Incidence of abnormal positron emission tomography in patients with unexplained cardiomyopathy and ventricular arrhythmias: The potential role of occult inflammation in arrhythmogenesis.

Background: The incidence of myocardial inflammation in patients with unexplained cardiomyopathy referred for ventricular arrhythmias (VAs) is unknown.

Objective: The purpose of this study was to report fasting positron emission tomographic (PET) scan findings in consecutive patients referred with unexplained cardiomyopathy and VA.

Methods: Fluorine-18 fluoro-2-deoxyglucose (18-FDG) PET/computed tomographic (CT) scans with a >16-hour fasting protocol were prospectively ordered for patients referred for VA and unexplained cardiomyopathy (ejection fraction <55%). Patients with focal myocardial FDG uptake were labeled as arrhythmogenic inflammatory cardiomyopathy (AIC) and classified into 4 groups based on the presence of lymph node uptake (AIC+) and perfusion abnormalities (early vs late stage).

Results: Over a 3-year period, 103 PET scans were performed, with 49% (AIC+ 17, AIC 33) exhibiting focal FDG uptake. Mean patient age was 52 ± 12 years (ejection fraction 36% ± 16%). Patients with AIC were more likely to have a history of pacemaker (32% vs 6%, P = .002) compared to those with normal PET. When biopsy was performed, histologic diagnosis revealed nongranulomatous inflammation in 6 patients and sarcoidosis in 18 patients. Ninety percent of patients with AIC/AIC+ were prescribed immunosuppressive therapy, and 58% underwent ablation. Correlation between low voltage regions on electroanatomic mapping and FDG uptake was observed in 74%. Magnetic resonance imaging findings matched abnormal PET regions in only 40%.

Conclusion: Nearly 50% of patients referred with unexplained cardiomyopathy and VA demonstrate ongoing focal myocardial inflammation on FDG PET. These data suggest that a significant proportion of patients labeled "idiopathic" may have occult AIC, which may benefit from early detection and immunosuppressive medical therapy.