Hemodynamic effects of nifedipine in coronary surgery

Nifedipine is a potent vasodilator. Until now, its positive effect on cardiac performance after coronary artery bypass graft (CABG) operation was interpreted as the result of a decrease in the afterload. So as to have a better understanding of the precise role of nifedipine under these circumstances, an investigation was carried out on 20 patients, at the end of the CABG operation. Cardiac output (CO), CABG-flow to left anterior descending artery (LAD), mean aortic pressure (AP), mean left atrial pressure (LAP) systemic vascular resistances (SVR), LAD resistances and electrocardiogram (ECG) were recorded at the end of cardiopulmonary bypass (Step 1). Thereafter, a bolus of 0.1 mg nifedipine was injected directly through the CABG to LAD. The same measurements as above were recorded 1 min (Step 2), 4 min (Step 3), and 9 min (Step 4) later, respectively. The most striking results were an average increase of coronary flow of 120% at step (S) 2, and a decrease of mean LAP of 18.9% at S 3. A slight but significant decrease of AP (11% in average) could be observed at S 2-3. No significant effect on CO and peripheral SVR could be noted in the first nine minutes after injection of nifedipine. Decrease of coronary vascular resistance was the earliest and perhaps the most important alteration. It caused an increase of coronary perfusion, improvement of myocardial relaxation and performance followed by a reduction of LAP. The absence of ST alteration in the ECG was representative of a flow which effectively passed through the coronary capillaries, without significant A-V shunt.