title: Influence of pacing site characteristics on response to cardiac resynchronization therapy.
abstract: BACKGROUND
  Transmural scar occupying left ventricular (LV) pacing regions has been associated with reduced response to cardiac resynchronization therapy (CRT). However, spatial influences of lead tip delivery relative to scar at both pacing sites remain poorly explored. This study evaluated scar distribution relative to LV and right ventricular (RV) lead tip placement through coregistration of late gadolinium enhancement MRI and cardiac computed tomographic (CT) findings. Influences on CRT response were assessed by serial echocardiography.
  
  
  RESULTS
  Sixty patients receiving CRT underwent preimplant late gadolinium enhancement MRI, postimplant cardiac CT, and serial echocardiography. Blinded segmental evaluations of mechanical delay, percentage scar burden, and lead tip location were performed. Response to CRT was defined as a reduction in LV end-systolic volume ≥15% at 6 months. The mean age and LV ejection fraction were 64±9 years and 25±7%, respectively. Mean scar volume was higher among CRT nonresponders for both the LV (23±23% versus 8±14% [P=0.01]) and RV pacing regions (40±32% versus 24±30% [P=0.04]). Significant pacing region scar was identified in 13% of LV pacing regions and 37% of RV pacing regions. Absence of scar in both regions was associated with an 81% response rate compared with 55%, 25%, and 0%, respectively, when the RV, LV, or both pacing regions contained scar. LV pacing region dyssynchrony was not predictive of response.
  
  
  CONCLUSIONS
  Myocardial scar occupying the LV pacing region is associated with nonresponse to CRT. Scar occupying the RV pacing region is encountered at higher frequency and seems to provide a more intermediate influence on CRT response.
authors.affiliation: Division of Cardiology, Department of Medicine, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada.
authors.forename: Jorge A
authors.initials: JA
authors.lastname: Wong
authors.forename: Raymond
authors.initials: R
authors.lastname: Yee
authors.forename: John
authors.initials: J
authors.lastname: Stirrat
authors.forename: David
authors.initials: D
authors.lastname: Scholl
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Krahn
authors.forename: Lorne J
authors.initials: LJ
authors.lastname: Gula
authors.forename: Allan C
authors.initials: AC
authors.lastname: Skanes
authors.forename: Peter
authors.initials: P
authors.lastname: Leong-Sit
authors.forename: George J
authors.initials: GJ
authors.lastname: Klein
authors.forename: David
authors.initials: D
authors.lastname: McCarty
authors.forename: Nowell
authors.initials: N
authors.lastname: Fine
authors.forename: Aashish
authors.initials: A
authors.lastname: Goela
authors.forename: Ali
authors.initials: A
authors.lastname: Islam
authors.forename: Terry
authors.initials: T
authors.lastname: Thompson
authors.forename: Maria
authors.initials: M
authors.lastname: Drangova
authors.forename: James A
authors.initials: JA
authors.lastname: White
mesh_terms: D000368:Aged; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D002921:Cicatrix / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D003287:Contrast Media; D005260:Female; D006329:Heart Conduction System / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D054143:Heart Failure, Systolic / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D006352:Heart Ventricles / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D016015:Logistic Models; D019028:Magnetic Resonance Imaging, Cine; D008297:Male; D008875:Middle Aged; D061330:Multidetector Computed Tomography; D015999:Multivariate Analysis; D015588:Observer Variation; D009942:Organometallic Compounds; D011237:Predictive Value of Tests; D011446:Prospective Studies; D015203:Reproducibility of Results; D013318:Stroke Volume; D016896:Treatment Outcome; D014463:Ultrasonography; D016277:Ventricular Function, Left; D016278:Ventricular Function, Right
chemical_list: D003287:Contrast Media; D009942:Organometallic Compounds; C090600:gadobutrol
keywords: cardiac MRI; cardiac computed tomography; cardiac resynchronization therapy; cicatrix; dyssynchrony; late gadolinium enhancement; response