title: Left ventricular volume shifts and aortic root expansion during isovolumic contraction.
abstract: OBJECTIVE
  Aortic valve opening involves conformational changes of the aortic root, including the ventricular-aortic junction (VAJ), sinotubular junction (STJ), and cusps. Moreover, the aortic root is contiguous with the left ventricular outflow tract (LVOT), which changes diameter throughout the cardiac cycle. Aortic root expansion prior to valve opening facilitates outward displacement of aortic cusp attachments, which helps flatten the cusps, thereby reducing cusp stress and fatigue, ultimately enhancing functional valve durability. The mechanisms underlying aortic root expansion prior to valve opening, however, remain incompletely characterized. The study aim was to establish a link between such aortic root expansion and intraventricular volume shifts into the LVOT during isovolumic contraction (IVC).
  
  
  METHODS
  Miniature radiopaque markers were implanted on the left ventricle, VAJ, STJ, and aortic cusps of six sheep. After one week, 3-D marker coordinates were obtained using biplane videofluoroscopy (60 Hz). Triangular areas at the VAJ and STJ were calculated; LV main chamber (non-LVOT) and LVOT volumes were calculated using multiple tetrahedra. End-diastole was defined as the peak of the electrocardiogram R-wave, and end-IVC when aortic cusp separation began.
  
  
  RESULTS
  During IVC, blood within the left ventricle was redistributed to the LVOT: mean LVOT volume was increased (+0.2 +/- 0.1 ml, p = 0.009) as non-LVOT volume fell (-0.8 +/- 0.4 ml, p = 0.006). Concomitantly, the aortic root expanded as both VAJ and STJ areas increased (+0.23 +/- 0.12 cm2 (p = 0.005) and +0.25 +/- 0.14 cm2 (p = 0.007), respectively) prior to aortic cusp separation.
  
  
  CONCLUSIONS
  Aortic root expansion prior to valve opening is closely related to intraventricular volume shifts into the LVOT during IVC. Such volume shifts may 'prime' the aortic valve for ejection. These findings expand our understanding of cardiac dynamics by showing that blood acts as a coupling link between various cardiac units. Preservation of these normal aortic root dynamics may enhance the efficacy and durability of aortic surgical interventions.
authors.affiliation: Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, California 94305-5247, USA.
authors.forename: Filiberto
authors.initials: F
authors.lastname: Rodríguez
authors.forename: G Randall
authors.initials: GR
authors.lastname: Green
authors.forename: Paul
authors.initials: P
authors.lastname: Dagum
authors.forename: J Francisco
authors.initials: JF
authors.lastname: Nistal
authors.forename: Katherine B
authors.initials: KB
authors.lastname: Harrington
authors.forename: George T
authors.initials: GT
authors.lastname: Daughters
authors.forename: Neil B
authors.initials: NB
authors.lastname: Ingels
authors.forename: D Craig
authors.initials: DC
authors.lastname: Miller
mesh_terms: D000818:Animals; D001011:Aorta / Q000502:physiology*; D004562:Electrocardiography; D005471:Fluoroscopy; D006439:Hemodynamics; D007700:Kinetics; D008297:Male; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000502:physiology*; D034561:Sheep, Domestic; D016277:Ventricular Function, Left / Q000502:physiology*; D014741:Video Recording