New-onset heart failure in infants: when the aetiological diagnosis becomes a challenge

This study aimed to report the findings of cardiac magnetic resonance imaging (CMR) with quantitative mappings in infants presenting with new-onset heart failure, as well as to assess the capabilities of endomyocardial biopsy (EMB) and CMR in detecting inflammatory cardiomyopathies and determining their etiology. In a prospective analysis of infants who underwent CMR with tissue mappings, EMB, and genetic testing, the sample was categorized into two groups: those with inflammatory cardiomyopathy and negative genetics (indicative of possible myocarditis) and those with positive genetics (indicative of possible dilated cardiomyopathy). All patients exhibited similar clinical presentations, echocardiographic dysfunction, and elevated troponins and NT-proBNP levels. Additionally, they all met the diagnostic criteria for inflammatory cardiomyopathy based on EMB findings (≥14 mononuclear cells, ≥7 T-lymphocytes/mm2). EMB results unveiled significant differences in the presence of inflammation and edema between the two groups, with higher troponin levels correlating with increased inflammation. Notably, when focusing on CMR, neither the classic criteria nor the 2018 Lake Louise criteria (LLC) could effectively differentiate between the two groups. Only late gadolinium enhancement (LGE) appeared to be associated with myocarditis in this cohort, while other LLC and tissue mappings did not exhibit a similar correlation. Importantly, there was no observed correlation between the inflammation detected through EMB and CMR.

The onset of heart dysfunction in infants can result from either inherited factors or viral infections, both of which may involve inflammation. However, the precise role of EMB and CMR in determining the etiology of such cases remains poorly defined. While CMR demonstrates high sensitivity in detecting inflammation, our experience suggests that it may not effectively differentiate between these two groups. A comprehensive diagnostic approach is essential when addressing this challenge, which includes considering EMB (with attention to the number of T-lymphocytes and the presence of oedema), specific CMR criteria, notably LGE and tissue mappings, as well as the identification of viral agents in cardiac tissue and troponin levels. Additionally, genetic tests should be conducted when evaluating these patients.

• EMB is the gold standard diagnostic test for myocarditis but it is not universally accepted. • The diagnostic value of the 2018-LLC in pediatric patients is still undefined.

• Both EMB and CMR may show inflammation in infants with new-onset heart failure of any aetiology. • A global approach should be used when facing this diagnostic challenge, including the EMB (number of T-lymphocytes and oedema), some CMR criteria, specially LGE and mappings, the detection of viral agents in cardiac tissue and troponins. Genetic tests should also be performed when studying these patients.