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What is Left bundle branch block and explain in detail?
Left bundle branch block (LBBB) is a conduction abnormality in the heart that can be seen on an electrocardiogram (ECG). 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
Among the causes of LBBB are:
Aortic stenosis
Dilated cardiomyopathy
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
Lyme disease

Mechanisms
Slow or absent conduction through the left bundle branch means that it takes longer than normal for the left ventricle to fully depolarise.  This can be due to a damaged bundle branch that is completely unable to conduct, but may represent intact conduction that is slower than normal.  LBBB may be fixed, present at all times, but may be intermittent for example occurring only during rapid heart rates