Comparative effects of captopril and isosorbide dinitrate on pulmonary arteriolar resistance and right ventricular function in patients with severe left ventricular failure: Results of a randomized crossover study

We compared the short-term hemodynamic effects of isosorbide dinitrate (40 mg orally) and captopril (25 mg orally) in 18 patients with severe chronic heart failure in a randomized, crossover study conducted on consecutive days. Captopril and isosorbide dinitrate produced similar decreases in systemic vascular resistance, but whereas nitrate therapy decreased pulmonary arteriolar resistance significantly, captopril did not; the difference between the two drugs was highly significant (-25% vs -5%, p < 0.001). Left ventricular filling pressures declined similarly with both captopril (-10.5 mm Hg) and with isosorbide dinitrate (-9.3 mm Hg), but because pulmonary arteriolar resistance fell significantly with nitrate therapy, mean right atrial pressure decreased more with isosorbide dinitrate than with captopril (-5.4 vs -2.8 mm Hg, respectively; p < 0.001). Although systemic resistance declined similarly with both drugs, cardiac index increased more with nitrate therapy than during converting-enzyme inhibition (+0.47 vs +0.23 L/min/m²) (p < 0.01), and therefore mean arterial pressure fell less with isosorbide dinitrate than with captopril (-10.5 mm Hg vs -16.7 mm Hg); p < 0.05); two patients developed symptomatic hypotension with captopril, whereas none did so with the nitrate. The difference in the effects of the two drugs on cardiac index was not due to differences in their effects on heart rate, since heart rate fell similarly with both drugs, and thus both drugs produced similar increases in stroke volume index. These data indicate that, in patients with severe chronic heart failure, nitrates exert favorable dilating effects on the pulmonary circulation not shared by captopril. This residual functional obstruction in the pulmonary circuit limits the degree to which right ventricular output can increase during converting-enzyme inhibition, which may explain captopril's greater hypotensive effects, despite similar effects of both drugs on left ventricular filling pressure and systemic vascular resistance.