Diagnostic Criteria and Limitations for Myocarditis

Introduction to Myocarditis Diagnosis

The American Heart Association, American College of Cardiology, and European Society of Cardiology joint scientific statement defines myocarditis histologically as an inflammatory infiltrate of the myocardium with necrosis and/or degeneration of adjacent myocytes, not typical of ischemic damage associated with coronary artery disease 1, 2

The American Heart Association, American College of Cardiology, and European Society of Cardiology joint scientific statement explicitly questions the Dallas criteria as the gold standard for myocarditis diagnosis due to three major flaws: sampling error, interobserver variability, and lack of correlation with viral genomes 1, 2
Significant disagreement exists among pathologists interpreting the same biopsy specimens using Dallas criteria, with studies showing wide variation in myocarditis diagnosis rates (0% to 63%) when different pathologists apply these criteria 1, 2, 3, 4
Dallas criteria myocarditis does not correlate well with demonstration of viral genomes in heart tissue by molecular techniques, and patients can have positive viral PCR without meeting Dallas criteria, and vice versa 1, 5

The information gained from Dallas criteria does not alter prognosis or therapy in most patients with acute dilated cardiomyopathy, as demonstrated by the Myocarditis Treatment Trial, which showed no benefit from 24-week immunosuppression in patients with active or borderline myocarditis by Dallas criteria 1, 3
The IMAC-1 Trial found that only 16% of patients with acute nonischemic dilated cardiomyopathy had Dallas criteria myocarditis, and intravenous immunoglobulin showed no benefit 1, 5
The Grogan et al study found that survival rates in patients with Dallas criteria myocarditis were identical to those without inflammation 1, 5

The AHA/ACC/ESC Writing Group does NOT recommend performing EMB using Dallas criteria for routine evaluation of new-onset heart failure of 2 weeks to 3 months duration that responds to usual care within 1-2 weeks, as it rarely changes clinical management and does not predict response to immunosuppressive therapy 1, 3, 5
The American College of Cardiology recommends against using Dallas criteria results alone to guide immunosuppressive therapy decisions, as clinical trials show no benefit even when Dallas criteria are positive 1, 3, 5