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
Heartbeat: Anatomy of the Heart
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Bradycardia may be caused by:
  • Normal responses to:
    • Deep relaxation
    • Being in excellent physical shape
  • The heart’s natural pacemaker developing an abnormal rate or rhythm
  • The normal electrical conduction pathway being interrupted
  • Another part of the heart taking over as pacemaker

Risk Factors

Factors that may increase your chance of bradycardia include:

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