J Thorac Cardiovasc Surg 2001;121:1222
© 2001 The American Association for Thoracic Surgery
Reply
Vivek Rao, MD, PhD,
Richard D. Weisel, MD, FRCS
Department of Cardiovascular Surgery
The Toronto Hospital
200 Elizabeth St, EN 14-215
Toronto, Ontario M5G 2C4, Canada
Reply to the Editor:
We appreciate the comments of Doenst, Ayres, and Beyersdorf regarding our recently published study on the effects of insulin cardioplegia during coronary artery bypass grafting.
1 We agree that the exact mechanism of insulin's beneficial effect remains unknown. However, as stated in our article, the improved transition from anaerobic to aerobic metabolism remains the most likely responsible factor. 2 Although we failed to demonstrate a stimulation of pyruvate dehydrogenase (PDH) activity in this small study, we 3 have previously reported a significant increase in myocardial PDH activity after insulin exposure independent of the ambient glucose concentration. A study by Doenst's group 4 also demonstrated that insulin exposure resulted in increased glucose uptake and glucose oxidation as long as 75 minutes after reperfusion of the ischemic rat heart. Although we agree that a direct inotropic effect of insulin may be present, the study by Lewandoski and White 2 directly correlates recovery of left ventricular function to the recovery of myocardial PDH activity. Although our small clinical study failed to demonstrate a statistically significant difference in PDH activity between groups, we believe that the improved hemodynamic recovery observed in the insulin cardioplegia groups is directly related to enhanced aerobic capacity.
12/8/114348doi:10.1067/mtc.2001.114348
References
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Rao V, Borger MA, Weisel RD, Ivanov J, Christakis GT, Cohen G, et al. Insulin cardioplegia for elective coronary bypass surgery. J Thorac Cardiovasc Surg 2000;119:1176-84.[Abstract/Free Full Text]
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Lewandoski ED, White LT. Pyruvate dehydrogenase influences postischemic heart function. Circulation 1995;91:2071-9.[Abstract/Free Full Text]
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Rao V, Merante F, Weisel RD, Shirai T, Ikonomidis JS, Cohen G, et al. Insulin stimulates pyruvate dehydrogenase and protects human ventricular cardiomyocytes from ischemia and reperfusion. J Thorac Cardiovasc Surg 1998;116:485-94.[Abstract/Free Full Text]
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Doenst T, Richwine RT, Bray MS, Goodwin GW, Frazier OH, Taegtmeyer H. Insulin improves functional and metabolic recovery of reperfused working rat heart. Ann Thorac Surg 1999;67:1682-8.[Abstract/Free Full Text]
