Improved myocardial protection with nifedipine and potassium-based cardioplegia

Thirty dogs were studied acutely on cardiopulmonary bypass in four groups. Hearts in Groups 1C (standard cardioplegia, n = 5) and 2c (n = 10) were subjected to periods of global ischemia of 1 and 2 hours, respectively. Both groups received 300 cc boluses of hypothermic (4 degrees C), potassium-based cardioplegic solution infused via an 18 gauge needle proximal to the aortic cross-clamp, at every 30 minute interval of ischemia. Groups 1CN (standard cardioplegia plus nifedipine, n = 5) and 2CN (n = 10) were treated similarly, except that nifedipine (5 microgram/kg) was added to each 300 cc bolus of cardioplegic solution. The addition of nifedipine in Groups 1CN and 2CN resulted in statistically significant reduction in myocardial water content (p less than 0.005), mean left atrial pressure (MLAP) (p less than 0.05), and myocardial compliance (p less than 0.005) as compared to the control groups (1C and 2C). Recovery of left ventricular dp/dt in Experimental Group 2CN was also statistically better (p less than 0.025) than in Control Group 2C. Examination of myocardial biopsy tissue by electron microscopy was not conclusive. Nifedipine used in combination with hypothermic, potassium-based cardioplegia provided significant additional myocardial protection over cardioplegia alone.