Left Ventricular Endocardial Surface Research Articles

The importance of scar border zone size in VT presentation and recurrence in post MI patients

Abstract Introduction Available mapping data in post-myocardial infarction patients describe ventricular tachycardia (VT) re-entry circuit characteristics of slow VT, that are typically related to transmural scars. Fast VTs with cycle lengths close to the refractory period may be related to functional re-entry in the scar border zone. Functional re-entry related border zone VTs may be difficult to control by ablation. Purpose The aims of this study are (1) to describe electroanatomical voltage map (EAVM) characteristics in post myocardial infarction (MI) patients with spontaneous and inducible fast VTs and (2) to assess the relation between scar border zone size and ablation outcomes. Methods Consecutive post-MI patients undergoing VT ablation at a tertiary referral center from January 2012 to November 2018 were included. Fast VT was defined as a VT cycle length (VTCL) = ventricular refractory period + max. 30ms. Areas of scar border zone (using 0.5 – 2.1mV/3.0mV cut-offs (according to LV remodeling stage; LVEF<47% and LV end-systolic volume index of >50 ml/m2)) were measured on the EAVM and correlated with clinical outcomes. Results In total, 138 patients were included (86% male; left ventricular ejection fraction 35±10%; 86% remodeled LV). Twenty-three patients (17%) had ≥1 fast VT (mean VTCL 275±52ms) at presentation, mean VTCL of the remaining patients 397±88ms). The median scar border zone size was 27% [IQR 20-38] of the left ventricular endocardial surface. Patients who presented with a spontaneous fast VT had a larger border zone than patients with slower VT (32% [IQR 28 – 41] vs. 25% [IQR 16 – 36], p=0.01). After ablation, 79 (57%) patients remained inducible for any VT, including 59/79 (75%) for a fast VT (median VTCL fast VT 260ms [IQR 236 -280]). Patients who remained inducible for fast VTs had a larger border zone than patients who remained inducible for slower VTs (35% [IQR 27 – 44] vs. 26% [IQR 20 – 36], p<0.001). During a median follow-up of 26 months [IQR 8 – 47], 45 patients (33%) had a VT recurrence (mean VTCL 357±98ms). Patients with a below median (27%) scar border zone area had a lower VT recurrence rate compared to patients with an above median scar border zone area (recurrence rate: 16/66 (24%) vs. 29/72 (40%), p=0.03). Kaplan-Meier survival analysis showed better free VT survival in the below median border zone patients (Log-rank: p<0.05) (Figure 1). Conclusion Patients who present with spontaneous fast VTs or who remain inducible for fast VTs after ablation have larger scar border zones during EAVM compared to patients with presenting or remaining slower VTs. A larger border zone appeared to be associated with higher VT-recurrence rates. The scar border zone may play an important role as VT substrate for (fast) VTs and may not be easily targeted by current ablation techniques.VT-free survival stratified by median BZ

Attenuation of stretch-induced arrhythmias following chemical ablation of Purkinje fibres, in isolated rabbit hearts.

Purkinje fibres (PFs) play an important role in some ventricular arrhythmias and acute ventricular stretch can evoke mechanically-induced arrhythmias. We tested whether Purkinje fibres, play a role in these arrhythmias. Pseudo-ECGs were recorded in isolated, Langendorff-perfused, rabbit hearts in which the left ventricular endocardial surface was also irrigated with Tyrode, via an indwelling catheter placed in the left ventricular lumen. The number and period of ectopic activations was measured during left ventricular lumen inflation via an indwelling fluid-filled balloon (500μL added over 2s and maintained for 15s in total). Mechanically-induced arrhythmias occurred in 70% of balloon inflations: they were maximal in the first 5s and ceased within 15s. Brief, (10s) irrigation of the left ventricular lumen with Lugol solution (IK/I2), via the indwelling catheter, reduced inflation-induced ectopics by 98% (p < 0.05). Ablation of endocardial PFs by Lugol was confirmed by Triphenyltetrazolium Chloride staining. Optical mapping revealed the left ventricular epicardial activation patterns of ectopics could have PF-mediated and focal sources. In silico modelling predicted ectopic sources originating in the endocardial region propagate to and through the Purkinje fibres network. Acute distention-induced ectopics are multi-focal, their attenuation by Lugol, their activation patterns and in silico modelling indicate a participation of Purkinje fibres in these arrhythmias.

Endocardial role in arrhythmias induced by acute ventricular stretch and the involvement of Purkinje fibres, in isolated rat hearts

Purkinje fibres (PFs) play an important role in some ventricular arrhythmias and acute ventricular stretch can evoke mechanically-induced arrhythmias. We tested whether PFs and specifically TRPM4 channels, play a role in these mechanically-induced arrhythmias. Pseudo-ECGs and left ventricular (LV) activation, measured by optical mapping, were recorded in isolated, Langendorff-perfused, rat hearts. The LV endocardial surface was irrigated with experimental agents, via an indwelling catheter. The number and period of ectopic activations was measured during LV lumen inflation via an indwelling fluid-filled balloon (100 μL added over 2 s, maintained for 38 s). Mechanically-induced arrhythmias occurred during balloon inflation: they were multifocal, maximal in the first 5 s and ceased within 20 s. Optical mapping revealed activation patterns indicating PF-mediated and ectopic focal sources. Irrigation of the LV lumen with Lugol solution (IK/I2) for 10s reduced ectopics by 93% (n = 16, P < 0.001); with ablation of endocardial PFs confirmed by histology. Five min irrigation of the LV lumen with 50 μM 9-Phenanthrol, a blocker of TRPM4 channels, reduced ectopics by 39% (n = 15, P < 0.01). Immunohistochemistry confirmed that TRPM4 was more abundant in PFs than myocardium. Our results show that the endocardial surface plays an important role in these mechanically-induced ectopic activations. Ectopic activation patterns indicate a participation of PFs in these arrhythmias, with a potential involvement of TRPM4 channels, shown by the reduction of arrhythmias by 9-Phenanthrol.

Abstract 12985: Extensive Valvular and Mural (Endocardial) Papillary Elastofibromatosis

Introduction: Papillary fibroelastomas (PFEs) are benign, often isolated, valvular tumors of endocardial origin although they may originate from non-valvular tissue and can be multiple. We report a unique case of PFE that involved 2 cardiac valves and nearly entire left ventricular (LV) endocardial surface. Case: A 73-year-old white woman with a history of non-valvular atrial fibrillation was admitted with intermittent worsening headaches and loss of peripheral vision in the right eye. An occipital-parietal hematoma was detected on brain computed tomography. Transthoracic echocardiogram showed multiple mobile masses on the mitral valve and the subvalvular apparatus. Transesophageal echocardiography showed additional involvement of the aortic valve and LV endocardium and no otherpotential source of embolism. She experienced recurrent systemic embolism and underwent surgery for the removal of cardiac masses. At surgery, more than 40 loosely attached individual and clustered PFEs (some shown in Figures A and B) confirmed by histology (Figure C) covered both aortic (Figure D and E) and mitral (Figure F) valves and nearly the entire LV endocardial surface (including papillary muscles,Figure G). All LV masses were removed and aortic and mitral valves were replaced. Conclusion. Although cases of multiple valvular PFEs have been reported previously, we report a unique case with a large number of PFEs that involved 2 cardiac valves and the entire mural surface of LV. We have used the term papillary elastofibromatosis to describe such an extensive tumor growth.

Regional left ventricular endocardial strains estimated from low-dose 4DCT: Comparison with cardiac magnetic resonance feature tracking.

Estimates of regional left ventricular (LV) strains provide additional information to global function parameters such as ejection fraction (EF) and global longitudinal strain (GLS) and are more sensitive in detecting abnormal regional cardiac function. The accurate and reproducible assessment of regional cardiac function has implications in the management of various cardiac diseases such as heart failure, myocardial ischemia, and dyssynchrony. To develop a method that yields highly reproducible, high-resolution estimates of regional endocardial strains from 4DCT images. A method for estimating regional LV endocardial circumferential and longitudinal ( ) strains from 4DCT was developed. Point clouds representing the LV endocardial surface were extracted for each time frame of the cardiac cycle from 4DCT images. 3D deformation fields across the cardiac cycle were obtained by registering the end diastolic point cloud to each subsequent point cloud in time across the cardiac cycle using a 3D point-set registration technique. From these deformation fields, were estimated over the entire LV endocardial surface by fitting an affine transformation with maximum likelihood estimation. The 4DCT-derived strains were compared with strains estimated in the same subjects by cardiac magnetic resonance (CMR); twenty-four subjects had CMR scans followed by 4DCT scans acquired within a few hours. Regional LV circumferential and longitudinal strains were estimated from the CMR images using a commercially available feature tracking software (cvi42). Global circumferential strain (GCS) and global longitudinal strain (GLS) were calculated as the mean of the regional strains across the entire LV for both modalities. Pearson correlation coefficients and Bland-Altman analyses were used for comparisons. Intraclass correlation coefficients (ICC) were used to assess the inter- and intraobserver reproducibility of the 4DCT-derived strains. The 4DCT-derived regional strains correlated well with the CMR-derived regional strains ( : r=0.76, p<0.001; : r=0.64, p<0.001). A very strong correlation was found between 4DCT-derived GCS and 4DCT-derived EF (r=-0.96; p<0.001). The 4DCT-derived strains were also highly reproducible, with very low inter- and intraobserver variability (intraclass correlation coefficients in the range of [0.92, 0.99]). We have developed a novel method to estimate high-resolution regional LV endocardial circumferential and longitudinal strains from 4DCT images. Except for the definition of the mitral valve and LV outflow tract planes, the method is completely user independent, thus yielding highly reproducible estimates of endocardial strain. The 4DCT-derived strains correlated well with those estimated using a commercial CMR feature tracking software. The promising results reported in this study highlight the potential utility of 4DCT in the precise assessment of regional cardiac function for the management of cardiac disease.

Automated intraprocedural localization of origin of ventricular activation using patient-specific computed tomographic imaging

To facilitate catheter ablation of ventricular tachycardia (VT), we previously developed an automated method to identify sources of left ventricular (LV) activation in real time using 12-lead electrocardiography (ECG), the accuracy of which depends on acquisition of a complete electroanatomic (EA) map. The purpose of this study was to assess the feasibility of using a registered cardiac computed tomogram (CT) rather than an EA map to permit real-time localization and avoid errors introduced by incomplete maps. Before LV VT ablation, 10 patients underwent CT imaging and 3-dimensional reconstruction of the cardiac surface to create a triangle mesh surface, which was registered to the EA map during the procedure and imported into custom localization software. The software uses QRS integrals from leads III, V2, and V6; derives personalized regression coefficients from pacing at ≥5 sites with known locations; and estimates the location of unknown activation sites on the 3-dimensional patient-specific LV endocardial surface. Localization accuracy was quantified for VT exit sites in millimeters by comparing the calculated against the known locations. The VT exit site was identified for 20 VTs using activation and entrainment mapping, supplemented by pace-mapping at the scar margin. The automated localization software achieved incremental accuracy with additional pacing sites and had a mean localization error of 6.9 ± 5.7 mm for the 20 VTs. Patient-specific CT geometry is feasible for use in real-time automated localization of ventricular activation and may avoid reliance on a complete EA map.

Localization of Activation Origin on Patient-Specific Endocardial Surface by the Equivalent Double Layer (EDL) Source Model With Sparse Bayesian Learning.

Ablation treatment of ventricular arrhythmias can be facilitated by pre-procedure planning aided by electrocardiographic inverse solution, which can help to localize the origin of arrhythmia. Our aim was to improve localization accuracy of the inverse solution for activation originating on the left-ventricular endocardial surface, by using a sparse Bayesian learning (SBL). The inverse problem of electrocardiography was solved by reconstructing endocardial potentials from time integrals of body-surface electrocardiograms and from patient-specific geometry of the heart and torso for three patients with structurally normal ventricular myocardium, who underwent endocardial catheter mapping that included pace mapping. Complementary simulations using dipole sources in patient-specific geometry were also performed. The proposed method is using sparse property of the equivalent-double-layer (EDL) model of cardiac sources; it employs the SBL and makes use of the spatio-temporal features of the cardiac action potentials. The mean localization error of the proposed method for pooled pacing sites ( n=52) was significantly smaller ( p=0.0039) than that achieved for the same patients in the study of Erem etal. Simulation experiments localized the source dipoles ( n=48) from forward-simulated potentials with the error of 9.4 ± 4.5mm (mean ± SD). The results of our clinical and simulation experiments demonstrate that localization of left-ventricular endocardial activation by means of the Bayesian approach, based on sparse representation of sources by EDL, is feasible and accurate. The proposed approach to localizing endocardial sources may have important applications in pre-procedure assessment of arrhythmias and in guiding their ablation treatment.

Localization of Ventricular Activation Origin from the 12-Lead ECG: A Comparison of Linear Regression with Non-Linear Methods of Machine Learning.

We have previously developed an automated localization method based on multiple linear regression (MLR) model to estimate the activation origin on a generic left-ventricular (LV) endocardial surface in real time from the 12-lead ECG. The present study sought to investigate whether machine learning-namely, random-forest regression (RFR) and support-vector regression (SVR)-can improve the localization accuracy compared to MLR. For 38 patients the 12-lead ECG was acquired during LV endocardial pacing at 1012 sites with known coordinates exported from an electroanatomic mapping system; each pacing site was then registered to a generic LV endocardial surface subdivided into 16 segments tessellated into 238 triangles. ECGs were reduced to one variable per lead, consisting of 120-ms time integral of the QRS. To compare three regression models, the entire dataset ([Formula: see text]) was partitioned at random into a design set with 80% and a test set with the remaining 20% of the entire set, and the localization error-measured as geodesic distance on the generic LV surface-was assessed. Bootstrap method with replacement, using 1000 resampling trials, estimated each model's error distribution for the left-out sample ([Formula: see text]). In the design set ([Formula: see text]), the mean accuracy was 8.8, 12.1, and 12.9mm, respectively for SVR, RVR and MLR. In the test set ([Formula: see text]), the mean value of the localization error in the SVR model was consistently lower than the other two models, both in comparison with the MLR (11.4 vs. 12.5mm), and with the RFR (11.4 vs. 12.0mm); the RFR model was also better than the MLR model for estimating localization accuracy (12.0 vs. 12.5mm). The bootstrap method with 1,000 trials confirmed that the SVR and RFR models had significantly higher predictive accurate than the MLR in the bootstrap assessment with the left-out sample (SVR vs. MLR ([Formula: see text]), RFR vs. MLR ([Formula: see text])). The performance comparison of regression models showed that a modest improvement in localization accuracy can be achieved by SVR and RFR models, in comparison with MLR. The "population" coefficients generated by the optimized SVR model from our dataset are superior to the previously-derived "population" coefficients generated by the MLR model and can supersede them to improve the localization of ventricular activation on the generic LV endocardial surface.

2D and 3D Echocardiography-Derived Indices of Left Ventricular Function and Shape: Relationship With Mortality

ObjectivesThis study hypothesized that left ventricular (LV) ejection fraction (EF) and global longitudinal strain (GLS) derived from 3-dimensional echocardiographic (3DE) images would better predict mortality than those obtained by 2-dimensional echocardiographic (2DE) measurements, and that 3DE-based LV shape analysis may have added prognostic value. BackgroundPrevious studies have shown that both LVEF and GLS derived from 2DE images predict mortality. Recently, 3DE measurements of these parameters were found to be more accurate and reproducible because of independence of imaging plane and geometric assumptions. Also, 3DE analysis offers an opportunity to accurately quantify LV shape. MethodsWe retrospectively studied 416 inpatients (60 ± 18 years of age) referred for transthoracic echocardiography between 2006 and 2010, who had good-quality 2DE and 3DE images were available. Mortality data through 2016 were collected. Both 2DE and 3DE images were analyzed to measure LVEF and GLS. Additionally, 3DE-derived LV endocardial surface information was analyzed to obtain global shape indices (sphericity and conicity) and regional curvature (anterior, septal, inferior, lateral walls). Cardiovascular (CV) mortality risks related to these indices were determined using Cox regression. ResultsOf the 416 patients, 208 (50%) died, including 114 (27%) CV-related deaths over a mean follow-up period of 5 ± 3 years. Cox regression revealed that age and body surface area, all 4 LV function indices (2D EF, 3D EF, 2D GLS, 3D GLS), and regional shape indices (septal and inferior wall curvatures) were independently associated with increased risk of CV mortality. GLS was the strongest prognosticator of CV mortality, superior to EF for both 2DE and 3DE analyses, and 2D EF was the weakest among the 4 functional indices. A 1% decrease in GLS magnitude was associated with an 11.3% increase in CV mortality risk. ConclusionsGLS predicts mortality better than EF by both 3DE and 2DE analysis, whereas 3D EF is a better predictor than 2D EF. Also, LV shape indices provide additional risk assessment.

Real-Time Localization of VentricularTachycardia Origin From the 12-Lead Electrocardiogram.

The aim of this study was to develop rapid computational methods for identifying the site of origin of ventricular activation from the 12-lead electrocardiogram. Catheter ablation of ventricular tachycardia in patients with structural heart disease frequently relies on a substrate-based approach, which may use pace mapping guided by body-surface electrocardiography to identify culprit exit sites. Patients undergoing ablation of scar-related VT (n= 38) had 12-lead electrocardiograms recorded during pacing at left ventricular endocardial sites (n= 1,012) identified on 3-dimensional electroanatomic maps and registered to a generic left ventricular endocardial surface divided into 16 segments and tessellated into 238 triangles; electrocardiographic data were reduced for each lead to 1 variable, consisting of QRS time integral. Two methods for estimating the origin of activation were developed: 1) a discrete method, estimating segment of activation origin using template matching; and 2) a continuous method, using population-based multiple linear regression to estimate triangle of activation origin. A variant of the latter method was derived, using patient-specific multiple linear regression. The optimal QRS time integral included the first 120 ms of the QRS interval. The mean localization error of population-based regressions was 12 ± 8 mm. Patient-specific regressions can achieve localization accuracy better than 5mm when at least 10 training-set pacing sites are used; this accuracy further increases with each added pacing site. Computational intraprocedure methods can automatically identify the segment and site of left ventricular activation using novel algorithms, with accuracy within<10 mm.

Validation of electromechanical wave imaging in a canine model during pacing and sinus rhythm

Accurate determination of regional areas of arrhythmic triggers is of key interest to diagnose arrhythmias and optimize their treatment. Electromechanical wave imaging (EWI) is an ultrasound technique that can image the transient deformation in the myocardium after electrical activation and therefore has the potential to detect and characterize location of triggers of arrhythmias. The objectives of this study were to investigate the relationship between the electromechanical and the electrical activation of the left ventricular (LV) endocardial surface during epicardial and endocardial pacing and during sinus rhythm as well as to map the distribution of electromechanical delays. In this study, 6 canines were investigated. Two external electrodes were sutured onto the epicardial surface of the LV. A 64-electrode basket catheter was inserted through the apex of the LV. Ultrasound channel data were acquired at 2000 frames/s during epicardial and endocardial pacing and during sinus rhythm. Electromechanical and electrical activation maps were synchronously obtained from the ultrasound data and the basket catheter, respectively. The mean correlation coefficient between electromechanical and electrical activation was 0.81 for epicardial anterior pacing, 0.79 for epicardial lateral pacing, 0.69 for endocardial pacing, and 0.56 for sinus rhythm. The electromechanical activation sequence determined by EWI follows the electrical activation sequence and more specifically in the case of pacing. This finding is of key interest in the role that EWI can play in the detection of the anatomical source of arrhythmias and the planning of pacing therapies such as cardiovascular resynchronization therapy.

Influence of catheter orientation on lesion formation in bovine myocardium by using an open-irrigated laser ablation catheter.

Lesion sizes and quality are crucial for successful catheter ablation procedures. We sought to test the influence of catheter orientation towards the endocardial surface on lesion formation in bovine myocardium by using an open-irrigated laser ablation catheter. Continuous wave 1064-nm laser catheter applications at 15W (4.5W/mm²)/30s, (135J/mm²), irrigation flow 30mL/min, were aimed at the left ventricular endocardial surface of bovine myocardium. The catheter was kept in vertical, in slanting (67.5°, 45°, 22.5°), and in flat positions; in flat position, also 60s of radiation times were applied (n = 10, each). Lesions were evaluated morphometrically. Maximum depth of lesion was achieved with the catheter in a vertical orientation. Catheter inclination of <22.5 showed a highly significant decrease of lesion depth from 5.6 ± 1.1 to 3.7 ± 0.5mm (p = 0.0001). In a flat catheter position, laser radiation of 30s achieved the smallest lesions. However, after 60s of radiation, the flat lesions were similar in depth (p = 087) and were larger in width (p = 0.0004) and in volumes (p = 0.0025) as compared to the lesions achieved with the catheter in vertical position after 30s of radiation. Steam-pop with intramural cavitation or tissue vaporization with crater formation did not occur. Longer radiation times can achieve larger lesions regardless of catheter orientation. Catheter orientation is not a major determinant for laser ablation lesion size and quality, and a steerable support may not be needed when using the open-irrigated electrode-laser mapping and ablation (ELMA) catheter RytmoLas.

A Reminder of Treatments Past

The Wolff-Parkinson-White (WPW) syndrome was initially described in 1930 as a clinical syndrome of paroxysmal tachycardias in healthy young people that demonstrated “bundle-branch block and short P-R interval”. These tachycardias were eventually determined to be macro-reentrant arrhythmias utilizing accessory pathways. Surgical approaches for transecting these accessory pathways were being developed as early as the 1960s. Since 1984, catheter ablation has developed into a safe and highly effective therapy option, and the treatment of choice for WPW syndrome today. We present a unique case of a patient with previous surgically treated WPW syndrome that serves as a reminder of treatments past and caution for current therapies. A 54-year-old man with a remote history of WPW syndrome, treated in 1989 with surgical cryoablation of a left ventricular free wall accessory pathway, now presented with an hour of sustained palpitations after a triathlon practice session. He was found to have ventricular tachycardia at a rate of 180 bpm on EKG requiring external cardioversion. The troponin I level peaked at 2.59 ng/mL. Left heart catheterization revealed a peculiar truncated 100% occlusion of the proximal circumflex artery with extensive bridging collaterals to the mid circumflex artery, and also confirmed an infero-basal aneurysm. The cause of the ventricular tachycardia (VT) was deemed non-ischemic and he was referred for electrophysiology study. 3D electroanatomic mapping of the left ventricular (LV) endocardial surface was performed, revealing a discrete posterior wall scar. Reentrant VT was repeatedly induced utilizing a zone of slow conduction along the border zone of the scar. Radiofrequency ablation of Purkinje potentials on the LV septum, running alongside the scar border zone, eliminated the VT. The entire endocardial surface of the postero-basal scar was electrically silenced to prevent further VT events. Typically, during the surgical approach of WPW, a wide endocardial (rarely an epicardial) incision was made along the atrial surface of the mitral valve annulus, dissecting deeply and caudally until ventricular myocardium was exposed. Despite the close proximity of the circumflex artery to the epicardial incision line during these surgeries, there are only rare reports of coronary artery complications, generally considered to be either catheter-induced dissections or embolic events. The development of a network of extensive bridging collaterals in our patient supports progressive stenosis of the left circumflex artery from cryoablation thermic injury, leading to scar formation and VT years later. In conclusion, this case reminds us that current ablative therapies are still relatively new, and long-term follow-ups for delayed complications remain a necessity. J Med Cases. 2016;7(6):216-219 doi: http://dx.doi.org/10.14740/jmc2488w

A REMINDER OF TREATMENTS PAST

The Wolff-Parkinson-White (WPW) syndrome was initially described in 1930 as a clinical syndrome of paroxysmal tachycardias in healthy young people that demonstrated “bundle-branch block and short P-R interval”. These tachycardias were eventually determined to be macro-reentrant arrhythmias utilizing accessory pathways. Surgical approaches for transecting these accessory pathways were being developed as early as the 1960s. Since 1984, catheter ablation has developed into a safe and highly effective therapy option, and the treatment of choice for WPW syndrome today. We present a unique case of a patient with previous surgically treated WPW syndrome that serves as a reminder of treatments past and caution for current therapies. A 54-year-old man with a remote history of WPW syndrome, treated in 1989 with surgical cryoablation of a left ventricular free wall accessory pathway, now presented with an hour of sustained palpitations after a triathlon practice session. He was found to have ventricular tachycardia at a rate of 180 bpm on EKG requiring external cardioversion. The troponin I level peaked at 2.59 ng/mL. Left heart catheterization revealed a peculiar truncated 100% occlusion of the proximal circumflex artery with extensive bridging collaterals to the mid circumflex artery, and also confirmed an infero-basal aneurysm. The cause of the ventricular tachycardia (VT) was deemed non-ischemic and he was referred for electrophysiology study. 3D electroanatomic mapping of the left ventricular (LV) endocardial surface was performed, revealing a discrete posterior wall scar. Reentrant VT was repeatedly induced utilizing a zone of slow conduction along the border zone of the scar. Radiofrequency ablation of Purkinje potentials on the LV septum, running alongside the scar border zone, eliminated the VT. The entire endocardial surface of the postero-basal scar was electrically silenced to prevent further VT events. Typically, during the surgical approach of WPW, a wide endocardial (rarely an epicardial) incision was made along the atrial surface of the mitral valve annulus, dissecting deeply and caudally until ventricular myocardium was exposed. Despite the close proximity of the circumflex artery to the epicardial incision line during these surgeries, there are only rare reports of coronary artery complications, generally considered to be either catheter-induced dissections or embolic events. The development of a network of extensive bridging collaterals in our patient supports progressive stenosis of the left circumflex artery from cryoablation thermic injury, leading to scar formation and VT years later. In conclusion, this case reminds us that current ablative therapies are still relatively new, and long-term follow-ups for delayed complications remain a necessity. J Med Cases. 2016;7(6):216-219 doi: http://dx.doi.org/10.14740/jmc2488w

Can left ventricular endocardial surface roughness be measured by fractal dimension on fast gradient echo sequences?

Can left ventricular endocardial surface roughness be measured by fractal dimension on fast gradient echo sequences?

Simulation Methods and Validation Criteria for Modeling Cardiac Ventricular Electrophysiology.

We describe a sequence of methods to produce a partial differential equation model of the electrical activation of the ventricles. In our framework, we incorporate the anatomy and cardiac microstructure obtained from magnetic resonance imaging and diffusion tensor imaging of a New Zealand White rabbit, the Purkinje structure and the Purkinje-muscle junctions, and an electrophysiologically accurate model of the ventricular myocytes and tissue, which includes transmural and apex-to-base gradients of action potential characteristics. We solve the electrophysiology governing equations using the finite element method and compute both a 6-lead precordial electrocardiogram (ECG) and the activation wavefronts over time. We are particularly concerned with the validation of the various methods used in our model and, in this regard, propose a series of validation criteria that we consider essential. These include producing a physiologically accurate ECG, a correct ventricular activation sequence, and the inducibility of ventricular fibrillation. Among other components, we conclude that a Purkinje geometry with a high density of Purkinje muscle junctions covering the right and left ventricular endocardial surfaces as well as transmural and apex-to-base gradients in action potential characteristics are necessary to produce ECGs and time activation plots that agree with physiological observations.

Abstract 17790: Can 3D Echocardiography Play a Role in Left Ventricular Assist Device Optimization?

Introduction: Left ventricular (LV) assist device (LVAD) has emerged as a valuable option for patients with severe congestive heart failure both as bridge to transplantation or destination therapy. Speed optimization of LVAD is currently based on the position of the inter-ventricular septum, mitral regurgitation severity and aortic valve opening. Hypothesis: We hypothesized that 3D transthoracic echocardiography (3DE) would provide additional information on left and right ventricular (RV) volumes and shape, which could be valuable in determining optimal LVAD speed. Our aim was to assess the feasibility of combined 3D LV and RV analysis during an incremental RAMP study. Methods: Six consecutive patients undergoing a RAMP test were studied. Device speed was increased from 8000 to 12000 rpm in 400-rpm increments for axial-flow pumps (n=2) and from 2300 to 3200 rpm in 100 rpm increments for centrifugal-flow pumps (n=4). Transthoracic 3DE apical full-volume datasets of the LV and the RV were acquired (Philips) at every other step. RV and LV endocardial surfaces were reconstructed using commercial software (TomTec) and used to calculate ventricular volumes. Custom software was used to calculate LV shape indices of sphericity and conicity (a perfectly spherical/conical ventricle would result in 1.0 value). Results: Data acquisition and post-processing was feasible in 5/6 patients. In axial pumps (Figure), increments in LVAD speed were associated with gradually decreasing LV volume, while RV volume initially decreased to a minimum and then increased at higher speeds. These volumetric changes were associated with alterations in LV shape, with the LV becoming less spherical and more conical at higher speeds. With centrifugal pumps, increased speed was associated with similar changes in LV shape but with minimal changes in volumes. Conclusions: Acquisition of 3D datasets during RAMP studies is feasible and could become a valuable aid in optimizing LVAD pump speed.

Three-dimensional left ventricular segmentation from magnetic resonance imaging for patient-specific modelling purposes.

To propose a nearly automated left ventricular (LV) three-dimensional (3D) surface segmentation procedure, based on active shape modelling (ASM) and built on a database of 3D echocardiographic (3DE) LV surfaces, for cardiac magnetic resonance (CMR) images, and to test its accuracy for LV volumes computation compared with 'gold standard' manual tracings and discs-summation method. The ASM was created based on segmented LV surfaces (4D LV analysis, Tomtec) from 3DE datasets of 205 patients. Then, it was applied to the cardiac magnetic resonance imaging short-axis (SAX) images stack of 12 consecutive patients. After proper realignment using two- and four-chambers CMR long-axis views both as reference and for initializing LV apex and base (six points in total), the ASM was iteratively and automatically updated to match the information of all the SAX planes contemporaneously, resulting in an endocardial LV 3D mesh from which volume was directly derived. The same CMR images were analysed by an experienced cardiologist to derive end-diastolic and end-systolic volumes. Linear correlation and Bland-Altman analyses were applied vs. the manual 'gold standard'. Active shape modelling results showed high correlations with manual values both for LV volumes (r(2) > 0.98) and ejection fraction (EF) (r(2) > 0.90), non-significant biases and narrow limits of agreement. The proposed method resulted in accurate detection of 3D LV endocardial surfaces, which lead to fast and reliable measurements of LV volumes and EF when compared with manual tracing of CMR SAX images. The segmented 3D mesh, including a realistic LV apex and base, could constitute a novel starting point for more realistic patient-specific finite element modelling.

Segmentation of Multi-Center 3D Left Ventricular Echocardiograms by Active Appearance Models

Segmentation of 3D echocardiograms (3DEs) is still a challenging task due to the low signal-to-noise ratio, the limited field of view, and typical ultrasound artifacts. We propose to segment the left ventricular endocardial surface by using Active Appearance Models (AAMs). Separate end-diastolic (ED) and end-systolic (ES) AAMs were built from presegmented 3DEs of the CETUS training data and 25 previously acquired 3DEs, imaged using various 3DE equipment. The AAMs fully automatically segmented the 15 training sets in a leave-one-out cross validation, comparing two training populations and various initialization strategies. All segmentations took about 15 seconds per patient. The comparison on the CETUS training data shows that the AAM benefits from additional training data and more accurate initialization. The results on the CETUS training and testing data confirm good ED and ES segmentation accuracy on multi-center, multi-vendor, multi-pathology data, and corresponding EF estimation. Selection from different initialization strategies, based on the minimal residual error, and propagation of detected ED contours to initialize ES detection, contributed to more accurate segmentations in this heterogeneous population.

AUTOMATED LOCALIZATION OF LEFT VENTRICULAR PACING SITES FROM THE 12-LEAD ELECTROCARDIOGRAM DURING CATHETER ABLATION STUDY

Catheter ablation of scar-mediated VT often uses substrate mapping, and could be facilitated by a rapid method to localize VT exit sites. We sought to assess the accuracy of a novel real-time automated computer algorithm used to localize the site of ventricular activation. In patients undergoing ablation of VT, 12-lead ECGs were acquired during left ventricular (LV) endocardial pacing at sites (n = 589) corresponding to those identified on electroanatomic maps. The sites were registered to one of 238 triangular area elements within a 16-segment anatomical model of the LV endocardial surface. The algorithm calculated the ECG parameters consisting of normalized QRS time-integrals and applied segmental template matching, followed by an estimate of the anatomic origin by high-resolution method based on regression coefficients relating an idealized LV geometry to the ECG parameters. Localization error and accuracy were calculated for each pacing site. Robustness of the algorithm was assessed using the bootstrap-with-replacement method. 26 patients (62 ± 14 years old) with predominantly ischemic cardiomyopathy (77%) and reduced EF (mean 35 ± 11%) undergoing ablation of VT (89%) or PVCs (11%) were enrolled. The calculated localization error was 13.1 ± 9.9 mm (n= 589 sites) with a median of 10.7 mm. Real-time computerized localization of sites of ventricular activation during ablation of VT is feasible and robust between patients and may facilitate concentrating ablation at culprit sites.