John Whitaker

John Whitaker
Guy's and St Thomas' NHS Foundation Trust · Cardiovascular Department

Doctor of Philosophy

About

142
Publications
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Publications

Publications (142)
Article
Background: The right ventricular moderator band and papillary muscle (RV MB-PM) complex is an uncommon source of ventricular arrhythmias (VAs). Success rates following the ablation of intracavity structures are lower than for other sites of origin of VAs because of challenging catheter stability and a tendency for hemodynamically unstable automat...
Article
Full-text available
Background Atrial fibrillation (AF) is associated with atrial septal defects (ASDs), but the mechanism of arrhythmia in these patients is poorly understood. We hypothesised that right-sided atrial ectopy may predominate in this cohort. Here, we aimed to localise the origin of spontaneous and provoked atrial ectopy in ASD patients. Methods Followin...
Article
Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Research Council Background SBRT is currently restrained to the most severe patients with drug- and catheter ablation-refractory VT, often associated with advanced heart failure. Purpose To analyze the determinants of mortality after S...
Article
Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Research Council Background Optimal SBRT planning methods for VT ablation are yet to be defined. Purpose To evaluate a multimodal approach for SBRT planning. Methods 30 pts (age 70±10, 90% men, LVEF 26±9%, 67% ICM, 47% NICM or mixed,...
Article
Catheter ablation is currently the only curative treatment for scar-related ventricular tachycardias (VTs). However, not only are ablation procedures long, with relatively high risk, but success rates are punitively low, with frequent VT recurrence. Personalized in-silico approaches have the opportunity to address these limitations. However, state-...
Article
Background Current ablation therapy for atrial fibrillation is suboptimal, and long-term response is challenging to predict. Clinical trials identify bedside properties that provide only modest prediction of long-term response in populations, while patient-specific models in small cohorts primarily explain acute response to ablation. We aimed to pr...
Article
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Background The effect of chronic ischemic scar on repolarization is unclear, with conflicting results from human and animal studies. An improved understanding of electrical remodeling within scar and border zone tissue may enhance substrate-guided ablation techniques for ventricular tachycardia. Computational modeling studies have suggested increas...
Article
Full-text available
Atrial arrhythmias, including atrial fibrillation and atrial flutter, may be treated through catheter ablation. The process of atrial arrhythmia catheter ablation, which includes patient selection, pre-procedural planning, intra-procedural guidance, and post-procedural assessment, is typically characterized by the use of several imaging modalities...
Article
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Background Computational models of the heart built from cardiac MRI and electrophysiology (EP) data have shown promise for predicting the risk of and ablation targets for myocardial infarction (MI) related ventricular tachycardia (VT), as well as to predict paced activation sequences in heart failure patients. However, most recent studies have reli...
Article
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The majority of data regarding tissue substrate for post myocardial infarction (MI) VT has been collected during hemodynamically tolerated VT, which may be distinct from the substrate responsible for VT with hemodynamic compromise (VT-HC). This study aimed to characterize tissue at diastolic locations of VT-HC in a porcine model. Methods: Late Gado...
Article
The implanted cardioverter defibrillator (ICD) is an effective direct therapy for the treatment of cardiac arrhythmias, including ventricular tachycardia (VT). Anti-tachycardia pacing (ATP) is often applied by the ICD as the first mode of therapy, but is often found to be ineffective, particularly for fast VTs. In such cases, strong, painful and da...
Article
Aims Atrial septal defects (ASD) are associated with atrial arrhythmias, but the arrhythmia substrate in these patients is poorly defined. We hypothesized that bi-atrial fibrosis is present and that right atrial fibrosis is associated with atrial arrhythmias in ASD patients. We aimed to evaluate the extent of bi-atrial fibrosis in ASD patients and...
Article
Full-text available
Electrical activation during atrial fibrillation (AF) appears chaotic and disorganised, which impedes characterisation of the underlying substrate and treatment planning. While globally chaotic, there may be local preferential activation pathways that represent potential ablation targets. This study aimed to identify preferential activation pathway...
Preprint
Full-text available
Catheter ablation is currently the only curative treatment for scar-related ventricular tachycardias (VTs). However, not only are ablation procedures long, with relatively high risk, but success rates are punitively low, with frequent VT recurrence. Personalized in-silico approaches have the opportunity to address these limitations. However, state-...
Article
Full-text available
Objectives: The aim of this study is to develop a scar detection method for routine computed tomography angiography (CTA) imaging using deep convolutional neural networks (CNN), which relies solely on anatomical information as input and is compatible with existing clinical workflows. Background: Identifying cardiac patients with scar tissue is impo...
Chapter
Current biophysical atrial models for investigating atrial fibrillation (AF) mechanisms and treatment approaches use imaging data to define patient-specific anatomy. Electrophysiology of the models can be calibrated using invasive electrical data collected using electroanatomic mapping (EAM) systems. However, these EAM data are typically only avail...
Chapter
Electrophysiology is one of the most rapidly growing area of cardiology. Currently >50,000 catheter ablations are performed in Europe every year and >200,000 patients receive a device for arrhythmia treatment, sudden death prevention, or cardiac resynchronization. The advantages and limitations of fluoroscopy are well known. The rapid development o...
Article
Full-text available
Cardiac anatomy plays a crucial role in determining cardiac function. However, there is a poor understanding of how specific and localised anatomical changes affect different cardiac functional outputs. In this work, we test the hypothesis that in a statistical shape model (SSM), the modes that are most relevant for describing anatomy are also most...
Article
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Background Electroanatomic mapping systems are used to support electrophysiology research. Data exported from these systems is stored in proprietary formats which are challenging to access and storage-space inefficient. No previous work has made available an open-source platform for parsing and interrogating this data in a standardized format. We t...
Article
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Aims Left atrial (LA) remodelling is a common feature of many cardiovascular pathologies and is a sensitive marker of adverse cardiovascular outcomes. The aim of this study was to establish normal ranges for LA parameters derived from coronary computed tomographic angiography (CCTA) imaging using a standardised image processing pipeline to establis...
Article
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Background Identification of targets for ablation of post-infarction ventricular tachycardias (VTs) remains challenging, often requiring arrhythmia induction to delineate the reentrant circuit. This carries a risk for the patient and may not be feasible. Substrate mapping has emerged as a safer strategy to uncover arrhythmogenic regions. However, V...
Article
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Anisotropy is the property of directional dependence. In cardiac tissue, conduction velocity is anisotropic and its orientation is determined by myocyte direction. Cell shape and size, excitability, myocardial fibrosis, gap junction distribution and function are all considered to contribute to anisotropic conduction. In disease states, anisotropic...
Article
Background Pathological atrial fibrosis is a major contributor to sustained atrial fibrillation. Currently, late gadolinium enhancement (LGE) scans provide the only noninvasive estimate of atrial fibrosis. However, widespread adoption of atrial LGE has been hindered partly by nonstandardized image processing techniques, which can be operator and al...
Article
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Background: Pace-mapping is a commonly used electrophysiological (EP) procedure which aims to identify exit sites of ventricular tachycardia (VT) by matching ventricular activation patterns (assessed by QRS morphology) at specific pacing locations with activation during VT. However, long procedure durations and the need for VT induction render thi...
Article
Background Atrial arrhythmias are common in patients with atrial septal defects (ASD) but the effects of percutaneous closure on atrial arrhythmia prevalence is unclear. We investigated the effects of ASD device closure and the impact of age at time of closure on prevalent atrial arrythmia. Methods Meta-analysis of studies reporting atrial arrhyth...
Article
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Objective To develop a three-dimensional (3D) high-resolution free-breathing magnetization transfer ratio (MTR) sequence for contrast-free assessment of myocardial infarct and coronary vein anatomy.Materials and methodsTwo datasets with and without off-resonance magnetization transfer preparation were sequentially acquired to compute MTR. 2D image...
Article
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Aims : A point-by-point workflow for pulmonary vein isolation (PVI) targeting pre-defined Ablation Index values (a composite of contact force, time, and power) and minimizing interlesion distance may optimize the creation of contiguous ablation lesions whilst minimizing scar formation. We aimed to compare ablation scar formation in patients underg...
Article
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Background: Ex-vivo cardiovascular magnetic resonance (CMR) imaging has played an important role in the validation of in-vivo CMR characterization of pathological processes. However, comparison between in-vivo and ex-vivo imaging remains challenging due to shape changes occurring between the two states, which may be non-uniform across the diseased...
Conference Paper
Background Uncorrected atrial septal defects (ASD) are associated with atrial arrhythmias (AAs) however little is known about the bi-atrial arrhythmia substrate in these patients and optimal rhythm management strategies remain unclear. Hypothesis We hypothesised that the right atrium (RA) is important to atrial arrhythmogenesis in the ASD cohort a...
Article
Introduction: Multiple 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), LVEF, LA shape (sphericity) and pulmonary vein anatomy have all been shown to correlate with late AF recurrence. Thi...
Article
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The development of effective and safe therapies for scar-related ventricular tachycardias requires a detailed understanding of the mechanisms underlying the conduction block that initiates electrical re-entries associated with these arrhythmias. Conduction block has been often associated with electrophysiological changes that prolong action potenti...
Article
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Implanted cardiac defibrillators (ICDs) seek to automatically detect and terminate potentially lethal ventricular arrhythmias by applying strong internal electric shocks across the heart. However, the optimisation of the specific electrode design and configurations represents an intensive area of research in the pursuit of reduced shock strengths a...
Article
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Background: Conventional myocardial T1 mapping techniques such as modified Look-Locker inversion recovery (MOLLI) generate one T1 map per breathhold. T1 mapping with full left ventricular coverage may be desirable when spatial T1 variations are expected. This would require multiple breathholds, increasing patient discomfort and prolonging scan tim...
Article
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Geometrical structure of the myocardium plays an important role in understanding the generation of arrhythmias. In particular, a heterogeneous tissue (HT) channel defined in cardiovascular magnetic resonance (CMR) has been suggested to correlate with conduction channels defined in electroanatomic mapping in ventricular tachycardia (VT). Despite the...
Article
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Aims: Potential advantages of real-time magnetic resonance imaging (MRI)-guided electrophysiology (MR-EP) include contemporaneous three-dimensional substrate assessment at the time of intervention, improved procedural guidance, and ablation lesion assessment. We evaluated a novel real-time MR-EP system to perform endocardial voltage mapping and as...
Article
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Background The multiple wavelet and functional re‐entry hypotheses are mechanistic theories to explain atrial fibrillation (AF). If valid, a chamber's ability to support AF should depend upon left atrial size, conduction velocity and refractoriness. Measurement of these parameters could provide a new therapeutic target for AF. We investigated the r...
Article
Background: Conduction velocity (CV) is an important property that contributes to the arrhythmogenicity of the tissue substrate. The aim of this study was to investigate the association between local CV versus late gadolinium enhancement (LGE) and myocardial wall thickness in a swine model of healed left ventricular infarction. Methods: Six swin...
Article
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Background Myocardial T1 mapping shows promise for assessment of cardiomyopathies. Most myocardial T1 mapping techniques, such as modified Look–Locker inversion recovery (MOLLI), generate one T1 map per breath‐held acquisition (9–17 heartbeats), which prolongs multislice protocols and may be unsuitable for patients with breath‐holding difficulties....
Article
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Background: Cardiovascular magnetic resonance (CMR) imaging may be used to visualize post-ablation atrial scar (PAAS), and three-dimensional late gadolinium enhancement (3D LGE) is the most widely employed technique for imaging of chronic scar. Detection of PAAS provides a unique non-invasive insight into the effects of the ablation and may help g...
Article
Full-text available
Aims: Treatments for persistent atrial fibrillation (AF) offer limited efficacy. One potential strategy aims to return the right atrium (RA) to sinus rhythm (SR) by ablating interatrial connections (IAC) to isolate the atria, but there is limited clinical data to evaluate this ablation approach. We aimed to use simulation to evaluate and predict pa...
Article
Full-text available
Background: Cardiac conduction properties exhibit large variability, and affect patient-specific arrhythmia mechanisms. However, it is challenging to clinically measure conduction velocity (CV), anisotropy and fibre direction. Our aim is to develop a technique to estimate conduction anisotropy and fibre direction from clinically available electric...
Conference Paper
Background The ‘Close Protocol’ workflow for pulmonary vein isolation (PVI) targeting pre-defined ‘Ablation Index’ (AI, a composite of contact force, time and power) values and minimising inter-lesion distance may optimise the creation of durable lesions. Cardiac MRI (CMR) is a useful tool to assess the appearances of post ablation scar. Aims To c...
Conference Paper
Background Atrial fibrillation (AF) is common in atrial septal defect patients (ASD) but little is known about the triggers for these arrhythmias. Hypothesis Since right atrial dilatation is well described in ASD patients we hypothesised that atrial ectopy in ASD patients would be predominantly right-sided in origin. Objective 1. To determine the...
Conference Paper
Introduction Atrial septal defects (ASDs) are associated with atrial arrhythmias (AAs) however little is known about the arrhythmia substrate in these patients. Left atrial (LA) fibrosis, detected by cardiac MRI (CMR) is well described in patients with atrial fibrillation and structurally normal hearts but fibrosis has not been described in either...