To study the effect of
prazosin therapy on left ventricular function in patients with chronic stable
heart failure, first pass
radionuclide angiography at rest and during exercise was performed in 15 patients before the administration of
prazosin and after seven to 12 weeks of
prazosin therapy. There was no significant change in resting ejection fraction before and during
prazosin therapy (36 +/- 14 per cent versus 37 +/- 14 per cent) (mean +/- standard deviation). However, exercise ejection fraction increased from 34 +/- 14 per cent to 42 +/- 17 per cent (p less than 0.01). The difference in ejection fraction from rest to exercise (ejection fraction response) changed significantly from -2 +/- 6 per cent before
prazosin therapy to +5 +/- 7 per cent during
prazosin therapy (p less than 0.01). Exercise duration increased from 368 +/- 82 seconds to 476 +/- 82 seconds (p less than 0.01). Total work capacity measured in kilojoules increased from 12.6 +/- 8.3 to 18.6 +/- 10.4 (p less than 0.01). The improved ejection fraction response during
prazosin therapy correlated with the improved work capacity (r = 0.69, p less than 0.01) and exercise duration (p = 0.59, p less than 0.05). This improvement occurred despite a significant
weight gain with
prazosin from 72.2 +/- 20.8 kg to 73.5 +/- 20.8 kg (p less than 0.01). These data suggest that long-term
prazosin therapy is effective in the treatment of
heart failure. However, the beneficial effects of
prazosin, an alpha 1 blocking agent, may be evident only during exercise.