Acute effects of nitrates on left ventricular performance and energetics

Left ventricular myocardial performance and efficiency were analyzed on the basis of two new energetic parameters in patients with coronary heart disease. The myocardial energy consumed during one cardiac cycle is related on the one hand to the work performed (E1) and on the other to the stress-time integral (E2). E1 was obtained by analysis of the pressure-volume integral divided by the left ventricular muscle mass. E2 was obtained as follows: The stress-time integral was analyzed from pressure-volume data and wall thickness using an ellipsoidal calculation model. In order to transfer the stress-time integral into energy units, the value is multiplied by a constant factor which was obtained experimentally in myothermal studies. In patients with coronary heart disease, a single dose of nitroglycerin (1.6 mg s.l.) reduced the total energy sigma (E1 + E2) from 6.1 mcal/g to 4.7 mcal/g (n = 10; P less than 0.01). The efficiency of myocardial contraction (E1/sigma (E1 + E2] was not changed significantly. These data explain quantitatively the beneficial effect of preload and afterload reduction due to nitroglycerin.