Effect of xamoterol on myocardial energetics in man.

We analyzed the effect of xamoterol (beta 1-partial agonist) on myocardial energetics in 8 patients with normal left ventricular function. We measured resting systemic and coronary hemodynamics before and after a single intravenous injection of xamoterol (0.1 mg/kg). This agent increased heart rate from 70 +/- 7 to 80 +/- 11 beats/min (p less than 0.05) and cardiac index from 2.9 +/- 0.5 to 3.2 +/- 0.5 L/min.m2 (p less than 0.01), respectively. Left ventricular peak positive dp/dt (1870 +/- 350 vs 2620 +/- 580 mmHg/sec (p less than 0.01) and left ventricular ejection fraction (62 +/- 7 vs 70 +/- 7% (p less than 0.01] also increased, while left ventricular end-diastolic pressure (9 +/- 3 vs 5 +/- 3 mmHg (p less than 0.01] and volume index (70 +/- 14 vs 58 +/- 16 ml/m2 (p less than 0.01] decreased. Coronary blood flow and total myocardial oxygen consumption did not change significantly after intervention. As a result, xamoterol enhanced left ventricular external mechanical work versus myocardial oxygen consumption ratio (mechanical efficiency) from 20 +/- 4 to 24 +/- 5% (p less than 0.01). Myocardial oxygen extraction ratio decreased significantly (p less than 0.01) from 66 +/- 5 to 62 +/- 5% after xamoterol. We conclude that xamoterol augments left ventricular mechanical efficiency accompanied by a decrease in coronary vascular tone in patients with normal cardiac function.