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Rapid Review·Cardiovascular

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Arrhythmias: Supraventricular

T1Must know

AV Nodal Reentrant Tachycardia

Focus on

The most common paroxysmal SVT: a young adult with abrupt-onset palpitations, a regular narrow tachycardia at 150–220 with no visible P waves, stopped by a Valsalva or by adenosine. Cardiovert if unstable; slow-pathway ablation cures recurrent episodes.

Key takeaways

What it is and how it works

AV nodal re-entrant tachycardia (AVNRT)

the most common paroxysmal supraventricular tachycardia, from a re-entry circuit inside a dysfunctional atrioventricular (AV) node.
  • AV re-entrant tachycardia (via an accessory pathway) is the second most common.

Who

idiopathic, usually starting in young adulthood.
AV nodal re-entrant tachycardia. Top: in sinus rhythm the impulse runs down the fast pathway (long refractory period), and the slow-pathway impulse is blocked. Bottom: a premature atrial beat finds the fast pathway still refractory, goes down the slow pathway, returns up the fast pathway (the P wave buried in the QRS), and the circuit keeps itself going.
What this shows
AV nodal re-entrant tachycardia. Top: in sinus rhythm the impulse runs down the fast pathway (long refractory period), and the slow-pathway impulse is blocked. Bottom: a premature atrial beat finds the fast pathway still refractory, goes down the slow pathway, returns up the fast pathway (the P wave buried in the QRS), and the circuit keeps itself going.

Mechanism

a loop between two pathways inside the node.
  • Two pathways: a fast pathway with a long refractory period and a slow pathway with a short one.
  • Normal beats: the fast pathway conducts, and the slow impulse dies against the refractory fast pathway.
  • A premature atrial beat: arrives while the fast pathway is still refractory, so it goes down the slow pathway.
  • The loop: it returns up the fast pathway, and a re-entrant loop starts.
  • The hidden P wave: the atria depolarize retrogradely, almost together with the ventricles, so the P wave hides in the QRS.

Clinical features and diagnosis

Paroxysms with abrupt onset and abrupt end

palpitations, dizziness, presyncope, chest discomfort, diaphoresis, dyspnea.
  • Syncope is uncommon and mostly in older adults.

Electrocardiogram (ECG)

a regular narrow-complex tachycardia at 150 to 220 with no visible P waves or retrograde P waves, as in the AVNRT ECG pattern.
  • The ECG may be normal between episodes.

Inconclusive ECG

a Holter or event recorder over 24 to 48 hours.

Management

Unstable

immediate synchronized cardioversion.

Stable

in order.
  • Vagal maneuvers: Valsalva, carotid sinus massage, the diving reflex; they raise parasympathetic tone and prolong AV nodal refractoriness.
  • Intravenous adenosine: beta blockers and calcium-channel blockers are the alternatives.

Infrequent mild episodes

self-guided vagal maneuvers.

Frequent episodes

catheter ablation of the slow pathway first line; a beta blocker, verapamil or diltiazem second line.
A 26-year-old woman has sudden palpitations; she is stable, and the ECG shows a regular narrow-complex tachycardia at 190 with no visible P waves. What are the first two steps, and what is the long-term fix if episodes are frequent?

AV nodal re-entrant tachycardia. First vagal maneuvers, then intravenous adenosine. Frequent episodes: catheter ablation of the slow pathway.

How it's tested

A 26-year-old woman with sudden palpitations; ECG shows a regular narrow tachycardia at 190 with no P waves; BP 115/75: AVNRT — modified Valsalva, then adenosine.

Same rhythm with BP 70/40: synchronized cardioversion.

Adenosine transiently slows the rate and sawtooth waves appear before it speeds back up: atrial flutter, not AVNRT.

Third episode this year despite metoprolol: catheter ablation of the slow pathway.

Regular narrow tachycardia in a patient with a known delta wave on his resting ECG: orthodromic AVRT — same acute treatment (vagal, adenosine) because the AV node is part of the circuit.

Go deeper

Guidelines: 2015 ACC/AHA/HRS Supraventricular Tachycardia Guideline · 2025 AHA Adult Advanced Life Support Guidance

Related Step 2 pages: Approach to Tachyarrhythmias, Wolff-Parkinson-White Syndrome, Atrial Flutter, Sinus Tachycardia, Antiarrhythmic Drugs

High-yield images2
AV nodal re-entrant tachycardia. Top: in sinus rhythm the impulse runs down the fast pathway (long refractory period), and the slow-pathway impulse is blocked. Bottom: a premature atrial beat finds the fast pathway still refractory, goes down the slow pathway, returns up the fast pathway (the P wave buried in the QRS), and the circuit keeps itself going.
A regular narrow tachycardia with P waves hidden in or immediately after the QRS complex is typical of AVNRT.
PreviousMultifocal Atrial TachycardiaNextWolff-Parkinson-White Syndrome

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