cardiovascular magnetic resonance imaging for structural and...

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STATE-OF-THE-ART REVIEW

Cardiovascular Magnetic ResonanceImaging for Structural and ValvularHeart Disease Interventions
João L. Cavalcante, MD,a Omosalewa O. Lalude, MBBS,b Paul Schoenhagen, MD,c Stamatios Lerakis, MDb
JACC: CARDIOVASCULAR INTERVENTIONS CME

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From the aDepartment of Medicine, Division of Cardiology, UPMC Heart & Va

Pennsylvania; bDepartment of Medicine, Division of Cardiology, Emory UnivcRobert and Suzanne Tomsich Department of Cardiovascular Medicine, Clev

Institute, Cleveland, Ohio. Dr. Cavalcante has received research grant suppo

Edwards Lifesciences. All other authors have reported that they have no re

disclose.

Manuscript received October 22, 2015; revised manuscript received Novemb

CME Objective for This Article: At the end of this activity the reader

should be able to: 1) recognize the advantages and limitations of

cardiac magnetic resonance imaging in structural and valvular heart

disease interventions; 2) discuss the utility of late gadolinium

enhancement imaging in the evaluation of patients with aortic

stenosis pre- and post-intervention; and 3) describe the role of

cardiac magnetic resonance imaging and phase contrast velocity

mapping in the assessment of valvular stenosis/regurgitation and

cardiac shunts.

CME Editor Disclosure: JACC: Cardiovascular Interventions CME Editor

Bill Gogas, MD, PhD, has received research grant support from

NIH T32, Gilead Sciences, and Medtronic Inc.

Author Disclosures: Dr. Cavalcante has received research grant

support from Medtronic Inc. Dr. Lerakis is a consultant for

Edwards Lifesciences. All other authors have reported that they

have no relationships relevant to the contents of this paper to

disclose.

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CME Term of Approval

Issue Date: March 14, 2016

Expiration Date: March 13, 2017

scular Institute, University of Pittsburgh, Pittsburgh,

ersity School of Medicine, Atlanta, Georgia; and the

eland Clinic, Imaging Institute and Heart & Vascular

rt from Medtronic Inc. Dr. Lerakis is a consultant for

lationships relevant to the contents of this paper to

er 30, 2015, accepted November 30, 2015.

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Cavalcante et al. J A C C : C A R D I O V A S C U L A R I N T E R V E N T I O N S V O L . 9 , N O . 5 , 2 0 1 6

CMR for Structural and Valvular Interventions M A R C H 1 4 , 2 0 1 6 : 3 9 9 – 4 2 5

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Cardiovascular Magnetic Re
sonance Imaging forStructural and Valvular Heart Disease Interventions
ABSTRACT

The field of percutaneous interventions for the treatment of structural and valvular heart diseases has been expanding

rapidly in the last 5 years. Noninvasive cardiac imaging has been a critical part of the planning, procedural guidance,

and follow-up of these procedures. Although echocardiography and cardiovascular computed tomography are the most

commonly used and studied imaging techniques in this field today, advances in cardiovascular magnetic resonance

imaging continue to provide important contributions in the comprehensive assessment and management of these

patients. In this comprehensive paper, we will review and demonstrate how cardiovascular magnetic resonance imaging

can be used to assist in diagnosis, treatment planning, and follow-up of patients who are being considered for and/or

who have undergone interventions for structural and valvular heart diseases. (J Am Coll Cardiol Intv 2016;9:399–425)

© 2016 by the American College of Cardiology Foundation.

C ardiac magnetic resonance (CMR) is anoninvasive imaging modality that allowsdetailed visualization of cardiac anatomy

and functional assessment, including wall motionanalysis, quantification of chambers size and vol-ume, systolic and diastolic function, and myocardialtissue characterization, without exposure to ionizingradiation. Similar to cardiovascular computed to-mography, CMR also provides imaging with excellentspatial resolution and ability for 3-dimensional (3D)multiplanar reconstruction. Strengths, limitations,and contraindications of this technique are listedin Table 1.

OVERVIEW OF CMR IMAGING TECHNIQUE

Initial routine axial images are obtained along theentire thorax providing an overview of the cardio-thoracic morphology and anatomy (1). Subsequently,more specific views are acquired to define the struc-ture and/or pathology of interest. A particularstrength of CMR is the capability to assess cardiacfunction using cine sequences with high temporaland spatial resolution, while not being limited by aspecific imaging plane. Quantification of left ventric-ular (LV) and right ventricular (RV) mass, volumes,and systolic function with CMR is considered thegold-standard for noninvasive imaging. This is typi-cally performed applying breath-holding techniques,in the short-axis orientation covering the entire leftand right ventricles from the base to the apex.Either manual tracing or semiautomated contourdetection of the endocardial and epicardial bordersis then performed. The end-diastolic and -systolicframes are identified as the frames with the largest

and smallest areas, respectively. These contoursare used to calculate end-diastolic and -systolicvolumes, stroke volumes, and ejection fraction(2) (Figure 1). Technological advances now allowadequate free-breathing imaging acquisition, which isadvantageous in patients with advanced heart failure,in those unable to perform breath-hold, and/or inthose with cardiac arrhythmias.

Cine images can also provide excellent evaluationof valvular morphology and function. Quantificationof disease severity (stenosis or regurgitation) isusually performed with the combination of2-dimensional (2D) cine imaging and flow quantifi-cation using the phase-contrast technique. Further-more, CMR can also ascertain the effects of thevalvular disease on chamber remodeling, which is notonly important for decision making, but also prog-nostically relevant.

Additional volumetric data acquisition allows 3Dmultiplanar reconstruction, similar to multidetectorcomputed tomography (MDCT) or 3D echocardiogra-phy. This is especially helpful for the patient withcomplex cardiovascular disease before and aftercorrective surgery. Use of navigator-echo methods,like noncontrast electrocardiography (ECG)-gated 3Dsteady-state free precession magnetic resonanceangiography, synchronizes respiratory and cardiacgating, allowing 3D dataset acquisitions without theneed for intravenous contrast (hereafter abbreviatedas 3D whole heart), which can be reconstructed withexcellent spatial resolution (Figure 2).

Another strength of CMR is the capability ofproviding tissue characterization. Most CMR contrastagents are gadolinium chelates, which in normalcircumstances remain in the blood pool because

TABLE 1 CMR Imaging: Advantages, Limitations, and

Contraindications

Advantages

� High test-retest reproducibility for quantification of chambervolume, mass, infarction size, and so on.

� Precise quantification of complex flow patterns withoutgeometrical assumptions.

� Enables tissue characterization and the understanding ofpathophysiological processes.

� Provides a large field of view, not limited to echocardiographicwindows or lung/breast interface.

� High spatial resolution with excellent temporal resolution.

� 3-dimensional cardiovascular anatomy visualization withoutthe need for intravenous contrast (advantageous for patientswith advanced renal failure and/or those with iodine allergy).

� No ionizing radiation to the patient.

Limitations

� Not portable and relative less accessible. Usually limited totertiary referral centers with experienced team.

� Claustrophobia requires patient education and anxiolytic/sedation for study completion.

� Test may not be possible for severely obese individuals(usually a torso circumference >70 cm).

� Patient should be medically stable.

� Cardiac arrhythmia and respiratory motion can compromiseimage quality.

� Mechanical prosthesis, implantable stents, or cardiovasculardevices can create imaging artifacts.

� Pregnancy: avoid if possible. Pediatrics: children <8 years likelyneed general anesthesia.

Contraindications*

� Severe renal impairment (GFR <30 ml/min/1.73 m2) should notreceive gadolinium given the risk of nephrogenic systemicfibrosis.

� Cerebral aneurysm clips.

� Pacemakers/ICDs (relative). New CMR-conditional systems arenow FDA approved and available.*

� Pulmonary artery catheters.

� Cochlear implants.

� Retained metallic foreign bodies.

*Consult website: www.mrisafety.com for updated details. Intravascular coils,stents, and filters are usually safe. Prosthetic heart valves, including TAVRbioprosthesis, are safe at 1.5-T. An exception is the pre-1968 Starr Edwards Valve.

CMR ¼ cardiac magnetic resonance; FDA ¼ Food and Drug Administration;GFR ¼ glomerular filtration rate; ICD ¼ implantable cardioverter-defibrillator.

AB BR E V I A T I O N S

AND ACRONYM S

2D = 2-dimensional

3D = 3-dimensional

AS = aortic stenosis

ASD = atrial septum defect

CMR = cardiac magnetic

resonance

LGE = late gadolinium

enhancement

LV = left ventricular

MDCT = multidetector

computed tomography

MF = myocardial fibrosis

PDA = patent ductus arteriosus

PVL = paravalvular leak

RV-PA = right ventricular–

pulmonary artery

TAVR = transcatheter aortic

valve replacement

TOF = tetralogy of Fallot

TTE = transthoracic

echocardiography

VSD = ventricular septum

defect

J A C C : C A R D I O V A S C U L A R I N T E R V E N T I O N S V O L . 9 , N O . 5 , 2 0 1 6 Cavalcante et al.M A R C H 1 4 , 2 0 1 6 : 3 9 9 – 4 2 5 CMR for Structural and Valvular Interventions

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the myocardial extracellular space is not disrupted.However, in acute or chronic myocardial infarction,cellular necrosis causes cell membrane rupture andincrease in the extracellular space where gadoliniumcan distribute. The paramagnetic effect of gadoliniumcauses a shortening of T1 relaxation time, thus causingareas with gadolinium to be bright on T1-weightedimages. The technique used for T1-weighted late gad-olinium enhancement (LGE) imaging starts withintravenous contrast injection of 0.1 to 0.2 mmol/kgbolus of gadolinium-based contrast, and after 10 to 20min (steady-state), the acquisition of T1-weightedimages with adequate inversion time to null thesignal from normal myocardium (dark). The optimal

inversion time is that which results in sup-pression of normal myocardium (with lowsignal and, thus, dark image) along with abrighter signal from the myocardial cavity anda very bright signal in the scar tissue. Thelandmark study by Kim et al. (3) was the firstin vivo study to demonstrate the capability ofCMR to visualize and quantify ischemicmyocardial infarct using LGE imaging.The authors also showed that the trans-murality of the myocardial scar was akey predictor for functional improvementpost-revascularization.

However, over the last few years, LGEimaging has also been shown to be prog-nostically important in nonischemic cardio-myopathies and, more recently, in patientswith valvular disease. The association ofmid-wall fibrosis in LGE imaging withadverse cardiovascular outcomes suggeststhat we need to consider a change in theconcept of “bright is dead to bright is bad”(4). Myocardial tissue characterization byCMR can also be obtained by applyingdifferent pulse sequences, each exploitingdifferent features of tissue composition,
magnetization transfer, and spin relaxation, and notnecessarily requiring intravenous contrast agent. Forexample, T1 mapping can evaluate for diffuse myo-cardial fibrosis and T2 mapping can determine areaswith focal myocardial edema/inflammation, whereasthe T2* (star) sequence has been validated for iden-tification and quantification of myocardial ironcontent, which can be increased in patients withhemochromatosis. This increased capability of eval-uating the “myocardial health” might become use-ful, as will be discussed, for future risk stratificationof patients with valvular disease, in particular forthose with aortic stenosis.
It is important to mention that CMR imagingquality can be compromised in some patients due tosusceptibility artifacts, which can arise from coils,stents, and other post-operative hardware (5). In mostcases, however, the study analysis and interpretationis still possible despite the presence of the localizedartifact, which tends to extend slightly beyond theperimeter surrounding the implanted medical device/hardware.

CMR FOR VALVULAR DISEASE

Echocardiography remains the most established im-aging modality for assessment and follow-up ofpatients with valvular disease. However, over the

http://www.mrisafety.com

FIGURE 1 CMR Quantification of LV Mass, Volumes, Ejection Fraction, and Cardiac Output

LV short-axis cine stack from the base to the apex is used for the contouring and calculation of LV volumes and mass. In this example,

measurements for a patient with severe chronic aortic regurgitation were performed. High-output state causes progressive left ventricular (LV)

remodeling with eccentric hypertrophy confirmed by increased LV volumes and LV mass index. ED ¼ end-diastolic; ES ¼ end-systolic.



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last few years, CMR has emerged as an important,complementary noninvasive imaging modality spe-cifically in patients with difficult echocardiographicwindows and history of (repaired) congenital heartdisease. CMR can evaluate the valvular morphology,mechanism of dysfunction, and consequences of thestenosis/regurgitation on the ventricular functionand remodeling (Central Illustration).

Significant stenosis or regurgitation can occur onthe same valve or involving different valves on thesame patient. Although this is not an uncommonscenario, the diagnostic subtleties using echocardio-graphic evaluation and lack of specific managementguidelines create important challenges in caring forthese complex patients (6). Given its previouslydescribed quantification capabilities for flow andventricular remodeling, CMR can be advantageous forthe evaluation of patients presenting with multiplevalvular disease, although more data is needed tovalidate this approach (7).

AORTIC STENOSIS

DETERMINING THE SEVERITY OF AORTIC STENOSIS

AND ITS EFFECT ON LEFT VENTRICULAR REMODELING

AND RISK STRATIFICATION. Calcific aortic stenosis(AS) is the most common cause of acquired valvulardisease. It is associated with progressive LV pressureoverload, which leads to maladaptive ventricularremodeling (myocyte hypertrophy and myocardialfibrosis) and eventually diastolic and systolicdysfunction.

Although transthoracic echocardiography (TTE)remains the primary noninvasive imaging technique,CMR may be needed to confirm severity of AS mea-surement of the anatomical aortic valve area (AVA)and precise quantification of LV mass, function, andvolumes. Another advantage of CMR imaging in-cludes the ability to identify the site of flow acceler-ation, differentiating subvalvular from valvular orsupravalvular stenosis (Figure 3, Online Video 1).

http://jaccinter.acc.org/video/2016/1278_VID1.wmv

FIGURE 2 3-Dimensional CMR Dataset Used for Multiplanar Reconstruction of the Aortic Annulus, Aortic Root, and Ascending Aorta

Multiplanar reconstruction obtained from cardiac magnetic resonance imaging without gadolinium and using the free-breathing technique

(noncontrast respiratory- and cardiac-gated 3-dimensional magnetic resonance angiography using balanced steady-state free-precession sequence).


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The evaluation of the aorta is particularly impor-tant in patients with a bicuspid aortic valve, which isfrequently associated with thoracic aortopathy and/orcoarctation. Aortopathy is defined by initially sub-clinical connective tissue abnormalities and, only inadvanced stages, by aortic enlargement or dissection.CMR can also provide comprehensive imaging ofthe entire thoracic aorta with 3D multiplanar re-constructions without the need for intravenouscontrast. Knowledge of associated aortopathy mayalter surgical management at the time of valvereplacement. In most circumstances, 3D whole heartacquisitions can be obtained without the need forintravenous contrast. After acquisition is completed,the entire 3D dataset can be manipulated using anoff-line workstation for post-processing. Dedicatedmultiplanar reconstructions along the vessel center-line can be done for the necessary measurements(Figure 2).

The use of phase-contrast velocity mapping tech-niques offers the opportunity for quantification offlow-derived parameters (i.e., stroke volume, peak

aortic valve velocity, peak gradient, and aorticregurgitant volume and fraction) with high repro-ducibility and without need for intravenous gado-linium contrast (8). For this particular imageacquisition, it is very important for the imagingplane to be oriented as perpendicular as possible tothe orientation of the blood flow. If the angle ofintercept is not 90�, an increased likelihood exists ofinaccurate velocity measurements. Also, carefuladjustment of the encoding velocity (i.e., 1.5 � peakaortic valve velocity measured by TTE) can avoidaliasing, and the velocity within that pixel is thencorrectly registered. In clinical practice, however, the2D phase-contrast imaging techniques often under-estimate the peak velocity and gradient measured byTTE. This can be due to several reasons: local signalloss (from flow turbulence), background noise, par-tial volume effects (large intravoxel size), phase shifterrors due to fast acceleration, intravoxel dephasing(particularly with velocities >3.5 to 4 m/s) and rela-tively low temporal resolution (20 to 25 ms), whichmay not be able to capture high jet velocity of short

CENTRAL ILLUSTRATION Cardiac Magnetic Resonance Imaging Applications in Structural and Valvular Heart Disease Interventions



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duration, resulting in underestimation of peak jetvelocities (9).

An additional parameter for assessment of ASseverity is the direct measurement of the anatomicalAVA using a direct 2D planimetry method. Usingorthogonal views (i.e., 3-chamber and/or coronal LVoutflow tract), one can use the scout line method todetermine the exact position (leaflet tips) for mea-surement of the anatomical orifice area. Given thepotential limitations in spatial and temporal resolu-tion, we would recommend to average 3 anatomicalAVA planimetry measurements at the peak systolic

frame (largest aortic valve opening) after carefulconfirmation of the correct imaging plane (Figure 4).This method has been shown to be a reproducibletechnique when using echocardiography (TTE ortransesophageal echocardiography) as the referencestandard (10). Of note, TTE and cardiac catheteriza-tion measure the effective orifice area (physiologicalfunctional stenosis at the vena contracta), whereasthe direct 2D planimetry with CMR and/or trans-esophageal echocardiogram measure the AVA open-ing (anatomical stenosis), which tends to be slightlybigger.

FIGURE 3 CMR Imaging of a Patient With Subaortic Membrane

3-chamber (top left) and coronal (top right) views in a patient with subvalvular obstruction secondary to subaortic membrane. Red arrows

indicate subvalvular obstruction. Note on the short-axis view (bottom center) the tunneled-shape format of these complex subaortic

membranes (Online Video 1).


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CMR FOR AS ASSESSMENT IN THE CONTEXT OF

TRANSCATHETER AORTIC VALVE REPLACEMENT.

In the context of transcatheter aortic valve replace-ment (TAVR) therapies, accurate 3D imaging of theaortic annulus is key to determining the appropriatebioprosthetic valve sizing to avoid potential compli-cations, such as aortic annular rupture and/or para-valvular leak (PVL). Although this is typicallyperformed by MDCT or 3D echocardiography (11),CMR can be a valuable alternative. Direct comparisonbetween CMR and MDCT measurements of the aorticannulus, root, and ascending aorta have shown closeagreement and similar ability to predict PVL (12)(Figure 5). This imaging acquisition, however,required breath-hold, which is not always feasible. Amore attractive and alternative technique has beenthe use of noncontrast 3D whole heart acquisitionsallowing 3D multiplanar reconstructions (13) andprecise evaluation of the established measurements(14). Importantly, this technique can be used in

patients with cardiac arrhythmias, allowing for reli-able annulus measurement and assessment of calci-fications comparable to MDCT (15).

PVL represents the most common complicationpost-TAVR. Although difficult to reconcile withtraditional physiological and hemodynamic under-standing, presence of even mild PVL has been asso-ciated with unfavorable outcomes including latemortality. TTE is the first-line test for PVL quantifi-cation. However, it can be flawed due to pooracoustic windows, eccentricity of PVL jet(s), imagedegradation associated with the implanted pros-thesis, irregular orifices, and subjectivity and incon-sistency on the imaging method and grading (16–18).In these situations, an advantage of CMR in thecharacterization of PVL is the ability to quantifyregurgitant flow regardless of whether a regurgitantjet has been visually identified. Aortic regurgitantvolume and regurgitant fraction are determined onthe basis of the forward and reversal flows quantified


FIGURE 4 CMR Evaluation of Aortic Stenosis Severity Using Planimetry Method

Two orthogonal cine views in a patient with degenerative calcific aortic stenosis (mid-systolic frame). (A) 3-chamber view, and (B) coronal view.

The scout line is used on both views to determine the appropriate level (aortic valve leaflet tips) for the measurement of the anatomical aortic

valve orifice area by 2-dimensional planimetry on the short-axis plane (C). The derived aortic valve area measurement of 0.95 cm2 is consistent

with severe aortic stenosis (dashed outline).



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by phase-contrast imaging (Figures 6 to 8,Online Videos 2 and 3) (19). However, investiga-tional, preliminary single-center studies using CMRphase-contrast imaging post-TAVR have shown aconsistent underestimation of PVL severity whencomparing TTE and CMR (20–23).

It is important to highlight that, at the presenttime, there are no definite cutoffs that have beenestablished and validated to define what constitutesmild, moderate, or severe PVL by CMR phase-contrast evaluation. Most of the current publisheddata has used the values previously identified fornative aortic regurgitation and extrapolates thosecutoffs to PVL post-TAVR. Other important unan-swered questions using this new technique for PVLquantification post-TAVR would include: 1) in whom,when, and how should we measure it; 2) what should

be the parameter to follow (i.e., aortic regurgitantfraction or volume); and 3) how to measure in pa-tients with atrial fibrillation and/or those who areunable to perform breath-hold?

CMR has 2 potential shortcomings in patients un-dergoing TAVR. The first is regarding the CMR’sdetection of calcification of cardiac structures, whichis not well seen by this technique in comparison withcomputed tomography. Advances in post-processingimaging technology (syngo.via, Siemens Health-care, Erlangen, Germany) allow for fusion of gatednoncontrast 3D datasets of cardiac CMR and com-puted tomography, providing exquisite anatomicalinformation about the aortic annulus size, location,and extent of calcifications (Figure 9). This imagingplatform of combined information might present analternative to the current imaging standard with



FIGURE 5 CMR Cine Imaging for the Aortic Annulus Measurements

Gated breath-held cines of 2 orthogonal planes (3-chamber and coronal/left ventricular outflow tract) are necessary for the delineation and

measurement of the aortic annulus area, minimal and maximal annulus diameters. In the double oblique orthogonal short-axis view (bottom

center figure); A refers to the major annular diameter, 27.4 mm, whereas B refers to the minor annular diameter, 21.5 mm.


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gated computed tomography angiography for valvesize selection while being able to improve the pre-diction of post-TAVR complications. The secondshortcoming is that CMR scanning is relatively con-traindicated in patients with conventional cardiacdevices, including certain permanent pacemakersand intracardiac defibrillators. New Food and DrugAdministration–approved CMR imaging conditionalpacemakers provide a comprehensive solution toallow imaging of the entire body under 1.5-T fieldstrength and specific scanning settings (24,25).In addition, new intracardiac defibrillators haverecently demonstrated necessary safety for wholebody CMR imaging scanning, which will soon opennew possibilities for heart failure patients whorequire such devices (26).

Importantly, these CMR imaging-conditionalintracardiac devices could produce and introduceimportant imaging artifacts, which might compro-mise the image quality and study interpretation. Theartifacts could arise from either the generator (right-sided devices produce much less artifact then

conventionally placed left-sided device) and/or fromthe intracardiac leads (intracardiac defibrillator coilproduces more susceptibility artifact than a conven-tional pacing lead). In a patient with a left-sidedpacemaker, attempting to scan him/her with thearms up and/or temporarily moving the subcutaneousgenerator pocket more cranially are tricks that candiminish the generator-related artifact. Use ofgradient-echo cine sequences (instead of conven-tional balanced steady-state free precession) andincreasing the bandwidth are other alternatives thatcan be employed to minimize the artifacts related toimplantable cardiac devices.

CMR FOR AS: QUANTIFICATION OF MYOCARDIAL

FIBROSIS AND PROGNOSTIC SIGNIFICANCE. Use ofLGE imaging with CMR is the gold-standard methodfor noninvasive quantification of focal myocardialfibrosis (MF), which has prognostic value in bothischemic and nonischemic cardiomyopathy.

More recently, several single-center studies havedemonstrated that presence of ischemic myocardial

FIGURE 6 CMR Imaging of 78-Year-Old Male Patient 1-Month Post-TAVR With Balloon-Expandable Bioprosthesis Presenting With

Decompensated Heart Failure

Transcatheter aortic valve replacement (TAVR) was performed with a 26-mm Edwards SAPIEN Transcatheter Heart Valve bioprosthesis

(Edwards Lifesciences Corporation, Irvine, California) 1 month prior, and the patient was now presenting with heart failure symptoms.

Transthoracic echocardiography showed mild paravalvular leak (PVL). Cardiac magnetic resonance (CMR) identified 2 distinct paravalvular leaks

(PVL 1 and 2, blue arrows). CMR quantification suggested moderate PVL (regurgitant fraction ¼ 30%, regurgitant volume ¼ 30 ml/beat)

(Online Video 2).



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scarring and/or replacement MF using LGE imagingappears to be prognostically important in AS patients.Several LGE patterns of MF have been describedin patients with AS, even in the absence of priormyocardial infarction or coronary artery disease.These include: punctate or focal, subendocardial(resembling myocardial infarction), mid-wall, andextensive diffuse fibrosis (Figure 10). Weidemannet al. (27) demonstrated that severe AS patients withextensive focal fibrosis and reduced LV longitudinalshortening do not show clinical improvement (NewYork Heart Association functional class changes) aftersurgical aortic valve replacement (SAVR). Dweck et al.(28) have also shown that focal mid-wall fibrosispattern can be observed in the myocardium of up to

38% of patients with moderate or severe AS andis associated with a more advanced hypertrophicresponse and worse prognosis despite SAVR. A recentsingle-center study including 154 consecutive pa-tients (the largest to date) with severe AS but withoutprior myocardial infarction has shown that presenceand extent of MF detected by LGE imaging pre–aorticvalve replacement predicted increased perioperativerisk and decreased all-cause and cardiovascular-related survival. In a smaller subgroup of patientsthat underwent TAVR, the same findings were alsoobserved—the more MF, the worse the outcomes (29).Even in asymptomatic patients with moderately se-vere AS, indirect evidence of MF by CMR appearsto identify a subgroup of patients at risk for LV


FIGURE 7 CMR Imaging of an 83-Year-Old Male Patient 2 Weeks Post-TAVR With Self-Expandable Bioprosthesis Presenting With

Decompensated Heart Failure

TAVR was performed with a 31-mm Medtronic CoreValve bioprosthesis (Medtronic Inc., Minneapolis, Minnesota) admitted with heart failure

symptoms. Transthoracic echocardiography showed moderate PVL. CMR identified 2 distinct paravalvular leaks (PVL 1 and 2, blue arrows) with

quantification consistent with severe PVL (regurgitant fraction ¼ 53%, regurgitant volume ¼ 46 ml/beat) (Online Video 3).


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decompensation in whom early aortic valve replace-ment could be considered (30,31).

In another interesting recent study from Germany,Kim et al. (32) studied a small cohort of 61 patientspre- and post-TAVR intervention using CMR with LGEimaging. There were different TAVR approaches (43%transapical) and various valve types used. AfterTAVR, new ischemic MF pattern occurred in 11 pa-tients (18%) and was associated with decreased LVfunction (LV ejection fraction pre-TAVR: 55.5 � 14.1%vs. post-TAVR: 45.3 � 14.9%; p ¼ 0.001). It is thoughtthat this could be related to embolic events duringTAVR procedure. However, the data did not point outany clinical and/or procedural predictors for thedevelopment of this new MF post-TAVR (32). Morework is needed to better understand the mechanismand significance of these findings.

Although focal MF is an important marker in AS,diffuse MF appears to be more prevalent according to

histological data (33,34). Recent technological ad-vances in CMR, such as with T1 mapping and extra-cellular volume fraction quantification, allow for anoninvasive imaging “biopsy” and precise quantifi-cation of diffuse MF (35–37).

Whether identification of focal or diffuse MF byCMR, pre- or post-intervention, will translate into anincremental prognostic value for severe AS patientstreated with SAVR or TAVR remains to be determined.Several ongoing studies are investigating the role ofmyocardial fibrosis in AS, and results will be impor-tant to determine the prognostic significance of thesepromising imaging biomarkers.

AORTIC REGURGITATION

Aortic regurgitation eventually leads to LV volumeoverload with eccentric LV remodeling, causing bothincreases in volume and mass (Figure 1). In addition,


FIGURE 8 CMR Quantification of PVL Using Through-Plane Phase-Contrast Imaging in a Patient Post-TAVR

Axial through-plane non–breath-hold phase-contrast sequence at the level of the main pulmonary artery used for quantification of forward

and backward flow into the ascending (red circle) and descending aorta (green circle). Automated post-processing software analysis

demonstrates holodiastolic flow and reversal in the descending thoracic aorta. In addition, precise calculation of the aortic regurgitant flow

(30 ml/beat) and regurgitant fraction (40%) is also derived supporting severe PVL post-TAVR.



410

CMR can help elucidate the mechanism of aorticregurgitation (annular vs. root dilation, leaflet pa-thology: restriction vs. prolapse) and precisely assessaortic morphology and size. This evaluation does notrequire the use of intravenous contrast and can beentirely performed in <30 min.

The most common method for aortic regurgitationquantification is phase-contrast velocity mapping.After choosing a plane above the aortic valve(without significant aliasing and/or flow turbulence),the volume of blood moving in an anterograde andretrograde fashion within the cardiac cycle can bedetermined, allowing calculation of regurgitant vol-ume and regurgitant fraction. Holodiastolic flowreversal can be identified in the descending thoracicand abdominal aorta, which supports the significanceand severity of aortic regurgitation (38) (Figure 11). In

the absence of intracardiac shunts and/or other sig-nificant valvular regurgitation, another method thatcan be used for aortic regurgitation volume quantifi-cation is the difference between the LV and RV strokevolumes.

A particular strength of CMR, in comparison withTTE, is the reproducible and accurate assessment ofaortic regurgitant volume and fraction using phase-contrast imaging. This allows for adequate patientmonitoring of disease progression using serialmeasurements over time (39). CMR quantification ofaortic regurgitation fraction using phase-contrastmethod was also able to predict hard outcomes suchas development of heart failure symptoms andneed for aortic valve replacement. Myerson et al. (40)have shown that a regurgitant fraction >33% hadhigh sensitivity (85%) and specificity (92%) for

FIGURE 9 Co-Registered 3D Datasets of Noncontrast CT and 3D Whole Heart Steady-State Free Precession CMR Imaging in a Patient

With Severe Aortic Stenosis

Fusional imaging with coregistration of the 2 datasets allows for knowledge integration of calcium location and extent by computed to-

mography (CT) with anatomical details of cardiac magnetic resonance (CMR) imaging. HU ¼ Hounsfield units; MRI ¼ magnetic resonance

imaging; SSFP ¼ steady-state free precession; 3D ¼ 3-dimensional.


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identifying patients who progressed to symptoms andsurgery. Furthermore, when LV end-diastolic volume(>246 ml) and aortic regurgitant fraction (>33%) werecombined, a higher association with outcome wasobserved (40).

However, limitations of the technique need to beconsidered. In regards to the image acquisition, theeffects and differences between breath-hold andnonbreath acquisitions cannot be downplayed andcan affect the measurements obtained. This isimportant to the follow-up of patients that will bescanned serially using the same protocol (41). It is veryimportant for the slice position chosen for the phase-contrast plane of interrogation to be consistent. Forexample, downstream assessment of aortic regur-gitant flow at the ascending aorta produces differentresults if it is measured at the sinotubular junction(42). The same applies for peak aortic jet velocityquantification by phase-contrast in patients with AS.

Inhomogeneity of the magnetic field and eddy-currents can cause phase offset errors identified bynonzero velocities in the stationary tissue (i.e., pec-toralis muscle). This can be minimized by applying, atthe post-processing stage, background correctionwith either a pre-determined region of interest for thestationary tissue or using a static phantom baselinecorrection scanned using the same parameters,immediately after the patient leaves the CMR scan-ner. The latter approach is more time consuming andis not practical for routine clinical use. These phase-offset errors appear to be vendor-independent andmust be considered in the planning and standardi-zation of multicenter protocol studies using phase-contrast measurements as 1 of the main endpoints.Although commercially available software allows forthe correction of these phase-offset errors, morestudies are necessary to validate the accuracy of itsalgorithms (43).

FIGURE 10 CMR Imaging of Myocardial Fibrosis Seen With Aortic Stenosis

Late-gadolinium enhancement images approximately 10 to 15 min post-contrast injection using single-shot phase sensitive inversion recovery

sequence. Note the different patterns of myocardial fibrosis seen in aortic stenosis (red arrows and arrowhead). Linear mid-wall fibrosis

involving the interventricular septum (A to C), patchy mid-wall fibrosis (D), and infarct LGE with a subendocardial pattern (E and F).



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MITRAL STENOSIS

Evaluation of mitral stenosis by CMR has been limitedto small, single-center studies. One of the main CMRlimitations in evaluating this valvular pathology isthe inability to visualize calcification. However, givenits excellent spatial resolution, planimetry of mitralvalve area can be measured at the leaflet tips usingbreath-held cine images (44,45). Similar to what wasdescribed for AS, this measurement will provide theanatomic valve area, which is slightly higher thanthat calculated by echo-Doppler method (effectiveorifice area at the vena contracta). Another approachapplied phase-contrast imaging to derive velocities,pressure half-time, and delineation of the mitralvalve opening area. One has to be careful, however,because underestimation of peak velocities can occurgiven the inferior temporal resolution of this method(45,46).

MITRAL REGURGITATION

Mitral regurgitation is a common valvular disorderthat can arise from primary abnormalities of anypart of the mitral valve apparatus. These include

the valve leaflets, annulus, chordae tendineae, andpapillary muscles. Mitral regurgitation can also besecondary to geometrical remodeling changes of theLV anatomy and alterations of the LV contractility,leading to leaflet tethering and incomplete coapta-tion. Echocardiography remains the initial modality,with extensive experience and validation ofquantitative Doppler methods. The advent of 3Dechocardiography, in particular 3D transesophagealechocardiography, has enabled excellent visualiza-tion and understanding of the mitral regurgitationmechanism and helped in the pre-proceduralplanning.

Similar to aortic regurgitation, CMR can also pro-vide excellent quantification of mitral regurgitantvolume/fraction and resultant ventricular remodel-ing. CMR quantification of mitral regurgitation isbased on indirect calculation of mitral regurgitantvolume, derived as the difference between aorticforward stroke volume (using phase-contrast imag-ing) and total LV stroke volume obtained fromvolumetric contours (47). Furthermore, CMR is notdependent on body habitus; it can be performed invarious planes for interrogation of the regurgitant jetand is not limited to the available echocardiographic

FIGURE 11 CMR Phase-Contrast Imaging Findings in Patient With Chronic Severe Aortic Regurgitation

Axial through-plane non–breath-hold phase-contrast sequence at the level of the main pulmonary artery (left panel) used for quantification of forward and backward

flow into the ascending (red circle) and descending aorta (green circle). Automated post-processing software analysis demonstrates holodiastolic flow and reversal in

the descending thoracic aorta. In addition, precise calculation of the aortic regurgitant flow (45 ml/beat) and regurgitant fraction (54%) is also derived. On the right

panel, abdominal aorta non-breath-hold phase-contrast demonstrates again severe holodiastolic flow reversal, which supportive and consistent with severe aortic

regurgitation. This is the same patient from Figure 1 with chronic severe aortic regurgitation who presented with eccentric hypertrophic LV remodeling.


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acoustic windows. Pulmonary hypertension, whichalso tends to accompany the hemodynamic conse-quences of chronic mitral regurgitation, can beinferred by dilation of the right ventricle, increasedRV wall thickness, D-shaped septum, and pulmonaryartery dilation. CMR can also estimate pulmonaryvascular resistance, which rises with the progressionof pulmonary hypertension. A recent study validatedthis noninvasive method, which takes into accountthe mean pulmonary artery ejection velocity and RVejection fraction. It had excellent correlation withinvasive hemodynamic measurements (48). Larger,

multicentric studies are necessary before we canconsider CMR as an alternative initial step or as ameans to monitor interventional therapeutics forthese patients.

The prognosis and decision regarding timing ofsurgery are highly dependent on the accurate quan-tification of mitral regurgitation severity. A recentprospective multicenter study by Uretsky et al. (49)compared echocardiography and CMR imaging inthe assessment of mitral regurgitation severity usingthe degree of LV remodeling after mitral valvesurgery as the reference standard. The majority of



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patients had primary degenerative mitral regurgita-tion with modest severity agreement between the 2modalities (37 of 103 patients, 36%) and over-estimation by echocardiography. The authors alsofound lower interobserver variability with CMR(Intra-class correlation ¼ 0.90 for CMR vs. 0.65 forechocardiography), and importantly, CMR-derivedregurgitant volume accurately predicted post-surgical LV remodeling (49).

When imaging a patient with suspected mitralvalve abnormality, it is essential that all segments ofthe mitral valve leaflets are interrogated with indi-vidual cine images. CMR has the potential to visu-alize all parts of the valve (leaflets, chordaetendineae, and papillary muscles) throughout theentire cardiac cycle, provide insight into the mech-anism (i.e., prolapse, flail, restriction), and also aidin localization of the abnormality. Congenitallyabnormal valve leaflets (i.e., cleft), aberrant papil-lary muscles or aberrant chordal attachments (para-chute mitral valve), leaflet thickening, presenceand extent of calcification, leaflet redundancy andprolapse, and commissural fusion are all anatomicdescriptions that have been reported by CMR. In

FIGURE 12 CMR Evaluation of Mitral Valve Anatomy and Examples

Normal anatomy of the mitral valve in short axis (top left) and example

secondary mitral regurgitation, CMR can provideimportant insights related to the visualization ofunfavorable LV remodeling with commonly associ-ated regional wall motion abnormalities. This couldbe related to chronic myocardial ischemia, priormyocardial infarction with or without direct papil-lary muscle involvement. All of these processes canbe also visualized with CMR. Some examples areshown in Figure 12.

Transcatheter mitral valve repair with the use ofthe MitraClip system (Abbott Vascular StructuralHeart, Menlo Park, California) has been approved bythe Food and Drug Administration for the treatmentof high surgical-risk patients with primary severedegenerative mitral regurgitation. It creates a percu-taneous edge-to-edge repair (figure of 8) similar tothat performed surgically by Dr. Alfieri (50). Althoughechocardiography is the primary method for guidanceand assessment of severity post-implant (51), it can bedifficult to quantify the residual mitral regurgitationpost-MitraClip. This can be due to artifacts createdby the clip limiting visualization of the jet origin,eccentricity of mitral regurgitation jet, and alterednative mitral valve anatomy. CMR, therefore, might

of Both Primary and Secondary Causes of Mitral Regurgitation

s of causes of both primary and secondary mitral regurgitation (MR).


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have a potential role in evaluating the severity ofresidual mitral regurgitation in selected patientspost-MitraClip implant. In a small, single-centerstudy including 25 patients post-MitraClip, CMR wasshown to have excellent reproducibility and lowerinterobserver variability in comparison with echo-cardiography (52). Susceptibility artifact from theMitraClip occurs, and more experience and studiesare necessary to evaluate the complementary rolethat CMR might have for these patients, in addition toLV remodeling evaluation post-transcatheter inter-vention (53).

Another exciting recent development is possibilityof transcatheter mitral valve replacement (54). Plan-ning of the procedure will likely rely on precise pre-procedural assessment of the mitral annular planeand several other measurements, which currently arebeing evaluated with gated MDCT (55). There is aneed to define the potential role of CMR for this newintervention.

Last, CMR can be helpful for the assessment andquantification of PVL associated with long-standingsurgically placed aortic and mitral valves (Figure 13).

FIGURE 13 CMR Imaging of a Patient Status Post-Mitral

Valve Replacement With a 33-mm Bioprosthetic Mitral

Valve Presenting With Hemolysis

He was subsequently found to have 2 paravalvular leaks (PVLs).

The first posteromedial PVL was closed via an apical off-pump

approach using a ventricular septum defect closure device

(6 o’clock position, short red arrow). A percutaneous approach

was planned for a residual moderately-severe anterolateral PVL

(12 o’clock position, long red arrow). The residual PVL was

calculated using an indirect approach of total LV stroke volume

minus forward aortic volume (47). The regurgitant volume was

41 ml with a regurgitant fraction of 36%.

At the present time, intraprocedural guidance for PVLclosure remains reserved to the use of trans-esophageal echocardiogram, fusional imaging withfluoroscopy, and potentially, intracardiac echocardi-ography (56).

PULMONIC VALVE STENOSIS/

REGURGITATION

Right ventricular outflow tract (RVOT) obstructioncan be subvalvular, valvular, or supravalvular.Infundibular (subvalvular) stenosis is a componentof tetralogy of Fallot (TOF). Initial repair of TOFoften involves surgical disruption of the pulmonaryvalve with resultant pulmonary regurgitation.Subsequent repairs involve placement of rightventricular–pulmonary artery (RV-PA) conduits orbioprosthetic valves. Dysfunction of the RV-PA con-duits and bioprosthetic valves post-repair of TOFoften leads to varying degrees of stenosis andregurgitation. Phase-contrast velocity mapping isuseful for the estimation of severity of RVOTobstruction or pulmonary regurgitation that occursde novo (Figure 14) or post-surgical or -percutaneousrepair (Figure 15). In TOF, CMR-derived parametersof RV size and function are important for deter-mining timing of reintervention (57,58). Surgicalreintervention should be performed in patients withRV-PA conduit or bioprosthetic valve stenosis (peakgradient >50 mm Hg) or conduit regurgitation and atleast 1 of the following: decreased exercise capacity,depressed RV function, at least moderately enlargedRV end-diastolic size, or at least moderate tricuspidregurgitation (57). Surgical or percutaneous therapycan be useful in symptomatic patients with discreteRV-PA conduit stenosis >50% diameter narrowing orwhen a bioprosthetic pulmonary valve has a peakgradient by Doppler >50 mm Hg or a mean gradient>30 mm Hg (57). Surgical and percutaneous therapycan be useful in asymptomatic patients with a bio-prosthetic pulmonary valve peak Doppler gradient>50 mm Hg (57).

CMR also allows for 3D multiplanar reconstructionand provides accurate information on anatomy, size,and geometry of the RVOT, pulmonary arteries, andexisting RV-PA conduits and bioprosthetic valves.This is crucial in pre-procedural assessment fortranscatheter pulmonary valve implantation (Melody,Medtronic Inc., Minneapolis, Minnesota) as certainanatomic criteria have to be met before valve im-plantation (59–61). The Melody valve is available indiameter sizes of 18, 20, and 22 mm and has a stentlength of 28 mm. In the multicenter U.S. Melody valvetrial, recently published by McElhinney et al. (60), 136

FIGURE 14 CMR Imaging of a Patient With Tetralogy of Fallot Repaired in Infancy

Right ventricular outflow tract (RVOT) cine image showing the absence of a pulmonary valve likely surgically disrupted (A) and RVOT phase

contrast in-plane view at 250 cm/s showing free pulmonary regurgitation (B, black jet extending into right ventricle). Note the dilated right

ventricle on the 4-chamber cine image (C). Flow curves showing flow across the RVOT (D). The forward volume was 95 ml and reverse volume

45 ml corresponding to a pulmonic regurgitant fraction of 47%. The direction of the flow curves are reversed due to the direction of the

velocity encoding.



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patients with RVOT conduit and/or prosthetic pul-monary valve dysfunction were enrolled. Patientswere considered to be anatomically suitable if diam-eter was <20 mm by angiography or balloon sizing(60). CMR imaging demonstrated significant reduc-tion of pulmonary regurgitation (regurgitation frac-tion decreased from 26.7% to 1.8%), with significantdecrease in RV end-diastolic volumes, albeit withunchanged RV systolic function. Delineation of thecoronary artery course is essential prior to any RVOTintervention, as 5% to 10% of patients with TOF havean anomalous left coronary artery that may courseacross the RVOT, which could complicate possibleinterventions (62). A comprehensive CMR imaging

consensus for repaired TOF patients is availableelsewhere (63).

CMR FOR ASSESSMENT OF

INTRACARDIAC SHUNTING

Atrial septum defects (ASDs), ventricular septum de-fects (VSDs) and patent ductus arteriosus (PDA) arethe most common adult congenital heart defects.CMR is well-established as an excellent noninvasiveimaging modality for the diagnosis of patients withsuspected intracardiac shunting and/or for thefollow-up post-corrective surgery. The degree of left-to-right shunting as assessed by the ratio of flow in

FIGURE 15 CMR Evaluation of a Patient With RV-PA Conduit Stenosis, Status Post-Transcatheter Melody Valve Placement

A 22-year-old patient with tetralogy of Fallot status post RV-PA conduit at age 2 years, followed by conduit change and pulmonary homograft placement at

age 4 years. A 22-mm Melody valve (Medtronic Inc., Minneapolis, Minnesota) was subsequently placed at age 19 years. Transthoracic echocardiogram was

significant for stenosis of the Melody valve with peak/mean gradients of 69/28 mm Hg. RVOT cine image showing black parallel lines of signal void consistent with

susceptibility artifact caused by the platinum-iridium stent frame of the Melody valve (A). RVOT phase contrast in-plane view with maximal encoding velocity

(Venc) set at 250 cm/s (B), 300 cm/s (C), and 400 cm/s (D). The aliasing noted within the conduit in B (red arrows) gradually diminishes with increases in

the maximal encoding velocity (from C to D).


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the pulmonary and systemic circulation is crucial inthe management of these conditions. This calculationrequires obtaining quantitative forward stroke vol-ume with phase-contrast imaging at the level of themain pulmonary artery (Qp) and dividing by the for-ward left-sided stroke volume at the level of theproximal ascending aorta (Qs).

In addition, given its capability of imaging an un-restricted field of view, the study can be tailored toevaluate complex anatomy. As described in the pre-vious text, CMR is also the gold-standard for accurateand reproducible assessment of RV volume andfunction. This is important because 2D transthoracicimaging has intrinsic limitations given the complexanatomy of the right ventricle.

ATRIAL SEPTAL DEFECT. For the evaluation of ASDs,echocardiographic imaging (in particular trans-esophageal imaging) remains the initial imaging mo-dality to determine the anatomy of the defect andassess suitability and guidance for percutaneousclosure. Although echocardiography can be used as ascreening tool, the diagnosis can be difficult bystandard transthoracic imaging, and delayed presen-tation in adult life is not uncommon (64,65). Inparticular, sinus venosus ASD represents a particu-larly challenging case given its anatomical location

and is commonly associated with anomalous pulmo-nary venous return.

The Qp/Qs calculation by CMR has been shown tobe very accurate and should be considered asfirst line for shunt quantification. CMR should bestrongly considered in particular cases where: 1) thecalculation of intracardiac shunting has beenequivocal by echocardiography or invasive hemo-dynamics; and/or 2) where right ventricular dilationhas been suspected on TTE without obviousanatomic defect. In addition to the anatomicdemonstration of the ASD defect, anomalous pul-monary venous return can be visualized, andimportantly, the calculation of the pulmonic to sys-temic flow ratio (Qp/Qs) can support hemodynami-cally significant left-to-right shunting if Qp/Qs >1.5(Figure 16, Online Video 4).

VENTRICULAR SEPTAL DEFECT. VSD is the mostcommon congenital heart defect at birth (66). By farthe most common location of a congenital VSD iswithin the perimembranous septum, where most ofpercutaneous closures have been reported (67). Giventhe proximity to the aortic valve, concerns forpossible impingement in the valve leaflets causingaortic regurgitation and development of early or lateatrioventricular block have been reported (67,68).


FIGURE 16 CMR Evaluation of a Patient With Sinus Venosus ASD

(A) Sagittal projection superior vena cava (SVC)/inferior vena cava (IVC) projection. Note the confluence of the SVC, right atrium (RA), and left

atrium (LA). The red arrow points to the superior sinus venosus atrial septal defect (ASD). (B) Magnetic resonance angiogram (MRA) image

showing a dilated SVC connected to the right atrium (RA), which is in continuity with the LA. The left inferior pulmonary vein enters the LA, but

there is absence of attachment of the right upper pulmonary vein, which would normally be seen at this level. (C) Posterior projection of a

volume-rendered MRA image showing pulmonary vein drainage into the left atrium (LA). (D) Anterior projection of a volume rendered MRA

image showing anomalous right superior pulmonary vein draining into the SVC which is dilated at its junction with the RA (Online Video 4). AO ¼ascending aorta; BCV ¼ brachiocephalic vein; LPA ¼ left pulmonary artery; MPA ¼ main pulmonary artery; PV ¼ pulmonary vein; RPA ¼ right

pulmonary artery.



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In adulthood, most VSDs are small, asymptomatic,and compatible with a normal life (about 40% closespontaneously in childhood). A restrictive VSD issmall enough that there is a pressure gradient be-tween the ventricles, and the pulmonary ventricleand pulmonary vasculature are protected from thesystemic pressure of the contralateral ventricle(Figure 17).

Post-infarct VSDs are anatomically challengingand variable in morphology. Many defects haveserpiginous/nonlinear tears rather than holes in theventricular septum. Current technology allowsclosure of circular defects up to 24 mm. Isolated casereports have demonstrated the value of CMR forappropriate device sizing and selection based on the

VSD anatomy, location, infarct extent, and hemody-namic consequences of left-to-right shunting (69,70).CMR can also visualize healed VSDs, which tend to beassociated with aneurysmal formation of the basalseptum and sometimes involve adjacent septal leafletof the tricuspid valve (71).

PATENT DUCTUS ARTERIOSUS. PDA is a fetalvascular structure connecting the proximal descend-ing aorta to the roof of the main pulmonary artery.Although it is essential in fetal life, permitting rightventricle ejection into the aorta, it normally closesspontaneously after birth. PDA is commonly seen inpre-term newborns, and depending on its persis-tency, size and magnitude of left-to-right shunting


FIGURE 17 CMR Imaging of a Patient With Small Restrictive Membranous VSD

The Qp/Qs ratio on flow quantification was 1.3 and closure was not indicated. Cardiac magnetic resonance imaging was performed to reconcile

the Qp/Qs values obtained on transthoracic echocardiogram and heart catheterization. Short-axis views of the ventricles showing the small

ventricular septal defect (VSD) entering the right ventricle just below the tricuspid valve (A, short red arrow). Short-axis phase-contrast

in-plane view with maximal encoding velocity set at 200 cm/s (B) and increased to 400 cm/s (C). The aliasing noted in B disappeared with

increase in the maximal encoding velocity in C (long red arrows).

FIGURE 18 CMR Evaluation of a Patient With Patent Ductus

Arteriosus

Sagittal reconstruction using noncontrast 3-dimensional mag-

netic resonance angiogram demonstrating patent ductus arte-

riosus (PDA) (red arrow) connecting the distal aortic arch (Aorta)

with the left pulmonary artery (PA).


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can cause important pulmonary overcirculation andleft heart volume overload. With long-standing left-to-right shunting, pulmonary vascular remodelingoccurs, and the progressive increase in pulmonaryvascular resistance leads to the development of pul-monary hypertension. Indications for closure includesymptomatic left-chamber dilation/heart failure.Eisenmenger’s syndrome due to right-to-left shunt-ing can develop increasing the morbidity and mor-tality (72). Transcatheter closure has been theestablished treatment of choice. CMR allows for theassessment of the PDA anatomy, evaluation of asso-ciated abnormalities in the aortic arch, and quantifi-cation of ductal shunt volume. Larger PDA can beseen on spin-echo images, breath-hold magneticresonance angiogram (MRA), or cine sequences. Theflow disturbance produced by even small PDA in thepulmonary artery can be visible as signal loss on cineMRA. Sagittal reconstructions using 3D noncontrastMRA can demonstrate the small PDA (Figure 18).Direct quantification of the PDA shunting can bedifficult with CMR due to the variations in the PDAanatomy, morphology, and position. Therefore, 2 in-direct ways have been proposed. The first assessesthe difference between the LV stroke volume and thetotal systemic flow (SVC þ descending aorta), whichshould equal the ductal shunt volume (73). The sec-ond uses the traditional phase-contrast method at the



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ascending aorta (Qs) and main pulmonary artery (Qp).Given that the level of left-to-right shuntingcaused by the PDA does not increase the right ven-tricular stroke volume, the Qp/Qs in this instance willbe <1.

CMR FOR AORTIC COARCTATION

INTERVENTIONS

Provided there is local expertise and no contraindi-cations, we believe that CMR should be consideredthe first imaging modality for evaluation of patientswith aortic coarctation. This is due to the abilityof CMR to evaluate both anatomic and func-tional hemodynamic information without radiationexposure (Figures 19 and 20) (74–77). CMR can alsoassess the presence of collateral vessels, hemody-namic manifestations of aortic coarctation (LVhypertrophy), and other commonly associatedcomorbidities such as bicuspid aortic valve with orwithout aortopathy.

CMR is an important diagnostic tool prior to eithertranscatheter or surgical intervention. Contrast-enhanced MRA provides 3D visualization of arch ge-ometry, aneurysmal formation, and collateral vessels.The combination of morphological changes, including

FIGURE 19 CMR Evaluation of a Patient With Aortic Coarctation

Contrast-enhanced magnetic resonance angiogram in the sagittal projec

dilated left subclavian artery (A, red arrow). 3-dimensional volume-rende

the aortic coarctation. The area of coarctation had dimensions of 1.2 cm �relative to area of a normal portion of the descending aorta) was 0.24

small indexed cross-sectional area <56 mm2/m2

and heart rate–corrected mean flow deceleration>�350 ml/s1.5, had an excellent sensitivity (95%) andgood specificity (82%) to predict hemodynamicallysignificant aortic coarctation (i.e., gradient bycatheterization $20 mm Hg) (74). Similar to ASseverity assessment (see Aortic Stenosis section),coarctation gradient measurement with through-plane phase-contrast imaging can be misleading inassessing severity, because the turbulent flow cancreate spin dephasing and there is inferior temporalresolution when compared with Doppler echocar-diography. In addition, important collateral flowentering the distal descending aorta raises pressurebeyond the coarctation, minimizing the severityassessment.

Phase-contrast imaging, however, can be quitehelpful in evaluating the magnitude of collateral flow.Typically, hemodynamically important collateral flowwill produce an increase in the distal descendingaortic flow when compared with the proximaldescending aortic flow (78). This is relevant not onlyfor interpreting coarctation gradients, but also in thetherapeutic planning and assessment of adequateresults post-angioplasty and stenting with the rever-sion of the flow pattern to normal.

tion showing a discrete area of aortic coarctation just distal to the

red image also in the sagittal projection rotated for maximal display of

1.2 cm (B, red arrow). The coarctation index (i.e., area at coarctation

(normal <0.25) (77).

FIGURE 20 CMR of a Patient With Aortic Coarctation Using In-Plane Phase-Contrast Imaging for Stenosis Quantification

Phase-contrast in-plane views of the aorta in the sagittal projection. (A) At 150 cm/s and (B) at 350 cm/s. The “aliasing” noted in A disappeared

with increase in the maximal encoding velocity in B. Phase-contrast through-plane short-axis views in the descending aorta just distal to the

site of coarctation (red line in A) at the maximal encoding velocity of 200 cm/s in C and 400 cm/s in D. On flow quantification, the maximum

velocity through the discrete coarctation was 3.9 m/s corresponding to a peak gradient of 60 mm Hg.


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With regard to the follow-up, current practiceguidelines recommend screening cardiovascular CMRfor all patients after aortic coarctation repair (79). It isuseful for the surveillance after reparative procedure(surgery or stenting) to assess potential complicationssuch as stent migration, pseudoaneurysm, endoleak,or recoarctation. As mentioned previously, aorticstent frames placed during intervention can be chal-lenging because they can interfere with the imagingquality and assessment post-intervention in coarcta-tion patients treated with endovascular stents. How-ever, collateral flow estimation should be unaffected.

CMR FOR PULMONARY VEIN PROCEDURES

Partial anomalous pulmonary venous return oftenpresents a diagnostic challenge. Diagnosis of partialanomalous pulmonary venous return is usually sus-pected by echocardiography with right-sided chamberdilation. Among the different imaging modalities usedfor the evaluation of pulmonary veins, magneticresonance is the most comprehensive in assessinganatomy and pathophysiology at the same time. Brightblood cine sequences and 3D contrast-enhanced MRAcan allow detailed studies in a single breath-hold using



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a minimally invasive technique. Contrast-enhancedMRA can be added to the protocol to outline thecourse and connections of the pulmonary veins.Even for patients who are unable to receive intra-venous gadolinium (i.e., those with advancedchronic kidney disease with glomerular filtrationrate <30 ml/min/1.73 m2), nonenhanced ECG-gated 3Dsteady-state free precession MRA can provide exqui-site detailed anatomic information, enough to excludeor confirm partial anomalous pulmonary venous re-turn. The degree of left-to-right shunting as assessedby the Qp/Qs ratio can be calculated to support theanatomical findings (Figure 21).

The pulmonary vein ostia are frequent sites ofre-entry circuits in patients with atrial fibrillation.Transcatheter or intraoperative ablation procedurestarget these pathways, applying selective segmentalablation typically in the vein antrum of the left

FIGURE 21 CMR Imaging of Patient With Remote Sinus Venosus ASD

Volume Overload

A 4-chamber in-plane breath-hold phase-contrast sequence showing an

atrium (RA) causing significant left-to-right shunting confirmed by right

ratio (Qp/Qs ¼ 2.4). LA ¼ left atrium; LV ¼ left ventricle; RV ¼ right ve

atrium. Guidance of these procedures (initial andredo ablations) by presence and extent of atrial wallfibrosis has been described (80). However, secondaryto the thin wall of the left atrium, segmentationanalysis and reproducibility of these results is ques-tionable outside of a few single centers. Furthermore,in-human histological validation is extremely limited(81), and controversy still exist whether dense leftatrial fibrosis is truly the epicenter, because the ma-jority of atrial wavelets appear to come from areaswithout delayed enhancement and/or within areaswith patchy enhancement but not from the dense leftatrial scar (82).

Pulmonary vein stenosis is a potential complica-tion of transcatheter pulmonary vein ablation.Pulmonary vein stenosis may be asymptomatic ormay present with potential signs and symptoms ofhemoptysis, fever, pleuritic chest pain, dry cough,

Repair Now Presenting With Right-Sided Chamber Dilation and

omalous right upper pulmonary vein (RUPV) drainage into the right

-sided chamber dilation as well as high pulmonic to systemic flow

ntricle.

FIGURE 22 CMR Imaging of Pulmonary Vein Anatomy Prior

to Electrophysiology Procedure

Posterior view of 3-dimensional volume-rendered reconstruction

of noncontrast magnetic resonance angiography dataset showing

an anatomical variant with a separate right middle pulmonary

vein (RMPV). Note also early-branching of the right inferior

pulmonary vein (RIPV). LIPV ¼ left inferior pulmonary vein;

LSPV ¼ left superior pulmonary vein; RSPV ¼ right superior

pulmonary vein.


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and/or dyspnea on exertion. Onset of symptoms canbe expected up to 3 to 6 months after pulmonary veinisolation. Of note, severe stenosis can also remainasymptomatic due to the formation of collateral ves-sels. When it is suspected, imaging modalities suchas contrast-enhanced gated computed tomographic

angiogram or noncontrast free-breathing 3D MRA(83–85) (Figure 22) should be performed. According tothe joint Heart Rhythm Society/European HeartRhythm Association/European Cardiac ArrhythmiaSociety expert consensus statement, this approachshould be considered in patients who develop respi-ratory symptoms after radio frequency ablation, asearly recognition of pulmonary vein stenosis mightimprove treatment outcomes (86).

SUMMARY

Transcatheter interventions for structural andvalvular heart disease are an exciting and evolvingfield in interventional cardiology. Multimodality im-aging has a central role for pre-procedural planning,intra-procedural guidance, and post-operative sur-veillance. The noninvasiveness of CMR and its abilityfor a comprehensive, accurate, and reproducibleassessment of cardiac morphology and function es-tablishes CMR as 1 of the key imaging modalities inthis context, complementary to angiography, echo-cardiography, and computed tomography. Currentdata summarized in this review will continue toexpand as increasing experience will certainlycontinue to further define and refine the current ap-plications of this robust imaging technique.

REPRINT REQUESTS AND CORRESPONDENCE: Dr.Stamatios Lerakis, Emory Structural and Valve HeartCenter, Emory University Hospital and Emory Clinic,1365 Clifton Road NE, Suite AT-503, Atlanta, Georgia30322. E-mail: [email protected].

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KEY WORDS cardiac MRI, structuralinterventions, valvular heart disease

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