Cardiac and systemic sympathetic activity in response to clonidine in human heart failure

Objectives. We studied the effects of clonidine on cardiac sympathetic activity and left ventricular function in patients with congestive heart failure (CHF). Background. Sympathetic activation has major prognostic implications in patients with heart failure. Clonidine, an imidazoline and alpha2-receptor agonist, has been shown to cause reduction in generalized sympathetic activity. Methods. Nine patients with CHF (left ventricular ejection fraction 22 ± 4% [mean ± SEM]) received 50 μg and 100 μg bolus of clonidine intravenously. Study measurements included right and left heart hemodynamics, cardiac output, rate of rise in left ventricular peak positive pressure (LV +dP/dt) and tau, along with cardiac and total body norepinephrine spillover. The radiotracer method was used for calculation of norepinephrine spillover. Results. Right and left heart filling pressures did not change in response to either dose of clonidine. Mean arterial pressure fell after the second dose of clonidine, from 94 ± 8 to 82 ± 6 mm Hg (p < 0.05). The LV + dP/dt was reduced from 737 ± 53 to 629 ± 43 mm Hg/s (p < 0.05). Clonidine also caused significant increase in tau, as measured by the method of Weiss (65 ± 3 vs. 74 ± 4 ms, p < 0.01) and the direct pressure half-time technique (48 ± 2 vs. 54 ± 3 ms, p < 0.01). Cardiac norepinephrine spillover fell from 121 ± 29 to 52 ± 20 pmol/min in response to 100 μg of clonidine (p < 0.01 vs. control). Conclusions. Despite significant fall in arterial pressure, clonidine caused marked reduction in sympathetic activity directed at the heart. The negative inotropic and lusitropic effects appear to be secondary to this reduction in sympathetic drive. Because increased cardiac and generalized sympathetic activity are strong predictors of an adverse outcome in patients with CHF, the role of centrally active sympathoinhibitory agents in the therapy of CHF deserves further exploration.