Evaluation of methods for estimating infarct size by myosin LC2: comparison with cardiac enzymes

The relationship between histologically determined infarct size and release or peak levels of circulating cardiac enzymes and myosin light chain 2 (LC2) was studied. Myocardial infarction was produced by ligating the left anterior descending coronary artery in 18 conscious closed-chest dogs. Creatine phosphokinase (CPK), cytosolic and mitochondrial isozymes of aspartate transaminase (sAST and mAST) in the plasma, and LC2 in the serum were measured serially until 10 days after infarction, when infarct size was determined histologically [range 4.0-38.8% of the left ventricular weight (%LV)]. Infarct size correlated most closely with LC2 release (r = 0.82, P less than 0.001) and less closely with peak sAST (r = 0.59, P less than 0.01), peak mAST (r = 0.49, P less than 0.05), peak CPK (r = 0.22), and CPK release (r = 0.14). The correlation between infarct size and CPK release was improved by limiting the analysis to the dogs with infarct size of less than 20% LV (n = 11, r = 0.53, P less than 0.1). Because, among cardiac enzymes and LC2, CPK activity decayed most rapidly in the lymph fluid when incubated in vitro, degeneration of CPK in the lymph stream may contribute to the nonlinear relationship between infarct size and CPK release.