VENTRICULOARTERIAL COUPLING AND LEFT-VENTRICULAR EFFICIENCY IN HEART-TRANSPLANT RECIPIENTS

Background. In heart transplants, left ventricular function may be imp aired in the absence of rejection or graft atherosclerosis, Matching b etween left ventricle and arterial receptor, i.e., ventriculoarterial coupling, and left ventricular efficiency have never been studied. Met hods. Left ventricular pressure-volume loops and single beat analysis were used to determine effective arterial elastance (Ea) and the slope of the end-systolic pressure-volume relation (end-systolic elastance; Ees), Left ventricular efficiency was evaluated by determination of e xternal work (EW), pressure-volume area (PVA), coronary blood flow (co ntinuous thermodilution), and myocardial oxygen consumption (MVO2). Me asurements were made at baseline in 11 control subjects and 9 heart tr ansplant recipients (HTX) without rejection and were repeated after ph enylephrine in the latter group. Results. At baseline, Ees, Ees/Ea, an d work efficiency (EW/PVA) were lower in HTX than in control subjects (2.51+/-0.87 vs, 3.70+/-1.15 mmHg/ml/m(2), P<0.01; 0.96+/-0.21 vs, 1.4 7+/-0.31, P<0.001; and 0.53+/-0.08 vs, 0.59+/-0.09, P<0.01, respective ly), Energy conversion efficiency (PVA/MVO2) and mechanical efficiency (EW/ MVO2) were higher in HTX (0.58+/-0.08 vs, 0.45+/-0.14, P<0.001; and 0.31+/-0.05 vs, 0.26+/-0.06, P<0.001, respectively), In HTX, pheny lephrine infusion increased Ees, Ea, EW, PVA, and MVO, without modifyi ng Ees/Ea, EW/PVA, PVA/MVO2, and EW/MVO2. Conclusions. In heart transp lants, (1) left ventricular contractility is moderately depressed; (2) elevation of energy conversion efficiency compensates for the decreas e in work efficiency, allowing normal mechanical efficiency; and (3) a lpha 1 adrenergic stimulation does not impair ventriculoarterial coupl ing and mechanical efficiency.