Pulsus alternans is a physical finding with arterial pulse waveform showing alternating strong and weak beats. It is almost always indicative of left ventricular systolic impairment, and carries a poor prognosis.

Pulse pressure waveform displaying the variation in pressure between beats in pulsus alternans.

Pathophysiology

In left ventricular dysfunction, the ejection fraction will decrease significantly, causing reduction in stroke volume, hence causing an increase in end-diastolic volume. There may initially be a tachycardia as a compensatory mechanism to try and keep the cardiac output constant. As a result, during the next cycle of systolic phase, the myocardial muscle will be stretched more than usual and as a result cause an increase in myocardial contraction, related to the Frank-Starling physiology of the heart. This results, in turn, in a stronger systolic pulse.

Euler D (1999) Cardiac alternans: mechanisms and pathophysiological significance. Cardiovascular Research. Vol. 42. P. 583-590.