Clinical Research Right Bundle Branch BlockeLike Pattern During Ventricular Pacing: A Surface Electrocardiographic Mapping Technique to Locate the Ventricular Lead Mohammed Almehairi, MD, CCDS, CEPS, a Andres Enriquez, MD, a Damian Redfearn, MD, MRCPI, a Kevin Michael, MD, PhD, a Hoshiar Abdollah, MD, FRCPC, a Ahmed Alfagih, MD, b Robert Nolan, MD, FRCPC, c Adrian Baranchuk, MD, FRCPC, a and Christopher S. Simpson, MD, FRCPC, FACC, FHRS a a Division of Cardiology, Kingston General Hospital, Queen’s University, Kingston, Ontario, Canada b Division of Cardiac Electrophysiology, Prince Sultan Cardiac Center, Military Hospital, Riyadh, Saudi Arabia c Department of Radiology, Kingston General Hospital, Queen’s University, Kingston, Ontario, Canada ABSTRACT Background: In patients with paced rhythm, a right bundle branch block (RBBB)-like pattern may suggest inadvertent left ventricular (LV) lead placement. However, in most cases, the lead is indeed in the right ventricle as intended. Methods: We performed a retrospective analysis of postimplantation electrocardiograms (ECGs) for the period 2000-2013 to determine the prevalence of a RBBB-like pattern. A 12-lead ECG was recorded in the standard position and with displacement of leads V 1 -V 2 to the fifth and sixth intercostal spaces (ICSs), assessing the ability of this manoeuvre to unmask a concealed LBBB-like pattern. Patients with true LV pacing, both endocardial and epicardial, were used as controls (n ¼ 10). Results: A total of 943 patients were analyzed. The prevalence of RBBB-like pattern was 8.1% (n ¼ 77), and 26 patients were included in the study. Displacement of leads V 1 -V 2 to the fifth ICS resulted in transition to a LBBB-like pattern with a QS wave in V 1 in 14 of 26 patients (sensitivity, 53%; specificity, 100%), whereas displacement to the sixth ICS resulted in a QS pattern in all patients (sensitivity and R  ESUM  E Introduction : Chez les patients ayant un rythme  electro-entraîn e, un profil simulant un bloc de branche droit (BBD) peut sugg erer le posi- tionnement par inadvertance de la sonde dans le ventricule gauche (VG). Cependant, dans la plupart des cas, la sonde se trouve en fait dans le ventricule droit comme pr evu. M ethodes : Nous avons r ealis e une analyse r etrospective d’ electrocardiogrammes (ECG) après l’implantation pour la p eriode de 2000 à 2013 afin de d eterminer la pr evalence d’un profil simulant un BBD. Un ECG à 12 d erivations a  et e enregistr e dans la position habituelle et avec le d eplacement des sondes V 1 -V 2 vers les cinquième et sixième espaces intercostaux (EIC) pour  evaluer la capacit e de cette manœuvre à d ecouvrir un profil simulant un BBD. Les patients ayant une r eelle stimulation du VG, endocardique et  epicardique, ont servi de t emoins (n ¼ 10). R esultats : Un total de 943 patients ont  et e analys es. La pr evalence du profil simulant un BBD  etait de 8,1 % (n ¼ 77). Parmi eux, 26 patients ont particip eàl’ etude. Le d eplacement des  electrodes V 1 -V 2 Since the early days of pacemaker implantation, a paced right bundle branch block (RBBB)-like pattern on the 12-lead electrocardiogram (ECG) has been considered a red flag sug- gesting inadvertent lead placement in the left ventricle, 1 which may result in adverse clinical outcomes, mainly systemic thromboembolism. 2 However, a RBBB configuration may be observed in up to 8% of patients with true right ventricular (RV) pacing and is far more common than accidental LV lead placement, which is rare (< 2%). 3-6 Small studies have shown favourable clinical outcomes with endocardial LV pacing in the context of cardiac resynchronization therapy (CRT), but pa- tients should undergo proper anticoagulation. 7 A manoeuvre has been previously described to differentiate true RV pacing from inadvertent LV lead placement. 3,4,6 This consists of dis- placing down precordial leads V 1 -V 2 from the standard posi- tion in the chest (fourth intercostal space [ICS]) to the fifth ICS and is expected to unveil the expected LBBB-like pattern; Canadian Journal of Cardiology - (2015) 1e6 Received for publication September 19, 2014. Accepted March 12, 2015. Corresponding author: Dr Christopher S. Simpson, Division of Cardi- ology, Heart Rhythm Service, Kingston General Hospital, Queen’s Univer- sity, Kingston, Ontario K7L 2V7, Canada. Tel.: þ1-613-549-6666 3377; fax: þ1-613-548-1387. E-mail: simpsonc@kgh.kari.net See page 6 for disclosure information. http://dx.doi.org/10.1016/j.cjca.2015.03.017 0828-282X/Ó 2015 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.