During the winter months of 2020/2021 a wave of multisystem inflammatory syndrome in children (MIS-C) emerged in Poland. We present the results of a nationwide register aiming to capture and characterise MIS-C with a focus on severity determinants. The first MIS-C wave in Poland was notably high, hence our analysis involved 274 children. The group was 62.8% boys, with a median age of 8.8 years. Besides one Asian, all were White. Overall, the disease course was not as severe as in previous reports, however. Pediatric intensive care treatment was required for merely 23 (8.4%) of children, who were older and exhibited a distinguished clinical picture at hospital admission. We have also identified sex-dependent differences; teenage boys more often had cardiac involvement (decreased ejection fraction in 25.9% vs. 14.7%) and fulfilled macrophage activation syndrome definition (31.0% vs. 15.2%). Among all boys, those hospitalized in pediatric intensive care unit were significantly older (median 11.2 vs. 9.1 years). Henceforth, while ethnicity and sex may affect MIS-C phenotype, management protocols might be not universally applicable, and should rather be adjusted to the specific population.

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Introduction: Balloon aortic valvuloplasty (BAV) is a common treatment method of aortic valve (AV) stenosis in neonates. Longterm BAV effects are suboptimal, and their predictors are not well acknowledged.Aim: To identify predictors of suboptimal short-and long-term BAV results.Material and methods: The study group comprised forty-three neonates (8 females; weight 3.34 ±0.56 kg) who underwent BAV between 1998 and 2021. Seventeen patients (39.53%) had critical AV stenosis. AV was bicuspid in 22 patients, tricuspid in 12, unicuspid in 2, and undefined in 7 patients. The mean balloon/annulus ratio was 0.9 ±0.07. Catheterization, clinical, and follow-up data were analysed.Results: The peak-to-peak gradient decreased from 67.5 ±26.3 to 21.3 ±12.6 mm Hg. Twenty-eight patients (65.1%) had adequate early outcome. Aortic regurgitation (AR) occurred in 13 (30.2%) patients. No predictors of inadequate early outcome were found. Twenty-year survival was 90.7%. Eleven (35.5%) patients underwent reintervention at a median of 12 (1-215) months; BAV in 5 patients, surgical valvuloplasty in 2, Ross operation in 2, AV replacement in 1, and Norwood operation in 1 patient. Fifteen-year freedom from reintervention (FFR) was 48%. Adequate early outcome resulted in higher FFR (71% vs. 22%), and so did no significant AR (60% vs. 30%).Conclusions: BAV provides satisfying early results. AR remains a significant aftermath of BAV. Risk factors and procedural techniques improving the outcome of BAV are unclear. Further research is needed to improve FFR.

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