After severe ischemic injury, it is usually necessary to prolong bypass to enhance recovery. This study tests the hypothesis that the best reversal of ischemic damage is achieved by briefly rearresting the postischemic heart with a continuous infusion of an oxygenated cardioplegic solution (secondary blood cardioplegia) during the period when bypass must be prolonged. Twenty dogs underwent 45 minutes of normothermic ischemic arrest. Fifteen minutes after unclamping, no heart could support the systemic circulation. In all dogs, oxygen demands were lowered by extending bypass for 30 minutes. In 10 of these dogs, demands were further lowered by rearresting the heart for 5 minutes with a continuous infusion of a 37°C blood cardioplegic solution (K+ 28 mEq/L; pH 7.6; Ca++ 1 mEq/L) at the pressure of 50 mm Hg. Hearts treated with secondary blood cardioplegia showed greater recovery in the rate of contraction (+dP/dt 75% versus 62%, p<0.05) and relaxation (-dP/dt 76% versus 58%, p<0.05), better recovery of compliance (85% versus 51%, p<0.05), a higher stroke work index (0.72 versus 0.50 gm-m/Kg, p<0.05), and more ability to augment oxygen uptake (85% versus 45%, p<0.05) to meet the demands of the working heart than hearts treated by prolonging bypass alone. It is concluded that rearresting the heart with a brief, continuous infusion of a blood cardioplegic solution results in more complete reversal of ischemic damage than possible by prolongation of a bypass alone. It is believed that the increased recovery with secondary cardioplegia results from diversion of delivered oxygen toward reparative processes rather than its being expended needlessly on electromechanical work during the time when bypass must be prolonged.
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine
- Cardiology and Cardiovascular Medicine