Abstract
In 1969, our group first reported that the intravenous administration of phentolamine can improve cardiac performance in patients with heart failure. 1 Positive inotropism and a reduction in afterload were shown to be the mechanisms that led to cardiac improvement. Since that time the literature is replete with articles attesting to the benefits of vasodilator drugs in the treat ment of acute and chronic heart failure.
A reduction in impedance or afterload should produce beneficial hemodynamic effects in patients with left ventricular volume overload due to aortic insufficiency or mitral insufficiency. This has been verified using an intravenous infusion of nitroprusside, 2,3 phentolamine4 and hydralazine.5,6
The effects of vasodilators on left ventricular wall stress can now be evaluated noninvasively. Recently Wilson and his group7 documented that nitroglycerin can effectively reduce the peak and end systolic wall stress in patients with aortic regurgitation. These authors concluded that the beneficial action of nitroglycerin on muscle mechanics might retard left ventricular enlargement and hypertrophy and consequently delay the onset of myocardial dysfunction.
Prazosin is an oral drug with sustained vasodilator properties similar to nitroprusside which is widely used in the treatment of heart failure. This drug is a quinazoline derivative structurally unrelated to other vasodilator drugs pre sently available. It acts principally by blockade of vascular alpha-adrenergic receptors. It selectively blocks the postsynoptic or alpha 1 receptor while having little affinity for the pre-synoptic or alpha 2 receptor.
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