Cause

• Electrical signal re-entering the atria from the ventricles
• This causes a self-perpetuating electrical loop without an end point and results in fast narrow complex tachycardia (QRS < 0.12)
  • Less than 3 small squares
• It looks like a QRS complex followed immediately by a T wave, QRS complex, T wave and so on.

typical' SVT appearance with absent P waves and tachycardia

Paroxysmal SVT

• Describes where SVT reoccurs and remits in the same pt
  • So periods of normal sinus rhythm inbetween

AVNRT VS AVRT

• “Atrioventricular nodal re-entrant tachycardia” is when the re-entry point is back through the AV node.
  • Used synonymously with SVT
• “Atrioventricular re-entrant tachycardia” is when the re-entry point is an accessory pathway (Wolff-Parkinson-White syndrome).
  • Most common type
  • Delta wave - slurred QRS complex

https://youtu.be/f5xC5ofq4aE

Acute management

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Required continuous ECG monitoring

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1. Vagal manoeuvres
   1. Valsalva manoeuvre: e.g. trying to blow into an empty plastic syringe
   2. Carotid sinus massage
      1. Massage the carotid sinus on one side gently with two fingers.
2. Intravenous adenosine
   1. Rapid IV bolus of 6mg
   2. If unsuccessful give 12mg
   3. If unsuccessful give further 18 mg
   4. Contraindicated in asthmatics - verapamil is a preferable option
3. DCl cardioversion

Adenosine

• Works by slowing the cardiac conduction primarily via the AV node