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We hypothesized that autonomic nervous ganglia, located at the junction of the superior vena cava\u2019s entrance to the heart, may be affected during the bidirectional Glenn procedure (BDG), resulting in reduced HRV. We aimed to investigate changes in heart rate and HRV in a cohort of children with univentricular heart defects, undergoing stepwise surgery towards total cavopulmonary connection (TCPC), and compare these results with healthy controls. Twenty four\u00a0hours Holter-ECG recordings were obtained before BDG (<jats:italic>n<\/jats:italic>\u2009=\u200947), after BDG (<jats:italic>n<\/jats:italic>\u2009=\u200947), and after total cavopulmonary connection (TCPC) (<jats:italic>n<\/jats:italic>\u2009=\u200945) in patients and in 38 healthy controls. HRV was analyzed by spectral and Poincar\u00e9 methods. Age-related <jats:italic>z<\/jats:italic> scores were calculated and compared using linear mixed effects modeling. Total HRV was significantly lower in patients before BDG when compared to healthy controls. The mean heart rate was significantly reduced in patients after BDG compared to before BDG. Compared to healthy controls, patients operated with BDG had significantly reduced heart rate and reduced total HRV. Patients with TCPC showed reduced heart rate and HRV compared with healthy controls. In patients after TCPC, total HRV was decreased compared to before TCPC. Heart rate was reduced after BDG procedure, and further reductions of HRV were seen post-TCPC. Our results indicate that autonomic regulation of cardiac rhythm is affected both after BDG and again after TCPC. This may be reflected as, and contribute to, postoperative arrhythmic events.<\/jats:p>","DOI":"10.1007\/s00246-021-02595-0","type":"journal-article","created":{"date-parts":[[2021,4,10]],"date-time":"2021-04-10T13:02:41Z","timestamp":1618059761000},"page":"1162-1169","update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Changes in Heart Rate and Heart Rate Variability During Surgical Stages to Completed Fontan Circulation"],"prefix":"10.1007","volume":"42","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-8818-8762","authenticated-orcid":false,"given":"Jenny Alenius","family":"Dahlqvist","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Urban","family":"Wiklund","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marcus","family":"Karlsson","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Katarina","family":"Hans\u00e9us","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Eva","family":"Str\u00f6mvall Larsson","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jens","family":"Johansson Ramgren","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"H\u00e5kan","family":"Berggren","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Annika","family":"Rydberg","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2021,4,10]]},"reference":[{"issue":"3","key":"2595_CR1","doi-asserted-by":"publisher","first-page":"240","DOI":"10.1136\/thx.26.3.240","volume":"26","author":"F Fontan","year":"1971","unstructured":"Fontan F, Baudet E (1971) Surgical repair of tricuspid atresia. 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