Despite expectations that excimer laser ablation would result in a low incidence of coronary dissection, studies have documented a 15-20% incidence of dissection (including a 4-6% incidence of clinically significant dissection) during excimer interventions. This investigation sought to determine if pressure pulses produced by the exposure of fluid phase media (blood and contrast) to 308-nm excimer radiation might contribute to untoward outcomes. Pressure pulses generated in these media were quantitated to be > 100 atm. In vitro ablation of porcine aorta in the presence of blood or contrast resulted in tissue dissection, while ablation in pure crystalloid did not. Next, a "flush and bathe" technique designed to replace all blood and contrast with crystalloid was applied to a pilot population of 57 consecutive patients. There were no rhythm disturbances or laser-related clinically significant dissections in this group, and the clinical success rate was 95%. In summary, this report quantitates a potential etiology for excimer dissection and suggests that replacement of blood and contrast with crystalloid might improve procedural and clinical success rates.

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A xenon chloride excimer laser system has been approved for use in the treatment of coronary artery disease for the following indications: (1) lesions longer than 20 mm, (2) moderately calcified lesions, ( 3 ) total occlusions crossable with a guidewire, (4) undilatable or uncrossable balloon angioplasty failures, (5) ostial lesions, ( 6 ) lesions in saphenous vein bypass grafts. This series of indications represent a set of lesions which have been associated with lower success rates when treated by balloon alone. This series of indications is also much broader than those available for atherectomy devices. The results of the US and European multicenter registries involving over 1500 patients have been reported by Baumbachl. Both 1.4 and 1.7 mm diameter catheters have been approved for use. The catheters are similar in design employing multiple optical fibers coaxially arranged around a central guidewire lumen. The precise ablation possible with this laser results in a channel through the lesion which is approximately equal to the diameter of the catheter. As a result, most cases require the use of adjunctive balloon angioplasty. The advantage of first using the laser, however, is that a more difficult lesion may be reduced in complexity for the subsequent balloon dilation.Although the treatment of these lesions represents an important advancement in the treatment of coronary artery disease, it is easy to imagine other indications for excimer laser angioplasty. Laser angioplasty can be a "forward looking treatment; I' therefore, the treatment of total occlusions not crossable with a guidewire is an important indication. A second important indication is "stand-alone" laser angioplasty, that is, eliminating the need to follow with subsequent balloon dilatation.Early attempts to treat occlusions with a laser involved the use of a balloon to support and center a single, bare fiber.2 These cases were less than successful, not only because of the configuration but also because of the choice of the laser2. Advances in the development of multifiber laser catheters have allowed for the design of wire-like devices that contain a bundle of small diameter optical fibers (<50 microns) .In addition, the outside diameter of the wire is less than 0.5 mm, reducing the risk of perforation. The challenge remains to insure adequate guidance across long obstructions and around bends.Similarly, the catheter technology has now progressed to the point where it is possible to build devices which manipulate the distal end of the catheter in such a way as to produce a channel larger than the primary diameter of the catheter. Devices such as these will lead to "stand-alone" laser angioplasty. Devices which 251