Pathological Views of Injured Myofibers After Myocardial Infarction in a 3D Reconstruction Obtained from Multiple Tissue Sections

摘要

Adverse left ventricular (LV) remodeling after acute myocardial infarction, characterized by LV dilatation and fibrosis, is a critical factor for prognosis in the subsequent development of heart failure. Though myofiber organization is a key component of cardiac structure, pathological views of injured myofibers during LV remodeling have not been characterized well. In our previous study using ischemia-reperfusion (I/R) injury models in mice, histological assays demonstrated the formation of a broad fibrotic scar extending from the initial infarct zone to a remote zone along mid-circumferential myofibers. However, the fibrosis was contained and did not extend into longitudinal myofibers within the internal and external aspects of the myocardium. We hypothesized that myocyte injury after I/R extends along myofibers but not coronary vessels. However, a histological analysis of tissue sections does not adequately indicate myofiber injury distribution throughout the entire heart. To address this, we investigated patterns of scar formation along myofibers using 3D images obtained from multiple tissue sections of the heart following I/R. Mice were subjected to surgical I/R (30 min-ischemia followed by reperfusion) injury by ligation of the left anterior descending coronary artery (LAD) and examined at 1 week after I/R. Each heart was fixed with 4% polyformaldehyde and cut serially into sections 5-µm thick from base to apex. In total, more than 100 sections were stained with Masson's trichome to identify regions of tissue fibrosis. Of those, 31 representative tissue sections were selected in equal distribution along the base to the apex. To generate the 3D model, digital images of the sections were outlined to highlight fibrotic areas, realigned for anatomic accuracy, and reconstructed using WinSurf v 1.0. The 3D model clearly delineates scar formation along myofibers beginning at the anterior wall of the base and extending inferiorly to the posterior wall of the apex. The pattern was consistent with distribution of the mid-circumferential myofibers. The data suggest that myocyte injury after temporal coronary ligation extends along myofibers rather than coronary vessels. Interestingly, recent clinical reports of patients with post-myocardial infarction evaluated with gadolinium-contrast MRI showed late enhancement of scar tissue limited only to the mid-myocardium in some cases. The same technique could be used to confirm the pattern of scar formation using autopsy samples. Computerized 3D images of histological assays are useful tools for visual analysis of myocardial architecture in I/R models and in the evolution of fibrosis in clinical settings.