AV Nodal Reentrant Tachycardia (AVNRT)

• Short RP tachycardia

• Typical AVNRT: Down the slow and up the fast

• Atypical AVNRT: Down the fast and up the slow

• AVNRT is the most common type of Supraventricular Tachycardia (SVT)

  • As with most SVTs, the QRS complex is usually narrow.

• AVNRT is aka “paroxysmal supraventricular tachycardia” (mostly by old school cardiologists)

• AVNRT Dual AV node physiology

  • both fast and slow conduction pathways are present in the AV node
  • rapidly conducting tissue has a long recovery time
    • fast boat, long wake
  • slow-conducting pathway
    • has a relatively short recovery time
  • Analogy: slow boats can follow more closely
    • ![[AV Nodal Reentrant Tachycardia AVNRT-1745547757223.webp]]
    • 2 beats on a slow path have quick recovery time, i.e. can come in quick succession to one another

• Pathophysiology

  • During sinus beats conduction occurs via fast pathway
    • conduction via slow pathway is blocked
  • Then you get a PAC → blocked in fast pathway
    • the slow pathway may permit reentry into the AV node (whereas normally conduction via slow pathway is blocked)
      • short recovery time
      • depolarizes both atria and ventricles

• If Atrial Fibrillation (AFib), Atrial Flutter, and sinus tachycardia are excluded from consideration, AV nodal reentrant tachycardia (AVNRT) is the most common cause of SVT

• AVNRT is an absolutely regular rhythm, with a rate usually between 150 and 250 beats per minute.

  • The rate is not useful in distinguishing AVNRT from other short RP narrow QRS tachycardias because it can range from 100 to 280 beats/min

• Most often driven by a reentrant circuit looping within the AV node.

• The onset of AVNRT is abrupt and frequently is initiated by an atrial premature complex.

• Termination is also abrupt, although some slowing may occur before termination

  • Adenosine is pretty effective for these folks
    • Also effective in AV Reentrant Tachycardia (AVRT)
    • Tends not to be effective in patients with Atrial Tachycardia
  • Mechanisms of Termination
    • properly timed PAC or PVC
    • ↑ in refractory time of AV node

• Ablation

  • AVNRT can be cured permanently with catheter ablation, using radio frequency to heat and destroy the cells in the slow pathway, creating a permanent line of block.
  • 95% lifetime cure rate
  • If you accidentally burn at Bundle of His, the patient will need a pacemaker.

![[AV Nodal Reentrant Tachycardia AVNRT-1745547985270.webp]]

P waves in AVNRT

• Retrograde P waves may sometimes be seen in leads II or III, V1-V3
• Your best bet would be to look in lead V1 for what is called a pseudo-R′, a little blip in the QRS complex that represents the superimposed retrograde P wave.
• More often than not, however, the P waves are so buried within the much larger QRS complexes that they cannot be identified with any confidence.

![[AV Nodal Reentrant Tachycardia AVNRT-1745548235651.webp]]

Appearance on EPS

![[AV Nodal Reentrant Tachycardia AVNRT-1745548311342.webp]]

• Start with the ECG (trop)
• Notice how the ventricular activity (RV) lines up exactly with the atrial activity (RA). If you see them lined up like this in a patient with narrow complex tachycardia, AVNRT is the most likely diagnosis.

Early atrial beat → prolonged A-H interval of 240 ms is an APC that initiates the tachycardia. The atrial activation is buried in the QRS. The circuit is in the AV node and activation occurs in parallel, rapid/near-simultaneous activation.

By contrast, AVRT has to activate in series (not in parallel). ∴, the V-A times will be longer in AVRT.