title: Correlation of maternal flecainide concentrations and therapeutic effect in fetal supraventricular tachycardia.
abstract: BACKGROUND
  Transplacental flecainide is an established therapy for fetal supraventricular tachycardia (SVT), but there is a paucity of data regarding the dose-response relationship.
  
  
  OBJECTIVE
  The purpose of this study was to investigate the relationship between maternal flecainide concentrations, arrhythmia control, and adverse fetal effects in fetal SVT.
  
  
  METHODS
  Fetuses with SVT treated with transplacental flecainide at our tertiary fetal cardiology unit between 1997 and 2012 were retrospectively studied. The maternal trough flecainide concentrations throughout treatment were collated, and clinical notes were reviewed to ascertain the response to therapy and fetal outcome.
  
  
  RESULTS
  Thirty-three fetuses were treated at a median (range) gestation of 28 weeks (20-38 weeks). Median fetal heart rate was 250/min (range 207-316/min). One patient was lost to follow-up, and this fetus was excluded from further analysis. In total, 25 of 32 fetuses (78%) converted to sinus rhythm. Median time to conversion to sinus rhythm was 3 days (range 2-12 days). Median flecainide concentration was 460 μg/L (range 250-866 μg/L) at conversion to sinus rhythm. Flecainide concentrations were not significantly different between responders and nonresponders (P = .849). Twelve of 14 hydropic and 13 of 18 nonhydropic fetuses converted to sinus rhythm with similar flecainide concentrations (P = .316). No fetus achieved cardioversion with a maternal serum flecainide concentration <250 μg/L. No fetus died while being treated with flecainide.
  
  
  CONCLUSIONS
  The clinical response to flecainide appears good, even in hydropic fetuses. Trough maternal flecainide concentrations, once therapeutic, do not predict cardioversion in the fetus with SVT. Flecainide therapy appears both safe and effective for the fetus when monitored appropriately.
authors: Department of Congenital Heart Disease, Evelina London Children's Hospital, Guy's and St. Thomas' Hospitals, London, United Kingdom. Electronic address: trisha.vigneswaran@gmail.com.
authors: Trisha V
authors: TV
authors: Vigneswaran
authors: Department of Congenital Heart Disease, Evelina London Children's Hospital, Guy's and St. Thomas' Hospitals, London, United Kingdom.
authors: Nicky
authors: N
authors: Callaghan
authors: Department of Cardiothoracic Transplantation, Great Ormond Street Hospital, London, United Kingdom.
authors: Rachel E
authors: RE
authors: Andrews
authors: Department of Congenital Heart Disease, Evelina London Children's Hospital, Guy's and St. Thomas' Hospitals, London, United Kingdom.
authors: Owen
authors: O
authors: Miller
authors: Department of Congenital Heart Disease, Evelina London Children's Hospital, Guy's and St. Thomas' Hospitals, London, United Kingdom.
authors: Eric
authors: E
authors: Rosenthal
authors: Department of Congenital Heart Disease, Evelina London Children's Hospital, Guy's and St. Thomas' Hospitals, London, United Kingdom.
authors: Gurleen K
authors: GK
authors: Sharland
authors: Department of Congenital Heart Disease, Evelina London Children's Hospital, Guy's and St. Thomas' Hospitals, London, United Kingdom.
authors: John M
authors: JM
authors: Simpson
mesh_terms: D000328:Adult; D000465:Algorithms; D000889:Anti-Arrhythmia Agents / Q000493:pharmacokinetics / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D004452:Echocardiography; D005260:Female; D005315:Fetal Diseases / Q000188:drug therapy*; D005424:Flecainide / Q000493:pharmacokinetics / Q000627:therapeutic use*; D005865:Gestational Age; D006801:Humans; D008431:Maternal-Fetal Exchange; D011247:Pregnancy; D012189:Retrospective Studies; D013617:Tachycardia, Supraventricular / Q000000981:diagnostic imaging / Q000188:drug therapy*; D016896:Treatment Outcome
chemical_list: D000889:Anti-Arrhythmia Agents; D005424:Flecainide
keywords: Arrhythmia; Fetus; Flecainide; Supraventricular tachycardia