Hemodynamic effects of atrial pacing and prenalterol infusion in patients taking beta-adrenergic blocking drugs.

Prenalterol, a beta-adrenergic agonist, was given to nine patients with angiographically proved coronary artery disease. Subjects were studied during chronic beta-adrenergic blockade. The adequacy of blockade was assessed by the exercise heart rate response and by plasma concentrations of blocking agents. After incremental doses of 2.5 mg, 5.0 mg and 7.5 mg of prenalterol, heart rate was increased by 20%, 24% and 38%, respectively, and left ventricular dP/dt max by 55%, 73% and 61%, respectively. Systolic and diastolic blood pressures did not change significantly; pulmonary artery wedge pressure fell from 10 +/- 0.5 mm Hg to 7.1 +/- 0.9 and 6.7 +/- 0.7 mm Hg after 2.5 mg and 5.0 mg, respectively (p less than 0.01 for both). The net inotropic response to prenalterol was assessed, independent of the chronotropic response, using incremental atrial pacing before and after drug infusion. At identical heart rates, left ventricular dP/dt max increased by 40%, 49% and 48% after 2.5 mg, 5.0 mg and 7.5 mg, respectively. Left ventricular cineangiography before and after infusion showed an increase in ejection fraction from 0.73 +/- 0.02 to 0.83 +/- 0.03 (p less than 0.001). Plasma prenalterol concentration estimations demonstrated a clear, dose-related inotropic response, the level of response in each patient being largely determined by the degree of beta-adrenergic blockade at the time of the study.