Objectives The present study tried to investigate the diagnostic value of ambulatory ECG in screening CAD referred for CAG when several parameters were combined.

Methods One hundred and four inpatients with chest pain were enrolled. The CAG and ambulatory ECG were performed. All the patients were divided into the two groups according to CAG findings: the CAD group (at least a ≥ 50% diameter reduction of a major coronary artery or branch) and control group (a lumen diameter reduction < 50%). The diagnostic value of ambulatory ECG in screening CAD was evaluated.

Results The study population consisted of 57 CAD patients and 47 controls according to coronary angiogram. The patients in CAD group showed a significantly higher prevalence of diabetes mellitus, hypercholesterinemia, smoking, and body mass index than those in control group (P < 0.05). The sensitivity of ST-segment deviation in screening CAD was 64.9%; the specificity was 89.4%; and the Kappa value was 0.528. The sensitivity of at least three combined parameters including ST-segment deviation, apnea hypopnea index (AHI), QT interval dispersion (QTd) and heart rate variability (HRV) in screening CAD was 89.5%; the specificity was 87.2%; and the Kappa value was 0.767.

Conclusions Our study contradicts earlier data by Nair et al.⁷ reporting that the diagnostic accuracy of ambulatory ECG detected ST-segment deviation in predicting the presence of CAD was poor (33%), with a sensitivity of 19% and a specificity of 91%. In our study, we found a higher diagnostic value of ambulatory ECG, maybe because several parameters derived from ambulatory ECG were combined and analysed, which reflected different pathophysiological mechanisms of CAD.

Sleep apnea syndrome is an independent risk factor for the cardiovascular diseases including myocardial infarction, heart failure, hypertension, and others^12-14. In our study, AHI can be derived from ambulatory ECG. The higher the AHI, the more severe is the sleep apnea.

HRV has the potential to provide additional valuable insight into physiological and pathological conditions and to enhance risk stratification^9;10. Many studies suggested that HRV be a strong and independent predictor of CAD and mortality after an acute myocardial infarction^8;15. The study showed that HRV was decreased when myocardial ischaemia occurred⁹.

In addition, some studies found that QTd was prolonged in CAD patients^18;19 and an increased QTd could be used to predict the future cardiac event¹⁵.

So in the present study, the diagnostic value of ambulatory ECG was significantly improved when several parameters were combined, especially when three parameters were combined in parallel. The Kappa value reached 76.7%, with a sensitivity of 89.5% and a specificity of 87.2%, which reflected a good consistency of ambulatory ECG monitoring with coronary angiography.

Several weaknesses of the present study should be discussed. Firstly, the study was cross-sectional and in need of further follow-up. Secondly, combination in parallel was adopted when several parameters were analysed in the statistical analysis, which inevitably led to a higher specificity. Thirdly, the present study enrolled a relatively small number of patients, it needed further, prospective study in a larger population. In addition, a number of other confounders not controlled for in the present study could influence the results of ambulatory ECG, and these were not controlled for.