Letter to the Editor Electrocardiographic algorithms to predict true right ventricular pacing in the presence of right bundle branch block-like pattern Mohammed Almehairi a , Fariha Sadiq Ali a , Andres Enriquez a , Kevin Michael a , Damian Redfearn a , Hoshiar Abdollah a , Christopher Simpson a , Pablo A. Chiale b , Adrian Baranchuk a, ⁎ a Division of Cardiology, Kingston General Hospital, Queen's University, Kingston, Ontario, Canada b División Cardiología, Hospital General de Agudos J.M. Ramos Mejía, Buenos Aires, Argentina a r t i c l e i n f o Article history: Received 27 December 2013 Accepted 30 December 2013 Available online 10 January 2014 Keywords: RBBB LBBB Pacing ECG Right bundle branch block (RBBB) like pattern observed during right ventricular pacing (RVP) has traditionally been considered an electrocardiographic (ECG) marker of inadvertent left ventricu- lar pacing (LVP) [1–3].However, in the vast majority of the cases, the lead is indeed in the right ventricle. The aim of our study was to validate the frontal axis plane and transitional point over the precordial leads algorithm to determine the location of the pacing lead in the heart. Forty eight patients with a paced rhythm demonstrating RBBB-like pattern in lead V1 and/or V2 were enrolled in this study. RBBB-like pattern was defined as a dominant R-wave or any of the following patterns: R, Rs, RS, rsR' or qR in leads V1 and/or V2. Another ten patients with left ventricular (LV) leads were en- rolled as a control group.Eight of these patients had epicardial LV lead as part of cardiac resynchronization therapy (CRT) devices and 2 had endocardial LV lead placement. The study protocol was approved by the ethics committee of the Kingston General Hospital/Queens's University and written in- formed consent was obtained from all patients. Transthoracic echocardiogram was used to demonstrate the body of the lead crossing the tricuspid valve (TV) and rule out inad- vertent coronary sinus or middle cardiac vein placement. Chest X- ray in postero-anterior (PA) and left lateral (LL) projections was examined to localize the lead placement in the RV. A 12-lead ECG (filter 150 Hz, 25 mm/s, 10 mm/mV) was obtained with standard position of leads V1 and V2 at the fourth (4th) intercostal space for both the studied group and the control group. In patients with CRT devices, 12 lead ECGs were obtained during LVP only. Paced QRS axis in both groups was determined from the frontal plane. Point of tran sition in the precordial leads was defined as R equal to S-wave in both groups. Data were entered into an Excel spreadsheet and imported into SPSS (PASW Statistics, version 18.0, IBM Incorporated, Somers, New York) for statisticalanalysis.Calculation ofthe sensitivity and specificity was performed for the specified ECG algorithms. Frontal axis plane was estimated between 0 and −90° in 43 patients (89%) ( Fig. 1A) and between −90 and −180° in 5 patients (11%) (Fig. 1B). In the studied group, the point of transition was noticed at lead V4 in 2 patients (4%), at V3 in 27 patients (56%), at V2 in 11 patien (23%) and at V1 in 8 patients (16%). In the control group the frontal axi degree was estimated between −90 and −180° in 2 patients, between 0 and −90° in 3 patients and between +90 and +180° in the remaining 5 patients (Table 1). Table 2 summarizes the sensitivity and specificity of the electrocar- diographic parameters to predict the lead position in the presence of the RBBB like pattern. All patients in the studied group (n = 48) had evidence of the lead crossing the TV. In the same group, all had true apical placement excep one patient that had mid septal placement.In the control group,4 patients with epicardial LV leads had antero-lateral placement, 2 had lat eral placement and 2 had postero-lateral placement. One patient with surgically corrected transposition of the great arteries had the lead plac in the mid apical region of the non-systemic (LV) chamber. One patient had inadvertent placement in the left apical region through an atrial sep tal defect and was confirmed by trans-esophageal echocardiogram. The presence of RBBB-like pattern during RVP dictates prompt action to rule out inadvertent placement of the lead in the LV, which could resu in adverse outcomes. Therefore, many studies in the past sought to con reliable ECG parameters to obviate the need for extensive radiographic work up to identify true RVP. RBBB-like pattern during RVP has a reporte prevalence of 8– 10% [4–6]. In this study, the validation of the previously International Journal of Cardiology 172 (2014) e403–e405 ⁎ Corresponding author at: Division of Cardiology, Heart Rhythm Service, Kingston General Hospital, Queen's University, Canada. Tel.: +1 613 549 66663377; fax: +1 613 548 1387. E-mail address: barancha@kgh.kari.net (A. Baranchuk). 0167-5273/$ – see front matter © 2014 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijcard.2013.12.258 Contents lists available at ScienceDirect International Journal of Cardiology j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / i j c a r d