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Microvascular evidence for a transition zone around a chronic myocardial infarct in the rat
Insights
Viable heart muscle fibers near an infarction show reduced capillary supply long after coronary artery occlusion. This subnormal microvascular supply zone persists for at least 5 weeks in rats.
Area of Science:
- Cardiovascular Science
- Pathology
- Microcirculation Research
Background:
- Muscle fibers in the border zone of infarcted hearts may experience ischemia early after coronary artery occlusion.
- The long-term viability and microvascular status of these marginal muscle fibers remain uncertain.
Purpose of the Study:
- To investigate the existence and extent of reduced microvascular supply in the transition zone of chronic myocardial infarcts.
- To characterize the capillary supply in the margin of necrosis following coronary artery occlusion.
Main Methods:
- Myocardial infarcts were induced in male rats via left coronary artery ligation.
- Capillary supply in the transition zone was quantified 5 weeks post-occlusion using five variables: capillary-to-fiber ratio (C/F), vessels around fiber (Vf), fibers around vessel (Fv), capillary density, and fiber diameter.
Main Results:
- A significant reduction in capillary supply was observed in the transition zone compared to controls.
- Key indicators of capillary supply, including C/F, Vf, and Fv, were significantly decreased.
- This region of reduced capillary supply extended 225-525 microns from the necrotic edge.
Conclusions:
- A distinct transition zone of viable muscle fibers with subnormal microvascular supply exists long-term after coronary artery occlusion.
- This finding highlights a persistent microcirculatory deficit in the border zone of myocardial infarcts.
Abstract:
Muscle fibers in the transition zone of an infarcted heart are thought to be potentially ischemic during the first 6-9 h following coronary artery occlusion. However, the long-term fate of the muscle fibers at the margin of the necrosis is uncertain. Ischemia implies reduced oxygenation, possibly owing to a reduced capillary supply; thus our objective was to determine whether a region of reduced microvascular supply exists at the margin of a necrosis produced by chronic coronary artery occlusion. Five variables were used to quantitate the capillary supply in the transition zone: C/F (capillary to fiber) ratio, Vf (number of vessels around a fiber), Fv (number of fibers surrounding a vessel), capillary density, and fiber diameter. Infarcts were induced in young male rats by ligating the left coronary artery midway between its origin and the apex of the heart. Five weeks later, the capillary supply in the transition zone was significantly below control values, i.e., significant reductions in C/F, Vf, and Fv were found. This region of reduced capillary supply extended 225-525 microns laterally from the edge of the necrosis. Thus, a narrow transition zone, defined as a region of viable muscle fibers with a subnormal microvascular supply, exists as long as 5 weeks following coronary artery occlusion in the rat.