Supraventricular tachycardias (SVT)
Regular narrow‑complex tachycardias are common in the ED and pre‑hospital care. Most are AV‑nodal or accessory‑pathway re‑entrant arrhythmias that are often reversible with vagal manoeuvres, rapid AV‑nodal blockade (adenosine) or synchronized cardioversion. Rapid rhythm recognition, assessment of haemodynamic stability and prompt ECG documentation guide therapy (Resuscitation Council UK).
Definition and clinical importance
SVT describes tachyarrhythmias originating above the ventricular conduction system (atria or AV junction). In emergency practice the focus is regular, narrow‑complex SVT - typically AV nodal re‑entry tachycardia (AVNRT) and AV re‑entry tachycardia (AVRT). Presentations range from mild palpitations to syncope or cardiovascular collapse.
Immediate goals are to terminate the arrhythmia when possible, relieve symptoms and identify patients who need urgent cardiology input or definitive therapy (electrophysiology/ablation).
Mechanisms and common types
Understanding the mechanism helps interpret the ECG and choose therapy.
- Atrial tachycardia: focal atrial automaticity or micro‑reentry outside the sinoatrial node. P waves are abnormal; RP interval is often long.
- AVNRT: re‑entry within the AV node using fast and slow pathways. Typical presentation is sudden onset/offset palpitations and a short RP interval.
- AVRT (including WPW): macro‑reentry using an accessory pathway between atrium and ventricle (orthodromic or antidromic). May show pre‑excitation (delta wave) in sinus rhythm.
- Junctional tachycardia: arising from the AV junction; retrograde P waves may precede, be within, or follow the QRS.