CHARACTERIZATION OF REGIONAL MYOCARDIAL DYNAMICS DURING MECHANICAL ALTERNANS IN HEART OF ANESTHETIZED PIG

Objective: The aim was to investigate the behaviour of regional myocar dium during mechanical alternans in a multidirectional manner. Methods : Mechanical alternans was induced in 12 anaesthetised open chested pi gs by rapid atrial pacing. In contrast to previous studies, regional m echanical activity was simultaneously assessed at up to three differen t sites on the left ventricle using epicardial measuring devices able to provide multidirectional information on segment motion. Pressure-le ngth loops were plotted to assess different patterns of segmental moti on. The integral of pressure and length was calculated to obtain a reg ional work index for each beat. Results: Pressure-length loops reveale d profound abnormalities in segment motion and work index during regio nal mechanical alternans. Myocardial segments either performed alterna te amounts of positive work on each beat or alternate amounts of posit ive and negative work on each beat. Alternating segments contracted ou t of phase with each other and were occasionally stretched during syst ole. Conclusions: The spatio-temporal heterogeneity of regional mechan ical behaviour is greatly increased during mechanical alternans.