BACKGROUND: Placement of an elastic biodegradable patch onto a subacute 
myocardial infarct (MI) provides temporary elastic support that may act to 
effectively alter adverse left ventricular (LV) remodeling processes.
METHODS: Two weeks after permanent left coronary ligation in Lewis rats, the 
infarcted anterior wall was covered with polyester urethane urea (MI + PEUU; n = 
15) or expanded polytetrafluoroethylene (MI + ePTFE; n = 15) patches, or had no 
implantation (MI + sham; n = 12). Eight weeks after surgery, cardiac function 
and histology were assessed.
RESULTS: The ventricular wall in the MI + ePTFE and MI + sham groups was 
composed of fibrous tissue, whereas PEUU implantation induced α-smooth muscle 
actin-positive muscle bundles coexpressing sarcomeric α-actinin and 
cardiac-specific troponin-T. This pattern of colocalization was also found in 
developing embryonic myocardium. Cardiac transcription factors Nkx-2.5 and 
GATA-4 were strongly expressed in the muscle bundles. In the MI + sham group, 
end-diastolic LV cavity area (EDA) increased and the percentage of fractional 
area change (%FAC) decreased. For ePTFE patched animals, both EDA and %FAC 
decreased. In contrast, with MI + PEUU patching, %FAC increased and EDA was 
maintained. With dobutamine-stress echocardiography, MI + PEUU patched LVs 
possessed contractile reserve significantly larger than the MI + sham group.
CONCLUSIONS: MI + PEUU patch implantation onto subacute infarcted myocardium 
induced muscle cellularization with characteristics of early developmental 
cardiomyocytes as well as providing a functional reserve.