Supraventricular Tachycardias

Supraventricular tachycardias (SVTs) represent a group of cardiac rhythm disorders that require at least one anatomical structure located above the bundle of His for their maintenance.^1 2

They encompass a series of distinct disturbances, the most common being AV nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT) via an accessory pathway, and atrial flutter. This article also covers less common arrhythmias: atrial tachycardia and inappropriate sinus tachycardia.

On the EKG, supraventricular tachycardias are characterized by elevated heart rates, are typically regular, and present with narrow QRS complexes in the majority of cases.^1 2

Although less frequent, wide-QRS supraventricular tachycardias do occur, such as antidromic AVRT via an accessory pathway, or when a bundle branch block or aberrant conduction is present.

By definition, atrial fibrillation is a supraventricular tachycardia, but we prefer to study it individually in a separate article.

Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

Related article: AV Nodal Reentrant Tachycardia..

AV nodal reentrant tachycardia, also known as intranodal tachycardia, is the most common form of paroxysmal supraventricular tachycardia (PSVT) in structurally normal hearts.^1 2 3

Women are more prone to developing AVNRT, and it is most frequently observed in middle-aged individuals, between 40 and 50 years of age.²

It is caused by the presence of dual conduction pathways within the AV node—a fast pathway and a slow pathway—which, upon the occurrence of an atrial premature contraction, initiate a reentrant mechanism that perpetuates the tachycardia.^1 3

Typical AVNRT:
Regular, narrow-QRS tachycardia at 188 bpm.

From an electrophysiological standpoint, three forms of AVNRT are distinguished: the typical form (slow-fast) and the atypical forms (fast-slow and slow-slow).¹

On the electrocardiogram, AVNRT is characterized by:

• A regular, narrow-QRS tachycardia with a heart rate between 120 and 250 bpm.
• Typical Form: Absence of visible P waves, a false r' wave image in lead V1, or a false S wave image in the inferior leads (retrograde P waves masked by the QRS complexes).¹
• Atypical Form: Retrograde P waves are typically observed before the QRS complex (RP interval > PR interval).^1 5 However, in some cases, the PR interval may be longer than the RP interval.⁴

Because it is a supraventricular tachycardia that involves the AV node, termination can typically be achieved via vagal maneuvers or the administration of intravenous adenosine.

Clinical Warning: Intravenous adenosine administration must be performed by experienced medical personnel under continuous patient monitoring.

The definitive treatment for AVNRT is catheter ablation of the slow pathway.

More information: AV Nodal Reentrant Tachycardia.

Atrioventricular Reentrant Tachycardia (AVRT) via an Accessory Pathway

Related article: Pre-excitation Syndromes..

Up to one-third of patients diagnosed with ventricular pre-excitation on a surface electrocardiogram may present with supraventricular tachycardias associated with an accessory pathway.³

These tachycardias are driven by a macroreentrant mechanism involving the atria, the specialized conduction system, the ventricles, and the accessory pathway. The electrical impulse propagates continuously through all of these structures, sustaining the tachycardia.^1 2

Depending on the direction of anterograde and retrograde impulse propagation, two distinctly different electrocardiographic patterns present:

Orthodromic AVRT via an Accessory Pathway:

Orthodromic tachycardia is the most common supraventricular tachycardia in patients with a manifest accessory pathway, accounting for approximately 90% to 95% of episodes.¹

The impulse conducts anterogradely to the ventricles via the normal conduction system (AV node, bundle of His) and returns retrogradely to the atria via the accessory pathway.¹

Because the ventricles are depolarized via the normal conduction system, the QRS complexes are narrow.

Orthodromic AVRT at 250 bpm
Narrow-QRS tachycardia. Retrograde P waves following the QRS are highlighted in red.d.

EKG Characteristics of Orthodromic AVRT:

• Narrow-QRS tachycardia with a heart rate between 200 and 300 bpm.
• Non-sinus (retrograde) P waves can be observed following the QRS complex.

Antidromic AVRT via an Accessory Pathway:

Antidromic tachycardia accounts for approximately 5% of SVT episodes in patients with a manifest accessory pathway.¹

The impulse conducts anterogradely to the ventricles via the accessory pathway and returns retrogradely to the atria via the normal conduction system.¹

Because ventricular depolarization occurs entirely via the accessory pathway, the QRS complex is wide.

Antidromic AVRT presents as a wide-QRS supraventricular tachycardia.

EKG Characteristics of Antidromic AVRT:

• Wide-QRS tachycardia with a heart rate between 200 and 300 bpm
• Absent a prior baseline ECG in sinus rhythm showing pre-excitation, it is difficult to differentiate from ventricular tachycardiaventricular tachycardia.

More information: Pre-excitation Syndromes..

Atrial Flutter

Related article: Atrial Flutter.

Atrial flutter is an arrhythmia caused by a macroreentrant circuit within the atria (most commonly in the right atrium), which self-perpetuates in a circular fashion within the chamber.

There are two main types of atrial flutter: cavotricuspid isthmus (CTI)-dependent atrial flutter, also referred to as typical flutter (classified as counterclockwise or clockwise depending on the direction of the impulse propagation), and atypical or non-CTI-dependent atrial flutter.¹

Typical Atrial Flutter

Typical atrial flutter is readily identifiable on an EKG by its well-defined "sawtooth" F waves. By evaluating the inferior leads, the direction of the macroreentrant circuit can be determined to classify it as counterclockwise or clockwise.^1 2

Counterclockwise typical atrial flutter is the most common presentation.

Typical counterclockwise atrial flutter:
Regular rhythm at 100 bpm with negative F waves in the inferior leads.

In counterclockwise typical flutter, the sawtooth F waves are typically negative in the inferior leads and positive in lead V1, whereas in clockwise (reverse) flutter, they are typically positive in the inferior leads and negative in V1.¹

Atypical Atrial Flutter

The macroreentrant mechanism in atypical flutter does not involve the cavotricuspid isthmus. It can be caused by a wide variety of reentrant circuits, such as those propagating around the mitral valve annulus or areas of scar tissue within the left or right atrium.¹

Atypical atrial flutter:
Regular rhythm at 100 bpm with small F waves resembling P waves, lacking the classic sawtooth morphology.

Electrocardiographically, atypical flutter is more challenging to classify because the ventricular rate is more variable, and the flutter waves on the EKG do not suggest typical circuits—meaning the characteristic "sawtooth" waves are not clearly visualized.^1 2

More information: Atrial Flutter.

Atrial Tachycardia

Related article: Atrial tachycardia.

Atrial tachycardia is an uncommon supraventricular tachycardia. As the name suggests, it originates within the atrial myocardium and does not require the atrioventricular node or the ventricles for its maintenance.^4 6

There are several types of atrial tachycardia, differentiated primarily by their electrophysiological mechanism and clinical presentation. The most clinically relevant are focal atrial tachycardia, multifocal atrial tachycardia, and sinus node reentrant tachycardia.

Focal Atrial Tachycardia

On the EKG, three or more consecutive non-sinus P waves are observed, with an atrial rate typically between 100 and 180 bpm.

A QRS complex follows each P wave, and the QRS complex morphology usually resembles that of a baseline sinus complex unless aberrant ventricular conduction is present.

The rhythm is typically regular, although irregularity can be observed, particularly at onset ("warm-up" phenomenon) and termination ("cool-down" phenomenon) of the tachycardia.^1 2

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

Multifocal Atrial Tachycardia

Multifocal atrial tachycardia is defined as a rapid, irregular rhythm with at least three distinct P-wave morphologies on the surface EKG.²

Multifocal atrial tachycardia is typically associated with underlying comorbidities, such as pulmonary disease, pulmonary hypertension, coronary artery disease, and valvular heart disease, as well as hypomagnesemia and theophylline therapy.²

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 EKG can be challenging; therefore, a 12-lead EKG is indicated to confirm the diagnosis.⁴

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

Sinus Node Reentrant Tachycardia

Sinus node reentrant tachycardia is an uncommon type of focal atrial tachycardia generated by a microreentrant circuit in the region of the sinoatrial node. This produces a P-wave morphology identical to that of sinus tachycardia, despite not being a true sinus tachycardia.¹

The clinical features that distinguish sinus node reentry from sinus tachycardia and inappropriate sinus tachycardia are its paroxysmal nature, characterized by an abrupt onset and termination.^1 2

On the electrocardiogram, the polarity and configuration of the P waves are identical to those of normal sinus P waves.^1 2

More information: Atrial tachycardia.

Inappropriate Sinus Tachycardia

Related article: Inappropriate sinus tachycardia.

Inappropriate sinus tachycardia is an uncommon supraventricular tachycardia caused by an elevated sinus node heart rate at rest or with minimal exertion.^7 8

Sinus tachycardia at 136 bpm

The electrocardiographic features of inappropriate sinus tachycardia are identical to those of classic sinus tachycardia.

Inappropriate sinus tachycardia is more common in young women and is typically highly symptomatic. Diagnosis is established only after ruling out other supraventricular tachycardias as well as secondary causes of sinus tachycardia.

More information: Inappropriate sinus tachycardia.

Summary of Supraventricular Tachycardias

Supraventricular tachycardias are a group of cardiac rhythm disorders that cause regular, narrow-QRS tachycardias in the vast majority of cases.

Mechanistically, the maintenance of the arrhythmia requires the participation of at least one structural component located above the bundle of His.

They generally carry a benign prognosis, though they tend to be highly symptomatic with frequent recurrences.

While medical management with antiarrhythmic drugs is often effective, catheter ablation offers a definitive cure with excellent success rates, making it the clinical treatment of choice in modern practice.

We hope this article has helped expand your clinical knowledge of supraventricular tachycardias.