Cardiac MRI Findings in Patients presenting With Advanced Conduction System Disease

Abstract

Conduction system disturbance can be the first presentation of underlying structural heart disease, including infiltrative disorders such as sarcoidosis. Appropriate diagnosis may critically influence patient care, including immunosuppression and ICD therapy. We sought to investigate the clinical utility of cardiac MRI in this patient population. We evaluated all patients undergoing cardiac MRI between 2005–2021 at The Alfred for investigation of complete AV block or advanced distal conduction system disease (Mobitz II 2nd degree AV block, LBBB or bifascicular block). Patients with pre-existing devices were included in the analysis. We identified 122 patients (mean age 48±15 yrs, 57% male) fulfilling inclusion criteria. Complete heart block was the leading conduction abnormality (37%), followed by LBBB (17%) and Mobitz II second degree AV block (12%). Twenty-nine patients (24%) had a diagnosis of extra-cardiac sarcoidosis at the time of CMR referral. The majority of patients (80%) had normal LV systolic function (LVEF > 50%) on echocardiography. Left ventricular fibrosis (LGE) was seen in 33/122 (27%) patients. Cardiac sarcoid was the most common final diagnosis (n=16, 13%), of whom only 5 (31%) had known extracardiac sarcoid prior to CMR. Other diagnoses were: non-ischaemic cardiomyopathy (n=2), myocarditis (n=2), amyloid (n=1). Nearly a third of patients undergoing CMR for investigation of conduction disease had evidence of fibrosis. Cardiac sarcoid was diagnosed in nearly half of these patients, most of whom had no features of extra-cardiac sarcoid. Cardiac MRI may be an important adjunctive tool for investigation of conduction disease, particularly in younger patients.