Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-11-18
2001-12-04
Layno, Carl (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06327499
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to implantable medical interventional devices and methods for treating cardiac rhythm disorders, and more particularly to an implantable defibrillator for ventricular defibrillation, 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 arrhythnias, 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 fublfilled, 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 ifretrograde 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 defibrillation 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 defibrillation.
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-blockers. 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 defibrillation of the ventricle. DDD, of course, is part of the three-position ICHD (Inter-Society Cormission 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 capabil
Blank Rome Comisky & McCauley LLP
Layno Carl
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