title: Left ventricular mechanical dyssynchrony by cardiac magnetic resonance is greater in patients with strict vs nonstrict electrocardiogram criteria for left bundle-branch block.
abstract: BACKGROUND
  Left bundle-branch block (LBBB) is a marker of increased delay between septal and left ventricular (LV) lateral wall electrical activation and is a predictor of which patients will benefit from cardiac resynchronization therapy. Recent analysis has suggested that one-third of patients meeting the conventional electrocardiogram criteria for LBBB are misdiagnosed, and new strict LBBB criteria have been proposed. We tested the hypothesis that patients with strict LBBB have greater LV mechanical dyssynchrony than do patients meeting the nonstrict LBBB criteria, whereas there is no difference between patients with nonstrict LBBB and LV conduction delay with a QRS duration of 110 to 119 ms.
  
  
  METHODS
  Sixty-four patients referred for primary prevention implantable cardioverter-defibrillators underwent 12-lead electrocardiogram and cardiac magnetic resonance myocardial tagging. The patients were classified as strict LBBB, nonstrict LBBB, or non-LBBB (nonspecific LV conduction delay with a QRS duration of 110-119 ms). The time delay between septal and lateral LV wall peak circumferential strain (septal-to-lateral wall delay) was measured by cardiac magnetic resonance.
  
  
  RESULTS
  Patients with strict LBBB (n = 31) had a greater septal-to-lateral wall delay compared with patients with nonstrict LBBB (n = 19) (210 ± 137 ms vs 122 ± 102 ms, P = .045). There was no significant difference between nonstrict LBBB and non-LBBB (n = 14) septal-to-lateral wall delay (122 ± 102 ms vs 100 ± 86 ms, P = .51).
  
  
  CONCLUSIONS
  Strict LBBB criteria identify patients with greater mechanical dyssynchrony compared with patients only meeting the nonstrict LBBB criteria, whereas there was no significant difference between patients with nonstrict LBBB and non-LBBB. The greater observed LV dyssynchrony may explain why patients with strict LBBB have a better response to cardiac resynchronization therapy.
authors.affiliation: Department of Clinical Physiology, Cardiac MR Group, Karolinska Institute and Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Linus G
authors.initials: LG
authors.lastname: Andersson
authors.forename: Katherine C
authors.initials: KC
authors.lastname: Wu
authors.forename: Björn
authors.initials: B
authors.lastname: Wieslander
authors.forename: Zak
authors.initials: Z
authors.lastname: Loring
authors.forename: Terry F
authors.initials: TF
authors.lastname: Frank
authors.forename: Charles
authors.initials: C
authors.lastname: Maynard
authors.forename: Gary
authors.initials: G
authors.lastname: Gerstenblith
authors.forename: Gordon F
authors.initials: GF
authors.lastname: Tomaselli
authors.forename: Robert G
authors.initials: RG
authors.lastname: Weiss
authors.forename: Galen S
authors.initials: GS
authors.lastname: Wagner
authors.forename: Martin
authors.initials: M
authors.lastname: Ugander
authors.forename: David G
authors.initials: DG
authors.lastname: Strauss
mesh_terms: D002037:Bundle-Branch Block / Q000175:diagnosis* / Q000503:physiopathology / Q000628:therapy; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D003937:Diagnosis, Differential; D004562:Electrocardiography; D005260:Female; D005500:Follow-Up Studies; D006352:Heart Ventricles / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000502:physiology*; D011379:Prognosis; D011446:Prospective Studies; D018487:Ventricular Dysfunction, Left / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology