title: Left ventricular isovolumic flow sequence during sinus and paced rhythms: new insights from use of high-resolution Doppler and ultrasonic digital particle imaging velocimetry.
abstract: OBJECTIVE
  We sought to clarify the role of isovolumic intervals during a cardiac cycle by in vivo visualization of left ventricular (LV) intracavitary flow dynamics.
  
  
  BACKGROUND
  Asynchronous LV deformation during isovolumic contraction (IVC) and isovolumic relaxation (IVR) might represent a transient feature of myocardial wall mechanics that reverses the direction of blood flow.
  
  
  METHODS
  In 10 beating porcine hearts, the changes in LV intracavitary flow were recorded at baseline and after LV epicardial and right atrial pacing with high-resolution Doppler and contrast echocardiography. Two-dimensional vector flow fields were generated offline from B-mode contrast images with particle imaging velocimetry.
  
  
  RESULTS
  During IVC, flow from the LV apex accelerated toward the base, whereas blood from the base was redirected toward the outflow through formation of an anterior vortex. Conversely, during IVR, flow was initially directed toward the apex and then briefly reversed toward the base. Epicardial pacing from the LV base altered the stages of flow redirection during the pre-ejection period and delayed mitral valve closure (28 +/- 14 ms vs. 61 +/- 13 ms, p < 0.001) and aortic valve opening (77 +/- 18 ms vs. 111 +/- 18 ms, p = 0.004).
  
  
  CONCLUSIONS
  Isovolumic intervals are not periods of hemodynamic stasis but, rather, phases with dynamic changes in intracavitary flow. Experimentally induced aberrant epicardial electrical activation alters stages of flow redirection and prolongs the pre-ejection period. Normal electromechanical activation through the His-Purkinje system in mammalian hearts maintains an inherent synchrony with the sequence of intracavitary flow redirection.
authors.affiliation: Division of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota 55905, USA.
authors.forename: Partho P
authors.initials: PP
authors.lastname: Sengupta
authors.forename: Bijoy K
authors.initials: BK
authors.lastname: Khandheria
authors.forename: Josef
authors.initials: J
authors.lastname: Korinek
authors.forename: Arshad
authors.initials: A
authors.lastname: Jahangir
authors.forename: Shiro
authors.initials: S
authors.lastname: Yoshifuku
authors.forename: Ilija
authors.initials: I
authors.lastname: Milosevic
authors.forename: Marek
authors.initials: M
authors.lastname: Belohlavek
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002304:Cardiac Pacing, Artificial; D003326:Coronary Circulation / Q000502:physiology; D015150:Echocardiography, Doppler / Q000379:methods*; D017078:Laser-Doppler Flowmetry / Q000379:methods*; D023421:Models, Animal; D009200:Myocardial Contraction / Q000502:physiology; D013552:Swine; D016277:Ventricular Function, Left / Q000502:physiology*