Atrial ectopic beats - Atrial arrhythmias

Atrial arrhythmias

Atrial ectopic beats

Definition

Atrial ectopic beats include extrasystoles and premature beats.

Aetiology

Atrial ectopics are common in normal individuals. All cardiac cells have intrinsic pacemaker ability. They gradually depolarise until a threshold is reached at which point rapid depolarisation occurs and a cardiac action potential is fired. This is most rapid in the sinoatrial node, the normal pacemaker of the heart. If in a single or group of cells the gradual depolarisation is more rapid than usual, or if the voltage threshold for rapid depolarisation is reduced they may stimulate a cardiac depolarisation resulting in an ectopic beat. This process is termed enhanced automaticity. Common causes are electrolyte abnormalities, alcohol or nicotine excess, anaemia, medications such as Î²-agonists, and hypoxaemia.

Pathophysiology

As the depolarisation of the heart arises from within the atria, the QRS complex of the ECG is preceded by a P wave which may be of different configuration as atrial depolarisation has a different origin to normal. The QRS complex is the same as normal because the depolarisation of the ventricles begins from the AV node.

Clinical features

Patients are often asymptomatic but may complain of an irregular or thumping heartbeat. The patient may complain of a skipped beat, as there is a compensatory pause after an extrasystole.

Investigations

ECG shows early, abnormal P waves followed by a normal QRS complex and a compensatory pause. Ectopic P waves are often best seen in lead V1.

Management

Atrial ectopic beats do not require treatment, although underlying causes of increased automaticity should be identified and managed. If atrial ectopic beats are frequent they may progress to other atrial arrhythmias.