Predictive value of QT dispersion in non-ST segment elevation acute coronary syndrome

Abstract

Myocardial ischemia leads to nonhomogeneous repolarization, which is reflected in an increasing QT interval duration. The repolarization is prolonged in the ischaemic zone while in the non-ischemic zone it is not; this can be observed on the dispersion of the QT interval. The objective of this research is to analyse the dispersion of the QT interval (QTd) on patients who suffered from
non-ST elevation acute coronary syndrome in order to assess the association with severe coronary artery disease of one or several vessels and the determination of their predictive value. Methods: Patients who were diagnosed with non-ST elevation acute coronary syndrome were evaluated according to demographic characteristics, coronary risks factors, troponin test, measurement of left ventricular ejection fraction by echocardiogram, coronary arteriography and the manual measuring of QT interval. These data were analysed with the Fisher’s exact test. Results: over a total of 137 patients, 77 had angina during rest in less than 48 hours. Troponin test was positive in 32.1%, 11.6% had decreased left ventricular ejection fraction. Coronary arteriography showed
severe lesions in the left anterior descending artery (LADA) (36.5%), in the circumflex one it was 8.2% and in the right coronary artery it was 24.8%. QTd was higher than 0.04 seconds on 54% of the patients. The Fisher’s exact test shows significant association of the QTd over 0.06 seconds, with patients with chronic stable angina, angioplasty and stenting, decreased left ventricular ejection fraction and significant coronary lesions in the LADA or right coronary artery. The predictive value (PV) was 2% on severe lesions in the LADA with 32% of sensitivity (Sn) and 59% specificity (Sp) and 97% negative predictive value (NPV). In the circumflex artery the PPV was 4%, NPV was 97% with Sn 20% y Sp 84%, in the right coronary artery the PPV was 7% and NPV 98% with Sn of 34% and Sp of 86%.
Conclusions: QTd could be useful on the diagnosis of non-ST elevation acute coronary syndrome, considering that it was associated in a significant way with severe coronary lesions.