SVT & Tachyarrhythmias

Tachyarrhythmias are a very common on-call review in NHS hospitals.
You’ll often be called for:

“Patient tachycardic HR 160 — ?SVT”

Your role is not to memorise every rhythm — it is to:

👉 recognise dangerous patterns
👉 assess stability
👉 treat safely using a structured approach
👉 escalate appropriately

Most errors happen from treating before assessing stability.

What do we mean by SVT?

Supraventricular tachycardia (SVT) refers to rapid rhythms originating above the ventricles.

Common types you’ll encounter:

  • AVNRT (most common true SVT)
  • AVRT (e.g. WPW-related)
  • Atrial tachycardia
  • Fast AF/flutter (often mistaken as SVT)

Typical rate:
👉 150–220 bpm

First question always: Stable or unstable?

Before analysing ECG:

🚨 Signs of instability

  • Hypotension
  • Chest pain
  • Pulmonary oedema
  • Syncope/reduced consciousness
  • Shock

👉 Immediate DC cardioversion
(Call senior / crash team)

Do NOT delay for drugs.

Stable tachycardia — structured approach

Use this simple framework:

1️⃣ Confirm rhythm (ECG)
2️⃣ Narrow or wide complex?
3️⃣ Regular or irregular?
4️⃣ Treat accordingly

ECG classification (practical on-call method)

Narrow complex (<120 ms)

Regular → likely SVT

  • AVNRT
  • AVRT
  • Atrial tachycardia

Irregular → usually AF/flutter

Wide complex (>120 ms)

Assume:
👉 Ventricular Tachycardia (VT) until proven otherwise

Especially in older or cardiac patients.

Never assume SVT with aberrancy first.

Stable narrow-complex regular tachycardia (classic SVT)

Step 1 — Vagal manoeuvres

Try first.

Examples:

  • Modified Valsalva (REVERT technique)
  • Carotid sinus massage (only if trained & no carotid disease)

Often works surprisingly well.

Step 2 — Adenosine

If vagal manoeuvres fail:

Adenosine 6 mg rapid IV push
→ flush immediately

If unsuccessful:

  • 12 mg
  • then 12 mg again

Must be given via large vein + rapid flush.

Warn patient:
“brief chest tightness / flushing”.

Contraindications

Avoid or senior discussion if:

  • Severe asthma
  • Irregular rhythm (likely AF)
  • Known WPW with AF

If adenosine works

You may see:

  • transient asystole (normal)
  • rhythm converts to sinus
  • underlying rhythm revealed

Document ECG before & after.

Wide complex tachycardia

Treat as VT unless proven otherwise.

Management:

  • Senior help early
  • Amiodarone (if stable, specialist-led)
  • Prepare for cardioversion

Never give AV nodal blockers blindly.

Common triggers on wards

Always search for cause:

  • Sepsis
  • Electrolyte imbalance
  • Hypoxia
  • Pain/anxiety
  • Stimulants
  • Post-operative stress
  • Ischaemia

Correcting physiology prevents recurrence.

When to escalate urgently

  • Uncertain rhythm
  • Wide complex tachycardia
  • HR >180 persistent
  • Haemodynamic instability
  • Recurrent episodes
  • Structural heart disease

If unsure → escalate early.

Common on-call mistakes

  • Giving adenosine to irregular rhythm
  • Missing VT
  • Treating monitor reading without ECG
  • Skipping vagal manoeuvres
  • Not documenting rhythm strips
  • Forgetting underlying cause

Always print the ECG.

Practical bedside mindset

When bleeped:

“HR 170 ?SVT”

Think:

  1. Stable?
  2. Narrow or wide?
  3. Regular?
  4. Vagal manoeuvre
  5. Adenosine if appropriate
  6. Escalate if uncertain

Simple algorithm prevents panic.

Take-home concept

Tachyarrhythmia management is about pattern recognition and stability assessment, not perfect ECG expertise.

If unstable → shock.
If stable SVT → vagal → adenosine.
If wide complex → treat as VT.