Production and abolition of alternation in mechanical action of the ventricle

¹ Department of Physiology, Downstate Medical Center, State University of New York, Brooklyn, New York

Persisting alternation in mechanical response of the ventricle, pulsus alternans, develops when the heart is driven above certain rates. This critical rate varies, but tends to occur between rates of 200 and 300 beats/min. The ventricle can be driven slightly faster (10–20 beats/min) by direct than by indirect drive, through atrial electrodes, without showing pulsus alternans. There is a rate "threshold" for persisting alternation which represents the rate limits of compensation. Alternation appears at lower rates but the contractile process can gradually accelerate and alternation disappears even in denervated hearts and after adrenalectomy. Slower progressive accelerations delay onset of pulsus alternans and compensation occurs more quickly than when stepwise rate changes are made. Fast drives above the threshold for pulsus alternans can produce some additional acceleration of the contraction-relaxation process: if the rate is reduced to a level which previously produced a persisting alternation, pulsus alternans does not occur for a number of seconds. The resemblances of these phenomena to "treppe" and "postextrasystolic potentiation" and implications relative to catecholamine release and action are discussed.

Key Words: pulsus alternans, alternation in response to drive • failure of excitation-contraction coupling • treppe-like cardiac action • contractile process-limits of rate of mechanical response • adaption of mechanical response of heart • limits of response to fast rates of drive • cardiac contraction-rate limits • mechanical response of heart • heart rate, limits of mechanical response • excitation-contraction uncoupling • cardiac electrical-mechanical response relations

Submitted on November 2, 1964

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