PREVALENCE AND FUNCTIONAL-SIGNIFICANCE OF TRANSIENT ST-SEGMENT DEPRESSION DURING DAILY LIFE ACTIVITY - COMPARISONS OF AMBULATORY ECG WITH STRESS REDISTRIBUTION TL-201 SINGLE-PHOTON EMISSION COMPUTED TOMOGRAPHIC IMAGING

To assess the prevalence and functional significance of ischemic ambul atory ECG responses, we prospectively performed ambulatory ECG monitor ing in 244 patients (mean age 61 +/- 10 years) referred for stress red istribution thallium 201 myocardial perfusion scintigraphy. The preval ence of ST-segment depression during ambulatory ECG was 33% among pati ents with a positive exercise ECG, but prevalence varied in selected p atient subgroups. Among three groups with coronary artery disease (CAD ), the group with ambulatory ECG ischemia (group 1) had a greater freq uency of ischemic thallium responses (p = 0.07), a greater median numb er of reversible thallium defects (p < 0.05), and a greater summed tha llium ''reversibility'' score (p < 0.05) than did the group with a pos itive exercise ECG but negative ambulatory ECG response (group 2) or t hat with negative exercise and ambulatory ECG responses (group 3). Exe rcise ST depression in group 1 versus group 2 was significantly greate r (p = 0.002), occurred at a lower heart rate threshold (p = 0.002), a nd lasted longer after exercise (p = 0.001). Notably, one third of gro up 1 patients also manifested evidence of transient ischemic dilation of the left ventricle after exercise (p < 0.01 vs groups 2 and 3), a s ign of severe ischemia. However, although functionally less ''sick'' t han group 1 patients, 66% of group 2 patients and 50% of group 3 patie nts still had an ischemic thallium response, which was sometimes sever e. Thus transient ischemia during ambulatory ECG monitoring identifies a functionally sicker cohort of patients with CAD and occurs in appro ximately one third of CAD patients with positive results of exercise t ests. A negative ambulatory ECG response, however, does not exclude fu nctionally significant disease among CAD patients. These results imply that caution should be applied in the interpretation of a negative am bulatory ECG response for the purpose of patient risk stratification.