Bundle branch block is a heart abnormality that causes the electrical impulse that makes the heart beat travel unevenly, resulting in slightly asynchronous ventricle contractions (uneven pumping of blood through the lower chambers of the heart and into the arteries).In the heart, a specialized group of cells called the sinoatrial (SA) node acts as a natural pacemaker by sending an electrical impulse to the ventricles of the heart at a regular interval, usually between sixty and one hundred times a minute, making the ventricles contract and pump blood through the arteries. To travel through the heart properly, the electrical impulse must move along particular pathways of specialized tissue. One of these pathways is called the bundle of His, and this bundle splits, or branches, into two separate bundles of specialized tissue, one diverted to the left ventricle, and one diverted to the right ventricle. In a normally functioning heart, the impulse travels through these bundles and makes both the left and right ventricle contract at the same time.
Sometimes, however, one of the branches responsible for transmitting the electrical impulse to the ventricles cannot successfully do so, because the electrical impulse is blocked. Right-sided bundle branch block occurs more frequently than left-sided bundle branch block, and is most always the result of a defect present from birth. Other culprits may include high blood pressure, coronary artery disease, valve disease, cardiomyopathy, or prior heart attack resulting in damage to the electrical pathway. Impulses that run into a block in one of the bundles must seek other pathways, causing a delay in the electrical activation of a portion of the heart muscle, resulting in slightly asynchronous pumping of blood by the ventricles.
