Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-12-21
2004-08-03
Jastrzab, Jeffrey R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06772005
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to cardiac pacers, and more particularly to a dual chamber rate responsive pacemaker that incorporates a novel ADI/R pacing mode. More particularly, this pacing mode is one that gives preference to atrial pacing and, at the same time, suppresses ventricular pacing wherever possible and provides the DDI/R or DDD/R modes with ventricular pacing only as backup modes.
BACKGROUND OF THE INVENTION
Early pacemakers were asynchronous (VOO) and stimulated the heart at a fixed rate, independent of the patient's underlying cardiac rhythm or metabolic demand. Although such pacers, typified by U.S. Pat. No. 3,057,356 to Greatbatch, provide a ventricular pacing rate sufficient to sustain life, this pacing mode often competed with native ventricular rhythms. Such competition is undesirable.
Subsequently, demand pacemakers (VVI) were developed. This type of pacer interacts with the patient's heart to provide pacing pulses only when spontaneous ventricular activity is absent. U.S. Pat. No. 3,478,746 to Greatbatch demonstrates an example of such a pacer. This form of pacer provides a ventricular sense amplifier for detecting ventricular depolarizations. A ventricular sensed event resets the pacer's V—V timer. The ventricular sensed event also cancels or inhibits the scheduled ventricular stimulus and thus avoids competition with the native ventricular rhythm.
Atrial synchronized pacers (VAT) were developed almost simultaneously with VVI demand pacemakers. This type of pacer paces the ventricle in response to the detected atrial rate of the patient. The VAT pacer, as typified by U.S. Pat. No. 3,253,596 to Keller, provides an atrial sense amplifier for detecting atrial depolarizations. An atrial sensed event starts the pacer's A-V delay timer. When the A-V timer times out, a ventricular stimulus is provided. Conceptually, such a pacer can be considered as a prosthetic conduction pathway that simulates the natural A-V conduction pathways of the heart. One drawback to this form of pacing is the possibility of competing with ectopic ventricular activity. An ectopic ventricular beat (PVC) may be detected in the atrium. In such cases, an AV interval starts and will result in the generation of a ventricular stimulus a short time after the ventricular depolarization. Although such a pacing regimen is considered harmless when the A-V delay is short, it is possible to deliver the pacing stimulus into the vulnerable period of the ventricle, and thereby initiate a ventricular arrhythmia.
Continued development of pacemakers was marked by the invention of the AV sequential pacer (DVI), as disclosed in U.S. Pat. No. 3,595,242 issued to Berkovits. This form of pacer provides for stimulation in both the atria and the ventricles though providing sensing only in the ventricle. In this DVI mode pacer, a ventricular sense event starts both a V-A escape interval and an A-V interval. The pacer delivers an atrial stimulus at the end of the V-A interval and, at the end of the A-V interval, the pacer delivers a ventricular stimulus. If a ventricular sense event occurs during the V-A or A-V time intervals, the pacer will resynchronize to the ventricular sense event and inhibit the delivery of the scheduled ventricular stimulus.
The DDI mode pacer described by U.S. Pat. No. 3,747,604 to Berkovits further includes an atrial sense amplifier to inhibit the atrial stimulus when an atrial sense event occurs during the V-A interval. The atrial sense event does not start and A-V interval; such timing makes this device especially suitable in patients where atrial competition must be avoided.
The atrial synchronized ventricular inhibited or VDD mode pacer, as disclosed in U.S. Pat. No. 3,648,707 issued to Greatbatch has mechanisms for sensing in the atrium and ventricle while providing stimulating pulses only in the ventricle. In operation, the VDD pacer starts and A-V interval on detected atrial activity and provides a ventricular stimulus if one does not occur within the A-V delay. A ventricular sensed event inhibits the scheduled ventricular stimulus and resets the pacer's V—V timer.
The dual sense, dual pace DDD mode pacers, have been described in U.S. Pat. No. 4,312,355 issued to Funke. The DDD pacer addresses many of the shortcomings of the prior art devices. The DDD mode pacer, as described by Funke, has had wide applications. This type of pacer has sense amplifiers for detecting atrial and ventricular events, as well as output pulse circuitry for stimulating both the atrium and the ventricle.
This form of prior art pacer provides timing circuitry to initiate an A-V delay upon the occurrence of an atrial event. If, during the A-V delay period, no spontaneous ventricular event is sensed, the pacer will produce a ventricular stimulus at the conclusion of the A-V delay. If, during the V-A interval, no spontaneous atrial event is sensed, the pacer provides an atrial stimulus at the conclusion of the V-A interval.
In this type of pacemaker, in the absence of spontaneous P-waves and R-waves, the heart will be stimulated at fixed A—A and V—V intervals with a programmable AV delay. However, if the ventricle depolarizes spontaneously, then the A-V delay is truncated and the observed A—A interval is not fixed and will be shorter than the arithmetic sum of the programmed A-V and V-A intervals.
The dual chamber modalities, DVI, VAT, VDD and DDD, have proven to be especially efficacious pacemakers since they restore A-V synchrony and thus improve cardiac output by ensuring the hemodynamic contribution of the atrial chambers within the pacing regimen. The latter three modes also synchronize the pacing rate to the patient's native atrial or sinus rate and thus provide an increased pacing rate in response to bodily activity. Increasing cardiac rate is the major contributor to increased cardiac output. More recently, other pacers, which increase cardiac output in response to exercise, have been proposed. They include pacemakers that rely upon the sensing of physical via an activity sensor or accelerometer, changes in blood pH, respiratory rate, or QT interval. These data are used to alter the pacemaker's escape interval.
One approach that is important to the understanding of the present invention is the activity responsive pacer described in U.S. Pat. No. 4,428,378, issued to Anderson et al, and which is incorporated by reference. The pacer disclosed in that patent monitors the physical activity of the patient and increases the pacing rate in response to increasing patient activity.
Other publications that provide background information for the operation of the present invention include U.S. Pat. No. 4,890,617 issued to Markowitz et al. that is incorporated herein by reference. This patent describes a dual chamber activity responsive pacemaker that senses and paces in both the atrium and the ventricle. The pacing rate is determined by the sensed activity of the patient, the programmed lower rate, and the patient's atrial or sinus rate.
U.S. Pat. No. 4,932,046, entitled “Dual Chamber Rate Responsive Pacemaker”, assigned to Medtronic, Inc. of Minneapolis, Minn., which is incorporated herein by reference, describes a dual chamber rate responsive pacemaker. The pacemaker operates in an atrial-synchronized modality when the sensed atrial rate is present, and paces at the sensor-determined rate when the sensed atrial rate is absent or below the programmed lower rate.
The above pacing modes may, in a certain sense, be considered as subsets to the DDD/R mode though, in reality, they were all developed from the VVI mode in one way or another. All such possibilities have been described in The NBG Code, a five-position code, published and updated as a joint effort of the North American Society of Pace and Electrophysiology (NASPE) and the British Pacing and Electrophysiology Group (BPEG). This code is generally used by those familiar with the state of the art and may be found in publications too numerous to mention.
DDD pacemakers are often implanted
Belk Paul A.
Casavant David
Mullen Thomas J.
Stroebel John C.
Chapik Daniel G.
Jastrzab Jeffrey R.
McDowall Paul H.
Medtronic Inc.
Oropeza Frances P.
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