Presystolic mitral annular septal-lateral shortening is independent from left atrial and left ventricular contraction during acute volume depletion.
BACKGROUND
The mitral annulus (MA) is a dynamic structure that joins the left atrium (LA) and left ventricle (LV), but it is unknown whether MA motion is coupled to the LA or the LV or neither of the two. Since a well orchestrated coordination of LA, MA and LV septal-lateral (S-L) dynamics is essential for efficient valve closure, we assessed their functional coupling in an experimental ovine model. To assess the coupling under a wide range of physiological conditions, data were acquired in normal and acutely volume depleted hearts.


METHODS
In 10 sheep, radiopaque markers were placed in LA, MA and LV base (LVbase). Twelve weeks postoperatively, 4-D marker coordinates were obtained by stereo videofluoroscopy (60 frames/s) before (CTRL) and during acute inferior vena caval occlusion (VCO). Septal-lateral dimensions were calculated as distances between corresponding marker pairs in the LA, MA and LVbase 5 frames before end-diastole (ED-84 ms) and at end-diastole. Dynamics during late diastole are described as changes from ED-84 ms versus end-diastole. To study the functional coupling between LA, MA and LVbase we calculated slopes during late diastole from simple linear regressions on an animal-by-animal basis.


RESULTS
During late diastole in CTRL, the LA and MA both shortened along the S-L dimension (32.9 +/- 6.6 mm vs 31.0 +/- 5.5 mm, p = 0.026 and 27.3 +/- 3.7 mm vs 24.6 +/- 4.1 mm, p = 0.005, respectively) whereas the LVbase lengthened (56.2 +/- 9.3 mm vs 57.3 +/- 9.3 mm, p = 0.012). VCO abolished septal-lateral dynamics of LA and LVbase during late diastole (27.8 +/- 4.3 mm vs 27.4 +/- 3.9 mm, p = 0.155 and 49.4 +/- 7.7 mm vs 49.5 +/- 7.5 mm, p = 0.752, respectively) while the MA still shortened (19.0 +/- 2.9 vs 18.0 +/- 2.8, p = 0.042). Under CTRL conditions LA dynamics were linearly dependent from MA dynamics (average coefficient 0.57, p = 0.001), suggesting that LA and MA are functionally coupled. With acute volume depletion, MA dynamics were linearly independent from both, LA and LV (average coefficient 0.28, p = 0.159 and 0.58, p = 0.192, respectively).


CONCLUSIONS
Whereas MA and LA dynamics are coupled during late diastole in hearts with normal LV volumes, presystolic mitral annular septal-lateral shortening is independent from LA and LV dynamics with acute volume depletion. A better understanding of mitral annular dynamics and their functional coupling may help improve mitral valve repair strategies.
Bothe
Wolfgang
W
Department of Cardiothoracic Surgery, Falk Cardiovascular Research Center, Stanford University School of Medicine, Stanford, CA 94305-5247, USA.
Nguyen
Tom C
TC
Roberts
Margaret E
ME
Timek
Tomasz A
TA
Itoh
Akinobu
A
Ingels
Neil B
NB
Miller
David Craig
DC
D000208:Acute Disease; D000818:Animals; D003971:Diastole / Q000502:physiology; D004195:Disease Models, Animal; D006325:Heart Atria / Q000503:physiopathology; D006352:Heart Ventricles / Q000503:physiopathology; D006439:Hemodynamics / Q000502:physiology; D020896:Hypovolemia / Q000503:physiopathology*; D008297:Male; D008943:Mitral Valve / Q000503:physiopathology*; D009200:Myocardial Contraction / Q000502:physiology*; D012756:Sheep; D013599:Systole / Q000502:physiology