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Kindberg K.,Linkoping University | Oom C.,Linkoping University | Ingels N.B.,Stanford University | Ingels N.B.,Research Institute of the Palo Alto Medical Foundation | Karlsson M.,Linkoping University
Biomechanics and Modeling in Mechanobiology | Year: 2011

Left ventricular myofibers are connected by an extensive extracellular collagen matrix to form myolaminar sheets. Histological cardiac tissue studies have previously observed a pleated transmural distribution of sheets in the ovine heart, alternating sign of the sheet angle from epicardium to endocardium. The present study investigated temporal variations in myocardial fiber and sheet architecture during the cardiac cycle. End-diastolic histological measurements made at subepicardium, midwall, and subendocardium at an anterior-basal and a lateral-equatorial region of the ovine heart, combined with transmural myocardial Lagrangian strains, showed that the sheet angle but not the fiber angle varied temporally throughout the cardiac cycle. The magnitude of the sheet angle decreased during systole at all transmural depths at the anterior-basal site and at midwall and subendocardium depths at the lateral-equatorial site, making the sheets more parallel to the radial axis. These results support a previously suggested accordion-like wall-thickening mechanism of the myocardial sheets. © Springer-Verlag 2010.

Dimasi A.,Polytechnic of Milan | Cattarinuzzi E.,Polytechnic of Milan | Stevanella M.,Polytechnic of Milan | Conti C.A.,Polytechnic of Milan | And 6 more authors.
Cardiovascular Engineering and Technology | Year: 2012

Recent studies have demonstrated that, due to the active involvement of leaflet contractile elements, the anterior mitral leaflet (AML) is very stiff and maintains a compound curvature during ventricular systole. Studies based on structural mechanics have shown that both leaflet stiffness and compound curvature are key factors limiting AML deformation in the presence of high left ventricular (LV) systolic pressures. In the present study, we tested the hypothesis that maintenance of this physiological AML compound curvature also plays a role in the optimization of LV outflow during ejection. The LV cavity, mitral valve and aortic root of a healthy human were reconstructed from cardiac magnetic resonance images on 18 evenly rotated long-axis cut-planes at peak systole. Computational fluid dynamics was used to assess hemodynamics within the ventricular outflow tract in the presence of three different AML profiles: (i) physiologically compound as measured in vivo, (ii) flat, (iii) concave (i. e., prolapsed) towards the ventricle. Relative to the physiologic profile, AML flat and concave profiles induced progressively increasing hemodynamic alterations at the LV outflow and immediately downstream to the aortic valve, characterized at peak systole by flow detachment, a mean vorticity increase of 15.6 and 53.1% and an instantaneous power loss increase of 12 and 46%, respectively. These results support the hypothesis that the physiological AML shape plays an important role in optimizing LV ejection. This implies that AML profile alterations associated with valvular disease or surgical repair procedures can significantly reduce LV ejection efficiency. © 2012 Biomedical Engineering Society.

Kindberg K.,Linkoping University | Haraldsson H.,Linkoping University | Sigfridsson A.,Linkoping University | Engvall J.,Linkoping University | And 4 more authors.
BMC Medical Imaging | Year: 2012

Background: The ability to measure and quantify myocardial motion and deformation provides a useful tool to assist in the diagnosis, prognosis and management of heart disease. The recent development of magnetic resonance imaging methods, such as harmonic phase analysis of tagging and displacement encoding with stimulated echoes (DENSE), make detailed non-invasive 3D kinematic analyses of human myocardium possible in the clinic and for research purposes. A robust analysis method is required, however.Methods: We propose to estimate strain using a polynomial function which produces local models of the displacement field obtained with DENSE. Given a specific polynomial order, the model is obtained as the least squares fit of the acquired displacement field. These local models are subsequently used to produce estimates of the full strain tensor.Results: The proposed method is evaluated on a numerical phantom as well as in vivo on a healthy human heart. The evaluation showed that the proposed method produced accurate results and showed low sensitivity to noise in the numerical phantom. The method was also demonstrated in vivo by assessment of the full strain tensor and to resolve transmural strain variations.Conclusions: Strain estimation within a 3D myocardial volume based on polynomial functions yields accurate and robust results when validated on an analytical model. The polynomial field is capable of resolving the measured material positions from the in vivo data, and the obtained in vivo strains values agree with previously reported myocardial strains in normal human hearts. © 2012 Kindberg et al; licensee BioMed Central Ltd.

Swanson J.C.,Stanford University | Krishnamurthy G.,Stanford University | Kvitting J.E.,Stanford University | Miller D.C.,Stanford University | And 2 more authors.
American Journal of Physiology - Heart and Circulatory Physiology | Year: 2011

Anterior leaflet (AL) stiffening during isovolumic contraction (IVC) may aid mitral valve closure. We tested the hypothesis that AL stiffening requires atrial depolarization. Ten sheep had radioopaque-marker arrays implanted in the left ventricle, mitral annulus, AL, and papillary muscle tips. Four-dimensional marker coordinates (x, y, z, and t) were obtained from biplane videofluoroscopy at baseline (control, CTRL) and during basal interventricular-septal pacing (no atrial contraction, NAC; 110-117 beats/min) to generate ventricular depolarization not preceded by atrial depolarization. Circumferential and radial stiffness values, reflecting force generation in three leaflet regions (annular, belly, and free-edge), were obtained from finite-element analysis of AL displacements in response to transleaflet pressure changes during both IVC and isovolumic relaxation (IVR). In CTRL, IVC circumferential and radial stiffness was 46 ± 6% greater than IVR stiffness in all regions (P < 0.001). In NAC, AL annular IVC stiffness decreased by 25% (P = 0.004) in the circumferential and 31% (P = 0.005) in the radial directions relative to CTRL, without affecting edge stiffness. Thus AL annular stiffening during IVC was abolished when atrial depolarization did not precede ventricular systole, in support of the hypothesis. The likely mechanism underlying AL annular stiffening during IVC is contraction of cardiac muscle that extends into the leaflet and requires atrial excitation. The AL edge has no cardiac muscle, and thus IVC AL edge stiffness was not affected by loss of atrial depolarization. These findings suggest one reason why heart block, atrial dysrhythmias, or ventricular pacing may be accompanied by mitral regurgitation or may worsen regurgitation when already present. © 2011 the American Physiological Society.

Bothe W.,Stanford University | Kvitting J.-P.E.,Stanford University | Swanson J.C.,Stanford University | Goktepe S.,Stanford University | And 4 more authors.
European Journal of Cardio-thoracic Surgery | Year: 2010

Objectives: To define the effects of annuloplasty rings (ARs) on the dynamic motion of anterior mitral leaflet (AML) and posterior mitral leaflet (PML). Methods: Fifty-eight adult, Dorsett-hybrid, male sheep (49±5kg) had radiopaque markers inserted: eight around the mitral annulus, four along the central meridian (from edge to annulus) of the AML (#A1-#A4) and one on the PML edge (#P1). True-sized Edwards Cosgrove (COS, n=12), St Jude RSAR (St. Jude Medical, St. Paul, MN, USA) (n=12), Carpentier-Edwards Physio (PHYSIO, n=12), Edwards IMR ETlogix (ETL, n=10) or Edwards GeoForm (GEO, n=12) ARs were implanted in a releasable fashion. Under acute open-chest conditions, 4D marker coordinates were obtained using biplane videofluoroscopy with the respective AR inserted (COS, RSAR, PHYSIO, ETL and GEO) and after release (COS-Control, RSAR-Control, PHYSIO-Control, ETL-Control and GEO-Control). AML and PML excursions were calculated as the difference between minimum and maximum angles between the central mitral annular septal-lateral chord and the AML edge markers (α1exc-α4exc) and PML edge marker (β1exc) during the cardiac cycle. Results: Relative to Control, (1) RSAR, PHYSIO, ETL and GEO increased excursion of the AML annular (α4exc: 13±6° vs 16±7°*, 16±7° vs 23±10°*, 12±4° vs 18±9°*, 15±1° vs 20±9°*, respectively) and belly region (α2exc: 41±10° vs 45±10°*, 42±8° vs 45±6°, n.s., 33±13° vs 42±14°*, 39±6° vs 44±6°*, respectively, α3exc: 24±9° vs 29±11°*, 28±10° vs 33±10°*, 16±9° vs 21±12°*, 25±7° vs 29±9°*, respectively), but not of the AML edge (α1exc: 42±8° vs 44±8°, 43±8° vs 41±6°, 42±11 vs 46±10°, 39±9° vs 38±8°, respectively, all n.s.). COS did not affect AML excursion (α1exc: 40±8° vs 37±8°, α2exc: 43±9° vs 41±9°, α3exc: 27±11° vs 27±10°, α4exc: 18±8° vs 17±7°, all n.s.). (2) PML excursion (β1exc) was reduced with GEO (53±5° vs 43±6°*), but unchanged with COS, RSAR, PHYSIO or ETL (53±13° vs 52±15°, 50±13° vs 49±10°, 55±5° vs 55±7°, 52±8° vs 58±6°, respectively, all n.s); *=p<0.05. Conclusions: RSAR, PHYSIO, ETL and GEO rings, but not COS, increase AML excursion of the AML annular and belly region, suggesting higher anterior mitral leaflet bending stresses with rigid rings, which potentially could be deleterious with respect to repair durability. The decreased PML excursion observed with GEO could impair left ventricular filling. Clinical studies are needed to validate these findings in patients. © 2010 European Association for Cardio-Thoracic Surgery.

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