Modeling Cardiac Mechanics: Surgical Interventions

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Modeling Cardiac Mechanics Surgical Interventions

• Julius M. Guccione, Ph.D.
• Cardiac Biomechanics Laboratory
• UCSF Department of Surgery
• UCB/UCSF Joint Graduate Bioengineering Group

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Specific Interventions

• Partial Left Ventriculectomy (J Thorac Cardiovasc
  Surg. 2001 Sep122(3)592-9)
• Myocor Myosplint (Ann Thorac Surg. 2003
  Oct76(4)1171-80 discussion 1180)
• Surgical Anterior Ventricular Restoration (Ann
  Thorac Surg. 2005 Jan79(1)185-93)
• Matrix-Assisted Myocardial Stabilization
  (Circulation. 2006 in press)

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Surgery for Heart FailureBatistas Operation
Direct Surgical Therapy
Excision of lateral wall
Linear closure

• Operation Partial Ventriculectomy (PLV)
• Surgical inventor Batista - 1996
• Rationale May reduce LV volume and wall stress
  (LaPlaces law TPR/2H).
• High initial enthusiasm.
• Between 1996 and 2000 - 58 papers and editorials
  describe experience with Batistas operation.

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Surgery for Heart FailureNew Devices Shape
Change Therapy

• Device Myosplint intracardiac struts.
• Company Myocor
• Rationale May prevent further LV dilation,
  reduce wall stress
• Trials Pre-clinical 1

1. Chaudhry PA et al., Passive epicardial
containment prevents ventricular remodeling in
heart failure, Ann Thorac Surg, 701275, 2000
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Surgical Anterior Ventricular Endocardial
Restoration

• SAVER described by Athanasuleas, Buckberg in
  2001
• Uses Dacron patch to exclude akinetic segment
• Overlaps 2 layers of myocardium

Before
After
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Mesenchymal Stem Cells for Cardiac Regeneration
Images courtesy of Dara L. Kraitchman, V.M.D.,
Ph.D.
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Prolate Spheroidal Coordinates
Costa et al, J Biomech Eng. 1996
Nov118(4)464-72 www.continuity.ucsd.edu
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Ventricular Muscle Fiber Orientation
Walker et al, J Thorac Cardiovasc Surg. 2005
Feb129(2)382-90
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Definition of (Cauchy) Stress
Fung, A First Course in Continuum Mechanics, 1994
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Governing Equilibrium Equations
Costa et al, J Biomech Eng. 1996 Nov118(4)464-72
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Constitutive Equations
Guccione et al, J Biomech. 1995 Oct28(10)1167-77
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Model of Shortening Deactivation
Guccione and McCulloch, J Biomech Eng. 1993
Feb115(1)72-81
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Muscle Contraction Model Comparison
Guccione et al, J Biomech Eng. 1993
Feb115(1)82-90
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(Time Varying) Elastance Model
Guccione et al, J Biomech Eng. 1993
Feb115(1)82-90
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LV Pressure-Volume Loops
McCulloch and Omens, Theory of Heart, 1991
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Partial Ventriculectomy Finite Element Model
DCM Model
Simulated Ventricular Resection
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Effect of Partial Ventriculectomy on Fiber Stress
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Effect of Partial Ventriculectomy on P-V
Relationships
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Ejection Fraction is not enough1,2
1. Dickstein et al., 1131032, 1997 2. Ratcliffe
et al., JTCVS 116566, 1998
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Partial Ventriculectomy (Batista)Conclusions

• Stress was reduced by approx. 25
• Shift in end-diastolic compliance was greater
  than the reduction in end-systolic elastance.
• As a result there was a reduction in cardiac
  output and decrement in Starlings law.
• Ejection fraction was not a good measure of LV
  function.

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Shape Change Therapy Finite Element Model
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Myocor MyosplintEffect on Fiber Stress
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Myocor MyosplintStarling Relationship
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Myocor MyosplintConclusions

• Reduction in diastolic fiber stress was approx.
  to Batista.
• Balanced shift of end-diastolic compliance and
  end-systolic elastance.
• As a result, there was an improvement in
  Starlings law that was related to the amount of
  Myosplint tension.

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SAVER
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SAVER
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SAVER
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Transesophageal Echocardiogram

• The echocardiogram of an ovine heart with
  experimentally induced ischemia and reperfusion
  at 1 hour was used
• Echo image
• _at_ 12 weeks
• post-infarct

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Akinetic Infarct Model (unloaded)
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LV w/ MI Dilated
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Post-SAVER LV Dilated
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Effect of SAVER on Stress
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Effect of SAVER on Function
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Surgical Anterior Ventricular Restoration
(SAVER)Conclusions

• SAVER was more beneficial in dilated ventricles,
  where the reduction in cardiac output without
  patch was minimal
• Stiffer patch material causes a greater reduction
  in stress yet has the greatest negative effect on
  cardiac output
• These simulations support the use of SAVER in
  dilated hearts without a patch

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Matrix-Assisted Myocardial Stabilization (FE
Model Simulation)
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Single Anterior BZ Injection Effect on Fiber
Stress
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Multiple Peri-Infarct BZ Injections Effect on
Fiber Stress Distributions
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Effect on LV Pressure-Volume Relationships
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Effect on Ejection Fraction
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Matrix-Assisted Myocardial StabilizationConclusio
ns

• Injection of small volumes of material can change
  cardiac mechanics in a volume and location
  dependant manner, with border zone placement the
  most likely to reduce pathological wall stresses
  and infarct placement able to change performance
  metrics with no meaningful pump function
  improvement.
• There is both the significant potential for
  therapeutic application of material implantation
  to the myocardium as well as potential
  confounding mechanical effects to be aware of.
• There is a need for critical evaluation of past
  and present studies that alter ventricular
  geometry through implantation of cells and/or ECM
  like materials, while still using LV volume
  dependant metrics such as EF to evaluate clinical
  success.

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Finite Element Modeling of Operations for Heart
FailureConclusions

• Can rapidly test a wide range of design
  parameters (amount of resection, patch materials,
  etc.) and determine the effect on Starlings law
  and wall stress
• The most promising operations can then be tested
  in animals and humans