THE DYNAMICS OF PULSUS ALTERNANS: ALTERNATING END-DIASTOLIC FIBER LENGTH AS A CAUSATIVE FACTOR

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Abstract
In this study the weak beat in pulsus alternans was initiated from a shorter end-diastolic fiber length than was the strong beat, whether the end-diastolic pressure was lower, the same, or higher. This was brought about by an inadequate diastolic period for ventricular relaxation, ventricular filling, or both, relative to the inflow volume required to produce any given end-diastolic fiber length from any given end-systolic volume. Pulsus alternans occurred when the continuous level of myocardial contractility was not sufficient for a given imposed heart rate, stroke volume, and aortic pressure to allow an adequate time for diastole before the weak beat. Pulsus alternans was abolished when an increase in myocardial contractility was induced by norepinephrine infusion or by reflex cardiac sympathetic nerve stimulation.