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Supraventricular tachycardia and WPW
A regular narrow-complex tachycardia in a stable patient is treated in a fixed order — vagal manoeuvre, adenosine, then an AV-node blocker — and in an unstable patient by electrical cardioversion; the long-term answer is ablation.
Why it matters in the exam
SVT questions usually show a young patient with palpitations that start and stop abruptly and an ECG with a narrow, regular QRS at 150–250 per minute. The question asks for the first step (a vagal manoeuvre, including the modified Valsalva with the patient laid flat and legs raised), the adenosine dose and its side effects (flushing, chest tightness, brief asystole, transient AF), and when adenosine is forbidden — severe asthma and atrial fibrillation with WPW.
For WPW candidates must recognise on the resting ECG a PR shorter than 120 ms, a delta wave and a wide QRS, and understand the difference between orthodromic AVRT (narrow QRS) and atrial fibrillation conducted down the accessory pathway, which can degenerate into ventricular fibrillation. Atrial flutter (saw-tooth waves, a rate of 150 with 2:1 conduction) is also asked: it is anticoagulated like atrial fibrillation, and isthmus ablation is the treatment of choice.
Key points
- Stable SVT: vagal manoeuvre, then adenosine 6 mg followed by 12 mg.
- Unstable: synchronised electrical cardioversion.
- WPW on the ECG: PR shorter than 120 ms, delta wave, wide QRS.
- AF with WPW: no adenosine or AV-node blockers — cardioversion or procainamide.
- Long-term treatment of AVNRT, AVRT and typical flutter is ablation.
Summary table
| Arrhythmia | ECG | Acute treatment | Long-term treatment |
|---|---|---|---|
| AVNRT (most common) | Narrow regular QRS, P waves hidden or just after the QRS | Vagal manoeuvre, adenosine 6 mg then 12 mg | Ablation (about 95% success) or beta-blocker/calcium blocker |
| Orthodromic AVRT | Narrow QRS, P after the QRS | As for AVNRT | Ablation of the accessory pathway |
| WPW in sinus rhythm | PR shorter than 120 ms, delta wave, wide QRS | — | Ablation if symptomatic; risk assessment if asymptomatic |
| Pre-excited atrial fibrillation | Irregular, wide and changing QRS, very fast | Electrical cardioversion or procainamide | Ablation; AV-node blockers are forbidden |
| Atrial flutter | Saw-tooth waves, usually 2:1 conduction at 150 | Rate control or electrical cardioversion | Cavotricuspid isthmus ablation; anticoagulate as for AF |
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Sources
- ESC Guidelines for the management of patients with supraventricular tachycardia, 2019 — Acute management and catheter ablation
- Harrison's Principles of Internal Medicine, 21st edition (2022) — Supraventricular Tachyarrhythmias
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.