Differentiating JET & AVJRT: Atrial Overdrive Pacing

Answer: This EGM is diagnostic of a focal arrhythmia arising from the His Bundle/AV node due to an AHHA response following successful atrial overdrive pacing, consistent with Junctional Ectopic Tachycardia.

 

JET Prevalence:

Junctional Ectopic Tachycardia is a fairly rare phenomenon in Adults with a poorly understood pathogenesis probably involving enhanced automaticity from the AV nodal/Bundle of His region.

 

• Some literature seems to dispute this “rare” narrative, describing a prevalence as high as 5% in patients with AVJRT ablation in the the days to weeks immediately following their ablation procedure.

 

• This is known as “Secondary JET” or “Post Operative JET” and is usually a transient self-limiting phenomenon, induced by oedema and j=injury to the AVJ junction region poster surgery/ablation.

 

JET Presentation in the EP lab.

Since the JET arises from the AV node, it’s presentation appears very similar to typical AVJRT, with a short VA time of <70ms, and the earliest A occurring in the His A catheter (close to the AV node).

 

• Importantly, it does not necessarily initiate with an AH jump, helping us differentiate it from AVJRT.

 

• It also tends to oscillate more wildly in tachycardia CL, and VA block during tachycardia is commonly described. These can occur in AVJRT, but lend evidence towards JET.

 

JET Ablation:

Will be a topic for another day. Suffice to say, that ablation requires closer proximity to the AV node, with higher risk of AV block, lower procedural success and higher risk of recurrence.

 

The below illustration attempts to recreate sites of  attempted JET ablation and demonstrates perilous proximity to the AV node where catastrophic injury to the AV node is risked with ablation. For this reason, JET ablation is often abandoned in favour of medication, or performed with cryomapping and cryoablation. Alternative methods, such as ablation from the NCC have been proposed, but are not the subject of todays discussion.

 

Atrial Overdrive Pacing

Pacing the atrium 20ms faster the the TCL is useful in differentiating JET from AVJRT in patients with 1:1 AV conduction.

 

You must accelerate tachycardia to your pacing cycle length and the tachycardia must continue at it’s original TCL.

 

1. An AHHA response is diagnostic for JET.
2. An AHAH response indicates Reentry (AVJRT/AVRT).

 

Top tip: Always confirm your last entrained His/V signal! Measure it, don’t assume it.

 

My Two Cents:

• JET should always be suspected in the setting of a short VA tachycardia, especially when the TCL oscillates wildly, theres spontaneous VA block during tachycardia or slow pathway ablation fails to abolish tachycardia.

 

• JET can be differentiated from AVJRT by performing Atrial Overdrive pacing (assuming 1:1 AV conduction is present).

 

• An AHHA response is diagnostic for JET in most circumstances.

 

Thanks for tuning in :)

Cheers

Mitch & CPiP Team

 

This BeatBox post was based on the JET lectures contained in the Complex SVT Program 4, part of EP in Practice. EP Mastery in 2 years. No shortcuts. No compromises.

https://cardiacphysinpractice.com/ep-in-practice/

 

References

• (Question image based on) – Fan R, Tardos JG, Almasry I, Barbera S, Rashba EJ, Iwai S. Novel use of atrial overdrive pacing to rapidly differentiate junctional tachycardia from atrioventricular nodal reentrant tachycardia. Heart Rhythm. 2011 Jun;8(6):840-4.

 

• Majumdar S, Mohanan Nair KK, Namboodiri N, Valaparambil A. Response to atrial overdrive pacing during narrow QRS tachycardia. What is the mechanism? Indian Pacing Electrophysiol J. 2020 Sep-Oct;20(5):203-205.

 

• Alasti M, Mirzaee S, Machado C, Healy S, Bittinger L, Adam D, Kotschet E, Krafchek J, Alison J. Junctional ectopic tachycardia (JET). J Arrhythm. 2020 Jul 27;36(5):837-844.

 

• Dar T, Turagam MK, Yarlagadda B, Parikh V, Pillarisetti J, Gopinathannair R, Gianni C, Mohanty S, Mansour M, Di Biase L, Bunch TJ, Natale A, Lakkireddy D. Outcomes of junctional ectopic tachycardia ablation in adult population-a multicenter experience. J Interv Card Electrophysiol. 2021 Jun;61(1):19-27.

 

• Rosen KM: Junctional tachycardia. Mechanisms, diagnosis, differential diagnosis, and management. Circulation1973; 47: 654- 664.

 

• Kusterer N, Morales G, Butt M, Darrat Y, Parrott K, Ogunbayo G, Bidwell K, Patel R, Delisle B, Czarapata M, Elayi CS. Junctional ectopic rhythm after AVNRT ablation: An underrecognized complication. Pacing Clin Electrophysiol. 2018 Feb;41(2):182-193.