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Modeling Cardiac Mechanics: Surgical Interventions

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UCB/UCSF Joint Graduate Bioengineering Group. Specific Interventions ... 2003 Oct;76(4):1171-80; discussion 1180) ... High initial enthusiasm. ... – PowerPoint PPT presentation

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Title: Modeling Cardiac Mechanics: Surgical Interventions


1
Modeling Cardiac Mechanics Surgical Interventions
  • Julius M. Guccione, Ph.D.
  • Cardiac Biomechanics Laboratory
  • UCSF Department of Surgery
  • UCB/UCSF Joint Graduate Bioengineering Group

2
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)

3
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.

4
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
5
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
6
Mesenchymal Stem Cells for Cardiac Regeneration
Images courtesy of Dara L. Kraitchman, V.M.D.,
Ph.D.
7
Prolate Spheroidal Coordinates
Costa et al, J Biomech Eng. 1996
Nov118(4)464-72 www.continuity.ucsd.edu
8
Ventricular Muscle Fiber Orientation
Walker et al, J Thorac Cardiovasc Surg. 2005
Feb129(2)382-90
9
Definition of (Cauchy) Stress
Fung, A First Course in Continuum Mechanics, 1994
10
Governing Equilibrium Equations
Costa et al, J Biomech Eng. 1996 Nov118(4)464-72
11
Constitutive Equations
Guccione et al, J Biomech. 1995 Oct28(10)1167-77
12
Model of Shortening Deactivation
Guccione and McCulloch, J Biomech Eng. 1993
Feb115(1)72-81
13
Muscle Contraction Model Comparison
Guccione et al, J Biomech Eng. 1993
Feb115(1)82-90
14
(Time Varying) Elastance Model
Guccione et al, J Biomech Eng. 1993
Feb115(1)82-90
15
LV Pressure-Volume Loops
McCulloch and Omens, Theory of Heart, 1991
16
Partial Ventriculectomy Finite Element Model
DCM Model
Simulated Ventricular Resection
17
Effect of Partial Ventriculectomy on Fiber Stress
18
Effect of Partial Ventriculectomy on P-V
Relationships
19
Ejection Fraction is not enough1,2
1. Dickstein et al., 1131032, 1997 2. Ratcliffe
et al., JTCVS 116566, 1998
20
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.

21
Shape Change Therapy Finite Element Model
22
(No Transcript)
23
Myocor MyosplintEffect on Fiber Stress
24
Myocor MyosplintStarling Relationship
25
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.

26
SAVER
27
SAVER
28
SAVER
29
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

30
Akinetic Infarct Model (unloaded)
31
LV w/ MI Dilated
32
Post-SAVER LV Dilated
33
Effect of SAVER on Stress
34
Effect of SAVER on Function
35
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

36
Matrix-Assisted Myocardial Stabilization (FE
Model Simulation)
37
Single Anterior BZ Injection Effect on Fiber
Stress
38
Multiple Peri-Infarct BZ Injections Effect on
Fiber Stress Distributions
39
Effect on LV Pressure-Volume Relationships
40
Effect on Ejection Fraction
41
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.

42
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
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