Substrate Mapping of RVOT VT

Shih-Lin Chang, MD

Division of Cardiology, Taipei Veterans General Hospital

and National Yang-Ming University, Taipei, Taiwan

Procedure I

• EnSite Array that consists of sixty-four 0.0025-in diameter wires

creating a multielectrode unipolar array mounted on a 7.5 mL

balloon and 9 F catheter.

• RV graphy was performed to identify the anatomical locations of

the PA and RVOT.

• To prevent thromboembolic complications when using the MEA,

ACT was maintained 300 s for RV, and 350 s for LV.

Procedure II• A stiff 0.35 (260 cm in length) guidewire was passed into the

LPA using a multipurpose catheter or angled pigtail before

delivering the array into the RVOT (favor from L’t femoral vein).

• The equatorial region of the array should be positioned in the

mid-RVOT with the upper third of the array protruding through

the level of the pulmonary valve.

• 4-6 ml contrast was injected into balloon depended on the size

of RVOT.

• Fix the sheath and device.

Procedure III• Array is deployed within the RVOT and a 3-D geometry created

using a roving catheter, then virtual electrograms of

endocardial activation on a beat-to-beat basis are

reconstructed.

• The main advantage is that single beats can be captured and

analysed to guide ablation.

• The main limitation: positioned within the cavity at no greater

than 4 mm from the likely region of interest to ensure signal

integrity.

VT origin was defined as

the earliest activation (EA)

site showing a QS pattern

of noncontact unipolar

electrogram.

Breakout (BO) site defined as

the site of dV/dt max along the

depolarisation pathway from

the EA site.

• RVOT VT focus was defined as the earliest color-coded

spot on the isopotential map with a QS pattern.

• Pace mapping shows at least 11 of 12 leads match.

• Fractionated electrograms were recorded at this site pre-

QRS with a double potential.

• Occasionally, late potentials were evident post-ablation

suggesting exit block from the RVOT focus deep within the

septum.

Target Site

High pass filter settings by signal type

Chinitz HR 2006

Voltage Map during SR Dynamic substrate map (DSM)

Taipei VGH

LVZ LVZ

Low voltage zone

border (30% of

maximal PNV)Low voltage zone

border (30% of

maximal PNV)

RVOT VPC form the LVZ border

Taipei VGH

Isopotential Map during VPC Dynamic substrate map (DSM)

EnSite DSM maps is comparable to the

CARTO bioplar voltage

Sivagangabalan. Cir EP 2008

Measurements of EA and BO

Okumura. JICE 2011

Easy RFA

Okumura. JICE 2011

Difficult RFA

EA slope5 of ≤0.50 mV required a greater total RF energy

to eliminate PVCs/VT than EA slope5 of >0.50 mV

Deep RVOT

Okumura. JICE 2011

Non-RVOT

Comparison between the RVOT and non-

RVOT in EA-to-QRS onset time

Okumura. JICE 2011

Comparison between the RVOT and non-RVOT

in EA and BO slope

Okumura. JICE 2011

Non-RVOT VT

RVOT VT

Cutoff values for the EA-to-QRS onset time of ≥8 ms

and EA slope5 of >0.30 mV

differentiated the RVOT from non-RVOT group

(sensitivity of 100% and specificity of 100%)

Depth- and shape-dependent changes in EA and BO

Okumura. JICE 2011

The origin is shaped like an ellipse rather than a spot

Heart Rhythm 2007; 4:959-963

Small PA potentials preceding ectopy

from RVOT

Very-low-amplitude prepotential seen 40 ms

earlier than the PVC exit.

Comparison between noncontact mapping and

conventional mapping in RVOT VT ablation

Ribbing. JCE 2003

Ribbing. JCE 2003

Conclusions Noncontact mapping system is useful for patients with

only RVOT ectopy or very limited VT episodes.

Noncontact DSM (PNV) maps is comparable to the

CARTO bipolar voltage map.

Earlier activation with a steeper negative deflection at

the EA site can differentiate RVOT VT from non-RVOT

origin, whereas an initial r wave was observed at EA or

BO site in most non-RVOT cases.

The activation time and initial slope of the EA can

predict a potentially difficult ablation.

Pitfall

• Occasionally ectopics may occur due to the array

“bumping” the myocardium.

• These can occasionally be misleading on surface ECGs

as their morphology may be similar to the clinical

ectopics.

• They are easily identified by the fact that the signal

channels are usually saturated with noise (purple).

• A focus was defined as epicardial if virtual electrograms

at the earliest activation site had an R-wave (not QS

pattern) and the color map at this site had a broad (as

opposed to discrete, focal) appearance.

• ECG morphology: an aortic coronary cusp focus will

have evidence of a slurred R-wave in V1 (R/QRS

duration > 50% and R/S amplitude > 30%).

Possible Cause of Failure