Cardiovascular · Topic 17 of 48

Supraventricular Tachycardia (AVNRT/AVRT)

Cardiovascular · narrow-complex tachycardia

Supraventricular Tachycardia (AVNRT/AVRT)

A reentrant regular narrow-complex tachycardia. Stable: vagal maneuvers, then adenosine 6 then 12 mg. Unstable: synchronized cardioversion.

Key numbers

Regular narrow tachycardia with abrupt onsetQRS < 0.12 s

Unstable: synchronized cardioversion, 100 J100 J synchronized

Adenosine 6 mg, then 12 mg6 mg → 12 mg IV push

01 · DoStable: vagal maneuvers first

In a stable patient, start with vagal maneuvers; a modified Valsalva (strain, then lie flat with the legs raised) terminates up to 50% of episodes versus 20–30% for standard Valsalva.

02 · GiveAdenosine 6 mg, then 12 mg

If vagal maneuvers fail, give adenosine 6 mg by rapid IV push with an immediate saline flush; if the rhythm persists, give 12 mg.

03 · DoUnstable: synchronized cardioversion, 100 J

If the tachycardia causes hypotension, acute altered mental status, shock, ischemic chest pain or acute heart failure, perform synchronized cardioversion now; the 2025 AHA initial energy for narrow-complex tachycardia is 100 J.

Presentation

What you'll see

AVNRT: P hidden or pseudo-R′ in V1In typical AVNRT the retrograde P wave hides in or at the end of the QRS (pseudo-R′ in V1); in orthodromic AVRT the P wave always follows the QRS — both are short-RP tachycardias.

Diagnosis & monitoring

Work-up

Regular narrow tachycardia with abrupt onset must knowReentrant SVT is a sudden-onset, sudden-offset, regular narrow-QRS (< 0.12 s) tachycardia of 120–250 bpm; AVNRT (50–60%) is most common, then AVRT over an accessory pathway (20–30%).

Do right now

In this order

First moves

Unstable: synchronized cardioversion, 100 J100 J synchronized

→

Stable: vagal maneuvers first

→

Adenosine 6 mg, then 12 mg6 mg → 12 mg IV push

→

Next: IV diltiazem or verapamil

Why each step

Unstable: synchronized cardioversion, 100 JIf the tachycardia causes hypotension, acute altered mental status, shock, ischemic chest pain or acute heart failure, perform synchronized cardioversion now; the 2025 AHA initial energy for narrow-complex tachycardia is 100 J.

Stable: vagal maneuvers firstIn a stable patient, start with vagal maneuvers; a modified Valsalva (strain, then lie flat with the legs raised) terminates up to 50% of episodes versus 20–30% for standard Valsalva.

Adenosine 6 mg, then 12 mgIf vagal maneuvers fail, give adenosine 6 mg by rapid IV push with an immediate saline flush; if the rhythm persists, give 12 mg.

Next: IV diltiazem or verapamilIf adenosine fails or SVT recurs, give IV diltiazem 0.25 mg/kg or verapamil 5 mg slowly (or an IV beta-blocker); avoid diltiazem and verapamil when systolic heart failure is suspected.

Management

Orders

Refer recurrent SVT for catheter ablationFor frequent or bothersome episodes, catheter ablation is the preferred, usually curative treatment; oral AV-nodal blockers are the alternative, but never alone in manifest WPW.

Red flags & don'ts

Avoid harm

No adenosine in AV block or bronchospasm avoidAdenosine is contraindicated in second- or third-degree AV block or sick sinus syndrome without a functioning pacemaker, and should be avoided in active bronchospasm such as asthma.

Reduce adenosine: central line, transplant, dipyridamole interactionAdenosine acts more strongly through a central line, after heart transplant (as little as 1 mg may work) and with dipyridamole; caffeine and theophylline blunt its effect.

Avoid carotid massage with carotid atherosclerosis avoidCarotid sinus massage is a vagal option, but it can precipitate a stroke in patients with carotid atherosclerosis.

The rules

Know these

Wide-complex tachycardia: treat as VTA wide-QRS tachycardia is treated as ventricular tachycardia unless known to be SVT with aberrancy; verapamil and diltiazem are harmful in undifferentiated wide-complex tachycardia.

Cardiovert only rhythm-caused instabilityCardiovert only when the tachycardia is causing the instability, not when it is a response to another illness (for example, sinus tachycardia in sepsis).

AVNRT or orthodromic AVRT?

Commonly confused

Circuit	Slow and fast pathways within the AV node
Retrograde P wave	Hidden in the QRS or a pseudo-R′ in V1
Typical patient	More often women, 20s–30s
Usual rate	150–200 bpm
Acute treatment	Vagal maneuvers, then adenosine

Commonly confused

Tell apart

Adenosine unmasks flutter and atrial tachycardiaWhen adenosine causes transient AV block without terminating the rhythm, previously hidden flutter waves or atrial P waves appear, revealing atrial flutter or atrial tachycardia rather than AV-node-dependent SVT.

Teach & follow up

Patient education

Warn of flushing, dread and a brief pauseWarn the patient before adenosine: flushing and a feeling of dread are expected, and a 2–3-second period of cardiac standstill may occur before the rhythm converts.

More detail

Reference

Show 6 reference facts

Typical (slow-fast) AVNRT, about 90% of AVNRT, conducts down the slow AV-nodal pathway and up the fast one; orthodromic AVRT (about 95% of AVRT) conducts down the AV node and up the accessory pathway.

Typical AVNRT patients are more often women presenting in their 20s–30s at 150–200 bpm; orthodromic AVRT patients are more often men presenting in their teens–20s at 180–220 bpm.

Termination of the tachycardia with a P wave as the final event argues against an atrial tachycardia, because AV-node-dependent circuits stop when one AV-nodal transmission is blocked.

Permanent junctional reciprocating tachycardia, a near-incessant long-RP AVRT over a slowly conducting concealed pathway, can cause tachycardia-induced cardiomyopathy and heart failure.

Adenosine has a half-life of under 10 seconds and may be less effective through a peripheral vein; inject it as close to the patient as possible, followed immediately by a rapid saline flush.

Patients with recurrent SVT can be taught vagal maneuvers (Valsalva, ice-cold water to the face) to use at home early in an episode.

Pearl

Regular, narrow and abrupt: vagal first, then adenosine 6 then 12 — and if the rhythm is causing instability, shock it.

Sources · Merck Manual Professional — Reentrant (Paroxysmal) Supraventricular Tachycardias (PSVT) · 2025 AHA Guidelines for CPR and ECC — Part 9: Adult Advanced Life Support (Circulation 2025; doi 10.1161/CIR.0000000000001376), cpr.heart.org text · AHA 2025 Interim Training Materials — ACLS Provider Manual changes (synchronized cardioversion energies) · AHA 2025 ACLS algorithms poster set (Adult Tachyarrhythmia With a Pulse and Adult Bradycardia With a Pulse — doses/details), international edition · Adenosine injection (antiarrhythmic) prescribing information — DailyMed · Merck Manual Professional — Overview of Arrhythmias · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).