PULSED LASER AND THERMAL ABLATION OF ATHEROSCLEROTIC PLAQUE - MORPHOMETRICALLY DEFINED SURFACE THROMBOGENICITY IN STUDIES USING AN ANNULAR PERFUSION CHAMBER

Although clinical trials using laser and thermal angioplasty devices h ave been underway, the effects of pulsed laser and thermal ablation of atherosclerotic plaque on surface thrombogenicity are poorly understo od. This study examined the changes in platelet adherence and thrombus formation on freshly harvested atherosclerotic aorta segments from Wa tanabe-heritable hyperlipidemic rabbits after ablation by two pulsed l aser sources (308-nm xenon chloride excimer and 2,940-nm erbium:yttriu m-aluminum-garnet [YAG] lasers) and a prototype catalytic hot-tip cath eter. Specimens were placed in a modified Baumgartner annular chamber and perfused with citrated whole human blood, followed by quantitative morphometric analysis to determine the percent surface coverage by ad herent platelets and thrombi in the treated and contiguous control are as. Pulsed excimer laser ablation of plaque did not change platelet ad herence or thrombus formation in the treated versus control zones. How ever, photothermal plaque ablation with a pulsed erbium:YAG laser resu lted in a 67% reduction in platelet adherence, compared with levels in control areas (from 16.7 +/- 2.2% to 5.5 +/- 1.8%; p < 0.005). Simila rly, after plaque ablation using a catalytic thermal angioplasty devic e, there was a 74% reduction in platelet adherence (from 29.2 +/- 5.1% to 7.7 +/- 1.6%; p < 0.005) and a virtual absence of platelet thrombi (from 8.6 +/- 2.3% to 0.03 +/- 0.03%; p < 0.005). This reduced surfac e thrombogenicity after plaque ablation with either an erbium: YAG las er or a catalytic hot-tip catheter suggests that thermal modifications in the arterial surface ultra-structure or thermal denaturation of su rface proteins, or both, may be responsible for reduced platelet adher ence. These in vitro findings indicate that controlled thermal plaque ablation by catheter-based techniques may elicit endovascular response s that can reduce early thrombus formation during angioplasty procedur es.