Relation between left ventricular function at rest and with exercise and silent myocardial ischemia

The prognostic value of radionuclide measures of left ventricular function at rest and exercise is well established. Some studies have suggested that the frequency and duration of silent ischemia during ambulatory monitoring provide similar prognostic information; however, studies comparing these two techniques have not been performed. This study examines the relation between left ventricular function at rest and exercise-induced ischemia assessed by radionuclide ventriculography with myocardial ischemia during ambulatory electrocardiographic (ECG) monitoring. Of the 155 patients with coronary artery disease studied, 88% had left ventricular dysfunction with exercise, defined as failure of the ejection fraction to increase by >4% with exercise, and 33% of patients had left ventricular dysfunction at rest (ejection fraction <45%); 52% had transient episodes of ST segment depression during 48-h ambulatory ECG monitoring. Exercise-induced left ventricular dysfunction during radionuclide ventriculography was extremely sensitive (94%) in detecting patients with ischemic episodes during ambulatory ECG monitoring; however, only 55% of patients with exercise-induced left ventricular dysfunction had ST segment depression during ambulatory monitoring. Moreover, patients with left ventricular dysfunction at rest had a lower prevalence of transient episodes of ST segment depression (31%) than did patients with normal left ventricular function at rest (62%) (p = 0.008). The relation between prognostically important variables during exercise radionuclide ventriculography and the number and duration of transient episodes of ST depression was examined. By multivariate regression analysis only the change in left ventricular ejection fraction with exercise was independently related to the number and duration of episodes of ST depression, but these correlations were weak (r² = 0.04, p < 0.01 and r² = 0.03, p = 0.05, respectively). Thus, myocardial ischemia during daily life detected by ST segment monitoring correlates poorly with radionuclide ventriculographic measures of ischemia. This is particularly evident in patients with left ventricular dysfunction at rest in whom episodes of transient ST segment depression are infrequent. Ambulatory ST segment monitoring must be used with caution in risk stratification of patients with coronary artery disease, especially in patients with left ventricular dysfunction after myocardial infarction.