What is Intraventricular Conduction Blocks

Intraventricular Conduction Blocks or Bundle Branch Blocks occur in the conduction system of the heart.

Intraventricular Conduction BlocksThere are two main bundles of conducting fibers in the heart conducting the electrical signal through the ventricles – the right bundle, and the left bundle (which has an anteriour and a posterious fascicle).

Hence the possible abnormalities are:
– Right bundle branch block;
– Left bundle branch block;
– anteriour hemi-block;
– posterior hemi-block;
– bifascicular block (right bundle and left anterior).

Statistics on Intraventricular Conduction Blocks

These kinds of electrical disturbances are relatively common. Right bundle branch block is seen in 1% of young adults and 5% of elderly adults, and is considered a normal finding.

Risk Factors for Intraventricular Conduction Blocks

Causes of a right bundle branch block include:
– congenital heart disease;
myocardial infarction;
– pulmonary heart disease;
– drugs and electrolyte imbalances.

Causes of a left bundle branch block include myocardial disease, particularly myocardial infarction, left ventricular outflow obstructions and fibrosis of the conducting system.

Progression of Intraventricular Conduction Blocks

A block of either branch of the ventricular conducting system produces a de-coordination of the contraction of the two ventricles (the left and the right). For instance right bundle branch block results in delayed right ventricular contraction and left bundle branch block causes delayed left ventricular contraction. The importance of bundle branch blocks is that they can indicate conduction disease of the heart, and they may progress to complete heart block.

How is Intraventricular Conduction Blocks Diagnosed?

Blood Tests should exclude electrolyte imbalances as a cause of bundle branch block.
-A chest x-ray will show any obvious ventricular disease such as hypertrophy or cardiomyopathies

-Cardiac enzymes may be elevated if the bundle branch block is secondary to an acute myocardial infarction, but only if this is an acute event.

Prognosis of Intraventricular Conduction Blocks

The prognosis of bundle branch blocks depends on what caused the disorder, and whether the conduction disturbs progress. Treatment such as insertion of a pacemaker is available if complete heart block becomes imminent.

How is Intraventricular Conduction Blocks Treated?

Mild partial bundle branch blocks require no treatment. More severe arrhythmias may require permanent pacing.

The underlying cause of a bundle branch block should always be treated- the conduction defecit may resolve.

Intraventricular Conduction Blocks References

[1] Hurst’s The Heart 8th Edition, McGRAW-HILL 1994.
[2] Kumar and Clark Clinical Medicine 4th Edition, W.B SAUNDERS 1998.

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