Paradox of improved exercise but not resting hemodynamics with short-term prazosin in chronic heart failure

In patients with chronic heart failure exercise allows the simultaneous observation of the cardiovascular pathophysiology and the symptoms of these patients. We administered short-term, oral prazosin to 10 patients with severe chronic heart failure. Prazosin increased cardiac output and stroke volume significantly during exercise (both P < 0.05) but not at rest (both P > 0.10). Prazosin decreased the arteriovenous oxygen difference and left ventricular filling pressure significantly during exercise (both P < 0.05) but not at rest (both P > 0.10). There was no significant correlation between prazosin-induced changes at rest and during exercise in cardiac output ( r = 0.12), stroke volume ( r = 0.02), arteriovenous oxygen difference ( r = 0.33) or left ventricular filling pressure ( r = 0.43). Prazosin predominantly affects hemodynamics during exercise because its pharmacologic activity as an alpha-adrenergic blocking agent is most prominent during exercise. The full evaluation of prazosin-induced changes in the hemodynamics of patients with chronic heart failure requires evaluation during exercise.