Comparative Vasodilator Effects of Nitroprusside, Phentolamine, and Nitroglycerin on Hemo dynamics, Regional Myocardial Function and Epicardial Electrogram in Dogs with Acute Myocardial Ischemia
The effects of nitroprusside(NP), phentolamine(PH) and nitroglycerin(NTG) on systemic hemodynamics, regional contraction and epicardial ST segment were studied in the border and non-ischemic zones of the left ventricle of anesthetized open-chest dogs. The anterior descending coronary artery (LAD) was completely occluded. NP (5 .mu.g/kg per min) or PH (100 .mu.g/kg per min) was drip i.v. infused, or a bolus injection of NTG (20 .mu.g/kg) was administered i.v. The 3 vasodilator agents produced similar reductions in systemic arterial pressure. NP caused a greater reduction in total peripheral resistance (TPR) than in left ventricular end-diastolic pressure (LVEDP), and caused a decline, in the ischemic marginal zone, in both ST segment elevation and paradoxical systolic lengthening. PH decreased TPR without reducing LVEDP and elevated the ST segment. NTG markedly reduced LVEDP and TPR slightly. NTG improved the elevated ST segment and paradoxical systolic expansion of the segmental myocardium in the border zone. Cardiac output rose with NP and PH, but injected NTG caused a reduction in cardiac output. NP apparently affects the ischemic myocardium favorably mainly by reducing the afterload and the NTG-induced improvement of myocardial ischemia probably can be attributed mainly to preload reduction. PH enhances cardiac function with slight or no improvement of myocardial ischemia in the border zone.