Abstract: An implantable cardiac stimulation device including a ventricular defibrillator and a rate adaptive cardiac pacer automatically adjusts post-pacing sensing parameters dependent upon pacing rate. The device includes a pulse generator that applies stimulation pulses to a heart at a calculated variable stimulation rate as a function of physiologic demand. A sensing circuit senses ventricular activity of the heart responsive to a plurality of sensing parameters including post-pace sensing parameters and a processor adjusts the post-pace sensing parameters responsive to the selected pacing rate.

Abstract: A system for providing medical electrical stimulation includes a pulse generator coupled to a lead having two electrodes for placement in the right atrium or for placement of one in the right atrium and one in the coronary sinus or coronary vein. In the preferred embodiment the surface area of the first electrode is smaller than that of the second electrode so that the sensed signal from the first electrode is less than that from the second. The system provides dual site pacing with essentially single site sensing without the use of extra switches, connectors, or adaptors.

Abstract: An implantable cardiac stimulation device includes a system for detecting noise in an electrogram signal. The system for detecting noise generates an event signal when the electrogram signal exceeds a threshold. A timer times a refractory time period responsive to an event signal. During the refractory time period, a zero crossing detector generates a zero crossing signal when the electrogram signal transitions between positive and negative values. A counter counts the zero crossing signals during the time period and a comparator determines if the counter reached a predetermined count during the time period. If the counter exceeds a programmable count, a noise detection flag is set and the controller is alerted to the presence of noise in its input signal.

Abstract: A method for defibrillating a patient's atria with an implantable defibrillator having defibrillation synchronized to the atrial fibrillation waveform. The defibrillator is used to detect fibrillation in a patient's aria, monitor at least one atrial fibrillation signal across two electrodes, then deliver a high energy shock during a period of atrial fibrillation when the cycle lengths are stable within a desired measure of the cycle lengths monitored during the monitoring time period. The shock is then delivered synchronous with the R wave to avoid inducing ventricular fibrillation. The defibrillator also includes a timer so that if the desired cycle length stability is not reached within a specified time limit, the shock will be delivered with less stringent cycle length stability criteria.