Approach to Narrow QRS Tachycardia

Raja Selvaraj

Introduction

Narrow QRS tachycardia

  • Regular, rate > 100, QRSd < 120
  • AT, AVNRT, orthodromic AVRT
  • Preexcitation in sinus rhythm / with atrial pacing
  • Dual AV nodal physiology
  • Manner of induction

Narrow QRS tachycardia, central atrial activation, very short VA

typical_avnrt.jpg

Preexcitation with narrow QRS tachycardia

preexc_ort.jpg

Narrow QRS tachycardia with VA > 70 ms and central VA

svt.jpg

General approach

  • What is the situation ?
  • What are the differential diagnoses ?
  • What are the electrophysiologic differences ?
  • What pacing maneuvers can differentiate ?

How to do

  • Setup the stimulator
  • How to measure
  • How to interpret
  • Practice

Scenarios

Commonest Setting

  • Regular narrow QRS tachycardia
  • 1:1 VA
  • Atrial activation central
  • VA > 70 ms

SVT

svt.jpg

Differential diagnoses (important ones)

  • AVNRT
  • Orthodromic AVRT
  • Atrial tachycardia

EP differences

  • A / V essential to tachycardia
  • Focal versus reentry
  • Presence of extranodal pathway
  • VA linking
  • Distance of circuit from RV apex
  • V and A activation - serial versus simultaneous

Chamber essential to circuit

essential_parts.gif

Focal / reentry

essential_parts.gif

Extranodal pathway

essential_parts.gif

VA linking

essential_parts.gif

Distance from RV apex

essential_parts.gif

Sequential vs simultaneous activation

seq_parallel.jpg

Pacing maneuvers

Single most useful maneuver ?

RV overdrive pacing - most useful maneuver

  • Easy to perform and interpret
  • Can distinguish AT from AVNRT / AVRT (VAAV versus VAV)
  • Can distinguish between AVNRT / AVRT (cPPI-TCL, SA-VA)
  • Onset of entrainment can provide clues
  • Can help even if not entrained !

Setting up

  • Burst pacing from right ventricle
  • Sync on
  • Tachycardia CL - 30 ms
  • Pace until atrium entrained
  • Stop pacing

What to look for ?

  • Don't 'eyeball'
  • Does tachycardia continue ?
  • Was the atrium entrained ?
  • Which is the last entrained A ?
  • Sequence - VAV or VAAV

What to look for ?

  • corrected PPI - TCL
  • SA - VA
  • Is there fusion during entrainment ?
  • Beginning of entrainment - A or His ?
  • How many beats to entrain ?

RV pacing in narrow QRS tachycardia - Rule out (or in) AT

vav.jpg

RV pacing in narrow QRS tachycardia - Rule out (or in) AT

vav_measurements_atrium_entrain.jpg

RV pacing in narrow QRS tachycardia.

pseudoVAAV.png

Why all this fuss about measurement ?

pseudo_vaav_measurements.jpg

RV pacing in AT - VAAV

VAAV.jpg

RV pacing in narrow QRS tachycardia - AVNRT / AVRT

vav_measurements_ppi.jpg

SA / VA intervals

sa_va.jpg

Fusion during entrainment ?

fusion.jpg

Entrainment

VOP_entrainment.jpg

Beginning of entrainment can give a clue

entrainment_onset.jpg

  • Atrial acceleration in transition zone
  • A entrainment before H entrainment

Could not entrain - useful information ?

av_dissociation.jpg

Summary

  • VAAV identifies AT, VAV rules out
  • SA - VA and PPI - TCL are longer for AVNRT
  • Can use basal pacing if responses are equivocal
  • A entrained earlier for AVRT, entrained before His

His refractory PVC

  • Little more difficult to perform and interpret
  • Very useful maneuver
  • Especially differentiate septal AP from AVNRT

His refractory PVC - setting up

  • R synchronised single extrastimuli
  • Check that sync is working
  • Start 30 ms less than RR
  • Decrement by 10 ms
  • Continue until refractoriness or tachycardia termination

His refractory PVC - measurement and interpretation

  • Confirm cycle length is stable
  • Measure AA around each PVC to find longest CI at which PVC preexcites A
  • Decide if His is refractory at this time

His refractory PVCs - responses

  • Advance atrial activation without change in sequence
  • Delay atrial activation without change in sequence
  • Terminate tachycardia without conduction to atrium
  • Does not alter atrial activation

PVC during tachycardia

his_pvc.jpg

PVC terminates tachycardia

his_ref_pvc.jpg

Other clues during narrow QRS tachycardia

  • VA unlinking - spontaneous or after atrial burst
  • Cycle length and VA changes with bundle branch block
  • Spontaneous termination

Spontaneous termination

spont_term.jpg

Bundle branch block

lbbb_narrow.jpg

Bundle branch block

lbbb_narrow_measurements.jpg

Bundle branch block

coumel.jpg

Maneuver in sinus rhythm - Central VA conduction with ventricular pacing

Scenario

Central VA conduction

Setting

  • During ventricular pacing, 1:1 VA conduction
  • Central atrial activation

Differential diagnoses

  • Nodal conduction
  • Septal accessory pathway

EP differences

  • Decremental conduction
  • His is a waypoint
  • Distal insertion (entry point)
  • Adenosine sensitivity

Decremental single ventricular extrastimuli

  • Easy to perform (must be routine)
  • Atrial activation pattern
  • VA interval - Decremental conduction
  • VA relation to VH

Setting up and measurements

  • Pace from RV apex
  • His catheter and RA / CS catheters
  • Decrement by 10-20 ms
  • VA interval measured to earliest A

Decremental conduction

  • Classical property of nodal conduction
  • Can also be seen with AP
  • How to differentiate

RV 500/300 ms

rv500_300.jpg

RV 500/280 ms

rv500_280.jpg

RV 500/260 ms

rv500_260.jpg

Parahisian pacing

  • Somewhat difficult to perform
  • Often difficult to interpret
  • Still very useful sometimes

Parahisian pacing

parahisian_explanation.jpg

Parahisian pacing - setting up

  • His catheter, slightly pushed in (small A)
  • Start with low output and increase gradually
  • Watch QRS morphology for intermittent His capture

Parahisian pacing - interpretation

  • His capture - narrower QRS, His not seen, RVA early
  • Beware of atrial capture
  • Beware of pure His capture
    • Narrower QRS
    • Isoelectric interval from pacing spike to QRS

Parahisian pacing - interpretation

  • Identify beats with and without His capture
  • Look at atrial activation sequence
  • Measure VA interval

Parahisian pacing - with His capture

  • Nodal conduction - same sequence, shorter VA
  • AP conduction - same sequence, same VA
  • Mixed response - different sequence, shorter VA

Parahisian

parahisian.jpg

Parahisian

parahisian_latha_2013-12.jpg

Pre-ablation

parahisian_pre.jpg

Post ablation

parahisian_post.jpg

Other maneuvers

Response to adenosine

adenosine_post_abl_ramesh_2013-12.jpg

Differential pacing

  • VA interval during pacing from apex and base
  • Shorter from apex for nodal conduction
  • Shorter from base for AP conduction

RV apex pacing

rv_apex_va.jpg

RV base pacing

rv_base_va.jpg

Summary

  • Understanding of basic electrophysiology of arrhythmias
  • Practice is important
  • Although not required at most time, will prove critical in select cases