Calcium-channel blockade as an adjunct to heterogeneous delivery of cardioplegia.

The clinical situation of heterogeneous cardioplegia was simulated in a canine model by temporary ligation of the circumflex coronary artery during a three-hour interval of cardioplegic arrest. Nifedipine and lidoflazine, administered prior to aortic clamping, were evaluated as adjuncts to cold (2 degrees C) crystalloid cardioplegia. Assessment was made of regional function (sonomicrometer systolic shortening) and of global function by measuring left atrial (LA) pressure at constant cardiac output (CO), aortic pressure, and heart rate, and by measuring stroke work at constant LA pressure, aortic pressure, and heart rate. Among 14 control dogs, only 7 could achieve a CO of 5 liters per minute following cardioplegic arrest. Left anterior descending coronary arterial systolic shortening recovered to only 86% of prearrest values (p less than 0.05), circumflex coronary arterial systolic shortening recovered only 28% (p less than 0.01), stroke work recovered 59% (p less than 0.01), and LA pressure was 6.7 mm Hg higher (p less than 0.01) than prior to cardioplegic arrest. Lidoflazine provided no statistically significant benefit in these animals (N = 4). However, dogs given nifedipine (N = 6) had very little change in left anterior descending coronary arterial systolic shortening (99% recovery), stroke work (93% recovery), and LA pressure (delta = 0.4 mm Hg). None of these changes was statistically significant. There was some deterioration in circumflex coronary arterial systolic shortening (56% recovery; p less than 0.05). All 6 dogs given nifedipine achieved a CO of 5 L/min following cardioplegic arrest. Clinical cardioplegia is typically heterogeneous cardioplegia. Calcium-channel blockade appears to be useful in this situation.