A wolf in sheep’s clothing—unmasking cardiac sarcoidosis through pacemaker dysfunction: a case report

Cardiac sarcoidosis may present with arrhythmias and conduction disease years before the diagnosis is established. Device-related issues, such as elevated pacing thresholds, can be misleading and may reflect myocardial inflammation rather than true lead malfunction.

A 49-year-old woman with atrial fibrillation underwent dual-chamber pacemaker implantation in 2018 for syncope and alternating bundle branch block. Cardiac magnetic resonance imaging revealed septal fibrosis, while coronary angiography and biopsy were unremarkable. Two years later, she developed recurrent presyncope and elevated right ventricular pacing thresholds, prompting lead revision. In 2024, at age 56, she was re-hospitalized with syncope and again exhibited very high right ventricular pacing thresholds with intermittent loss of capture (LOC) and pacing dependency. Echocardiography revealed localized septal aneurysms, and implantation of a new right ventricular pacing lead was impossible due to superior vena cava occlusion. A hybrid pacing approach was therefore adopted, combining atrial pacing through the transvenous pacemaker and ventricular pacing in VDD mode (atrial-tracked ventricular pacing) via a leadless pacemaker. Given her young age, septal fibrosis, and aneurysms, further evaluation with positron emission tomography–computed tomography revealed increased metabolic activity in the myocardium, lungs, and lymph nodes, consistent with systemic sarcoidosis. Diagnosis was confirmed by bronchoscopy with biopsy. Immunosuppressive therapy with corticosteroids and mycophenolate led to complete resolution of myocardial inflammatory activity and normalization of right ventricular pacing thresholds over 6 months.

This case highlights that elevated pacing thresholds in cardiac sarcoidosis may reflect disease activity rather than lead failure. Furthermore, in selected complex scenarios where conventional lead implantation is not feasible, combined transvenous atrial pacing and leadless ventricular pacing can provide effective and physiologic atrioventricular synchrony.