Hemodynamic and cardiac effects of clonidine.

Clonidine produces hemodynamic effects that are mediated through both the heart and the peripheral vascular system. The cardiac effects (decrease in heart rate and stroke volume) appear to predominate early in treatment, but peripheral vascular resistance is usually reduced. In some studies, the reduction in peripheral resistance was found to persist beyond the initial period of therapy. The sympathetic tone in various parts of the cardiovascular system probably determines whether the drug preferentially affects the heart or the resistance vessels. The clonidine-induced reduction in blood pressure and heart rate decreases the cardiac workload. The drug is also beneficial in patients with coronary artery disease, and appears to have a coronary vasodilating effect. Clinically, the drug is useful when given alone or in combination with either a peripheral vasodilator or a diuretic. Although clonidine reduces the heart rate, severe bradycardia is uncommon. The drug should be used with caution in patients with AV conduction disease.