COMPLETE UNLOADING ALONE MAY NOT ADEQUATELY PROTECT THE LEFT-VENTRICLE

Background. The benefit of left ventricular (LV) unloading for preserv ing LV function is commonly accepted, but its efficacy remains incompl etely defined. Methods. We studied the influence of complete LV unload ing on LV systolic and diastolic mechanics using an in situ isovolumic preparation with two different coronary perfusion pressures (CPPs) in 12 dogs during prolonged normothermic cardiopulmonary bypass. Results . Multivariate analysis of covariance with time as a covariate reveale d that a high CPP (143 +/- 36 mm Hg: n = 6) was associated with better preservation of systolic LV function over time as assessed by LV end- systolic elastance (p < 0.001) and the end-systolic pressure-volume re lation physiologic intercept (p < 0.001) compared with a moderate CPP (107 +/- 18 mm Hg; p < 0.005 versus a high CPP by t-test; n = 6). Dobu tamine (2 mu g. kg(-1).min(-1)) improved LV end-systolic elastance (p < 0.005) and LV physiologic intercept (p < 0.01) only in the high-CPP group. Conversely, impaired LV diastolic function (as measured by LV s tiffness) was observed (p < 0.001) with a high CPP, but did not change with a moderate CPP. Conclusions. These observations in canine hearts suggest that complete LV unloading may not preserve EV systolic funct ion adequately over time when CPP is maintained in the accepted clinic al range. A higher CPP if required to prevent deterioration over prolo nged cardiopulmonary bypass times, but diastolic dysfunction still occ urs. (C) 1997 by The Society of Thoracic Surgeons.