Comparison of continuous-wave lasers for endarterectomy of experimental atheromas

Development and application of modern devices in vascular surgery including comment on modern antithrombotic and lytic drug therapy

Since modern vascular surgery started with the discovery of heparin and the development of modern vascular grafts including autogenous saphenous vein, the speciality has been technologically driven. At the outset, vascular surgery depended almost entirely on the development of specialized clamps, instruments, and tools to permit decisive attack on the problems of occlusion. No less important was the development of insight into the basis of atherosclerosis, the discovery that atherogenesis with thrombosis is electrochemically identical to corrosion in pipes and therefore subject to chemical forces, which have not yet been delineated, as well as mechanical forces which have been delineated and permit one to attack the atheroma directly. Thus, classic replumbing techniques including bypass and endarterectomy have long been a part of the fundamental firmament of vascular surgery. Most recently, modern techniques in cleaning out blood vessels, removing occlusive processes, and modern thrombus-dissolving enzymes have all come to the forefront. Frequently multiple techniques are used simultaneously. This article is an attempt to summarize various aspects of this activity and describe several of the patents which have been seminal in the ultimate application of the techniques in both experimental animals and man. This should be the first of a series of efforts to summarize this area. The process of change has never been more kinetic than now.

Neodymium:yttrium-aluminum-garnet laser fusion of endarterectomy flaps

PURPOSE

This study evaluated the efficacy of neodymium:yttrium-aluminum-garnet laser welding of flaps in canine arteries and in securing the distal flap during human carotid endarterectomy.

METHODS

Endarterectomy flaps were created in both common carotid and both common femoral arteries in 12 dogs. The flaps were repaired with either the neodymium:yttrium-aluminum-garnet laser or with 6-0 polypropylene sutures. The arteries were removed after duplex scanning at either 7 or 28 days. Eighteen high carotid endarterectomy flaps in 16 patients have been subsequently secured with the laser welding technique.

RESULTS

Laser repairs (125 +/- 19 joule) of the canine arteries were completed more quickly than suture repairs (mean 25 seconds vs 135 seconds, respectively; p < 0.04). Duplex ultrasonography revealed no discernable differences between the two groups of arteries. Arteries studied at 7 days revealed three microscopic flaps (two suture, one laser), more subintimal fibroblastic proliferation in suture than laser-repaired carotid arteries (3: 1, p = 0.0530), and similar amounts of inflammation in suture- and laser-repaired arteries. Arteries studied at 28 days revealed one microscopic intimal flap (suture-repaired); equal fibroblastic and inflammatory responses in suture- and laser-repaired vessels; and no evidence of laser thermal injury. Eighteen carotid endarterectomy flaps have been successfully fused with no immediate or long-term complications in 16 patients (follow-up of 0 to 24 months).

CONCLUSION

Laser fusion appears to be a safe and effective method for securing distal carotid endarterectomy flaps.

Excimer laser radiation for endarterectomy of experimental atheromas

Open laser endarterectomy produces a smooth arterial surface with welded distal end points. This report evaluates 308-nm excimer laser radiation for the laser endarterectomy operation. Arteriosclerotic New Zealand white rabbits (N = 15) were studied. A thoraco-abdominal exploration was performed, the aorta was isolated, heparin was administered, and multiple endarterectomies were performed in each rabbit. A line of laser craters was created at the proximal and distal ends of an atheroma. Laser radiation was used to connect the craters to form the proximal and distal end points. The atheromas were dissected from the aorta with laser light and the end points were fused. The aortas were removed for light and electron microscopy and the animals were sacrificed. Excimer radiation was delivered by a 600-microns fiber at 50 mJ/pulse, 120-ns pulses and either 15- or 20-Hz frequency. At 15 Hz excimer laser endarterectomies showed no perforations along the surface or at the end points. The surfaces were smooth but the end points were not welded in place. At 20 Hz, perforations were seen along 7/11 surfaces and at 5/11 end points. Excimer laser endarterectomy is best performed at 15 Hz. The end points, however, cannot be welded with excimer laser radiation.

Comparison of contact and free beam laser endarterectomy

Free beam laser endarterectomy (LE) and contact laser endarterectomy (CLE) were compared in 15 arteriosclerotic New Zealand white rabbits. The rabbits underwent balloon catheter trauma to the thoracoabdominal aorta and were fed a 2% cholesterol diet for 18 weeks. Thoracoabdominal exploration was performed under general anesthesia and multiple endarterectomies were performed in each rabbit. Atheromas were dissected from arteries with laser radiation and end points were welded in place with laser radiation. LEs (N = 8) were performed with argon ion radiation delivered through a 400 microns fiberoptic. Power was kept constant at 1 W and the average fluence was 97.5 +/- 6.6 J/cm2. CLEs were performed with conical sapphire probes powered by either argon ion radiation (N = 12) or Nd-YAG radiation (N = 10). Power used was 1 W to 4 W for each laser. Average argon ion fluence was 117.8 +/- 3.1 J/cm2 and average Nd-YAG fluence was 611.1 +/- 34.4 J/cm2. Following the operations, aortas were removed, fixed, serially sectioned, and stained. Microscopic study revealed welded end points with LE but not with CLE. There were no perforations with LE. There were 11/12 perforations with argon ion CLE and 8/10 perforations with Nd-YAG CLE. Free beam laser endarterectomy is superior to contact laser endarterectomy for experimental atheromas.