ABSTRACT
To understand the structure-function relationship in the postinfarcted myocardium in rabbits, we induced cardiac ischemia by ligating the left circumflex coronary artery. Sham controls underwent thoracotomy only. At 7 and 30 d after ligation, cardiac MRI was conducted by using pulse-oxymetry-gated cine acquisition to provide complete phases of the heartbeat. The rabbits were anesthetized under 1.5% isoflurane ventilation, and ultrafast techniques made breath-hold 3D coverage in different cardiac axes feasible. Viability imaging was performed after intravenous injection of 0.15 mmol/kg gadolinium to assess the extent of infarction. Data (n ≥ 6) are presented as mean ± SEM and analyzed by ANOVA and ANCOVA. In postligation rabbits, end-systolic (mean ± SEM, 2.3 ± 0.3 mL) and end-diastolic (4.2 ± 0.4 mL) volumes were increased compared with preligation values (end-systolic, 1.1 ± 0.1 mL; end-diastolic, 2.98 ± 0.2 mL). Ejection fraction was influenced adversely by the presence of scar tissue at both 7 and 30 d after ligation and apparently nonlinear with the heart rate. Cardiac force was increased in the basal region in both end-systole and end-diastole in postligation hearts but progressively decreased toward the apex. Late gadolinium enhancement delineated 15.2 ± 5.8% myocardial infarction at 7 d after ligation and 14.5 ± 5.8% at 30 d, with limited wall motion and wall thinness. Compensatory wall thickening was present in the basal region when compared with that in preligation hearts. MRI offers detailed spatial resolution and tissue characterization after myocardial infarction.
Subject(s)
Magnetic Resonance Imaging, Cine , Myocardial Infarction/pathology , Myocardium/pathology , Ventricular Remodeling , Analysis of Variance , Animals , Contrast Media , Disease Models, Animal , Heart Rate , Male , Meglumine/analogs & derivatives , Myocardial Contraction , Myocardial Infarction/physiopathology , Organometallic Compounds , Oximetry , Predictive Value of Tests , Rabbits , Stroke Volume , Time Factors , Ventricular Function, LeftABSTRACT
Provided is the surgical procedure for ligating the left circumflex coronary artery to simulate heart ischemia by using a rabbit model. Heart rate monitored by electrocardiogram was increased at 5 min after ligation (mean ± SEM, 205 ± 13 bpm) when compared with that before ligation (170 ± 12 bpm), but returned to baseline at 25 min after ligation (183 ± 11 bpm). A marked elevation in the ST segment and reduction of the QRS wave of the electrocardiogram indicated the evolving myocardial infarct. The ejection fraction derived from MRI was decreased by 20% in the infarcted heart. The extent of necrosis and fibrosis in the myocardium due to ischemia led to decreased compliance and efficiency of the left ventricle. Masson trichrome staining showed blue-stained fibrils with the appearance of loose, threadlike scar tissue dispersed transmurally in the left ventricle and extending toward the apex. This study demonstrates the feasibility of MRI analysis of myocardial infarction in a rabbit model. The myocardial architecture, including the geometry of the myofibers which determines the contractile function of the heart, is clearly demonstrated by using cardiac MRI. Understanding the 3-dimensional arrangement of the myocardial microstructure and how remodeling of the infarcted myocardium affects cardiac function in an animal model has important implications for the study of heart disease in humans.
