Myocardial oxygen consumption and lactate production during antegrade warm blood cardioplegia

Continuous warm blood cardioplegia has recently been recommended as an alternative to multidose cold blood cardioplegia for myocardial protection during coronary bypass operations. Cardioplegia may have to be interrupted in order to provide a bloodless operating field during coronary anastomosis. To determine the effects of ischemia at normothermia on myocardial oxygen consumption and lactate production we randomized 17 dogs to receive either warm blood cardioplegia (37 degrees C) or cold blood cardioplegia combined with systemic and topical cooling. After initiating arrest, cardioplegia was interrupted for periods of 1, 2, 3, 4, 5, 6, and 10 min. Myocardial oxygen debt occurred after 3.5 min of ischemia in the 9 animals receiving warm blood cardioplegia. In contrast, myocardial oxygen consumption never exceeded oxygen availability during cold blood cardioplegia (P less than 0.001). Lactate production increased linearly in both groups but was much greater in those animals receiving warm blood cardioplegia (P less than 0.001). Spontaneous electromechanical activity was much more common during warm blood cardioplegia which required frequent infusions of cardioplegia to maintain cardiac arrest (P less than 0.0003).

(1) Oxygen debt occurred after 3.5 min of warm ischemia; (2) spontaneous electromechanical activity is more common during warm heart protection which necessitates the use of larger volumes of cardioplegia to maintain cardiac arrest.