Supraventricular Tachycardia

Overview

The term supraventricular tachycardia (SVT), whilst often used synonymously with AV nodal re-entry tachycardia (AVNRT), can be used to refer to any tachydysrhythmia arising from above the level of the Bundle of His. Different types of SVT arise from or are propagated by the atria or AV node, typically producing a narrow-complex tachycardia (unless aberrant conduction is present). Classification of SVT is based on site of origin & regularity. 

There are many causes of SVT (see classification) but this page will focus on 3 main types:

• Atrial fibrillation
• Paroxysmal SVT
  • Atrioventricular re-entry tachyvardia (AVRT) – Wolff-Parkinson-White syndrome
  • AV nodal re-entry tachycardia (AVNRT)
• Atrial Flutter

Classification

	Regular	Irregular
Atrial	Physiological sinus tachycardia	Atrial fibrillation
	Atrial tachycardia	Multifocal atrial tachycardia
	Atrial flutter
	Inappropriate sinus tachycardia
Atrioventricular	Atrioventricular re-entry tachycardia (AVRT)
	AV nodal re-entry tachycardia (AVNRT)
	Automatic junctional tachycardia

Physiology of Conduction System

ECG

P wave:

• P waves should be upright, inverted in aVR
• < 120 ms duration
• < 2.5 mm amplitude in the limb leads

QRS complex (Narrow/Wide):

• < 120 ms duration
• Narrow complex or Broad complex
• Amplitude <10mm (precordial) or <5mm limb leads (minor increase)

T wave:

• Upright in all leads except aVR and V1
• Amplitude < 5mm in limb leads, < 15mm in precordial leads

PR interval:

• Reflects conduction through the AV node.
• Normal PR interval is between 120 – 200 ms duration
• Utilise for heart block

QT interval:

• <400 ms

ST segment:

• ST elevation >1mm in 2 contiguous limb leads
• ST elevation >2mm in 2 contiguous precordial leads
• ST depression