Relationship between exercise-induced ST segmental depression and myocardial ischemia assessed by technetium-99m tetrofosmin SPECT imaging in patients with inferior Q wave myocardial infarction.

BACKGROUND

ST segment depression (STD) is a standard electrocardiographic sign of myocardial ischemia. Although STD may represent reciprocal changes in patients with previous myocardial infarction, studies of reciprocal changes during exercise testing are scarce.

METHODS

From December 1999 to December 2000, 160 patients (119 males, 41 females, mean age 54 +/- 8 years), undergoing, maximal or symptom-limited exercise treadmill test (Bruce-protocol), myocardial perfusion scintigraphy using technetium-99m tetrofosmin single photon emission computed tomography (SPECT) imaging, within 30 days of an uncomplicated inferior Q wave myocardial infarction. The location of STD at the electrocardiogram (ECG) was defined as anterior (V1-4), high lateral (I, aVL), and lateral (V5-6). Ischemia was defined as reversible perfusion abnormalities.

RESULTS

STD occurred in anterior leads in 29 patients (18.1%), in the lateral leads in 41 patients (25.6%), in the high lateral leads in 20 patients (12.5%). In 70 patients (43.8%) no significant STD occurred during the exercise test. ST segment elevation occurred in 28 patients (17.5%) in inferior leads. High lateral STD was associated with inferior ST elevation in 16 patients (80%), whereas only eight patients (19.5%) with lateral STD and nine patients (31%) with anterior STD were associated with inferior ST elevation. Ischemia was detected in 63 of 90 patients (70%) with and in 10 of 70 patients (14.3%) without STD (p < 0.0001). Patients with high lateral STD had a higher prevalence of fixed perfusion defects in the inferior wall (95 vs. 27.8%) and in posterolateral wall (75 vs. 18.9%) compared with other patients (p = 0.003 and 0.002, respectively). Ischemia was more prevalent in patients with lateral STD than without (87.8 vs. 14.3%, p < 0.0001).

CONCLUSION

In patients with inferior Q wave, the presence of exercise-induced STD in lateral and anterior leads appears to be a sign of myocardial ischemia, and may require invasive evaluation; on the other hand, the presence of STD in high lateral leads should be recognized as a reciprocal change for ST elevation in the inferior leads, and may not be an indication for invasive evaluation.