REGIONAL ELECTROMECHANICAL ALTERNANS IN ANESTHETIZED PIG HEARTS - MODULATION BY MECHANOELECTRIC FEEDBACK

Electrical and mechanical alternans have often been found to coexist. However, the factors controlling their interdependence are not known. In this study we measure regional electrical and mechanical activity d uring mechanical alternans to investigate this relationship. Mechanica l alternans was induced by rapid atrial pacing in 18 anesthetized, ope n-chest pigs. Regional segmental contraction and monophasic action pot ential were measured in three areas of left ventricle using epicardial tripodal strain gauges and suction electrodes. Electrical alternans a lways accompanied pulsus alternans. The phase of electrical alternans was not related to any measure of regional mechanical activity but did show a constant discordant relation to peak ventricular pressure. Thi s suggested that mechanically dependent changes in action potential du ration (mechanoelectric feedback) may be important in modulation elect rical alternans. In support of this, pulsus alternans simulated by cla mping the proximal aorta on alternate beats was associated with electr ical alternans comparable to that produced with rapid atrial pacing. M echanoelectric feedback modulates regional electrophysiology in the in tact heart and may be important in the generation of electrical altern ans.