(417) Subclinical Myocardial Leukocyte Infiltration after Covid-19-Vaccination in Heart-Transplant Recipients

PURPOSE: It was reported that mRNA-based Covid-19 vaccines rarely cause myocarditis. Although endomyocardial biopsy (EMB) is considered the gold standard for diagnosing myocarditis, no standardized study has been performed after Covid-19 vaccination in humans. Because routine EMB is frequently performed in heart transplant recipients (HTX), we aimed here to investigate effects of Covid-19 vaccination by analyzing myocardial inflammation with state-of-the-art quantitative immunohistochemistry. METHODS: Consecutive patients after HTX who underwent routine EMB at a median of 167 days before and 136 days after the first Covid 19 vaccination with an mRNA vaccine were included and divided into groups with and without postvaccination inflammatory response, defined as increased CD3+ lymphocyte count >14/ mm2. Patients with evidence of rejection (ISHLT grade >1) or >14 CD3+ lymphocytes/mm2 at baseline were excluded. RESULTS: The final analysis included 46 patients with a mean age of 63 years and a time after HTX of 2.4 years. Thirty-six (78%) patients remained below the threshold of 14 CD3+ lymphocytes/mm2. However, in 10 (22%) recipients, we detected significant leukocyte infiltration by quantitative analysis of EMB after vaccination (4 vs. 33.7 leukocytes/ mm2, p=0.001). The groups did not differ with respect to age (63 vs. 57 years, p=0.21), body mass index (25 vs. 24 kg/m2, p=0.24), NYHA class (≥2 at 19 vs. 10%, p=0.4), NT-ProBNP levels (592 vs. 514 ng/l, p=0.55) or myocardial CD3+ cell count (4.9 vs. 2.6 cells/mm2, p=0.07) before vaccination. Patients with leukocyte infiltration remained clinically inapparent with stable NYHA class (≥2 in 10 vs. 20%, p=0.99) and did not have increased NT-ProBNP levels (514 vs. 478 ng/l, p=0.03). No hospitalizations for suspected myocarditis were reported. CONCLUSION: For the first time, we report subclinical myocardial leukocyte infiltration after Covid-19 mRNA vaccination in one in five patients without clinical sequelae during the short observation period.