Left ventricular aneurysm repair in rats: Structural, functional, and molecular consequences

Objectives: This study examined the effects of aneurysm repair in a rat model of myocardial infarction on functional indices and on the spatiotemporal distribution of cardiac contractile protein and natriuretic peptide messenger RNA. Methods: In a rat infarct model, expanded left ventricular aneurysms were plicated 4 weeks after infarction. At 30 weeks, transverse heart sections were taken at 4 levels (apex [level 1] through base [level 4]) and assessed by in situ hybridization histochemistry to determine regional messenger RNA levels of pre-pro-atrial natriuretic peptide, cardiac α-actin, skeletal α-actin, myosin light chain-2v, and β-myosin heavy chain. Results: Rats with plicated left ventricular aneurysms had reduced left ventricular endocardial circumference (19%, P < .005), lower heart weight ratio (31%, P < .05), left ventricular end-diastolic pressures (51%, P < .05), and increased ±dP/dt (34%-38%, P < .05). Cardiac messenger RNA levels of pre-pro-atrial natriuretic peptide were reduced in the septum (levels 2 and 3), and skeletal α-actin levels were reduced in the septum and left ventricular free wall of plicated rats (level 3). β-Myosin heavy chain levels were markedly reduced in peri-infarct regions of the left ventricular free wall, septum, and right ventricle in plicated rats at level 4, whereas myosin light chain-2v levels were reduced at levels 2 and 4 in the left ventricular free wall and at level 4 in the right ventricle. Conclusions: Plication of left ventricular aneurysm after infarction in the rat significantly reduced cardiac hypertrophy, improved cardiac function, and reduced the upregulation of pre-pro-atrial natriuretic peptide and both fetal and adult contractile protein isoforms associated with cardiac hypertrophy.