Although bundle branches are just one small part of the electrical network of the heart, the role they play is significant. A bundle branch block diagnosis can be scary, but it is not necessarily a medical emergency. It can be a sign of underlying heart disease or a normal part of aging. Knowing how the electrical system in the heart works is essential to understanding what a bundle branch block is and how it affects the heart's ability to pump effectively.
The human heart is made of muscle and relies on electrical signals to pump blood through the body. The process starts in the sinoatrial (SA) node, the "pacemaker", a small collection of muscle cells at the top of the right atrium. The SA node sends an electric signal through the muscle fibers, which pumps blood from the right atrium into the lower chambers of the heart -- the ventricles. A second node in the ventricles, the atrioventricular (AV) node, receives this signal from the SA node and stimulates the lower chambers to pump blood out of the heart. To do this, it sends a signal that travels along muscle fibers into the wall that separates the ventricles. There, it splits into two paths or bundle branches.
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