Introduction to AVNRT

Clinical Electrophysiology Conference

Anish S. Shah, MD, MS

Division of Cardiology @ UIC

December 7, 2022

When you come to a fork in the road, take it.

~ Yogi Berra

Objectives

  1. Understand the relevant anatomy and physiology that allow for AVNRT
  2. Know how to diagnose typical AVNRT from …
    • Clinical history
    • Surface ECG
    • Intracardiac electrograms
  3. Understand the underlying mechanisms behind treatment strategies

Outline

  1. Introduction to AVNRT
  2. Non-invasive diagnosis
  3. Non-invasive treatment approach
  4. Relevant anatomy and physiology
  5. Intracardiac electrograms

Abbr. Abbreviation
AAD antiarrhythmia drugs
AH atrial-His
AP accessory pathway
AVNRT AV nodal reentrant tachycardia
CS coronary sinus
HPS His-Purkinje system
HB His bundle
HA His-atrial interval
HV His-ventricular interval
ST sinus tachycardia
SVT supraventricular tachycardia
TCL tachycardia cycle length

Definition

  • SVT implies involvement of ≥ 1 structure above bifurcation of the His bundle (HB).
  • AVNRT is usually a narrow-complex tachycardia that uses the AV node, and functional/anatomical pathways (slow/fast)

Remains unclear if there are anatomical correlates with the regions of slow versus fast conduction.

Requirements

To initiate and maintain a re-entrant rhythm:

  1. ≥ 2 functionally/anatomically distinct pathways that join proximally and distally to form a closed circuit of conduction
  2. unidirectional block in one of those potential pathways
  3. slow conduction down the unblocked pathway, allowing the previous pathway to recover

Sina qua non of reentrant arrhythmia is the ability to reproducibly intiate the tachycardia by timed extrastimuli

Diagnosis

  • Most common paroxysmal supraventricular tachycardia (1)
  • Approximately 50% of SVT cases in adults are from an AVNRT mechanism (2)
  • Woman are affected twice as frequently as men (3)
  • Most patients are between 18-40 years of age (3)
  • Typical AVNRT accounts for 90% of cases

Porter et al 2004, HRS (4)

What’s the rhythm?

A differential for a regular SVT?

Narrow QRS

  • AVNRT
  • AT
  • Orthodromic AVRT due to an accessory pathway
  • AFL with fixed AV conduction
  • SANRT
  • High septal VT
  • ST

Wide QRS

  • AVNRT or AT with aberrancy
  • AVNRT with a bystander accessory pathway
  • Antidromic AVRT due to an accessory pathway
  • SVT with wider QRS due to electrolyte/AAD therapies

Does the history matter?

  • Sudden onset and termination (often positional) more often re-entrant
  • Abortive measures such as drinking iced water
  • Dizziness and hypotension occur more commonly in short RP tachycardias
  • Polyuria/diuresis during tachycardia or at termination due to increased ANP secretion (5)

What next?

  • Physical exam?
  • 24-48 hour Holter?
  • 2-4 weeks of cardiac event monitoring?
  • Exercise testing?
  • Echocardiogram?
  • EP testing?

https://youtu.be/csVn_kvdeBM

Does the exam matter?

  • Neck pounding manifests with continuous pulsing cannon A waves, as the RA contracts against a closed tricuspid valve, described as the frog sign (6)
    • Does not occur in orthodromic AVRT, as longer VA interval separates the chamber contractions
    • 7-fold increase in AVNRT over other SVT with this symptom

Treatment

Guidelines

2019 ESC SVT Guidelines (7)

Vagal Maneuvers

Valsalva maneuver

  • Also called Flack’s test, where intrapleural pressure is raised to 40 mm Hg (expiration against closed airway)
  • Bradycardia effect seen within first 10-15 seconds

Carotid sinus massage

  1. Holding constant pressure (not a “massage”) for 5-10 seconds
  2. Increases pressure in carotid body, firing baroreceptors
  3. SNS afferent response leads to PNS efferents via vagus (right = SA, left = AV)
  4. Responses…
    • cardioinhibitory with ≥ 3s pause
    • vasodepressor is drop of ≥ 50 mm Hg in pressure
    • mixed

Adenosine

  • an endogenous purine nuceloside, binding to cardiac adenosine A1 receptors
  • dose-related prolongation of AV conduction at AH interval

90% success rate:

  1. 6 mg bolus
  2. 12 mg bolus
  3. 18 mg bolus

Repeat dosing after 1 minute (30 seconds for complete effect). Better efficacy with “single syringe strategy” (8)

Right Atrial Anatomy

Fork in the Road

Sinus Rhythm

  • Normal P and R axis
  • RR = 900
  • PP = 900
  • QRS = 80
  • P = 120
  • PR = 160
  • QT = 440

SVT

  • Suspected retro-grade P
  • RR = 350
  • QRS = 70
  • PR = 300
  • RP = 40

Normal sinus beat on multiple electrodes

Tachycardia initiation

A beat from the tachycardia

A beat from the sinus

APD leads to tachycardia

Decremental pacing at 800 ms

Decremental pacing at 400 ms

References

1. Kwaku KF, Josephson ME. Typical AVNRT - An update on mechanisms and therapy. 2002;6:414–421. Available at: https://link.springer.com/article/10.1023/A:1021140509804.
2. Issa ZF, Miller JM, Zipes DP. Clinical arrhythmology and electrophysiology: A companion to braunwald’s heart disease. Elsevier; 2018:1–752. Available at: https://linkinghub.elsevier.com/retrieve/pii/C20140032935.
3. Goyal R, Zivin A, Souza J, et al. Comparison of the ages of tachycardia onset in patients with atrioventricular nodal reentrant tachycardia and accessory pathway-mediated tachycardia. American Heart Journal 1996;132:765–767. Available at: https://pubmed.ncbi.nlm.nih.gov/8831363/.
4. Porter MJ, Morton JB, Denman R, et al. Influence of age and gender on the mechanism of supraventricular tachycardia. Heart Rhythm 2004;1:393–396.
5. Abe H, Nagatomo T, Kobayashi H, Miura Y, Masaru Araki AK, Nakashima Y. Neurohumoral and hemodynamic mechanisms of diuresis during atrioventricular nodal reentrant tachycardia. PACE - Pacing and Clinical Electrophysiology 1997;20:2783–2788. Available at: https://pubmed.ncbi.nlm.nih.gov/9392809/.
6. Sakhuja R, Smith LM, Tseng ZH, et al. Test characteristics of neck fullness and witnessed neck pulsations in the diagnosis of typical AV nodal reentrant tachycardia. Clinical Cardiology 2009;32:E13. Available at: /pmc/articles/mid/NIHMS319317/ /pmc/articles/mid/NIHMS319317/?report=abstract https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3200305/.
7. Brugada J, Katritsis DG, Arbelo E, et al. 2019 ESC Guidelines for themanagement of patients with supraventricular tachycardia. European Heart Journal 2020;41:655–720. Available at: www.escardio.org/guidelines.
8. Kotruchin P, Chaiyakhan I on, Kamonsri P, et al. Comparison between the double-syringe and the single-syringe techniques of adenosine administration for terminating supraventricular tachycardia: A pilot, randomized controlled trial. Clinical Cardiology 2022;45:583–589.