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Understanding ECGs: bradycardias--fit and fitting

BMJ 2001; 323 doi: https://doi.org/10.1136/sbmj.0112453 (Published 01 December 2001) Cite this as: BMJ 2001;323:0112453
  1. Dominic Cox, specialist registrar in cardiology1,
  2. Hamish Dougall, general practitioner and research fellow in general practice2
  1. 1Newcastle upon Tyne
  2. 2University of Dundee

In the fourth article in our series Dominic Cox and Hamish Dougall look at bradycardias--their diagnosis, significance, and management

Symptoms from slowing of the heart can be very varied, from sudden death, recurrent syncope, and epileptic-type fits, to much milder symptoms, such as lethargy, breathlessness, etc. The history can be very revealing, but can also be very unreliable in those patients who truly lose consciousness. Some bradycardias are only intermittent problems with bothersome recurrent blackouts but no abnormality found after many years of medical investigation. Getting evidence of an intermittent problem can be very difficult.

Bradycardia is “slow” cardiac rhythm and results from either a failure of initiation of the heart beat or failure of passage of this electrical message through the heart--that is, normal sinus node “spark plug” activity is disturbed or there is interruption of the passage of this activity to tell the pump to work. This second type of failure usually occurs at the atrioventricular (AV) node.

The intrinsic rate of the sinoatrial (SA) node, which controls the heart rate in normal circumstances, is 60 to 70 beats per minute, and a bradycardia is defined as a pulse rate of <60 beats per minute. Such a rate may be physiological (and therefore acceptable) in athletes, young people, or during sleep, but it can be of profound clinical significance resulting from acute myocardial infarction, sick sinus syndrome, or from a variety of different drugs--for example, beta blockers. Several non-cardiac disorders, such as hypothyroidism, hypothermia, jaundice, and raised intracranial pressure can also cause sinus bradycardia.

Identifying the important different types of bradycardias is relatively straightforward and will be considered in turn: sick sinus syndrome (sinoatrial disease); carotid sinus hypersensitivity; vasovagal syndrome; AV heart block; agonal rhythm; asystole.

Likewise the treatment options are few in number and basically consist of …

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