Acute haemodynamic effects of oral prazosin in severe mitral regurgitation.

Acute haemodynamic effects of single dose oral prazosin were studied in eight patients with mitral regurgitation. Heart rate, mean systemic arterial pressure, pulmonary arterial pressure, left ventricular filling pressure, and forward cardiac output were measured in all patients. At peak effect, prazosin reduced mean systemic arterial pressure (95 +/- 4 to 86 +/- 4 mmHg), pulmonary arterial pressure (45 +/- 6 to 23 +/- 4 mmHg), and left ventricular filling pressure (30 +/- 4 to 21 +/- 3 mmHg). Pulmonary and systemic vascular resistance also fell (316 +/- 49 to 208 +/- 43 dynes s cm-5 and 2132 +/- 148 to 1491 +/- 94 dynes s cm-5, respectively). Forward cardiac index increased from 1.89 +/- 0.12 to 2.43 +/- 0.13 l/min per m2 and stroke volume from 43 +/- 5 to 57 +/- 6 ml/beat after prazosin. The onset of these changes occurred between 15 and 30 minutes, peaked between 45 and 60 minutes, and persisted for six hours. These data indicate that in patients with mitral regurgitation oral prazosin promptly improves cardiac performance (judged by increased forward cardiac output and reduced left ventricular filling pressure) as systemic and pulmonary vascular resistance are reduced.