Effect of xamoterol on myocardial energetics in man.

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We analyzed the effect of xamoterol (β1-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 < 0.05) and cardiac index from 2.9 ± 0.5 to 3.2 ± 0.5 L/min·m2 (p < 0.01), respectively. Left ventricular peak positive dp/dt (1870 ± 350 vs 2620 ± 580 mmHg/sec (p < 0.01)) and left ventricular ejection fraction (62 ± 7 vs 70 ± 7% (p < 0.01)) also increased, while left ventricular end-diastolic pressure (9 ± 3 vs 5± 3 mmHg (p < 0.01) and volume index (70 ± 14 vs 58 ± 16 ml/m2 (p < 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 < 0.01). Myocardial oxygen extraction ratio decreased significantly (p < 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.
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