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Refractory rundown

-a clinical case on cardiac recovery-

Patient presentation

  • 471 year old male

  • recurrent palpitations

  • multiple documented tachycardia on ILR
    -    sudden onset/offset
    -narrow & broad complex
    -regular (rates (~180ms)
    -longest 10 minutes.

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Differential diagnosis

  • AVNRT (+ with aberrancy)

  • orthodromic AVRT (+ with aberrancy or antidromic conduction)

  • Junctional tachycardia (+ with aberrancy)

  • Atrial tachycardia (+ with aberrancy)
    Ventricular tachycardia and one of the options above

Baseline ECG/EGM

  • AH: 72

  • HV: 58

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Retrograde incremental pacing

  • Midline retrograde atrial activation (earliest HIS A)

  • Decremental VA conduction

  • VA wenckebach at 335ms

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Retrograde paced extras

  • MIdline (CS 9,10) decremental VA conduction

  • No retrograde jumps

  • VERP 260ms, VAERP <270ms

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Antegrade incremental pacing

  • Decremental AV conduction

  • No evidence of pre-excitation

  • AV wenckebach 365ms

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Antegrade incremental pacing

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  • Occurs when the ERP of a distal site is longer than the FRP of a proximal site

  • When closely coupled stimuli are delayed enough at the proximal site to allow distal site recovery
     

  • Types

Gap phenomenon

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  • No evidence of pre-exictation

  • expected AH lengthening and jump with echoes 320ms

  • Atrial latency

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  • Atrial ERP

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  • •elay between the initiation of an electrical stimulus and the subsequent mechanical contraction of the atria

  • •acing latency, the time from atrial pacing to atrial contraction

  • Can be prolonged in certain conditions
    -Hyperkelemia
    -Myocardial disease
    -Myocardial infarction
    -antiarrhythmia drug toxicity

Atrial latency

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Tachycardia induction

  • Atrial paced doubles 1:1 with shortly became 2:1 (AVRT ruled out)

  • and then into a left bundle branch block - no change in VA interval also ruling out left sided pathway

  • midline atrial activation

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  • May still be AVNRT with block from the slow pathway to the ventricle (lower common pathway block)

  • Also possible to have block from the fast pathway to the atrium (upper common pathway block) but is very rare

Lower common pathway block

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Ventricular entrainment -280ms

  • Ventricular entrainment performed which changed conduction back to narrow complex

  • V entrainment resulted in VAV response

  • >1 beat to entrain

  • PPI-TCL 150ms

  • Stim A - VA = 138ms

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  • •The shortening of ERP due to an induced extra stimuli

Peeling back refractoriness

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Late APB

  • Advances following HV (node part of antegrade circuit - JT effectively ruled out)

  • Same VA interval - node part of retrograde circuit (effectively ruling out ATc) 

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Tachycardia termination

  • Ends witt an A (Atc very unlikely)

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Diagnosis

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Slow pathway ablation performed

  • Good junctional rhythm seen during ablation.

  • No further tachycardia inducible post ablation. 

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References

  • Akrawinthawong, K. & Yamada, T. (2019). Typical atrioventricular nodal reentrant tachycardia with 2:1 conduction block: what is the mechanisms? Journal of arrhythmia, 21;35(2), 317-319

  • Cerna, L. et al., (2023). 1:1 Tachycardia initiated by a premature ventricular contraction: The curious appeal of the peel. Heart Rhythm Case Reports, Vol 9 (6), 391-395

  • Delon, W, Denes, P., Dhingra, R., & Rosen, K.M. (1974). Nature of the gap phenomenon in man. Circulation research, 34(5)

  • Klabundle, R.E. (2021). Cardiovascular physiolpogy concepts (3rd ed.).

  • Olshansky, B. & Sandesara, C.M. (2007). ECG 101: closing the gap phenomenon. EP Lab Digest

  • Tanabe, J., Fujita, S., Watanabe, N. & Tanabe, T. (2020). A case of prolonged atrial pacing latency. European heart journal, 4(4), 1-2

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