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

Causes[edit]

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Among the causes of LBBB are:^[2]

• Acute myocardial infarction
• Extensive coronary artery disease
• Primary disease of the cardiac electrical conduction system
• Long standing hypertension leading to aortic root dilatation and subsequent aortic regurgitation
• Side effect of some cardiac surgeries (e.g., aortic root reconstruction)

Diagnosis[edit]

The criteria to diagnose a left bundle branch block on the electrocardiogram:^{[citation needed]}

• The heart rhythm must be supraventricular in origin
• The QRS duration must be ≥ 120 ms^[3]
• There should be a QS or rS complex in lead V1
• There should be a notched ('M'-shaped) R wave in lead V6.

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.^{[citation needed]}

There are also partial blocks of the left bundle branch: 'left anterior fascicular block' (LAFB)^[4] and a 'left posterior fascicular block' (LPFB).^[5] This refers to the block after the bifurcation of the left bundle branch.

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Diagnostic consequences[edit]

The presence of LBBB results in that electrocardiography (ECG) cannot be used to diagnose left ventricular hypertrophy or Q wave infarction, because LBBB in itself results in widened QRS complex, and changes in the ST segment consistent with ischemia or injury.^[6]

Treatment[edit]

• Patients with LBBB require complete cardiac evaluation, and those with LBBB and syncope or near-syncope may require a pacemaker.
• Some patients with LBBB, a markedly prolonged QRS (usually > 150 ms), and systolic heart failure may benefit from a biventricular pacemaker, which allows for better synchrony of heart contractions.^[7]

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See also[edit]

References[edit]

1. ^'Conduction Blocks 2006 KCUMB'. Retrieved 2009-01-20.
2. ^'Symptoms and causes - Mayo Clinic'. www.mayoclinic.org. Retrieved 2021-04-06.
3. ^'Lesson VI - EKG Conduction Abnormalities'. Retrieved 2009-01-07.
4. ^'more detailed information about left anterior fascicular block'. GPnotebook.
5. ^'more detailed information about left posterior fascicular block'. GPnotebook.
6. ^Emily Groepper; Nasar Nallamothu; Wilfred Lam; Frank Aguirre; Kristi Bergman; Patricia Good; Patricia Wright (May 13, 2014). 'Electrocardiography > Left Bundle Branch Block (LBBB)'. Southern Illinois University School of Medicine. Retrieved 2015-07-02.
7. ^Stevenson WG, Hernaddez AF, Carson PE, et al. Indications for cardiac resynchronization therapy: 2011 update from the Heart Failure Society of America guideline committee. J Card Fail 2012; 18:94-106.

External links[edit]