We studied microvascular injury after myocardial cryothermia in rats u
sing intravital fluorescence microscopic techniques. Cryolesions were
induced to the right ventricle by freezing with -160 degrees C (probe
diameter: 5 mm) for a total of 5 min. Fluorescence microscopy was perf
ormed at 15, 30, 60, 90, and 120 min as well as at 3 and 7 days after
cryothermia. Analysis of the epicardial microvasculature 15 min after
cryothermia revealed an area of 24.6 +/- 3.8 mm(2) of nonperfused tiss
ue, which was reduced to 5.3 +/- 1.5 mm(2) (P < 0.05) after the initia
l 2-h observation period. Vital microscopic images of reperfused tissu
e characteristically demonstrated extravasation of the macromolecular
fluorescent tracer FITC-dextran (21.7 +/- 3.4 mm(2)), suggesting subst
antial loss of endothelial integrity. In vivo propidium iodide stainin
g confirmed membrane damage of microvascular endothelial cells. Three
days after cryoinjury the area of nonperfused tissue was reduced furth
er to 1.1 +/- 0.4 mm(2) in the center of the lesion, while the area of
perfused tissue with disruption of endothelial integrity was found si
gnificantly increased to 47.4 +/- 5.9 mm(2) (P < 0.05) toward the peri
phery. Analysis at 7 days revealed endothelial repair at the periphery
of the cryolesion, but now a central necrotic area was found demarcat
ed (nonperfused), presenting with a size (26.0 +/- 3.5 mm(2)) similar
to that shown during the very early (15 min) reperfusion period. Our s
tudy demonstrates recovery of microvascular perfusion during the first
hours and days after myocardial cryothermia. This is, however, associ
ated with endothelial injury, i.e., damage of plasma membrane and loss
of barrier function. Infarction with capillary perfusion failure is e
vident at 7 days with a size which strikingly corresponds to the size
of nonperfused tissue observed immediately after cryointervention. (C)
1998 Academic Press.