Makindo Medical Notes

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 |Resuscitation - Advanced Life Support

⚡ Supraventricular Tachycardia (SVT) is a group of rapid heart rhythms originating above the ventricles (atria or AV node). 🫀 While usually benign, it can cause distressing symptoms (palpitations, dizziness, syncope) and occasionally serious complications. 🎯 Correct diagnosis and management are essential to relieve symptoms and prevent adverse outcomes.

📌 About

• SVT = any tachycardia arising from above the Bundle of His.
• Mainly includes reentrant tachycardias such as AVRT and AVNRT.
• 🚶 Generally benign, but can mimic panic attacks and be disabling.
• 💉 Often curable with catheter ablation, especially in Wolff-Parkinson-White (WPW).

🔄 Aetiology of Reentrant SVT

• Needs two pathways (fast vs slow) ➝ reentrant circuit 🔄 like a Catherine wheel firework 🎆.
• Pathway properties:
• 🐢 Slow Pathway: Long refractory period.
• 🐇 Fast Pathway: Short refractory period.
• Classifications:
• ✅ Slow-Fast AVNRT: Most common (>90%).
• ⚡ Fast-Slow AVRT: 10–15%.
• 🔸 Slow-Slow AVRT: Rare (<5%).

📊 Diagram – Pathways of AVRT and AVNRT

📖 Definition Includes

• ❤️ Sinus Tachycardia – from sinus node.
• ⚡ Atrial Tachycardia – ectopic atrial focus.
• 🎯 Multifocal Atrial Tachycardia – multiple atrial foci.
• ♻️ Atrial Fibrillation – chaotic atrial activity.
• 🔄 Atrial Flutter – reentry circuit, regular.
• But in practice, “SVT” usually means:
  • AVNRT
  • AVRT (often with WPW)

🧑‍⚕️ Clinical Features

• Seen in all ages; more common in women (M:F ~1:2).
• Symptoms:
  • 💓 Palpitations
  • 😵 Dizziness/lightheadedness
  • 🫁 Dyspnoea
  • 💢 Chest pain
  • 💫 Syncope/presyncope
• Common triggers: ☕ caffeine, 🍷 alcohol, 🚬 smoking, stress, 💊 drugs.

🔍 Investigations

• 📊 ECG: Key test. Narrow complex tachycardia (120–240 bpm), may mimic VT if bundle branch block.
• 📈 Holter / Event Recorder: For transient episodes.
• 🧪 Labs: FBC, U&E, TFTs, LFTs.
• 🫀 Echocardiogram: Rule out structural disease.
• 🩻 CXR: Exclude lung causes if relevant.
• Consider 💡 pheochromocytoma if hypertension + SVT (rare).

💡 Clinical Pearls

• ⏱️ Sudden onset + sudden termination → classic PSVT.
• 👕 “Shirt-flapping” or “neck pounding” → highly suggestive of AVNRT.
• ⚠️ Hypotension/syncope → unstable → urgent treatment/referral.
• 🩺 WPW with delta waves → high risk ➝ ablation referral.

📊 Examples

🛠️ Management

• 🚑 Initial Assessment: ABC, IV access, urgent DC cardioversion if unstable.
• 🙂 Stable SVT:
  • 🙌 Vagal manoeuvres (Valsalva, carotid sinus massage, cold water face immersion).
  • 💉 If fails → IV Adenosine (6 mg, then 12 mg if needed; warn about flushing & chest tightness).
• 💊 Drugs:
  • 📉 Calcium channel blockers (IV verapamil, diltiazem).
  • 🛡️ Beta-blockers in some cases (avoid in WPW + AF).
  • ⚡ Amiodarone for broad/unstable SVT.
• ❌ Special Situations:
  • WPW + AF ➝ avoid AV nodal blockers (adenosine, beta-blocker, digoxin, verapamil) ➝ use flecainide/propafenone/amiodarone or cardiovert.
• 🏥 Long-term:
  • Electrophysiology referral for ablation in recurrent cases.
  • Nodal ablation as last resort.

📚 References

• American College of Cardiology – SVT Toolkit
• AAFP – SVT: Diagnosis and Management