title: Vectorcardiographic and electrocardiographic criteria to distinguish new and old left bundle branch block.
abstract: BACKGROUND
  There are no established criteria to differentiate new from old left bundle branch block (LBBB). This complicates management of patients with LBBB and suspected acute coronary syndrome.
  
  
  OBJECTIVE
  The purpose of this study was to develop electrocardiographic (ECG) criteria to differentiate new and old LBBB.
  
  
  METHODS
  All LBBB tracings (n = 3,706) in a hospital ECG database were retrieved. New (<24 hours, n = 39) and old (>24 hours, n = 1,760) LBBB tracings were identified. QRS and T-wave amplitudes, directions, and durations were measured digitally. Vectorcardiograms were reconstructed from 12-lead ECGs using inverse Dower transform and analyzed with Cardio3KG software. Receiver operator characteristic (ROC) curves were used to develop decision rules to distinguish new and old LBBB.
  
  
  RESULTS
  The new LBBB group had larger T-vector magnitude (1.20 +/- 0.07 vs. 0.71 +/- 0.01 mV), smaller QRS vector magnitude (2.13 +/- 0.12 vs. 2.47 +/- 0.02 mV), and a lower QRS/T vector magnitude ratio (QRS/T; 1.79 +/- 0.03 vs. 3.92 +/- 0.04) compared with the old LBBB group (mean +/- standard error of the mean, P <.001). The ratio of deepest S to largest T wave in precordial leads (Max S/T) was significantly smaller in the new compared with in the old LBBB group (1.66 +/- 0.05 vs. 3.54 +/- 0.08; P <.001). A decision rule using QRS/T <2.25 and Max S/T <2.5 had 100% sensitivity and 96%-68% specificity in diagnosing new LBBB, including subsets of patients with tachycardia and ischemia.
  
  
  CONCLUSIONS
  QRS/T and Max S/T allow accurate discrimination between new and old LBBB suitable for both computerized and manual analysis. If confirmed in prospective studies, this finding can improve management of patients with chest pain and LBBB.
authors.affiliation: South Shore Hospital, South Weymouth, Massachusetts, USA.
authors.forename: Alexei
authors.initials: A
authors.lastname: Shvilkin
authors.forename: Bosko
authors.initials: B
authors.lastname: Bojovic
authors.forename: Branislav
authors.initials: B
authors.lastname: Vajdic
authors.forename: Ihor
authors.initials: I
authors.lastname: Gussak
authors.forename: Kalon K
authors.initials: KK
authors.lastname: Ho
authors.forename: Peter
authors.initials: P
authors.lastname: Zimetbaum
authors.forename: Mark E
authors.initials: ME
authors.lastname: Josephson
mesh_terms: D000368:Aged; D002037:Bundle-Branch Block / Q000175:diagnosis*; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013997:Time Factors; D014672:Vectorcardiography