Dr Iain Sim

Dr Iain Sim is a Consultant Cardiologist and Electrophysiologist at Frimley Health NHS Trust. He specialises in the diagnosis and treatment of heart rhythm disorders (arrhythmias) and has NHS practices across Frimley Park, Wexham Park and Harefield Hospitals.

He manages a full range of cardiac conditions including chest pain, breathlessness, palpitations, fainting (syncope), coronary artery disease and heart failure — with a specialist focus on arrhythmia and cardiac devices.

His clinical expertise spans catheter ablation for atrial fibrillation (including pulsed field ablation), atrial flutter, supraventricular tachycardia (SVT), ectopic beats and ventricular tachycardia, alongside complex cardiac device implantation including pacemakers, defibrillators (ICDs) and conduction system pacing. His further interests include inherited cardiac conditions, and identifying and protecting patients at risk of dangerous heart rhythms.

Qualifications & training

MBBS, St George's, University of London · Member of the Royal College of Physicians (MRCP(UK)) · PhD, King's College London · CCT in Cardiology, with specialist accreditation in cardiac electrophysiology and devices.

Dr Sim held senior registrar posts at leading UK centres including the Royal Brompton and Harefield Hospitals, King's College Hospital and the Royal Sussex County Hospital, where he developed his expertise in cardiac electrophysiology.

Research & academic interest

Dr Sim completed his PhD within the cardiac electrophysiology and imaging group at King's College London, under Professor Mark O'Neill. His research focuses on the mechanisms and substrate of atrial fibrillation, and on using advanced imaging to guide treatment. His published work includes the quantification of atrial cardiomyopathy and atrial fibrosis using late-gadolinium cardiac magnetic resonance and electroanatomic voltage mapping, patient-specific computational modelling to predict ablation outcomes in persistent atrial fibrillation, and atrial arrhythmia in adult congenital heart disease. His work has appeared in journals including Circulation: Arrhythmia and Electrophysiology, the Journal of Cardiovascular Electrophysiology and Europace.

This research background informs his everyday practice: a detailed, evidence-based approach to diagnosing the cause of a patient's symptoms and tailoring treatment to the individual. Known for his patient-centred approach, Dr Sim combines clinical excellence with clear communication to ensure patients feel informed, reassured and supported throughout their care.

Selected publications

1. Sim I, Solís-Lemus JA, O’Shea C, et al. Quantification of atrial cardiomyopathy disease severity by electroanatomic voltage mapping and cardiac magnetic resonance imaging. J Cardiovasc Electrophysiol. 2025;36(2):467–479.
2. Sim I, Bishop M, O’Neill M, Williams SE. Left atrial voltage mapping: defining and targeting the atrial fibrillation substrate. J Interv Card Electrophysiol. 2019;56(3):213–227.
3. Roney CH, Sim I, Yu J, et al. Predicting atrial fibrillation recurrence by combining population data and virtual cohorts of patient-specific left atrial models. Circ Arrhythm Electrophysiol. 2022;15(2):e010253.
4. Razeghi O, Sim I, Roney CH, et al. Fully automatic atrial fibrosis assessment using a multilabel convolutional neural network. Circ Cardiovasc Imaging. 2020;13(12):e011512.
5. O’Neill L, Sim I, O’Hare D, et al. Provocation and localization of atrial ectopy in patients with atrial septal defects. J Interv Card Electrophysiol. 2022;65(2):271–286.
6. Bodagh N, Sim I, Haghighat Ghahfarokhi M, et al. Combining clinical and left atrial electromechanical remodelling data to improve atrial fibrillation ablation outcome prediction. BMC Med Inform Decis Mak. 2025.

A complete and up-to-date list of publications is available on Dr Sim's Google Scholar profile.