Substrate mapping for Ventricular Tachycardia

Raja Selvaraj JIPMER

Introduction

History

josephson_sinus_abnormal.png stevenson_reentry_circuit.png

  1. Cassidy … Josephson. The value of catheter mapping during sinus rhythm to localize site of origin of ventricular tachycardia. Circulation 1984;69:1103
  2. Stevenson et al. Identification of Reentry Circuit Sites During Catheter Mapping and Radiofrequency Ablation of Ventricular Tachycardia Late After Myocardial Infarction. Circulation 1993;88:1647

Current status

  • Historical progression
    • Obligatory
      • Not inducible
      • Not mappable
      • multiple morphologies
    • By choice
  • Personal / general trend
  • Evidence / change in scar characteristics

VISTA

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VISTA

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What is the rationale for substrate based ablation?

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Zipes et al. Catheter ablation of Arrhythmias. 2nd Ed. 2002

Pros and cons

  • More lesions
  • Tackle all potential circuits
  • Ablation in sinus rhythm - more stable, more effective lesions
  • Hemodynamic stability of patient better

Electrograms of abnormal substrate

Low voltage zones

Importance

  • Substrate usually located within
  • Safe to ablate inside
  • Dense scar forms anatomic barrier to anchor lesions

Cut-offs

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  • Cut off from normal humans (1), validated in a porcine model (2)
  1. Marchlinsky et al. Linear Ablation Lesions for Control of Unmappable Ventricular Tachycardia in Patients With Ischemic and Nonischemic Cardiomyopathy. Circ 2000;101:1288
  2. Wrobleski … Vivek Reddy. Use of Electrogram Characteristics During Sinus Rhythm to Delineate the Endocardial Scar in a Porcine Model of Healed Myocardial Infarction. JCE 2003;14:524

Voltage cut-offs for endocardial signals 0.5 - 1.5 mV

  • Apply to both RV and LV
  • Both cut offs are flexible
  • Higher voltage cut off (2.5) in patchy scar (early reperfusion)
  • Patient specific cut offs ?
    • Uniform, homogenous lvz with rest of myocardium not changing color (upper cut off)
    • See channels / isthmus - lower cut off

High output pacing to identify scar

  • No capture at 10 mA, 2 ms (1)
  • May require higher outputs for capture (2)
  1. Soejima / Stevenson
  2. Sarrazin … Morady, Bogun. High-output pacing in mapping of postinfarction ventricular tachycardia. Heart Rhythm 2008;5:1709.

Unipolar voltage

  • Normal > 8.27 (95th centile) (1)
  • 5.5 for RV (2)
  • Multiple caveats, especially in RV
    • more overlap between normal and abnormal
    • adjust for lvh
    • 7.5 for RV septum
    • 6 - RV septum over aortic root
  1. Hutchinson … Marchlinski. Endocardial unipolar voltage mapping to detect epicardial ventricular tachycardia substrate in patients with nonischemic left ventricular cardiomyopathy. Circ Arrhythm Electrophysiol 2011;4:49
  2. Polin … Marchlinski. Endocardial unipolar voltage mapping to identify epicardial substrate in arrhythmogenic right ventricular cardiomyopathy/dysplasia. Heart Rhythm 2011;8:76

Unipolar voltage

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Delayed potentials

Principle

  • Bundles of surviving muscle fibers within scar
  • Slow conduction because of poor coupling
  • Far field early signal and near field late signal

Late potential - How late is late ?

  • EGM extending beyond surface QRS (1)
  • Remnant from SAECG
  • More likely to identify in late activated regions
  • 2 or more components, separated by isoelectric segment >50 ms (sinus) or 150 ms (RV pacing) (2)
  • High frequency signals distinct from far-field electrogram (3)
  1. Cassidy … Josephson. Endocardial catheter mapping in patients in sinus rhythm: relationship to underlying heart disease and ventricular arrhythmias. Circulation. 1986;73:645-652
  2. Arenal et al. Ablation of electrograms with an isolated, delayed component as treatment of unmappable monomorphic ventricular tachycardias in patients with structural heart disease. JACC 2003;41:81.
  3. Jais P … Haissaguerre M. Elimination of local abnormal ventricular activities: a new end point for substrate modification in patients with scar-related ventricular tachycardia. Circulation 2012;125:2184

Variables

  • Catheter tip
  • Sinus rhythm / pacing, pacing site
  • Gain
  • Window
  • Density
  • Contact force

Ablation approaches

Different approaches

  • Linear ablation (1)
  • Late potentials (2)
  • LAVA (3)
  • Scar homogenization (4)
  • Scar dechanneling (5)
  • Core isolation (6)
  1. Marchlinski et al. Linear ablation lesions for control of unmappable ventricular tachycardia in patients with ischemic and nonischemic cardiomyopathy. Circulation 2000;101:1288
  2. Arenal A et al. Ablation of electrograms with an isolated, delayed component as treatment of unmappable monomorphic ventricular tachycardias in patients with structural heart disease. J Am Coll Cardiol 2003;41:81
  3. Jais P … Haissaguerre M. Elimination of local abnormal ventricular activities: a new end point for substrate modification in patients with scar-related ventricular tachycardia. Circulation 2012;125:2184
  4. De Biase … Natale A. Endo-epicardial homogenization of the scar versus limited substrate ablation for the treatment of electrical storms in patients with ischemic cardiomyopathy. J Am Coll Cardiol 2012;60:132–141.
  5. Berruezo A … Brugada J. Combined endocardial and epicardial catheter ablation in arrhythmogenic right ventricular dysplasia incorporating scar dechanneling technique. Circ Arrhythm Electrophysiol 2012;5:111–121.
  6. Tzou WS … Marchlinski FE. Core isolation of critical arrhythmia elements for treatment of multiple scar-based ventricular tachycardias. Circ Arrhythm Electrophysiol 2015;8:353–361.

In practice

VT induction before mapping

  • Not essential for substrate mapping
  • Useful
    • Provides baseline inducibility
    • Pacemaps during mapping

Sinus rhythm or pacing ?

  • Bipolar voltage comparable in sinus rhythm / ventricular pacing (1)
  • RV pacing better than sinus to identify late potentials (2)
  1. Brunckhorst … Stevenson. Impact of Changing Activation Sequence on Bipolar Electrogram Amplitude for Voltage Mapping of Left Ventricular Infarcts Causing Ventricular Tachycardia. JCE 2005;12:137.
  2. Arenal et al. Ablation of electrograms with an isolated, delayed component as treatment of unmappable monomorphic ventricular tachycardias in patients with structural heart disease. JACC 2003;41:81.

Sinus rhythm or pacing

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Arenal et al. Ablation of electrograms with an isolated, delayed component as treatment of unmappable monomorphic ventricular tachycardias in patients with structural heart disease. JACC 2003;41:81.

Prefer pacing unless

  • Ventricular pacing not tolerated
  • RV being mapped

Pacing for RV mapping

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Unknown

  • multiple pacing vectors at each point
  • LV pacing for RV substrate ?
  • Extrastimuli ?

Choosing a window

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Setting gain

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Identifying abnormal electrograms

  • Setting right gain
  • Operator supervised annotation
  • 'Beat averaging'

Differentiate from artifact

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Annotating points - binary / continuous

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Pacing from abnormal sites

  • Non capture to identify scar
  • Latency - correlates with late potential - may be discordant in 40% (1)
  • Differentiate far field from near field (1)
  • Paced morphology
  • Putative isthmus (2)
  1. Baldinger … Stevenson. Electrogram Analysis and Pacing Are Complimentary for Recognition of Abnormal Conduction and Far-Field Potentials During Substrate Mapping of Infarct-Related Ventricular Tachycardia. Circulation: Arrhythmia and Electrophysiology. 2015;8:874-881
  2. de Chillou C … Marchlinski FE. Localizing the critical isthmus of postinfarct ventricular tachycardia: the value of pace-mapping during sinus rhythm. Heart Rhythm 2014;11:175

Pacemap

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Multiple exits with pacing

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Ablation - Individualized strategy

  • Scar with pacemap - linear abl along scar border
  • Isthmus within scar / between scar and annulus - linear ablation
  • Late potentials - target late potentials
  • Channel seen - dechanneling
  • Activation map / entrainment - Partial maps, correlation with substrate

Rapid, partial activation map

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Ablating channels to eliminate LP

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Ablating channels to eliminate LP

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Isthmus - inferior wall MI

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Isthmus - inferior wall MI

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LP ablation

  • May not always eliminate
  • Ablate at entrance
  • Post ablation re-mapping

Power settings

  • safety of high power in scar
  • 30W / 40 W
  • longer duration (1)

Tzou WS … Marchlinski FE. Core isolation of critical arrhythmia elements for treatment of multiple scar-based ventricular tachycardias. Circ Arrhythm Electrophysiol 2015;8:353–361.

Conclusion

Summary

  • "Substrate mapping" - common term for a collection of approaches
  • Characterisation of locations are based on rhythm other than tachycardia
  • Tailored mix of approaches for an individual patient
  • Principally substrate based strategy for mapping and ablation remains the cornerstone