Prognostic importance of exercise electrocardiography in patients with suspected microvascular disease

BACKGROUND: Coronary microvascular dysfunction (CMD) is associated with a poor prognosis but is difficult to diagnose non-invasively. In a recent paper, ST-segment depression on exercise-ECG was found to have a very high positive predictive value (PPV) for CMD in a highly selected group of patients. OBJECTIVES: In the present study of chest pain patients, we used myocardial perfusion single photon emission CT (MPS) to rule out ischaemia due to epicardial coronary stenosis. In the remaining patients with suspected CMD, we studied the prognostic value of ex-ECG findings. METHODS: A single-centre observational study of 1021 consecutive patients examined with MPS and ex-ECG. Follow-up data were acquired from national registries. Major adverse cardiac events (MACE) were defined as cardiovascular death, myocardial infarction, unstable angina and unplanned revascularisation. A total of 113 patients were excluded due to inconclusive ex-ECG findings or missing data, and 148 due to ischaemia on MPS. RESULTS: In the final study cohort (n=760) with a mean age of 63 years and 55% female, ex-ECG was abnormal in 126 patients (17%). During a mean follow-up of 8.5 years, MACE occurred in 31 (25%) patients with abnormal ex-ECG and 103 (16%) patients with normal ex-ECG. The Kaplan-Meier curves for cumulative events separated significantly (log-rank p=0.01), but when adjusting for age, sex, comorbidities and exercise capacity, abnormal ex-ECG was no longer significantly associated with MACE (HR 1.1, CI 0.7 to 1.7, p=0.6). The prognostic PPV of an abnormal ex-ECG was only 25% (31/126) and this decreased to 17% (11/66) when excluding patients with known coronary artery disease (n=323). CONCLUSIONS: In patients with suspected CMD, ischaemic ST-segment changes are of limited prognostic value, showing poor sensitivity and low PPV for the occurrence of MACE. However, reduced exercise capacity was an independent risk factor and, therefore, ex-ECG testing could be considered if a functional assessment of patients is warranted.