12-lead electrocardiogram in a patient with Wolff-Parkinson-White syndrome in sinus rhythm before and after catheter ablation

12-lead ECG tracing of a 16-year-old male with WPW syndrome before (panel A) and after (panel B) successful catheter ablation of the accessory pathway. Panel A illustrates the characteristic features of the WPW pattern, which include a short PR interval (<0.12 seconds), a delta wave (closed arrow), and widened QRS (open arrow). Though the pattern is present throughout the ECG, the arrows show the most evident leads. This pattern results from ventricular preexcitation via an accessory pathway. Panel B shows the ECG tracing from the same patient following successful ablation of the accessory pathway. The pathognomonic findings of WPW are absent (the PR interval has normalized, the delta wave is no longer present [closed arrow], and the QRS is now narrow [open arrow]).

Normal sinus rhythm at a rate of 71 beats/minute, a P wave axis of 45°, and a PR interval of 0.15 seconds.