title: Left bundle-branch block: the relationship between electrocardiogram electrical activation and echocardiography mechanical contraction.
abstract: BACKGROUND
  The relationship between myocardial electrical activation by electrocardiogram (ECG) and mechanical contraction by echocardiography in left bundle-branch block (LBBB) has never been clearly demonstrated. New strict criteria for LBBB based on a fundamental understanding of physiology have recently been independently published for both ECG and echocardiography. The relationship between the 2 modalities and the relation to cardiac resynchronization therapy (CRT) response was investigated.
  
  
  METHODS
  Sixty-six patients with LBBB by conventional criteria had a standard 12-lead ECG and 2-dimensional strain echocardiography performed before CRT implantation. Criteria for LBBB by echocardiography included early termination of contraction in one wall and prestretch and late contraction in opposing wall(s). New strict criteria by ECG included QRS duration ≥140 ms (men) or 130 ms (women), QS or rS in leads V1 and V2, and mid-QRS notching or slurring in ≥2 of leads V1, V2, V5, V6, I, and aVL. Response was defined as >15% decrease in left ventricular end-systolic volume after 6 months.
  
  
  RESULTS
  In 64 of 66 patients, ECG analysis was possible. Echo and ECG readings for LBBB presence were concordant in 54 (84%) of 64. Thirty-seven (82%) of 45 patients with LBBB by strict ECG criteria responded to CRT, whereas only 4 (21%) of the 19 patients without LBBB responded (sensitivity 90% and specificity 65%). Thirty-six (95%) of 38 patients with concordance for the presence of LBBB responded to CRT. In patients with concordance for the absence of LBBB, 15 (94%) of 16 did not respond.
  
  
  CONCLUSIONS
  For the first time, a close relation has been demonstrated between electrical activation by ECG and mechanical contraction by echocardiography. These findings may help identify CRT candidates.
authors.affiliation: Department of Cardiology, Gentofte University Hospital, Hellerup, Denmark. nielsrisum@gmail.com
authors.forename: Niels
authors.initials: N
authors.lastname: Risum
authors.forename: David
authors.initials: D
authors.lastname: Strauss
authors.forename: Peter
authors.initials: P
authors.lastname: Sogaard
authors.forename: Zak
authors.initials: Z
authors.lastname: Loring
authors.forename: Thomas Fritz
authors.initials: TF
authors.lastname: Hansen
authors.forename: Niels Eske
authors.initials: NE
authors.lastname: Bruun
authors.forename: Galen
authors.initials: G
authors.lastname: Wagner
authors.forename: Joseph
authors.initials: J
authors.lastname: Kisslo
mesh_terms: D000368:Aged; D002037:Bundle-Branch Block / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000628:therapy; D058406:Cardiac Resynchronization Therapy; D004452:Echocardiography / Q000379:methods; D004562:Electrocardiography; D055724:Electrophysiological Phenomena; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged