Prevalence of lateral wall myocardial fluorodeoxyglucose uptake in patients with left bundle branch block or ventricular pacing referred for sarcoidosis fluorodeoxyglucose positron emission tomography/computed tomography imaging.

BACKGROUND: In suspected cardiac sarcoidosis, the interpretation of myocardial fluorodeoxyglucose (FDG) uptake on positron emission tomography/computed tomography (PET/CT) can be challenging and can have important clinical implications. In this study, we aimed to study the prevalence of lateral wall FDG uptake in patients with suspected cardiac sarcoidosis, particularly in patients with ventricular pacing (V-pacing) or left bundle branch block (LBBB). METHODS: We retrospectively reviewed sarcoidosis-protocol FDG PET/CT studies performed at our center for clinical suspicion for cardiac sarcoidosis where an electrocardiogram (ECG) was available within three months of the PET/CT. We identified the absence or presence of LBBB or V-pacing on ECG, reviewed perfusion and FDG PET/CT findings, and classified all patients according to whether they met Heart Rhythm Society (HRS) criteria for cardiac sarcoidosis or probable cardiac sarcoidosis (meeting all HRS criteria except biopsy-proven disease and having extracardiac FDG uptake present). We also reviewed the results of cardiac magnetic resonance imaging (MRI) and follow-up FDG PET/CT imaging if applicable. Patients were followed until a composite endpoint of durable left ventricular assist device placement, cardiac transplant, or death. RESULTS: Five hundred thirty patients met inclusion criteria, 169 patients (31.9%) had V-pacing (N = 133 (78.7%)) or LBBB (N = 36 (21.3%)) on ECG, and 361 (68.1 %) had neither. Sixty-six of the 169 patients (39.1%) with V-pacing or LBBB had focal or focal-on-diffuse lateral wall myocardial FDG uptake without an associated perfusion defect, compared with 39 of the 361 patients (10.8%) without either (P < 0.001). Of the 66 patients with V-pacing/LBBB and lateral wall FDG uptake, 27 (40.9%) underwent cardiac MRI, and only six (22.2 %) had evidence of lateral wall late gadolinium enhancement (LGE). Twenty-four (36.4%) of the 66 patients had extracardiac FDG uptake, and these were the only patients with definite/probable cardiac sarcoidosis in follow-up. There was no difference in outcomes between patients with or without definite/probable cardiac sarcoidosis stratified by lateral wall myocardial FDG uptake pattern. CONCLUSIONS: Lateral wall myocardial FDG uptake without an associated perfusion defect was significantly more common among patients with LBBB or V-pacing referred for sarcoidosis FDG PET/CT imaging than among those without LBBB or V-pacing. LBBB and V-pacing should be considered as potential causes of lateral wall myocardial FDG uptake in patients with and without biopsy-proven sarcoidosis, and diagnoses other than cardiac sarcoidosis should be considered when this pattern is present but metabolically active extracardiac sarcoidosis is absent.