Natural history of left ventricular function during 1 year after acute myocardial infarction: Comparison with clinical, electrocardiographic and biochemical determinations

To assess the value of determining left ventricular function during exercise to predict the natural history of left ventricular function and survival after acute myocardial infarction, 45 patients were studied 1 day before and again 6 to 14 months after hospital discharge. Initial study included: (1) 24 hour ambulatory electrocardiographic monitoring and (2) technetium-99m radionuclide cineangiography, electrocardiography and plasma norepinephrine assay, each at rest and during submaximal exercise. Radionuclide cineangiography, electrocardiography and norepinephrine assays were repeated at rest and at submaximal and maximal exercise at the later study. Ejection fraction at rest was subnormal at the early study (average 39 ± 5 percent [mean ± standard error of the mean], normal average 57 ±1 percent, p < 0.001) and showed little change during submaximal exercise (average 37 ± 5 percent, normal average 69 ± 7 percent, p < 0.001). Ejection fraction correlated significantly with the complexity of ventricular arrhythmias during 24 hour electrocardiography, but neither exercise electrocardiographic S-T segments nor plasma norepinephrine content correlated with ejection fraction or with frequency or complexity of arrhythmias. Four of the 45 patients died within 1 year of infarction; each had an ejection fraction less than 35 percent at rest at the early study, but neither the presence of complex arrhythmias nor the determination of ejection fraction during exercise provided additional help in predicting these deaths. Ejection fraction in the later study (average 42 ± 4 percent at rest and 40 ± 4 percent during submaximal exercise) was not significantly different from that in the early study. However, the subgroup of 17 patients with an exercise ejection fraction greater than 40 percent in the early study showed a small but significant increase in ejection fraction at the later study, indicating that the capacity for improvement in myocardial function does exist during the year after acute infarction.