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Wide awake

-decoding broad complex tachycardias-

Patient presentation

  • 29 year old female

  • history of slow pathway ablation for typical AVNRT

  • Recurrent palpitations

  • reported wide complex tachycardia by ambulance (not documented)

Baseline ECG

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Baseline ECG/EGM

  • AH: 62

  • HV: 48

  • CL: 874

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Retrograde incremental pacing

  • Non decremental VA conduction

  • Midline activation

  • 2:1 block

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Antegrade incremental pacing

  • Broad complex tachycardia induced

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12 lead ECG - tachycardia

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Differential diagnosis

  • SVT with aberrancy

  • Antidromic AVRT

  • Ventricular tachycardia

Tachycardia characteristics

  • Long VA - 92ms

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  • Tachycardia terminate with a V
    VT unlikely diagnosis

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Diagnostic maneouvres in tachycardia

  • HIS synchronous VPB showing atrial advancment

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  • Ventricular entrainment 
    -entrains the atrium on <1 fully captured beats
    VAV response

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  • Ventricular entrainment 
    -PPI-TCL 404-314= 80ms
    -Stim A - VA 150-80 = 70ms

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  • Atrial entrainment 
    -pseudo AVVA response
    -same QRS morphology
    -VT excluded

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  • All findings consistent with AVRT

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Antidromic or orthodromic

  • HV 0ms during tachycardia (excludes aberrancy and consistent with antidromic AVRT)

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Antidromic AVRT

  • HV interval 0ms during tachycardia

  • AVRT only tachycardia not ruled out

  • LBBB morphology

  • Retrograde conduction non-decremental (fixed VA)

  • Decremental antegrade pathway. AH prolongation seen with HV shortening with incremental atrial pacing

  • Pseudo AVVA interval with atrial entrainment pacing occurs due to antegrade decremental properties

  • However, all pacing maneouvres also showed a likely retrograde accessory pathway too.
    -number of beats to entrain <1, +ve zipes

  • Antidromic and orthodromic AVRT?
     

  • To prove antridromic limb is part of circuit - assess with a lateral RA extra

Lateral RA extra

  • Advances next V without effecting immediate septal atrial activation

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Mahaim Fibers

  • Atriofasicular pathway (RA connects to RBB fibers rather than RV)

  • Slow antegrade conduction via atriofasicular fibre with retrograde conduction via HIS bundle/AV node

  • Typically along the lateral tricuspid annulus

  • May be composed of AV node like tissue (decremental properties, adenosine sensitive)

  • Has a degree of automaticity & can spontaneously trigger AVRT

  • Minimal pre-excitation on ECG – often normal PR interval

  • LBBB appearance during AVRT or pre-excitation

  • Delivering an early A from the lateral wall advances or delays the ventricular signal, but the septal atrial electrogram is not advanced on the APB beat.

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Mapping atriofasicular fibers

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  • M potential during atrial pace

  • M potential during tachycardia

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  • Morphology

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  • Bump map with ablator

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  • 3D map - RAO

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  • 3D map - LAO

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Post ablation testing

  • No evidence of pre-excitation

  • Decremental AV nodal properties shown

  • No inducible tachycardia
     

  • Confirmation that the tachycardia was antidromic AVRT using mahaim pathway is the antegrade limb and the AV node as the retrograde limb.

References

  • Alasti, M., Pawade, T., & Alison, J. (2022). Ventricular tachycardia or supraventricular tachycardia? Journal of Arrhythmia. 38; 259-262

  • Smeets, J.L.R.M, Hsia, H.H., Sanchex, J.M. et al (2019). Understanding the Mahaim pathway in the context of catheter ablation. Journal of innovations in cardiac rhythm management, 10 (1); 3509-3513 

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