Restraining acute infarct expansion decreases collagenase activity in borderzone myocardium

Background. After acute myocardial infarction, regional myocardial wall str ains and stresses change and a complex cellular and biochemical response is initiated to remodel the ventricle. This study tests the hypothesis that c hanges in regional ventricular wall strains affect regional collagen accumu lation and collagenase activity. Methods. Fourteen sheep had acute anteroapical infarction that progressivel y expands into left ventricular aneurysm within 8 weeks. In 7 sheep, infarc t expansion was restrained by prior placement of mesh over the area at risk . Fourteen days after infarction, and after hemodynamic and echocardiograph ic measurements, animals were euthanized for histology, measurements of hyd roxyproline, matrix metalloproteinase-1 (MMP-1 or collagenase) and MMP-2 (g elatinase) activity, as well as collagen type I and III in infarcted, borde rzone, and remote myocardium. Results. Restraining infarct expansion does not change collagen content or MMP-1 or MMP-2 activity in the infarct, but significantly increases the rat io of collagen I/III. In borderzone and remote myocardium infarct, restrain t significantly increases collagen content and significantly reduces MMP-1 activity. MMP-2 activity is reduced (p = 0.059) in borderzone myocardium on ly. Between groups, the ratio of type I/III fibrillar collagen does not cha nge in borderzone myocardium. Conclusions. Fourteen days after acute myocardial infarction, restraining i nfarct expansion increases collagen accumulation in borderzone and remote m yocardium, which may prevent expansion of hypocontractile, fully perfused " remodeling myocardium" adjacent to the infarct. This study demonstrates tha t changes in regional myocardial wall strain alter the cellular and biochem ical processes involved in postinfarction ventricular remodeling. (C) 2001 by The Society of Thoracic Surgeons.