Incidence rate ratio for cumulative AF burden among 419 AF patients. The figure shows the incidence rate ratio for cumulative AF burden according to dichotomized ECG parameters among 419 patients who developed AF. The interatrial block was defined as P-wave duration ≥120 ms combined with biphasic (positive–negative) P-wave in any inferior lead. QTc interval was estimated using the Framingham formula. Incidence rate ratios were determined in multivariate negative binomial regression models. Abbreviations: AF, atrial fibrillation; CI, confidence interval; ECG, electrocardiogram; QTc, heart rate-corrected QT interval.