Regional topical hypothermia of the beating heart: preservation of function and tissue

Abstract

Background. Protection of the myocardium during beating heart operations is paramount. The goal of this study is to determine if regional topical hypothermia (RTH) preserves myocardial viability and function during periods of temporary coronary artery occlusion. Methods. Sixteen pigs were divided into two groups (RTH and control). Each group received 40 minutes of midleft anterior descending coronary occlusion followed by 3 hours of reperfusion. The RTH group (n = 10) received RTH and the control group (n = 6) received no cooling. Myocardial and core temperatures were measured with thermistors. Sonomicrometers and micromonameters were used to determine load independent indices of myocardial function. These indices were measured at base line, during coronary occlusion, and at 3 hours of reperfusion. The myocardium at risk and the infarct area were determined with monastral blue dye and triphenyl tetrazolium chloride staining. Results. The mean myocardial temperature in the risk zone during coronary occlusion was significantly less in the RTH group (29.4°C ± 5.6°C versus 35.7°C ± 1.1°C, p < 0.05). After 40 minutes of coronary occlusion, both the RTH group and control had a significant reduction in regional elastance (9.38 ± 3.54 and 11.05 ± 1.67 mm Hg/mm) compared with base line measurements (14.70 ± 2.42 and 16.80 ± 4.79 mm Hg/mm), p < 0.05. However, after 3 hours of reperfusion, the elastance returned to base line levels in the RTH group (15.83 ± 3.06 mm Hg/mm) but remained significantly depressed in the control group (9.97 ± 3.63 mm Hg/mm, p < 0.04). Myocardial necrosis as a percentage of the risk zone was significantly less in the hypothermia group (25% ± 2% versus 62% ± 5%, p < 0.001). Conclusions. Regional topical hypothermia during isolated temporary coronary occlusion provides regional myocardial protection expressed as a return of function and decreased necrosis. Regional topical hypothermia may be clinically applicable to myocardial preservation during beating heart operations.