ST-segment/heart rate loop analysis on treadmill exercise testing can provide diagnostic and prognostic information in patients with stable effort angina

J Kamata, K Nakai, K Kawazoe, K Hiramori
Coronary Artery Disease 1995, 6 (7): 547-54

BACKGROUND: In the assessment of myocardial ischemia and its severity using treadmill exercise testing (TMET), the magnitude of ST-segment depression is conventionally used. It is often difficult to distinguish false-positive from true ST-segment depression and to assess the severity of coronary artery disease (CAD). The purpose of the present study was to assess the ability of ST-segment/heart rate loop (ST/HR loop) analysis to provide diagnostic and prognostic information in patients with stable effort angina.

METHODS: ST/HR loop analysis was studied in 118 patients with stable effort angina without previous myocardial infarction who were taking medication. ST/HR loop patterns were classified into four types: type A (n = 38), simple clockwise rotation; type B (n = 34), clockwise rotation with quick ST recovery in the first half; type C (n = 21), ST-segment depression that recovered at a constant rate; and type D (n = 25), simple counter-clockwise rotation. The control group consisted of 40 patients who had no ST-segment depression but were proved to have significant stenosis on coronary angiography. The ST/HR loop types were compared with (1) the conventional TMET parameters, (2) findings of coronary angiography, (3) severity of ischemia evaluated by exercise thallium-201 myocardial single-photon emission computed tomography (exercise TI-201 myocardial SPECT), and (4) short-term prognosis by follow-up study.

RESULTS: The value of the simple heart-rate-adjusted ST-segment depression index (delta ST/HR index) in the type A group (6.1 +/- 5.8 microV/bpm) was higher (P < 0.05) than in the type C and D groups (2.7 +/- 2.0 microV/bpm and 1.7 +/- 1.2 microV/bpm, respectively). In the type A group, 68% of the patients had multiple diseased coronary arteries. In the type D group, 88% of the patients had either no significant coronary artery stenosis or significant stenosis in a single coronary artery. The ischemic size calculated by exercise TI-201 myocardial SPECT was higher (P < 0.05) in the type A group (47.6 +/- 24.6%) than in the type B, C, and D groups (21.4 +/- 16.6%, 14.9 +/- 15.8% and 7.8 +/- 7.4%, respectively). During the follow-up study nine cardiac events occurred in the type A group, three in the type B group, and one in the type C group. The prognosis of the type A patients was significantly worse than that of the type D and control patients (P < 0.01).

CONCLUSION: We conclude that the ST/HR loop analysis is a simple and useful parameter for providing diagnostic and prognostic information for patients with stable effort angina.

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