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Loss of three-dimensional canine mitral annular systolic contraction with reduced left ventricular volumes
J R Glasson1, M Komeda, G T Daughters
1Department of Cardiovascular and Thoracic Surgery, Stanford University School of Medicine 94305-5247, USA.
Background:
We have recently described an inhomogeneous pattern of systolic contraction of the mitral annulus (MA) in normovolemic dogs: the posterior annulus shortens, and the anterior annulus lengthens. MA dynamics, however, have not been studied in volume-depleted hearts.
Methods And Results:
Eight radiopaque markers were placed equidistant from each other around the MA in seven dogs. As viewed from the left atrium, the segment between markers 1 and 2 (seg12) began at the posteromedial commissure, and remaining segments were numbered sequentially clockwise around the MA (ie, posterior MA encompassed seg12, seg23, seg34, and seg45; anterior MA encompassed seg56, seg67, seg78, and seg81). Marker images were obtained in sedated dogs by simultaneous biplane videofluoroscopy 7 to 12 days after marker implantation, and three-dimensional marker coordinates at end diastole (ED) and end systole (ES) were computed. Vena caval occlusion (VCO) was used to reduce left ventricular end-diastolic volume to 70 +/- 5% of baseline (BL). With VCO, mean MA area did not change from ED to ES (3.4 +/- 0.8 versus 3.6 +/- 0.7 cm2, P = NS) during the cardiac cycle. MA segmental systolic shortening values (negative values indicate lengthening) were as follows for BL and VCO, respectively (mean +/- SD): seg12, 7 +/- 9% and 0 +/- 13%; seg23, 8 +/- 10%* and 1 +/- 11%; seg34, 16 +/- 6%* and 4 +/- 9% seg45, 10 +/- 7%* and 2 +/- 13%; seg56, -4 +/- 5%* and -16 +/- 11%*; seg67, -7 +/- 7%* and -14 +/- 7%*; seg78, 3 +/- 2%* and -1 +/- 6%; and seg81, 6 +/- 5%* and -5 +/- 11% (*P < or = .05 versus zero changes, paired t test).
Conclusions:
With acute volume depletion, the five annular segments that shortened at BL no longer changed length; two anterior segments (seg56 and seg67) that lengthened at BL continued to lengthen significantly, and to a greater extent. These findings indicate that the anterior MA is a more dynamic structure than previously thought. Such dynamic motion may be important for normal mitral valvular function and possibly needs to be taken into account in the design of mitral valve reparative techniques.
Insights
Acute volume depletion alters mitral annulus dynamics, causing previously shortening posterior segments to stabilize and anterior segments to lengthen more significantly. This highlights the anterior mitral annulus
Area of Science:
- Cardiovascular Physiology
- Cardiac Mechanics
- Biomedical Engineering
Background:
- Mitral annulus (MA) contraction is typically inhomogeneous in normovolemic states, with posterior segments shortening and anterior segments lengthening.
- MA dynamics under conditions of reduced cardiac volume have not been previously investigated.
Purpose of the Study:
- To investigate the impact of acute volume depletion on the systolic dynamics of the canine mitral annulus.
Main Methods:
- Eight radiopaque markers were implanted equidistantly around the mitral annulus in seven dogs.
- Three-dimensional marker coordinates were computed using biplane videofluoroscopy at end diastole and end systole.
- Acute volume depletion was induced using vena caval occlusion (VCO) to reduce left ventricular end-diastolic volume.
Main Results:
- During vena caval occlusion, the mitral annulus area did not significantly change from end diastole to end systole.
- Posterior mitral annulus segments that normally shortened showed no significant change in length with volume depletion.
- Anterior mitral annulus segments that normally lengthened exhibited significantly greater lengthening during volume depletion.
Conclusions:
- Acute volume depletion alters mitral annulus systolic motion, diminishing posterior shortening and enhancing anterior lengthening.
- The anterior mitral annulus demonstrates greater dynamic motion than previously recognized, particularly under volume-depleted conditions.
- These findings have implications for understanding mitral valvular function and designing mitral valve repair techniques.