Prognostic implications of an early peak in plasma MB creatine kinase in patients with acute myocardial infarction

To determine the prognostic implications of an early peak in plasma MB creatine kinase (MB CK) in patients with acute myocardial infarction who were not treated with an acute intervention, 342 patients with myocardial infarction confirmed by MB CK were retrospectively studied. The patients were classified into those with an early peak MB CK (≤15 hours after the onset of symptoms, n = 84) and those with a late peak MB CK (>15 hours after the onset of symptoms, n = 258). Patients with an early peak MB CK were slightly older, were more frequently female and had a higher incidence of prior myocardial infarction, congestive heart failure and arrhythmias compared with patients with a late peak MB CK. Patients with an early peak MB CK more frequently presented with ST segment depression (23 versus 11%, p < 0.01), with anterior location of ischemia or infarction (71 versus 52%, p < 0.01) and with a lower mean left ventricular ejection fraction (41.4 versus 47.4%, p < 0.01). Despite more extensive left ventricular dysfunction at initial presentation, patients with an early peak MB CK had a smaller mean MB CK infarct size index (12.6 versus 18.9 g-Eq/m², p < 0.01), with no difference in the incidence of in-hospital complications, including death. The early left ventricular dysfunction improved in the patients with an early peak MB CK, evidenced by a 4.5% increase in ejection fraction from admission to 10 days after infarction, whereas the ejection fraction did not improve in patients with a late peak MB CK. However, the patients with an early peaking MB CK had myocardium in jeopardy as reflected by a higher incidence of ST segment depression and a decrement in the global left ventricular ejection fraction with exercise. The 4 year life table estimate for the rate of recurrent myocardial infarction after hospital discharge was higher in patients with an early peak MB CK (33 versus 22%, p < 0.05), with an even more striking difference in the 4 year estimate for the rate of fatal recurrent infarction (20 versus 8%, p < 0.001). The 4 year mortality estimate was markedly higher in hospital survivors with an early peak MB CK than in those with a late peak (47 versus 19%, p < 0.0001) and, even after adjustment for differences in baseline characteristics, the residual excess mortality in those with an early peak was still significant (p < 0.02). Thus, observation of an early peak MB CK may conveniently identify a high risk subset of patients with myocardial infarction who require intensive investigation and aggressive management. This finding will require confirmation in a prospective study.