Purpose: Exercise stress testing is a cost-effective, noninvasive and safe approach for assessing coronary artery disease (CAD), but it is documented that it has low specificity and predictive value. Consequently, there is a search for other factors that might enhance this test's precision. This work aimed to determine if QT interval prolongation or dispersion in a positive exercise electrocardiographic test (ECG) patient may indicate CAD.
Methods
A cross sectional study included 150 stress ECG positive patients; clinical history and physical examination data were collected from the recruited patients; they also were subjected to coronary angiography. Occlusion rate≥ 70% in the left anterior descending artery, circumflex or right coronary artery or ≥ 50% in the left main coronary artery was considered obstructive CAD. Patients were divided into 3 groups (normal, non-obstructive CAD and obstructive CAD). Gensini score was calculated to quantify angiographic atherosclerosis.
Results
Among the studied patients, 19 (12.7%) patients had normal angiogram, 20.7% had non obstructive CAD and 67.3% of them had obstructive CAD. QT interval significantly increased in obstructive CAD patients at peak exercise and at recovery, QT dispersion (QTd) significantly increased in obstructive CAD at beginning and peak exercise, corrected QT also significantly increased in obstructive CAD. QTd at peak exercise had the best validity to predict obstructive CAD patients with sensitivity 86.1%, specificity 56.7% at a cutoff point 39.
Conclusion
QT dispersion had good sensitivity and total accuracy 79.4% that increase capability of stress ECG to detect obstructive CAD.