Background: Myocarditis is defined by inflammatory involvement of the myocardium, either histologically by evidence of myocardial necrosis and cellular infiltration on endomyocardial biopsy (EMB), or non-invasively by presence of myocardial oedema using tissue mapping with cardiovascular magnetic resonance (CMR). Objective: to undertake intra-individual comparisons of EMB vs. CMR diagnostic algorithms of myocardial inflammation, as well as against an independent gold-standard of myocardial injury, high-sensitive troponin (hs-TropT).
Methods: Prospective multicentre study of consecutive patients (n=109) with clinical diagnosis of myocarditis. EMBs were analysed by 2 reference centres using the ESC diagnostic and their local algorithms. The CMR criteria used sequence-specific cut-offs for native T1 and T2 (standard deviation, SD); myocardial inflammation T1=2SD, T2=2SD and no inflammation: T1 and T2<2SD, with subcategories for acute/high-grade: T1=5SD, T2=2SD; chronic/low-grade: T1=2SD, T2=2SD; healed: T1<2SD, T2<2SD but myocardial impairment and non-inflammatory cardiomyopathy: T1=2SD, T2<2SD.
Results: The agreement between ESC criteria and CMR criteria (AUC:0.56, p=0.381) was poor. There was a significant agreement between myocardial injury (hs-TropT=13.9 ng/L) and CMR criteria (AUC:0.84, p<0.001), but not ESC algorithm. hs-TropT levels had significant associations with native T1 and T2 (r=0.37 and 0.35, p<0.001), but not with immunohistochemical inflammatory markers. Viral presence was similarly proportioned between inflammatory/non-inflammatory subjects, irrespective of the algorithm.
Conclusions: Poor agreement between CMR and EMB-based diagnostic algorithms suggests non-overlapping definitions of myocardial inflammatory involvement. Excellent agreement between CMR algorithm and hs-TropT reiterates its high sensitivity for inflammatory myocardial injury.