Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-02-12
2001-06-19
Kamm, William E. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06249701
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to medical stimulators and leads generally, and more particularly to implantable pacemakers, cardioverters and defibrillators.
In the context of implantable pacemakers or other stimulators which stimulate and sense electrical activity in multiple chambers of the heart, it has been conventional to provide a blanking period for the amplifier associated with one chamber of the heart, during delivery of a pacing pulse to another chamber of the heart. An earlier example of this feature may be found in U.S. Pat. No. 4,312,355 issued to Funke. It is also conventional to provide a blanking period for the sense amplifier coupled to the chamber being paced, during delivery of the pacing pulse and to provide atrial refractory and/or blanking periods associated with sensed ventricular depolarizations, as in U.S. Pat. No. 5,027,815, issued to Funke and U.S. Pat. No. 5,123,412, issued to Betzold.
Particularly in the context of devices which detect tachyarrhythmias, amplifiers have been developed which automatically adjust the effective sensing threshold, in order to facilitate sensing of the relatively lower amplitude depolarization wave forms that may be associated with tachyarrhythmias without sensing the repolarization wave forms associated with depolarizations occurring during normal sinus rhythm. The adjusting of the effective sensing threshold may be accomplished by adjusting the gain of the amplifier and comparing the amplified signal to a fixed threshold and/or by adjusting the threshold level of the detector associated with the amplifier, which adjustments should be understood to be equivalent alternatives in the context of the present invention. One such auto-adjusting amplifier is disclosed in U.S. Pat. No. 5,117,824 issued to Keimel et al, incorporated herein by reference in its entirety. An alternative implementation of an auto adjust amplifier is disclosed in U.S. Pat. No. 5,269,300 issued to Kelly et al., also incorporated herein by reference in its entirety. In these references, following a detected depolarization, the amplifier is automatically adjusted so that the effective sensing threshold is set to be equal to a predetermined portion of the amplitude of the sensed depolarization, and the effective sensing threshold decays thereafter to a lower or base sensing threshold. Following delivery of a pacing pulse, in the system disclosed in the Keimel et al patent, no adjustment is made to the sensing threshold, while in the Kelly et al. patent, following delivery of a pacing pulse the effective sensing threshold is set to a preset value and remains at this value for a defined period of time, after which the threshold decays to the lower or base value.
In the context of a device which paces and senses in multiple chambers of the heart, employing blanking and refractory periods as described above, alone or in conjunction with auto adjusting amplifiers as described above, does provide a useful and workable device. However, this approach does not address the difficulties which arise when the signal associated with a depolarization in the ventricle is of sufficient amplitude to be sensed by the atrial sense amplifier, commonly referred to as far-field R-wave sensing. This problem is addressed to some extent by provision of atrial blanking or refractory periods following sensing in the ventricle, but at the cost of the ability to accurately respond to atrial depolarizations occurring within these periods. In addition, the far-field R-wave may sometimes be sensed in the atrium before the R-wave is sensed by the ventricular sense amplifier, prior to initiation of blanking or refractory periods associated with the R-wave.
SUMMARY OF THE INVENTION
The present invention addresses the problem of far field R-wave sensing by defining a time window associated with a ventricular event (sensed or paced R-wave) during which far field R-wave sensing is likely to occur (hereafter referred to as the “far-R window”) and by automatically increasing the atrial sensing threshold following a ventricular event until the expiration of the far-R window. The atrial sensing threshold is adjusted from a programmed base sensing threshold to a level which will allow for appropriate sensing of P-waves in the atrium while preventing inappropriate sensing of far field R-waves. The atrial sensing threshold may be adjusted as a function of the amplitude of one or more preceding P-waves as sensed by the atrial sense amplifier. Only sensed atrial events which exceed this increased sensing threshold are classified as P-waves.
In one embodiment of the invention, the adjustment of the sensing threshold is accomplished in a hardware implementation, in which the atrial sensing threshold following a ventricular event preceded by a sensed P-wave is adjusted to a level selected as a function of the amplitude of the preceding sensed P-wave. In this embodiment, the atrial sensing threshold following a ventricular event preceded by a delivered atrial pacing pulse is adjusted to a level selected as a function of the programmed base sensing threshold. In a second, software based embodiment, the device defines a minimum amplitude which a sensed atrial event must exceed to be classified as a P-wave or more preferably a range of amplitudes in which a sensed atrial event must fall to be classified as a P-wave. The minimum amplitude or the range of amplitudes is set as a function of the amplitudes of previously sensed P-waves. In both embodiments, the device preferably employs only the amplitudes of sensed atrial events which are classified as P-waves for purposes of defining the sensing threshold or range of amplitudes indicative of a sensed P-wave.
The present invention may be employed in the context of any implantable pacemaker which senses and/or paces in both the atrium and ventricle, including pacemakers capable of pacing in DDD, DDDR, VDD, VDDR, DDI, DDIR and VAT modes. The invention is particularly desirable in the context of a device such as a pacemaker/cardioverter/defibrillator which detects and/or treats atrial and/or ventricular arrhythmias.
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“Automatic Tachycardia Recognition”, by Arzbaecher et al., published in PACE, May-Jun., 1984, pp. 541-547.
“Onset and Stability for Ventricular Tachyarrhythmia Detection in an Implantable Pacer-Cardioverter-Defibrillator” by Olson et al., published inComputers in Cardiology,Oct. 7-10, 1986, IEEE Computer Society Press, pp. 167-170.
Application Ser. No. 09/112,917, by Borgerding et al. for an Implantable Device With Automatic Sensing Adjustment, filed by Jul. 9, 1998.
Borgerding Girard B.
Keimel John G.
Rajasekhar Suribhotla V.
Duthler Reed A.
Kamm William E.
Medtronic Inc.
Wolde-Michael Girma
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