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
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