Arrythmias And Conduction Disturbances

Clinical assessment of an arrythmia should attempt to identify and correct reversible underlying causes (e.g. hypoxia, continuing ischaemia, acidosis, hypothermia, electrolyte disturbance), as well as quantify the haemodynamic consequences of the arrhythmia. The urgency of treatment depends upon the haemodynamic state of the patient.

Ventricular arrythmias

Ventricular fibrillation accounts for the majority of pre-hospital sudden deaths in patients suffering AMI. Treatment for ventricular fibrillation or pulseless ventricular tachycardia requires immediate defibrillation in accordance with current resuscitation guidelines. Ventricular tachycardia without significant haemodynamic compromise may require treatment with amiodarone or lignocaine or, if haemodynamic compromise is significant, synchronised electrical cardioversion.

An accelerated idioventricular rhythm, which may resemble ventricular tachycardia, is an innocent finding that occurs during reperfusion: it does not cause haemodynamic compromise, is spontaneously self-limiting and requires no intervention.

Ventricular extrasystoles are common following AMI and usually require no specific treatment.

Supraventricular arrythmias

Atrial fibrillation is the most common supraventricular tachycardia to complicate AMI. It is often recurrent and ultimately self-limiting. Treatment with beta-blockers, amiodarone or digoxin may be indicated or, if there is significant haemodynamic compromise, synchronised DC cardioversion. Patients with atrial fibrillation should also receive anti-thrombotic treatment, although this is already likely to have occurred in the setting of AMI.

Conduction defects

Various conduction defects and degrees of heart block can occur following AMI.

First-degree heart block is benign and requires no intervention.

Type one second-degree heart block (Wenckebach), in association with an inferior infarct, is rarely associated with haemodynamic compromise and is usually self-limiting. However, in the setting of anterior infarction, Wenckebach has a worse prognosis and may require pacing. Atropine should be used as an initial measure.

Type two second-degree and third-degree (complete) heart block are indications for transvenous pacing, which is more likely to be permanent in the presence of anterior infarction. Axis deviation should be identified in patients with right bundle branch block, since this indicates bifascicular block that may progress to complete heart block.