Infarct size measurement by triphenyltetrazolium chloride staining versus in vivo injection of propidium iodide

Infarct size delineation by triphenyltetrazolium chloride (TTC) staining is dependent on sufficient reperfusion. We therefore evaluated the possibility of using propidium iodide (PI), a reagent conventionally used in flow cytometry to fluorescently stain dead cells, for infarct size analysis after short periods of reperfusion. Forty-five rabbits were subjected to either 15 min, 2 h or 4.5 h of coronary artery occlusion without reperfusion, or to 15 min, 30 min and 2 h of coronary artery occlusion followed by 30 min, 1 h and 3 h of reperfusion. Fifteen min before terminating the experiment, PI was injected into the left atrium. Patent blue violet was used to delineate the area at risk. Following incubation in TTC, the area at risk was excised and cross sections obtained for microscopical infarct size quantification by PI fluorescence. PI fluorescence was absent after permanent occlusion and in control areas. Infarct sizes measured by TTC staining were significantly smaller after 1 h of reperfusion as compared to 3 h of reperfusion (30 min occlusion: 1+/-1 v 34+/-9%; P<0.05; 2 h occlusion: 9+/-6 v 47+/-8%; P<0.01). In contrast, infarct sizes determined by PI fluorescence reached values comparable to those measured by TTC staining or conventional histology after longer times of reperfusion already after 30 min of reperfusion (30 min occlusion: 35+/-16.5%; 2 h of occlusion: 61+/-8%). Therefore, after short times of reperfusion infarct size measurement by PI fluorescence is more reliable than by TTC staining.