Assessment of the inotropic and vasodilator effects of amrinone versus isoproterenol

The hemodynamic effects of graded-dose infusions of amrinone (maximal dose 30 μg/kg/min) (10 patients) and isoproterenol (maximum dose 4 μg/min) (11 patients) were assessed in patients with a range of left ventricular (LV) function. LV rejection fraction ranged from 0.13 to 0.77 (mean ± standard deviation 0.47 ± 0.23) among the patients who received amrinone and from 0.24 to 0.77 (mean 0.52 ± 0.18) among those who received isoproterenol. Peak-dose amrinone produced a reduction in LV filling pressure (from 15 ± 10 to 10 ± 7 mm Hg, p < 0.001), but no significant change in heart rate, cardiac output, mean aortic pressure, total systemic vascular resistance (TSVR) or LV dP/dt max. In contrast, peak-dose isoproterenol produced a similar reduction in LV filling pressure (from 17 ± 12 to 13 ± 13 mm Hg, p <0.05), but also caused increases in heart rate, cardiac output and LV dP/dt max and decreases in mean aortic pressure and TSVR (p <0.001). The absolute change in cardiac output and stroke volume correlated closely with the change in TSVR in response to amrinone (r = -0.90, p <0.001 and r = -0.84, p = 0.002, respectively), but not in response to isoproterenol. Although isoproterenol produced a marked increase in cardiac output and LV dP/dt max (not explained by heart rate changes alone) in all patients, amrinone produced an increase in cardiac output only in those with markedly elevated LV filling pressures (who had a reduction in TSVR), and an increase in LV dP/dt in a minority.