Treatment strategies for daily life silent myocardial ischemia: a correlation with potential pathogenic mechanisms

Recent investigations of SMI occurring during daily life have advanced our understanding of the pathophysiology of myocardial ischemia. These contributions have directed our attention away from "chest pain" alone and physical exertion as the central provoking factor toward transient myocardial ischemia and its broader triggers and consequences. Transient myocardial ischemic episodes, the majority of which are silent, are found in a subset of patients with any clinical manifestations of CAD (eg, stable angina, unstable angina, myocardial infarction, and sudden death), as well as in those patients with CAD who are and have been totally asymptomatic. These episodes are an independent predictor of increased risk for future cardiac events. Most medical therapy and revascularization therapies have the potential to prevent or relieve these silent episodes; however, we do not yet know which method is superior in reducing SMI episodes or preventing future cardiac events. Furthermore, the benefit of reducing SMI versus the cost and potential morbidity of these chosen therapies is not known. At least three trials are now underway to examine some of these concerns (Table 2). Focus on pain relief alone does not appear to be an adequate approach to alter outcome in patients with CAD and may prove insufficient to control SMI. Until these issues are resolved, we believe a conservative approach to the management of patients with CAD is warranted. Documentation of ischemia (painful or painless) is essential. Three general principles should be kept in mind. First, the presence of detectable ischemia is of central importance. This information should be used in the overall risk assessment of the patient. Second, the level of concern or aggressiveness of treatment should be based on the risk associated with the ischemic abnormalities documented (Table 3). The exercise stress test is the most useful to begin this process. The detection of ischemic-type ST-segment depression, either silent or painful, at a low workload (eg, less than or equal to 120 beats per minute or less than or equal to 6.5 metabolic equivalents [METS]) implies high risk for adverse outcome. Likewise, these ST-segment changes occurring in leads that reflect multiple coronary artery distribution, of greater than 2 mm in magnitude and persisting for greater than 6 minutes, are all markers for high risk. Thallium redistribution defects occurring at low work loads, in multiple areas, associated with increased lung uptake and enlargement of the cardiac pool all imply high risk.(ABSTRACT TRUNCATED AT 400 WORDS)