The role of endomyocardial biopsy in suspected myocarditis in the contemporary era: a 10-year National Transplant Centre experience

Diagnostic endomyocardial biopsy (EMB) in patients with suspected myocarditis helps to direct therapy and guide prognosis. This study aimed to investigate the correlation between the 2007 clinical guideline indications for EMB and the presence of a diagnostic biopsy result and associated outcomes in patients with suspected myocarditis in a national quaternary referral center in a contemporary cohort.All cases of suspected myocarditis referred to the National Cardiac Transplant Centre who underwent EMB between 2009 and 2019 were identified retrospectively through pathology records. Outcomes including subsequent need for inotrope and/or mechanical circulatory support (MCS), heart transplantation and in-hospital mortality were recorded.In total, 25 (68% male, mean age of 45 ± 15 years) EMBs were performed for this indication across this time period, 64% (n = 16) of which demonstrated diagnostic results, the majority (75%, n = 12) identifying acute lymphocytic myocarditis, 13% (n = 2) giant cell, one patient (6.3%) eosinophilic and one (6.3%) an immune checkpoint inhibitor myocarditis. The majority of those with histologically confirmed myocarditis had a Class I or IIa guideline indication for EMB (n = 12, 75%). The remaining 4 patients (25%), either met Class IIb criteria (n = 2) or would not have been accounted for in this guideline. The majority of patients requiring inotropes and/or MCS (n = 9/11), and/or heart transplant (n = 3/4), or who later died (n = 4/5) were in the diagnostic biopsy group.In this 10-year National referral sample, 75% of patients with histologically confirmed myocarditis had a Class I or IIa indication for EMB, reinforcing the usefulness of traditional guidelines in this contemporary era. However, 25% of patients with a subsequent confirmed histological diagnosis had either none or a less well-established indication for EMB, highlighting the need for clinical suspicion outside of accepted clinical scenarios.