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Utility of cardiac MRI for identifying the Arrhythmia Substrate during VT ablation

Timm Dickfeld, MD, PhDDirector of Electrophysiology, VA Baltimore

Associate Professor of Medicine, University of MarylandMACIG (Maryland Arrhythmia and Cardiac Imaging Group)

www.umm.edu/heart/macig

Disclosure-of-Relationship

- Research Grants, Consulting –Biosense-Webster

Unlabeled Indications

- Use of Gadolinium for MRI Scar Imaging

Why Substrate Characterization?

4.3g myocardium = 1.4% LV mass

• In 193 patients LGE of 1.4% resulted in HR >7 for MACE Kwong R. et al. Circulation. 2006;113:2733

Anatomic Substrate of Reentrant Arrhythmias

De Bakker et al. Circulation 1988 Adapted: Stevenson W. Circulation. 1993;88:1647

Inner Loop

Outer Loop

Bystander

ExitIsthmusEntry

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Anatomic Substrate of Reentrant Arrhythmias

De Bakker et al. Circulation 1988

LV Scar

Imaging for Scar Characterization

Clinical Armentarium 2012

Hussein. AHA 2012.

Dickfeld. JACC CV IM;1:73:2008Tian. Circ AE 2010;3:496

Tian. JNM. 2012;53:894Dickfeld .Circ AE. 2011;4:172

ICE

SPECT

PETCT

MRI

Current Routing Use of Scar Imaging

N on e I C E C T MR I P ET

S PE C

T S e

v e ra l M

o da l i .

. .

38%

17%

7%

14%

3%

0%

21%

1. None

2. ICE

3. CT4. MRI

5. PET

6. SPECT7. Several Modalities

Magnetic Resonance Imaging

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MRI: Near-Cellular SubstrateResolution

• LAD ligation Rat-infarct model

• LGE ex-vivo 7T MRI

• Voxel: 50x50x50µm

• MRI/histoloy correlation (R2=0.96)

• Ability to detect clefts 2-4 myocytes thick

Schelbert et al. Circ Cardiovasc Imaging 2010;3;743

Results- MRI: 3D Imaging Extraction -

RV MyocardiumLV Endocardium

LV Epicardium

LV Scar

SA MRI Slices

Registration Accuracy: 3.8±1.0mm

3D MRI Integration Correlation: MRI and Voltage

DE MRI Voltage Map

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01234567

0 50 100

Scar Transmurality [%]

Bip

olar

Vol

tage

[mV

] r = 0.72

Correlation of Scar Transmurality and Voltage

Dickfeld et al. Circ Arrhythm Electrophysiol. 2011;4:172

MRI Scar and Voltage Mapping

• Best voltage cut-off for MRI scar:- Bipolar voltage: 1.0-1.54mV- Unipolar voltage: 4.46-6.52mV

Desjardins. Heart Rhythm 2009;6:644Codreanu . JACC. 2008;52:839

Dickfeld . Circ Arrhythm Electrophysiol. 2011;4:172

• Comparison MRI and Voltage Scar Area:- MRI scar ~ <0.5mV scar area- MRI scar ~ <1.5mV scar+border zone area

- MRI scar slightly larger than 1.5mV area

• Significant Mismatch: 1/3 of patients

Nakahara . Heart Rhythm 2011;8:1060

Wijnmaalen . Eur Heart J. 2011;32:104

Desjardins. Heart Rhythm 2009;6:644; Dickfeld . Circ Arrhythm Electrophysiol. 2011;4:172

Codreanu . JACC. 2008;52:839Wijnmaalen et al . Eur Heart J. 2011;32:104

A

B

A

B

Mismatch: MRI Scar > Voltage Scar

• Endocardial scar <50% with bipolar voltage ≥ 1.5mVTian J et al. Heart Rhythm 2009; 6:825

Wijnmaalen et al. Eur Heart J. 2011;32:104Dickfeld et al. Circ Arrhythm Electrophysiol. 2011;4:172;

Endocardial layer of ~2mm normal myocardium masks intramural scar (predominantly in septal location)

Mismatch: MRI Scar > Voltage Scar

Dickfeld et al. Circ Arrhythm Electrophysiol. 2011;4:172; Wijnmaalen et al.. Eur Heart J. 2011;32:104

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• Suboptimal Catheter Contact:- Frequently basal “pseudoscar”

- Early registration algorithm (e.g. CartoSOUND) corrected 4.1±1.9% falsely low voltage points

• Decreased MRI Sensitivity to detect patchy scar

• Limited Mapping Density: incorrect low voltage extrapolation

Mismatch: Voltage Scar > MRI Scar

Dickfeld et al. Circ Arrhythm Electrophysiol. 2011;4:172

Nakahara et al. Heart Rhythm 2011;8:1060

Desjardins et al. Heart Rhythm 2009;6:644

Codreanu A et al. JACC. 2008;52:839Nakahara et al. Heart Rhythm 2011;8:1060 Image-Guided VT Ablation

MRI-Guided Ablation: Border Zone

Pacemapping Guided by MRI Scar Pacemap Match

Dickfeld et al. Circ Arrhythm Electrophysiol. 2011;4:172

PM 2

- Pacemapping/Fractionation -

Reprojection of PM Site

80-Sector Segmentation

MRI-Guided Ablation: Border Zone

PM 2

Transmurality Display

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Surviving Pap. Muscle

Substrate-Guided Mapping

1

2

12

MRI-Guided Ablation: Abnormal Substrate

PM Match

Dickfeld et al. Circ Arrhythm Electrophysiol. 2011;4:172VTLV Voltage Map

MRI-Guided Ablation: Substrate Identification

Mid- and Epicardial Scar with Preserved Endocardial Voltage

MRI-Guided Ablation: Midmyocardial Scar

Dickfeld et al. Circ Arrhythm Electrophysiol. 2011;4:172

Successful RF Site Characteristics

• Bipolar Voltage: 0.60-0.72mV (SD≤0.9)Unipolar Voltage: 1.9-2.20mV (SD≤2.1)

• Fractionated Signals: 32-62%Diastolic Potentials: 23-66%

• Transmurality: 60-68% (SD≤38%)

• Infarct core 17-71%Grey zone/periphery 29-83%

• MRI LGE: 100%

Wijnmaalen et al. . Eur Heart J. 2011;32:104Desjardins et al. Heart Rhythm 2009;6:644

Dickfeld et al. Circ Arrhythm Electrophysiol. 2011;4:172

Perez-David E et al. J Am Coll Cardiol 2011;57:184Gupta et al. JACC CV Imaging. 2012;5:207

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VT Case #1• 76 yo pt with PHM of HTN, DM, new recurrent

VT on Amio, CC in OSH: no CAD, EF 35%

LBRI axisCL 420ms

Transition V4, no notching V1/2, QRS onset-nadir V1 <90msWinjmaalen et al. Circ Arrhythm Electrophysiol. 2011;4:486

VT Case #1

12/12 PM

NS VT inducible with burst pacing and PES (2ES)

VT Case #1

What is the VT mechanism?

R ee n t

r a nt V T

A ut o m

a t i c/ t r i

g . . .

D on ’ t

k n ow

27%30%

43%

1. Reentrant VT

2. Automatic/triggered VT

3. Don’t know

Ablation Lesion extending into Scar Substrate

MRI-Guided Ablation: Scar + Ablation

Pre-RFA

PostRFA

Tian et al. Circ Arrhythm Electrophysiol. 2012.1;5(2):epub31

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• Further refinement of binary concept (DE+/-)• Introduction of MRI scar core and periphery• Analogous to voltage-defined border zone

De Bakker JM. Circ Arrhythm Electrophysiol 2010; 3:204

‘Grey Zone’- Mixture of Scar and Normal Myocardium -

Schmidt A et al. Circulation. 2007;115:2006

• Grey zone correlated in ischemic patients with all-cause mortality, inducibility of MMVT and appropriate ICD shocks

• Three different definitions:- Scar (>3SD), Grey Zone (2-3 SD), - Scar (>50% max SI), Grey Zone(>peak remote/<50%max SI)- Scar (>50% max SI), Grey Zone (35-50% max SI)

‘Grey Zone’- Mixture of Scar and Normal Myocardium -

Yan A. et al. Circulation 2006;114;32

Roes S. Circ Cardiovasc Imaging. 2009;2:183

• Ischemic swine model (n=17)

• Inducible VT correlated with larger grey zone (25±10% vs. 13±5%)

• Successful RFA of 22 VT, at least one lesion in grey zone

• Residual inducibility found with preserved grey zone

‘Grey Zone’- Mixture of Scar and Normal Myocardium -

Esthner H. Heart Rhythm 2011, doi: 10.1016

Grey Zone – Human Studies

• 18 patients with ischemic CMP and MMVT compared with 18 matched patients

• Scar core (>3SD) and Grey zone (2-3SD)• Continuous grey zone corridors (88% vs. 33%,

p<0.001)• Voltage-map channels corresponded to Grey

zone channels

Perez-David E et al. J Am Coll Cardiol 2011;57:184

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Grey Zone – Human Studies

• 10 patients with ischemic CMP and VT RFA• Voltage as gold standard• Best MRI match with FWHM 60% and

subendocardial half-wall thickness (scar r2=0.808; p<0.001 and BZ: r2=0.485; p=0.025)

• Identified 81% of voltage-defined channels

Andreu D. et al. Circ Arrhythm Electrophysiol. 2011;4:674

Scar=redBZ=green

Comparison of Three Grey Zone Algorithms

FWHM NSD Mod. FWHM

Grey Zone Mass (n=41)

Mesubi AHA 2012

Comparison of Three Grey Zone Algorithms

Modified from DeHaan et al. Heart 2011;97:1951

FWHM NSD Mod. FWHM

- 55 ischemic ICD patients; Follow-up of 2.0 years- 26% ventricular arrhythmias

Resolution-Dependency of Grey Zone (partial volume effect)

• LAD-occlusion model in rats (n=8)• 7T MRI with voxel size of 50x50x50 µm• Grey zone increase from 7 to 14% (p<0.01)

Schelbert et al. Circ Cardiovasc Imaging 2010;3;743

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Diffusion Spectrum MRI Tractography

• Excised paraffin-embedded rabbit hearts

• LAD occlusion

• 4.6T MRI

• 515 diffusion-encoding gradient vectors

Sosnovik D. Circ Cardiovasc Imaging. 2009;2: 206

Virtual EP Study8 Week Swine LAD/LCX Occlusion Model (n=8)

Ng J et al. JACC 2012;60:423

Simulation Non-contact Mapping

-3T MRI based scar/grey zone reconstruction- GZ Model: +20% ADP, -50% conduction velocity- Predicted inducibility in 6/7 swine; 4 correct/2 opposite channel propagation

Take-Home Points• MRI limitations in clinical practice (ICD, resolution etc)

• Good correlation, some mismatch:- <25% endocardial scar- ≥ 2mm viable endocardial myocardium- catheter contact?

• Facilitate substrate-guided ablation:- Epi/endo approach- Pacemap sites- Ablation sites?

• Grey zone/DTI: Heterogenicity as Possible RF Target

• Possible Future Application: Ablation Lesions Arrhythmic Modelling

Thanks

• Jean Jeudi

• Charlie White

• Jing Tian• Ghada Ahmad

• Steve Shorofsky

• Alejandro Jimenez• Rich Kuk

• Alan McMillan

• Carrol Fitzpatrick

• Kathy Lynch• Debbie Nolan-Reily

• Erma White

• Correy Deans• Rao Gallupalli

www.umm.edu/heart/macig