Source: http://www.google.com/patents/US5716379?dq=5,941,947
Timestamp: 2014-03-07 22:13:46
Document Index: 128581619

Matched Legal Cases: ['art 2', 'art 2', 'art 2', 'art 2', 'art 2', 'art 2', 'art 2']

Patent US5716379 - Cardiac assist device having muscle augmentation prior to defibrillation - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA cardiac assist device having muscle augmentation during confirmed arrhythmia. In particular the present invention operates, in a first embodiment, to sense a cardiac event, next it determines whether the cardiac event is a cardiac arrhythmia, if the event is not a cardiac arrhythmia the devices delivers...http://www.google.com/patents/US5716379?utm_source=gb-gplus-sharePatent US5716379 - Cardiac assist device having muscle augmentation prior to defibrillationAdvanced Patent SearchPublication numberUS5716379 APublication typeGrantApplication numberUS 08/516,419Publication dateFeb 10, 1998Filing dateAug 17, 1995Priority dateAug 17, 1995Fee statusLapsedAlso published asCA2183304A1, EP0759308A2, EP0759308A3Publication number08516419, 516419, US 5716379 A, US 5716379A, US-A-5716379, US5716379 A, US5716379AInventorsIvan Bourgeois, Pierre A. GrandjeanOriginal AssigneeMedtronic, Inc.Export CitationBiBTeX, EndNote, RefManPatent Citations (13), Non-Patent Citations (12), Referenced by (7), Classifications (11), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetCardiac assist device having muscle augmentation prior to defibrillationUS 5716379 AAbstract A cardiac assist device having muscle augmentation during confirmed arrhythmia. In particular the present invention operates, in a first embodiment, to sense a cardiac event, next it determines whether the cardiac event is a cardiac arrhythmia, if the event is not a cardiac arrhythmia the devices delivers stimulation to a skeletal muscle grafted about a heart, but if the event is a cardiac arrhythmia the device inhibits delivery of skeletal muscle stimulation and once the arrhythmia is confirmed, then delivers therapeutic stimulation to the heart. In a second embodiment the present invention operates to re-initiate skeletal muscle stimulation once the arrhythmia is confirmed but prior to the delivery of the therapeutic stimulation to the heart.
What is claimed is: 1. An apparatus for stimulating a skeletal muscle grafted about a heart, detecting cardiac events and delivering therapeutic stimulation to the heart comprising:means for sensing a cardiac event; means for classifying the cardiac event as a normal sinus rhythm or as a cardiac fibrillation; means for delivering a normal sinus rhythm skeletal muscle pulse train to a skeletal muscle grafted about a heart upon the classification of a normal sinus rhythm, the normal sinus rhythm skeletal muscle pulse train having a first amplitude; means for delivering a defibrillation therapy upon the classification of a cardiac fibrillation, the defibrillation therapy comprising a defibrillation skeletal muscle pulse train and a defibrillation shock, the defibrillation skeletal muscle pulse train delivered upon the detection of a cardiac fibrillation, the defibrillation skeletal muscle pulse train having a second amplitude, the second amplitude being greater than the normal sinus rhythm skeletal muscle pulse train amplitude, the defibrillation shock delivered a first amount after defibrillation skeletal muscle pulse train; whereby the defibrillation skeletal muscle pulse train causes the heart to achieve a systolic position. 2. The apparatus of claim 1 wherein the normal sinus rhythm skeletal muscle pulse train has a first interpulse interval, the defibrillation skeletal muscle pulse train has a second interpulse interval, the first interpulse interval greater than the second interpulse interval.
3. The apparatus of claim 2 wherein the normal sinus rhythm skeletal muscle pulse train has a first interpulse interval, the defibrillation skeletal muscle pulse train has a second interpulse interval, the first interpulse interval less than the second interpulse interval.
4. An apparatus for stimulating a skeletal muscle grafted about a heart, detecting cardiac events and delivering therapeutic stimulation to the heart comprising:means for sensing a cardiac event; means for classifying the cardiac event as a normal sinus rhythm or as a cardiac fibrillation; means for delivering a normal sinus rhythm skeletal muscle pulse train to a skeletal muscle grafted about a heart upon the classification of a normal sinus rhythm, the normal sinus rhythm skeletal muscle pulse train having a first interpulse interval; means for delivering a defibrillation therapy upon the classification of a cardiac fibrillation, the defibrillation therapy comprising a defibrillation skeletal muscle pulse train and a defibrillation shock, the defibrillation skeletal muscle pulse train delivered upon the detection of a cardiac fibrillation, the defibrillation skeletal muscle pulse train having a second interpulse interval, the second interpulse interval being greater than the normal sinus rhythm skeletal muscle pulse train interpulse interval, the defibrillation shock delivered a first amount after the defibrillation skeletal muscle pulse train; whereby the defibrillation skeletal muscle pulse train causes the heart to achieve a systolic position. 5. The apparatus of claim 4 wherein the normal sinus rhythm skeletal muscle pulse train has a first amplitude, the defibrillation skeletal muscle pulse train has a second amplitude, the first amplitude greater than the second amplitude.
6. The apparatus of claim 5 wherein the normal sinus rhythm skeletal muscle pulse train has a first amplitude, the defibrillation skeletal muscle pulse train has a second amplitude, the first amplitude less than the second amplitude.
7. An apparatus for stimulating a skeletal muscle grafted about a heart, detecting cardiac events and delivering therapeutic stimulation to the heart comprising:means for delivering stimulation to a skeletal muscle grafted about a heart; means for sensing depolarizations of a patient's heart; means for measuring the intervals separating successive depolarizations of the patient's heart; means for defining first and second interval ranges; means for determining the number of the measured intervals falling within the first and second interval ranges; means for inhibiting the means for delivering stimulation to a skeletal muscle grafted about a heart upon the sensing of a depolarization within the first or second interval range; first means for detecting the occurrence of a first type of arrhythmia when the number of the measured intervals falling within the first interval range equals a first predetermined value; second means for detecting the occurrence of a second type of an arrhythmia when the number of the intervals falling within the second interval range equals a second predetermined value; means for delivering a first type of arrhythmia therapy in response to the detection of the first arrhythmia by the first detecting means; and means for delivering a second type of arrhythmia therapy in response to the detection of the second arrhythmia by the second detecting means, the second type of arrhythmia therapy having a cardiac stimulation component and a arrhythmia skeletal muscle component, the arrythmia skeletal muscle component comprising a skeletal muscle pulse train having a first section and a second section, the first section having a first frequency, the second section having a second frequency. 8. The apparatus of claim 7 wherein the first frequency greater than the second frequency.
9. The apparatus of claim 7 wherein the first frequency less than the second frequency.
The System of the Present Invention FIG. 1 illustrates an example of a system 1 for performing both long-term stimulation of skeletal muscles for cardiac assistance using systolic augmentation as well as direct electrical stimulation of a heart 2. As seen, skeletal muscle graft 3 is positioned about the heart 2. In the preferred embodiment the latissimus dorsi muscle is used for the skeletal muscle graft, as is well known in the art. The longitudinal fibers of the muscle graft 3 are oriented generally perpendicular to the longitudinal axes of the right ventricle 4, left ventricle 5 and interventricular septum 10 of the heart. Muscle graft 3 is positioned in this manner so that when it is stimulated, muscle graft 3 compresses ventricles 4, 5 and particularly left ventricle 5, to thereby improve the force of right and left ventricular contraction. In such a manner the overall hemodynamic output of heart 2 is increased.
As seen, electrical stimulation and sensing of heart 2 is accomplished through lead 15. In particular, lead 15 electrically couples pulse generator 6 to heart 2. Lead 15 provides both cardiac pacing as well as defibrillation therapies. In the preferred embodiment lead 15 is the model 6936 tri-polar TRANSVENE lead from Medtronic Inc., Minneapolis, Minn. As seen, lead 15 is implanted in right ventricle 4 such that bi-polar pacing electrode assembly 16 is in the right ventricular apex and defibrillation coil 17 is within the right ventricle 4. Although in the preferred embodiment a single lead is provided for both pacing as well as defibrillation therapies, other types of lead configurations, such as multiple transvenous or subcutaneous or any combination thereof, may be used.
Muscle graft 3 is electrically stimulated through a pair of leads 21, 22. In particular leads 21, 22 couple pulse generator 6 to skeletal muscle graft 3. In the preferred embodiment leads 21, 22 are the model 4750 intramuscular lead from Medtronic, Inc., Minneapolis, Minn. As seen, each lead 21, 22 extends from pulse generator 6 to latissimus dorsi muscle graft 3. The electrodes (not shown) of each lead 21, 22 are placed to cause muscle graft 3 to contract when electrically stimulated, as is well known in the art. Other types of leads, however, may be used, such as epimysial or neuromuscular leads.
In response to the detection of fibrillation or a tachycardia requiring a cardioversion pulse, microprocessor 524 activates cardioversion/defibrillation control circuitry 554, which initiates charging of the high voltage capacitors 556, 558, 560 and 562 via charging circuit 550, under control of high voltage charging line 552. During charging, microprocessor 524 enables pacer/timing control 520 to pace out 522 and switch matrix 512 to deliver muscle stimulation pulses until the high voltage capacitors 556 are sufficiently charged. As discussed in more detail below, these muscle stimulation pulses delivered during capacitor charging, may be either delivered synchronously or asynchronously. In addition, such muscle stimulation pulses may have greater amplitude, duration or repetition rate or any combination, as compared to the muscle stimulation pulse trains delivered prior to a tachyarrhythmia. In addition such muscle stimulation pulses may also have a shorter interpulse interval in either the whole pulse train or only a portion thereof, as compared to the muscle stimulation pulse trains delivered prior to a tachyarrhythmia. The voltage on the high voltage capacitors is monitored via VCAP line 538, which is passed through multiplexer 532, and, in response to reaching a predetermined value set by microprocessor 524, results in generation of a logic signal on CAP FULL line 542, terminating charging. The CAP FULL line 542 signal is sent over DATA/ADDRESS 540 to the pace timer/control 520, which then inhibits delivery of the muscle stimulation pulses.
In addition to varying the therapy delivered following a failed attempt to terminate a tachyarrhythmia, it is also known that adjustment of detection criteria may be appropriate. For example, adjustment may comprise reducing the number of intervals required to detect a tachyarrhythmia to allow a more rapid redetection or by changing the interval ranges to bias detection towards detection of ventricular fibrillation, for example as disclosed in U.S. Pat. No. 4,971,058, issued to Pless et al and incorporated herein by reference.
For example, if a first event is sensed and a second event is sensed 200 ms later, ventricular fibrillation is provisionally detected. As a second example, if a first event is sensed and second event is sensed 320 ms later, then a ventricular tachycardia (hereafter "VT") is provisionally detected. As a third example, if a first event is sensed and second event occurs 100 ms later and a third event occurs 210 ms after the second event, then a ventricular tachycardia (hereafter "VT") is also provisionally detected. This is so because the second event occurred during blanking and thus was not sensed; the third event was thereafter sensed a sum of 320 ms after the first, well within the VT zone.
FIG. 4 is an arrhythmia detection/therapy muscle state diagram of the present invention. As discussed above the present invention features both skeletal muscle graft stimulation as well as cardiac stimulation. One of the important requirements of such a system, however, is to accurately detect cardiac arrhythmias and respond with the appropriate therapy. As discussed above, concurrent skeletal muscle graft stimulation may interfere with the detection and diagnosis of arrhythmias. Thus, one important feature of the present invention is the manner in which it provides for skeletal muscle graft stimulation as well as cardiac stimulation while also managing the prompt detection and diagnosis of arrhythmias. In particular, the present invention temporarily stops or inhibits skeletal muscle stimulation once the onset of an arrhythmia is sensed.
As seen, during normal sinus rhythm the system remains at normal sinus rhythm state 30. In state 30 device provides both skeletal muscle graft stimulation and any bradycardia stimulation required. Bradycardia stimulation may take the form of any suitable electrical stimulation therapy, and preferably is given in the form of VVI pacing, although other types of pacing therapy may be delivered, such as VOO, OVO and VVT. Bradycardia stimulation is delivered, in the preferred embodiment, upon the detection of a sequence of cardiac events in which the range of intervals between events would be greater than BEI.
Second look criterion is used only after combined count state 38 is reached. Second look criterion is applied to determine whether VT or VF therapy should be delivered. In the preferred embodiment second look criterion is as follows: If all of the previous 8 intervals are greater than or equal to FDI, then the VF detected path should be followed and deliver VT therapy state 36 is reached, but if one of the previous 8 intervals is less than FDI, then the VF detected path will be followed and deliver VF therapy state 40 is reached.
Once deliver VF therapy state 40 is reached, VF therapy is completed or aborted and VT/VF termination detection state 42 is reached. Similarly once deliver VT therapy state 36 is reached, VF therapy is completed or aborted and VF/VF termination detection state 42 is reached.
While in VT/VF termination detection state 42, the device determines whether VT or VF is re-detected. If either VT or VF is detected, then the device returns to the relevant therapy state. If neither VF nor VF is re-detected, the device returns to normal sinus state 30. VT/VF termination detection is accomplished as follows: If VT detection is programmed "Off" and eight consecutive events having intervals greater than FDI are sensed, then VF termination is detected and the device returns to normal sinus state 30. If VT detection is programmed "On" and eight consecutive events having intervals greater than TDI (which by definition is greater than FDI) are sensed, then VT termination is detected and the device returns to normal sinus state 30.
While in deliver VF therapy state 40, device performs several operations, including charging of the output capacitors, depicted as line 208. In addition, skeletal muscle stimulation is re-initiated and a series of asynchronous muscle stimulation bursts 210, 212 are delivered. In the preferred embodiment asynchronous bursts 210, 212 have a greater amplitude than muscle stimulation burst 201, on the order of one and a half times as large. In an alternate embodiment, asynchronous bursts 210, 212 have a higher repetition rate, greater amplitude, interpulse interval and train duration than muscle stimulation burst 201. Of course, in alternate embodiments asynchronous bursts 210, 212 may have any of the following different as compared to muscle stimulation burst 201: higher repetition rate, amplitude, pulse width, interpulse interval or train duration.
Once charging of the output capacitors is completed, a sequence to synchronize the defibrillation discharge to a sensed R-wave is undertaken. In particular, device begins a synchronization sequence during synchronization time 216. Synchronization sequence is undertaken to both synchronize defibrillation discharge to a sensed cardiac event as well as to re-confirm the presence of the arrhythmia. Defibrillation discharge 214 only occurs after a specified synchronization time 216. In addition during synchronization time 216, device re-inhibits skeletal muscle stimulation in order to permit reliable sensing of any intrinsic cardiac events.
Muscle Stimulation Prior to Delivery of Defibrillation Pulse FIG. 6 is a timing diagram showing the relationship between muscle stimulation and cardiac events of an alternate embodiment. In particular, in an alternate embodiment, if synchronization is unsuccessful, then the device delivers an asynchronous muscle stimulation burst 322 immediately prior to defibrillation discharge 214, as best seen in FIG. 6. Muscle stimulation burst 322 is intended to cause the heart to be squeezed by the skeletal muscle graft and achieve roughly a systolic position when defibrillation discharge 214 is delivered. Because the volume of the heart in such a position is decreased, the defibrillation threshold is likewise decreased. In an alternate embodiment, burst 322 has a higher repetition rate, greater amplitude, interpulse interval and train duration than muscle stimulation burst 201. Of course, in alternate embodiments burst 322 may have any of the following different as compared to muscle stimulation burst 201: higher repetition rate, amplitude, pulse width, interpulse interval or train duration.
Muscle Stimulation Featuring Muscle Catch FIG. 7 depicts an alternate muscle stimulation burst which may be used with the present system. These muscle stimulation bursts may be used at any suitable time within the present system, and are not limited to only use prior to delivery of the defibrillation therapy. As seen muscle stimulation burst 300 occurs after QRS 303 in the amount of a synchronization delay 305. In the preferred embodiment synchronization delay 305 is programmable and is undertaken in order to synchronize the muscle stimulation burst 300 with the ventricular contraction. Muscle stimulation burst 300 has essentially two section, first section 301 and second section 302, often referred to as "muscle catch" and "muscle pulse train" respectively. As seen, first section 301 has a smaller interpulse interval 304 within the burst, i.e. a higher frequency. In comparison second section 302 has a relatively larger interpulse interval 304 within the burst, i.e. a relatively smaller frequency. The higher frequency first section 301 increases the velocity and force of the skeletal muscle graft contraction. In the preferred embodiment interpulse interval 304 and number of pulses in the catch may be selected by the physician. The pulse waveform, amplitude 308 and width of the muscle catch are the same for the remainder of the burst.
FIG. 8 depicts an alternate embodiment of the muscle burst stimulation which may be used with the present system. As seen all parameters of the muscle stimulation burst 300 are the same as that described above with respect to FIG. 7 but for the amplitude of second section 302.
FIG. 9 depicts an alternate embodiment of the muscle burst stimulation which may be used with the present system. As seen all parameters of the muscle stimulation burst 300 are the same as that described above with respect to FIG. 7 but for the amplitude of second section 302. In particular amplitude of each burst within second section 302 decreases. The rate of decrease of pulse amplitude within each burst decreases as a function of rate, i.e. the faster the rate of muscle stimulation, the greater the decrease of pulse amplitude within the pulse train.
FIG. 10 depicts an alternate embodiment of the muscle burst stimulation which may be used with the present system. As seen muscle stimulation burst 300 consists of a number of pulses 309. The amplitude of each pulse 309 differs from the amplitude of each preceding and following pulse. In addition, the interpulse interval between each pulse 309 is different. None of 320, 321, 322, 323, 324, 325 or 326 are equal to another. Each of the various parameters, such as amplitude 308 and the rate of change of amplitude 308, synchronization delay 305 and interpulse intervals 320, 321, 322, 323, 324, 325 and 326 are programmed on a patient by patient basis, as well as within the training regime of the patient so as to attain the most efficient muscle contraction while minimizing muscle fatigue as well as energy expenditure.
FIG. 11 depicts an alternate embodiment of the muscle burst stimulation designed for an ultra-fast muscle contraction and which may be used with the present system. Muscle stimulation burst 300 consists of a number of pulses 331-336. As seen, the amplitude of each pulse 331-336 decrease from the preceding pulse. In addition, the interpulse interval between each pulse 331-336 increases from each of the preceding pulse intervals. That is, interpulse interval 320 is less than interpulse interval 321, which, in turn, is less than interpulse interval 322, etc. Each of the various parameters, such as amplitude 308 and the rate of change of amplitude 308, synchronization delay 305 and rate of change of interpulse interval are programmed on a patient by patient basis, as well as within the training regime of the patient so as to attain the most efficient muscle contraction while minimizing muscle fatigue as well as energy expenditure.
As discussed above, the mechanically induced cardiac output augmentation of the present invention during VF (which is associated with loss of cardiac output) leads to maintaining defibrillation thresholds during prolonged episodes of fibrillation, thus resulting in longer battery life or smaller device size or both. It also permits a longer charging interval without the concern of a dangerously low or temporarily lost cardiac output.
FIG. 3 is an illustration of a detection interval ranges employed in a preferred embodiment of the present invention.
FIG. 8 depicts an alternate embodiment of the muscle burst stimulation which may be used with the present system.
FIG. 9 depicts an alternate embodiment of the muscle burst stimulation which may be used with the present system.
FIG. 10 depicts an alternate embodiment of the muscle burst stimulation which may be used with the present system.
FIG. 11 depicts an alternate embodiment of the muscle burst stimulation designed for an ultra-fast muscle contraction and which may be used with the present system.
FIELD OF THE INVENTION The present invention generally relates to cardiac assist systems, including cardiomyoplasty, for the treatment of patients needing augmented cardiac output. More specifically, the present invention relates to a cardiac assist system which provides muscle augmentation prior to the delivery of a defibrillation therapy.
In order to treat these potentially life-threatening cardiac arrhythmias, some cardiac assist systems have been proposed which combine both a muscle stimulator as well as a cardiac pacer-cardioverter-defibrillator. In such a manner a patient who has had a cardiomyoplasty may, in addition to receiving muscle-powered cardiac assistance, also receive various types of therapeutic cardiac electrical stimulation. One example of such a system may be seen in the U.S. Pat. No. 5,251,621 issued to Collins and entitled "Arrhythmia Control Pacer Using Skeletal Muscle Cardiac Graft Stimulation."
One problem associated with devices which combine both a muscle stimulator as well as a cardiac pacer-cardioverter-defibrillator is that the muscle stimulation may interfere with the reliable sensing of cardiac events. During ventricular arrhythmias, such as ventricular fibrillation or ventricular tachycardia (hereafter "VF" and "VT" respectively) the cardiac signals may have very low amplitudes. This is especially the case during VF. The stimulation of the muscle wrap at that time could thus interfere with reliably sensing the VF or VT due to post-pace polarization, cross talk, et cetera.
The U.S. Pat. No. 5,251,621 issued to Collins offers one solution to this problem. The Collins patent discloses a cross channel blanking control signal to disable pacemaker sensing during generation of a skeletal muscle stimulation pulse. This is intended to prevent the pacemaker from incorrectly classifying a skeletal muscle stimulation pulse as an episode of intrinsic cardiac activity. At all times, however, muscle stimulation is continued. In fact, during arrhythmic events besides muscle stimulation continuing, Collins discloses adjusting various parameters of the muscle stimulation bursts, such as pulse amplitude, duration as well as the interval between pulses within a burst. One problem with this approach, however, is the continuation of skeletal muscle stimulation may interfere with the reliable sensing of the arrhythmia. Moreover, adjusting the various parameters of the muscle stimulation signal, such as amplitude or duration, creates an even greater likelihood that the device will not be able to reliably sense the arrhythmia.
Rapid detection of a cardiac tachyarrhythmia, and especially VF, is very important. A typical cardiac pacer-cardioverter-defibrillator detection algorithm requires the detection of a certain number of tachyarrhythmic events within a specified time period. In the case of VF detection, these devices will typically initiate the charging of a cardiac output circuit. This charging period may last between 1 to 21 seconds, depending on the therapy to be delivered. Following charging, the detection algorithm would once again confirm VF and deliver the therapy. Once the therapy is delivered, the detection algorithm would remain active until the tachyarrhythmic episode termination was confirmed.
At high energy levels, the period from tachyarrhythmia detection until tachyarrhythmia termination confirmation and muscle therapy reactivation could be extremely long, for example, up to 35 seconds or even longer. The consequence of this inhibition of the cardiac assistance during an episode of tachyarrhythmia is that cardiac output is highly compromised. In addition, while in fibrillation the threshold to achieve defibrillation through electrical shock rises exponentially. Higher defibrillation thresholds, however, mean the device must feature larger capacitors or higher voltages or both.
Of course others have addressed solutions to the increasing defibrillation thresholds. Idriss, et al., J. Cardiovascular Electrophysiology, V. 6, N. 5, pgs. 368-78, showed mechanically bringing the heart to a systolic position prior to the delivery of a defibrillation shock could cause a decrease in defibrillation thresholds. Geddes, et al., Jpn. Heart J., V. 35, January 1994, pgs. 73-80, showed stimulation of a skeletal muscle wrapped about the heart during VF increase cardiac output. None of these disclose, however, a system which permits the rapid detection of a cardiac arrhythmia and which provides cardiac assistance during a cardiac arrhythmia. Finally none disclose a system which uses skeletal muscle to bring the heart into systolic position so as to lower the defibrillation threshold.
SUMMARY OF THE INVENTION It is thus an object of the invention to provide a cardiac assist system which permits the rapid detection of a cardiac arrhythmia.
It is a further object of the present invention to provide a cardiac assist system which provides cardiac assistance during a cardiac arrhythmia.
It is a further object of the present invention to provide a cardiac assist system which provides muscle augmentation prior to the delivery of a defibrillation therapy.
These and other objects are met by the present invention which comprises a cardiac assist device having muscle augmentation during confirmed arrhythmia. In particular the present invention operates, in a first embodiment, to sense a cardiac event, next it determines whether the cardiac event is a cardiac arrhythmia, if the event is not a cardiac arrhythmia the devices delivers stimulation to a skeletal muscle grafted about a heart, but if the event is a cardiac arrhythmia the device inhibits delivery of skeletal muscle stimulation and once the arrhythmia is confirmed, then delivers therapeutic stimulation to the heart. In a second embodiment the present invention operates to re-initiate skeletal muscle stimulation once the arrhythmia is confirmed but prior to the delivery of the therapeutic stimulation to the heart.
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