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Twelve-lead electrocardiograms. (Left) Typical atrial flutter and 2:1 atrioventricular conduction with left bundle branch block (QRS duration 160 msec) was observed on admission. (Middle) Sinus rhythm was maintained after ablation for atrial flutter (QRS duration 160 msec). (Right) Electrocardiogram of biventricular pacing shows the narrowing of QRS duration (100 msec).
