Histologic analysis of transmyocardial channels: comparison of CO2 and holmium:YAG lasers.

Background. Transmyocardial laser revascularization using different lasers is being tested in the treatment of refractory angina. We conducted comparative analysis of the acute and chronic myocardial effects of these different lasers. Methods. Transmyocardial channels were made in normal dog hearts with either a holmium: yttrium-aluminum garnet or a CO 2 laser. Channels were examined histologically 6 to 24 hours, 2 to 3 weeks, and 6 weeks after creation. Results. Regardless of the laser source, the channels were occluded by thrombus within 6 to 24 hours. Subsequently, organization and neovascularization of the channel region occurred. Thermoacoustic damage was initially greater with the holmium: yttrium-aluminum garnet laser, but the channel appearances were indistinguishable from those made with the CO 2 laser by 6 weeks. Conclusions. Histologically, the myocardial effects of the CO 2 and holmium: yttrium-aluminum garnet lasers are similar and differ predominantly in the amount of acute thermoacoustic injury. Channels are rapidly occluded by thrombus and are replaced by neovascularized collagen. This suggests that the physiologic effects of these two lasers may be similar and that mechanisms other than blood flow through chronic patent channels should be considered as contributing to the clinical benefits observed with this procedure.