What is atrial tachycardia?

What is Atrial Tachycardia

Atrial tachycardia is a supraventricular arrhythmia characterized by an atrial rate ≥100 beats per minute originating from atrial tissue outside the sinus node region, with discrete P waves and organized atrial activation sequences. 1

Core Definition and Mechanisms

Atrial tachycardia represents a regular rhythm at a constant rate that originates outside the sinus node region, and can arise through two fundamental mechanisms: focal or macroreentrant. 1

Focal Atrial Tachycardia

Focal atrial tachycardia arises from a localized atrial site and is characterized by regular, organized atrial activity with discrete P waves, typically with an isoelectric segment between P waves. 1

• Electrophysiological mapping reveals a focal point of origin from which activation spreads centrifugally to both atria 1
• The underlying mechanism can be enhanced automaticity, triggered activity, or microreentry (very small reentry circuits) 1
• At times, irregularity is seen, especially at onset ("warm-up") and termination ("warm-down") 1

Macroreentrant Atrial Tachycardia

Macroreentrant atrial tachycardia involves a reentry circuit of large size with fixed and/or functional barriers, and these circuits can be entrained during atrial pacing. 1 This category includes typical atrial flutter, reverse typical atrial flutter, and various lesion-related macroreentrant tachycardias. 1

Specific Subtypes

Multifocal Atrial Tachycardia (MAT)

Multifocal atrial tachycardia is an irregular supraventricular tachycardia characterized by ≥3 distinct P-wave morphologies and/or patterns of atrial activation at different rates, with the rhythm always being irregular. 1

• The atrial activation sequence and P-wave morphology vary from beat to beat 1
• MAT is usually seen in the setting of severe cardiopulmonary illness and is often difficult to differentiate from atrial fibrillation 2

Inappropriate Sinus Tachycardia

Inappropriate sinus tachycardia is a specific form of atrial tachycardia originating along the superior aspect of the crista terminalis (in the 'sinus node region') at rates above the physiological range, but with no relationship to metabolic or physiological demands. 1

• Defined as sinus heart rate >100 bpm at rest, with a mean 24-hour heart rate >90 bpm not due to appropriate physiological responses or primary causes such as hyperthyroidism or anemia 1

Sinus Node Reentry Tachycardia

This is a specific type of focal atrial tachycardia due to microreentry arising from the sinus node complex, characterized by abrupt onset and termination, resulting in a P-wave morphology that is indistinguishable from sinus rhythm. 1

Key Distinguishing Features from Other Arrhythmias

Atrial tachycardia differs fundamentally from atrial fibrillation, which has uncoordinated atrial activation, absence of distinct P waves, and irregular R-R intervals. 1

• Unlike physiologic sinus tachycardia, which has gradual onset and termination with R-R intervals that vary over several seconds, atrial tachycardia has abrupt, sudden onset without gradual acceleration 3
• The P-wave morphology in atrial tachycardia differs from sinus rhythm and may be negative in leads where sinus P waves are positive 3
• After the first 10-20 beats, atrial tachycardia becomes extremely regular with minimal R-R interval variation 3

Clinical Significance

Atrial tachycardia accounts for approximately 10-15% of patients presenting to experienced arrhythmia centers for radiofrequency catheter ablation. 4 When incessant tachycardia is present, tachycardiomyopathy may develop, making recognition and treatment critical. 4, 5