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38 m a s s a g e & b o d y w o r k n o v e m b e r / d e c e m b e r 2 0 2 0 education PATHOLOGY PERSPECTIVES Skipping a Beat Cardiac Arrhythmias By Ruth Werner You may remember that in a normal heartbeat the two atria contract simultaneously, pushing their contents into the relaxed ventricles. Then, the ventricles contract, while the relaxed atria refill. When it works correctly, the heartbeat is strong, coordinated, and surprisingly responsive to minute changes in the environment. For more on heart rate variability and its connection to health, see the accompanying video. The heartbeat begins in a small bundle of cells in the right atrium called the sinoatrial node (SA node). A "normal sinus rhythm" refers to the work of the SA node. The impulse that originates here causes muscle fibers throughout the left and right atria to contract. Lub-dub. Lub-dub. Lub-dub. How we rely on that steady rhythm. Everything in human function depends on a heartbeat that never falters, never rests, never stops until the day we die. If something interferes with that unceasing cadence, the consequences can be deadly. What if a heartbeat isn't lub-dub but l-l-l-lub-dub or (worse) lub-d-d-d-d-dub-b-b? This edition of Pathology Perspectives will address cardiac arrhythmias—interruptions in our most fundamental life-sustaining function. ARRHYTHMIA BASICS Arrhythmia or dysrhythmia is a label for when a normal heartbeat is interrupted. It can become irregular and disorganized, or fully organized but faster or slower than is healthy. An abnormally fast heartbeat is called tachycardia, and a slow one is called bradycardia. Episodes of arrhythmia can be short-lived or long-lasting. Arrhythmias are relatively common, affecting 3–6 million adults in the United States at any given time. It is possible that in the coming years we will see this number rise, because long-term arrhythmias may be among the permanent changes in function that some survivors of COVID-19 experience. Other risk factors include long-term exposure to certain types of air pollution; age; family history and genetics; lifestyle habits, including the use of alcohol, tobacco, and stimulant drugs; and medical history—some autoimmune diseases like lupus or rheumatoid arthritis are seen more often with arrhythmias, along with eating disorders (related to electrolyte imbalances), heart attack, heart failure, and heart inflammation. A HEARTBEAT PRIMER The heart rate is controlled by coordinated signals from the sympathetic and parasympathetic nervous systems, but the heartbeat is generated by special tissues inside the heart itself. The pathway of electrical impulses through the myocardium is clear and predictable, and any disruptions to this process can wreak havoc.

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