Atrial Tachycardia

Atrial tachycardia (AT) is defined as a supraventricular arrhythmia originating from the atrial tissue outside of the sinus node, typically presenting with a heart rate between 100 and 250 bpm. Atrial tachycardia is independent of sinus node activity.^1 2

Atrial tachycardia is an uncommon type of supraventricular tachycardia and can be either paroxysmal or sustained, depending on its duration and clinical characteristics.^3 4

There are several types of atrial tachycardia, which are differentiated primarily by their electrophysiological mechanisms and clinical presentations. The most relevant types are:

• Focal atrial tachycardia.
• Multifocal atrial tachycardia.
• Sinus node reentrant tachycardia.

Focal Atrial Tachycardia

Focal atrial tachycardia (FAT) is defined as an atrial supraventricular tachycardia with a heart rate greater than 100 bpm, arising from a discrete origin and propagating throughout both atria in a centrifugal pattern.^3 4

The ventricular rate varies depending on atrioventricular nodal conduction and is typically characterized by a regular rhythm. However, irregularity may occasionally be observed, particularly during onset ("warm-up" phenomenon) and termination ("cool-down" phenomenon).^3 4

Symptoms may include palpitations, dyspnea, chest pain, and, in rare instances, syncope or presyncope. The arrhythmia can be sustained or incessant.⁴

Dynamic forms featuring recurrent interruptions and resets (reinitiations) are frequently observed.⁴

Focal Atrial Tachycardia:
A regular, narrow-QRS tachycardia at 120 bpm with negative P waves in the inferior and precordial leads.

The identification of the P wave on a 12-lead electrocardiogram (EKG) during tachycardia is critical

Depending on AV conduction and the heart rate, P waves may be concealed within the QRS complexes or T waves.⁴

Electrocardiographic Findings in Focal Atrial Tachycardia

According to Chou's Electrocardiography in Clinical Practice,¹ the electrocardiographic criteria for focal atrial tachycardia are as follows:¹

• 1. Presence of three or more consecutive abnormal P waves with a morphology distinctly different from that of sinus P waves.
• 2. The atrial rate is typically between 100 and 180 bpm.
• 3. The rhythm is regular (following the initial complexes).
• 4. The paroxysm consists of three or more consecutive complexes.
• 5. A QRS complex follows each P wave; the QRS complex usually resembles that of the sinus complex unless aberrant ventricular conduction is present.
• 6. The PR interval is typically normal or prolonged.
• 7. Tachycardia-induced ST-segment and T-wave changes may occur.¹

Adenosine administration can aid in diagnosis by slowing the ventricular rate or, less frequently, by terminating the focal atrial tachycardia.⁴

A discrete P wave with an intervening isoelectric interval strongly suggests a focal atrial tachycardia. However, it is not always possible to definitively distinguish focal from macroreentrant arrhythmias on a surface EKG.⁴

The duration of individual episodes can assist in differentiation; reentrant tachycardias tend to be more sustained than episodes of atrial tachycardia, which may present as a series of repetitive runs.⁴

Focal tachycardias typically exhibit a gradual acceleration ("warm-up" phenomenon) at onset, followed by a deceleration period ("cool-down" phenomenon) prior to termination.^2 4

In the adult population, focal atrial tachycardia is generally associated with a benign prognosis, although atrial tachycardia-mediated cardiomyopathy has been reported in up to 10% of patients. Non-sustained focal atrial tachycardia is common and frequently requires no intervention.³

Multifocal Atrial Tachycardia

Multifocal atrial tachycardia (MAT) is defined as a rapid, irregular rhythm characterized by at least three distinct P-wave morphologies on the surface EKG.⁴

Multifocal atrial tachycardia is commonly associated with underlying comorbidities, such as pulmonary disease, pulmonary hypertension, coronary artery disease, and valvular heart disease, as well as hypomagnesemia and theophylline therapy.⁴

It may also be observed in healthy infants under 1 year of age, carrying an excellent prognosis in the absence of structural heart disease.⁴

Multifocal Atrial Tachycardia:
An irregular tachycardia at 125 bpm with ectopic P waves (negative in lead II).

Differentiating multifocal atrial tachycardia from atrial fibrillation on a surface ECG can be challenging; therefore, a 12-lead ECG is indicated to confirm the diagnosise.⁴

On the electrocardiogram, the atrial rate exceeds 100 bpm and, distinct from atrial fibrillation, a well-defined isoelectric period is present between visible P waves.

The P-P, P-R, and R-R intervals are inherently variable. Although variability in P-wave morphology implies a multifocal origin, very few mapping studies of multifocal atrial tachycardia have been performed.⁴

First-line treatment involves management of the underlying condition. Intravenous magnesium may also be beneficial in patients with normal baseline magnesium levels.³

Antiarrhythmic drugs are generally ineffective in suppressing multifocal atrial tachycardia..³

Electrical cardioversion is typically not effective for multifocal atrial tachycardia.³

Sinus Node Reentrant Tachycardia

Sinus node reentrant tachycardia is an uncommon type of focal atrial tachycardia generated by a microreentrant circuit within the sinoatrial nodal region. This produces a P-wave morphology identical to that of sinus tachycardia, despite not being a true sinus tachycardia.³

The features that distinguish sinus node reentry from sinus tachycardia and inappropriate sinus tachycardia are its paroxysmal nature—demonstrating abrupt onset and termination—and frequently a longer RP interval than that observed during normal sinus rhythm.^3 4

On the electrocardiogram, the polarity and configuration of the P waves are similar to those of sinus P waves.^3 4

Diagnosis of Sinus Node Reentrant Tachycardia

Sinus node reentrant tachycardia is suspected based on surface ECG and Holter monitoring. Diagnosis can be definitively confirmed via an electrophysiology study.⁴

Treatment of Sinus Node Reentrant Tachycardia

Medical therapy remains empirical; verapamil and amiodarona have demonstrated variable success, whereas beta-blockers are typically ineffective.⁴

Sinus node reentrant tachycardia can be safely and effectively treated via catheter ablation targeting the site of earliest atrial activation relative to the P wave.⁴

Atrial tachycardia is a complex arrhythmia that demands a precise diagnostic approach and individualized management.

The electrocardiogram remains the cornerstone of identification, and current guidelines provide a robust framework for its clinical management.