Cardioplegia and slow calcium-channel blockers. Studies with verapamil.

The ability of dl-verapamil to enhance myocardial protection when given before, during, or after myocardial ischemia was assessed with the use of an isolated working rat heart model of cardiopulmonary bypass and ischemic cardiac arrest. Under conditions of normothermic ischemic arrest (30 minutes at 37 degrees C), the addition of verapamil enhanced the protective properties of the St. Thomas' Hospital cardioplegic solution. Optimal protection was observed with verapamil concentrations of 0.5 mg/L (1.09 mumol/L) of cardioplegic solution. Under these conditions, postischemic enzyme leakage was reduced by 32.2% and the postischemic recovery of aortic flow was improved by 18.7%. Despite the additional protection at normothermia, the drug at several concentrations appeared unable to improve functional recovery after an extended period of hypothermic arrest (150 minutes at 20 degrees C), although under these conditions its inclusion in the cardioplegic solution could substantially reduce enzyme leakage. In other studies, the ability of various doses of verapamil alone as a substitute for the cardioplegic solution was examined. At the optimal dose (again 0.5 mg/L), and under normothermic conditions, verapamil alone was a good protection against ischemic injury, although this protection did not match that afforded by the St. Thomas' Hospital cardioplegic solution. In similar studies under hypothermic conditions, the drug failed to afford tissue protection, perhaps indicating some common modality between hypothermia and verapamil-induced protection. Pretreatment with verapamil (0.1 mg/L) prior to ischemia offered moderate additional protection, but its use during reperfusion failed to enhance overall recovery.