Abstract: An implantable medical device for electrically stimulating the heart to beat includes a sense circuit for detecting cardiac electrical activity. The sense circuit includes a band pass filter with an adjustable frequency response. The frequency response can be repeatedly adjusted after implantation of the medical device and preferably is adjusted upon detection of the loss of normal sinus rhythm (NSR) in the heart's atria. The loss of NSR often indicates atrial fibrillation (AF), and the filter's frequency response is adjusted to increase the sensitivity of the sense circuit to the cardiac electrical activity typical during AF. The medical device is calibrated during implantation or at subsequent doctor visits with the aid of a calibration device external to the body. Cardiac electrical activity in the form of an electrogram is transmitted from the medical device to the external calibration device. The transmitted electrogram preferably includes both NSR and AF rhythms.

Abstract: An implantable medical device for electrically stimulating the heart to beat includes a sense circuit for detecting cardiac electrical activity. The sense circuit includes an amplifier with a dynamically adjustable gain to provide increased sensitivity to the electrogram during atrial fibrillation. Alternatively, sensitivity control is provided by dynamically adjusting threshold limits associated with a threshold detector included in the sense circuit. The sensitivity level of the medical device to the electrogram can be repeatedly adjusted after implantation and preferably is increased upon detection of the loss of normal sinus rhythm (NSR) in the heart's atria. The medical device is calibrated with the aid of a calibration device external to the body to determine appropriate sensitivity levels. A method for calibrating and operating an implanted medical device with dynamically adjustable sensitivity is also disclosed for improving the medical device's sensitivity to atrial fibrillation.

Abstract: An implantable medical device for electrically stimulating the heart to beat including a sense circuit for detecting cardiac electrical activity. The sense circuit includes a sense amplifier, band pass filter, and threshold detector. The threshold detector determines whether sensed cardiac electrical activity resulted from a normal heart beat or an ectopic beat such as a premature ventricular contraction. In a preferred embodiment, latches in the threshold detector are activated by output pulses from a pair of comparators. A positive comparator produces an output pulse upon detection of cardiac electrical activity exceeding a positive threshold voltage and a negative comparator produces an output pulse upon detection of cardiac electrical activity more negative than a negative threshold. Threshold logic produces output signals indicative of which comparator first produced an output pulse.

Abstract: A programmable dual-chamber artificial cardiac pacemaker senses atrial activity and normally tracks the sensed atrial activity in pacing the ventricular activity. An accelerometer located in the case of the pulse generator portion senses physical exercise by a patient when the pacemaker is implanted in the patient, and generates a rate control signal indicative of extent of the sensed physical exercise. The pulse generator is programmed for ventricular pacing rate control in multiple rate zones bounded by rate limits including a ventricular tracking limit (VTL) that varies dynamically with sensed physical exercise and a higher mode switch rate. The ventricular pacing rate tracks the sensed atrial activity on a 1:1 basis for atrial rates below the dynamic VTL (DVTL) during a predetermined interval of time for which the DVTL applies, and tracks the sensed atrial activity in Wenckebach behavior for atrial rates above the DVTL up to the mode switch rate with the ventricular pacing rate limited by the DVTL.