ELECTRICAL ALTERNANS AND THE ONSET OF RATE-INDUCED PULSUS ALTERNANS DURING ACUTE REGIONAL ISCHEMIA IN THE ANESTHETIZED PIG-HEART

Objectives: Electrical alternans and mechanical alternans are both ass ociated with cardiac ischaemia and in the case of electrical alternans there is a strong link with serious ventricular arrhythmia. We electe d to investigate the relationship between electrical and mechanical al ternans in control and acutely ischaemic myocardium in the intact porc ine heart to determine the nature of their interaction and in particul ar to determine if abnormal mechanical events play a role in arhythmog enesis as has been suggested in non-ischaemic preparations. Methods: W e used rapid atrial pacing to induce regional mechanical alternans and pulsus alternans before and then at 5-min intervals after the onset o f acute ischaemia induced by a 30-min ligation of a diagonal branch of the left anterior descending artery. Regional mechanical activity is measured with epicardial tripodal strain gauges and regional electrica l activity is measured using suction-based monophasic action potential electrodes. To test whether alternate stretching of ischaemic segment s during pulsus alternans contributed to electrical alternans we simul ated pulsus alternans by clamping the proximal aorta on alternate beat s. Results: In control areas there was a constant discordant relations hip between peak systolic pressure during alternans and action potenti al duration. In contrast, the ischaemic areas showed electromechanical alternans that was most frequently concordant. Clamping the proximal aorta on alternate beats produced an electrical alternans in control a reas but not in the ischaemic area. Conclusions: Pulsus alternans duri ng acute ischaemia is associated with electrical alternans that can be out of phase in control and ischaemic areas. This could increase elec trical dispersion which may be pro-arrhythmic.