Supraventricular Tachycardia (SVT)

SVT is a narrow complex tachycardia (usually QRS <120ms) with regular rhythm and rate typically 140–280bpm. Most commonly AVNRT (re-entry via AV node). Key decision: is the patient haemodynamically stable? Stable → vagal manoeuvres then adenosine…

Resuscitation Council SVT Algorithm

The pathway

1 · Confirm SVT

12-lead ECG: narrow complex, regular, rate >100. Exclude: VT (broad complex, irregular, fusion beats), AF (irregular), flutter (saw-tooth P waves). Check BP, SpO₂, conscious level.

2 · Vagal manoeuvres

Valsalva manoeuvre first: patient blows hard into 10ml syringe for 15 seconds while supine, then legs raised 45° for 15 seconds (modified Valsalva — 43% success). Carotid sinus massage: only if no carotid bruits, age <65, no TIA/stroke history. 30% success.

3 · Adenosine

If vagal manoeuvres fail: adenosine 6mg rapid IV bolus into large antecubital vein, followed by 20ml saline flush immediately. Patient will feel chest tightness/flushing — warn them. If no response after 1–2 min: 12mg. Repeat 12mg once if required. Maximum 3 doses. CI: asthma, WPW.

4 · Adenosine fails or CI

Verapamil 5mg IV over 2 min (not if on beta-blocker — risk of complete AV block). Or metoprolol 5mg IV slowly. Or DC cardioversion if haemodynamically compromised at any point.

5 · Haemodynamically unstable

SBP <90, chest pain, reduced consciousness → DO NOT give adenosine. Synchronised DC cardioversion 100–200J. Sedate with IV midazolam 2.5–5mg if time allows. Call for help immediately.

6 · Post-cardioversion

12-lead ECG in sinus rhythm. Look for delta waves (WPW). If WPW: refer cardiology urgently — avoid AV nodal blocking drugs in future. All patients with first SVT need cardiology follow-up. Consider long-term prophylaxis if recurrent.

Drugs

Drug	Dose	Route	Notes
Adenosine	6mg → 12mg → 12mg	IV rapid bolus	Must be followed immediately by 20ml saline flush. Warn about transient chest tightness.
Verapamil	5mg over 2 min	IV	Do NOT use if on beta-blockers. Do NOT use in broad complex tachycardia.
Metoprolol	5mg over 2 min	IV	Alternative to verapamil. May repeat x2.
Midazolam	2.5–5mg	IV	Sedation before DC cardioversion if time allows.

When to escalate

Haemodynamic instability at any point → DC cardioversion immediately,Broad complex tachycardia — treat as VT until proven otherwise,WPW on post-cardioversion ECG → urgent cardiology referral,Refractory SVT not responding to adenosine + verapamil → cardiology,SVT in pregnancy → seek obstetric and cardiology input before adenosine

Reference: Resuscitation Council UK Advanced Life Support 7th Edition / ESC 2019

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