Overview 

Bradycardia, when the heart rate is less than 60 beats per minute, can be normal. Athletes, in particular, will often have a resting heart rate less than 60, and a slow heart rate in young, otherwise healthy individuals is common during sleep. 

However, diseases affecting the normal electrical activity can cause interruption or block of signals resulting in slower heart rates. 

Symptoms 

Often a slow heart rate is associated with no symptoms and can be picked up incidentally. However, it can be associated with: 

  • light-headedness 
  • transient loss of consciousness (syncope) 
  • breathlessness 
  • Fatigue 

Causes 

Bradycardia can be caused by: 

  • age related heart tissue damage 
  • a heart attack. 
  • something you are born with (congenital) 
  • inflammation of heart muscle (myocarditis) 
  • complication of heart surgery. 
  • underactive thyroid gland (hypothyroidism) 
  • inflammatory diseases (e.g. lupus) 
  • Medications 

The heart is essentially two pumps working in parallel. Each pump consists of two chambers (atria and ventricles).  

The heart has a natural pacemaker (SA node) in the right atrium which initiates each heartbeat. The electrical signal spreads from the SA node through the atria before crossing to the ventricles via the AV node.  

Block in any part of this system can cause bradycardia. 

Diagnosis 

Problems with the conduction system of the heart can often be identified on a standard 12-lead ECG. If the issue is intermittent, then continuous ECG monitoring may be required. 

For less frequent issues, insertion of an implantable loop recorder may be needed. 

Treatment 

Bradycardia does not always need treated, especially if not associated with symptoms. 

However, if associated with symptoms and no reversible cause can be identified, implantation of a permanent pacemaker may be needed. 

Occasionally if there is evidence of significant conduction disease, a pacemaker may be recommended, even in the absence of symptoms.