Myocarditis describes myocardial inflammation. The most common cause is viral infection (active infection or post-infective inflammation). Other causes include autoimmune disease, drugs and toxins. Endomyocardial biopsy (EMBx) is the gold standard diagnostic investigation. EMBx specimens are evaluated using histological, immunological and immunohistochemical criteria which can confirm diagnosis as well as identify the underlying aetiology and type of inflammation. This has implications for treatment and prognosis. There are treatment implications in giant cell myocarditis, eosinophilic myocarditis and sarcoidosis. EMBx may establish the cause for myocarditis persistence (viral persistence vs autoimmunity to cardiac proteins) and determine suitability for immunosuppressive therapy. A placebo-controlled trial of immunosuppression in patients with inflammatory cardiomyopathy and undetectable viral genomes has previously demonstrated significant improvements in LV function.(1)
EMBx is an invasive procedure which carries up to 1% risk of complication. It is prone to sampling error in focal disease. In clinical practice, EMBx has tended to be reserved for patients with severe phenotype or disease that is refractory to treatment. The European Society of Cardiology Working Group on Myocardial and Pericardial Diseases has called for broader use of EMBx to improve the diagnosis of myocarditis.(2) They recommend that EMBx should be considered for all patients with suspected myocarditis. A subset of patients with biopsy proven myocarditis appear to progress to dilated cardiomyopathy (DCM). If the recommendations are applied to DCM, this proposal may lead to EMBx in all symptomatic patients without clear aetiology. This represents a departure from previous consensus statements and international heart failure guidelines. Increased use of EMBx is likely to improve recognition of myocarditis and aid selection of patients requiring specific treatments but there are risks associated with the procedure and availability of EMBx is not universal. Transfer of patients with suspected myocarditis to specialist centres would help to ensure procedural safety and optimise diagnostic yield. However, suspected myocarditis is common and frequently uncomplicated. Increasing patient transfers to specialist centres may result in capacity issues. Perhaps a rational approach at present would be to consider the incremental value of EMBx on a case by case basis?
- Frustaci A et al. Randomized study on the efficacy of immunosuppressive therapy in patients with virus-negative inflammatory cardiomyopathy: the TIMIC study. Eur Heart J 2009;30:1995-2002.
- Caforio AL et al. Current state of knowledge on aetiology, diagnosis, management, and therapy of myocarditis: a position statement of the European Society of Cardiology Working Group on Myocardial and Pericardial Diseases. Eur Heart J 2013;34: 2636–48, 2648a–d.