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

Background. Protection of the myocardium during beating heart operations is paramount. The goal of this study is to determine if regional topical hypo thermia (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 an d the control group (n = 6) received no cooling. Myocardial and core temper atures were measured with thermistors. Sonomicrometers and micromonameters were used to determine load independent indices of myocardial function. The se indices were measured at base line, during coronary occlusion, and at 3 hours of reperfusion. The myocardium at risk and the infarct area were dete rmined with monastral blue dye and triphenyl tetrazolium chloride staining. Results. The mean myocardial temperature in the risk zone during coronary o cclusion was significantly less in the RTH group (29.4 degreesC +/- 5.6 deg reesC versus 35.7 degreesC +/- 1.1 degreesC, p < 0.05). After 40 minutes of coronary occlusion, both the RTH group and control had a significant reduc tion in regional elastance (9.38 +/- 3.54 and 11.05 +/- 1.67 mm Hg/mm) comp ared with base line measurements (14.70 +/- 2.42 and 16.80 +/- 4.79 min Hg/ mm), p < 0.05. However, after 3 hours of reperfusion, the elastance returne d to base line levels in the RTH group (15.83 +/- 3.06 mm Hg/mm) but remain ed significantly depressed in the control group (9.97 +/- 3.63 min Hg/mm, p < 0.04). Myocardial necrosis as a percentage of the risk zone was signific antly less in the hypothermia group (25% +/- 2% versus 62% +/- 5%, p < 0.00 1). Conclusions. Regional topical hypothermia during isolated temporary coronar y occlusion provides regional myocardial protection expressed as a return o f function and decreased necrosis. Regional topical hypothermia may be clin ically applicable to myocardial preservation during beating heart operation s. (C) 2001 by The Society of Thoracic Surgeons.