title: Pulmonary vein flow pattern in children with bidirectional cavopulmonary connection or Fontan circuit.
abstract: BACKGROUND
  Typical flow velocity profiles in the extraparenchymal pulmonary veins (PVs) demonstrate two major antegrade flow waves: a biphasic systolic wave (S), with S1 and S2 peaks and a monophasic early diastolic wave (D). Flow reversal during atrial systole (A) is common. There is agreement that the forward diastolic PV flow wave is caused by left ventricular relaxation with opening of the mitral valve. The origin of the PV systolic wave, however, remains a topic of debate. Some studies have suggested that the S wave is created by the relaxation of the left atrium and descent of the mitral valve plane. These studies have concluded that forces generated by the right ventricle (RV) have no effect on the S wave. Others suggest that the forward propagation of the right ventricular systolic pressure pulse is the major contributor to the S wave.
  
  
  OBJECTIVE
  To determine whether any part of the systolic wave of PV flow is dependent on forces created by the right ventricle.
  
  
  METHODS
  We assessed PV flow pattern, as obtained by cardiac MRI in 12 cases (39 pulmonary veins) with RV-independent pulmonary circulation (bidirectional cavopulmonary connection or Fontan circulation). Phase-contrast imaging of the PVs was performed on a 1.5-T MR scanner with velocity encoding set at 120 cm/s. We compared these flow patterns with those of a control group of ten children (15 pulmonary veins) who had RV-dependent pulmonary circulation and underwent CMR for other indications.
  
  
  RESULTS
  In all PVs of children with RV-independent pulmonary circulation the flow curves showed a single systolic peak in early systole (S1) with the S2 peak consistently absent. PV flow pattern in the control group consistently showed distinct early and late systolic peaks.
  
  
  CONCLUSIONS
  This study supports the concept that S2 is caused by forward propagation of the right ventricular systolic pressure pulse. It also demonstrates that the S1 is independent of the right ventricle.
authors.affiliation: Department of Radiology, Hospital for Sick Children, 555 University Ave., Toronto, Canada. masoudshariat@gmail.com
authors.forename: Masoud
authors.initials: M
authors.lastname: Shariat
authors.forename: Lars
authors.initials: L
authors.lastname: Grosse-Wortmann
authors.forename: Jonathan
authors.initials: J
authors.lastname: Windram
authors.forename: Shi-Joon
authors.initials: SJ
authors.lastname: Yoo
mesh_terms: D001783:Blood Flow Velocity; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D003971:Diastole / Q000502:physiology; D005260:Female; D018729:Fontan Procedure; D006330:Heart Defects, Congenital / Q000503:physiopathology* / Q000601:surgery; D006352:Heart Ventricles / Q000002:abnormalities / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D007223:Infant; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011667:Pulmonary Veins / Q000502:physiology*; D012189:Retrospective Studies; D012984:Software; D013599:Systole / Q000502:physiology