XM. Gao*, RJ. Dilley, E. Percy, M. Follerton, E. Woodcock and XJ. Du.

Baker Medical Institute, Melbourne, Australia.

Left ventricular (LV) rupture is a fatal complication after acute myocardial infarction (MI).  Transgenic (TG) mice overexpressing B₂‑-adrenergic receptor (AR) in the heat have enhance LV contractility, which may raise the incidence of rupture after MI.

TG and wild type (WT) mice underwent surgery to induce LV MI.  Haemodynamics were measured by a LV catheter.  Deaths occurred during 24 h~7 days post MI were analyzed.  Infarct size (IS, % LV) was measured digitally and collagen content in LV was determined by both sirius red staining and hydroxyproline assay.

IS in TG and WT mice was not different.  32 mice died within 24 h~7 days due to acute heart failure (HF) or rupture, post .MI mortality was 30.5%.  13 WT but only 1 TG mice died of rupture during 3-~5 days after MI and all ruptures were located at LV free wall.  At day 7, haemodynamics remained significantly higher in TG mice with MI.  In the infarcted zone, TG mice had a smaller area of coagulative necrosis (5.4±0.9% vs. 12±2.1%, P<0.01) and a higher collagen content (sirius red staining) than WT mice (15.7±1.6% vs. 10.3±1.8%, P<0.05).  TG mice without MI also had a higher concentration of hydroxyproline in the LV than WT mice at age of 4 (2.1±0.1 vs. 1.2±0.2:g/mg) and 10 months (2.9±0.2 vs. 1.7±0.1:g/mg. both P<0.01).

Conclusion:  TG mice overexpressing $₂ .AR have a lower risk of cardiac rupture during the acute phase after MI despite a higher LV contractility.  The mechanisms are most likely due to a higher collagen content in the LV and a facilitated repair process after MI.  Our results demonstrate the importance of collagen in maintaining tensile strength of the infarcted LV.

*P<0.05 vs. TG.

[ Back to 48th ASM Abstract Index ]