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Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.
Dr. Kulick received his undergraduate and medical degrees from the University of Southern California, School of Medicine. He performed his residency in internal medicine at the Harbor-University of California Los Angeles Medical Center and a fellowship in the section of cardiology at the Los Angeles County-University of Southern California Medical Center. He is board certified in Internal Medicine and Cardiology.
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
The heart is a two stage electric pump whose job it is to circulate blood through the body. There is a group of cells that serve as an automatic pacemaker located in the atrium that generates an electrical current that spreads to the heart muscle cells to generate a coordinated squeeze, so that the pump can function.
The heart has four chambers, the right and left atria (singular= atrium) and the right and left ventricles. The right side of the heart pumps blood to the lungs while the left side pumps it to the rest of the body.
Blood from the body is collected in the right atrium and is pushed into the right ventricle with a small beat of the upper chamber of the heart. The right ventricle then pumps the blood to the lungs to pick up oxygen. They oxygen-rich blood returns to the left atrium where the small atrial beat pushes it to the left ventricle. The left ventricle is much thicker than the right because it needs to be strong enough to send blood to the entire body.
There are special cells in the right atrium called the sino-atrial node (SA node) that generate the first electrical impulse, allowing the heart to beat in a coordinated way. The SA node is considered the "natural pacemaker" of the heart. This pacemaker function begins the electrical impulse which follows pathways in the atrial walls, almost like wiring, to a junction box between the atrium and ventricle called the atrio-ventricular node (AV node). This electric signal causes muscle cells in both atria to contract at once. At the AV node, the electric signal waits for a very short time, usually one to two tenths of a second, to allow blood pumped from the atria to fill up the ventricles. The signal then passes through electric bundles in the ventricle walls to allow these chambers to contract, again in a coordinated way, and pump blood to the lungs and body.
The SA node generates an electric beat about 60-80 times a minute, and each should result in a heart beat. That beat can be felt as an external pulse. After a heart beat, the muscle cells of the heart need a split second to get ready to beat again, and the electrical system allows a pause for this to happen.
The heart and its electrical activity depend upon a relatively narrow normal state for it to work. Fortunately, the body tends to protect the heart as best as it can. Still, rhythm disturbances are frequent. Some disturbances are normal physiologic responses, but some are potentially life threatening.
Every cell in the heart can act as a pacemaker. The SA node has an intrinsic heart beat generation rate of 60-80. If the atrium fails to generate a heart beat the AV node can do so a rate of about 40, and if needed, the ventricles themselves can generate heart beats at a rate of about 20 and may kick in if the cells of the upper chamber fail or if the electrical signals to the ventricle are blocked.
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