Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-04-03
2003-01-14
Jastrzab, Jeffrey R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S025000
Reexamination Certificate
active
06507756
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to dual chamber pacing systems, including rate responsive pacing systems, and more particularly to the employment of a time-dependent AV delay for pacing hearts in Congestive Heart Failure (CHF) with Dilated Cardiomyopathy (DCM).
BACKGROUND OF THE INVENTION
Dual chamber pacing systems operating in the multi-programmable, DDD and DDDR pacing modes have been widely adopted in implantable dual chamber pacemakers and certain implantable cardioverter/defibrillators (ICDs) for providing atrial and ventricular (AV) synchronized pacing on demand. A DDD pacemaker implantable pulse generator (IPG) includes an atrial sense amplifier to detect atrial depolarizations or P-waves and generate an atrial sense event (A-EVENT) signal, a ventricular sense amplifier to detect ventricular depolarizations or R-waves and generate a ventricular sense event (V-EVENT) signal, atrial and ventricular pacing pulse generators providing atrial and ventricular pacing (A-PACE and V-PACE) pulses, respectively, and an operating system governing pacing and sensing functions. If the atria fail to spontaneously beat within a pre-defined time interval (atrial escape interval), the pacemaker supplies an A-PACE pulse to the atria through an appropriate lead system. The IPG supplies a V-PACE pulse to the ventricles through an appropriate lead system at the time-out of an AV delay timed from a preceding A-EVENT or generation of an A-PACE pulse unless a non-refractory V-EVENT is generated in response to an R-wave during the AV delay. Such AV synchronous pacemakers which perform this function have the capability of tracking the patient's natural sinus rhythm and preserving the hemodynamic contribution of the atrial contraction over a wide range of heart rates.
The rate-adaptive DDDR pacing mode functions in the above-described manner but additionally provides rate modulation of a pacing escape interval between a programmable lower rate and an upper rate limit (URL) as a function of a physiologic signal or rate control parameter (RCP) developed by one or more physiologic sensors and related to the need for cardiac output. In the DDDR pacing mode, reliance on the intrinsic atrial heart rate is preferred if it is appropriately between the URL and the programmed lower rate. At times when the intrinsic atrial rate is inappropriately high, a variety of “mode switching” schemes for effecting switching between tracking modes and non-tracking modes (and a variety of transitional modes) based on the relationship between the atrial rate and the sensor derived pacing rate have been proposed as exemplified by commonly assigned U.S. Pat. No. 5,144,949, incorporated herein by reference in its entirety.
The DDD and DDDR pacing modes were initially perceived to be of greatest benefit to cardiac patients whose hearts have an intact sinoatrial (SA) node that generates the atrial depolarizations detectable as P-waves, but also suffer defective A-V conduction, or AV block, wherein the ventricles fail to depolarize in synchrony with the atria. The DDD pacing mode paces the ventricles in synchrony with the atria after a timed out AV delay and is generally adequate to restore cardiac output for sedentary patients. Active patients with Sick Sinus Syndrome (SSS) have an atrial rate which can be sometimes appropriate, sometimes too fast, and sometimes too slow. For SSS patients, the DDDR pacing mode provides some relief by pacing the atria and ventricles at a physiologic rate determined by an algorithm responsive to the RCP indicative of the patient's metabolic needs.
A loss of A-V electrical and mechanical synchrony can result in series of asynchronous atrial and ventricular depolarizations at independent rates that periodically result in an atrial depolarization that closely follows a ventricular depolarization. When this occurs, the left atrium contracts against a closed mitral valve, resulting in impeded venous return from the pulmonary vasculature due to increased atrial pressure and possibly even retrograde blood flow into the pulmonary venous circulation. As a result, the volume and pressure in the pulmonary venous circulation rise. Increased pulmonary pressures may lead to pulmonary congestion and dyspnea. Distention of the pulmonary vasculature may be associated with peripheral vasodilation and hypotension. In addition, the concomitant atrial distention is associated with increased production of atrial natriuretic factor and increases the susceptibility to atrial arrhythmias and possibly rupture of the atrial wall. Finally, turbulence and stagnation of blood within the atrium increase the risk of thrombus formation and subsequent arterial embolization. Maintenance of AV mechanical synchrony is therefore of great importance as set forth in greater detail in commonly assigned U. S. Pat. No. 5,626,623, incorporated herein by reference in its entirety.
Theoretically, AV synchrony is best maintained during dual chamber cardiac pacing by setting the AV delay interval in a physiological range related to the spontaneous atrial rate or the sensor derived rate, depending on which is the controlling pacing mode. However, while “physiological” AV delays may ensure right heart AV electrical synchrony, in patients with significant interatrial and/or interventricular conduction delays, left heart electrical and mechanical synchrony, and thus hemodynamic performance, may be significantly compromised.
The maintenance of AV mechanical synchrony is of vital importance in patients with compromised cardiac function, including CHF, DCM, hypertrophic cardiomyopathy, hypertensive heart disease, restrictive cardiomyopathy, and other disorders that are characterized by significant diastolic dysfunction. In such patients, passive ventricular filling is reduced due to poor ventricular compliance and incomplete or delayed relaxation. Consequently, there is increased reliance on atrial contraction for ventricular filling sufficient to achieve adequate stroke volume and maintain low atrial and pulmonary pressure.
Carefully controlled AV delays have been found to be beneficial to increase cardiac output of hearts of certain patients that exhibit cardiomyopathy and forms of CHF, and in particular Hypertrophic Obstructive Cardiomyopathy (HOCM). HOCM is characterized by a narrowed left ventricular outflow tract (LVOT), which causes a significant increase in the left ventricular end systolic pressure. The narrowed LVOT is caused by an increased thickness of the interventricular septum which obstructs blood flow during systole, the time of cardiac ejection.
Symptomatic improvement of patients with HOCM can be obtained in some cases with the use of standard pharmacotherapy. However, drugs in use for this therapy have disadvantages which have been cited in the literature. Likewise, surgical intervention, e.g., septal myectomy or mitral valve replacement, is another optional treatment. However, such surgical treatments carry a significant operative mortality and have not been shown to alter the natural history of the disease. See, for example, “Permanent Pacing As Treatment For Hypertrophic Cardiomyopathy,” by Kenneth M. McDonald et al.,
American Journal of Cardiology
, Vol. 68, pp. 108-110, July 1991.
The value of dual chamber cardiac pacing and treatment of patients suffering from HOCM has been recognized in the literature. Studies have indicated that patients suffering from HOCM may benefit from a specific mode of dual chamber pacing, wherein a ventricular pacing pulse is delivered in timed synchrony with the sensed or paced atrial depolarization. Pacing the right ventricular apex before spontaneous atrio-ventricular conduction activates the ventricles is understood to alter the ventricular septal activation pattern. Since the right ventricle is caused to contract first, it pulls the septum toward the right ventricle thereby reducing the LVOT obstruction. The literature uniformly acknowledges the potential advantages of synchronized AV pacing for HOCM patients, stressing the importance of achieving ventricular
Heynen Henri G. M.
Struble Chester
Berry Tom G.
Jastrzab Jeffrey R.
Medtronic Inc.
Oropeza Frances P.
Waldkoetter Eric R.
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