Abstract: An implantable cardiac stimulator for detecting and treating cardiac arrhythmias includes a sense amplifier responsive to sensed cardiac signals for detecting and distinguishing normal and abnormal cardiac activity within the sensed signals. The sense amplifier includes an automatic gain control amplifier, a filter and quad comparator having a pair of signal channels for processing the sensed signals according to different frequency bandpass characteristics to establish sensing thresholds, margins and signal gain. The sense amplifier has a feedback loop containing a microprocessor which implements preselected algorithms in conjunction with the outputs of the quad comparator to variably adjust the amplifier gain and to programmably control the sensing margin.

Abstract: An implantable cardiac stimulator integrates the functions of bradycardia and anti-tachycardia pacing-type therapies, and cardioversion and defibrillation shock-type therapies. The stimulator is programmable to provide a multiplicity of hierarchical detection algorithms and therapeutic modalities to detect and treat classes of ventricular tachycardia according to position within rate range classes into which the heart rate continuum is partitioned, and thus according to hemodynamic tolerance, with backup capabilities of defibrillation and bradycardia pacing at the higher and lower regions of the rate continuum outside the range of the ventricular tachycardia classes. Aggressiveness of the therapy is increased with elapsed time and increasing heart rate, and detection criteria are relaxed with increasing heart rate and thus with increasing hemodynamic intolerance of the tachycardia.

Abstract: In a method and apparatus for defibrillating a heart in fibrillation, the onset of fibrillation of the heart is detected, and a biphasic waveform having only a first phase and a second phase is applied to the fibrillating heart. Each phase of the waveform is characterized by a predetermined time duration and by a predetermined polarity and magnitude of voltage, the duration of the first phase being greater than the duration of the second phase, and the initial voltage magnitude of the first phase being greater than that of the second phase. The biphasic waveform is applied by delivering it to a pair of patch electrodes affixed over and contoured to conform substantially to the surface of the right and left ventricles, respectively. The patch electrodes are affixed to either the epicardium or the pericardium. The left ventricular patch electrode is used as the cathode for the first phase of the applied biphasic waveform, and as the anode for the second phase.