Abstract: A system is provided for preventing cross-stimulation between the atrium and ventricle during cardiac pacing using a dual chamber cardiac pacer. A first output capacitor is connected in series with the atrium lead and a second output capacitor is connected in series with the ventricle lead. The first output capacitor is isolated from being charged until an atrial stimulus pulse is issued and the second output capacitor is isolated from being charged until a ventricle stimulus pulse is issued. The isolation means comprises analog switches that are controlled by a pacer logic circuit so that a current flow line is provided to the first output capacitor only when a stimulus pulse is issued to the atrium and a current flow line is provided to the second output capacitor only when a stimulus pulse is issued to the ventricle.

Abstract: A biphasic cardiac pacer is provided having a novel system for detecting the evoked response from the heart after a stimulating pulse is applied. A relatively short, high absolute amplitude stimulating pulse is applied to the heart. Thereafter, a compensating pulse having an absolute amplitude that is smaller than the absolute amplitude of the stimulating pulse, and having a duration that is longer than the duration of the stimulating pulse, is provided. The stimulating pulse and compensating pulse together comprise a biphasic waveform that provides rapid electrode charge neutralization and enhances subsequent capture detection. The biphasic waveform is automatically and dynamically balanced so that the electrical charge of the stimulating pulse portion is equal to the electrical charge of the compensating pulse portion. After the compensating pulse is provided, the evoked response is detected using the same electrodes that are used for providing the stimulating and compensating pulses.