IS SILENT-MYOCARDIAL-ISCHEMIA REALLY AS SEVERE AS SYMPTOMATIC ISCHEMIA - THE ANALYTICAL EFFECT OF PATIENT SELECTION BIASES

Background The clinical significance of exercise-induced chest pain re mains controversial, as reflected by sharply discordant clinical resul ts within the medical literature. Thus, we developed a prospective stu dy to compare the functional significance of silent versus symptomatic ischemia and to evaluate whether patient selection biases influence t his analysis. Methods and Results We evaluated 117 patients (mean age, 63+/-9 years) with ischemic ST-segment depression during treadmill te sting. Each patient underwent Tl-201 myocardial perfusion single-photo n emission computed tomography (SPECT) after exercise followed by 24-a mbulatory ECG monitoring. Patients were divided into silent versus sym ptomatic cohorts and were compared for the degree of hemodynamic, exer cise and ambulatory ECG, and thallium abnormalities during stress test ing. Analyses were repeated as the patient population became increasin gly restricted. Compared with the silent patients, patients with chest pain during exercise had a shorter exercise duration (P<.009), lower peak heart rate (P=.009) and double product (P=.005), lower heart rate threshold for ST depression (P<.05), more episodes of ambulatory ST-s egment depression (P<.05), a higher frequency of ischemia abnormalitie s during Tl-201 SPECT (P=.02), and higher summed Tl reversibility scor es (P=.002). As the population became increasingly restricted, the rel ative magnitude of differences in silent versus symptomatic cohorts di minished, whereas the absolute magnitude of ischemic abnormalities pro gressively increased in both cohorts. For example, within the restrict ed group having ischemia on both exercise and ambulatory ECG, 50% of t he silent cohort had severe ischemia on Tl SPECT (five or more reversi ble defects) and more than one third demonstrated the ominous finding of transient left ventricular dilation after exercise. Conclusions The induction of chest pain is associated with substantially more functio nal abnormalities when it is analyzed in a relatively ''broad-spectrum '' coronary artery disease population; by contrast, chest pain tends t o lose its apparent value as a clinical test parameter when its analys is is restricted to coronary artery disease populations with a greater a priori likelihood of manifesting inducible ischemia. These findings may help resolve some of the previous discordant literature reports.