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.
Types of atrial tachycardia
- Incessant ectopic
- Atrial tachycardia with block (digoxin toxicity)
Conditions associated with atrial tachycardia
- Chronic obstructive pulmonary disease
- Ischaemic heart disease
- Rheumatic heart disease
- Sick sinus syndrome
- Digoxin toxicity
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. Although often referred to as "paroxysmal atrial tachycardia with block" this arrhythmia is usually sustained.