Early detection of myocardial ischemia in resting ECG: Analysis by HHT

Background: Exercise electrocardiography (ECG) is a noninvasive test aiming at producing ischemic changes. However, resting ECG cannot be adopted in diagnosing myocardial ischemia till ST-segment depressions. Therefore, this study aimed to detect myocardial energy defects in resting ECG using the Hilbert–Huang transformation (HHT) in patients with angina pectoris. Methods: Electrocardiographic recordings of positive exercise ECG by performing coronary imaging test (n=26) and negative exercise ECG (n=47) were collected. Based on the coronary stenosis severity, patients were divided into three categories: normal, <50%, and ≥50%. During the resting phase of the exercise ECG, all 10-s ECG signals are decomposed by HHT. The RT intensity index, composed of the power spectral density of the P, QRS, and T components, is used to estimate the myocardial energy defect. Results: After analyzing the resting ECG using HHT, the RT intensity index was significantly higher in patients with positive exercise ECG (27.96%) than in those with negative exercise ECG (22.30%) (p<0.001). In patients with positive exercise ECG, the RT intensity index was gradually increasing with the severity of coronary stenosis: 25.25% (normal, n=4), 27.14% (stenosis <50%, n=14), and 30.75% (stenosis ≥50%, n=8). The RT intensity index of different coronary stenoses was significantly higher in patients with negative exercise ECG, except for the normal coronary imaging test. Conclusions: Patients with coronary stenosis had a higher RT index at the resting stage of exercise ECG. Resting ECG analyzed using HHT could be a method for the early detection of myocardial ischemia.