Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-03-17
2001-07-03
Evanisko, George R. (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06256537
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to cardiac pacing systems with the capability of responding to episodes of atrial fibrillation and other atrial arrhythmias and, in particular, implantable pacing systems which respond to such an episode by controllably inhibiting conduction of at least some of the atrial signals to the ventricle until the episode terminates naturally.
BACKGROUND OF THE INVENTION
Modern cardiac pacing systems have incorporated substantial capability for detecting and dealing with various arrhythmias. Of particular importance are atrial arrhythmias such as atrial fibrillation (AF), which may lead to serious complications. Atrial fibrillation is manifested as an irregular disorganized activity of the heart, and in the absence of complete AV block, the ventricular response is irregular and random. The irregularity of the resulting cardiac rhythm adversely affects the contractile performance of the heart. It is a source of considerable morbidity and mortality; AF is the leading cause of embolic stroke. As used hereinafter, the term atrial fibrillation, or AF, refers broadly to the class of dangerous atrial arrhythmias, during episodes of which it is desired to inhibit conduction of most of the atrial signals to the ventricles. Pacemakers have attempted to deal with such arrhythmias by simply switching into an asynchronous mode, such that ventricular pacing does not try to track the dangerous atrial excitations. However, with ordinary asynchronous ventricular pacing and continued conduction of the atrial signals through the AV node, a certain percentage of the atrial signals will get through to the ventricle and thus cause chaotic spontaneous ventricular contractions and paced contractions, resulting in an undesirable cardiac condition. Patients with paroxysmal or chronic AF and intact AV conduction who are highly symptomatic and drug refractory are presently candidates for His ablation. This is, of course, a procedure which stops conduction of all atrial signals to the ventricle permanently. The result is that the ventricle needs to be paced permanently even though the atrium contracts normally most of the time.
Another technique that is in use is that of delivering a cardioversion shock to the patient's heart. This can be done during general anesthesia, which of course is impractical for a patient who has repeated and rather long-occurring episodes. Such a patient would also be a candidate for an implantable cardioverter device. However, such devices are very expensive, and the shocks are not welcome to the patient, i.e., they may be painful. Further, if the episodes occur too frequently, these devices have a limited lifetime due to the energy expenditure of each shock.
Another approach known in the literature is to cool the atrium, thereby slowing conduction in the atrial tissue to the point of terminating the atrial fibrillation. See Abstract, Scaglione et al, PACE, Vol. 16, p 880, April 1993, Part II. In this approach, the entire atrium is cooled by introduction of a bolus of cold saline solution. See also U.S. Pat. No. 5,876,422, issued Mar. 2, 1999, showing a system for Peltier cooling of the AV node during which the ventricle must be paced asynchronously for the duration of the AF episode.
Another approach to the problem is for the pacemaker to respond by aggressively pacing at a higher, but more stable rate. See, for example, U.S. Pat. No. 5,480,413. See also U.S. Pat. No. 5,792,193, which smooths the ventricular rate by an algorithm that allows some spontaneous ventricular contractions, and delivers some pace pulses which overdrive the spontaneous rate.
However, there remains a substantial need for an improved system and technique for effectively regulating the ventricular rate until the atrium can return on its own to a normal sinus rhythm, and without requiring a high ventricular rate so that the ventricle be paced asynchronously.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a stimulating system, preferably an implantable system such as a pacemaker system, which is responsive to atrial fibrillation by regulating the rate of atrial signals which are conducted through the AV node, thereby regulating the rate of ventricular contractions. The invention is thus aimed at cardiac patients who have normal AV conduction but are susceptible to episodes of atrial fibrillation, and provides for limiting the ventricular rate by allowing passage of enough signals through to the ventricle to maintain at least a predetermined rate, and for inhibiting passage of other atrially generated excitation signals through the AV node. In this manner, the ventricle contracts synchronously with some of the atrial beats, but does not receive others, resulting in synchronous ventricular beats at a regulated rate.
The above object is achieved by responding to an episode of atrial fibrillation by generating and delivering subthreshold bursts of pulses to the patient's AV node, the bursts being controlled in energy level and frequency to inhibit conduction of signals through the node while they are being applied. Each burst is timed relative to a last sensed ventricular contraction so as to inhibit AV conduction for a period that is related to a desired V—V interval, or ventricular rate. The start of the burst, and the end of the burst are automatically adjusted to provide a desired burst duration; and the energy level of the burst is also automatically adjusted to ensure inhibition while minimizing energy expenditure. Inhibition threshold is tested by determining the percentage of ventricular contractions that occur at intervals shorter than that which corresponds to the predetermined regulation rate; when the percentage is too high, pulse level and/or frequency of pulses within the burst are adjusted to regain optimum inhibition. When the AF episode stops of its own accord, the system returns to a normal mode of pacing.
REFERENCES:
patent: 5320642 (1994-06-01), Scherlag
patent: 5480413 (1996-01-01), Greenhut et al.
patent: 5792193 (1998-08-01), Stoop
patent: 5876422 (1999-03-01), van Groeningen
patent: 5916239 (1999-06-01), Geddes et al.
Prystowsky, Eric N., “Subthreshold Conditioning Stimuli Inhibit Human Atrial and Ventricular Myocardium,” Chapter 3,Prevention of Tachyarrhythmias With Cardiac Pacing, Futura Publishing Company, 1997.
Scaglione, Jorge, et al., “Reversion of Atrial Fibrillation in Dogs By Rapid Infusion of Cold Saline Solution,” NASPE Abstracts,Pace, vol. 16, Apr. 1993, Part II.
Wittkampf, Frederik, et al., “Rate Stabilization by Right Ventricular Pacing in Patients with Atrial Fibrillation,”Pace, vol 9, Nov-Dec. 1986, Part II, pp. 1147-53.
Wittkampf, Frederik, et al., “Effects of Right Ventricular Pacing on Ventricular Rhythm during Atrial Fibrillation,”JACC, vol. 11, Mar. 1988, pp. 539-45.
Lau, Chu-Pak, et al., “A New Pacing Method for Rapid Regularization and Rate Control in Atrial Fibrillation”American Journal of Cardiology, vol. 65, May 15, 1990, pp. 1198-1203.
Smit Josephus P. A.
Stoop Gustaaf A. P.
Van Dam Peter
Evanisko George R.
Jaro Michael J.
Medtronic Inc.
Patton Harold
Woods Thomas F.
LandOfFree
Pacemaker system with inhibition of AV node for rate... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pacemaker system with inhibition of AV node for rate..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pacemaker system with inhibition of AV node for rate... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2532061