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 that are typically consistent from beat to beat. 1
Core Definition and Rate Characteristics
Atrial tachycardia represents a regular rhythm at a constant rate originating outside the sinus node region, with mechanisms that can be either focal or macroreentrant. 1 The defining atrial rate threshold is ≥100 bpm, distinguishing it from normal sinus rhythm. 1
Electrocardiographic Features
The hallmark ECG finding is regular, organized atrial activity with discrete P waves, typically with an isoelectric segment between P waves. 1 This isoelectric baseline distinguishes focal atrial tachycardia from atrial flutter, which classically shows continuous undulation without a flat baseline between deflections. 1
The P-wave morphology differs from sinus rhythm and may be negative in leads where sinus P waves are positive. 2 Atrial activation is most commonly the same from beat to beat, though some irregularity may be seen at onset ("warm-up") and termination ("warm-down"). 1
Mechanistic Classification
Atrial tachycardia divides into two primary mechanistic categories:
Focal Atrial Tachycardia
Focal atrial tachycardia arises from a circumscribed area with centrifugal spread to both atria. 1 Electrophysiological mapping reveals a focal point of origin. 1 The mechanism can be:
Macroreentrant Atrial Tachycardia
Macroreentrant atrial tachycardia involves a reentry circuit of large size with fixed and/or functional barriers. 1 These circuits can be entrained during atrial pacing. 1 Well-characterized forms include typical atrial flutter, reverse typical atrial flutter, and lesion-related macroreentrant tachycardia. 1
Special 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 This contrasts with focal atrial tachycardia where atrial activation remains consistent. 1
Sinus Node Reentry Tachycardia
This specific focal atrial tachycardia subtype results from microreentry arising from the sinus node complex, characterized by abrupt onset and termination with P-wave morphology indistinguishable from sinus rhythm. 1
Inappropriate Sinus Tachycardia
Inappropriate sinus tachycardia is a 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 It is defined by sinus heart rate >100 bpm at rest with mean 24-hour heart rate >90 bpm not due to appropriate physiological responses or primary causes such as hyperthyroidism or anemia. 1
Critical Distinguishing Features from Sinus Tachycardia
Atrial tachycardia has abrupt, sudden onset without gradual acceleration, with one beat being normal sinus and the next beat initiating the arrhythmia. 2 In contrast, sinus tachycardia shows gradual onset and termination with R-R intervals that vary over several seconds, getting progressively faster or slower. 2
After the first 10-20 beats, atrial tachycardia becomes extremely regular with minimal R-R interval variation. 2 The P-wave morphology differs from sinus rhythm, whereas sinus tachycardia maintains identical P-wave axis to baseline sinus rhythm. 2
Clinical Context and Prevalence
Atrial tachycardia accounts for approximately 10-15% of patients presenting to experienced arrhythmia centers for radiofrequency catheter ablation. 3 More than 70% of these cases are focal and occur in patients with no records of cardiac surgery or ablation of atrial fibrillation. 4
Important Clinical Pitfall
When incessant tachycardia is present, tachycardiomyopathy may develop. 3 This represents a reversible form of cardiomyopathy that can occur with sustained atrial tachycardia, emphasizing the importance of prompt recognition and treatment.