Myocardial protection during heart surgery. An experimental evaluation of normothermic and hypothermic cardioplegia.

Heart surgery with hypothermic cardioplegia during normothermic bypass is sometimes complicated by rewarming of the myocardium caused by collateral flow of arterial blood. This problem is particularly evident in surgery of congenital malformations. The present work is a comparative study in dogs on 3 methods of avoiding the rewarming problem. In the first group, the heart was kept cold and the warm blood was drained off from the left atrium. In the second group, total body hypothermia to the level desired was used and in the third group, normothermic cardioplegia was induced (Cardioplegin) in normothermic animals. In the two latter groups, the undesired temperature gradient between heart and body was eliminated. Evaluation of the differences was made by means of ventricular function determinations. Local, hypothermic cardioplegia showed the best postoperative function (69%) followed by the total body cooling which was fully acceptable (41%). Normothermic cardioplegia after the same duration of arrest showed a too low myocardial performance (20%).