First degree atrioventricular block - Conduction disturbances

First degree atrioventricular block

Definition

Atrioventricular block describes an alteration in the transmission of action potentials between the atria and the ventricles. First degree block is a prolongation of the time required for AV transmission.

Aetiology

First degree block occurs occasionally in normal individuals but may follow rheumatic fever, ischaemic heart disease or digoxin toxicity. In the young it is often caused by high vagal tone. First degree block may progress onto other forms of heart block.

Clinical features

First degree atrioventricular block is asymptomatic.

Investigations

·         ECG shows a prolongation of the PR interval >0.2 seconds (one large square on a standard ECG) with QRS complexes following every P wave (see Fig. 2.11).

·        Digoxin level in patients on digoxin to exclude overdose.

Management

No treatment is required.