1. Finite Element Modeling of Cardiac Tissue Megan McCain ES240 - Solid Mechanics Final Project December 12, 2006

2. Cardiac Tissue Structure http://www.math.utah.edu/~keener/lectures/defib/theory1/ cell_structure2.jpg Cardiac cells (myocytes) are cylindrically shaped Mechanically attached end to end by intercalated disks –Site of electrical communication 50 µm Human Ventricle

3. Motivation Stretching isotropic monolayers of cardiac tissue shows a remodeling of gap junctions Relate stresses to changes in protein expression Zhuang J, KA Yamada, JE Saffitz, AG Kleber. Pulsatile Stretch Remodels Cell-to-Cell Communication in Cultures Myocytes. Circulation Research. 2000;87:316.

4. Model of Tissue Structure 100 µm x 20 µm myocytes separated by 2.5 µm x 20 µm gap junctions E myocytes = 35 kPa (literature) E intercalated disk = 60 kPa (guess) = 0.5 (literature) 100 µm 20 µm ABAQUS Lieber SC, et al. Aging Increases Stiffness of Cardiac Myocytes Measured by Atomic Force Microscopy Nanoindentation. Am J Physiol Heart Circ Physiol 287: H645-H651,2004.

5. Horizontal Stretch Load Surface Traction 5 kPa

6. Horizontal Stretch Stress

7. Horizontal Stretch Strain

8. Vertical Stretch Load

9. Vertical Stretch Stress

10. Vertical Stretch Strain

11. Comparing Stresses and Strains Gap junctions experience higher stresses Myocytes experience higher strains Stresses and strains higher during vertical stretch compared to horizontal stretch

12. Clinical Implications Myocardial infarctions (heart attacks) change the stresses on cardiac tissue Gap junctions and myocytes remodel in response to stress –Electrical remodeling can be arrhythmogenic http://forte.fh-hagenberg.at/cardiac/images/medical/infarct.jpg http://medlib.med.utah.edu/WebPath/jpeg5/CV021.jpg