HEART RATE-INDEPENDENT PROLONGATION OF QTC INTERVAL IN WOMEN WITH SYNDROME-X

Background: Cardiac syndrome X is usually diagnosed in the presence of typical exertional chest pain, a positive response to exercise testin g, and normal coronary angiograms. The underlying pathogenic mechanism s are speculative, but myocardial ischemia and increased sympathetic a ctivity have been implicated. Hypothesis: The present study examined w hether QTc interval is prolonged in women with syndrome X when confoun ding factors such as heart rate, gender, and environmental conditions are accounted for. Methods: Maximum QTc interval and its relationship to clinical and exercise variables were evaluated in 32 women with syn drome X (exertional chest pain, positive exercise testing, and complet ely normal coronary arteries) and 34 normal controls. Results: Patient s with syndrome X had significantly longer QTc interval (440 +/- 24 ms ) than normal subjects (410 +/- ms, p < 0.004). However, this QTc prol ongation appears to be heart rate-independent as patients with syndrom e X showed longer QT and QTc intervals than controls despite an identi cal heart rate. No relation was found between QTc prolongation and cli nical or exercise test variables in patients with syndrome X. Conclusi on: Although increased sympathetic drive is present in syndrome X, and this variable is likely to modulate QTc duration, the mechanism and c linical implications of QTc interval prolongation in syndrome X remain speculative.