The effect of nitroglycerin upon pulmonary and left atrial pressures in patients with mitral stenosis.

In all nine patients studied with mitral stenosis and no evidence of left ventricular failure, nitroglycerin caused a decrease in pulmonary arterial, left atrial, and left ventricular pressures and pulmonary vascular resistance. The decrease in left atrial pressure was attributable to the combination of a reduction in left ventricular filling pressure and a reduction in mitral valve gradient. While there was no significant mean change in heart rate, cardiac index, or mitral valve flow, there was a significant correlation between a decrease in each of these determinants of mitral valve gradient and the observed decline in left atrial pressure in individual patients. However, even those patients who had an increase in heart rate or cardiac output, either of which normally aggravates pulmonary congestion in mitral stenosis, had a decrease in their pulmonary and left atrial pressures in response to TNG. It is likely that nitroglycerin reduced pulmonary and left atrial pressures by either (1) systemic venous dilatation, causing a reduction in right heart filling and pulmonary blood volume, or (2) pulmonary arteriolar and venous dilatation, causing a decrease in pulmonary vascular resistance and an increase in pulmonary vascular compliance. Because of the efficacy of TNG in lowering pulmonary and left atrial pressures in this study, TNG may prove useful in the clinical management of symptomatic pulmonary congestion in mitral stenosis.