Selective Topical Cooling for Myocardial Protection

Abstract

Limitations of myocardial cooling using antegrade infusion cardioplegia have led to the routine use of topical myocardial cooling. However, topical myocardial cooling can injure the phrenic nerves, lungs and heart. Red blood cells are also discarded with the irrigation fluid. To evaluate the selective use of topical cooling, data were collected prospectively from 67 consecutive patients undergoing isolated coronary artery bypass operation. All patients received an inductive dose of 1 liter blood cardioplegia solution. Intramyocardial temperatures were determined in the distribution of the three major coronary arteries after the first 500 ml of cardioplegia solution was administered. If the three temperature readings were all ≤20° C, patients (group 1, n = 31) received no topical myocardial cooling. If any temperature was >20°C, patients (group 2. n = 36) received topical cooling while the second 500 ml cardioplegia solution was administered. Cardioplegia solution was subsequently administered at approximately 20-min intervals, at which time the patient did or did not receive topical myocardial cooling, depending on the selected group. Although patients in group 2 were older (mean (s.e.m.) age 63.3(1.6) versus 56.8(1.8) years, P<0.05), the two groups were not significantly different with respect to sex. ejection fraction, risk factors, and class of the New York Heart Association. There were also no significant differences in the mean number of grafts per patient, use of the internal mammary artery, and cross-clamp or pump times. There were no deaths and only one patient (3%) in group 2 developed new Q waves. Patients in group 2 received significantly more homologous blood transfusions (mean(s.e.m.) 1.03(0.4) versus 0.06(0.04) units, P<0.05). Postoperative hemodynamics and creatinine phosphokinase isozyme profiles did not significantly differ between groups. In patients with adequate myocardial cooling using cardioplegia alone, the omission of topical myocardial cooling did not increase operative risk, spared the patient from potential hypothermia-induced injury, and may have helped to reduce the need for homologous blood transfusion.