Pathological Q waves as an indicator of prior myocardial infarction in patients with coronary artery disease and diabetes mellitus: a comparison of the prevalence and diagnostic accuracy according to present and former criteria

Introduction. Electrocardiography (ECG) is a widely used diagnostic method for identification of patients with previous myocardial infarction (MI). The ECG manifestation of prior MI is the presence of the pathological Q waves. Patients with coronary artery disease (CAD) and diabetes are at high risk of MI. The aim of this study was to compare the prevalence and diagnostic accuracy of the pathological Q waves as an indicator of prior MI in patients with CAD and diabetes according to the present and former criteria. Methods. A cross-sectional, multi-centre study was conducted in outpatient clinics across Poland. Family physicians performed physical examinations, registered ECGs, and collected relevant information about onset of CAD and diabetes, presence and onset of hypertension, dyslipidaemia, heart failure, diabetic complications, history of MI, and pharmacotherapy. Centralised manual assessment of the obtained ECG tracings was performed. Two definitions of the pathological Q-waves were used — a present one according to the Universal Definition of MI and a former one based on the definition of MI developed by the World Health Organization. Results. We enrolled 796 patients (48.1% women, mean age 67.5 ± 10.2 years, and 51.9% men, mean age 64.3 ± 10.3 years) into the study. There were 158 patients (19.8%) — 102 men (24.7%) and 56 women (14.6%), who met the present definition of the pathological Q waves and 106 patients (13.3%) — 74 men (17.9%) and 32 women (8.4%), who met the former definition of the pathological Q waves. The prevalence of the pathological Q waves varied due to the certain group of leads. It was highest in the inferior leads — 104 and 75 according to the present and former definitions, respectively. Of note, the rate of the pathological Q waves increased up to 2.6 times in the lateral leads after the introduction of the less restrictive present definition. Sensitivity of prior MI detection by means of the present and former criteria was 26.8% and 19.8%, and specificity was 87.0% and 92.8%, respectively. The application of the present and former definitions detected prior MI with 65.6% and 71.6% positive predictive value, and with 56.3% and 55.6% negative predictive value, respectively. Conclusions. In the era of reperfusion therapy, ECG appears to be a poor diagnostic tool for detection of previous MI due to its low sensitivity. However, it may identify individuals without previous MI with rather high specificity. In diabetics with CAD, the present definition of the pathological Q waves increases sensitivity of prior MI detection by 7%, with a decrease in specificity by 6% as compared with the former definition.