Complications
The main complication of bundle branch block, right or left, is to progress to a complete block of the electric conduction from the upper chambers of the heart to the lower. This can slow your heart rate, which can cause fainting and lead to serious complications and abnormal heart rhythms.
People who have a heart attack and develop a left bundle branch block have a higher chance of complications, including sudden cardiac death, than do people who don't develop the condition after a heart attack.
Because bundle branch block affects the electrical activity of your heart, it can sometimes complicate the accurate diagnosis of other heart conditions, especially heart attacks, and lead to delays in proper management of those problems.