Left Bundle Branch Block

ECG Features

Figure 1: ECG Strip[1]

A left bundle branch block occurs when "the normal direction of septal depolarization is reversed (becomes right to left), as the impulse spreads first to the RV via the right bundle branch and then to the LV via the septum."[2] The reversed direction of depolarization produces deep S waves in the right precordial leads (V1) and tall R waves in the lateral leads (V6).[2]

Table 1: ECG Characteristics[3]

Clinical Significance[4]

  • The presence of a LBBB often indicates the presence of significant underlying heart disease.
  • A LBBB alone can also cause the heart to work less efficiently.
  • LBBB occurs mostly in older adults.

ECM Features

Figure 2: ECM Analysis, Record 109[5][6]

ECM Example

Additional Example of a LBBB

Figure 3: Record 214[5][6]

Additional Information


  1. LBBB [Online image]. (2011). Retrieved July 19, 2016, from http://en.ecgpedia.org/index.php?title=Textbook
  2. Left Bundle Branch Block. (n.d.). Retrieved July 27, 2016, from http://lifeinthefastlane.com/ecg-library/basics/left-bundle-branch-block/
  3. Bundle Branch Block. (n.d.). Retrieved July 27, 2016, from http://www.practicalclinicalskills.com/ekg-reference-guide-details?lessonID=39
  4. Fogoros, R. N. (n.d.). What Does It Mean to Have a Left Bundle Branch Block? Retrieved August 08, 2016, from https://www.verywell.com/left-bundle-branch-block-lbbb-1745784
  5. MIT-BIH Arrhythmia Database. (1980). Retrieved June, 2016, from https://physionet.org/physiobank/database/mitdb/
  6. Goldberger AL, Amaral LAN, Glass L, Hausdorff JM, Ivanov PCh, Mark RG, Mietus JE, Moody GB, Peng C-K, Stanley HE. PhysioBank, PhysioToolkit, and PhysioNet: Components of a New Research Resource for Complex Physiologic Signals. Circulation101(23):e215-e220 [Circulation Electronic Pages;http://circ.ahajournals.org/cgi/content/full/101/23/e215]; 2000 (June 13).