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

BACKGROUNDIn 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. METHODSST/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 typestype 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. RESULTSThe value of the simple heart-rate-adjusted ST-segment depression index (ΔST/HR index) in the type A group (6.1 ± 5.8μV/bpm) was higher (P < 0.05) than in the type C and D groups (2.7 ± 2.0μV/bpm and 1.7 ± 1.2μV/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). CONCLUSIONWe conclude that the ST/HR loop analysis is a simple and useful parameter for providing diagnostic and prognostic information fo