1. MRI-Based Finite-Element Analysis of Left Ventricular Aneurysm Julius M. Guccione, Ph.D. Walker et al, Am J Physiol. 289:H692-700, 2005. UCSF/VAMC Cardiac Biomechanics Laboratory San Francisco, California

2. Important Points Forces or stresses in the intact heart wall cannot be measured directly. Mathematical models for computing ventricular wall stress must be “validated” using regional 3-D strain measurements. Ventricular function (e.g., stroke volume versus end-diastolic pressure) is more important than ejection fraction and ventricular wall stress.

3. Prolate Spheroidal Coordinates Costa et al, J Biomech Eng. 1996 Nov;118(4):464-72

4. Ventricular Muscle Fiber Orientation Walker et al, J Thorac Cardiovasc Surg. 2005 Feb;129(2):382-90

5. Definition of (Cauchy) Stress Fung, A First Course in Continuum Mechanics, 1994

6. Governing Equilibrium Equations Costa et al, J Biomech Eng. 1996 Nov;118(4):464-72

7. Constitutive Equations Guccione et al, J Biomech. 1995 Oct;28(10):1167-77

8. Model of Shortening Deactivation Guccione and McCulloch, J Biomech Eng. 1993 Feb;115(1):72-81

9. Muscle Contraction Model Comparison Guccione et al, J Biomech Eng. 1993 Feb;115(1):82-90

10. (Time Varying) Elastance Model Guccione et al, J Biomech Eng. 1993 Feb;115(1):82-90

11. LV Pressure-Volume Loops McCulloch and Omens, Theory of Heart, 1991

12. Sheep Model of LV Aneurysm Markovitz et al, Ann Thorac Surg. 1989 Dec;48(6):838-45.

13. Tagged MRI-Based LV Model Geometry Walker et al, Am J Physiol. 289:H692-700, 2005. Figure 1 ABC

14. Automated BZ Detection Walker et al, Am J Physiol. 289:H692-700, 2005. BA Figure 2

15. Schematic of Biaxial Stretcher

16. LV Aneurysm Biaxial Mechanical Properties

17. Contractile Dysfunction in Border Zone (BZ) Regions of LV Aneurysm

18. End-Systolic Circumferential Strain Comparison Walker et al, Am J Physiol. 289:H692-700, 2005. BA Figure 45

19. Effect of Active Cross-Fiber Stress Walker et al, Am J Physiol. 289:H692-700, 2005. Figure 56

20. Regional End-Systolic 3-D Stress Walker et al, Am J Physiol. 289:H692-700, 2005. Figure 67

21. Conclusions Active cross-fiber stress development is an integral part of LV systole; FE analysis with only uniaxial contraction is insufficient. Stress calculations from our validated models show 24% increase in fiber stress and 115% increase in cross-fiber stress at the BZ relative to remote regions.

22. Study Limitations No validation of estimated myocardial material properties using direct measurements (e.g., biaxial testing). In vivo boundary conditions are extremely complicated to model mathematically. A formal optimization of myocardial material parameters was not performed. Tagged MRI methodology was not state- of-the-art (e.g., C-SPAMM).

23. Virtual Tools for Cardiac Ventricular Remodeling Surgery

24. Necrosis-Specific MR Contrast Media in Rats Saeed et al, Circulation. 2001 Feb 13;103(6):871-6.

25. Effect of Aneurysm Repair on Stress ABC

26. Effect of SAVER on LV Function Dang et al, Ann Thorac Surg. 2005 Jan;79(1):185-93.

27. Thank You