Cardiac Restraint and Support Following Myocardial Infarction - Cardiovascular and Cardiac Therapeutic Devices - page 192

opposed to ventricular restraint. In addition to the increased variability observed in
volume changes, there is also slightly more variability in the reported functional
changes following local versus global reinforcement. For example, Kelley et al.
showed that patch reinforcement of an LAD infarct could reduce LV volumes and
improve EF, SV, CO, and ESPVR slope, but using the same patch to reinforce an
LCx infarct failed to improve any of these parameters compared to the control
group [ 50 , 51 ]. In addition, Zimmermann et al. found that reinforcing an LAD
infarct with a different type of patch produced no changes in LV volumes, EF, SV,
CO, FAS or dP/dt [ 56 ]. With the exception of one report of worsened dilation and
FS following seeded patch application, most of the other studies discussed showed
decreases in LV volumes and improvements in EF or FS.
When looking at the patch studies discussed in this chapter as a whole,
somewhat consistent reductions in both LV EDV and ESV are observed. Remi-
niscent of global restraint, however, the metrics used to evaluate changes in LV
function make it difficult to distinguish geometric changes from actual improve-
ments in pumping. Additionally, as discussed in the beginning of this chapter and
above, the two most consistently reported improved indices (EF and FS) are
difficult to interpret due to their dependence on geometry and material properties.
Across studies, consistent increases in EF and FS, FAC or WT are unaccompanied
by increases in SV, CO, or dP/dt. However, as seen in Table 2 , few studies actually
measured more than one or two indices, so it is possible that there are true
functional changes occurring that are not being captured simply because they
aren't being measured. Comparing the pool of local reinforcement studies
described here to the global restraint studies discussed earlier, it appears that patch
restraint can successful generate similar geometric and contractile changes to
global restraint, although with slightly less consistency. However, since nearly
every patch study described used a different type of patch material and attachment
scheme, while global reinforcement studies employed commercialized devices
with standard implantation procedures, it is not at all surprising that we see sig-
nificantly more variability in the results of the patch studies.
6.1 Importance of Patch Material Properties
The studies reviewed above used patches with a variety of material properties,
applied under different degrees of tension, and exerting a variable degree of bio-
logic influence on infarct healing, in addition to direct mechanical effects. As a
result, it is very difficult to distill conclusions about how these individual variables
affect remodeling and function, or to articulate clear design goals for the next
generation of patches. However, some consensus is beginning to emerge regarding
the impact of one key variable, the mechanical properties of the patch itself.
Early computational models that simulated the functional impact of changes in
infarct material properties over the time course of healing found an interesting
trade-off between the effect of scar stiffening on systolic versus, diastolic function