John Whitaker
King's College London
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Publication
Featured researches published by John Whitaker.
Pacing and Clinical Electrophysiology | 2011
Steven E. Williams; Aruna Arujuna; John Whitaker; Anoop Shetty; Julian Bostock; Nikhil Patel; Margaret Mobb; Michael Cooklin; Jaswinder Gill; Christopher Blauth; Cliff Bucknall; Shoaib Hamid; C. Aldo Rinaldi
Background: Cardiac resynchronization therapy (CRT) device and coronary sinus (CS) lead extraction is required due to the occurrence of system infection, malfunction, or upgrade. Published series of CS lead extraction are limited by small sample sizes. We present a 10‐year experience of CRT device and CS lead extraction.
Europace | 2016
John Whitaker; Ronak Rajani; Henry Chubb; Mark Gabrawi; Marta Varela; Matthew Wright; Steven Niederer; Mark O'Neill
Changes in the structure and electrical behaviour of the left atrium are known to occur with conditions that predispose to atrial fibrillation (AF) and in response to prolonged periods of AF. We review the evidence that changes in myocardial thickness in the left atrium are an important part of this pathological remodelling process. Autopsy studies have demonstrated changes in the thickness of the atrial wall between patients with different clinical histories. Comparison of the reported tissue dimensions from pathological studies provides an indication of normal ranges for atrial wall thickness. Imaging studies, most commonly done using cardiac computed tomography, have demonstrated that these changes may be identified non-invasively. Experimental evidence using isolated tissue preparations, animal models of AF, and computer simulations proves that the three-dimensional tissue structure will be an important determinant of the electrical behaviour of atrial tissue. Accurately identifying the thickness of the atrial may have an important role in the non-invasive assessment of atrial structure. In combination with atrial tissue characterization, a comprehensive assessment of the atrial dimensions may allow prediction of atrial electrophysiological behaviour and in the future, guide radiofrequency delivery in regions based on their tissue thickness.
Pacing and Clinical Electrophysiology | 2012
Steven E. Williams; Aruna Arujuna; John Whitaker; Manav Sohal; Anoop Shetty; D. Roy; Julian Bostock; Michael Cooklin; Jaswinder Gill; Mark D. O’Neill; Matthew Wright; Nikhil Patel; Cliff Bucknall; Shoaib Hamid; C. Aldo Rinaldi
Background: As the population receiving cardiac device therapy ages, the number of extraction procedures performed in octogenarians is increasing. This group has more comorbidities and may be at higher risk of such procedures.
Case Reports | 2011
John Whitaker; Mrinal Saha; Rahul Fulmali; Divaka Perera
A 71-year-old patient suffered a transmural (ST elevation) myocardial infarction (MI) as a result of a septic embolus from an infected tissue aortic valve replacement. Following failed fibrinolysis, his MI was successfully treated with thrombectomy using an export catheter. He suffered bleeding complications following the administration of tenectaplase and required aortic valve and root replacement due to ongoing systemic embolisation.
Magnetic Resonance in Medicine | 2018
Giulia Ginami; Radhouene Neji; Alkystis Phinikaridou; John Whitaker; René M. Botnar; Claudia Prieto
To develop a 3D whole‐heart Bright‐blood and black‐blOOd phase SensiTive (BOOST) inversion recovery sequence for simultaneous noncontrast enhanced coronary lumen and thrombus/hemorrhage visualization.
Arrhythmia and Electrophysiology Review | 2014
Henry Chubb; John Whitaker; Steven E. Williams; Catherine E Head; Natali Ay Chung; Matthew Wright; Mark D. O’Neill
Atrial septal defects (ASDs) are among the most common of congenital heart defects and are frequently associated with atrial arrhythmias. Atrial and ventricular geometrical remodelling secondary to the intracardiac shunt promotes evolution of the electrical substrate, predisposing the patient to atrial fibrillation and other arrhythmias. Closure of an ASD reduces the immediate and long-term prevalence of atrial arrhythmias, but the evidence suggests that patients remain at an increased long-term risk in comparison with the normal population. The closure technique itself and its timing impacts future arrhythmia risk profile while subsequent transseptal access following surgical or device closure is complicated. Newer techniques combined with increased experience will help to alleviate some of the difficulties associated with optimal management of arrhythmias in these patients.
Journal of Cardiovascular Electrophysiology | 2017
Steven E. Williams; Nick Linton; Louisa O'Neill; James Harrison; John Whitaker; Rahul K Mukherjee; Christopher Aldo Rinaldi; Jaswinder Gill; Steven Niederer; Matthew Wright; Mark O'Neill
Bipolar voltage is used during electroanatomic mapping to define abnormal myocardium, but the effect of activation rate on bipolar voltage is not known. We hypothesized that bipolar voltage may change in response to activation rate. By examining corresponding unipolar signals we sought to determine the mechanisms of such changes.
JACC: Clinical Electrophysiology | 2017
Steven E. Williams; Nick Linton; James Harrison; Henry Chubb; John Whitaker; Jaswinder Gill; Christopher Aldo Rinaldi; Reza Razavi; Steven Niederer; Matthew Wright; Mark O'Neill
Objectives This study sought to characterize direction-dependent and coupling interval–dependent changes in left atrial conduction and electrogram morphology in uniformly classified patients with paroxysmal atrial fibrillation (AF) and normal bipolar voltage mapping. Background Although AF classifications are based on arrhythmia duration, the clinical course, and treatment response vary between patients within these groups. Electrophysiological mechanisms responsible for this variability are incompletely described. Methods Intracardiac contact mapping during incremental atrial pacing was used to characterize atrial conduction, activation dispersion, and electrogram morphology in 15 consecutive paroxysmal AF patients undergoing first-time pulmonary vein isolation. Outcome measures were vulnerability to AF induction at electrophysiology study and 2-year follow-up for arrhythmia recurrence. Results Conduction delay showed a bimodal distribution, occurring at either long (high right atrium pacing: 326 ± 13 ms; coronary sinus pacing: 319 ± 16 ms) or short (high right atrium pacing: 275 ± 11 ms; coronary sinus pacing: 271 ± 11 ms) extrastimulus coupling intervals. Arrhythmia recurrence was found only in patients with conduction delay at long extrastimulus coupling intervals, and patients with inducible AF were characterized by increased activation dispersion (activation dispersion time: 168 ± 29 ms vs. 136 ± 11 ms). Electrogram voltage and duration varied throughout the left atrium, between patients, and with pacing site but were not correlated with AF vulnerability or arrhythmia recurrence. Conclusions Within the single clinical entity of paroxysmal AF, incremental atrial pacing identified a spectrum of activation patterns correlating with AF vulnerability and arrhythmia recurrence. In contrast, electrogram morphology (characterized by electrogram voltage and duration) was highly variable and not associated with AF vulnerability or recurrence. An improved understanding of the electrical phenotype in AF could lead to improved mechanistic classifications.
IEEE Transactions on Medical Imaging | 2017
Marta Varela; Ross Morgan; Adeline Theron; Desmond Dillon-Murphy; Henry Chubb; John Whitaker; Markus Henningsson; Paul Aljabar; Tobias Schaeffter; Christoph Kolbitsch; Oleg Aslanidi
Knowledge of atrial wall thickness (AWT) has the potential to provide important information for patient stratification and the planning of interventions in atrial arrhythmias. To date, information about AWT has only been acquired in post-mortem or poor-contrast computed tomography (CT) studies, providing limited coverage and highly variable estimates of AWT. We present a novel contrast agent-free MRI sequence for imaging AWT and use it to create personalized AWT maps and a biatrial atlas. A novel black-blood phase-sensitive inversion recovery protocol was used to image ten volunteers and, as proof of concept, two atrial fibrillation patients. Both atria were manually segmented to create subject-specific AWT maps using an average of nearest neighbors approach. These were then registered non-linearly to generate an AWT atlas. AWT was 2.4 ± 0.7 and 2.7 ± 0.7 mm in the left and right atria, respectively, in good agreement with post-mortem and CT data, where available. AWT was 2.6 ± 0.7 mm in the left atrium of a patient without structural heart disease, similar to that of volunteers. In a patient with structural heart disease, the AWT was increased to 3.1 ± 1.3 mm. We successfully designed an MRI protocol to non-invasively measure AWT and create the first whole-atria AWT atlas. The atlas can be used as a reference to study alterations in thickness caused by atrial pathology. The protocol can be used to acquire personalized AWT maps in a clinical setting and assist in the treatment of atrial arrhythmias.
Heart Lung and Circulation | 2016
Hariharan Raju; John Whitaker; Carly Taylor; Matthew Wright
BACKGROUND We evaluated Carto 3, transoesophageal echocardiography (TOE) and contact force (CF) sensing catheter in atrial fibrillation (AF) ablation. METHODS Unselected consecutive ablations performed under general anaesthesia (GA) were studied with modified protocol (cases, n=11) and compared to retrospective consecutive controls (n=10). Patent foramen ovale (PFO) or single transseptal puncture enabled left atrial (LA) access; ablation strategy was stepwise approach. Modified protocol utilised right atrial (RA) electrograms, CF and TOE to localise SmartTouch and create RA and CS electroanatomic map (EAM) without fluoroscopy. Transseptal puncture was performed with fluoroscopy in absence of PFO. Fluoroless pulmonary vein and LA EAM was created using TOE to locate circular-mapping catheter. RESULTS Mean age of cases was 57±11 years with 64% male compared with 60±11 (70% male) for controls. Patent foramen ovale was identified in four cases (36%) and two controls (20%). No early complications occurred. Shorter fluoroscopy time (median 36 vs 390seconds; p=0.038) and trend to lower radiation dose (median 17 vs 165 cGym2; p=0.053) was seen in cases, with no increase in total procedure time (p=0.438). CONCLUSIONS General anaesthesia, TOE and CF mapping catheters facilitate minimised fluoroscopy for catheter ablation of LA arrhythmias. Zero fluoroscopy is possible in a majority of cases with PFO.