Cardiac Restraint and Support Following Myocardial Infarction - Cardiovascular and Cardiac Therapeutic Devices - page 185

to the inconsistencies in the functional changes observed in the studies discussed and
the difficultly in interpreting some of the indices used, the true effects of total
ventricular restraint on cardiac function remain unclear. The final two studies listed
in Table 1 will be discussed in the Optimizing Restraint section.
4.1 Limitations of Whole Ventricle Restraint
Although they have been shown to limit progression toward dilated heart failure
following MI, there are still significant limitations associated with CSD use. A
prominent drawback is the invasiveness of the procedures that are required to
implant most of the devices. The risks of performing an open chest procedure on a
patient who recently had a large MI make these devices unattractive as post-
infarction therapies. Their clinical relevancy has been limited to patient subpop-
ulations that are already scheduled to undergo an open chest procedure for a
concurrent pathology, such as a coronary artery bypass or mitral valve repair.
Another potential drawback of the total ventricular restraint approach for post-MI
reinforcement is the possibility of interference with the normal myocardium. For
example, implanting a globally stiff CSD may work well to reinforce a bulging
infarct scar, but may also inhibit diastolic filling throughout the ventricle.
Although several of the commercialized restraint devices (Acorn CorCap and
Paracor HeartNet) have been shown to be much less stiff than the native peri-
cardium that surrounds the heart, these devices have also been consistently shown
to affect LV volumes. While long-term reductions in LV volumes can be indicative
of attenuation of dilation, studies showing decreases in EDV during acute rein-
forcement suggest that global filling is immediately affected upon implantation.
Local restraint approaches have attempted to address this issue by reinforcing only
the nonviable infarct scar, and several variations of local restraint will be discussed
in the following sections.
5 Local Restraint: Cardiac Patches
Once the idea of physically preventing post-infarction remodeling was established,
it was natural to explore whether global restraint of the infarcted left ventricle is
really necessary, or whether local restraint of the infarct region might be sufficient.
Cardiac patches intended for local, post-infarction application have taken a variety
of forms, from synthetic to cell-seeded to completely tissue engineered. Some aim
to mechanically reinforce the infarct, while others are intended primarily to deliver
growth factors or cells to the damaged region. An extensive summary of materials
that have been used in the construction of cardiac patches can be found in
Rane and Christman 2011 [ 49 ]. Although a multitude of tissue engineered and
cell-seeded patches have been fabricated and tested, we will limit our discussion in