Oral beta-blockade with hypothermic potassium cardioplegia in cardiac surgery: is there an additive protective effect?

The possible myocardial protective effect of oral propranolol in combination with potassium cardioplegia and hypothermia was investigated in 30 greyhounds, divided into 2 sub-groups, by determining the changes in myocardial ATP and CP levels, ultrastructural changes and the changes in hemodynamics after a 2-hour period of myocardial ischemia. In group 1, in animals with multiple doses of cardioplegia during the 2-hour ischemic period, preoperative treatment with propranolol did not have a significant myocardial protective effect. In group 2, in animals with a single dose of cardioplegia, during the 2-hour ischemic period, propranolol resulted in a trend of improved survival, although the myocardial ATP and CP levels were the same in both sub-groups. In addition, the multiple doses of cardioplegia in group 1 caused increased subcellular edema in the myocardium. This study suggests that oral propranolol treatment may provide additional myocardial protection during ischemic periods when used with potassium cardioplegia and hypothermia. The mechanism of this effect is not established, but could relate to reduced transmembrane calcium influx.