Supraventricular tachycardia

Created by team@ekgdx.com on Feb. 12, 2023

Let’s talk about supraventricular tachycardia (SVT).

SVT refers to any tachyarrhythmia arising at or from above the atrioventricular (AV) node.

Criteria

  • Regular rhythm.
  • Rate >100 bpm.
  • QRS narrow unless with BBB or aberrancy.
  • If the HR is too fast, the P waves may not easily identified.  
  • ST segment depression may be seen.

NOTE: Paroxysmal SVT is an episodic condition with sudden onset and abrupt termination.

NOTE: There are several types of SVT: 

  1. AV Nodal Reentry Tachycardia (AVNRT).
  2. AV Reentrant (or reciprocating) Tachycardia (AVRT).
  3. Sinoatrial Nodal Reentrant Tachycardia (SANRT).

1- AVNRT is a type of paroxysmal supraventricular tachycardia that results due to the presence of a reentry circuit within or adjacent to the AV node.

In general, there are two types of AV node reentrant tachycardia (AVNRT):

  • Typical AVNRT when anterograde conduction occurs via the slow pathway and retrograde conduction via the fast pathway also known as short RP tachycardia (RP interval <50% of the RR interval).
  • Atypical AVNRT when anterograde conduction occurs via the fast pathway and retrograde conduction via the slow pathway also known as long RP tachycardia (RP interval >50% of the RR interval). 

Narrow QRS tacycardia at the rate of 170 bpm with short RP interval. The retrograde P waves are evident after the QRs complexes. 

 

Same rhythm strip with graphical explanation. 

 

Short RP tachycardia obtained from a 42-year old woman. 

 

NOTE: The slow pathway within the AV node is called "alpha" and has a short refractory period. The fast pathway is called "beta" and has a long refractory period.

There are three subtypes of AVNRT in terms of the dominant pathway:

1A: Slow-Fast AVNRT (80-90%).

  • Pseudo-S wave in leads II, III, and AVF.
  • Pseudo-R' wave in lead V1.

1B: Fast-Slow AVNRT (10%).

  • P waves between the QRS and T waves (QRS-P-T complexes).

1C: Slow-Slow AVNRT (1-5%).

  • Late P waves after the QRS.

2- AVRT is a form of paroxysmal supraventricular tachycardia that results due to the presence of reentry circuit formed by the normal conduction system and the accessory pathway resulting in circus movement.

There are two subtypes of AVRT:

2A: AVRT with orthodromic conduction: The anterograde conduction occurs via the AV node, with retrograde conduction occurring via the accessory pathway. This can occur in patients with a concealed pathway and often it is initiated by an APC. 

  • Rate >200 bpm.
  • P waves may be buried in QRS complex or retrograde.
  • Narrow QRS unless pre-existing bundle branch block or aberrant conduction.
  • T wave inversion and ST segment depression may be seen.

2B: AVRT with antidromic conduction: The anterograde conduction occurs via the accessory pathway with retrograde conduction via the AV node and occurring in <5% of patients with WPW.

  • Rate >200 bpm.
  • Wide QRS complexes due to the preexcitation.

3- Sinoatrial Nodal Reentrant Tachycardia (SANRT) is caused by reentry circuit close to or within the sinus node. What differentiates it from sinus tachycardia is the sudden onset and termination.

  • Sinus P waves.
  • Rate between 100 - 150 bpm (usually).
  • Usually with abrupt onset and termination. 

NOTE: Sometimes, is necessary an electrophysiology study to know what type of SVT is present. 

NOTE: SVT may occur spontaneously or can be triggered by emotional stress, caffeine, smoking, slcohol, beta-agonists (salbutamol) or sympathomimetics (amphetamines), and many others.

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Dr. Roig

Supraventricular tachycardia