DUAL-CHAMBERED PACEMAKER AND DEFIBRILLATOR

Abstract: A medical interventional device (13) is structured for implantation in a human patient (10), to respond to detection of cardiac dysrhythmias. Dysrhythmias in either the atrial or ventricular chambers (24, 29) are automatically treated by a selected therapy regimen consisting of pacing, cardioverting or defibrillating waveforms of predetermined type and energy content to the chamber diagnosed as that in which the dysrhythmia originated. The device incorporates a DDD or DDD-R pacemaker (not numbered) for dual chamber sensing of electrical (ECG) activity, and for constant atrioventricular synchronization. A microprocessor-based logic subsystem (not numbered) diagnoses the origin of a rhythm disorder and identifies the originating heart chamber. The electrode system (21, 26, 42, 38) for delivering the selected therapy includes a single lead (22, 27) for pacing, sensing, cardioversion and defibrillation associated with each of the right atrial and ventricular chambers (24, 29). The device's metal case (15) may be used as the defibrillator's counter-electrode. A cardiac electrode (42) implanted in the distal coronary sinus improves defibrillation and left heart stimulation for better hemodynamic response. Dual chamber rate responsive pacing further improves hemodynamics.

Description: CARDIAC STIMULATOR AND DEFIBRILLATOR Cross-Reference to Related Application This application is a continuation-in-part of co-pending United States patent application Serial No. 08/904,851, now U.S. Patent No. 6,076,014, of the applicant herein. Background of the Invention The present invention relates generally to implantable medical mterventional devices and methods for treating cardiac rhythm disorders, and more particularly to an implantable defibrillator for ventricular defibriUation, with pacing and sensing of the atrium and related methods of therapy using such implantable defibrillators. Current implantable defibrillators perform a variety of functions designed to treat ventricular arrhythmias, including sensing of ventricular signals, detection of ventricular arrhythmias consisting of bradycardia, tachycardia, and fibrillation, and delivery of appropriate therapy automatically selected from among bradycardia and antitachycardia pacing, cardioverting and defibrillating shocks of the ventricles to correct the disorder. A serious problem with these devices is that a significant percentage of the defibrillating shocks delivered to the ventricles - about 25% — are falsely fired, delivered while the patient is fully conscious. The statistic is supported by recordings of cardiac activity among patients whose implanted devices have Holter function capabilities, and study of the recorded time period immediately before and up to delivery of the defibrillating or cardioverting shock, as well as by numerous interviews of defibrillator patients. Aside from the extreme pain suffered from a false shock, the patient tends to quickly lose confidence in the reliability of the implant as a life-saving device. A large part of the reason for the false shocking is that many patients develop atrial fibrillation and atrial flutter spontaneously, and, with a tendency for fast conduction through the atrioventricular (AV) node, the ventricle is driven at a high rate. If the ECG criteria for ventricular tachycardia or fibrillation on which the implanted device relies for performing its therapy functions are fulfilled, a high energy cardioverting or defibrillating shock will be delivered to the ventricle. The shock — albeit false — is a proper response, given the criteria from which the determination was made. Rather, it is the data on which this response is based that is insufficient. The solution to this problem of intermittent atrial fibrillation and flutter that can give rise to false shocks is to give greater attention to the status of the atrium. Currently available implantable defibrillator devices are unable to provide the solution because their focus is on the status of the ventricle. Recognition of atrial activity together with that of ventricular activity enables better discrimination of sinus rhythm, sinus tachycardia, ventricular fibrillation and ventricular flutter from one another. The better discrimination of the dysrhythmia — or absence thereof — allows the device to more properly respond with a corrective therapy that is based on the true condition of the patient. In other words, the device can better distinguish which heart chamber is attributable to the arrhythmia, so as to respond in kind. It is a principal aim of the present invention to provide an implantable defibrillator that monitors the atrial status as well as the ventricular status, to discriminate arrhythmias of atrial origin from arrhythmias of ventricular origin, from which to better select the proper electrical therapy to be delivered to the patient's heart, and more specifically, to eliminate or at least substantially lessen the likelihood of false shocking. Another problem which is not solved by the currently available spate of implantable defibrillators is the prominence of atrial arrhythmias which occur in implant patients because of a failure to address the atrial chamber. For example, the current devices perform ventricular pacing, but if retrograde conduction occurs the patient has a relatively high risk — 40% or more — of developing atrial fibrillation. In contrast, patients who are experiencing constant atrial stimulation along with the ventricular pacing have a much lower risk — on the order of 5 to 10% — of developing intermittent or chronic atrial fibrillation. Accordingly, another aim of the present invention is to provide an implantable defibrillator that performs pacing of the atrium as well as the ventricle, so as to enable better prevention of atrial arrhythmias. It is a further aim of the present invention to operatively combine a dual chamber pacing function with enhanced criteria for classification of arrhythmias. Summary of the Invention According to one aspect of the present invention, an implantable defibrillator possesses the usual capability of ventricular defibriUation along with ventricular bradycardia and tachycardia pacing, and sensing of the ventricular signals (i.e., ECG or cardiac signals) for determination of which of those therapies is to be delivered, but also performs stimulation of the atrium. Specifically, the device has the capability to pace the atrium to assure a constant or continuous rate of depolarizations, e.g., whether spontaneous (intrinsic, i.e., triggered by electrical activity of the sinoatrial (SA) node) or paced (i.e., stimulated, in the absence of such intrinsic activity, by operation of the implanted device). This type of atrial pacing assures that AV synchrony will be maintained, i.e., ventricular depolarizations are continuously synchronous with atrial depolarizations as a consequence of ongoing depolarizations of the atrium at the specified rate, with each atrial beat followed sequentially by a ventricular beat, under conditions in which the device is not called on to provide other therapies of a priority hierarchy that necessitate a different stimulation of the atrium such as antitachycardia pacing or cardioversion or defibriUation. This fallback or "default" condition of continuous stimulation of the atrium at a fixed minimum rate by the implanted defibrillator device serves to significantly reduce the incidence of atrial arrhythmias, and can also reduce or even eliminate dependence of the patient on prescribed antiarrhythmic medications or beta-b lockers. Further, the assured synchronization of the atrial and ventricular contractions of the heart represents a hemodynamic improvement for many patients who are candidates for an implantable defibrillator, by which the overall cardiac performance of these patients is improved to an extent that additionally aids in reducing the occurrence of dysrhythmias. In addition to pacing the atrium at a fixed rate which is appropriate for the particular patient who is to receive the implant, the defibrillator device is provided with a capability to sense the atrial rhythm, i.e., the atrial signal, independently of the ventricular signal. By doing so, and applying appropriate algorithms which compare the atrial and ventricular status, the implanted device can provide a more precise diagnosis of the nature of the underlying rhythm disorder. For example, if ongoing ventricular tachycardia is detected by the implanted device, the presence of normal sinus rhythm at the atrial sense signal input facilitates a diagnosis that the tachycardia is of ventricular origin. On the other hand, if the device senses ventricular tachycardia while the atrial sense signal reveals atrial flutter or atrial fibrillation, the origin of the rhythm disorder is determined to be in the atrium with a fast ventricular response. Since both atrial and ventricular pacing are employed, as well as atrial and ventricular sensing, the implantable device of the invention effectively combines the advantages of DDD pacing with a conventional "full function" defibrillator, which as noted above, generally includes brachycardia and tachycardia pacing of the ventricle and cardioversion and defibriUation of the ventricle. DDD, of course, is part of the three-position ICHD (Inter- Society Commission on Heart Disease Resources) device code which indicates that the device is adapted to provide dual chamber pacing, dual chamber sensing, and both triggered and inhibited modes of response (atrial triggered and ventricular inhibited). It is also desirable to provide the device with a rate adaptive or rate responsive capability which enables it to recognize whether the patient is engaged is resting or engaged in exercise, which is then used to adjust the rate according to the nature and extent of the exercise, and can also be taken into account in diagnosing whether a rhythm disorder is present (for example, in assessing whether a tachycardia is physiologic or pathologic). In a preferred embodiment, the invention employs an accelerometer as a sensor of activity of the patient. Thus, the DDD pacemaker with which the defibrillator is combined becomes a DDD-R (the "R" suffix being indicative of rate adaptive capability in the ICHD device code). Atrial monitoring, detection and treatment which are effective to terminate an anhythmia have the added benefits of lower energy dissipation and greater likelihood that treatment will be administered while the patient is conscious (with consequent easing of the task of successful treatment), compared to treating anhythmias of ventricular origin. For example, atrial flutter is broken by rapid atrial stimulation and atrial fibrillation is terminated by applying a defibrillating shock to the atrium — to synchronize the atrium — using virtually the same antitachycardia or defibrillator subsystem as that for treating ventricular tachycardia and fibrillation, except that the energy requirements are significantly lower and can be tolerated by the conscious patient without significant pain. According to another aspect of the invention, further improvements in diagnosis and treatment are obtained in a preferred embodiment by the use of fuzzy logic, which examines the extent to which a particular finding is true or false, allowing the decision on appropriate therapy to be made without regard to non-linearity of the findings. Determinations and selections are made according to the degree of membership of a particular statement (a finding) has to a certain class (e.g., the extent of truth or falsity of the finding). Another feature of the invention is that the number of leads to be implanted for use with the device is reduced, with attendant simplification of surgical procedure and reduction of cost, because the same lead may be used for atrial and ventricular pacing, sensing and defibriUation. Two transvenous leads having a size of about 6-1/2 French may be employed, with pacing/sensing cathodal tip and sensing/pacing/shocking anodal ring for conventional bipolar pacing and sensing, and low polarization electrodes for shocking to allow intrinsic rhythm to be detected without masking by polarization currents. Other aims of the invention, then, are to provide an implantable device that combines the capability for ventricular pacing, sensing and defibriUation with a DDD or DDD-R pacing capability to improve detection, diagnosis, and treatment of arrhythmias, including origin as being atrial or ventricular; provision of rate adaptive capability for both pacing rate adjustment according to activity and improved diagnosis of anhythmias; use of fuzzy logic to simplify and enhance diagnosis and treatment; and capability to use fewer leads for device implantation. In U.S. Patent No. 5,243,980, an automatic cardioverter/defibrillator (ACD) is disclosed as having the capability to discriminate ventricular tachycardias from supraventricular tachycardias, and to distinguish sinus tachycardias from non-sinus tachycardias. The device electrically stimulates fat pads associated with the S A node and AV node, as part of the nervous system that regulates the rhythm of the heart. The device of the '980 patent detects a ventricular tachycardia and then stimulates the nodal fat pads in synchronism with detected atrial depolarizations and/or ventricular depolarizations. The origin of a tachyarrhythmia is determined from an observation of which fat pad, when stimulated, induces a predetermined change in the cardiac rhythm. If no change in the ventricular rate is observed upon stimulation of either fat pad, the ventricle is deemed the origin; whereas if the atrial rate or the ventricular rate decreases, depending on which fat pad is stimulated, the tachyarrhythmia is deemed to be supraventricular in origin, or a sinus tachycardia. Although the '980 patent describes an implantable pacemaker/cardioverter/ defibrillator including possible DDD pacing, neither the type of pacing nor the identification of rhythm disorders corresponds to that of the present invention. Rather, the fat pad stimulation technique is employed. Brief Description of the Drawings The above and still further aims, aspects, features and attendant advantages of the present invention will become apparent from a detailed description of the best mode presently contemplated for practicing the invention, with reference to certain prefened embodiments and methods, in conjunction with the accompanying drawings, in which: FIG. 1 is a cutaway view of the patient's heart showing placement of signal generator and associated cardiac leads and electrodes of the implanted defibrillator, according to an exemplary embodiment of the invention; FIG. 2 is a functional block diagram of the signal generator of FIG. 1 illustrating lead/electrode connections; FIG. 3 is a simplified partial block diagram of the signal generator of FIG. 1; and FIG. 4 is a simplified functional flow diagram of the operation of the implanted defibrillator using evaluation logic for analysis and diagnosis. Description of the Presently Prefened Embodiment and Method Referring to FIG. 1 , a medical mterventional device such as implantable defibrillator 13 includes a signal generator 14. The generator is implanted in a surgically-formed pocket in the flesh of the patient's chest 10, or other desired location of the body. Signal generator 14 is conventional except as will otherwise be described herein, incorporating electronic components for performing signal analysis and processing, waveform generation, data storage, control and other functions, power supply (battery or battery pack), which are housed in a metal case (can) 15 compatible with the tissue and fluids of the body (i.e., biocompatible). The device is microprocessor-based with substantial memory, logic and other components to provide the processing, evaluation and other functions necessary to determine, select and deliver appropriate therapy including electrical shocks and pulses of different energy levels and timing for ventricular defibriUation, cardioversion, and pacing to the patient's heart 16 in response to cardiac dysrhythmias including ventricular fibrillation (VF), ventricular tachycardia (VT), and ventricular bradycardia. Composite electrical lead 18 which includes separate leads 22 and 27 with distally located electrodes is coupled at the proximal end to signal generator 14 through an electrical connector 20 in the header of case 15. Preferably, case 15 is also employed as an electrode such as electrical ground, for unipolar sensing, pacing or shocking. Unlike the defibrillator devices of the prior art, the signal generator and lead(s) of the present invention are implemented for atrial sensing, pacing and shocking as well as the ventricular functions. Defibrillating shocks of appropriate energy level are applied between the case and electrode 21 on lead 22 implanted in the right atrium 24 through the superior vena cava (SVC) 31, or between the case and electrode 26 on lead 27 implanted through the SVC in the right ventricle 29, for treating atrial fibrillation (AF) or VF, respectively. Leads 22 and 27 and their associated distal tip electrode 32 (to a separate conductor) and distal tip electrode 35 (also to a separate conductor within the lead), respectively, are used for both sensing and pacing cardiac activity in conjunction with the circuitry of signal generator 14. To that end, electrode 32 is positioned in the right atrium against either the lateral or anterior atrial wall thereof, and electrode 35 is positioned in the right ventricle at the apex thereof. Active or passive fixation of the electrodes maybe used to assure suitable excitation. Tip electrode tip 35 preferably has a standard 4 to 8 millimeter (mm) configuration, and is provided with soft barbs (tines) to stabilize its position in the ventricle. Each of the electrodes, those used for defibriUation and cardioversion, as well as those used for sensing and for pacing, are electrically connected to separate conductors in leads 22 and 27. If desired, rather than simply using metal case 15 as an electrode, an additional electrode 38 implanted subcutaneously is used. This serves to enhance the effectiveness of the anodal electrode of the case and to establish a better vector for the electric field produced by the defibriUation shock waveform, and thereby lower the defibriUation threshold. The lead 38 is electrically connected directly to the high voltage output circuitry in signal generator 14 via connector block 20, and runs subcutaneously for connection to an epicardial or pericardial patch electrode (not shown) or as a wire electrode (as shown) through an opening formed by puncture surgery at 39. The conductor for electrode 36 of lead 38 may be implanted subcutaneously to a point 39, and then by puncture surgery through the thoracic cage and the pericardial sac, under a local anesthetic. The lead 38 is run parallel to the sternum, through the puncture, and then through the patient's thoracic cage and into the pericardial sac. It may even be threaded through the thoracic cage, the pericardial space about the left ventricle and atrium, and back along the right atrial appendage, external to the heart. The distal end 36 of lead 38 is preferably placed close to the left atrium of the patient's heart to provide an increase in electric field strength and support the strong vector of the electric field according to the heart chamber to be defibrillated. Selection of the chamber (atrium or ventricle) which is to undergo defibriUation is made by choosing the appropriate endocardial counter-electrode (21 or 26, respectively) to be energized together with the electrode 38, if the case 15 is not used directly as the other electrode. The path of conductor 38 and electrode 36 need not be as shown in the Figure, but may alternatively be run as described immediately above. The positioning improves the vector for defibriUation through the atrium as well as the ventricle. Atrial coil electrode 21 is used for bipolar sensing as well as a counter-electrode for atrial defibriUation or cardioversion shocking. Like electrode 36, electrode 21 is preferably composed of any conventional material that provides them with very low polarization and low defibriUation threshold, to allow the intrinsic rhythm to be detected almost immediately after delivery of a shock for accurate determination of the current status of electrical activity of the atrium. Low polarization and accurate sensing are especially desirable for detection and evaluation of atrial status since atrial signals have magnitudes of only about 20% to 25% those of ventricular signals because of the smaller atrial mass. The coil structure of electrode 21 is also desirable to provide a large effective electrical surface area (for example, in a range from three to six square centimeters), which provides greater energy efficiency for defibriUation. As with atrial electrode 21, ventricular electrode 26 of lead 27 is positioned for use as a defibriUation electrode as well as for bipolar sensing in the ventricle. For defibriUation, electrode 26 also cooperates with the metal case 15 and/or subcutaneous or pericardial electrode 36, whichever of these latter electrodes is used in the defibrillator implementation. The coil structure for electrode 26 provides it with an effective surface for defibriUation shocks. As an alternative, the electrode maybe composed of fine metallic filaments or fibers of platinum iridium alloy, and coiled, wound or braided to offer similarly desirable electrode characteristics. Thus, the tip electrodes of leads 22 and 27 are used for sensing and pacing of the respective atrial and ventricular chambers as in a conventional DDD pacemaker, with dual- chamber pacing, dual-chamber sensing, and both triggered and inhibited response. Further, the defibrillator 13 uses a transvenous electrode for ventricular defibriUation and stimulation and an atrial bipolar lead for sensing and atrial defibriUation, so that atrial defibriUation is performed with one of the same electrodes used for atrial stimulation and sensing. Rather than terminating at a distal tip electrode 32 in the left atrium, the atrial transvenous lead 22 may have electrode 21 positioned at a mid-point of that chamber, and be sufficiently extensive to be threaded through the right atrium into the coronary sinus, with an additional coil counter-electrode 42 to be positioned therein connected to a separate conductor of the lead 22. With this alternative embodiment, a defibrillating shock waveform can be applied between electrode 42 and atrial defibriUation electrode 21 upon detection of atrial fibrillation. In that configuration, electrode 42 would replace signal generator case 15 or lead electrode 36 as the selected electrode, and enables a strong vector for the electric field through the right and left atrial chambers. Thus, electrode 42 is desirably positioned in the distal coronary sinus for defibriUation of the atria in conjunction with electrode 21, and can also serve for defibriUation of the ventricle as well as for sensing and stimulation of especially the left ventricle for improved hemodynamics. DefibriUation of the atrium and ventricle is achieved by application of shock waveforms of suitable shape and energy content between appropriate electrodes, such as between electrode 36 and electrode 21 for atrial fibrillation, or between electrode 42 and electrode 21 for atrial fibrillation; or between electrode 36 and electrode 26 for ventricular fibrillation, in which atrial electrode 21 can be used additionally as either anode or cathode. The case 15 can serve as the anode for delivery of the shock as well, and can provide ground reference potential for unipolar sensing and pacing, in both chambers. In a prefened embodiment of the invention, the implantable defibrillator is provided with a rate-adaptive pacing capability by employing an accelerometer 40 as an activity sensor located on a hybrid electronic circuit (not shown) mounted within signal generator case 15. The hybrid electronic circuitry on which the accelerometer is located or with which it is associated may include a micro-miniaturized silicon structure incorporating an electro¬ mechanical (or mechano-electrical) converting element as the accelerometer, as well as another or other devices as a part of such circuitry or used in conjunction therewith for performing other logic and electronic circuit functions in connection with processing the sensor signal. An exemplary structure is described, for example, in U.S. Patent No. 5 ,031 ,614, but other conventional structures may be employed for the circuitry and/or for the accelerometer. The sensor detects movement or acceleration of the patient in the course of physical activity, which may simply be even a slight change in physical position. The accelerometer is preferably mechanically isolated from the wall of the case to avoid a false indication of physical activity as a result solely of pressure on the surface of the case itself. In a rate-adaptive (DDD-R) pacing mode, the accelerometer sensor signal is used to control the rate at which pacing pulses are generated by the signal generator 14, to vary the pacing rate according to the patient's metabolic need and thus to improve hemodynamic performance, especially for patients with enlarged heart. The physical activity-dependent regulation of the heart rate improves the patient's exercise capacity, and the activity sensor- controlled variation of the atrial rate serves as a detenent against atrial dysrhythmias. In addition to providing the rate adaptive pacing capability in the implanted device 13, accelerometer 40 also functions to provide information to confirm or reject a diagnosis or analysis of a dysrhythmia detected by the cardiac activity sensor(s). For example, the accelerometer may indicate that a tachycardia is physiologic rather than pathologic, or vice versa, by evidencing that a sudden jump in heart rate is attributable to abrupt physical activity of the patient, or by indicating that a ventricular tachycardia is pathologic because it occurced at a time that the patient was resting. From the data confirming or rejecting a cardiac event, an appropriate evaluation and decision maybe made as to whether the patient is experiencing a particular dysrhythmia, and, if so, identifying and selecting the most appropriate therapy to be delivered to return the patient's heart to normal cardiac rhythm. Additionally, the accelerometer may aid in demonstrating that a perceived ventricular dysrhythmia is in fact of atrial origin. An evaluation of the accelerometer signal will determine whether a given atrial rate is adequate or inadequate. A conditional ventricular tracking limit is established so that the maximum achievable atrial triggered rate is controlled by the sensor, which is especially important to limit the ventricular rate response in cases where atrial arrhythmias would trigger an inappropriately high ventricular rate, as in a pure DDD pacemaker. FIG.2 is a functional block diagram of signal generator 14. Cardiac activity (internal ECG) signals detected by tip electrodes 32 and 35 of atrial and ventricular transvenous leads 22 and 27 (or, for bipolar sensing, together with respective coil electrodes 21 and 26) are processed initially by sense amplifiers 51 and 52, respectively. Further processing of these signals is performed by atrial and ventricular evaluation logic 55 and 56, respectively; and separate activity evaluation logic 58 is used to process the activity output signal of accelerometer 40. The signal information generated by the accelerometer indicates physical movement and physical position of the patient, as additional information about the status of the patient which can be used to confirm or reject the indicia supplied by the other sensors. For example, if the ventricular sense channel shows a fast ventricular rate and the accelerometer sense channel shows that the patient is not moving, the two pieces of data confirm the existence of a pathologic tachycardia, albeit the origin maybe an atrial rhythm disorder. The latter can be confirmed or rejected by the signal information from the atrial sense channel. Thus, the non-ECG sense channel provides additional evidence for enhancing the determination of the nature and type of an anhythmia detected by one or both of the ECG electrode sensors in the atrial and ventricular chambers of the heart. Each evaluation logic circuit uses its input signal to develop a general finding or "statement" on the status of the respective sense channel. The statements may be, and typically are, imprecise. For example, atrial evaluation logic 55 may examine the processed signal from its sense channel and, based on a comparison with a preset normal heart rate, may indicate that the atrial rate is normal (or fast, or slow). Similarly, ventricular evaluation logic 56 may make a determination from its criteria that the ventricular rate is fast. And the activity evaluation logic 58 may determine that the patient has commenced walking, from the immediately preceding condition of rest. Statements or findings such as these are supplied, for example, to a fuzzy logic comparator 60 or other logic circuitry in the signal generator 14. ECG criteria may be applied to diagnose atrial tachycardia, including, for example, sudden rate change, increase in rate over time, absolute atrial rate, rate stability, variation of cycle length of the individual atrial pulses, and variation of the atrial pulse amplitude. These same ECG criteria may be applied to discriminate stable atrial rhythms, which may be sinus rhythm, be sinus anhythmia, sinus arcest, ectopic atrial beats, atrial flutter and atrial fibrillation. While fuzzy logic is somewhat imprecise, and other logic may be employed in its place, it is illustrated in an exemplary embodiment because it provides a practical approach to decision-making based on the extent to which a statement is either true or false, i.e., the degree of membership to a particular class. If the statement is 100% true or 100% false, the decision is simple. Usually, however, the statement is partly true and partly false — for example, it maybe 70% true and 30% false — so that the decision is less clear. Using fuzzy logic, a judgment is effectively based on how much a statement belongs to zero or one. The process is a type of bi-level logic in which the degree of membership in a statement is determined in a manner similar to a polling process. Fuzzy logic may be implemented in digital or analog circuitry, with very low power consumption, and fuzzy logic principles are well known. No claim is made herein to the invention of fuzzy logic per se. In the exemplary embodiment, fuzzy logic comparator 60 looks at the inputs derived from the three sense channels, and uses a predetermined set of rules or algorithms to govern which of a plurality of different therapies will be used to treat a perceived rhythm disorder. By application of appropriate algorithms which independently compare the atrial status, the ventricular status, and the physical activity status, the implanted defibrillator establishes an enhanced diagnosis of the nature of the underlying rhythm disorder; and this, in turn, leads to a more accurate selection of the proper therapy for treatment. To apply the appropriate therapy to the individual archythmia condition as quickly and accurately as possible, several algorithms may be used for the decision-making. An important aspect is not only to consider the momentary status of the atrial and ventricular rates and the ECG morphology, but also to incorporate into the decision process the historical trend and to compare it to the actual atrial and ventricular ECG signal with respect to cycle length, amplitude morphology vector, and cycle length stability. For example, if the atrial rate is more than 300 beats per minute (bpm) and the cycle length varies more in comparison to atrial rates less than 150 bpm (quotient of mean cycle length divided by standard deviation of cycle length) and the mean atrial signal amplitude is less than the atrial signal amplitude with atrial rates slower than 150 bpm, then the conditions of atrial fibrillation are fulfilled. If the ventricular rate is between 120 bpm and 190 bpm and has changed in the same moment as a change observed in the atrial rate — in comparison to the historical trend ~ a fast ventricular response following enhanced AV nodal conduction to the atrial fibrillation is most likely, and therapy appropriate for atrial fibrillation is called for. In another example, if the atrial rate exceeds 200 bpm to 350 bpm, and if the cycle length is relatively constant (i.e., the standard deviation from beat to beat is low in comparison to the mean of the cycle length), and the amplitude of the atrial ECG signal is rather constant and not less than 50% of the atrial signal amplitude with sinus rhythm, then atrial flutter is diagnosed by the detection algorithm. Further confirmation of this diagnosis is established by consideration of the historical trend. A sudden change in atrial rate from one beat to another confirms the pathologic atrial status. In this case, the implanted defibrillator applies a burst or other form of rapid atrial stimulation as a therapeutic option to interrupt the tachycardia. The therapy of choice if the rapid pacing fails to break the atrial flutter is to apply a low energy atrial shock starting with about 0.3 joule, and to increase the energy with successive shocks until successful termination of flutter is achieved. A further example is a situation in which the ventricular rate fulfills the criteria of ventricular fibrillation and the activity sensor output indicates sudden collapse (syncope) of the patient, which indicates compromised cerebral perfusion following a fast and inegular heart beat. In that situation, the defibrillator is directed to immediately commence charging to the maximum available energy to apply a ventricular defibrillating shock, irrespective of whatever the momentary atrial status may be. Byway of further example, stated in terms of a fuzzy logic diagnosis and therapeutic response, one rule maybe: LF (ventricular rate is FAST .AND. atrial rate is NORMAL. AND. patient activity is SLOW) THEN (ANTITACHYCARDIA PACING of ventricle). The evaluation of a rapid ventricular rate in the presence of normal sinus rhythm in the atrium is diagnosed as a pure ventricular tachycardia, leading to selection of antitachycardia pacing therapy applied to the ventricle. Another fuzzy logic rule may be: IF (atrial rate is FAST .AND. ventricular rate is FAST .AND. patient MOTIONLESS) THEN (DEFIBRILLATION of atrium). The evaluation of a rapid ventricular rate in the presence of a fast atrial rate while the patient is not moving, is diagnosed as a fast ventricular response to atrial flutter or atrial fibrillation, and as calling for the delivery of relatively low energy shocks (e.g., 5 joules or less) to the atrium from an atrial defibrillator or cardioverter. This is in marked contrast to a typical response to the detection of a rapid ventricular rate by a conventional automatic implantable defibrillator, in which a high energy (e.g., exceeding perhaps 30 joules) shock maybe delivered to the patient's heart despite the case that in fact the patient is experiencing only atrial flutter and is fully conscious. The high energy shock is not only painful, but serves no useful purpose in treating the underlying rhythm disorder. It may indeed exacerbate the problem by creating an environment conducive to true VF. The therapy designated by the output signal of the fuzzy logic comparator 60 is delivered by the applicable portion of the signal generator, which may be for bradycardia pacing (DDD-R) 62, antitachycardia pacing 63, atrial defibriUation (or cardioversion) 64, or ventricular defibriUation (or cardioversion) 65. It will be readily understood that each of these therapy-delivering subsystems need not be entirely separate or distinct from one another, but may, and generally will, share components among one another. If the therapy is successful to alleviate the detected rhythm disorder, the fuzzy logic comparator recognizes this state of affairs from the output signal information supplied by the evaluation logic circuits. For example, an appropriate rule may be: IF (atrial rate is NORMAL .AND. ventricular rate is NORMAL. AND. patient movement is DON'T CARE) THEN (MAINTENANCE). In this example, the specified maintenance may be to continue pacing the atrium at a constant rate and to synchronize the atrial and ventricular rates. FIG. 3 is a simplified block diagram of a portion of the signal generator 14 of the implantable defibrillator illustrating component blocks used in treating pacing problems such as bradycardia and tachycardia, as well as in treating both atrial and ventricular fibrillation. Circuit details are minimized or omitted for the sake of convenience and clarity, such as signal conversion components. The subsystem includes a microprocessor 70 with associated memory 71 which may, for example, be volatile SRAM, for storing cardiac rhythm data from each of the atrial and ventricular ECG sensors. If an evaluation of the ECG sense signals by logic 73 indicates that the patient is experiencing fibrillation, the microprocessor 70 will activate switching circuit 75 to charge output storage capacitors 76 to a predetermined appropriate level for delivering a defibrillating shock waveform to the defibriUation electrodes for the designated chamber of the heart. DDD-R pacemaker 80 is also responsive to the ECG sense signal inputs, and has variable rate control which is activated by module 81 in response to the physical activity sense signal supplied by accelerometer 40. In operation, evaluation logic circuits 55 and 56 (FIG.2) perform independent checks of the atrial rhythm status and the ventricular rhythm status, and fuzzy logic comparator 60 makes a comparison of these findings from the logic evaluations. The use of fuzzy logic, and avoidance of the linear mathematical approaches conventionally applied in the logic hardware and software of implantable defibrillators, is desirable because the inputs to the comparator display non-linearities, including those received from the cardiac activity (ECG) sense channels and the physical activity sense input from the accelerometer. The non- linearities present difficulties in performing standard linear mathematical computations. In contrast, fuzzy logic can more easily diagnose an atrial or ventricular rhythm disorder, and reach a decision, for example, of whether to shock the atrium to return the heart in atrial fibrillation or atrial flutter to sinus rhythm, or to pace the ventricle to break a ventricular tachycardia, or to apply a shock waveform to the ventricle to terminate ventricular fibrillation. Thus, the combination of a conventional defibrillator with a DDD-R pacemaker in an implantable device offers advantages over the prior art. By stimulating the atrium at a constant rate, the occurrence of atrial dysrhythmias is reduced, especially when the stimulation is applied in conjunction with antianhythmic medications or beta-blockers. The hemodynamic improvement obtained by synchronization of the atrial and ventricular contractions further improves the overall cardiac performance of the patient, and therefore helps to reduce the occunence of dysrhythmias. Further, the DDD-pacing renders the implanted device capable of sensing and responding to the status of the atrium, independent of ventricular sensing. Atrial stimulation is normally ca ied out to assure a constant or continuous rate of depolarizations, whether spontaneous or paced. The objective is to maintain AV synchrony, so that ventricular depolarizations are continuously synchronous with atrial depolarizations and each atrial beat is followed sequentially by a ventricular beat. Sensing and pacing are also performed in the DDD mode in both the atrium and ventricle. A method of treating any of multiple cardiac rhythm disorders with only the single implanted medical mterventional device includes device-implemented steps illustrated in the flow diagram of FIG. 4. Cardiac activity of the ventricle is sensed at 100 to detect whether rhythm disorders are present at 101. Concurcently, atrial activity is sensed at 103 to detect rhythm disorders in that chamber at 105. When a dysrhythmia is detected in the atrium or ventricle, a diagnosis is performed to identify the heart chamber in which it originated, and an appropriate therapy is then selected and delivered to the heart chamber identified as the origin of the detected disorder. Discrimination between the detected atrial and ventricular rhythm disorders is preferably performed by use of the device fuzzy logic at 106, but can alternatively be performed by other logic means which may be in or outside of the microprocessor of the device. Preferably, the ECG signal of the respective chamber is analyzed with respect to at least one of the attributes of cycle length, cycle length variation, amplitude, amplitude variation, and frequency content of the signal. Cunent ECG data from the atrial and ventricular chambers is compared with previous ECG data for the respective chambers, to assess trend and first in/first out data of the individual ECG signals, for classifying the dysrhythmia. If no dysrhythmia is present in the atrium, the implanted device continues pacing the atrium at a constant rate for AV synchronization. If a dysrhythmia is detected in either chamber (or in both), an appropriate therapy is selected at 108 from among a plurality of electrical waveform therapies, to treat the detected disorder. The atrium is paced continuously at the preselected minimum rate, except when the physical activity sensor (accelerometer 40) detects activity on the part of the patient which requires an applicable increase in the pacing rate, or when a different therapy regimen is selected and delivered to treat the detected disorder, or when the intrinsic atrial rate exceeds the minimum preselected pacing rate. Separate single transvenous cardiac leads are implanted for sensing, pacing, cardioverting and defibrillating the atrial and ventricular chambers, respectively. Although a prefened embodiment and method have been disclosed herein representing the best mode presently contemplated for practicing the invention, it will be apparent to those skilled in the art, from a consideration of the foregoing description, that variations and modifications of the described embodiment and method maybe made without departing from the true spirit and scope of the invention. Accordingly, it is intended that the invention shall be limited only to the extent required by the appended claims and the rules and principles of applicable law.

Claims: What is claimed is: 1. An implantable medical mterventional device having means for selectively supplying a plurality of therapeutic regimens to alleviate various ones of a plurality of cardiac rhythm disorders, including ventricular defibrillator means responsive to ventricular fibrillation of a patient's heart for use in defibrillating the ventricles of the heart, and an improvement to enhance recognition, discrimination and therapeutic treatment of cardiac rhythm disorders, said improvement comprising: an artificial pacemaker for pacing the patient's heart including continuous sensing and responsive pacing of cardiac activity of both the atrial and ventricular chambers for monitoring the status of cardiac activity of the atrial as well as the ventricular chambers and for maintaining atrioventricular synchrony of the patient's heart, and evaluation logic for evaluating cardiac activity detected by said artificial pacemaker and defibriUation means of said device to develop generalized findings indicative of presence of a particular cardiac rhythm disorder, for identification and treatment thereof. 2. The implantable medical mterventional device of claim 1, wherein: said artificial pacemaker includes: an atrial sensor for sensing electrical activity of the atrium of the patient's heart to produce a signal representative of the atrial activity, and a pacing generator for continuously supplying pulses to stimulate the atrium at a predetermined adequate rate. 3. The implantable medical mterventional device of claim 2, wherein: said pacing generator includes: a pulse generator for generating pulses at said predetermined adequate rate, a sensor for detecting a parameter indicative of a physiological need of the patient for pacing at an atrial rate different from said predetermined adequate rate and producing a signal indicative of such physiological need, and a variable control responsive to said signal indicative of physiological need for controllably varying the rate at which pulses are generated by the pulse generator to modify the paced atrial rate to a rate for satisfying said physiological need. 4. The implantable medical mterventional device of claim 3, wherein: said artificial pacemaker further includes a ventricular sensor for sensing ventricular activity of the patient's heart to produce a signal representative thereof, and said evaluation logic is responsive to the sensed atrial and ventricular activity of the patient's heart for comparing the atrial rate to the ventricular rate to diagnose the presence of a cardiac rhythm disorder experienced by the patient, and based thereon to prescribe an appropriate one of said plurality of therapeutic regimens to alleviate the diagnosed cardiac rhythm disorder. 5. The implantable medical mterventional device of claim 2, further including: an atrial defibrillator for generating shocks for application to the atrium responsive to detection of atrial fibrillation and, in conjunction with the artificial pacemaker, to return the atrial rate to said predetermined adequate rate synchronized with the ventricular rate. 6. The implantable medical mterventional device of claim 1 , further including: a single atrial lead and a single ventricular lead operatively coupled to said signal generator, each said lead including at least a portion composed of a conductive coil of a surface of more than 50 mm 2 to permit detection of intrinsic rhythm in a respective chamber of the patient's heart, and for application of defibrillating energy shocks from said signal generator to a respective chamber upon detection of fibrillation thereof. 7. The implantable medical mterventional device of claim 3, wherein: said evaluation logic is adapted to diagnose an apparent atrial rhythm disorder from said atrial sense signal, and said parameter detecting sensor detects the status of said physiological parameter of the patient other than ECG to verify or reject a diagnosis of atrial rhythm disorder derived from the atrial sense signal. 8. The implantable medical mterventional device of claim 7, wherein: said parameter detecting sensor comprises an accelerometer for detecting patient activity. 9. The implantable medical mterventional device of claim 4, wherein: said evaluation logic includes means for discriminating between detected atrial and ventricular rhythm disorders to identify the heart chamber in which a detected disorder originated, and means for automatically selecting pacing, cardioverting or defibrillating therapy for delivery to the identified heart chamber to alleviate the detected rhythm disorder. 10. The device of claim 6, wherein: said single atrial lead includes a first electrode adapted to be positioned in the right atrium and a second electrode adapted to be positioned in the distal coronary sinus of the patient when said atrial lead is implanted, for left ventricular stimulation and enhanced defibriUation capability. 11. An mterventional medical device structured and adapted for implantation into a patient to diagnose cardiac rhythm disorders and selectively deliver any of a plurality of electrical waveform therapies to treat a sensed disorder, the device comprising: ventricular therapy means for sensing and treating ventricular rhythm disorders, and atrial therapy means for sensing and treating atrial rhythm disorders, and including means to synchronize atrial and ventricular beats when atrial rhythm disorders are not present; said ventricular therapy means and said atrial therapy means including means for defibrillating the respective ventricular and atrial chambers, ECG data storage means, and logic means for comparing cunent ECG parameters with stored ECG parameters for enhancing the diagnosis to provide more precise rhythm disorder recognition and classification. 12. The mterventional medical device of claim 11, including: means for separating atrial and ventricular ECG signals into attributes including absolute voltage amplitude of the ECG signal, amplitude relative to stored ECG signals, variation of ECG signal amplitudes, cycle length, variation of cycle length, morphology of ECG signal, and vector of an intracardiac ECG. 13. A method of treating a plurality of cardiac rhythm disorders with a single medical mterventional device implanted in a human patient, including the device- implemented steps of: sensing both atrial and ventricular rhythm disorders of the patient's heart and responding with automatic therapeutic treatment from the device by application to a heart chamber of an appropriate therapy regimen selected from pacing, cardioverting and defibrillating electrical waveforms of predetermined type and energy content, and selecting the appropriate therapy regimen and the heart chamber to which it should be applied by evaluating atrial and ventricular ECG signals to develop therefrom generalized findings indicative of existence of a specific rhythm disorder and, from the generalized findings, to identify the heart chamber in which the specific rhythm disorder originated, including performing the step of evaluating the atrial and ventricular ECG signals by logic comparison of current ECG parameters with stored ECG parameters for enhanced recognition and classification of rhythm disorders. 14. The method of claim 13, further including: continuously pacing the atrium at a minimum rate except when a sensed disorder requires a different therapy regimen to be applied to the atrium. 15. The method of claim 13, further including: detecting patient physical activity and responding thereto by adjusting the pacing rate of both atrium and ventricle to satisfy the physiological need of the patient for a faster rate during the physical activity. 16. The method of claim 15, further including: using the detection of patient physical activity to confirm or to reject the indication of specific rhythm disorder from the evaluation. 17. An implantable cardioverter/defibrillator device, comprising: a DDD-R mode pacemaker having electrode means for continuously sensing and pacing atrial and ventricular chambers to maintain AV synchrony, and sensor means to generate a rate adaptive pacing signal to vary stimulation rate of a patient's heart according to the patient's metabolic need, cardioverter/defibrillator means in combination with said pacemaker, for treating atrial and ventricular arrhythmias including fibrillation; evaluation means operatively combining said DDD-R pacemaker and said cardioverter/defibrillator means for developing generalized findings indicative of the apparent presence of a specific anhythmia of the atrial or ventricular chamber from sensed signals therefrom by which to assess appropriate treatment therapy for the indicated anhythmia, and means for establishing a ventricular tracking limit for control of maximum achievable paced ventricular rate attributable to sensed atrial beats, whereby to limit ventricular rate response of the heart where atrial arrhythmias might otherwise trigger an excessively high ventricular rate with a pure DDD mode pacemaker. 18. The implantable cardioverter/defibrillator device of claim 17, further including: decision means for performing device-implemented logical decisions of heart rate; and wherein: said sensor means comprises an accelerometer for assisting said decision means in performing the device-implemented logical decisions through evaluation by said decision means of the signal generated by said accelerometer to determine whether a detected heart rate is adequate.

Inventors: ALT ECKHARD, ALT, ECKHARD
Applicants: INTERMEDICS INC, INTERMEDICS, INC.
Application year: 2000
Main classification: A61N1
IPC codes: A61N1