title: The right ventricular septum presents the optimum site for maximal electrical separation during left ventricular pacing.
abstract: Cardiac resynchronization 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 milliseconds 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 milliseconds; 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).
  
  
  CONCLUSIONS
  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.
authors: Division of Cardiology (Arrhythmia Service), Kingston General Hospital, Queen's University, Kingston, Ontario, Canada.
authors: Rodrigo I
authors: RI
authors: Miranda
authors: Michael
authors: M
authors: Nault
authors: Christopher S
authors: CS
authors: Simpson
authors: Kevin A
authors: KA
authors: Michael
authors: Hoshiar
authors: H
authors: Abdollah
authors: Adrian
authors: A
authors: Baranchuk
authors: Damian P
authors: DP
authors: Redfearn
mesh_terms: D000200:Action Potentials; D000368:Aged; D006328:Cardiac Catheterization; D058406:Cardiac Resynchronization Therapy / Q000009:adverse effects / Q000379:methods*; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006333:Heart Failure / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D006352:Heart Ventricles / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009864:Ontario; D011446:Prospective Studies; D020127:Recovery of Function; D013318:Stroke Volume; D013997:Time Factors; D016896:Treatment Outcome; D018487:Ventricular Dysfunction, Left / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D016277:Ventricular Function, Left; D054088:Ventricular Septum / Q000503:physiopathology