Impact of 18FDG-avidity and immunosuppression on idiopathic and genetic cardiomyopathies

BackgroundMyocardial 18fluorodeoxyglucose (18FDG)-avidity is frequently seen in patients with genetic cardiomyopathy (CMP), as well as a growing "idiopathic 18FDG-avidity" group of genotype-negative patients who do not clearly have cardiac sarcoidosis (CS). ObjectivesTo determine the prognostic implications of 18FDG-avidity in patients with and without genetic CMP, and the effects of immunosuppression in the latter. MethodsThis multicenter, retrospective study included all patients who were referred for both 18FDG-PET and CMP genetic testing. Patients with acute myocarditis, biopsy-proven sarcoidosis or extracardiac 18FDG-avidity were excluded. We investigated heart failure (HF) composite (left ventricular assist device, heart transplant, HF hospitalization, death) and arrhythmia composite (sustained ventricular arrhythmias (VT/VF), atrio-ventricular block, death) outcomes using survival analysis including Cox proportional hazards modeling and inverse probability of treatment weighting (IPWT). ResultsAmong 372 patients, 142 (38%) were 18FDG-avid. Prevalence of genetic CMP among 18FDG-avid patients (12%) was similar to that of 18FDG-negative patients (19%, p=0.07). 18FDG-avidity was associated with increased risk of HF composite (HR 1.69 (1.04-2.75), p=0.034) and arrhythmia composite (HR 1.63 (1.1-2.4), p=0.014) outcomes compared to 18FDG-negative patients. However, these associations were present only in genotype-negative patients, and not in genetic CMP. After IPWT, immunosuppression of 18FDG-avid patients (n=49) was not associated with a reduction in HF (HR 3.31 (1.25, 8.77), p=0.016) or arrhythmia composite outcomes (HR 1.61 (0.79, 3.25), p=0.19) compared with those who were not immunosuppressed (n=93). ConclusionsMyocardial-only 18FDG-avidity is only associated with adverse HF and arrhythmia outcomes in genotype-negative patients who do not clearly have CS. IST does not seem to modify the disease course, suggesting that not all myocardial 18FDG uptake reflects clinically significant inflammation.