title: Detailed analysis of ventricular activation sequences during right ventricular apical pacing and left bundle branch block and the potential implications for cardiac resynchronization therapy.
abstract: BACKGROUND
  Left bundle branch block (LBBB) leads to prolonged left ventricular (LV) total activation time (TAT) and ventricular electrical uncoupling (VEU; mean LV activation time minus mean right ventricular [RV] activation time); both have been shown to be preferential targets for cardiac resynchronization therapy (CRT). Whether right ventricular apical pacing (RVAP) produces similar ventricular activation patterns has not been well studied.
  
  
  OBJECTIVE
  The purpose of this study was to compare electrical ventricular activation patterns during RVAP and LBBB.
  
  
  METHODS
  We performed ECG mapping during sinus rhythm, RVAP, and CRT in 24 patients with LBBB.
  
  
  RESULTS
  We observed differences in the electrical activation pattern with RVAP compared to LBBB. During LBBB, RV activation occurred rapidly; in contrast, RV activation was prolonged during RVAP (46 ± 21 ms vs 69 ± 17 ms, P <.001). There was no significant difference in LVTAT; however, differences in conduction pattern were observed. During LBBB, LV activation was circumferential, whereas with RVAP, LV activation proceeded from apex to base. Differences in the number, size, and orientation of lines of slow conduction also were observed. With LBBB, VEU was nearly twice as long as during RVAP (73 ± 12 ms vs 38 ± 21 ms, P <.001). CRT resulted in a greater reduction in VEU relative to LBBB activation (P <.001).
  
  
  CONCLUSIONS
  RVAP produces significant differences in ventricular activation characteristics compared to LBBB. Significantly less VEU occurs with RVAP, and as a result CRT produces a smaller relative reduction in VEU. This may explain the finding that CRT appears to be more effective in patients with LBBB than in those who were upgraded because of high percentages of RV pacing.
authors.affiliation: Hôpital Cardiologique du Haut-Lévêque, CHU Bordeaux, Université Bordeaux, IHU LIRYC, Bordeaux, France; Clermont Université, Université d'Auvergne, Cardio Vascular Interventional Therapy and Imaging (CaVITI), Image Science for Interventional Techniques (ISIT), UMR6284, and CHU Clermont-Ferrand, Cardiology Department, F-63003 Clermont-Ferrand, France.
authors.forename: Romain
authors.initials: R
authors.lastname: Eschalier
authors.affiliation: Hôpital Cardiologique du Haut-Lévêque, CHU Bordeaux, Université Bordeaux, IHU LIRYC, Bordeaux, France. Electronic address: sylvain.ploux@gmail.com.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Ploux
authors.affiliation: Hôpital Cardiologique du Haut-Lévêque, CHU Bordeaux, Université Bordeaux, IHU LIRYC, Bordeaux, France; Maastricht University, Cardiovascular Research Institute Maastricht (CARIM), Maastricht, The Netherlands.
authors.forename: Joost
authors.initials: J
authors.lastname: Lumens
authors.affiliation: Imperial College London, London, United Kingdom.
authors.forename: Zachary
authors.initials: Z
authors.lastname: Whinnett
authors.affiliation: Cardiac Pacing and Electrophysiology, Cleveland Clinic, Cleveland, Ohio.
authors.forename: Niraj
authors.initials: N
authors.lastname: Varma
authors.affiliation: Hôpital Cardiologique du Haut-Lévêque, CHU Bordeaux, Université Bordeaux, IHU LIRYC, Bordeaux, France.
authors.forename: Valentin
authors.initials: V
authors.lastname: Meillet
authors.affiliation: Hôpital Cardiologique du Haut-Lévêque, CHU Bordeaux, Université Bordeaux, IHU LIRYC, Bordeaux, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Ritter
authors.affiliation: Hôpital Cardiologique du Haut-Lévêque, CHU Bordeaux, Université Bordeaux, IHU LIRYC, Bordeaux, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Jaïs
authors.affiliation: Hôpital Cardiologique du Haut-Lévêque, CHU Bordeaux, Université Bordeaux, IHU LIRYC, Bordeaux, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Haïssaguerre
authors.affiliation: Hôpital Cardiologique du Haut-Lévêque, CHU Bordeaux, Université Bordeaux, IHU LIRYC, Bordeaux, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Bordachar
mesh_terms: D000368:Aged; D002037:Bundle-Branch Block / Q000503:physiopathology* / Q000628:therapy*; D058406:Cardiac Resynchronization Therapy; D015331:Cohort Studies; D004562:Electrocardiography; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D016277:Ventricular Function, Left / Q000502:physiology*
keywords: Cardiac resynchronization therapy; Electrical dyssynchrony; Electrocardiography; Left bundle branch block; Ventricular mapping