Myocardial preservation with nifedipine: a comparative study at normothermia

Sixty-four dogs were placed on normothermic total cardiopulmonary bypass, and global ischemia was induced for 1 hour during which continuous infusions (240 ml per hour) (N = 39) or bolus injections (150 to 200 ml every 30 minutes) (N = 23) into the proximal aortic root were performed. The control groups (N = 26) had infusion or injection of normal saline solution, normal saline solution + 25 mEq/L of potassium chloride, or Normosol-R pH 7.4. The cardioplegic solution (N = 15) contained 25 mEq/L of potassium chloride in Normosol-R pH 7.4, 0.25 mg/ml of lidocaine, 500 mg/dl of glucose, and 1.8 microU/ml of insulin. The nifedipine group (N = 23) had infusion or injection of 0.167 to 0.2 microgram/ml of nifedipine in saline solution, Normosol-R pH 7.4, or the cardioplegic solution. Left ventricular performance was assessed by phasic and mean measurements of left ventricular peak and end-diastolic pressures and its first derivative, left and right atrial pressures, and ascending aortic blood flow. Calculations of stroke work index and total peripheral resistance were performed. Morphological examinations, and light and electron microscopic examinations of heart slices were done. The results demonstrated a consistent superiority of the nifedipine group in terms of performance after bypass compared with the cardioplegic or control group. Normal preischemic stroke work indices and Sarnoff curves were present 2 hours after bypass for the nifedipine-treated groups. The cardioplegic solution was ineffective when given continuously but gave modest protection when given as a bolus injection. It is concluded that the concept of the efficacy of calcium blockade during ischemia and the initial reperfusion period for enhanced myocardial protection is valid.