Cardiac arrhythmias: diagnosis and management. The bradycardias.
OBJECTIVE
To review the diagnosis and management of cardiac arrhythmias in a two-part presentation.


METHODS
Articles and published peer-review abstracts on tachycardias and bradycardias.


RESULTS
Bradycardias are caused by a failure of the sinus node to generate normal impulses or due to a defect in cardiac conduction that in turn causes a delay or failure of impulse propagation. During sleep, the heart rate may decrease to 30 beats per minute (bpm) with episodes of sinoatrial block, junctional rhythms and first and second degree atrioventricular block that occur often enough (particularly in trained athletes) to be considered normal variants. However, treatment is required if symptoms of dizziness, confusion, fatigue Stokes-Adams attacks or heart failure occur. Sinus node dysfunction or 'sick sinus syndrome' is usually caused by intrinsic nodal disease and may present with episodes of tachycardia and bradycardia (tachycardia-bradycardia syndrome). Treatment usually requires a permanent pacemaker. Atrioventricular (AV) conduction disturbances are characterised by a delay or failure of the atrial impulse to be conducted through the AV conducting system. If the escape rhythm is unstable the patient also requires a pacemaker. In the critically ill patient tachycardias are more often encountered than bradycardias. However, the intensivist should be familiar and skilled in the management of complete heart block and asystole, correcting the underlying defect (drug toxicity, hyperkalaemia, etc), while using catecholamines, atropine aminophylline and a temporary pacemaker for initial resuscitation.


CONCLUSIONS
Bradycardias are uncommon in the critically ill patient and often are caused by an underlying disorder (e.g. hyperkalaemia, calcium channel blocker toxicity, beta adrenergic receptor blocker toxicity, etc). However, post cardiac bypass and acute myocardial infarction may cause cardiac conduction defects that may require urgent resuscitation with a temporary pacemaker.
Department of Critical Care Medicine, Flinders Medical Centre, Adelaide, South Australia.
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Durham
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Worthley