Spontaneous changes in left ventricular function over the first 24 hours of acute myocardial infarction: implications for evaluating early therapeutic interventions.

The spontaneous changes in left ventricular ejection fraction (LVEF) during the first 24 hours of a first transmural infarction were assessed in 34 patients by serial gated cardiac blood pool imaging. Major therapeutic interventions with a view to limit infarct size were not used. Four determinations of LVEF were performed. Study 1 was performed as soon as possible after admission to the hospital. Studies 2 and 3 were performed 2 and 4 hours, respectively, after study 1. Twenty-four patients (70%) had study 1 within 6 hours after the onset of acute chest pain and 10 had it 6-12 hours after the onset of chest pain. Study 4 was performed 24 hours after the onset of chest pain. Compared with study 1, 19 of 34 patients (56%) had spontaneous changes in LVEF in at least one of the subsequent studies, exceeding the expected variability in stable patients. The changes ranged from a 32% increase to 14% absolute decrease. LVEF improved in 11 patients and deteriorated in eight. These spontaneous changes in left ventricular performance indicate that a single assessment of LVEF during the early hours of transmural myocardial infarction may not properly characterize cardiac performance in an individual patient and may not be the most appropriate reference against which to compare subsequent evolution of left ventricular function. These data may have implications for studies of the effects of early therapeutic interventions on LVEF.