Topical myocardial cooling. An intensive laboratory investigation

To better understand efficacy of topical cooling in myocardial protection, three groups of 12 dogs each were studied. Group 1 dogs had systemic cooling to 30 C; group 2 had cooling to 30 C and outside cooling of left ventricle; group 3 was cooled in the same way as group 2 was but also had inside of left ventricle topically cooled. Measurements were taken of left ventricular function curves, regional blood flow distribution to the subendocardium, sequential pH, PCO2, PO2, and lactate and serum glutamic oxaloacetic transaminase (SGOT) levels. Lower midseptal and subendocardial temperature (means, 11 and 7 C, respectively) in group 3 correlated with higher survival and greater preservation of left ventricular function. Lower levels of SGOT and lactate in coronary sinus efflux, and higher regional flow to subendocardium postoperatively, also correlated with minimal evidence of subendocardial necrosis in group 3 dogs. Rapid of cooling of subendocardium was noted as achieving maximum preservation of left ventricular function.