Mechanisms of pulsus alternans: its relation to alternation of regional contraction and elevated ST segment

The aim of this study is to investigate the correlation between pulsus alternans and changes in regional myocardial contraction on the ST segment of the epicardial electrocardiogram (ECG) in open-chest dogs with coronary flow reduction and pacing. With flow reduction and pacing, alternation of regional contraction appeared primarily in shortening of the end-systolic length, and secondly in elongation of the end-diastolic length. Regional mechanical alternans was observed along with alternation of the ST segment of the epicardial ECG and was followed by pulsus alternans in some dogs. When adenosine triphosphate (ATP) content was measured at the end of the experiment, its level was preserved in dogs with pulsus alternans following regional mechanical alternans more than in those with regional mechanical alternans alone. We concluded that regional mechanical alternans is caused by the alternate changes in intrinsic contractility, probably due to alternations of Ca++ transients, since it was accompanied by ST electrical alternans. In addition, pulsus alternans might be beneficial to ischemic myocardium by causing a decrease in the consumption of high energy phosphates.