Clinical implications of ST segment time-course recovery patterns during the exercise stress test
The exercise stress test (EST) is the commonest non-invasive test to elucidate the nature of chest pain/discomfort. ST segment depression provides evidence of ischemia, but is hampered by a significant number of false negative and false positive tests. This study evaluated patterns and duration of ST depression in an attempt to differentiate false positive and false negative tests. One hundred consecutive patients with suspected angina referred to the Cardiac Clinic, who underwent an EST, and subsequently a coronary angiogram, were studied. The EST was classified as positive if significant ST depression (greater than 1mm 80msec after the J point) developed during exercise or the recovery phase. Based on the angiographic findings as the reference, the EST was classified as true positive (TP), true negative (TN), false positive (FP) or false negative (FN). Onset, magnitude and type of ST depression in relation to disease, the recovery time (RT), total ischemic time (TIT) and time-course patterns in TP versus FP results were compared by Chi square test. The EST was positive in 77 patients (true positive n = 65; false positive n = 12). The angiographic findings were classified as normal (17), non-occlusive atheroma (10) and as significant coronary stenosis in the remainder. Though the mean time to ST recovery (IRT) was shorter (183 + 118sec) in subjects with false positive compared to true positive (264 + 116sec) p<0.05, it was over three minutes and did not really help in differentiating FP from TP tests. TIT was more reliable than the IRT in delineating true positive from false positive tests. Up-sloping ST changes were more commonly associated with false positivity. Time-course patterns could not reliably distinguish TP from FP tests (TIT = 8/12, RT = 7/12), but TIT was more reliable in verifying TP (64/65) tests than IRT (59/65).
KEY WORDS: Exercise stress test; ST segment time course patterns