Diltiazem provides higher internal mammary artery flow than nitroglycerin during coronary artery bypass grafting...

Perioperative internal mammary artery (IMA) vasospasm in patients undergoing coronary artery bypass grafting (CABG) surgery may lead to morbidity and mortality. Surgical stimulus is one of the common causes of IMA vasospasm. Preventive measures, beside treatment should be taken into consideration to obtain vasospasm free IMA. The effect of a pharmacologic agent on IMA flow when it is administered before harvesting the artery has not been documented. We designed a prospective randomized clinical study to compare the IMA free blood flows in patients receiving either diltiazem or nitroglycerin, starting infusion of study drugs before a surgical stimulus was applied to the IMA region and continuing throughout the isolation period.

Sixty patients undergoing elective CABG surgery with the left IMA received diltiazem (n=30, 0.05-0.1 mg/kg per hour) or nitroglycerin (n=30, 0.25-2.5 microg/kg per minute) in a randomized manner. Infusions of study drugs were started before applying a surgical stimulus to the IMA region and continued throughout the harvesting period. The first free flow was measured after IMA was cut above its bifurcation and the second after its distal segment was resected. Heart rate, temperature, mean arterial and central venous pressures were recorded. Data were analyzed with Student's t-test and Fischer's exact test.

Preoperative and hemodynamic data were similar between the groups. The means of first and second IMA flows in patients treated with diltiazem (53.8+/-30.1 and 72.3+/-35.4 ml/min) were significantly higher than in those treated with nitroglycerin (25.7+/-16.2 and 48.9+/-23.8 ml/min; P=0.000, 0.004, respectively). IMA flows significantly increased after distal segment resection both in diltiazem (34%) and nitroglycerin groups (90%; P= 0.000, 0.000, respectively).

Diltiazem infusion which started prior to harvesting provided higher IMA blood flow compared to nitroglycerin infusion. Considering the percentage of increases in flows after resection of distal segment, the most prone part to vasospasm, we assume that a certain amount of spasm occurred in IMA in spite of infusion of study drugs, such that less with diltiazem and more with nitroglycerin. Diltiazem plays more important role than nitroglycerin in the prevention of vasospasm.