Clinical impact of follow‐up endomyocardial biopsy in myocarditis during or after immune‐suppressive therapy

Aims: While the diagnostic role of endomyocardial biopsy (EMB) in myocarditis is unquestioned, little is known about its indications and clinical value during long-term follow-up. We aim to report our experience on the clinical relevance of repeating EMB in a cohort of biopsy-proven myocarditis patients treated with immune-suppressive therapy (IMT). Methods and results: We retrospectively included 92 patients with virus-negative EMB-proven myocarditis treated with IMT, of whom 22 [73% male, 37 years, interquartile range (IQR) 33–48] received at least one, uneventful, follow-up EMB, 3.5 years (IQR 2.5–5.3) after the first one. Follow-up EMB was performed because of clinical worsening (n = 12) or suspected myocarditis relapse (n = 7) and to assess IMT response (n = 3). Patients receiving follow-up EMB more likely had abnormal troponin levels (P = 0.048) and a trend towards lower prevalence of anti-heart auto-antibodies positivity at diagnosis (P = 0.05) and showed worse imaging findings at follow-up. Active or borderline myocarditis on follow-up EMB was found in 12 patients, leading to a change in IMT regimen in 10 (83%); among patients with evidence of healed myocarditis, 2 had a change in IMT regimen, 2 underwent heart transplant evaluation check list, 2 had mitral valve treatment, 1 received ventricular tachycardia ablation and 1 primary prevention implantable cardioverter-defibrillator implantation. Conclusions: One-fourth of EMB-proven myocarditis patients had a clinical indication to repeat EMB at least once during long-term follow-up. Follow-up EMB was safe in all cases; it showed active or borderline myocarditis in 55% of patients and lead to a change in management in the majority of patients.