Coronary Embolization and Myocardial Microinfarction: MR Imaging and Histopathologic Characterization

Magnetic resonance imaging (MRI) has been proven to reliably assess regional perfusion and left ventricular (LV) function of microembolized myocardium. The visibility of microinfarct on delayed enhancement MRI (DE-MRI) is limited and dependent on technical and biological issues. Furthermore, MRI underestimates total microinfarct size compared with microscopy. MRI studies revealed that the presence of microemboli in pre-existing acute infarct delays infarct healing and magnifies LV remodeling. Discrimination of acute from chronic microinfarct is based on presence of inflammatory cells, edema and scar tissue, respectively. These noninvasive findings highlight the importance of prognostic utility of MRI and warrant larger clinical studies or registries to evaluate the significance of presence of focal microinfarct. Serial microscopic studies revealed that intravascular microemboli migrate into the extravascular space and this migration process is a function of time. This phenomenon may limit the use of microemboli therapy in occluding hemorrhagic blood vessels or treating tumors. Despite current standard of care, existing methods and therapies do not prevent coronary embolization nor reverse their deleterious effects.

Histochemistry of microinfarcts in the mouse brain after injection of fluorescent microspheres into the common carotid artery

The mouse model of multiple cerebral infarctions,established by injecting fluorescent microspheres into the common carotid artery,is a recent development in animal models of cerebral ischemia.To investigate its effectiveness,mouse models of cerebral infarction were created by injecting fluorescent microspheres,45–53μm in diameter,into the common carotid artery.Six hours after modeling,fluorescent microspheres were observed directly through a fluorescence stereomicroscope,both on the brain surface and in brain sections.Changes in blood vessels,neurons and glial cells associated with microinfarcts were examined using fluorescence histochemistry and immunohistochemistry.The microspheres were distributed mainly in the cerebral cortex,striatum and hippocampus ipsilateral to the side of injection.Microinfarcts were found in the brain regions where the fluorescent microspheres were present.Here the lodged microspheres induced vascular and neuronal injury and the activation of astroglia and microglia.These histopathological changes indicate that this animal model of multiple cerebral infarctions effectively simulates the changes of various cell types observed in multifocal microinfarcts.This model is an effective,additional tool to study the pathogenesis of ischemic stroke and could be used to evaluate therapeutic interventions.This study was approved by the Animal Ethics Committee of the Institute of Acupuncture and Moxibustion,China Academy of Chinese Medical Sciences(approval No.D2021-03-16-1)on March 16,2021.

An Overview of the Consequences of Distal Coronary Microembolization on Left Ventricular Function, Perfusion and Viability

Annually, an estimated 1,285,000 in-patient angioplasty procedures, 1,471,000 inpatient diagnostic cardiac catheteri-zations and 68,000 inpatient defibrillator implantations are performed. The direct and indirect cost of cardiovascular diseases for 2007 is approximately $431.8 billion. The occurrence of plaque rupture with subsequent microemboli of atherosclerotic and thrombolytic debris into small coronary vessels has been confirmed. Microinfarction results from microemboli that are shed following coronary interventions. The aims of this review are to: 1) detect heterogeneous microinfarction using viability imaging, 2) characterize the consequences of distal coronary microembolization on left ventricle function and perfusion and 3) illustrate the progress of non-invasive imaging modalities in assessing distal coronary microembolization.