Left bundle branch block
Classification and external resources
ECG characteristics of a typical LBBB showing wide QRS complexes with abnormal morphology in leads V1 and V6.
ICD-10	I44.4 - I44.7
DiseasesDB	7352
eMedicine	ped/2501

Left bundle branch block (LBBB) is a cardiac conduction abnormality seen on the electrocardiogram (ECG).^[1] In this condition, activation of the left ventricle is delayed, which results in the left ventricle contracting later than the right ventricle.

[edit] ECG diagnosis

Electrocardiogram showing left bundle branch block and irregular rhythm due to supraventricular extrasystoles.

A left bundle branch block

The criteria to diagnose a left bundle branch block on the electrocardiogram:

• The heart rhythm must be supraventricular in origin
• The QRS duration must be = or > 120 ms^[2]
• There should be a QS or rS complex in lead V1
• There should be a monophasic R wave in leads I and V6.

It should be noted that LBBB renders the ST segment of chest leads unreliable.

The T wave should be deflected opposite the terminal deflection of the QRS complex. This is known as appropriate T wave discordance with bundle branch block. A concordant T wave may suggest ischemia or myocardial infarction.

A mnemonic to remember the ECG changes is WiLLiaM MaRRoW, ie with LBBB there is an W in V1 and a M in V6 and with a RBBB there is a M in lead V1 and a W in lead V6

[edit] Causes

Among the causes of LBBB are:

• Aortic stenosis
• Dilated cardiomyopathy
• Acute myocardial infarction
• Extensive cases of coronary artery disease
• Primary disease of the cardiac electrical conduction system
• Long standing hypertension leading to aortic root dilation and subsequent aortic regurgitation

[edit] Treatment

• Medical Care: Patients with LBBB require complete cardiac evaluation, and those with LBBB and syncope or near-syncope may require a pacemaker.
• Surgical Care: Some patients with LBBB, a markedly prolonged QRS, and congestive heart failure may benefit from a pacemaker, which provides rapid left ventricular contractions.

[edit] Classification

There are also partial blocks of the left bundle branch: "left anterior fascicular block" (LAFB)^[3] and a "left posterior fascicular block" (LPFB).^[4] This refers to the bifurcation of the left bundle branch.

[edit] See also

• Bundle branch block
• Right bundle branch block

[edit] References

[edit] External links

• http://library.med.utah.edu/kw/ecg/mml/ecg_lbbb.html