Excessive myocardial cooling may have detrimental effects on donor heart integrity. This study assessed the standard technique for donor myocardial preservation using hearts from seven mongrel dogs (mean weight 192.7 gm), which were arrested, excised, and placed in a cooler containing saline and ice. Temperature probes placed in both the left and right ventricular free walls and the septum revealed that, after cardioplegia, temperatures fell to 10.3 degrees, 7.5 degrees, and 7.6 degrees C, respectively. 

Temperature decreased to below 1 degree C after 75, 75, and 60 minutes for the left ventricle, right ventricle, and septum, respectively, independent of the size of the heart (range = 104 to 322 gm). After 4 hours of cooling, temperature was below 0 degrees C throughout the myocardium. Examination with an electron microscope showed similar serial changes over 4 hours in all hearts, including moderate-to-severe cytoplasmic and nuclear swelling and mitochondrial calcium deposits. Cell membranes remained intact, which suggests that the damage was not irreversible. We conclude that current donor heart preservation techniques may result in unacceptably low myocardial temperatures that cause reversible myocardial injury.

Hendry PJ1, Walley VM, Koshal A, Masters RG, Keon WJ.
J Thorac Cardiovasc Surg. 1989 Oct; 98(4):517-22. 
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