ANGIOGENESIS IN TRANSMYOCARDIAL LASER REVASCULARIZATION - A NONSPECIFIC RESPONSE TO INJURY

Background-The mechanism of action of transmyocardial laser revascular ization (TMR) is poorly understood. TMR has been shown to stimulate an giogenesis in porcine and canine myocardium. Methods and Results-We ex amined the possibility that angiogenesis also occurs in ovine myocardi um and that it is a nonspecific tissue injury response. Five Dorset sh eep underwent creation of transmyocardial channels of equal diameter i n both the apical and basal regions of the left ventricle through the use of both CO2 laser in 1 region and a power drill in the alternate r egion of the same heart. All channels were closed at 4 weeks. Histolog y showed channel remnants composed of granulation tissue, fibrosis, an d new vessels (NV). These changes were not distinguishable on the basi s of the method of channel creation. The average diameter of the chann els was similar (laser, 630+/-180 mu m; drill, 750+/-280 mu m) (P=NS). NV with smooth muscle media were seen within the channel remnant and immediately surrounding this region using Verhoeff-Van Gieson (elastic ) stain. The densities of the NV within the channel remnants were simi lar (laser, 1.87+/-1.05 NV/high-power field [hpf]; drill, 1.92+/-1.09 NV/hpf; P=NS), and both were significantly greater than the density of vessels in remote regions, >5 mm from the channel center (remote lase r area, 0.09+/-0.28 NV/hpf; remote drill area, 0.04+/-0.21 NV/hpf; P=N S for remote areas, P<0.001 for laser versus remote laser, P<0.001 for drill versus remote drill area). Conclusions-These findings demonstra te that the CO2 laser stimulates angiogenesis in normal ovine myocardi um and suggest that this response represents a nonspecific reaction to tissue injury.