2.2 ECG Analysis
A 12-lead electrocardiogram was recorded at a paper speed of 25 mm/s and an amplification of 10 mm/mV. For each ECG, the following parameters were recorded: heart rate, rhythm, RR interval, PR interval, QRS duration, QT interval, QTc interval, presence of QTc prolongation (QTc interval ≥450 ms for men and ≥460 ms for women)11, premature atrial/ventricular contraction, atrial fibrillation, bradycardia, conduction disorder, and left ventricular hypertrophy. QT interval was defined as the beginning of the QRS to the end of the T wave, and QTc interval was calculated using Bazett’s formula12. Left ventricular hypertrophy was assessed using the Socolow–Lyon criteria13. All electrocardiograms were examined by two cardiologists (T.A. and X.S.) who were blinded to all other clinical data.