Left bundle branch block – LBBB

Left bundle branch block is the block in the signal conduction pathway to the left ventricle. Electrical signals from the upper part of the heart then travel a circuitous path from the right ventricle through the muscle fibres to the left ventricle. Hence the contraction of left ventricle is delayed. Delay is more for the part of the left ventricle is farthest on the left side (lateral wall) compared to the inner portion. Inner portion of the left ventricle is the partition between the two lower chambers of the heart known as interventricular septum. This causes a lack of synchrony between contractions of two parts of the left ventricle. When one part contracts, the other part is relaxing and vice versa. Lack of synchrony affects the pump function of the left ventricle. In long run this can cause heart failure in some cases.

What causes left bundle branch block?

Left bundle branch can get blocked by degenerative changes in the conduction system as age advances. It can be damaged in a heart attack when the blood vessel supplying it is blocked. LBBB is seen in heart muscle disease involving the left ventricle known as dilated cardiomyopathy, where it contributes to the decrease in the pumping function of the heart as described above.

How is LBBB recognized?

LBBB is recognized by the typical pattern it causes on the ECG (electrocardiogram).

What is the treatment for LBBB?

Treatment is directed at the cause. Isolated LBBB without any other heart problem is only kept under follow up to see whether there is worsening of conduction system disease. In a person with LBBB, if the right bundle branch gets damaged due some reason, complete heart block with very low heart rate ensues. Heart failure as a result of lack of synchrony of contraction of the left ventricle can be initially treated medically. If there is no optimal response to medical treatment, implantation of a device known as cardiac resynchronization therapy (CRT) can be considered. In CRT both left and right ventricles as well as the right atrium are paced with electrical signals from an implanted device connected to the heart by electrodes. When both ventricles are paced simultaneously, the contraction pattern improves in such a way that output of the left ventricle improves. In the long run this reduces the enlargement of the left ventricle which would have occurred due to heart failure.