Effects of acute cardioselective and non-selective beta-adrenergic blockade on left-ventricular volumes and vascular resistance at rest and during exercise.

The effects of intravenous metoprolol and propranolol on left-ventricular performance were studied by radionuclide cardiography in eight healthy young men at rest and during exercise. At rest, a fall of 7 to 10 mmHg was recorded in systolic blood pressure after both drugs (p less than 0.05). The decrease in cardiac output entirely ascribed to relative bradycardia was 18% after propranolol (p less than 0.01) compared with 6% after metoprolol (p less than 0.05). Left-ventricular volumes did not change at rest. Systemic vascular resistance increased by 14% after metoprolol and by 28% after propranolol (both p less than 0.05). During submaximal bicycle exercise the systolic blood pressure fell by 15 mmHg after both drugs (p less than 0.05). The reduction in exercise heart rate was 17 beats min-1 and 18 beats min-1 (both p less than 0.01), but propranolol reduced cardiac output by 18% (p less than 0.01) compared with 5% (p less than 0.05) after metoprolol, reflecting a reduction in stroke volume induced only by non-selective blockade. A more pronounced left-ventricular end-diastolic dilatation during exercise was allowed by metoprolol and the fall in the exercise ejection fraction was, therefore, smaller after this drug. Concomitantly, the calculated systemic vascular resistance was increased only 6% by metoprolol (p less than 0.05) compared with a 29% increase by propranolol (p less than 0.01). These findings suggest that, at least in healthy subjects, metoprolol is superior to propranolol in the ability to limit adverse cardiovascular changes.