title: Mechanistic insights into the benefits of multisite pacing in cardiac resynchronization therapy: The importance of electrical substrate and rate of left ventricular activation.
abstract: BACKGROUND
  Multisite pacing (MSP) of the left ventricle is proposed as an alternative to conventional single-site LV pacing in cardiac resynchronization therapy (CRT). Reports on the benefits of MSP have been conflicting. A paradigm whereby not all patients derive benefit from MSP is emerging.
  
  
  OBJECTIVE
  We sought to compare the hemodynamic and electrical effects of MSP with the aim of identifying a subgroup of patients more likely to derive benefit from MSP.
  
  
  METHODS
  Sixteen patients with implanted CRT systems incorporating a quadripolar LV pacing lead were studied. Invasive hemodynamic and electroanatomic assessment was performed during the following rhythms: baseline (non-CRT); biventricular (BIV) pacing delivered via the implanted CRT system (BIV(implanted)); BIV pacing delivered via an alternative temporary LV lead (BIV(alternative)); dual-vein MSP delivered via 2 LV leads; MultiPoint Pacing delivered via 2 vectors of the quadripolar LV lead.
  
  
  RESULTS
  Seven patients had an acute hemodynamic response (AHR) of <10% over baseline rhythm with BIV(implanted) and were deemed nonresponders. AHR in responders vs nonresponders was 21.4% ± 10.4% vs 2.0% ± 5.2% (P < .001). In responders, neither form of MSP provided incremental hemodynamic benefit over BIV(implanted). Dual-vein MSP (8.8% ± 5.7%; P = .036 vs BIV(implanted)) and MultiPoint Pacing (10.0% ± 12.2%; P = .064 vs BIV(implanted)) both improved AHR in nonresponders. Seven of 9 responders to BIV(implanted) had LV endocardial activation characterized by a functional line of block during intrinsic rhythm that was abolished with BIV pacing. All these patients met strict criteria for left bundle branch block (LBBB). No nonresponders exhibited this line of block or met strict criteria for LBBB.
  
  
  CONCLUSIONS
  Patients not meeting strict criteria for LBBB appear most likely to derive benefit from MSP.
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom; Cardiovascular Department, Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom,. Electronic address: manav.sohal@gstt.nhs.uk.
authors.forename: Manav
authors.initials: M
authors.lastname: Sohal
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Anoop
authors.initials: A
authors.lastname: Shetty
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Steven
authors.initials: S
authors.lastname: Niederer
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Angela
authors.initials: A
authors.lastname: Lee
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Tom
authors.initials: T
authors.lastname: Jackson
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Behar
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Simon
authors.initials: S
authors.lastname: Claridge
authors.affiliation: Cardiovascular Department, Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom.
authors.forename: Julian
authors.initials: J
authors.lastname: Bostock
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Eoin
authors.initials: E
authors.lastname: Hyde
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Reza
authors.initials: R
authors.lastname: Razavi
authors.affiliation: Maastricht University Medical Center, Cardiovascular Research Institute (CARIM), Maastricht, The Netherlands.
authors.forename: Frits
authors.initials: F
authors.lastname: Prinzen
authors.affiliation: Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom; Cardiovascular Department, Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom.
authors.forename: C Aldo
authors.initials: CA
authors.lastname: Rinaldi
mesh_terms: D000368:Aged; D002037:Bundle-Branch Block / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D058406:Cardiac Resynchronization Therapy / Q000379:methods; D058409:Cardiac Resynchronization Therapy Devices; D015331:Cohort Studies; D017147:Defibrillators, Implantable; D006333:Heart Failure / Q000150:complications / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016896:Treatment Outcome; D016277:Ventricular Function, Left / Q000502:physiology*
keywords: Acute hemodynamic response; Cardiac resynchronization therapy; Left bundle branch block; Multisite pacing; Noncontact mapping