Atrial tachycardia typically arises from an ectopic source in the atrial muscle and produces an atrial rate of 150-250 beats/min—slower than that of atrial flutter. The P waves may be abnormally shaped depending on the site of the ectopic pacemaker. The ventricular rate depends on the degree of atrioventricular block.
There are four commonly recognized types of atrial tachycardia. Benign atrial tachycardia is a common arrhythmia in elderly people. It is paroxysmal in nature, has an atrial rate of 80-140 beats/min and an abrupt onset and cessation, and is brief in duration. Incessant ectopic atrial tachycardia is a rare chronic arrhythmia in children and young adults. The rate depends on the underlying sympathetic tone and is characteristically 100-160 beats/min. It can be difficult to distinguish from a sinus tachycardia. Diagnosis is important as it may lead to dilated cardiomyopathy if left untreated. Multifocal atrial tachycardia occurs when multiple sites in the atria are discharging and is due to increased automaticity. It is characterised by P waves of varying morphologies and PR intervals of different lengths on the electrocardiographic trace. The ventricular rate is irregular. It can be distinguished from atrial fibrillation by an isoelectric baseline between the P waves. It is typically seen in association with chronic pulmonary disease. Other causes include hypoxia or digoxin toxicity. Atrial tachycardia with atrioventricular block is typically seen with digoxin toxicity. The ventricular rhythm is usually regular but may be irregular if atrioventricular block is variable.
Conditions associated with atrial tachycardia:
- Chronic obstructive pulmonary disease
- Ischaemic heart disease
- Rheumatic heart disease
- Sick sinus syndrome
- Digoxin toxicity