower rate, as reflected by the lower curve 174 in FIG. 13. The slope of the curve 174 is smaller than the slope of the curve 170 (for the patient not receiving electrical stimulus). The slope of the curve 174 is also lower than the slope of the curve 172 (for an embodiment that delivers a constant amount of electrical stimulus. [0096]FIGS. 15 and 16 illustrate two exemplary embodiments of the invention in which the amount of energy delivered to the patient varies as a function of the patient's heart rate. In FIG. 15, the curve 180 indicates an increasing number of pulses in the electrical stimulus delivered to the patient as the patient's heart rate increases. The curve 180 is shown in a stepped form to reflect the number of pulses delivered to the patient as a function of the patient's heart rate. The actual number of pulses and the increase in number of pulses for each period of stimulation may vary according to patient circumstances, and thus are not numerically set forth in FIG. 15. For example, for one patient, each stimulus may be comprised of five pulses for a heart rate between 85 bpm and 90 bpm, seven pulses for a heart rate of 90-95 bpm, 10 pulses for a heart rate of 95-100 bpm, etc. For another patient, each stimulus may be comprised of 10 pulses for a heart rate of 80-87 bpm, 12 pulses for a heart rate of 87-95 pbm, 16 pulses for a heart rate of 95-100 bpm, etc. The present invention is not limited by the number of pulses nor the increase in number of pulses for any particular heart rate. After evaluating a patient's condition, a physician may program the device 10 to operate in accordance with a curve 180 using the telemetry features discussed above. [0097] An alternative embodiment of the invention may increase the amount of stimulus energy delivered to the patient by decreasing the stimulus to heart beats ratio. As noted earlier, the present invention does not require delivery of an electrical stimulus during a refractory period of every heart beat. As shown by the curve 182 in FIG. 16, for a lower heart rate, the device 10 may deliver one period of electrical stimulus for every four heart beats. As the patient's heart rate increases, the ratio may be reduced to one period of stimulus for every three heart beats. The ratio may eventually be reduced such that a period of stimulus is delivered after every heart beat (i.e., a 1:1 ratio). The curve 182 in FIG. 16 is exemplary only, and does not limit the present invention. Other embodiments of the invention may start with one period of stimulus for every 10 heart beats, for example, with a reduction in the ratio as the patient's heart rate increases. [0098] Both of the curves 180 and 182 in FIGS. 15 and 16 demonstrate the operation of a device in which stimulus is delivered to the patient without a target heart rate. Those with ordinary skill in the art will recognize that a numerical calculation of the heart rate is not necessary in this regard. For example, the detection of a P-wave (or R-wave) may trigger a timer circuit (analog or digital) that causes a stimulus to be delivered during the next refractory period if the interval between P-waves (or R-waves) is too long. At a very basic level, in fact, a device constructed according to the invention may not count the detection of P-waves at all and instead deliver a constant amount of electrical energy at a programmed stimulus to heart beat ratio. [0099] Embodiments of the invention may also include alternative lead configurations such as the helical lead configuration shown in FIG. 17. In FIG. 17, the device 10 is shown connected to a catheter containing an electrical lead 190 that has been implanted in a patient's heart 16. The electrical lead 190, as illustrated, enters the heart 16 through the superior vena cava and is wound in a helical shape. Although multiple windings are shown, the electrical lead 190 may have as few as one winding as it enters the heart 16. [0100] The electrical lead 190 also illustrates the use of more than one electrode in an electrical lead according to the invention. Specifically, the electrical lead 190 includes three electrodes 192, 194, and 196. Preferably, at least two of the electrodes are positioned closely to the tissue in the area of the post-ganglionic right vagus nerves. The positioning of the electrodes is assisted by the helical winding of the lead. As with the lead 12 discussed earlier, the spacing between the electrodes 192, 194, 196 is preferably greater than that which is common in pacing leads so that the electrodes capture a wider area of tissue around the sinoatrial node. The electrical lead 190, as illustrated, also includes a helical screw at the tip to secure the lead to the heart tissue. The ring electrodes 192, 194 and tip electrode 196 may be comprised of conventional components similar to the electrodes in the electrical leads 12 and 14 shown in FIGS. 1A and 1B. [0101] While the above disclosure provides various exemplary embodiments of the invention, it should not be considered limiting with respect to the scope of the invention. The scope of the invention should be determined from the following claims and equivalents thereto. Referenced byCiting PatentFiling datePublication dateApplicantTitleUS6907295Jul 24, 2002Jun 14, 2005Biocontrol Medical Ltd.Electrode assembly for nerve controlUS7097618 *Mar 9, 2004Aug 29, 2006Transoma Medical, Inc.Devices and methods for detecting and treating inadequate tissue perfusionUS7142917 *Dec 3, 2003Nov 28, 2006Terumo Kabushiki KaishaHeart treatment equipment and method for preventing fatal arrhythmiaUS7486991Dec 24, 2003Feb 3, 2009Cardiac Pacemakers, Inc.Baroreflex modulation to gradually decrease blood pressureUS7493161May 10, 2005Feb 17, 2009Cardiac Pacemakers, Inc.System and method to deliver therapy in presence of another therapyUS7542800Apr 5, 2005Jun 2, 2009Cardiac Pacemakers, Inc.Method and apparatus for synchronizing neural stimulation to cardiac cyclesUS7555341Apr 5, 2005Jun 30, 2009Cardiac Pacemakers, Inc.System to treat AV-conducted ventricular tachyarrhythmiaUS7570999Dec 20, 2005Aug 4, 2009Cardiac Pacemakers, Inc.Implantable device for treating epilepsy and cardiac rhythm disordersUS7596413 *Jun 8, 2004Sep 29, 2009Cardiac Pacemakers, Inc.Coordinated therapy for disordered breathing including baroreflex modulationUS7657312 *Nov 3, 2003Feb 2, 2010Cardiac Pacemakers, Inc.Multi-site ventricular pacing therapy with parasympathetic stimulationUS7668594Aug 19, 2005Feb 23, 2010Cardiac Pacemakers, Inc.Method and apparatus for delivering chronic and post-ischemia cardiac therapiesUS7676275 *May 2, 2005Mar 9, 2010Pacesetter, Inc.Endovascular lead for chronic nerve stimulationUS7706884 *Dec 24, 2003Apr 27, 2010Cardiac Pacemakers, Inc.Baroreflex stimulation synchronized to circadian rhythmUS7751891 *Jul 28, 2004Jul 6, 2010Cyberonics, Inc.Power supply monitoring for an implantable deviceUS7761156Jan 29, 2007Jul 20, 2010St. Jude Medical AbMethod for operating an implantable cardiac stimulator to set the atrial stimulation time interval dependent on the evoked response amplitudeUS7769446Mar 11, 2005Aug 3, 2010Cardiac Pacemakers, Inc.Neural stimulation system for cardiac fat padsUS7813805Jan 11, 2006Oct 12, 2010Pacesetter, Inc.Subcardiac threshold vagal nerve stimulationUS7869869Jan 11, 2006Jan 11, 2011Pacesetter, Inc.Subcardiac threshold vagal nerve stimulationUS7881782Apr 20, 2005Feb 1, 2011Cardiac Pacemakers, Inc.Neural stimulation system to prevent simultaneous energy dischargesUS7899526May 10, 2005Mar 1, 2011Regents Of The University Of MinnesotaPortable device for monitoring electrocardiographic signals and indices of blood flowUS7917230Jan 30, 2007Mar 29, 2011Cardiac Pacemakers, Inc.Neurostimulating lead having a stent-like anchorUS7925352Mar 27, 2009Apr 12, 2011Synecor LlcSystem and method for transvascularly stimulating contents of the carotid sheathUS7949409Jan 30, 2007May 24, 2011Cardiac Pacemakers, Inc.Dual spiral lead configurationsUS7966076 *Mar 13, 2007Jun 21, 2011Cardiac Pacemakers, Inc.Lead and apparatus for stimulation of the cardiac plexusUS7967758Jul 12, 2006Jun 28, 2011Data Sciences International, Inc.Devices and methods for detecting and treating inadequate tissue perfusionUS8116883Feb 2, 2007Feb 14, 2012Synecor LlcIntravascular device for neuromodulationUS8131359Apr 23, 2008Mar 6, 2012Cardiac Pacemakers, Inc.System and method to deliver therapy in presence of another therapyUS8140155Mar 10, 2009Mar 20, 2012Cardiac Pacemakers, Inc.Intermittent pacing therapy delivery statisticsUS8145304Jul 15, 2010Mar 27, 2012Cardiac Pacemakers, Inc.Neural stimulation system for cardiac fat padsUS8175705Oct 12, 2004May 8, 2012Cardiac Pacemakers, Inc.System and method for sustained baroreflex stimulationUS8190257May 28, 2009May 29, 2012Cardiac Pacemakers, Inc.System to treat AV-conducted ventricular tachyarrhythmiaUS8200331Nov 4, 2004Jun 12, 2012Cardiac Pacemakers, Inc.System and method for filtering neural stimulationUS8244378Jan 30, 2007Aug 14, 2012Cardiac Pacemakers, Inc.Spiral configurations for intravascular lead stabilityUS8311647Apr 4, 2011Nov 13, 2012Cardiac Pacemakers, Inc.Direct delivery system for transvascular leadUS8412350Mar 7, 2011Apr 2, 2013Cardiac Pacemakers, Inc.Neurostimulating lead having a stent-like anchorUS8504149Feb 15, 2012Aug 6, 2013Cardiac Pacemakers, Inc.System and method to deliver therapy in presence of another therapyUS8620426Mar 22, 2012Dec 31, 2013Cardiac Pacemaker, Inc.Neural stimulation system for cardiac fat padsUS20100114227 *Oct 30, 2008May 6, 2010Pacesetter, Inc.Systems and Methds for Use by an Implantable Medical Device for Controlling Vagus Nerve Stimulation Based on Heart Rate Reduction Curves and Thresholds to Mitigate Heart FailureUS20120029586 *Jul 28, 2010Feb 2, 2012Medtronic, Inc.Parasympathetic stimulation to enhance tachyarrhythmia detectionUS20130041204 *Feb 9, 2012Feb 14, 2013Marlin Stephen HeilmanControl of blood flow assist systemsEP1740264A2 *Apr 4, 2005Jan 10, 2007CVRX, Inc.Stimulus regimens for cardiovascular reflex controlEP1897586A1Sep 7, 2007Mar 12, 2008Biocontrol Medical Ltd.Techniques for reducing pain associated with nerve stimulationWO2005097256A2Apr 4, 2005Oct 20, 2005Cvrx IncStimulus regimens for cardiovascular reflex controlWO2006107675A1 *Mar 29, 2006Oct 12, 2006Cardiac Pacemakers IncCardiac cycle - synchronized neural stimulator* Cited by examinerClassifications U.S. Classification607/9International ClassificationA61N1/368, A61N1/36, A61N1/362Cooperative ClassificationA61N1/3627, A61N1/36114European ClassificationA61N1/36Z3J, A61N1/362CLegal EventsDateCodeEventDescriptionFeb 4, 2003ASAssignmentOwner name: SCOUT MEDICAL TECHNOLOGIES, LLC, WASHINGTONFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:ADAMS, JOHN M.;ALFERNESS, CLIFTON A.;REEL/FRAME:013738/0743Effective date: 20030127RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google