Abnormal Mechanics Relate to Myocardial Fibrosis and Ventricular Arrhythmias in Patients With Mitral Valve Prolapse.

BACKGROUND: The relation between ventricular arrhythmia and fibrosis in mitral valve prolapse (MVP) is reported, but underlying valve-induced mechanisms remain unknown. We evaluated the association between abnormal MVP-related mechanics and myocardial fibrosis, and their association with arrhythmia. METHODS: We studied 113 patients with MVP with both echocardiogram and gadolinium cardiac magnetic resonance imaging for myocardial fibrosis. Two-dimensional and speckle-tracking echocardiography evaluated mitral regurgitation, superior leaflet and papillary muscle displacement with associated exaggerated basal myocardial systolic curling, and myocardial longitudinal strain. Follow-up assessed arrhythmic events (nonsustained or sustained ventricular tachycardia or ventricular fibrillation). RESULTS: Myocardial fibrosis was observed in 43 patients with MVP, predominantly in the basal-midventricular inferior-lateral wall and papillary muscles. Patients with MVP with fibrosis had greater mitral regurgitation, prolapse, and superior papillary muscle displacement with basal curling and more impaired inferior-posterior basal strain than those without fibrosis (P<0.001). An abnormal strain pattern with distinct peaks pre-end-systole and post-end-systole in inferior-lateral wall was frequent in patients with fibrosis (81 versus 26%, P<0.001) but absent in patients without MVP with basal inferior-lateral wall fibrosis (n=20). During median follow-up of 1008 days, 36 of 87 patients with MVP with >6-month follow-up developed ventricular arrhythmias associated (univariable) with fibrosis, greater prolapse, mitral annular disjunction, and double-peak strain. In multivariable analysis, double-peak strain showed incremental risk of arrhythmia over fibrosis. CONCLUSIONS: Basal inferior-posterior myocardial fibrosis in MVP is associated with abnormal MVP-related myocardial mechanics, which are potentially associated with ventricular arrhythmia. These associations suggest pathophysiological links between MVP-related mechanical abnormalities and myocardial fibrosis, which also may relate to ventricular arrhythmia and offer potential imaging markers of increased arrhythmic risk.

Cardiovascular Magnetic Resonance in Nonischemic Myocardial Inflammation: Expert Recommendations.

This JACC Scientific Expert Panel provides consensus recommendations for an update of the cardiovascular magnetic resonance (CMR) diagnostic criteria for myocardial inflammation in patients with suspected acute or active myocardial inflammation (Lake Louise Criteria) that include options to use parametric mapping techniques. While each parameter may indicate myocardial inflammation, the authors propose that CMR provides strong evidence for myocardial inflammation, with increasing specificity, if the CMR scan demonstrates the combination of myocardial edema with other CMR markers of inflammatory myocardial injury. This is based on at least one T2-based criterion (global or regional increase of myocardial T2 relaxation time or an increased signal intensity in T2-weighted CMR images), with at least one T1-based criterion (increased myocardial T1, extracellular volume, or late gadolinium enhancement). While having both a positive T2-based marker and a T1-based marker will increase specificity for diagnosing acute myocardial inflammation, having only one (i.e., T2-based OR T1-based) marker may still support a diagnosis of acute myocardial inflammation in an appropriate clinical scenario, albeit with less specificity. The update is expected to improve the diagnostic accuracy of CMR further in detecting myocardial inflammation.

Effect of the 2010 task force criteria on reclassification of cardiovascular magnetic resonance criteria for arrhythmogenic right ventricular cardiomyopathy.

BACKGROUND: We sought to evaluate the effect of application of the revised 2010 Task Force Criteria (TFC) on the prevalence of major and minor Cardiovascular Magnetic Resonance (CMR) criteria for Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) versus application of the original 1994 TFC. We also assessed the utility of MRI to identify alternative diagnoses for patients referred for ARVC evaluation. METHODS: 968 consecutive patients referred to our institution for CMR with clinical suspicion of ARVC from 1995 to 2010, were evaluated for the presence of major and minor CMR criteria per the 1994 and 2010 ARVC TFC. CMR criteria included right ventricle (RV) dilatation, reduced RV ejection fraction, RV aneurysm, or regional RV wall motion abnormalities. When quantitative measures of RV size and function were not available, and in whom abnormal size or function was reported, a repeat quantitative analysis by 2 qualified CMR physicians in consensus. RESULTS: Of 968 patients, 220 (22.7%) fulfilled either a major or a minor 1994 TFC, and 25 (2.6%) fulfilled any of the 2010 TFC criterion. Among patients meeting any 1994 criteria, only 25 (11.4%) met at least one 2010 criterion. All patients who fulfilled a 2010 criteria also satisfied at least one 1994 criterion. Per the 2010 TFC, 21 (2.2%) patients met major criteria and 4 (0.4%) patients fulfilled at least one minor criterion. Eight patients meeting 1994 minor criteria were reclassified as satisfying 2010 major criteria, while 4 patients fulfilling 1994 major criteria were reclassified to only minor or no criteria under the 2010 TFC.Eighty-nine (9.2%) patients had alternative cardiac diagnoses, including 43 (4.4%) with clinically significant potential ARVC mimics. These included cardiac sarcoidosis, RV volume overload conditions, and other cardiomyopathies. CONCLUSIONS: Application of the 2010 TFC resulted in reduction of total patients meeting any diagnostic CMR criteria for ARVC from 22.7% to 2.6% versus the 1994 TFC. CMR identified alternative cardiac diagnoses in 9.2% of patients, and 4.4% of the diagnoses were potential mimics of ARVC.

Navigated DENSE strain imaging for post-radiofrequency ablation lesion assessment in the swine left atria.

AIMS: Prior work has demonstrated that magnetic resonance imaging (MRI) strain can separate necrotic/stunned myocardium from healthy myocardium in the left ventricle (LV). We surmised that high-resolution MRI strain, using navigator-echo-triggered DENSE, could differentiate radiofrequency ablated tissue around the pulmonary vein (PV) from tissue that had not been damaged by radiofrequency energy, similarly to navigated 3D myocardial delayed enhancement (3D-MDE). METHODS AND RESULTS: A respiratory-navigated 2D-DENSE sequence was developed, providing strain encoding in two spatial directions with 1.2 × 1.0 × 4 mm(3) resolution. It was tested in the LV of infarcted sheep. In four swine, incomplete circumferential lesions were created around the right superior pulmonary vein (RSPV) using ablation catheters, recorded with electro-anatomic mapping, and imaged 1 h later using atrial-diastolic DENSE and 3D-MDE at the left atrium/RSPV junction. DENSE detected ablation gaps (regions with >12% strain) in similar positions to 3D-MDE (2D cross-correlation 0.89 ± 0.05). Low-strain (<8%) areas were, on average, 33% larger than equivalent MDE regions, so they include both injured and necrotic regions. Optimal DENSE orientation was perpendicular to the PV trunk, with high shear strain in adjacent viable tissue appearing as a sensitive marker of ablation lesions. CONCLUSIONS: Magnetic resonance imaging strain may be a non-contrast alternative to 3D-MDE in intra-procedural monitoring of atrial ablation lesions.

Left atrial appendage dimensions predict the risk of stroke/TIA in patients with atrial fibrillation.

UNLABELLED: Risk of Stroke/TIA in Patients With Atrial Fibrillation. INTRODUCTION: Most strokes in patients with atrial fibrillation (AF) arise from thrombus formation in left atrial appendage (LAA). Our aim was to identify LAA features associated with a higher stroke risk in patients with AF using magnetic resonance imaging and angiography (MRI/MRA). METHODS: The study included 144 patients with nonvalvular AF who were not receiving warfarin and who underwent MRI/MRA prior to catheter ablation for AF. LAA volume, LAA depth, short and long axes of LAA neck, and numbers of lobes were measured. RESULTS: Of the 144 patients, 18 had a prior stroke or transient ischemic attack (TIA) (13 and 5, respectively). Compared with patients who had no history of stroke/TIA, these patients were older, had higher prevalence of hypertension and hyperlipidemia and had higher LAA volume (22.9 ± 9.6 cm(3) vs. 14.5 ± 7.1 cm(3) , P < 0.001). Their LAA depth (3.76 ± 0.9 cm vs. 3.21 ± 0.8 cm, P = 0.006) and the long and short axes of the LAA neck (3.12 ± 0.7 cm vs. 2.08 ± 0.7 cm, P < 0.001; 2.06 ± 0.5 cm vs. 1.37 ± 0.4 cm, P < 0.001, respectively) were larger. Using stepwise logistic regression model, the only statistically significant multivariable predictors of events were age (OR = 1.21 per year, 95% CI 1.06-1.38, P = 0.004), aspirin use (OR = 0.039, 95% CI 0.005-0.28, P = 0.001), and LAA neck dimensions (short axis × long axis) (OR = 3.59 per cm(2) , 95% CI 1.93-6.69, P < 0.001). CONCLUSION: LAA dimensions predict strokes/TIAs in patients with AF. LAA assessment by MRI/MRA can potentially be used as an adjunctive tool for risk stratification for embolic events in AF patients.

Towards Effcient Label Fusion by Pre-Alignment of Training Data.

Label fusion is a multi-atlas segmentation approach that explicitly maintains and exploits the entire training dataset, rather than a parametric summary of it. Recent empirical evidence suggests that label fusion can achieve significantly better segmentation accuracy over classical parametric atlas methods that utilize a single coordinate frame. However, this performance gain typically comes at an increased computational cost due to the many pairwise registrations between the novel image and training images. In this work, we present a modified label fusion method that approximates these pairwise warps by first pre-registering the training images via a diffeomorphic groupwise registration algorithm. The novel image is then only registered once, to the template image that represents the average training subject. The pairwise spatial correspondences between the novel image and training images are then computed via concatenation of appropriate transformations. Our experiments on cardiac MR data suggest that this strategy for nonparametric segmentation dramatically improves computational efficiency, while producing segmentation results that are statistically indistinguishable from those obtained with regular label fusion. These results suggest that the key benefit of label fusion approaches is the underlying nonparametric inference algorithm, and not the multiple pairwise registrations.

Robust Atlas-Based Segmentation of Highly Variable Anatomy: Left Atrium Segmentation.

Automatic segmentation of the heart's left atrium offers great benefits for planning and outcome evaluation of atrial ablation procedures. However, the high anatomical variability of the left atrium presents significant challenges for atlas-guided segmentation. In this paper, we demonstrate an automatic method for left atrium segmentation using weighted voting label fusion and a variant of the demons registration algorithm adapted to handle images with different intensity distributions. We achieve accurate automatic segmentation that is robust to the high anatomical variations in the shape of the left atrium in a clinical dataset of MRA images.

Electroanatomic mapping and radiofrequency ablation of porcine left atria and atrioventricular nodes using magnetic resonance catheter tracking.

BACKGROUND: The MRI-compatible electrophysiology system previously used for MR-guided left ventricular electroanatomic mapping was enhanced with improved MR tracking, an MR-compatible radiofrequency ablation system and higher-resolution imaging sequences to enable mapping, ablation, and ablation monitoring in smaller cardiac structures. MR-tracked navigation was performed to the left atrium (LA) and atrioventricular (AV) node, followed by LA electroanatomic mapping and radiofrequency ablation of the pulmonary veins (PVs) and AV node. METHODS AND RESULTS: One ventricular ablation, 7 PV ablations, 3 LA mappings, and 3 AV node ablations were conducted. Three MRI-compatible devices (ablation/mapping catheter, torqueable sheath, stimulation/pacing catheter) were used, each with 4 to 5 tracking microcoils. Transseptal puncture was performed under x-ray, with all other procedural steps performed in the MRI. Preacquired MRI roadmaps served for real-time catheter navigation. Simultaneous tracking of 3 devices was performed at 13 frames per second. LA mapping and PV radiofrequency ablation were performed using tracked ablation catheters and sheaths. Ablation points were registered and verified after ablation using 3D myocardial delayed enhancement and postmortem gross tissue examination. Complete LA electroanatomic mapping was achieved in 3 of 3 pigs, Right inferior PV circumferential ablation was achieved in 3 of 7 pigs, with incomplete isolation caused by limited catheter deflection. During AV node ablation, ventricular pacing was performed, 3 devices were simultaneously tracked, and intracardiac ECGs were displayed. 3D myocardial delayed enhancement visualized node injury 2 minutes after ablation. AV node block succeeded in 2 of 3 pigs, with 1 temporary block. CONCLUSIONS: LA mapping, PV radiofrequency ablation, and AV node ablation were demonstrated under MRI guidance. Intraprocedural 3D myocardial delayed enhancement assessed lesion positional accuracy and dimensions.

Mitral leaflet adaptation to ventricular remodeling: prospective changes in a model of ischemic mitral regurgitation.

BACKGROUND: Ischemic mitral regurgitation is caused by systolic traction on the mitral leaflets related to ventricular distortion. Little is known about how chronic tethering affects leaflet area, in part because it cannot be measured repeatedly in situ. Recently, a new method for 3D echocardiographic measurement of mitral leaflet area was developed and validated in vivo against sheep valves, later excised. Clinical studies (n=80) showed that mitral leaflet area increased by >30% in patients with inferior myocardial infarction and dilated cardiomyopathy versus normal; greater adaptation independently predicted less mitral regurgitation. This study explored whether mitral valve area changes over time within the same heart with ischemic mitral regurgitation. METHODS AND RESULTS: Twelve sheep were studied at baseline and 3 months after inferior myocardial infarction by 3D echocardiography; 6 were untreated and 6 were treated initially with an epicardial patch to limit left ventricular dilation and mitral regurgitation. Untreated sheep developed left ventricular dilation at 3 months, with global dysfunction (mean+/-SD ejection fraction, 24+/-10% versus 44+/-10% with patching, P=0.02) and moderate mitral regurgitation (vena contracta, 5.0+/-1.0 versus 0.8+/-1.0 mm, P<0.0002). In untreated sheep, total diastolic leaflet area increased from 13.1+/-1.3 to 18.1+/-2.5 cm(2) (P=0.0001). In patched sheep, leaflet area at 3 months was not significantly different from baseline sheep values (13.0+/-1.1 versus baseline, 12.1+/-1.8 cm(2), P=0.31). CONCLUSIONS: Mitral valve area, independent of systolic stretch, increases over time as the left ventricular remodels after inferior myocardial infarction. This increase, however, fails to compensate adequately for tethering to prevent mitral regurgitation. Understanding the mechanism of valve adaptation can potentially suggest new biological and surgical therapeutic targets.

Cardiovascular magnetic resonance in myocarditis: A JACC White Paper.

Cardiovascular magnetic resonance (CMR) has become the primary tool for noninvasive assessment of myocardial inflammation in patients with suspected myocarditis. The International Consensus Group on CMR Diagnosis of Myocarditis was founded in 2006 to achieve consensus among CMR experts and develop recommendations on the current state-of-the-art use of CMR for myocarditis. The recommendations include indications for CMR in patients with suspected myocarditis, CMR protocol standards, terminology for reporting CMR findings, and diagnostic CMR criteria for myocarditis (i.e., "Lake Louise Criteria").

Pulmonary vein contraction: characterization of dynamic changes in pulmonary vein morphology using multiphase multislice computed tomography scanning.

BACKGROUND: The presence and extent of contraction within the pulmonary veins (PVs) have not been defined clearly. OBJECTIVE: The purpose of this study was to determine whether PV contraction exists and can be visualized using multislice computed tomography (MSCT) scanning as this may indicate that this modality may be useful for monitoring patients after PV isolation procedures. METHODS: Analysis was performed on 29 patients (mean age 57.5 +/- 12 years) undergoing MSCT for suspected coronary artery disease without structural heart disease or left atrial anatomical variants. Multiplane reconstructions were used to measure PV diameters at 0, 5, 10, and 15 mm from the ostium in two phases (maximum and minimum size). The ejection fractions of three 5-mm segments were calculated for each PV. RESULTS: Right-sided and left-sided PV contraction and maximal atrial contraction occurred at a median of 85% and 95% of the cardiac cycle, respectively. The temporal concordance of minimal PV volume during peak atrial contraction indicated that the PV volume changes are secondary to active contraction rather than passive reflux and PV distension. The ejection fractions were highest in the superior veins: right superior PV (36.7%, 27.8%, and 16%, respectively, for the three segments from proximal to distal) and left superior PV (26.9%, 21.3%, and 12.1%), in comparison with the right inferior PV (21.1%, 6.6%, and -0.7%) and left inferior PV (15%, 9.3%, and 7.6%). CONCLUSION: Volume changes related to active PV contraction occur extending up to 15 mm into the veins, and this effect is most pronounced in the superior veins.

Focal and linear endocardial and epicardial catheter-based cryoablation of normal and infarcted ventricular tissue.

BACKGROUND: This study of a chronic porcine postinfarction model examined whether linear epicardial cryoablation was capable of creating large, homogenous lesions in regions of the myocardium including scarred ventricle. Endocardial and epicardial focal cryolesions were also compared to determine if there were significant differences in lesion characteristics. METHODS: Eighty focal endocardial and 28 focal epicardial cryoapplications were delivered to eight normal caprine and four normal porcine ventricular myocardium, and 21 linear cryolesions were applied along the border of infarcted epicardial tissue in a chronic porcine infarct model in six swines. RESULTS: Focal endocardial cryolesions in normal animals measured 9.7+/-0.4 mm (length) by 7.3+/-1.4 mm (width) by 4.8+/-0.2 mm (depth), while epicardial lesions measured 10.2+/-1.4 mm (length) by 7.7+/-2 mm (width) by 4.6+/-0.9 mm (depth); P > 0.05. Linear epicardial cryolesions in the chronic porcine infarct model measured 36.5+/-7.8 mm (length) by 8.2+/-1.3 mm (width) by 6.0+/-1.2 mm (depth). The mean depth of linear cryolesions applied to the border of the infarct scar was 7+/-0.7 mm, as measured by magnetic resonance imaging. CONCLUSIONS: Cryoablation can create deep lesions when delivered to the ventricular epicardium. Endocardial and epicardial cryolesions created by a focal cryoablation catheter are similar in size and depth. The ability to rapidly create deep linear cryolesions may prove to be beneficial in substrate-based catheter ablation of ventricular arrhythmias.

Electroanatomic mapping of the left ventricle in a porcine model of chronic myocardial infarction with magnetic resonance-based catheter tracking.

BACKGROUND: X-ray fluoroscopy constitutes the fundamental imaging modality for catheter visualization during interventional electrophysiology procedures. The minimal tissue discriminative capability of fluoroscopy is mitigated in part by the use of electroanatomic mapping systems and enhanced by the integration of preacquired 3-dimensional imaging of the heart with computed tomographic or magnetic resonance (MR) imaging. A more ideal paradigm might be to use intraprocedural MR imaging to directly image and guide catheter mapping procedures. METHODS AND RESULTS: An MR imaging-based electroanatomic mapping system was designed to assess the feasibility of navigating catheters to the left ventricle in vivo using MR tracking of microcoils incorporated into the catheters, measuring intracardiac ventricular electrograms, and integrating this information with 3-dimensional MR angiography and myocardial delayed enhancement images to allow ventricular substrate mapping. In all animals (4 normal, and 10 chronically infarcted swine), after transseptal puncture under fluoroscopic guidance, catheters were successfully navigated to the left ventricle with MR tracking (13 to 15 frames per second) by both transseptal and retrograde aortic approaches. Electrogram artifacts related to the MR imaging gradient pulses were successfully removed with analog and digital signal processing. In all animals, it was possible to map the entire left ventricle and to project electrogram voltage amplitude maps to identify the scarred myocardium. CONCLUSIONS: It is possible to use MR tracking to navigate catheters to the left ventricle, to measure electrogram activity, and to render accurate 3-dimensional voltage maps in a porcine model of chronic myocardial infarction, completely in the MR imaging environment. Myocardial delayed enhancement guidance provided dense sampling of the proximity of the infarct and accurate localization of complex infarcts.

Effect of presenting rhythm on image integration to direct catheter ablation of atrial fibrillation.

INTRODUCTION: Magnetic resonance (MR) imaging of the left atrium (LA) can be integrated with electroanatomic mapping systems to guide catheter ablation of atrial fibrillation (AF). The usefulness of this technique is dependent on the accuracy of image integration. OBJECTIVE: The aim of this study is to determine the effect of heart rhythm at the time of pre-procedure MR imaging and heart rhythm at the time of ablation on integration error. METHODS: Fifty-two consecutive patients who underwent catheter ablation for AF were included. All patients underwent MR imaging of LA and pulmonary veins and image integration with real-time electroanatomic mapping. The rhythm at the time of MR imaging and on the day of ablation was recorded. CARTO-Merge software (Biosense-Webster) was used to calculate the average accuracy of integration of electroanatomic points with MR-derived reconstructions. RESULTS: There was no significant difference in integration error between patients who were in AF at the time of their MR vs. those who were in sinus rhythm at the time of their MR (1.76 +/- 0.26 vs. 1.88 +/- 0.31 mm, p = 0.15). There was also no significant difference in integration error between patients who were in concordant vs. discordant rhythms at the time of MR vs. day of ablation (1.81 +/- 0.23 vs. 1.89 +/- 0.32 mm, p = 0.40). There was a trend toward less integration error between patients who were in AF on the day of ablation vs. those in sinus rhythm (1.74 +/- 0.26 vs. 1.89 +/- 0.31 mm, p = 0.07). CONCLUSIONS: Image integration can be performed to direct catheter ablation of AF regardless of the rhythm at the time of imaging and ablation.

Arrhythmia recurrence after atrial fibrillation ablation: can magnetic resonance imaging identify gaps in atrial ablation lines?

After pulmonary vein isolation for the treatment of atrial fibrillation, clinical arrhythmia recurrence is often a result of vein reconnection. By selectively visualizing scarred tissue, delayed enhancement magnetic resonance imaging may provide for a noninvasive means to identify gaps in radiofrequency ablation lines. This report correlates three-dimensional magnetic resonance imaging with invasive electro-anatomical mapping in a patient with recurrent atrial arrhythmia after multiple unsuccessful ablations for atrial fibrillation.