Supraventricular Tachycardia (AVNRT / AVRT)

Risk factors

• AVNRT: most often no structural heart disease; female sex; triggers include stress, caffeine, alcohol, stimulants
• AVRT: accessory pathway is congenital; WPW prevalence ~1-3 per 1000
• Associations: Ebstein anomaly (right-sided pathways), hypertrophic cardiomyopathy
• Hyperthyroidism, fever, dehydration, stimulant use as triggers

Pathophysiology

AVNRT: dual AV nodal pathways (slow + fast) create a microreentry circuit confined to the AV node. Typical (slow-fast) form — antegrade slow, retrograde fast — has retrograde P waves buried in or just after the QRS. AVRT: macroreentry involves AV node and an accessory pathway. Orthodromic AVRT (antegrade through AV node, retrograde through accessory) is narrow QRS; antidromic AVRT (antegrade through accessory, retrograde through AV node) is wide QRS.

Clinical presentation

Differential diagnosis

• Sinus tachycardia — Rate <160, P waves identical to sinus, gradual onset/offset, identifiable trigger (fever, anemia, hypovolemia)
• Atrial fibrillation — Irregularly irregular without discrete P waves
• Atrial flutter — Sawtooth flutter waves, ventricular response often 150 from 2:1 conduction; consider flutter in any HR 150
• Atrial tachycardia — P-wave morphology different from sinus, may be incessant
• Multifocal atrial tachycardia — ≥3 P-wave morphologies in patient with COPD
• Junctional tachycardia — Narrow QRS without distinct P waves; rare in adults outside of post-cardiac surgery and digoxin toxicity
• VT or SVT with aberrancy — Wide QRS — see VT entry for distinguishing features

Diagnostic workup

Diagnostic algorithm

flowchart TD
  A[Regular narrow-complex<br/>tachycardia 150-220 bpm] --> B{Hemodynamically<br/>stable?}
  B -->|No| C[Synchronized<br/>cardioversion 50-100 J]
  B -->|Yes| D[Vagal maneuvers<br/>modified Valsalva]
  D --> E{Converted?}
  E -->|No| F[Adenosine 6 mg<br/>then 12 mg × 2]
  E -->|Yes| G[Identify SVT type<br/>on 12-lead]
  F --> H{Converted?}
  H -->|No| I[IV diltiazem or<br/>metoprolol]
  H -->|Yes| G
  G --> J{Recurrent or<br/>symptomatic?}
  J -->|Yes| K[Catheter ablation<br/>>95% cure for AVNRT/AVRT]
  J -->|No| L[Reassurance, vagal<br/>maneuvers PRN]

Treatment

Complications

• Hemodynamic compromise during sustained tachycardia
• Tachycardia-mediated cardiomyopathy with persistent or frequent arrhythmia
• WPW: pre-excited atrial fibrillation degenerating to ventricular fibrillation (rare but dreaded)
• Ablation complications: AV block (typical AVNRT ablation), cardiac tamponade, vascular access, stroke (left-sided ablation)

PANCE pearls

• Adenosine has a half-life of ~10 seconds — must push fast and flush; warn patient about chest pressure and impending doom feeling.
• AVOID adenosine and all AV nodal blockers in pre-excited atrial fibrillation (WPW + irregular wide complex) — use procainamide or DC cardioversion.
• AVNRT pseudo-R' in V1 and pseudo-S in inferior leads compared to sinus rhythm tracing is highly suggestive.
• Modified Valsalva (REVERT trial — passive leg raise after strain) converts >40% of SVT vs ~17% with standard Valsalva.
• Catheter ablation is curative for AVNRT and AVRT and is offered as first-line for any recurrent or symptomatic case.

Images

References

• ACC/AHA/HRS 2015 SVT — 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients With Supraventricular Tachycardia (Page et al., Circulation 2016)
• ESC 2019 SVT — 2019 ESC Guidelines for the Management of Patients with Supraventricular Tachycardia (Brugada et al., Eur Heart J 2020)
• REVERT Trial — Postural Modification to the Standard Valsalva Manoeuvre for Emergency Treatment of Supraventricular Tachycardias (Appelboam et al., Lancet 2015)