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. 2003 Oct 1;3(4):202–209.

Figure 5.

Figure 5

This patient presents with atrial fibrillation conducting along a left lateral accessory pathway (third set), although preexcitation is concealed on the sinus surface EKG due to rapid atrioventricular conduction and short PR (first two sets). Atrial pacing during the ablation session unmasks preexcitation (fourth set). This emphasizes the usefulness of atrial pacing in short PR accompanied by palpitations.