Mechanical LV support lowers diastolic LV pressure and prolongs diastolic coronary flow in the infarcted artery

Abstract

Abstract Background Percutaneous left ventricular (LV) assist device provides not only circulatory support but also LV unloading. However, impact of LV unloading on coronary flow and mechanisms by which it is regulated remain unclear. We aimed to elucidate potential effects of LV unloading on coronary physiology in a pig model of myocardial infarction (MI). Methods First, six Yorkshire pigs underwent mechanical LV unloading using Impella two weeks after percutaneous MI induction. Regional blood flow (RBF) in infarct, border and remote myocardium were measured by fluorescent microsphere injections before and 120 min after LV unloading (Study 1). Next, we investigated coronary flow patterns with detailed temporal information. Six Yorkshire pigs were subjected to 90-minute balloon occlusion of the middle left anterior descending artery followed by reperfusion. At 60 minutes after reperfusion, LV unloading was initiated and maintained at maximal support. LV pressure, coronary flow and pressure in the infarcted artery were simultaneously recorded. Measurements were repeated with and without LV mechanical support. Coronary wave intensity was calculated from the flow/pressure data (Study 2). Results In Study 1, RBF calculated using microsphere was significantly increased only in the infarct area, but not in the border or remote areas. In Study 2, LV unloading resulted in lower LV pressure during the whole diastolic phase and higher coronary pressure during the late diastolic phase in all animals. Coronary flow velocity was higher throughout the diastole under LV unloading. In addition, the proportion of diastole to the whole cardiac cycle was significantly prolonged with LV unloading. Accordingly, area under the curve of coronary flow was increased during diastole and also for the whole cardiac cycle. In the wave intensity analysis, the magnitude of forward wave intensity was reduced by LV unloading, suggesting that the impact of forces from the aortic side was less significant under continuous device support. The duration between backward suction and pushing waves was extended, implicating earlier relaxation and delayed contraction, further supporting prolonged diastole from the myocardial force perspective. Conclusions Mechanical LV unloading increases coronary flow by prolonging diastolic phase in the infarcted artery.