Unusual QRS morphology after a trans‐venous pacemaker

To the Editor Left bundle branch block (LBBB) configuration can be expected after pacemaker implantation. Right bundle branch block (RBBB) configuration, however, implies malposition of the pacemaker lead in the coronary sinus or left ventricle (LV), which can be complicated by the perforation of the free wall, intracardiac septum, or ventricle. Although an RBBB pattern may happen with right ventricle pacing, we should be vigilant of and confirm the position of the lead if the RBBB pattern occurs after pacemaker implantation. Of all the relevant modalities, echocardiography can confirm the lead position in a timely and convenient manner. An 87-year-old woman had hypotension and bradycardia after removal of her infected ruptured left forearm arteriovenous graft. A 12-lead electrocardiography (ECG) revealed complete atrioventricular block. No correctable etiologies were noted. A transvenous permanent pacemaker was implanted via a femoral venous access under fluoroscopy. However, the ECG after pacemaker pacing disclosed an RBBB pattern as RSR′ in V1-3, Q wave in V4-6 and lead I. The axis of the QRS was −71°, and the precordial transition of the pacing beat was at the V4 lead (Figure 1A). The chest X-ray showed that the tip of the temporary pacemaker was in the apex (Figure 1B). Transthoracic echocardiography revealed the pacemaker lead had penetrated the interatrial septum, passed through the mitral annulus, and inserted into the left ventricular apex in the parasternal long axis view (Figure 1C white arrows) and apical four chamber view (Figure 1D white arrows). The transvenous pacemaker's lead was revised to right ventricle (RV) apex under fluoroscopy, and the lead location was confirmed by echocardiography. The patient's blood pressure rose and was maintained after an adequate heart rate was achieved. (A) After transvenous pacemaker implantation, the pacing beats (*) were RBBB pattern as RSR′ in V1-3. Note the transition of the precordial leads of the pacing beat was at V4 lead. There were two VPC beats (+) which had different RBBB morphology compared with the RSR′ in V1-3 and Rs in lead I; (B) the tip of the temporary pacemaker was at the apex; and (C, D) transthoracic echocardiography demonstrated the path of the temporary pacemaker lead through a foramen ovale, mitral valve, and then onto the endocardium of left ventricle (white arrows). RBBB = right bundle branch block; VPC = ventricular premature contraction. RV pacing yielded LBBB pattern, and LV pacing yielded RBBB pattern. After pacing by a transvenous temporary pacemaker via the femoral vein, the LBBB configuration should be expected. However, when RBBB reappeared, malposition of the pacing lead was suspected. There are several possible causes of the RBBB pattern. One involves the lead possibly penetrating the RV free wall or interventricular septum and causing LV pacing with an RBBB pattern, and another when the lead passes through an atrial septum defect, then across the mitral annulus and directly to the LV and induces RBBB-like pacing beats [1]. A further possible cause of the RBBB configuration is when the lead of the pacemaker is placed at the coronary sinus [2]. In our case, the pacemaker lead perforated the intraatrial septum, crossed the mitral annulus, and inserted into the LV apex. Although an RBBB configuration may result from a mal-positioned pacemaker lead with LV pacing, “pseudo-RBBB” can also be seen if the pacemaker lead is at the correct site, the right ventricle [3]. In “pseudoRBBB”, the RBBB disappears after placing V1, V2 leads at the lower intercostal space [4]. Besides this, precordial transition can also differentiate RV or LV pacing, and if the transition of RBBB is at the V2 or V3 lead, RV pacing is most likely [5]. In conclusion, when RBBB is encountered after pacemaker implantation, we suggest to recheck with electrocardiography by pacing the V1 and V2 leads at the lower intercostal space. If the RBBB disappears and the chest roentgenogram confirms that the pacemaker lead is in the right ventricle, echocardiography is optional. But if the RBBB persists at the lower intercostal space ECG, we suggest echocardiography or nonenhanced chest computerized tomography.