• SVT = atria or AV node are sustaining the tachycardia
  • Most are AV nodal re-entry tachycardia (AVNRT), AN re-entry tachycardia (AVRT), or atrial tachycardia (AT)
  • AF more likely in older
  • M = F
  • "SVT" in 0.2% population, AF circa 1%



  • Palpitations (abrupt on/offset except sinus = slow on/offset)
  • Chest pain
  • SOB
  • Pre-syncope



  • Re-entrant circuit into AVN
  • 1 fast, 1 slow path into AVN = "circular" circuit
  • Slow pathway trigger then impulses move retrograde via fast path to the atria
  • P waves invisible in QRS (pseudo RSR' in V1)
  • Some get delta wave (if slow path = very slow - WPW)

Atrial tachycardia

  • AbN impulse formation or re-entrant
  • Focal or multifocal (unwell patient or Dig toxic)
  • P waves have different morphology in multifocal

AVRT (incl. WPW)

  • In sinus some impulse pass via the accessory pathway, early Vent. excitation (delta wave) but narrow QRS (most of the rest of the impulse down through His-Purkinje system)
  • In orthodromic AVRT, antergrade down His-Purkinje and retrograde up via accessory pathway = narrow complex tachy
  • Less common = antidromic AVRT = antegrade via accessory pathway and retrograde via AV node = broad complex tachycardia

DDx narrow complex tachy.

  • Sinus
  • Atrioventricular nodal re-entry tachycardia (AVNRT)
  • Atrioventricular re-entry tachycardia (AVRT)
  • Atrial tachycardia
  • Atrial flutter
  • AF
  • Sinus node re-entry
  • Junctional tachycardia


  • DC version if haemodynamically unwell (esp. if ?VT)
  • Modified valsalva
  • Reverse valsalva
  • Adenosine 6/12mg iv (have defib. ready and beware bronchospasm)
  • Most important ECG = rhythm strip on termination (record all)
  • Verapamil 5mg IV
  • Remember anticoagulation if AF or SVT duration >48hrs
  • Please avoid carotid massage

Modified valsalva (1)

Good evidence (RCT).

  • Patient semi-recumbent
  • Strain of 40 mm Hg pressure (blow 10ml syringe plunger) x 15 sec
  • Lie patient supine
  • Assistant elevates legs to 45°

Reverse valsalva (2)

Case series.

  • Exhale without forcing while sitting
  • Pinch nose and close mouth tight
  • Inhale against resistance for 10 sec


Content by Dr ÍOS. Last review Dr Kanti Dasari 4/08/21.