Symptoms of Patients With Silent Ischemia as Detected by Thallium Stress Testing: Conclusion
In contrast to these findings, in a study similar to ours, dyspnea was reported to be more frequent in those individuals with a positive thallium stress test who did not have chest pains. However, in that study, dyspnea was reported in the context of it being a test-limiting symptom and, therefore, the absence of chest pains might have produced a bias for other test endpoints, such as dyspnea. In our study, subjects were able to report and quantify any symptoms irrespective of the examiner’s reason for stopping the test, thereby providing a more reliable assessment of symptoms. canadian family pharmacy online
The lack of specificity of dyspnea as a symptom is well recognized. Dyspnea has been found to relate poorly to objective markers of cardiopulmonary disability. Nevertheless, cardiac dysfunction, particularly as evidenced by left ventricular diastolic indices, precedes other indications of myocardial ischemia. Our study suggests that, in general, within the time required for such changes to become evident as dyspnea, perhaps by producing stiffening of the lung, other determinants for stopping the test have already become manifest. Although dyspnea may lack specificity on stress testing, or even as an “anginal equivalent,” its importance as a presenting symptom for other myocardial ischemic syndromes, such as in pulmonary edema or myocardial infarction, is clear.
Individuals with silent ischemia on stress testing are derived from a heterogeneous population. Clearly, some have false-positive tests. At least as suggested from the sample of this study who had coronary angiography, the prevalence and extent of coronary disease of those with silent ischemia were similar to those with angina pectoris on the test. Also, the clinical features of the silent ischemia group, such as a history of myocardial infarction or a Q-wave infarction pattern on ECG, were not different from those with angina pectoris. In a larger series, however, differences in these findings might have emerged that would suggest greater severity of coronary disease in those with angina pectoris on stress testing. Alternatively, patients with silent ischemia may have a higher threshold for discomfort. This would seem to be the best general explanation for the differences. Not only was the group with silent ischemia less symptomatic on the test, but a history of chest pain with exertion was the only clinical feature that emerged as an independent predictor of angina pectoris on stress testing.
Because angina pectoris, or its equivalent, serves as a warning of myocardial ischemia with its attendant complications, the absence of such symptoms might augur serious consequences. Previous studies investigating the prognostic implications of silent ischemia have not, however, demonstrated that the presence of myocardial ischemia without angina pectoris predicts a worse clinical outcome. The present study seems to be consistent with that finding. Patients with silent ischemia on thallium stress testing had a comparable peak exercise double product—a good estimate of myocardial ischemic stress, average ST segment depression, and occurrence of arrhythmia as those with angina.