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Context: On electrocardiography (ECG), ventricular pacing appears as a spikes that precede induced QRS complexes. The induced complexes with a right ventricular lead have the morphology of a left bundle branch block (LBBB). We describe a case of malposition right ventricular (RV) lead in the coronary sinus diagnosed based on the changes noted in the ECG tracing. An 80-year-old man with a pacemaker implanted for high-grade AV block was found unresponsive. Six minutes of cardiopulmonary resuscitation resulted in return of spontaneous circulation. The ECG demonstrated a new paced right bundle branch block (RBBB) pattern. Chest radiography revealed a misplaced right ventricular (RV) lead in the coronary sinus which was confirmed by 2D-echocardiography. The patient’s healthcare proxy (HCP) declined invasive interventions. The patient expired due multiorgan failure secondary to ventilator associated pneumonia. When an RBBB pattern is seen with RV pacing, patients must be evaluated for mispositioning of the RV lead navigation through an atrial septal defect (ASD) or perforation of the ventricular septum, aberrant retrograde conduction, pre-existing right bundle disease and the “pseudo-RBBB” pattern (seen with the ventricular lead placed in the RV apex/distal septum). A frontal axis of 0˚ to 90˚ and precordial transition by lead V3 differentiates RV septal pacing from all forms of LV pacing, including lead placement in the coronary sinus. Our patient had precordial transition at V3.
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