4776Prevalence and clinical significance of abnormalities detected on positron emission tomography in patients with clinically suspected myocarditis

Abstract

Background: Myocarditis is responsible for up to 20% of sudden cardiac-related deaths and 50% of dilated cardiomyopathy in the young. Diagnosing myocarditis and predicting adverse clinical outcomes is significantly challenging. Positron emission tomography (PET) using 18F-Fluorodeoxyglucose (FDG) offers enormous potential for detecting disease, active inflammation and prognostication in myocarditis. Objective: This study sought to assess the prevalence and prognostic significance of PET abnormalities in patients with myocarditis. Methods: 395 consecutive patients with clinically suspected myocarditis (age 50±13 years, 261 males) underwent FDG-PET following a high-fat/lowcarbohydrate diet and 12-hour fast. Blinded image analysis was performed. Focal or focal-on-diffuse was categorized as a positive scan. Sensitivity and specificity of PET for diagnosing myocarditis was validated against the ESC guidelines and endomyocardial biopsy as the reference standards. The primary end point was a composite of death, aborted sudden cardiac death, sustained ventricular arrhythmia or appropriate implanted cardioverter-defibrillator discharge, complete heart block necessitating device implantation and hospital admission with decompensated heart failure. The secondary endpoints were a fall in left ventricular ejection fraction (LVEF) >10%, non-sustained ventricular tachycardia (NSVT) and other cardiac-related hospital admission. Results: The prevalence of myocarditis according to the ESC guidelines was 75% (n=295). 100 patients underwent EMB; 27 had histologically confirmed myocarditis. Cardiac PET abnormalities were seen in 164 (42%) subjects and more frequently within the ESC+ subgroup than within their ESC- counterparts (52% vs 12%; p<0.001). Cardiac PET had sensitivity, specificity, positive and negative predictive values of 88%, 52%, 93% and 38%, respectively, for detecting myocarditis according to the ESC criteria. Over a median follow-up of 4.6 years, there were 97 (25%) primary adverse events and 110 (28%) secondary adverse events with a significantly higher number of primary events within the ESC+subgroup (P<0.001). In the total cohort, abnormal cardiac PET uptake was predictive of adverse events with a hazard ratio of 2.0 (P=0.001; [95% CI 1.3-3.0]) and remained significant after adjusting for baseline clinical characteristics and LVEF. However, in the ESC+ subgroup, there was no adverse effect of PET abnormality on clinical outcome (p=0.31). Conclusion: PET is a valuable technique in suspected myocarditis. PET abnormalities correlate closely with the ESC diagnosis of myocarditis and enable targeted biopsy and longitudinal metabolic monitoring of disease activity and pharmacotherapeutic response. Prognostically, PET abnormalities are associated with a poorer outcome, yet were less predictive of adverse events in those fulfilling the ESC diagnostic criteria. PET should therefore be considered following careful initial evaluation using the ESC criteria.