IN VITRO ASSESSMENT OF ATHERECTOMY EFFICACY
Initial tests of the catheter prototype have been completed in human coronary artery necropsy specimens, in vitro. In order to assess the capability of this catheter to cut atherosclerotic plaque, it was used to excise plaque ranging from predominantly fatty and fibrous to calcific. Twenty-eight coronary specimens and 27 aortic specimens were used for this initial in vitro trial. Evidence of cutting was found in most (90~c) specimens on gross morphological examination. After atherectomy, each specimen was fixed with neutral buffered formalin and sent for histological examination. Arterial sections were stained with hematoxylin and eosin and the depth of plaque excision was measured microscopically by ocular micrometry as previously described elsewhere. Of the coronary specimens, there were 23 fibrous/fatty atherosclerotic plaque specimens and 5 calcified plaque specimens cut with the Halliburton endarterectomy catheter. Histological staining was adequate to assess the cut surface on a microscopic basis in 19 coronary artery and 19 aortic sections. The remaining specimens were cut at an angle or the cut edge was missed on the microscopic section; these could not be interpreted microscopically. Clean cut edges were observed on histological examination of l S/ l 9 coronary artery specimens and l S/ l 9 aortic specimens (78%).
Incomplete cut was seen in 4/15 coronary specimens and 4/19 aortic specimens. In both cases there was either complete cut with some ragged edge evident or at the very least partial excision of the plaque. Two specimens with
Incomplete cut had calcific plaque, which is notoriously difficult to cut. In each case of incomplete cut, the plaque had been excised to a residual edge of approximately 10% of the surface. When incomplete cuts were observed on the gross specimens, a second attempt removed the plaque in most instances. Calcified plaque was more difficult to cut, with a success rate of 3/5 (60%) on the 5 calcified coronary specimens attempted to date. This is comparable to the success rate seen with other atherectomy catheters to date. The maximum depth of excision was 120 - 1050ù in the coronary artery specimens and 30 -1000ù in the aortic plaque specimens.