The term Supraventricular Tachycardia can be used to refer to any tachycardia arising from above the bundle of His, although in clinical practice it usually refers to an AV node re-entry tachycardia (AVNRT).

Types

Classification is not always straightforward. Can be classified by site of origin, or regularity.

Regular Irregular
Atrial Sinus Tachycardia
Atrial flutter
Sinus node re-entrant tachycardia
Atrial Fibrillation
Atrial flutter with variable block
Atrioventricular Atrioventricular re-entry tachycardia (AVRT)
AV nodal re-entry tachycardia (AVNRT)
Automatic junctional tachycardia

(Adapted from a table at http://lifeinthefastlane.com/ecg-library/svt/ )

AV nodal re-entry tachycardia (AVNRT)

  • The most common cause of SVT in patients with structurally normal heart
  • More common in women (3:1)
  • Can occur at any age and may affect otherwise fit and healthy patients
  • Precipitated by: caffeine, alcohol, exercise, drugs; beta-agonists (e.g. salbutamol), sympathomimetics (amphetamines, hyperthyroidism. Often no cause can be identified.
  • Usually sudden onset, sensation of regular palpitations. May also be anxiety and shortness of breath
  • There may be a brief drop in blood pressure, although this rarely causes syncope
  • If there is underlying coronary artery disease, there may also be angina-like chest pain
  • Pathology; a re-entry circuit forms within the AV node, or anatomically adjacent very similar tissues located in the right atrium. Usually this circuit involves wither the fast pathway or the slow pathway. Not to be confused with atrioventricular re-entry tachycardia (e.g. Wolff-Parkinson-White syndrome), where the re-entry pathways are not part of, or very close to the AV node, and are usually located in the valvular rings.
  • Not usually life threatening
  • May resolve spontaneously

 

ECG findings

  • Usually narrow QRS (<120ms)
    • Beware of multiple pathologies which may give a mixed picture – e.g. bundle branch block, or accessory pathways
  • Often no p waves visible as they are hidden by QRS complexes
  • Tachycardia rate 140-280bpm
  • Regular
  • Sometimes, ST depression

 

Management

Vagal Manoeuvres

  • Ask the patient to blow hard onto the end of a 50ml syringe

Adenosine

  • If vagal manoeuvres are ineffective, consider using adenosine.
  • Resus Council guidelines suggest using 6mg bolus, then, if ineffective, a 12mg bolus, and a further 12mg if required
  • Boluses should be given quickly as adenosine is very quickly metabolised, and slow boluses may be metabolised before they reach the heart

Cardioversion

  • May be used in patients who are haemodynamically unstable
  • The resus council guidelines suggest synchronised DC shock for all unstable patients with tachycardia with pulse
  • Attempt three synchronised DC cardioversion shocks

If ineffective, give 300mg amiodarone IV over 10-20 minutes and repeat shock

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