Supraventricular Tachycardias

Abnormally fast heart rhythm arising from improper electrical activity in the upper part of the heart

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

  • Fast narrow complex tachycardia (QRS < 0.12)
  • Regular rhythm
  • Heart rate usually 150–250 bpm
  • P-waves may be absent, hidden in QRS, or retrograde
notion image

Management

Management of EAT

  • If ectopic beats are spontaneous and the patient has a normal heart, treatment is rarely required and reassurance to the patient will often suffice
  • If symptoms are particularly troublesome, β-blockers are sometimes effective
  • Patient advised to avoid stimulants (caffeine, cigarettes)

Stable patients with SVT

Stepwise approach:
  1. Valsalva manoeuvre
  1. Carotid sinus massage (avoid in elderly/bruit/hx of stroke/hx of VF/AF
  1. Adenosine IV 6 mg LD → If fail, increase to 12 mg LD
    1. Adenosine works by slowing cardiac conduction primarily though the AV node
    2. It interrupts the AV node / accessory pathway during SVT and 'resets' it back to sinus rhythm
  1. Adenosine IV 6-12 mg + Verapamil IV 2.5-5 mg or Diltiazem 15-20 mg

Unstable patients with SVT

Unstable (hypotension, shock, chest pain, altered consciousness):
  • Immediate synchronized cardioversion 100-150 J

Long term management of patients with paroxysmal SVT

  • Medication - beta blockers, calcium channel blockers or amiodarone
  • Radiofrequency ablation - preferred in younger patients