Failure of Integrated Cardiac Action at Supernormal Heart Rates.

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Abstract
Summary Hearts of anesthetized dogs were driven at slowly accelerating rates from atrial or ventricular electrodes. The rate thresholds for various abnormalities and failures were determined for both types of drive. Pulsus alternans occurs at a slower rate during atrial than during direct ventricular drive. Conduction from ventricle to atrium fails at slower rates than does A-V conduction. Alternation in electrical response voltage and ultimately 2:1 stimulus-electrical response ratios develop at high rates of drive in both atrium and ventricle much more commonly than do fibrillation or other irregularities of response. Sudden changes in rate and irregularities of stimulus pulse spacing are more apt to disorganize cardiac function than are progressive rate changes.

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