Left Bundle Branch Block - ECG

Left bundle branch block (LBBB) is a relatively common finding in the elderly and cardiac patients. The ECG image of LBBB may be variable. The QS pattern may be present in leads V1 (and sometimes also in V2- V3) and this may be followed by elevated ST segments that can resemble anterior wall infarction (STEMI). There is a RSR' QRS pattern in V6 (QRS looks like the letter “M”) followed by a negative T wave. QRS complexes are extended over 120 ms.


Left Bundle Branch Block - ECGTypical example of LBBB – There are wide QRS (over 120 ms), deep Q in V1 (red), ascending ST elevations in V1-V3 and deformed QRS pattern in V6 resembling the letter "M" followed by a negative T wave (blue).

Conclusion: LBBB is not always a significant finding but it should never be underestimated. LBBB is often associated with an advanced coronary artery disease including acute coronary syndromes, valvular heart diseases, cardiomyopathies, etc. Acute chest pain with a newly arisen LBBB is a very threatening sign that must be treated with caution. A heart attack occurring in patient with already present LBBB is a challenging problem as LBBB may disguise the infarction changes in ECG record. A patient with acute problems and LBBB should have repeatedly examined the cardiac enzymes and asymptomatic patient should be thoroughly examined including the echocardiography.


Jiri Stefanek, MD  Author of texts: Jiri Stefanek, MD
 Contact: jiri.stefanek@seznam.cz
 Sources: basic text sources