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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
Key points
- SVT = regular narrow-complex tachycardia (rate 140–250 bpm, QRS <120 ms)
- Most common types: AVNRT (60%), AVRT (30%, includes WPW syndrome), atrial tachycardia
- First-line: vagal manoeuvres (Valsalva, carotid sinus massage). Second-line: IV adenosine 6 mg rapid bolus → 12 mg → 12 mg
- If haemodynamically unstable → synchronised DC cardioversion
- Definitive treatment for recurrent SVT: catheter ablation (curative in >95%)
Overview
Supraventricular tachycardia (SVT) refers to any tachyarrhythmia originating from above the bundle of His, producing a narrow-complex (QRS <120 ms) regular tachycardia on ECG. The most common mechanisms are AVNRT (re-entrant circuit within the AV node) and AVRT (re-entrant circuit using an accessory pathway — including Wolff-Parkinson-White syndrome). Atrial tachycardia and atrial flutter are also technically SVTs. Episodes are typically paroxysmal, with sudden onset and offset. Most SVTs are not life-threatening but cause significant symptoms and anxiety.
Epidemiology
SVT affects approximately 2.3 per 1,000 population. AVNRT is more common in women (2:1). AVRT/WPW is more common in men. SVT can present at any age but typically begins in the 20s–30s. WPW syndrome has a small but real risk of sudden death if AF develops with rapid conduction via the accessory pathway. Most patients have structurally normal hearts.
Clinical Features
Symptoms
Sudden-onset palpitations — regular, rapid, "like a machine gun"
Sudden offset (may terminate with vagal manoeuvres)
Dizziness or lightheadedness
Dyspnoea and chest tightness
Polyuria during or after episode (ANP release)
Syncope (uncommon, suggests very fast rate or underlying structural disease)
Signs
Regular rapid pulse (140–250 bpm)
Hypotension (if prolonged or very fast)
Cannon A waves in JVP (if AV dissociation present — more suggestive of VT)
May terminate spontaneously during examination
Investigations
First-line
12-lead ECG during tachycardiaRegular narrow-complex tachycardia. AVNRT: P waves buried in QRS or just after (pseudo-r' in V1, pseudo-S in inferior leads). AVRT: retrograde P waves after QRS
Resting 12-lead ECG (sinus rhythm)Look for delta wave + short PR interval = WPW pattern (pre-excitation). Normal in AVNRT
Second-line
Ambulatory ECG monitoringIf episodes not captured on resting ECG — 24h Holter or event recorder
BloodsTFTs (exclude thyrotoxicosis), FBC, U&Es, Mg²⁺
EchocardiographyExclude structural heart disease (usually normal in SVT)
Specialist
Electrophysiology study (EPS)Definitive mapping of re-entrant circuit. Usually performed with catheter ablation as a combined diagnostic-therapeutic procedure
1
Acute termination
- Vagal manoeuvres first: modified Valsalva (blow into syringe for 15 s, then lie flat and passively raise legs) or carotid sinus massage
- If vagal manoeuvres fail: IV adenosine 6 mg rapid bolus into large (antecubital) vein with immediate 20 mL saline flush
- If no effect after 1–2 min: adenosine 12 mg IV, then repeat 12 mg if needed
- Warn patient: transient chest tightness, flushing, sense of impending doom (lasts <30 seconds)
- Contraindications to adenosine: asthma (severe bronchospasm), heart transplant (use lower dose)
- Alternative: IV verapamil 5 mg (if no beta-blocker, not in WPW) or IV beta-blocker
2
Haemodynamically unstable
- Synchronised DC cardioversion under sedation
3
Prevention of recurrence
- Pill-in-pocket verapamil or flecainide for infrequent episodes
- Regular beta-blocker or verapamil for frequent episodes
- Catheter ablation — definitive cure, >95% success rate for AVNRT and AVRT. Recommend for recurrent symptomatic SVT
4
WPW with AF — special consideration
- Avoid AV-nodal blocking drugs (adenosine, verapamil, digoxin, beta-blockers) — can facilitate conduction via accessory pathway → VF
- Use flecainide or procainamide, or DC cardioversion
- Definitive: catheter ablation of accessory pathway
Complications
- Haemodynamic compromise: Syncope, hypotension (rare with SVT unless very fast or underlying cardiac disease)
- Tachycardia-mediated cardiomyopathy: Persistent tachycardia → reversible LV dysfunction
- WPW + AF → VF: Potentially fatal if AF conducts rapidly via accessory pathway (pre-excited AF)
- Anxiety and quality of life: Recurrent episodes significantly impact daily living
UKMLA Exam Tips
- 1Regular narrow-complex tachycardia + sudden onset/offset = SVT (contrast with AF which is irregularly irregular)
- 2Adenosine dose: 6 mg → 12 mg → 12 mg. Must be rapid IV bolus with saline flush. Warn about transient side effects
- 3Delta wave on baseline ECG = WPW → NEVER give adenosine, verapamil, or digoxin in AF with WPW
- 4Modified Valsalva (blow + legs up) has higher success rate than standard Valsalva
- 5Catheter ablation is curative in >95% — the definitive treatment for recurrent SVT
- 6Polyuria after SVT = ANP release from atrial stretch — a classic clinical vignette
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