Myocardial protection in the acutely injured heart: Hyperpolarizing versus depolarizing hypothermic cardioplegia

Objectives: The superiority of hyperpolarized arrest with adenosine triphosphate-sensitive potassium channel openers over standard hyperkalemic depolarizing cardioplegia during normothermic ischemia has been documented. This study examined the hypothesis that pinacidil would provide superior protection in a more clinically relevant model of an acutely injured heart and hypothermic cardioplegic arrest. Methods: In a blood-perfused, parabiotic, rabbit heart Langendorff model, hearts underwent 15 minutes of unprotected global normothermic ischemia before the administration of 50 ml of cardioplegic solution at 4°C, followed by 50 minutes of hypothermic (15°C) ischemia and 30 minutes of reperfusion. The cardioplegic solutions administered consisted of Krebs-Henseleit solution alone (N = 6), Krebs- Henseleit solution with pinacidil (50 μmol/L; N = 10), Krehs-Henseleit solution with pinacidil (50 μmol/L) and glibenclamide (a potassium channel blocker, 10 μmol/L; N = 8), or St. Thomas' Hospital solution (N = 8). The percent recovery of developed pressure, linear diastolic pressure-volume relationships, and coronary blood flow were compared. Results: The percent recovery of developed pressure was 32.8% ± 2.8%, 43.0% ± 4.3%, 46.5% ± 2.2%, and 49.3% ± 2.7% for the Krebs-Henseleit, the Krebs-Henseleit with pinacidil and glibenclamide, the St. Thomas' Hospital, and the Krebs- Henseleit with pinacidil groups, respectively. No hearts had ventricular fibrillation on reperfusion. Conclusions: During hypothermic hyperpolarized arrest, as opposed to normothermic ischemia as in our previous studies, there was neither an increased incidence of ventricular fibrillation nor prolonged electrical activity when compared with results during traditional hyperkalemic arrest. Myocardial protection by St. Thomas' Hospital solution and pinacidil was superior (p = 0.009) to that with Krebs-Henseleit solution alone. The protection provided by pinacidil was lost with the addition of glibenclamide, indicating that the drug has adenosine triphosphate-sensitive potassium channel activity during hypothermia.