33 results found
Chubb H, Karim R, Mukherjee R, et al., 2019, A comprehensive multi-index cardiac magnetic resonance-guided assessment of atrial fibrillation substrate prior to ablation: Prediction of long-term outcomes., J Cardiovasc Electrophysiol, Vol: 30, Pages: 1894-1903
INTRODUCTION: Multiple cardiac magnetic resonance (CMR)-derived indices of atrial fibrillation (AF) substrate have been shown in isolation to predict long-term outcome following catheter ablation. Left atrial (LA) fibrosis, LA volume, LA ejection fraction (EF), left ventricular ejection fraction (LVEF), LA shape (sphericity) and pulmonary vein anatomy have all been shown to correlate with late AF recurrence. This study aimed to validate and assess the relative contribution of multiple indices in a long-term single-center study. METHODS AND RESULTS: Eighty-nine patients (53% paroxysmal AF, 73% male) underwent comprehensive CMR study before first-time AF ablation (median follow-up 726 days [IQR: 418-1010 days]). The 3D late gadolinium-enhanced acquisition (1.5T, 1.3 × 1.3 × 2 mm) was quantified for fibrosis; LA volume and sphericity were assessed on manual segmentation at atrial diastole; LAEF and LVEF were quantified on multislice cine imaging. AF recurred in 43 patients (48%) overall (31 at 1 year). In the recurrence group, LA fibrosis was higher (42% vs 29%; hazard ratio [HR]: 1.032; P = .002), left atrial ejection fraction (LAEF) lower (25% vs 34%; HR: 0.063; P = .016) and LVEF lower (57% vs 63%; HR: 0.011; P = .008). LA volume (135 vs 124 mL) and sphericity (0.819 vs 0.822) were similar. Multivariate Cox regression analysis was adjusted for age and sex (Model 1), additionally AF type (Model 2) and combined (Model 3). In Models 1 and 2, LA fibrosis, LAEF, and LVEF were independently associated with outcome, but only LA fibrosis was independent in Model 3 (HR: 1.021; P = .022). CONCLUSIONS: LAEF, LVEF, and LA fibrosis differed significantly in the AF recurrence cohort. However, on combined multivariate analysis only LA fibrosis remained independently associated with outcome.
Chubb H, Lal K, Kiedrowicz R, et al., 2019, The value of ablation parameter indices for predicting mature atrial scar formation in humans: An in vivo assessment using cardiac magnetic resonance imaging., J Cardiovasc Electrophysiol, Vol: 30, Pages: 67-77
INTRODUCTION: The VisiTag module (CARTO3) provides an objective assessment of radiofrequency (RF) ablation parameters. This study aimed to determine the predictive value and optimal VisiTag threshold settings for prediction of gaps in mature atrial scar, as assessed non-invasively using cardiac magnetic resonance (CMR) imaging. METHODS: Twenty-four subjects (11 paroxysmal atrial fibrillation) underwent first-time RF ablation with operators blinded to VisiTag data. Three-dimensional late gadolinium enhancement (LGE) CMR scans were performed at 3 months (1.3 × 1.3 × 4 mm3 ). A survey of UK operators defined the standard VisiTag settings ("Force," 8 g; "Time," 10 seconds; "Percentage Time," 50%; "Range," 3 mm; "Impedance" and "Temperature" "off"). Each ablation procedure was exported 27 times, varying single VisiTag parameters from default values. The presence of gaps in VisiTag markers (18 sectors) was assessed for each export and compared with gaps in CMR enhancement. RESULTS: At default settings, VisiTag gaps were specific (97.5%) but less sensitive (50.4%) for CMR gaps. Sensitivity improved at higher thresholds (89.2% at 20 g, 85.6% at 30 seconds, 88.5% impedance 10 Ω, 92.8% temperature 42°C), but with a lower positive predictive value (PPV) (42.3%, 42.7%, 41.1%, and 37.7%, respectively, vs 90.9% at baseline). "Force" thresholds demonstrated stable PPV from 2 to 8 g (P = 0.24), but a rapid fall at forces more than 10 g. The binomial logistic regression model explained 41.7% of gaps; χ 2 (4), 148; P < 0.0001, correctly classifying 82% of cases (specificity 94.9%, sensitivity 56.8%). CONCLUSION: Gaps in VisiTags predict gaps in CMR LGE enhancement with high specificity at default settings. Sensitivity may be improved using more stringent thres
Karim R, Blake L-E, Inoue J, et al., 2018, Algorithms for left atrial wall segmentation and thickness - Evaluation on an open-source CT and MRI image database., Med Image Anal, Vol: 50, Pages: 36-53
Structural changes to the wall of the left atrium are known to occur with conditions that predispose to Atrial fibrillation. Imaging studies have demonstrated that these changes may be detected non-invasively. An important indicator of this structural change is the wall's thickness. Present studies have commonly measured the wall thickness at few discrete locations. Dense measurements with computer algorithms may be possible on cardiac scans of Computed Tomography (CT) and Magnetic Resonance Imaging (MRI). The task is challenging as the atrial wall is a thin tissue and the imaging resolution is a limiting factor. It is unclear how accurate algorithms may get and how they compare in this new emerging area. We approached this problem of comparability with the Segmentation of Left Atrial Wall for Thickness (SLAWT) challenge organised in conjunction with MICCAI 2016 conference. This manuscript presents the algorithms that had participated and evaluation strategies for comparing them on the challenge image database that is now open-source. The image database consisted of cardiac CT (n=10) and MRI (n=10) of healthy and diseased subjects. A total of 6 algorithms were evaluated with different metrics, with 3 algorithms in each modality. Segmentation of the wall with algorithms was found to be feasible in both modalities. There was generally a lack of accuracy in the algorithms and inter-rater differences showed that algorithms could do better. Benchmarks were determined and algorithms were ranked to allow future algorithms to be ranked alongside the state-of-the-art techniques presented in this work. A mean atlas was also constructed from both modalities to illustrate the variation in thickness within this small cohort.
Karim R, Panayiotou M, Chowdhury O, et al., 2018, Image Data Analysis for Quantifying Scar Transmurality in MRI phantoms for Cardiac Resynchronisation Therapy, 2018 40th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Publisher: IEEE
Corrado C, Williams S, Karim R, et al., 2018, A work flow to build and validate patient specific left atrium electrophysiology models from catheter measurements, Medical Image Analysis, Vol: 47, Pages: 153-163, ISSN: 1361-8415
Mountney P, Behar JM, Toth D, et al., 2017, A Planning and Guidance Platform for Cardiac Resynchronization Therapy, IEEE Transactions on Medical Imaging, Vol: 36, Pages: 2366-2375, ISSN: 0278-0062
Ataollahi A, Karim R, Fallah AS, et al., 2016, Three-Degree-of-Freedom MR-Compatible Multisegment Cardiac Catheter Steering Mechanism, IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, Vol: 63, Pages: 2425-2435, ISSN: 0018-9294
Karim R, Bhagirath P, Claus P, et al., 2016, Evaluation of state-of-the-art segmentation algorithms for left ventricle infarct from late Gadolinium enhancement MR images, Medical Image Analysis, Vol: 30, Pages: 95-107, ISSN: 1361-8415
Studies have demonstrated the feasibility of late Gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) imaging for guiding the management of patients with sequelae to myocardial infarction, such as ventricular tachycardia and heart failure. Clinical implementation of these developments necessitates a reproducible and reliable segmentation of the infarcted regions. It is challenging to compare new algorithms for infarct segmentation in the left ventricle (LV) with existing algorithms. Benchmarking datasets with evaluation strategies are much needed to facilitate comparison. This manuscript presents a benchmarking evaluation framework for future algorithms that segment infarct from LGE CMR of the LV. The image database consists of 30 LGE CMR images of both humans and pigs that were acquired from two separate imaging centres. A consensus ground truth was obtained for all data using maximum likelihood estimation.Six widely-used fixed-thresholding methods and five recently developed algorithms are tested on the benchmarking framework. Results demonstrate that the algorithms have better overlap with the consensus ground truth than most of the n-SD fixed-thresholding methods, with the exception of the Full-Width-at-Half-Maximum (FWHM) fixed-thresholding method. Some of the pitfalls of fixed thresholding methods are demonstrated in this work. The benchmarking evaluation framework, which is a contribution of this work, can be used to test and benchmark future algorithms that detect and quantify infarct in LGE CMR images of the LV. The datasets, ground truth and evaluation code have been made publicly available through the website: https://www.cardiacatlas.org/web/guest/challenges.
Williams SE, Harrison J, Chubb H, et al., 2015, The Effect of Contact Force in Atrial Radiofrequency Ablation, JACC: Clinical Electrophysiology, Vol: 1, Pages: 421-431, ISSN: 2405-500X
Williams S, Harrison J, Chubb H, et al., The Effect of Contact Force in Atrial Radiofrequency Ablation : Electroanatomical, Cardiovascular Magnetic Resonance, and Histological Assessment in a Chronic Porcine Model, JACC: Clinical Electrophysiology
Harrison JL, Sohns C, Linton NW, et al., 2015, Response to letter from Bisbal et al regarding, "Repeat left atrial catheter ablation: cardiac magnetic resonance prediction of endocardial voltage and gaps in ablation lesion sets"., Circ Arrhythm Electrophysiol, Vol: 8, Pages: 754-755
Harrison JL, Sohns C, Linton NW, et al., 2015, Repeat left atrial catheter ablation: cardiac magnetic resonance prediction of endocardial voltage and gaps in ablation lesion sets., Circ Arrhythm Electrophysiol, Vol: 8, Pages: 270-278
BACKGROUND: Studies have reported an inverse relationship between late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) signal intensity and left atrial (LA) endocardial voltage after LA ablation. However, there is controversy regarding the reproducibility of atrial LGE CMR and its ability to identify gaps in ablation lesions. Using systematic and objective techniques, this study examines the correlation between atrial CMR and endocardial voltage. METHODS AND RESULTS: Twenty patients who had previous ablation for atrial fibrillation and represented with paroxysmal atrial fibrillation or atrial tachycardia underwent preablation LGE CMR. During the ablation procedure, high-density point-by-point Carto voltage maps were acquired. Three-dimensional CMR reconstructions were registered with the Carto anatomies to allow comparison of voltage and LGE signal intensity. Signal intensities around the left and right pulmonary vein antra and along the LA roof and mitral lines on the CMR-segmented LA shells were extracted to examine differences between electrically isolated and reconnected lesions. There were a total of 6767 data points across the 20 patients. Only 119 (1.8%) of the points were ≤ 0.05 mV. There was only a weak inverse correlation between either unipolar (r = -0.18) or bipolar (r = -0.17) voltage and LGE CMR signal intensities with low voltage occurring across a large range of signal intensities. Signal intensities were not statistically different for electrically isolated and reconnected lesions. CONCLUSIONS: This study demonstrates that there is only a weak point-by-point relationship between LGE CMR and endocardial voltage in patients undergoing repeat LA ablation. Using an objective method of assessing gaps in ablation lesions, LGE CMR is unable to reliably predict sites of electrical conduction.
Arujuna A, Karim R, Zarinabad N, et al., 2015, A randomized prospective mechanistic cardiac magnetic resonance study correlating catheter stability, late gadolinium enhancement and 3 year clinical outcomes in robotically assisted vs. standard catheter ablation., Europace, Vol: 17, Pages: 1241-1250, ISSN: 1532-2092
AIMS: To prospectively compare cardiac magnetic resonance late gadolinium enhancement (LGE) findings created by standard vs. robotically assisted catheter ablation lesions and correlate these with clinical outcomes. METHODS AND RESULTS: Forty paroxysmal atrial fibrillation patients (mean age 54 ± 13.8 years) undergoing first left atrial ablation were randomized to either robotic-assisted navigation (Hansen Sensei(®) X) or standard navigation. Pre-procedural, acute (24 h post-procedure) and late (beyond 3 months) scans were performed with LGE and T2W imaging sequences and percentage circumferential enhancement around the pulmonary vein (PV) antra were quantified. Baseline pre-procedural enhancements were similar in both groups. On acute imaging, mean % encirclements by LGE and T2W signal were 72% and 80% in the robotic group vs. 60% (P = 0.002) and 76%(P = 0.45) for standard ablation. On late imaging, the T2W signal resolved to baseline in both groups. Late gadolinium enhancement remained the predominant signal with 56% encirclement in the robotic group vs. 45% in the standard group (P = 0.04). At 6 months follow-up, arrhythmia-free patients had an almost similar mean LGE encirclement (robotic 64%, standard 60%, P = 0.45) but in recurrences, LGE was higher in the robotic group (43% vs. 30%, P = 0.001). At mean 3 years follow-up, 1.3 procedures were performed in the robotic group compared with 1.9 (P < 0.001) in the standard to achieve a success rate of 80% vs. 75%. CONCLUSION: Robotically assisted ablation results in greater LGE around the PV antrum. Effective lesions created through improved catheter stability and contact force during initial treatment may have a role in reducing subsequent re-do procedures.
Bhagirath P, van der Graaf M, Karim R, et al., 2015, Interventional cardiac magnetic resonance imaging in electrophysiology: advances toward clinical translation., Circ Arrhythm Electrophysiol, Vol: 8, Pages: 203-211
Bhagirath P, van der Graaf AWM, Karim R, et al., 2014, Multimodality imaging for patient evaluation and guidance of catheter ablation for atrial fibrillation — Current status and future perspective, International Journal of Cardiology, Vol: 175, Pages: 400-408, ISSN: 0167-5273
Harrison JL, Jensen HK, Peel SA, et al., 2014, Cardiac magnetic resonance and electroanatomical mapping of acute and chronic atrial ablation injury: a histological validation study., Eur Heart J, Vol: 35, Pages: 1486-1495
AIMS: To provide a comprehensive histopathological validation of cardiac magnetic resonance (CMR) and endocardial voltage mapping of acute and chronic atrial ablation injury. METHODS AND RESULTS: 16 pigs underwent pre-ablation T2-weighted (T2W) and late gadolinium enhancement (LGE) CMR and high-density voltage mapping of the right atrium (RA) and both were repeated after intercaval linear radiofrequency ablation. Eight pigs were sacrificed following the procedure for pathological examination. A further eight pigs were recovered for 8 weeks, before chronic CMR, repeat RA voltage mapping and pathological examination. Signal intensity (SI) thresholds from 0 to 15 SD above a reference SI were used to segment the RA in CMR images and segmentations compared with real lesion volumes. The SI thresholds that best approximated histological volumes were 2.3 SD for LGE post-ablation, 14.5 SD for T2W post-ablation and 3.3 SD for LGE chronically. T2-weighted chronically always underestimated lesion volume. Acute histology showed transmural injury with coagulative necrosis. Chronic histology showed transmural fibrous scar. The mean voltage at the centre of the ablation line was 3.3 mV pre-ablation, 0.6 mV immediately post-ablation, and 0.3 mV chronically. CONCLUSION: This study presents the first histopathological validation of CMR and endocardial voltage mapping to define acute and chronic atrial ablation injury, including SI thresholds that best match histological lesion volumes. An understanding of these thresholds may allow a more informed assessment of the underlying atrial substrate immediately after ablation and before repeat catheter ablation for atrial arrhythmias.
karim R, 2014, A Method to Standardize Quantification of Left Atrial Scar From Delayed-Enhancement MR Images, IEEE Journal of Translational Engineering in Health and Medicine, ISSN: 2168-2372
Sohns C, Karim R, Harrison J, et al., 2014, Quantitative Magnetic Resonance Imaging Analysis of the Relationship Between Contact Force and Left Atrial Scar Formation After Catheter Ablation of Atrial Fibrillation, JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Vol: 25, Pages: 138-145, ISSN: 1045-3873
Karim R, Surface flattening of the human left atrium and proof-of-concept clinical applications, Computerized Medical Imaging and Graphics, ISSN: 1879-0771
Karim R, Housden RJ, Balasubramaniam M, et al., 2013, Evaluation of current algorithms for segmentation of scar tissue from late Gadolinium enhancement cardiovascular magnetic resonance of the left atrium: an open-access grand challenge, Journal of Cardiovascular Magnetic Resonance, Vol: 15, ISSN: 1097-6647
Karim R, A novel skeleton based quantification and 3-D volumetric visualization of left atrium fibrosis using late gadolinium enhancement magnetic resonance imaging, IEEE Transactions on Medical Imaging, ISSN: 1558-254X
Malcolme-Lawes LC, Juli C, Karim R, et al., 2013, Automated analysis of atrial late gadolinium enhancement imaging that correlates with endocardial voltage and clinical outcomes: A 2-center study, HEART RHYTHM, Vol: 10, Pages: 1184-1191, ISSN: 1547-5271
Puntmann VO, Voigt T, Chen Z, et al., 2013, Native T1 mapping in differentiation of normal myocardium from diffuse disease in hypertrophic and dilated cardiomyopathy., JACC Cardiovasc Imaging, Vol: 6, Pages: 475-484
OBJECTIVES: The aim of this study was to examine the value of native and post-contrast T1 relaxation in the differentiation between healthy and diffusely diseased myocardium in 2 model conditions, hypertrophic cardiomyopathy and nonischemic dilated cardiomyopathy. BACKGROUND: T1 mapping has been proposed as potentially valuable in the quantitative assessment of diffuse myocardial fibrosis, but no studies to date have systematically evaluated its role in the differentiation of healthy myocardium from diffuse disease in a clinical setting. METHODS: Consecutive subjects undergoing routine clinical cardiac magnetic resonance at King's College London were invited to participate in this study. Groups were based on cardiac magnetic resonance findings and consisted of subjects with known hypertrophic cardiomyopathy (n = 25) and nonischemic dilated cardiomyopathy (n = 27). Thirty normotensive subjects with low pre-test likelihood of cardiomyopathy, not taking any regular medications and with normal cardiac magnetic resonance findings including normal left ventricular mass indexes, served as controls. Single equatorial short-axis slice T1 mapping was performed using a 3-T scanner before and at 10, 20, and 30 minutes after the administration of 0.2 mmol/kg of gadobutrol. T1 values were quantified within the septal myocardium (T1 native), and extracellular volume fractions (ECV) were calculated. RESULTS: T1 native was significantly longer in patients with cardiomyopathy compared with control subjects (p < 0.01). Conversely, post-contrast T1 values were significantly shorter in patients with cardiomyopathy at all time points (p < 0.01). ECV was significantly higher in patients with cardiomyopathy compared with controls at all time points (p < 0.01). Multivariate binary logistic regression revealed that T1 native could differentiate between healthy and diseased myocardium with sensitivity of 100%, specificity of 96%, and diagnostic accuracy of 98% (area under the curve 0
Malcolme-Lawes L, Juli C, Karim R, et al., 2012, AUTOMATED ANALYSIS OF ATRIAL DELAYED ENHANCEMENT CARDIAC MRI CORRELATES WITH VOLTAGE, AF RECURRENCE POST-ABLATION, AND HIGH STROKE RISK, Annual Conference of the British-Cardiovascular-Society (BCS)
Karim R, Arujuna A, Brazier A, et al., 2012, Validation of a novel method for the automatic segmentation of left atrial scar from delayed-enhancement magnetic resonance, Pages: 254-262, ISSN: 0302-9743
Delayed-enhancement magnetic resonance imaging is an effective technique for imaging left atrial (LA) scars both pre- and post- radio-frequency ablation for the treatment of atrial fibrillation. Existing techniques for LA scar segmentation require expert manual interaction, making them tedious and prone to high observer variability. In this paper, a novel automatic segmentation algorithm for segmenting LA scar was validated using digital phantoms and clinical data from 11 patients. The performance of the approach was compared to the two leading semi-automatic techniques and the ground truth of manual segmentations by 2 expert observers. The novel approach was shown to be accurate in terms of Dice coefficient, robust to typical image intensity variability, and much faster in terms of execution time. © 2012 Springer-Verlag.
Arujuna A, Karim R, Caulfield D, et al., 2012, Acute pulmonary vein isolation is achieved by a combination of reversible and irreversible atrial injury after catheter ablation: evidence from magnetic resonance imaging, Circ.Arrhythm Electrophysiol., Vol: 5, Pages: 691-700, ISSN: 1941-3084
BACKGROUND: Pulmonary vein reconnection after pulmonary vein isolation is common and is usually associated with recurrences of atrial fibrillation. We used cardiac magnetic resonance imaging after radiofrequency ablation to investigate the hypothesis that acute pulmonary vein isolation results from a combination of irreversible and reversible atrial injury. METHODS AND RESULTS: Delayed enhancement (DE; representing areas of acute tissue injury/necrosis) and T2-weighted (representing tissue water content, including edema) cardiac magnetic resonance scans were performed before, immediately after (acute), and later than 3 months (late) after pulmonary vein isolation in 25 patients with paroxysmal atrial fibrillation undergoing wide-area circumferential ablation. Images were analyzed as pairs of pulmonary veins to quantify the percentage of circumferential antral encirclement composed of DE, T2, and combined DE+T2 signal. Fourteen of 25 patients were atrial fibrillation free at 11-month follow-up (interquartile range, 8-16 months). These patients had higher DE (71+/-6.0%) and lower T2 signal (72+/-7.8%) encirclement on the acute scans compared with recurrences (DE, 55+/-9.1%; T2, 85+/-6.3%; P<0.05). Patients maintaining sinus rhythm had a lesser decline in DE between acute and chronic scans compared with recurrences (71+/-6.0% and 60+/-5.8% versus 55+/-9.1% and 34+/-7.3%, respectively). The percentage of encirclement by a combination of DE+T2 was almost similar in both groups on the acute scans (atrial fibrillation free, 89+/-5.4%; recurrences, 92+/-4.8%) but different on the chronic scans (60+/-5.7% versus 34+/-7.3%). CONCLUSIONS: The higher T2 signal on acute scans and greater decline in DE on chronic imaging in patients with recurrences suggest that they have more reversible tissue injury, providing a potential mechanism for pulmonary vein reconnection, resulting in arrhythmia recurrence.
Malcolme-Lawes LC, Karim R, Juli C, et al., 2011, Automated analysis of post-ablation atrial enhancement using delayed-enhanced cardiac magnetic resonance imaging, EUROPEAN HEART JOURNAL, Vol: 32, Pages: 629-629, ISSN: 0195-668X
Malcolme-Lawes L, Karim R, Juli C, et al., 2011, AUTOMATED ANALYSIS OF ATRIAL ABLATION-SCAR USING DELAYED-ENHANCED CARDIAC MRI, Annual Conference of the British-Cardiovascular-Society (BCS)
Karim R, Arujuna A, Brazier A, et al., 2011, Automatic Segmentation of Left Atrial Scar from Delayed-Enhancement Magnetic Resonance Imaging, 6th International Conference on Functional Imaging and Modeling of the Heart (FIMH), Publisher: SPRINGER-VERLAG BERLIN, Pages: 63-70, ISSN: 0302-9743
Karim R, Juli C, Malcolme-Lawes L, et al., 2010, Automatic Segmentation of Left Atrial Geometry from Contrast-Enhanced Magnetic Resonance Images Using a Probabilistic Atlas, 1st International Workshop on Statistical Atlases and Computational Models of the Heart, Publisher: SPRINGER-VERLAG BERLIN, Pages: 134-+, ISSN: 0302-9743
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