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- Krishnamurthy, G., et al.
(författare)
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Material properties of the ovine mitral valve anterior leaflet in vivo from inverse finite element analysis
- 2008
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Ingår i: American Journal of Physiology. Heart and Circulatory Physiology. - : American Physiological Society. - 0363-6135 .- 1522-1539. ; 295:3
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Tidskriftsartikel (refereegranskat)abstract
- We measured leaflet displacements and used inverse finite-element analysis to define, for the first time, the material properties of mitral valve (MV) leaflets in vivo. Sixteen miniature radiopaque markers were sewn to the MV annulus, 16 to the anterior MV leaflet, and 1 on each papillary muscle tip in 17 sheep. Four-dimensional coordinates were obtained from biplane videofluoroscopic marker images (60 frames/s) during three complete cardiac cycles. A finite-element model of the anterior MV leaflet was developed using marker coordinates at the end of isovolumic relaxation (IVR, when the pressure difference across the valve is ~0), as the minimum stress reference state. Leaflet displacements were simulated during IVR using measured left ventricular and atrial pressures. The leaflet shear modulus (Gcirc-rad) and elastic moduli in both the commisure-commisure (Ecirc) and radial (Erad) directions were obtained using the method of feasible directions to minimize the difference between simulated and measured displacements. Group mean (±SD) values (17 animals, 3 heartbeats each, i.e., 51 cardiac cycles) were as follows: Gcirc-rad = 121 ± 22 N/mm2, Ecirc = 43 ± 18 N/mm2, and Erad = 11 ± 3 N/mm2 (Ecirc > E rad, P < 0.01). These values, much greater than those previously reported from in vitro studies, may result from activated neurally controlled contractile tissue within the leaflet that is inactive in excised tissues. This could have important implications, not only to our understanding of mitral valve physiology in the beating heart but for providing additional information to aid the development of more durable tissue-engineered bioprosthetic valves. Copyright © 2008 the American Physiological Society.
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| 2. |
- Bothe, Wolfgang, et al.
(författare)
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Effects of acute ischemic mitral regurgitation on three-dimensional mitral leaflet edge geometry
- 2008
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Ingår i: European Journal of Cardio-Thoracic Surgery. - : Oxford University Press (OUP). - 1010-7940 .- 1873-734X. ; 33, s. 191-197
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Tidskriftsartikel (refereegranskat)abstract
- Background: Improved quantitative understanding of in vivo leaflet geometry in ischemic mitral regurgitation (IMR) is needed to improve reparative techniques, yet few data are available due to current imaging limitations. Using marker technology we tested the hypotheses that IMR (1) occurs chiefly during early systole; (2) affects primarily the valve region contiguous with the myocardial ischemic insult; and (3) results in systolic leaflet edge restriction. Methods: Eleven sheep had radiopaque markers sutured as five opposing pairs along the anterior (A1–E1) and posterior (A2–E2) mitral leaflet free edges from the anterior commissure (A1–A2) to the posterior commissure (E1–E2). Immediately postoperatively, biplane videofluoroscopy was used to obtain 4D marker coordinates before and during acute proximal left circumflex artery occlusion. Regional mitral orifice area (MOA) was calculated in the anterior (Ant-MOA), middle (Mid-MOA), and posterior (Post-MOA) mitral orifice segments during early systole (EarlyS), mid systole (MidS), and end systole (EndS). MOA was normalized to zero (minimum orifice opening) at baseline EndS. Tenting height was the distance of the midpoint of paired markers to the mitral annular plane at EndS. Results: Acute ischemia increased echocardiographic MR grade (0.5 ± 0.3 vs 2.3 ± 0.7, p < 0.01) and MOA in all regions at EarlyS, MidS, and EndS: Ant-MOA (7 ± 10 vs 22 ± 19 mm2, 1 ± 2 vs18 ± 16 mm2, 0 vs 17 ± 15 mm2); Mid-MOA (9 ± 13 vs 25 ± 17 mm2, 3 ± 6 vs 21 ± 19 mm2, 0 vs 25 ± 17 mm2); and Post-MOA (8 ± 10 vs 25 ± 16, 2 ± 4 vs 22 ± 13 mm2, 0 vs 23 ± 13 mm2), all p < 0.05. There was no change in MOA throughout systole (EarlyS vs MidS vs EndS) during baseline conditions or ischemia. Tenting height increased with ischemia near the central and the anterior commissure leaflet edges (B1–B2: 7.1 ± 1.8 mm vs 7.9 ± 1.7 mm, C1–C2: 6.9 ± 1.3 mm vs 8.0 ± 1.5 mm, both p < 0.05). Conclusions: MOA during ischemia was larger throughout systole, indicating that acute IMR in this setting is a holosystolic phenomenon. Despite discrete postero-lateral myocardial ischemia, Post-MOA was not disproportionately larger. Acute ovine IMR was associated with leaflet restriction near the central and the anterior commissure leaflet edges. This entire constellation of annular, valvular, and subvalvular ischemic alterations should be considered in the approach to mitral repair for IMR.
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| 3. |
- Carlhäll, Carljohan, et al.
(författare)
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Alterations in transmural myocardial strain - An early marker of left ventricular dysfunction in mitral regurgitation?
- 2008
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Ingår i: Circulation. - 0009-7322 .- 1524-4539. ; 118:14, s. S256-S262
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Tidskriftsartikel (refereegranskat)abstract
- Background-In asymptomatic patients with severe isolated mitral regurgitation (MR), identifying the onset of early left ventricular (LV) dysfunction can guide the timing of surgical intervention. We hypothesized that changes in LV transmural myocardial strain represent an early marker of LV dysfunction in an ovine chronic MR model. Methods and Results-Sheep were randomized to control (CTRL, n = 8) or experimental (EXP, n = 12) groups. In EXP, a 3.5-or 4.8-mm hole was created in the posterior mitral leaflet to generate "pure" MR. Transmural beadsets were inserted into the lateral and anterior LV wall to radiographically measure 3-dimensional transmural strains during systole and diastolic filling, at 1 and 12 weeks postoperatively. MR grade was higher in EXP than CTRL at 1 and 12 weeks (3.0 [2-4] versus 0.5 [0-2], 3.0 [1-4] versus 0.5 [0-1], respectively, both P < 0.001). At 12 weeks, LV mass index was greater in EXP than CTRL (201 +/- 18 versus 173 +/- 17 g/m(2), P < 0.01). LVEDVI increased in EXP from 1 to 12 weeks (P = 0.015). Between the 1 and 12 week values, the change in BNP (-4.5 +/- 4.4 versus-3.0 +/- 3.6 pmol/L), PRSW (9 +/- 13 versus 23 +/- 18 mm Hg), tau (-3 +/- 11 versus-4 +/- 7 ms), and systolic strains was similar between EXP and CTRL. The changes in longitudinal diastolic filling strains between 1 and 12 weeks, however, were greater in EXP versus CTRL in the subendocardium (lateral:-0.08 +/- 0.05 versus 0.02 +/- 0.14, anterior:-0.10 +/- 0.05 versus-0.02 +/- 0.07, both P < 0.01). Conclusions-Twelve weeks of ovine "pure" MR caused LV remodeling with early changes in LV function detected by alterations in transmural myocardial strain, but not by changes in BNP, PRSW, or tau.
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| 4. |
- Nguyen, Tom c., et al.
(författare)
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The effect of pure mitral regurgitation on mitral annular geometry and three-dimensional saddle shape
- 2008
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Ingår i: Journal of Thoracic and Cardiovascular Surgery. - : Elsevier BV. - 0022-5223 .- 1097-685X. ; 136:3, s. 557-565
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Chronic ischemic mitral regurgitation is associated with mitral annular dilatation in the septal-lateral dimension and flattening of the annular 3-dimensional saddle shape. To examine whether these perturbations are caused by the ischemic insult, mitral regurgitation, or both, we investigated the effects of pure mitral regurgitation (low pressure volume overload) on annular geometry and shape. Methods: Eight radiopaque markers were sutured evenly around the mitral annulus in sheep randomized to control (CTRL, n = 8) or experimental (HOLE, n = 12) groups. In HOLE, a 3.5- to 4.8-mm hole was punched in the posterior leaflet to generate pure mitral regurgitation. Four-dimensional marker coordinates were obtained radiographically 1 and 12 weeks postoperatively. Mitral annular area, annular septal-lateral and commissure-commissure dimensions, and annular height were calculated every 16.7 ms. Results: Mitral regurgitation grade was 0.4 ± 0.4 in CTRL and 3.0 ± 0.8 in HOLE (P < .001) at 12 weeks. End-diastolic left ventricular volume index was greater in HOLE at both 1 and 12 weeks, end-systolic volume index was larger in HOLE at 12 weeks. Mitral annular area increased in HOLE predominantly in the commissure-commissure dimension, with no difference in annular height between HOLE versus CTRL at 1 or 12 weeks, respectively. Conclusion: In contrast with annular septal-lateral dilatation and flattening of the annular saddle shape observed with chronic ischemic mitral regurgitation, pure mitral regurgitation was associated with commissure-commissure dimension annular dilatation and no change in annular shape. Thus, infarction is a more important determinant of septal-lateral dilatation and annular shape than mitral regurgitation, which reinforces the need for disease-specific designs of annuloplasty rings. © 2008 The American Association for Thoracic Surgery.
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