1 The Right Ventricular Septum Presents the Optimum Site for Maximal Electrical Separation During Left Ventricular Pacing RODRIGO I. MIRANDA, M.D., MICHAEL NAULT, M.D., CHRISTOPHER S. SIMPSON, M.D., F.R.C.P.C., KEVIN A. MICHAEL, M.B., Ch.B., HOSHIAR ABDOLLAH, M.B., Ch.B., ADRIAN BARANCHUK, M.D., F.A.C.C., DAMIAN P. REDFEARN, M.D., M.R.C.P.I. From the Division of Cardiology (Arrhythmia Service), Kingston General Hospital, Queen’s University, Kingston, Ontario, Canada Septum Presents the Optimum Site for Maximal Electrical Separation. Cardiac resynchro- nization therapy (CRT) benefits selected heart failure (HF) patients. The optimal placement of the right ventricle (RV) lead during biventricular pacing has not been assessed. Greater electrical separation (ES) between left ventricle (LV) and RV leads has been associated with better clinical outcomes. The site of maximal electrical separation(MES) in the RV is unknown. Methods: Prospective study of 50 CRT patients. The LV lead was placed in a postero-lateral branch of the coronary sinus. ES was recorded at 6 sites within the RV during LV pacing at 600 milliseconds cycle length (CL). The median ES was recorded with a roving deflectable catheter at the RV outflow tract (RVOT), high septum, inflow septum, mid-septum, apical septum and apex. Results: Mean age was 67 ± 7 years, 39 were male (78%). Thirty had ischemic etiology (60%). Mean left ventricular ejection fraction (LVEF) was 25 ± 7%, QRS duration pre and post was 165 ± 26 milliseconds and 138.5 ± 15.6 milliseconds (P < 0.001). Mapping ES showed a difference between 20 and 50 millisec- onds distributed across the RV in the majority of patients (40/49). However, 7 subjects demonstrated delay distribution of between 50 and 82 milliseconds. ES was significant greater in the RV mid-septum (161.2 ± 23.7 milliseconds) compared with RVOT (154.1 ± 20.8 milliseconds) and apex (148.0 ± 25.5 mil- liseconds; P< 0.001). The site of Maximal ES was most commonly found at the mid-septum (40 patients, 80%) and only rarely at the RVOT (5, 10%) and apex (5, 10%; P < 0.01). Conclusion: MES was observed most commonly at the RV septum and rarely at the RV apex. Better correction of electrical and mechanical dyssynchrony by CRT may be achieved by placing the RV lead in a site outside of the apex in the majority of patients. Clinical studies exploring RV septal pacing in CRT seem warranted. (J Cardiovasc Electrophysiol, Vol. pp. 1–5) cardiac resynchronization therapy, biventricular pacing, heart failure, implantable cardioverter defibrillator Introduction Cardiac resynchronization therapy (CRT) has demon- strated improved mortality and morbidity in selected heart failure (HF) patients with delayed electrical activation mani- fest as widened surface QRS; indeed, the wider the QRS, the greater the benefit observed. 1-4 However, fully one-third of patients are classified as nonresponders to treatment, and the reasons for this are debated and remain largely unknown. 1-4 The therapeutic benefit of CRT is achieved by correction of dysynchronous left ventricular (LV) mechanical contrac- tion by placement of a pacing lead within the postero-lateral This work is published in the memory of Dr. Michael Nault, who tragically passed during his EP fellowship. His contribution to this work and our lives will be remembered. No disclosures. Address for correspondence: Damian P. Redfearn, M.B., Ch.B., M.D., M.R.C.P.I., Departments of Medicine, Biomedical and Molecular Sciences, and School of Computing, Queen’s University, Kingston General Hospital, FAPC 3, 76 Stuart Street, Kingston, ON K7L 2V7, Canada. Fax: (01) 6135481387; E-mail: redfearn@queensu.ca Manuscript received 16 July 2011; Revised manuscript received 15 August 2011; Accepted for publication 31 August 2011. doi: 10.1111/j.1540-8167.2011.02207.x vein of the coronary sinus. 1 Many studies have observed this location to be associated with optimal outcome; moreover, some studies suggest the greater the physical separation of the right ventricular (RV) and LV leads the better the response. 5,6 Most recently, data was published suggesting electrical delay or separation between the RV and LV leads was positively correlated with improved clinical response to CRT. 7-10 The position of the RV lead has traditionally been api- cal; however, numerous studies have suggested alternate site RV pacing may be beneficial in HF patients without clinical indications for CRT. 11-16 Optimal placement of the RV lead during biventricular pacing has not been assessed. We hypothesized that electrical separation (ES) would vary depending on the position of the RV lead. Our primary objective was to assess the range of ES during pacing from the optimal LV site obtained during a CRT implant and record the sites that presented greatest ES most frequently. Methods The study was approved by the local ethics board. Con- secutive patients with conventional indications for CRT were recruited. The indication for CRT was standard according to current clinical guidelines; our criteria for CRT required a stable New York Heart Association (NYHA) functional class III despite optimal medical therapy, LV systolic dys- function with ejection fraction <35%, sinus rhythm, and