Bradycardia is an abnormally slow heart rate. In adults, it is defined as a heart rate of less than 60 beats per minute. Different types of bradycardia are collectively referred to as bradyarrhythmias. They include:
Sinus bradycardia—an unusually slow heartbeat due to heart disease, a reaction to medication, or harmless causes such as excellent fitness or deep relaxation
Sick sinus syndrome—an unusually slow heartbeat due to a malfunction of the sinoatrial node, which is the heart's natural pacemaker
Heart block (atrioventricular block or AV block)—an unusually slow heartbeat due to a slowing or blocking of electrical impulses in the heart’s conduction system
Bradycardia: Slow heart rate. American Heart Association website. Available at: http://www.heart.org/HEARTORG/Conditions/Arrhythmia/AboutArrhythmia/Bradycardia_UCM_302016_Article.jsp#.Wh2r8FWnFxA. Updated January 5, 2017. Accessed November 28, 2017.
Explore arrhythmia. National Heart, Lung, and Blood Institute website. Available at: https://www.nhlbi.nih.gov/health/health-topics/topics/arr. Updated July 1, 2011. Accessed November 28, 2017.
Overview of arrhythmias. Merck Manual Professional Version website. Available at: http://www.merckmanuals.com/professional/cardiovascular-disorders/arrhythmias-and-conduction-disorders/overview-of-arrhythmias. Updated September 2017. Accessed November 28, 2017.
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