Prevalence of cardiac fibrosis and infiltrative cardiomyopathy in patients with advanced conduction system disease.

Background: Conduction system disease may represent an early manifestation of underlying structural heart disease, including infiltrative disorders. Timely diagnosis of underlying cardiomyopathy has significant implications for clinical management, guiding both disease-modifying medical therapy and decisions around device implantation. Objective: We sought to investigate the utility of cardiac magnetic resonance imaging (CMR) in patients with conduction system disease and preserved LV function on echocardiography. Methods: We evaluated all patients undergoing CMR between 2005 and 2023 at our institution for the investigation of advanced conduction system disease (complete heart block, Mobitz II block, or bifascicular block). We excluded patients with known systolic heart failure (LVEF<50%) prior to CMR. We evaluated the prevalence of CMR-detected myocardial fibrosis and infiltrative cardiomyopathy in this cohort. Results: One hundred nineteen patients were identified (mean age 49 ± 15 years, 52% male). Complete heart block was the most common indication (50%), followed by bifascicular block (27%) and Mobitz II block (23%). Mean LVEF on echocardiography prior to CMR was 60.0 ± 3.1%. CMR-detected late gadolinium enhancement (LGE) was present in 32/119 patients (26.9%). Cardiac sarcoid was the most common final diagnosis ( Conclusion: Cardiac fibrosis is present in a substantial proportion of patients undergoing CMR for the investigation of conduction disease, even when LV function appears preserved on echocardiography. Cardiac MRI may be an important adjunctive tool for the investigation of conduction disease, particularly in younger patients.