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This study aimed to evaluate morning\u2013evening variations in electrocardiographic parameters in children with CAP compared to healthy controls.\u00a0Thirty-six children diagnosed with CAP and 47 healthy controls were included. Electrocardiographic recordings were obtained in the morning and evening. Heart rate, atrial conduction parameters, and ventricular repolarization indices were analyzed to assess time effects, group differences, and time\u2009\u00d7\u2009group interactions.\u00a0Children with CAP exhibited higher heart rates and shorter atrial conduction parameters than controls at both time points. Ventricular repolarization indices were increased in the pneumonia group. Tp-e\/QT and Tp-e\/QTc ratios were higher in children with CAP but did not show significant temporal variation. The frontal QRS\u2013T angle demonstrated limited diurnal variation in healthy controls, whereas no significant temporal change was observed in the pneumonia group. Associations between Tp-e\/QT, Tp-e\/QTc, and QTc differed according to measurement time.<\/jats:p>\n                  <jats:p>\n                    <jats:italic>Conclusion<\/jats:italic>\n                    : Children with CAP demonstrate alterations in atrial conduction and ventricular repolarization compared with healthy peers. These findings suggest that CAP may be associated with temporal changes in specific electrophysiological relationships rather than a complete loss of physiological circadian regulation.\n                  <\/jats:p>\n                  <jats:p>\n                    <jats:bold>Graphical Abstract<\/jats:bold>\n                  <\/jats:p>\n                  <jats:p>This figure illustrates the subclinical cardiac effects and selective circadian modulation of community-acquired pneumonia (CAP) in children. Children with CAP show increased heart rate, decreased atrial conduction (PR interval), and altered Tp-e ratios. Despite preserved circadian regulation, these functional and reversible changes highlight the need for multidimensional, time-sensitive ECG assessment.<\/jats:p>","DOI":"10.1007\/s00431-026-07006-1","type":"journal-article","created":{"date-parts":[[2026,4,30]],"date-time":"2026-04-30T18:12:56Z","timestamp":1777572776000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Community-acquired pneumonia alters circadian regulation of cardiac electrophysiology in children"],"prefix":"10.1007","volume":"185","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8691-1504","authenticated-orcid":false,"given":"Gul Sahika","family":"Gokdemir","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0505-9784","authenticated-orcid":false,"given":"Adem","family":"Aktan","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3042-6972","authenticated-orcid":false,"given":"\u00d6zhan","family":"Orhan","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1609-9773","authenticated-orcid":false,"given":"Feyat","family":"Tun\u00e7","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5546-9653","authenticated-orcid":false,"given":"Mehmet Tahir","family":"Gokdemir","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,4,30]]},"reference":[{"key":"7006_CR1","doi-asserted-by":"publisher","DOI":"10.3389\/fped.2025.1694856","volume":"13","author":"HH Zhou","year":"2025","unstructured":"Zhou HH, Qian KL (2025) Comparison of the systemic inflammatory response index and the systemic immune-inflammatory index in pediatric community-acquired pneumonia caused by respiratory syncytial virus and Mycoplasma pneumoniae. 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