Atrioventricular Nodal Reentrant Tachycardia AVNRT ❤️

Related Subjects: |Wolff-Parkinson White syndrome (WPW) AVRT |Lown Ganong Levine Syndrome AVRT |Supraventricular Tachycardia (SVT) |Atrioventricular Nodal Reentrant Tachycardia AVNRT |Atrial Flutter |Atrial Fibrillation |Sinus Tachycardia |Sinus Arrhythmia |Multifocal Atrial Tachycardia |Resuscitation - Adult Tachycardia Algorithm

📖 About

• Any tachycardia arising from above the level of the Bundle of His.
• Usually refers to reentrant tachycardias around the AV node (AVNRT).
• When the reentry pathway is beyond the node = AVRT (e.g., WPW, Lown-Ganong-Levine).

🧬 Aetiology of AVNRT

• Requires 2 pathways (dual physiology) around the AV node:
• ⚡ Slow pathway: short refractory period.
• ⚡ Fast pathway: long refractory period.
• An atrial ectopic impulse may travel down the slow and retrogradely up the fast pathway → like a “🎆 Catherine wheel firework”.

📊 Classification

• 🔹 Slow–Fast (≈90%, RP′ < P′R).
• 🔹 Fast–Slow (≈10–15%, RP′ > P′R).
• 🔹 Slow–Slow (<5%).

🖼️ Diagram showing AVNRT

• Occurs at any age; benign; more common in young females (2:1 ratio).
• Symptoms: palpitations, presyncope, breathlessness, dizziness, chest pain.
• Can be misdiagnosed as a panic attack (often delayed diagnosis).
• Triggers: stress, caffeine, alcohol, smoking, drugs.

🔍 Investigations

• Bloods: FBC, U&E, TFTs, LFTs. CXR.
• 12-lead ECG during episode: narrow complex tachycardia 120–240 bpm. May mimic VT if bundle branch block present.
• Implantable loop recorder if transient/undocumented episodes.
• Echo: exclude structural disease.
• Rarely: check for phaeochromocytoma if hypertension present.

💡 Clinical Pearls

• ⚡ Sudden onset/offset → suggests PSVT.
• 👔 “Shirt flapping” or “neck pounding” → highly suggestive of AVNRT.
• 🚨 Hypotension/syncope → poorly tolerated → urgent treatment/referral.
• Structural heart disease → consider atrial tachycardia.
• Pre-excitation (AVRT/WPW) → refer for specialist ablation.

📸 Examples

• 🛑 If unstable → immediate DC cardioversion.
• Stable:
  • ✅ Vagal manoeuvres (Valsalva, carotid sinus massage).
  • ✅ IV adenosine (6–24 mg rapid bolus). Warn about transient unpleasant sensations.
  • ✅ IV verapamil (2.5–5 mg slow IV) or diltiazem (if narrow complex only).
• ⚠️ If broad-complex SVT (aberrancy or accessory pathway) → get urgent expert advice. Avoid verapamil/diltiazem if pre-excited AF suspected.
• Pre-excited AF (AVRT): avoid AV nodal blockers (adenosine, digoxin, β-blockers, calcium blockers). Use IV flecainide/propafenone/amiodarone or cardioversion if unstable.
• 📅 Long-term: refer to electrophysiology for catheter ablation (high cure rates, low risk).

📚 References

• ACC SVT Toolkit
• AAFP: Common Types of SVT – Diagnosis & Management

Cases - AVNRT with Acute Management

• Case 1 - Young Woman with Palpitations: A 26-year-old woman presents to A&E with sudden-onset palpitations, HR 180 bpm, BP 120/70, regular narrow-complex tachycardia on ECG. Management: She is stable → start with modified Valsalva manoeuvre (reverts to sinus rhythm). Observe and discharge with cardiology follow-up. Education on avoiding triggers (caffeine, alcohol).
• Case 2 - Middle-aged Man with Dizziness: A 48-year-old man arrives with palpitations and dizziness. HR 170 bpm, BP 115/70, regular narrow-complex tachycardia. Vagal manoeuvres fail. Management: Give adenosine IV 6 mg rapid bolus → no effect. Repeat 12 mg → tachycardia terminates, sinus rhythm restored. Monitor in ED, advise GP/cardiology follow-up. If recurs frequently → consider prophylaxis or ablation.
• Case 3 - Elderly Patient with Chest Pain and Hypotension: A 70-year-old woman with history of hypertension presents with palpitations, chest pain, and lightheadedness. HR 190 bpm, BP 80/50. ECG: narrow-complex tachycardia. Management: She is unstable → immediate synchronised DC cardioversion. Once stabilised, admitted under cardiology, plan for further evaluation and long-term management (beta-blocker vs catheter ablation depending on comorbidities).

Teaching Commentary ⚡

These three cases highlight the spectrum: - Stable + young → vagal manoeuvres often suffice. - Stable but symptomatic → escalate to adenosine, with verapamil or beta-blocker as alternatives. - Unstable → don’t delay: immediate DC cardioversion. Always remember adenosine is contraindicated in asthma/COPD and should be avoided in patients on dipyridamole or with transplanted hearts (increased sensitivity). Long-term, radiofrequency ablation of the slow pathway is curative in most patients.