Definition

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 include (collectively referred to as “bradyarrhythmias”) :

• Sinus bradycardia—an unusually slow heartbeat due to heart disease, a reaction to medication, or normal causes (such as excellent fitness or deep relaxation)
• Sick sinus syndrome—an unusually slow heartbeat due to a malfunction of the heart’s natural pacemaker (sinoatrial node)
• 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

Heartbeat: Anatomy of the Heart

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