High-energy
phosphate content and mitochondrial function were analyzed at the initiation and completion of
ischemic contracture in dog hearts exposed to normothermic
ischemia while on
cardiopulmonary bypass.
Contracture initiation and completion were detected by a balloon
catheter placed within the left ventricle. In seven dogs, inner and outer layers of the myocardium were assayed for
adenosine triphosphate (
ATP) and
creatine phosphate (CP).
ATP and CP content in these two layers were compared prior to
ischemia and at
contracture initiation and completion. Inner layer
ATP levels were 23.88 +/- 0.73 (mean +/- SM) mu moles/gm dry weight prior to
ischemia, 5.14 +/- 0.49 at initiation, and 0.73 +/- 0.2 at completion. Inner layer CP content was 41.29 +/- 0.87 prior to
ischemia, 3.49 +/- 0.34 at initiation, and 4.06 +/- 0.48 at completion. Mitochondrial respiratory control indices (RCI) were assayed in a second group of seven dogs prior to
ischemia, at
contracture initiation, and at
contracture completion and were, respectively, 11.5 +/- 1.18, 3.1 +/- 0.43 and 1.76 +/- 0.29 (
alpha ketoglutarate as substrate). Despite the specific degrees of metabolic deterioration associated with the events of
contracture, ischemic time required to develop
contracture initiation and completion was variable, ranging from 29.5 to 72 minutes for initiation and 60.25 to 101 minutes for completion. A third group of five dogs had biopsy specimens taken for
ATP at fixed ischemic time intervals, and at 45 minutes of
ischemia they were found to have greater ranges in
ATP values than the ranges associated with
contracture initiation. In contrast to ischemic time, the physiological events of
ischemic contracture are reliable predictors of the degree of metabolic injury in the intact dog heart exposed to normothermic ischemic arrest during
cardiopulmonary bypass.