This study was undertaken in order to compare the effectiveness of
amrinone and
dobutamine as primary treatment of a
low cardiac output (CO) after
coronary artery bypass graft (CABG) surgery. Thirty patients with preoperative
left ventricular dysfunction participated in this open-label randomized study. Patients were included if they failed to separate from
cardiopulmonary bypass (CPB) without inotropic support or if they had a cardiac index (CI) less than 2.4 L/min/m2 after CPB regardless of the blood pressure, in the presence of adequate filling pressures. The treatment objectives were to separate from CPB and achieve a CI > or = 2.4 L/min/m2 and a mean arterial pressure > or = 70 mmHg. Patients treated with
amrinone received 0.75 mg/kg followed by 10 micrograms/kg/min; when the objectives were not achieved within five minutes, another 0.75 mg/kg was given. Patients treated with
dobutamine received an initial infusion of 5 micrograms/kg/min increased stepwise to 15 micrograms/kg/min if necessary. Eleven of 15
amrinone versus 6 of 15
dobutamine patients achieved the predefined treatment objectives with the test
drug alone (P = NS). Comparisons of hemodynamics in patients treated solely with
amrinone (n = 7) or
dobutamine (n = 6) after CPB showed no significant differences between the treatment groups. The incidence of
myocardial ischemia as detected by Holter monitor was 36% with
amrinone and 33% with
dobutamine. Two patients suffered
ventricular fibrillation and two had significant supraventricular
tachyarrhythmias (heart rate > 130/min) during treatment with
dobutamine alone, whereas no significant arrhythmias occurred in the
amrinone group (P = NS). Six
dobutamine patients (40%) had postoperative
myocardial infarction (MI) as opposed to none among the
amrinone patients (P = 0.017). These results indicate that
amrinone compares favorably with
dobutamine as a primary treatment of low CO after CABG. Further study in a larger number of patients will be required in order to determine if the lower incidence of MI in the
amrinone group was due to the treatment
drug.