Nitroprusside therapy in acute and chronic coronary heart disease

Abstract

To elucidate the effects of nitroprusside on the relations between systemic pressure, coronary blood flow and regional myocardial ischemia, dogs were subjected to constriction of the proximal left anterior descending (LAD) artery to induce ischemia determined by intramyocardial S-T segments and intramyocardial mass spectrometric oxygen tension (PO 2) and carbon dioxide tension (PCO 2). Nitroprusside was infused to incrementally lower mean blood pressure from 137 to 62 mm Hg. A decrease in mean blood pressure to 87 mm Hg lowered (p < 0.05) intramyocardial S-T segment elevations and diminished left ventricular filling pressure, but it did not alter (p > 0.05) poststenotic flow in the LAD artery, intramyocardial PCO 2 and PO 2, and cardiac oxygen uptake. With a further decrease in systemic arterial blood pressure below normal, S-T segments rose, LAD artery flow decreased, intramyocardial PCO 2 increased and intramyocardial PO 2 decreased. In addition, 12 patients with acute anterior infarction had 35-lead S-T segment maps before and after a 10 minute infusion of nitroprusside. Heart rate was unchanged, left ventricular pressure decreased from 139/19 to 115/11 mm Hg (p < 0.01), cardiac index was maintained, S-T segment sum was lowered from 42 to 29 mm (p < 0.001) and mean S-T segment elevation declined from 1.6 to 1.2 mm/lead (p < 0.001). Thus, modest nitroprusside-induced reduction in blood pressure has beneficial effects on multiple indices of experimental and clinical regional ischemia. In contrast, a further decrease in blood pressure below normal lowers poststenotic coronary blood flow and thereby ischemia worsens.