This electrocardiogram of a 62-year-old man with lightheadedness and fatigue shows sinus rhythm at a rate of 70 beats/min with slight sinus arrhythmia. There is a high-grade atrioventricular (AV) block with the sinus P waves dissociated from a regular ventricular escape rhythm which has a rate of 38 beats/min ( Figure 1 ). The seventh and the last P waves are conducted to the ventricles with a PR interval of 0.20 seconds, and the QRS complexes have a typical left-bundle-branch-block configuration. The conducted QRSs reset the ventricular escape rhythm, which has a QRS duration of 0.11 seconds and a configuration resembling left anterior fascicular block. Thus, it appears that there is infranodal AV block with persistent block in the left bundle branch, high-grade block in the right bundle branch, and a ventricular escape rhythm arising near the conduction system. There is frequent fusion of sinus P waves with the ventricular escape complexes.
