Verapamil cardioplegia: improved myocardial preservation during global ischemia

To determine whether the calcium antagonist verapamil can produce satisfactory myocardial preservation during global ischemia, we studied three groups of eight dogs. Serial left ventricular biopsy specimens were taken for adenosine triphosphate and creatine phosphate content. Arterial and coronary sinus blood samples were obtained for lactate and oxygen content determination prior to ischemia, immediately after the ischemic interval, and after a 30 minute reperfusion period. Starling and isovolumetric ventricular function curves were determined prior to ischemic arrest and after 45 minutes of reperfusion. All animals were systemically cooled to 25 degrees C, and the aorta was clamped for 120 minutes. Group I had a potassium cardioplegic solution (30 mEq/L) chilled to 4 degrees C and injected into the aortic root. The initial dose was 200 ml and an additional 100 ml was infused at 20 minute intervals. Group II had a solution containing verapamil (0.15 mg/kg/L), diluted in Ringer's solution (4 degrees C), injected into the aortic root. The initial and subsequent doses were as in Group I. Group III received the same solution as Group II, but at room temperature. Alterations in lactate metabolism were not significantly different in any of the three treatment groups. A reduction in oxygen consumption was seen in Group III, but was not found to be statistically significant. However, the reduction in coronary flow at the end of reperfusion was statistically significant in Group III (p less than 0.05). Verapamil given at room temperature resulted in poor preservation of left ventricular function and high-energy stores. Verapamil combined with extreme hypothermia (Group II) provided excellent preservation of left ventricular compliance and contractility. Cold verapamil cardioplegia was superior to potassium cardioplegia for the preservation of adenosine triphosphate.