Abstract
The fluorophore indocyanine green accumulates in areas of ischemia-reperfusion injury due to an increase in vascular permeability and extravasation of the dye. The aim of the study was to validate an indocyanine green-based technique of in vivo visualization of myocardial infarction. A further aim was to quantify infarct size ex vivo and compare this technique with the standard triphenyltetrazolium chloride staining. Wistar rats were subjected to regional myocardial ischemia (30 minutes) followed by reperfusion (n = 7). Indocyanine green (0.25 mg/mL in 1 mL of normal saline) was infused intravenously for 10 minutes starting from the 25th minute of ischemia. Video registration in the near-infrared fluorescence was performed. Epicardial fluorescence of indocyanine green corresponded to the injured area after 30 minutes of reperfusion. Infarct size was similar when determined ex vivo using traditional triphenyltetrazolium chloride assay and indocyanine green fluorescent labeling. Intravital visualization of irreversible injury can be done directly by fluorescence on the surface of the heart. This technique may also be an alternative for ex vivo measurements of infarct size.
Highlights
Experimental models of myocardial infarction are widely used to study the mechanisms and pathophysiology of ischemia-reperfusion injury, post-infarction cardiac remodeling and for studies on cardioprotection [1,2,3]
We introduced an arbitrary threshold for measurement of the size of myocardial infarction to delineate nonviable myocardium in the area at risk
Fig. 3. – Intravital and post-mortem visualization of the ischemic-reperfused area of the heart with indocyanine green (ICG). (a), (b) – Perfusion defect immediately after ICG administration; (c), (d) – Intravital epicardial ICG fluorescence; (e), (f) - Epicardial ICG fluorescence in the excised heart; (g), (h) – Transverse heart slices stained with Evans Blue and ICG obtained after 30 min of reperfusion
Summary
Experimental models of myocardial infarction are widely used to study the mechanisms and pathophysiology of ischemia-reperfusion injury, post-infarction cardiac remodeling and for studies on cardioprotection [1,2,3]. The consequences of myocardial infarction depend on the severity of the injury and the size of the myocardial infarction. The golden standard of assessing infarct size in experimental studies is the triphenyltetrazolium chloride (TTC) assay, functional and biochemical tests give additional information as secondary endpoints [2]. The method with TTC staining is based on histo-enzymatic reactions of dehydrogenase enzymes and cofactors in the tissue with TTC to form a formazan pigment [2]. Formazan stains viable myocardium in a red-brick color. A limitation of this method is that the results are reliable only after ≥ 60 min of reperfusion [4]
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