Clinical Applications of FDG-PET Scan in Arrhythmic Myocarditis

¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) scan has no recognized role in diagnosis, prognosis, and disease monitoring in patients with arrhythmic myocarditis.

The purpose of this study was to investigate the value of FDG-PET scan in arrhythmic myocarditis.

The authors enrolled 75 consecutive patients (age 47 ± 14 years, 65% men) undergoing FDG-PET scan for arrhythmic myocarditis. Myocarditis was diagnosed by endomyocardial biopsy (EMB) and, whenever applicable, cardiac magnetic resonance (CMR).

Indications for FDG-PET scan included either contraindication to CMR (n = 50) or mismatch between CMR and EMB (n = 25). Overall, 50 patients (67%) had positive FDG-PET. Sensitivity was 75% referring to EMB, and 73% to CMR. Specificity was 67% referring to EMB, and 59% to CMR. FDG-PET accuracy was lower in the presence of borderline myocarditis, and either late (>30 days) or on-immunosuppression FDG-PET scanning. Anteroseptal distribution pattern, found in 12 of 50 (24%) patients including 7 of 7 cardiac sarcoidosis cases, was associated with greater occurrence of ventricular arrhythmias and atrioventricular blocks in 4.2 ± 1.7 years of follow-up (10 of 12 vs 7 of 38, and 7 of 12 vs 0 of 38, respectively; both P < 0.001). In 39 patients (52%), FDG-PET was repeated by 13 ± 2 months, allowing immunosuppression withdrawal after FDG uptake normalization either by first (76%) or second reassessment (24%).

FDG-PET scan may be a clinically useful diagnostic technique in arrhythmic myocarditis, in particular when CMR is unsuitable because of irregular heartbeat or implantable cardioverter-defibrillator-related artifacts. Anteroseptal FDG distribution is associated with a worse arrhythmic outcome and should raise the suspicion of cardiac sarcoidosis. During follow-up, repeated FDG-PET allows myocarditis monitoring to guide immunosuppression withdrawal.