Sudden changes when Pacemapping locates the critical isthmus site in VT Ablation

The Basic concepts of pacemapping in Scar-VT:

• Identifying pacemap QRS morphologies with a high correlation (>95%) to the VT morphology indicates you are pacing from the exit site.

 

• Both an adjacent bystander and critical isthmus site may display:
  • Long stim-QRS
  • High correlation to VT morphology

 

What will be discussed here:

• Sudden changes in paced morphologies in two anatomically adjacent sites predicts an endocardial critical isthmus site.

 

• Centrifugal patterns of pace-map correlations indicate an intramural circuit.

 

These factors inform ablation strategy

 

An example of a “Sudden Change” in Pacemap Morphology

 

Key Concept!

• An abrupt 30% change in pacing correlation from a good pacemap to a poor pacemap correlates with a specifically endocardial diastolic isthmus sites critical for maintaining VT re-entry circuits.

 

 

Why does a sudden change pattern correlate with an endocardial isthmus site?

 

No sudden change = No Isthmus site :(

• If an abrupt change pattern is not seen, then you will likely obtain a “centrifugal pattern” of pacemap correlation (example below).

 

• • The pacemap correlation gradually becomes worse as you pace further from the exit site in all directions.

 

• A centrifugal pacemap correlation map indicates an intramural or epicardial isthmus site (when performing pacemapping from the endocardium).

 

An example of a centrifugal pattern of pacemap correlations is demonstrated in the example below, where the VT isthmus site was intramurally located.

 

My Two Cents:

• VT is often a 3-dimnentional re-entrant circuit involving the intramural substrate.

 

• In my opinion, in many centres, pacemapping is both underutilised & underappreciated in scar VT ablations.
  • It can reliably identify endocardial critical isthmus sites in unstable VT, or indicate the presence of an intramural circuit.

 

• A sudden change in pacemap morphology (>30% correlation) from good to bad pace-map at two anatomically adjacent sites strongly correlates with the location of an endocardial critical diastolic isthmus site.

 

• In contrast, a centrifugal pattern of gradually poorer pace-map morphology indicates an intramural critical isthmus site and possibly a more difficult endocardial ablation.

 

Thanks for tuning in :)
Cheers
Mitch & CPiP Team

Start your structured journey to mastering EP in 2 years with EP in Practice. 

EP in Practice – Product Overview

 

 

References:

• (SEMINAL PAPER RECOMMENDED) De Chillou C, Groben L, Magnin-Poull I et al. Localizing the critical isthmus of postinfarct ventricular tachycardia: the value of pace-mapping during sinus rhythm. Heart Rhythm. 2014;11:175–81

 

• Sadek MM, Schaller RD, Supple GE, Frankel DS, Riley MP, Hutchinson MD, Garcia FC, Lin D, Dixit S, Zado ES, Callans DJ, Marchlinski FE. Ventricular Tachycardia Ablation – The Right Approach for the Right Patient. Arrhythm Electrophysiol Rev. 2014 Nov;3(3):161-7.

 

• Sadek MM, Schaller RD, Supple GE, Frankel DS, Riley MP, Hutchinson MD, Garcia FC, Lin D, Dixit S, Zado ES, Callans DJ, Marchlinski FE. Ventricular Tachycardia Ablation – The Right Approach for the Right Patient. Arrhythm Electrophysiol Rev. 2014 Nov;3(3):161-7.