Pace mapping to unmask isthmus sites in post MI VT

Pace mapping to unmask isthmus sites in post MI VT

Raja Selvaraj, JIPMER

VT substrate in post MI VT

Conceptually model described by Stevenson best to understand the substrate

VT substrate in post MI VT

Circuit and the ECG

Isthmus activation is electrically silent Exit corresponds to QRS onset

Isthmus pacing during tachycardia

Entrainment with concealed fusion differentiates isthmus from other sites Stim-QRS and EGM-QRS also tell us where we are within the isthmus

Some times VT is

Not inducible
Not mappable

Sometimes VT is non inducible or unmappable Can we identify isthmus in sinus rhythm

Pacing in sinus rhythm - Attractive idea

Attractive idea Pacing within the circuit will reproduce morphology Stim to QRS can indicate location within isthmus (activation within isthmus is silent)

Pacing in sinus rhythm - Reality

In reality Pace match is usually poor

Functional block
Antidromic wavefront

Bystander cannot be differentiated

Pacing in sinus rhythm useful to delineate isthmus

Do not expect perfect pace match
Adjacent bystander cannot be differentiated

Evidence

Parts of VT reentry circuit isthmuses can be traced during sinus rhythm

11 patients
Match defined as 10/12
Pace match at short S-QRS - 85%
Pace match at long S-QRS - only 27%

Corrina B …. Williaim Stevenson. Identification of the ventricular tachycardia isthmus after infarction by pace mapping. Circ 2004;110:652-659

Pacemapping matches

Isthmus exit - 84%
Isthmus entrance - 32%
Central isthmus - 59%

Christian de Chillou … Francis Marchlinski. Localizing the critical isthmus of post infarct ventricular tachycardia: The value of pace-mapping during sinus rhythm. Heart Rhythm 2014;11:175-181

Color coding the match - Pacemapping map

Christian de Chillou … Francis Marchlinski. Localizing the critical isthmus of post infarct ventricular tachycardia: The value of pace-mapping during sinus rhythm. Heart Rhythm 2014;11:175-181

Practical ? - Old AWMI with recurrent VT of one morphology

Is it practical Case illustration

Delineating the circuit

Usefulness

Most post MI VT, substrate based ablation superior to targeting specific VTs (1)
But some patients with single dominant VT, useful to target VT
In these cases, when VT is not inducible / not mappable / to deduce circuit in SR
But be aware of limitations when using pacemapping

Di Biase …. Natale. VISTA multicenter randomized trial. JACC 2015;66:2872-2882

Is it useful? Concept of clinical VT ablation is less important than substrate ablation But cases with single arrhythmia

1

Pace mapping to unmask isthmus sites in post MI VT Raja Selvaraj, JIPMER