Cardiac sarcoidosis (CS) is an inflammatory cardiomyopathy that affects approximately 1 in every 3 general sarcoidosis patients.1 Pathophysiology entails myocardial inflammation and subsequent fibrosis, with recognised adverse outcomes including ventricular dysfunction, arrhythmogenesis and high-grade atrioventricular block (hgAVB).2 Global criteria stipulate the presence of multimodality imaging findings, symptoms and extra-cardiac biopsy proven disease for diagnostic confirmation, with endomyocardial biopsy increasingly reserved for cases of clinical uncertainty.3, 4, 5

Sustained ventricular arrhythmia (sVA) is a common complication of CS owing to ventricular scar formation; previous data from our institution, that analysed over 300 diagnosed CS patients, demonstrated an sVA occurrence of 7%.6 Similarly, CS scar tissue prohibits normal intrinsic cardiac conduction, with characteristic development of hgAVB.7 Utility of implantable cardiac devices is a crucial component of CS management – both with regards to non-defibrillating pacemakers in the emergent pacing of hgAVB,8 and defibrillating devices in both primary and secondary prevention.9,10

Current European Society of Cardiology (ESC) guidance recommends implantable cardiac defibrillator (ICD) or cardiac resynchronisation therapy defibrillator (CRT-D) implantation as secondary prevention in context of prior sVA, or primary prevention if left ventricular ejection fraction (LVEF) ≤35% (class I evidence).11 In those with an LVEF>35%, primary prevention guidance recommendations support ICD or CRT-D device insertion if a conventional indication for pacing is met, alongside in patients with significant scar (detected using late gadolinium enhancement [LGE] on cardiac magnetic resonance imaging [cMRI]), or if ventricular arrythmia is induced during electrophysiological study (EPS).11 The importance of scar burden and active myocardial inflammation (on Fluorodeoxyglucose Positron Emission Tomography [FDG PET]) is recognised in both European and American guidance.11,12 Overall, however, plausible concerns persist on the applicability of international guidance in the context of CS, given that guideline evidence has largely been drawn from non-CS cohorts. Numerous CS patients, therefore, who do not meet conventional criteria for device insertion may remain at risk of sVA and hgAVB.1,5,10,11

Implantable loop recorders (ILR) are used in surveillance of arrythmia in high-risk cohorts who present with syncopal episodes in the absence of detectable rhythm abnormality.11,13 Their implementation in CS remains poorly defined in international guidance. With only one study describing outcomes in CS patients undergoing ILR insertion14 we sought to retrospectively assess outcomes from our combined cardiac sarcoidosis service (CCSS) at the Royal Brompton Hospital (RBH), one of the largest CS services globally.