Any narrow complex tachycardia characterised by a heart rate of more than 100 bpm and a QRS width of less than 120 ms on an ECG

Aetiology

• Caused by the electrical signal re-entering the atria from the ventricles

Pathophysiology

There are three main types of SVT based on the source of the electrical signal:

AV nodal re-entrant tachycardia

• Re-entry circuit forms within the AV node
• Most common cause of SVT in patients with a structurally normal heart
• More common in women

AV re-entrant tachycardia (AVRT)

• Involves an accessory pathway usually located in the valvular rings
• Most commonly caused by Wolff-Parkinson-White syndrome

Ectopic atrial tachycardia (EAT)

• Occurs when the electrical signal originates in the atria somewhere other than the sinoatrial node
• A latent pacemaker discharges action potentials at a greater frequency than the SA node so overdrive suppression is lost

Clinical presentation

• Palpitations
• Dyspnoea

Investigations

ECG