Second degree atrioventricular block - Mobitz type II

Second degree atrioventricular block - Mobitz type II

Definition

In Mobitz type II second degree atrioventricular block there is intermittent failure of AV transmission with a normal PR interval.

Incidence

Rare, less common than Mobitz type I.

Aetiology

Second degree block occurs most commonly in association with underlying acute coronary pathology such as post-MI.

Pathophysiology

The site of pathology of Mobitz type II is low in the conducting system – infra nodal in the His–Purkinje system.

Clinical features

A low ventricular rate may result in symptoms and signs of heart failure or may be asymptomatic.

Investigations

The ECG shows regular P waves with a normal PR interval, with missed beats not preceded by increasing PR interval. Most commonly every third or fourth atrial beat fails to conduct to the ventricle. In 2:1 block it is not possible to categorise as type I or type II as there is no opportunity to see PR prolongation. Ventricular escape beats may be seen.

Complications

Patients are at risk of progression to third degree heart block, which may present as cardiac syncope. If the ventricular rhythm fails totally, sudden death results.

Management

Atropine may be used intravenously to reduce AV block and increase ventricular rate.

Post-MI prophylactic temporary pacing may be required. If patients do not return to sinus rhythm or if not associated with myocardial infarction permanent pacing is indicated.