Reevaluation of the electrocardiographic pattern of left bundle branch block for proper patient selection and better survival in cardiac resynchronization therapy

Research output: Contribution to journalReview article


According to the present guidelines, in New York Heart Association Class I-IV heart failure, ejection fraction ≤ 35%, and electrocardiographic (ECG) QRS width ≥ 120 ms and left bundle branch block, cardiac resynchronization therapy is indicated. Reevaluation of the MADIT-CRT data and electrophysiologic and pathologic findings of human left bundle branch block gave evidence that "true" left bundle branch block requires a QRS width of ≥ 130 ms (in woman) and ≥ 140 ms (in man). In true, (not continuously widening, but presenting with at least 40 ms abrupt QRS prolongation) left bundle branch block, the initial (septal) QRS forces lose their original left-to-right direction. After the right ventricular depolarization (30-40 ms) an interventricular (slow, muscular) activation occurs that takes ≥ 40 ms, whereas the final depolarization of the lateral wall of the left ventricle takes also ≥ 50 ms, that is to say the total QRS length ≥ 130 ms, or more. After the 40th ms from the beginning of depolarization, notched/ slurred R waves are characteristic, visible in a minimum two of the leads of the I, aVL, V1, V2, V5 and V6, and a ≥ 40 ms increase of QRS complex develops, if compared to the pre-LBBB QRS time. In contrast, the slow, continuously widened "LBBB-like" QRS pattern mostly belongs to left ventricular hypertrophy, or it is an ECG sign of a metabolic or infiltrative disease.

Original languageEnglish
Pages (from-to)308-313
Number of pages6
JournalCardiology Letters
Issue number4
Publication statusPublished - Sep 19 2013



  • Cardiac resynchronization therapy (CRT)
  • Heart failure
  • MADIT-CRT study
  • Morphology of left bundle branch block

ASJC Scopus subject areas

  • Cardiology and Cardiovascular Medicine

Cite this