Cardiac imaging in electrophysiology


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Cardiac imaging in electrophysiology

  1. 1. 37A. Auricchio et al. (eds.), Cardiac Imaging in Electrophysiology,DOI 10.1007/978-1-84882-486-7_2, © Springer-Verlag London Limited 2012Magnetic Resonance Imaging:Description of Technologyand ProtocolsGaston R. Vergara and Nassir F. Marrouche2N.F. Marrouche(*)Division of Cardiology, Comprehensive Arrhythmia Research &Management Center, University of Utah Health Sciences Center,Salt Lake City, UT, USAe-mail: nassir.marrouche@hsc.utah.eduAbstractSince its introduction in the late 1970s, catheter-based radiofrequency ablation has evolvedfrom a primitive and experimental procedure to the mainstay for arrhythmia management itis today. Initial intracardiac catheter navigation was fluoroscopy based, and therefore sub-ject to x-ray limitations and side effects. However, accurate catheter location within thecardiac chambers has required electrophysiologic confirmation of catheter positioning. Thisled to the development of conventional cardiac mapping techniques. The limitations of fluo-roscopy and conventional mapping techniques led to the development of electro-anatomicalmapping systems (EAM), in which information regarding catheter position in a 3D space iscombined with electrophysiological information in real time to provide an accurate local-ization of the catheter tip while, at the same time, data regarding electrophysiological prop-erties of the underlying myocardial substrate. Eventually, the mechanisms of more complexarrhythmias, such as atrial fibrillation and scar-based monomorphic ventricular tachycardia,started to be elucidated. This was followed by more difficult ablation procedures thatrequired more accurate mapping systems able to provide real-time information. The intro-duction of EAM combined with Cardiac Computerized Tomography (CCT), cardiacMagnetic Resonance Imaging (cMRI), and real-time intracardiac echocardiography (ICE)allows for more precise mapping with significant improvement in cure rates for ablationprocedures. However, most of these techniques are essentially x-ray based and expose thepatient and the operator to the noxious effects of ionizing radiation.KeywordsCatheter-based radiofrequency ablation • Electro-anatomical mapping systems • CardiacComputerized Tomography • Cardiac Magnetic Resonance Imaging • IntracardiacechocardiographySince its introduction1in the late 1970s, catheter-basedradiofrequency ablation has evolved from a primitive andexperimental procedure to the mainstay for arrhythmiamanagement it is today. Initial intracardiac catheter naviga-tion was fluoroscopy based, and therefore subject to x-raylimitations and side effects. However, accurate catheter loca-tion within the cardiac chambers has required electrophysi-ologic confirmation of catheter positioning. This led to thedevelopment of conventional cardiac mapping techniques.Initial and current conventional electrophysiologic mappingtechniques rely on astute observations and maneuvers touncover the arrhythmia anatomic substrate and pathophysi-ologic mechanisms. However, as progress was made in theunderstanding of the mechanisms underlying arrhythmias,the limitations of fluoroscopy and conventional mappingtechniques became apparent.
  2. 2. 38 G.R. Vergara and N.F. MarroucheThis led to the development of electro-anatomicalmapping systems (EAM), in which information regardingcatheter position in a 3D space is combined with electro-physiological information in real time to provide an accuratelocalization of the catheter tip while, at the same time, dataregarding electrophysiological properties of the underlyingmyocardial substrate.Eventually, the mechanisms of more complex arrhyth-mias, such as atrial fibrillation and scar-based monomorphicventricular tachycardia, were slowly being elucidated. Thiswas followed by more difficult ablation procedures whichrequired more accurate mapping systems able to providereal-time information.The introduction of EAM combined with CardiacComputerized Tomography (CCT), cardiac MagneticResonance Imaging (cMRI) and real-time intracardiacechocardiography (ICE) allows for more precise mappingwith significant improvement in cure rates for ablation pro-cedures. However, most of these techniques are essentiallyx-ray based and expose the patient and the operator to thenoxious effects of ionizing radiation.2.1 MRI for Arrhythmic SubstrateEvaluation: Tissue Characterizationand Anatomic Considerations2.1.1 Atrial Fibrillation Ablation2.1.1.1 Anatomical ConsiderationsAtrial fibrillation (AF) is the most common sustained cardiacarrhythmia, affecting more than two million people in theUnited States,2with an incidence rate of 0.4%3of the generalpopulation. Electrical pulmonary vein isolation (PVI) usingradiofrequency (RF) ablation is effective in symptomatic,drug-refractory AF. Still, reported success rates of the proce-dure vary significantly with reported AF recurrences rangingfrom 25% to 60%.Ever since it was first published in 1998 by Haissaguerreet al., pulmonary vein (PV) triggers have been recognized asthe most common source of paroxysmal atrial fibrillation;electrical isolation of the PV has remained the cornerstone ofatrial fibrillation ablation.4Most ablation techniques include,in one way or the other, a group of lesions distributed in acircular fashion to electrically isolate the PV so that itbecomes of utmost importance then to clearly define the leftatrial (LA) and PV anatomy prior to any ablation.PV anatomy is variable in the general population, and thisis more significant in the AF patient population. Kato et al.5observed up to 38% anatomical variants in patients with AF,these patients typically had larger PV diameter than controls.Wazni et al.3confirmed the presence of a right middle PV in18–29% of patients undergoing evaluation for AF ablation,and this structure has been described as a focus for AFinitiation. The importance of a clear understanding of thepatient’s anatomy is of paramount importance when plan-ning an ablation procedure. cMRI can very clearly demon-strate the presence, location, and anatomical variants of PV’sprior to ablation; allowing for procedural planning. Integration Between Left AtriumcMRI and Non-fluoroscopy BasedMapping SystemsIntegration of LA cMRI images with a non-fluoroscopy-based mapping system is a crucial step in AF ablation,since it allows for precise catheter monitoring in a real-timethree-dimensional manner during ablation. Integration typi-cally consists in fusing two images: CCT or cMRI with anelectro-anatomical map (EAM) or shell of the LA. This pro-cess usually consists of three steps: (1) image acquisition, (2)segmentation, and (3) registration. Accuracy of integrationis crucial for safe catheter navigation and positioning; how-ever, pitfalls related to integration of CCT/cMRI with EAMsystems could occur due to registration errors and changes inthe LA volume, size, and shape between the time of imageacquisition and integration with the EAM system. Tissue Characterization, Stagingof Atrial Fibrillation, and Predictionof AF Ablation SuccessLate gadolinium enhancement-MRI (LGE-MRI) of the LA hasbeen used as a marker for LA fibrosis and structural remodeling.Oakes et al.6have shown that the amount of LGE in the LA isa powerful predictor of AF ablation outcome. The rate of AFrecurrence post-ablation was directly related to the degree ofLA LGE pre-ablation.6The amount of LGE of the LA as amarker of scar formation post-AF ablation has also been directlycorrelated with ablation success in a pilot study.7The use of LGE-MRI pre-ablation for risk stratificationand ablation success prediction has allowed for the develop-ment of a personalized management approach to atrial fibril-lation. Upon initial clinical evaluation and after determiningthe AF burden, a cardiac MRI was acquired. The followingimage acquisition parameters are used. MRI Image AcquisitionPre-ablation cardiac MRI is obtained either on a 1.5 T Avantoor on a 3.0 T Veerio scanners (Siemens Medical Solutions,Erlangen, Germany) using a TIM phased-array receiver coil.The scan is acquired 15 min after 0.1 mmol/kg Multihance(Bracco Diagnostic Inc., Princeton, NJ) contrast agent injec-tion, using a 3D inversion recovery, respiration-navigated,ECG-gated, and gradient-echo pulse sequence. Typicalacquisition parameters were free-breathing using navigatorgating, a transverse imaging volume with voxel size=1.25 ×1.25 × 2.5 mm, and GRAPPA with R=2 and 46 reference
  3. 3. 392 Magnetic Resonance Imaging: Description of Technology and Protocolslines. ECG gating is used to acquire a small subset of phaseencoding views during the diastolic phase of the LA cardiaccycle. The time interval between the R-peak of the ECG andthe start of data acquisition was defined using the cine imagesof the LA. Fat saturation is used. The TE of the scan (2.3 ms)is chosen such that fat and water are out of phase and thesignal intensity of partial volume fat-tissue voxels wasreduced allowing improved delineation of the LA wallboundary. The T1 value for the LGE-MRI scan is identifiedusing a scout scan. Typical scan time for the LGE-MRI studyis 5–10 min. LGE-MRI Quantification of Pre-ablationFibrosis/Structural Remodelingand Post Ablation ScarringAfter image acquisition, the epicardial and endocardial LAborders are manually contoured using the CoreView imagedisplay and analysis software. The relative extent of pre-ablation enhancement and post-ablation scar is then quanti-fied within the LA wall with a threshold-based algorithmutilizing pixel intensities from normal based on a bimodaldistribution (Fig. 2.1). Since post-ablation scar pixel inten-sity is significantly higher than pre-ablation delayed enhance-ment, a different threshold is used for analysis and imagingof scar. Staging AF Using MRISupported by outcome data we have established at theUniversity of Utah, a clinical staging system composed offour stages based on the amount of pre-ablation delayedenhancement (fibrosis) as a percentage of the volume of theleft atrial wall.8This clinical staging system includes fourstages: Utah I£5% enhancement, Utah II>5–20%, UtahIII>20–35%, and Utah IV>35%. When performing aStep 1Acquire DE-MRIStep 6Render enhancement in 3DStep 5Detect enhancement of LA wallStep 4Analyze MRI pixel intensity0.0120.010.0080.0060.0040.00200 50 100 150 200Step 2Label LA wallStep 3Isolate LA wallFig. 2.1 LGE-MRI quantification of pre-ablation fibrosis/structuralremodeling and postablation scarring. After LGE-MR images areobtained (1), the endocardial and epicardial borders are manuallycontoured and isolated (2, 3), and the extent of LGE is then quantifiedusing a pixel intensity distribution (4), qualitative confirmation is thenperformed, a color lookup table mask is then applied to differentiateenhanced and non-enhanced tissue (5), and finally a 3D rendering of theLA is generated allowing for better visualization and spatial localiza-tion of the late gadolinium enhancement (6)
  4. 4. 40 G.R. Vergara and N.F. Marrouchemultivariate analysis, it was found that the number of PVisolated in patients with Utah stage II and the total amountof scar in those with Utah stage III were predictors of suc-cess. Patients with minimal pre-ablation fibrosis, Utah stageI, did well regardless of the number of PV isolated or thetotal amount of scar, whereas those with advanced atrialremodeling as assessed by LGE-MRI, Utah stage IV, didpoorly regardless.8Moreover, in a multivariate regression model, LGE-MRIevaluation of the left atrial substrate was shown to improvethe predictive value of the CHADS2score, allowing defin-ing patients at higher risk of stroke despite having a low ormoderate CHADS2score.9Patients with a previous strokehad a significantly higher percentage of LA fibrosis com-pared to those without (24.4%±12.4 vs. 16.1%±9.8,p=<0.001). There was also a significant difference in therate of thromboembolism between patients with Utah stageI and those with stage IV. Also it was found that patientswith higher risk for stroke (CHADS2score³2) had higheramounts of LA fibrosis. Using univariate and multivariateregression analysis, LGE-MRI quantified left atrial struc-tural remodeling was independently associated with stroke.9Based on this staging system, a comprehensive cMRI-basedAF management algorithm (Fig. 2.2) has been developed,which helps in triaging patients to AF ablation, as well asplanning a corresponding ablation strategy and future anti-coagulation strategy.2.1.2 SafetyControl of collateral damage is critical during AF ablation.The LA is anatomically related with several vital structures;the pulmonary artery runs along the LA dome, the ascendingaorta relates with the LA anterior wall and dome, thedescending aorta with the posterior wall, the phrenic nerve isanterior to the right pulmonary veins, and the esophagusruns behind the posterior wall and the left inferior PV.Understanding of these relationships and monitoring of theseanatomical structures during ablation is of paramount impor-tance to avoid disastrous complications. LGE of the esopha-gus has been used to monitor for post-ablation injury.10Inone report, Badger et al.11studied 41 patients’ LGE-MRIpre-AF ablation, 24 h post-AF ablation, and 3 months afterthe ablation. Five patients demonstrated esophageal enhance-ment 24 h post-ablation and esophageal injury confirmed byesophagogastroduodenoscopy (EGD). EGD and cMRI wererepeated a week later and confirmed resolution of esophagealLGE and endoscopic resolution of these lesions as well.Follow-up cMRI at 3 months post ablation demonstrated noLGE on the esophageal wall (Fig. 2.3).2.2 Ventricular Tachycardia AblationArrhythmia substrate evaluation is critical for ventriculartachycardia (VT) evaluation and ablation strategy planning.cMRI has the capacity to assess not only ventricular systolicfunction but also, and simultaneously, to provide insightsinto the myocardial underlying pathology.2.2.1 Scar-Based Monomorphic VentricularTachycardia: Ischemic VTVT associated with myocardial scars, either ischemic(Fig. 2.4a–c), due to sarcoidosis, or cardiomyopathy, isPatients with AFLGE-MRI to assess degreeof fibrosis (AF staging)Utah I Utah II Utah III Utah IVPulmonary VeinIsolationConsiderstop warfarinConsiderstop warfarinContinuewarfarinContinuewarfarinPulmonary VeinEncirclingPosteriorwall/septaldebulkingRate/RhythmControlFig. 2.2 University of Utahproposed LGE-MRI-basedmanagement algorithm forpatients with AF
  5. 5. 412 Magnetic Resonance Imaging: Description of Technology and Protocolstypically a monomorphic re-entrant arrhythmia dependentupon the presence of a conduction isthmus. This isthmuscould be inside the scar, around the scar, or around a fixedanatomical structure (i.e., cardiac valves). These arrhyth-mias are usually not well tolerated hemodynamically.Different strategies for the mapping of these VTs includescar/substrate assessment with electro-anatomical mappingsystem, pace mapping, and evaluation of diastolic potentials.These different strategies, however, are time consuming,adding length and risk to these procedures.Fig. 2.3 LGE-MRI of the esophagus and EGD. (a) LGE-MRI demon-strates enhancement of the anterior esophageal wall (arrows) whichcorrelates with a lesion (green arrow) found on EGD (c). (b) A weeklater, there has been resolution of late gadolinium enhancement on MRI(arrows) and resolution of the lesion on EGD (d and e)Fig. 2.4 Characteristic cMRI of patients with ischemic scar. CardiacLGE-MRI (late gadolinium enhancement phase sensitive inversionrecovery (PSIR) sequence) of patient with ischemic cardiomyopathy andscar-based monomorphic ventricular tachycardia (a: short axis view, b:two chamber view, and c: long axis view) demonstrating a scar (greenarrowheads) in the distal antero-septal segments of the LV (bright area)
  6. 6. 42 G.R. Vergara and N.F. MarroucheLGE-MRI provides a reliable assessment of myocardialscar, particularly in ischemic substrates. Bello et al. found,in 18 patients, a correlation between infarct surface area andinfarct mass as defined by LGE-MRI and VT inducibilityon EPS.12On another larger study, Schmidt et al. demon-strated the association between “scar border zone,” a dis-tinct zone than dense scar based on pixel intensity onLGE-MRI, and inducibility in EPS.13In this study, theamount of scar border zone was a good predictor of induc-ibility, whereas the total amount of dense scar was not.Information about VT substrate has been used, albeitexperimentally, to predict the VT circuit. Ashikaga et al.correlated, in an animal model, surface ventricular mappingwith ex-vivo high-resolution cMRI and found correlationbetween exit sites and conduction isthmus with isles of via-ble myocardium within the scar.142.2.2 Arrhythmogenic Right VentricularDysplasia/CardiomyopathyArrhythmogenic right ventricular dysplasia/cardiomyopa-thy (ARVD/C) is cardiomyopathy which affects mainly theright ventricle (RV). It is characterized by fatty/fibro-fattyreplacement and myocyte loss, ventricular aneurysms, ven-tricular arrhythmias, and right ventricular failure. There ismounting evidence that the underlying etiology of ARVD/Cis desmosomal dysfunction.15Its prevalence is estimated tobe around 1:5,000 in the United States, and accounts for 5%of all sudden cardiac death in patients younger than 35 yearsold in the United States. Its diagnosis is based on a set ofmajor and minor criteria established by the Task Force ofCardiomyopathy.16They include evaluation for structuraland electrophysiological abnormalities, as well as elementsfrom the patient history.Cardiac MRI is a very useful noninvasive tool for theevaluation of ARVD/C since it can define the presence ofmyocardial fat infiltration, observed in T1-weightedsequences,15and it can also allow for evaluation of the struc-ture of the RV and quantification of its function.2.2.3 Ventricular Tachycardia in StructurallyNormal Ventricles (Idiopathic VentricularTachycardia)Approximately 10% of all ventricular tachycardias occur inventricles that are structurally normal.17The presence of sub-clinical structural abnormalities is not always evident in theechocardiogram and/or coronary angiogram which are usu-ally normal. MRI in these cases may assist in the differentialdiagnosis and point toward a different etiology.2.3 Radiofrequency Ablation LesionCharacterizationCharacterization of the myocardial changes followingRFablationisofimportancesinceitwouldallowforvalidationof therapy delivered and ultimately for ablation endpoints.2.3.1 Acute Wall Edema Post AblationAcute edema, enhancement on T2w images performedimmediately after AF ablation, correlates significantly withlow voltage areas (defined as<0.05 mV) mapped using theCARTO system. However, the area enhanced with T2wimaging is much larger than the area covered by LGE onMRI acutely post-AF ablation.18Acute post-ablation edemais seen not only in regions directly subjected to RF energybut also in distant regions (Fig. 2.5) and it does not predictfinal scar formation defined by LGE-MRI at 3 months.18ALGE-MRI at 3 months after AF ablation shows loss ofenhancement on T2w images consistent with edema reso-lution in areas free of scar. Edema seen acutely in regionsother than in ablated areas suggests a mechanism other thandirect radiofrequency thermal lesion as its cause.Finally, the presence of edema in regions away from areasthat result in scar formation, as well as its association withlow voltage on electro-anatomical mapping may explain, atleast partially, the presence of acute PV disconnection, andlate reconnection with edema resolution, or ventricular myo-cardial recovery following VT ablation.182.3.2 Late Gadolinium-Enhanced DefinedScar and Non-reflow PhenomenonHeterogeneity in the LA wall is seen on acute post-ablationLGE-MRI scans with portions showing very little or noenhancement at all even in areas that received direct RFenergy (Fig. 2.6). In a porcine model of ablation, these areascorrelated well with lesion formation, particularly with areaswith the highest amount of injury. Within minutes there isresolution of these areas of non-enhancement and they mani-fest all the features of ablated/scarred areas. These areas ofno-enhancement are believed to correspond to areas of no-reflow, phenomenon similar to that seen in ventricles in theimmediate post-MI period.182.3.3 Late Imaging and RecurrencesThe amount of scar and the number of circumferentiallyscarred PVA on LGE-MRI is associated with better outcomes
  7. 7. 432 Magnetic Resonance Imaging: Description of Technology and Protocolsfor AF ablation, confirming earlier studies that total LA abla-tion scar burden is associated with AF termination.19However, complete PVA isolation is difficult to achieve andcomplicated by the fact that certain changes seen acutely arereversible over a 3-month period.Acutely post-ablation voltage and LGE-MRI definedscar do not have a good correlation. However, acuteLGE-MRI areas correlate well with areas of low voltageat 3 months. These areas of acute LGE-MRI likely rep-resent areas with irreversible damage from RF ablationwhereas the larger area of low voltage during the acutepost-ablation period likely represents a combination of tis-sue edema, other reversible changes, and areas that willscar completely.LGE-MRI can also accurately identify the location ofbreaks in ablation lesion sets, and its correlation with con-duction recovery, which may explain post-ablation AF recur-rences.19Badger et al.20demonstrated that AF recurrencesfollowing ablation are associated with significant gapsbetween lesions, and that these gaps correlated well withrecovery of local EGMs or PV electrical conduction. Thishas allowed to better plan and tailor re-do procedures forpatients with PV tachycardias, atrial/flutters, or atrialfibrillation.2.4 The Future: Real-Time-MRIThe assessment of lesion formation during electrophysio-logic procedures has always been a challenge; cMRI allowsfor visualization of location and extent of RF ablation lesion,scar formation in the myocardium, and potentially real-timeassessment of lesion formation. Real-time MRI (RT-MRI)–based imaging and ablation system has the potential advan-tage of tissue lesion visualization during RF delivery, whichcould be used as an ablation end point. ElectrophysiologyRT-MRI-guided procedures have been carried out by a fewlaboratories.Fig. 2.5 Post-ablation edema extends beyond ablated regions. CardiacMRI from six patients post-AF ablation demonstrates edema (brightT2w signal) extending not only in regions where RF energy wasdelivered (posterior wall and PV antrum) but also remote LA regions(anterior wall/dome and lateral wall)
  8. 8. 44 G.R. Vergara and N.F. MarroucheMRI-guided ablation in the atrium has recently beenreported by Schmidt et al.21and by Hoffmann et al.22In oneofthesestudies,MRIangiographyoftheatriumwasacquired,the atrium surface was segmented, and real-time catheternavigation was then carried out using this 3D reconstruction;however, no images were acquired during ablation21; rather,immediately postablation lesion formation was confirmed byLGE imaging. In the other study,22the catheters were navi-gated using RT-MRI sequences; however, there was noimmediate tissue visualization during RF delivery and lesionformation, although there was T2w evaluation of the abla-tion site just before and after the ablation of the cavo-tricus-pid isthmus. These two studies were done in 1.5-T MRI.At our EP-MRI suite, we could demonstrate the feasibil-ity to safely navigate and pace and record intracardiac EGMsin the atrial chambers under 3-T real-time MRI guidance.23We used a novel 3-T real-time (RT) MRI–based porcineRF ablation model with visualization of lesion formation inthe atrium during RF energy delivery (Fig. 2.7).In this model, RF energy was delivered under cMRIvisualization at 3-T using custom RT-MRI software. Anovel MRI-compatible mapping and ablation catheter wasalso used. Under RT-MRI, this catheter was guided andpositioned within either the left or right atrium. Unipolarand bipolar electrograms were recorded. The catheter tip-tissue interface was then visualized with a T1w FLASH(T1-weighted fast low angle shot) sequence. RF energy wasthen delivered in a power-controlled fashion, and myocar-dial changes and lesion formation were visualized with aT2w HASTE (half Fourier with single shot turbo spin echo)sequence during the ablation. The presence of a lesionwas confirmed by LGE- MRI and macroscopic tissueexamination.According to these studies, MRI-compatible catheters canbe navigated and RF energy safely delivered under 1.5- and3-T RT-MRI guidance. It was also feasible to record EGMsin the atrium and ventricle during real-time image acquisi-tion. Real-time visualization of lesion as it forms duringFig. 2.6 Non-reflowphenomenon on LGE-MRI.(a1, a2) Cardiac LGE-MRI oftwo patients immediatelyfollowing AF ablationdemonstrates areas of LGEmixed with areas of noenhancement in the posteriorwall (blue arrowheads). Thesesame patients underwentLGE-MRI at 3 months postablation. (b1,b2)The above areascorrelated well with scarformation in the posterior wall(blue arrows)
  9. 9. 452 Magnetic Resonance Imaging: Description of Technology and Protocolsdelivery of RF energy was possible and demonstrated usingT2-w HASTE imaging under 3-T.Finally, catheter visualization and myocardial tissueimaging under RT-MRI during RF energy could help improveablation procedure outcomes by immediate assessment ofablation endpoints in the myocardium.References1. Mitsui T, Ijima H, Okamura K, Hori M. Transvenous electrocauteryof the atrioventricular connection guided by the His electrogram.Jpn Circ J. 1978;42(3):313-318.2. Feinberg WM, Blackshear JL, Laupacis A, Kronmal R, Hart RG.Prevalence, age distribution, and gender of patients with atrial fibril-lation. Analysis and implications. Arch Intern Med. 1995;155:469-473.3. Wazni OM, Tsao HM, Chen SA, et al. Cardiovascular imaging in themanagement of atrial fibrillation. J Am Coll Cardiol. 2006;48(10):2077-2084. Epub 2006 Nov 1.4. Haïssaguerre M, Jaïs P, Shah DC, et al. Spontaneous initiation ofatrial fibrillation by ectopic beats originating in the pulmonary veins.N Engl J Med. 1998;339(10):659-666.5. Kato R, Lickfett L, Meininger G, et al. Pulmonary vein anatomy inpatients undergoing catheter ablation of atrial fibrillation: lessonslearned by use of magnetic resonance imaging. Circulation. 2003;107(15):2004-2010.6. Oakes RS, Badger TJ, Kholmovski EG, et al. Detection andquantification of left atrial structural remodeling with delayed-enhancement magnetic resonance imaging in patients with atrialfibrillation. Circulation. 2009;119(13):1758-1767.7. Peters DC, Wylie JV, Hauser TH, et al. Recurrence of atrial fibrilla-tion correlates with the extent of post-procedural late gadoliniumenhancement: a pilot study. JACC Cardiovasc Imaging. 2009;2(3):308-316.8. Akoum N, Daccarett M, McGann C, et al. Atrial fibrosis helpsselect the appropriate patient and strategy in catheter ablation ofatrial fibrillation: a DE-MRI guided approach. J CardiovascElectrophysiol. 2011;22(1):16-22.9. Daccarett M, Badger TJ, Akoum N, et al. Association of left atrialfibrosis detected by delayed-enhancement magnetic resonanceimaging and the risk of stroke in patients with atrial fibrillation. J AmColl Cardiol. 2011;57(7):831-838.10. Meng J, Peters DC, Hsing JM, et al. Late gadolinium enhancementof the esophagus is common on cardiac MR several months afterpulmonary vein isolation: preliminary observations. Pacing ClinElectrophysiol. 2010;33(6):661-666.11. Badger TJ, Adjei-Poku YA, Burgon NS, et al. Initial experience ofassessing esophageal tissue injury and recovery using delayed-enhancement MRI after atrial fibrillation ablation. Circ ArrhythmElectrophysiol. 2009;2(6):620-625.12. Bello D, Fieno DS, Kim RJ, et al. Infarct morphology identifiespatients with substrate for sustained ventricular tachycardia. J AmColl Cardiol. 2005;45(7):1104-1108.13. Schmidt A, Azevedo CF, Cheng A, et al. Infarct tissue heterogene-ity by magnetic resonance imaging identifies enhanced cardiacarrhythmia susceptibility in patients with left ventriculardysfunction. Circulation. 2007;115(15):2006-2014.Fig. 2.7 Real-time MRI ablation and lesion visualization at 3-T.(a and b) MRI-compatible RF catheter guided under RT-MRI from theIVC into RA, the signal from the tracking elements is displayed andcolor coded (red: distal and yellow: proximal) to allow the operatorcatheter visualization. (c–g) Real-time 20 W power lesion can beseen (T2w HASTE) as it is being formed from catheter touch down(c) to 45 (g) (green arrows)
  10. 10. 46 G.R. Vergara and N.F. Marrouche14. Ashikaga H, Sasano T, Dong J, et al. Magnetic resonance-basedanatomical analysis of scar-related ventricular tachycardia: impli-cations for catheter ablation. Circ Res. 2007;101(9):939-947.15. Jain A, Tandri H, Calkins H, Bluemke DA. Role of cardiovascularmagnetic resonance imaging in arrhythmogenic right ventriculardysplasia. J Cardiovasc Magn Reson. 2008;10(1):32.16. McKenna WJ, Thiene G, Nava A, et al. Diagnosis of arrhyth-mogenic right ventricular dysplasia/cardiomyopathy. Task Force ofthe Working Group Myocardial and Pericardial Disease of theEuropean Society of Cardiology and of the Scientific Council onCardiomyopathies of the International Society and Federation ofCardiology. Br Heart J. 1994;71(3):215-218.17. Klein LS, Shih HT, Hackett FK, Zipes DP, Miles WM.Radiofrequency catheter ablation of ventricular tachycardia inpatients without structural heart disease. Circulation. 1992;85(5):1666-1674.18. Vergara GR, Marrouche NF. Tailored management of atrial fibrilla-tion using a LGE-MRI based model: from the clinic to the electro-physiology laboratory. J Cardiovasc Electrophysiol. 2011;22(4):481-487.19. McGann CJ, Kholmovski EG, Oakes RS, et al. New magneticresonance imaging-based method for defining the extent of leftatrial wall injury after the ablation of atrial fibrillation. J Am CollCardiol. 2008;52(15):1263-1271.20. Badger TJ, Daccarett M, Akoum NW, et al. Evaluation of left atriallesions after initial and repeat atrial fibrillation ablation: lessonslearned from delayed-enhancement MRI in repeat ablation proce-dures. Circ Arrhythm Electrophysiol. 2010;3(3):249-259.21. Schmidt EJ, Mallozzi RP, Thiagalingam A, et al. Electroanatomicmapping and radiofrequency ablation of porcine left atria and atrio-ventricular nodes using magnetic resonance catheter tracking. CircArrhythm Electrophysiol. 2009;2(6):695-704.22. Hoffmann BA, Koops A, Rostock T, et al. Interactive real-timemapping and catheter ablation of the cavotricuspid isthmus guidedby magnetic resonance imaging in a porcine model. Eur Heart J.2010;31(4):450-456. Epub 2009 Nov 5.23. Vergara GR, Vijayakumar S, Kholmovski EG, et al. Real time MRIguided radiofrequency atrial ablation and visualization of lesionformation at 3-Tesla. Heart Rhythm. 2011;8(2):295-303.
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