Electrical Signals in the Healthy Heart

Founder of a company acquired by Abbott and now a professor of medicine at Stanford University, Dr. Sanjiv Narayan leads the university's atrial fibrillation program and serves as director of electrophysiology research. Responsible for treatment and research related to abnormal heart rhythms, Abbott-associated physician Dr. Sanjiv Narayan is currently involved in the creation of a new arrhythmia center on campus.

The human heartbeat is a function of natural electrical signals, which travel through the chambers of the heart and signal muscle cells to contract. They regulate the phases of diastole and systole which, respectively, allow the chambers of the heart to fill with and expel blood. The process begins as the vena cava supplies the right atrium with blood from the body. 

When the atrium has filled, the sinoatrial (SA) node located in that chamber begins systole in both atria. As the atria contract, the signal travels on to the atrioventricular (AV) node located near the tricuspid valve at the interatrial septum. There, the signal slows briefly so to allow diastole in the ventricles, which then fill with blood.

At the appropriate moment, the SA node releases the electrical signal and sends it through the bundle of His, a pathway that then sends the same signal through the Purkinje fibers. These fibers connect to the muscle cells in the ventricle walls. 

In a healthy heart, the signal reaches the left ventricle slightly before it arrives at the right ventricle. Contraction in the right ventricle sends blood through the pulmonary valve to the lungs, while the left ventricle pushes blood through the aortic valve and toward the rest of the body.

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