Stephan E. Friedl

A Model For Evaluation of Arterial Thrombosis Following Interventional Procedures

Abstract. A model to assess thrombus formation following vascular injury was evaluated using various interventional systems. The model consisted of a ‘stretchable’ shunt box that served as an arteriovenous shunt between the carotid artery and jugular vein in dogs. Arterial homografts obtained from both carotid and femoral arteries were mounted between two plastic connectors attached to either side of the shunt box. The opposing walls of the shunt box were then stretched apart to achieve the original length of the arteries. The arterial side of the box was connected to the ipsilateral carotid artery and the venous side was connected to the contralateral jugular vein. Haemostasis valves were placed at the exit ports on the venous side of the shunt box. These were used as an access to the various interventional catheters into the lumens of the homografts. Interventions were performed prior to initiating blood flow. After the interventions, 111indium-labelled platelets were injected on the arterial side of the shunt box and arterial blood flow initiated across the shunt. After one hour of circulation through the shunt box, the blood flow was interrupted, and the homografts were perfusion-fixed with glutaraldehyde and segments removed for radioactive counts and processed for histology.This shunt box was then used to compare platelet adhesion and thrombus formation after balloon angioplasty (BA) to direct laser (LA) and laser-thermal angioplasty (LTA). A total of 28 arteries were used from seven dogs. In each experiment, one homograft was used as control, and three other homografts were treated with either BA, LA or LTA. Following the interventions, 111indium-labelled platelets were injected and circulated for one hour using the dogs native circulation. Labelled platelet counts for BA (19102±4869/cm2; mean±SE) were significantly greater than LA (7038±980/cm2), thermal LTA (5189±1961/cm2), and control (1575±541/cm2), respectively (p<0.05, ANOVA). Histology examination showed few platelets at LA, LTA and control sites whereas extensive platelet adhesion was noted at BA treated sites. The model provided a means to conduct simultaneous comparison of several interventions under similar conditions. In this case thermal treatment of the arterial homografts had the least amount of platelet adhesion.

Laser recanalization of thrombosed arteries using thermal and/or modified optical probes; angiographic and angioscopic study.

The degree of residual stenosis by fresh thrombus after laser recanalization was compared by use of angiography and angioscopy. Fifteen NZW rabbits were used. Occlusive fresh thrombus in rabbit aorta was produced by mechani cal deendothelialization and external constrictions simulating clinical situations. Argon laser angioplasty using microlens-tipped optical fiber and/or 2 mm hot- tip probe was done to recanalize thrombosed aorta in 10 animals. Two-mm hybrid probe was used in 5. Percent area stenosis (% AST) was derived by use of the mean radius method obtained by angiography of stenotic segments in two orthogonal views and/or from angioscopy. All 15 totally occluded vessels with fresh thrombus were recanalized. Four minor perforations occurred. Following argon laser angioplasty with the microlens optical fiber, percent stenosis was reduced to 53% in diameter by angiography and 66 in % AST by angioscopy, and to 48% and 55 respectively following hot-tip probe. After laser angioplasty with the hybrid probe, residual stenosis by fresh thrombus was 37% in diameter on angiography and 63 in % AST on angioscopy. Mean percent AST was 62% with angiography and 52% with angioscopy, and there was no correla tion between them (r =-0.028). Angioscopy provided cross-sectional topo graphic views of thrombosed lumen and showed charring and shrinkage of thrombus following laser angioplasty. This study suggests that (1) continuous-wave laser angioplasty using modi fied optical fibers can recanalize thrombotic vascular occlusion, (2) laser angio plasty by hop-tip probe could evacuate fresh thrombus more than microlens fiber on angioscopy, and (3) angiographic % AST did not correlate with angio scopic % AST.

Effect of mechanical force with laser-thermal probes on the vaporization of atherosclerotic plaque

To define the effect of mechanical force during vaporization of atherosclerotic tissue, commercially available thermal and thermal-optical laser probe systems were used to irradiate fresh homogenous atherosclerotic cadaveric human aorta in air. Force was applied as perpendicular pressure ranging from 5 to 40 gm at 2.0, 3.0, or 4.0 watts. Probe vaporization rate [VR] (tissue penetration in mm/sec) and vaporzation efficiency [VE] (volume of tissue vaporized/joule) were calculated for each irradiation. Probe temperatures [PT] were monitored using K-type thermocouples. The volume of carbonization surrounding each crater was used to quantify the amount of thermal damage [TD]. The following observations were made using these probe systems: (1) For the thermal system, VR was found to be constant with regard to force, but rose abruptly with increasing power from 3 to 4 watts. No significant increase in VE was observed with increasing force (ANOVA, P < 0.10). PT and TD also showed no dependence on force. (2) For the thermal-optical system, VR increased with applied force up to 30 gm, but reached a plateau or even decreased at greater forces. VE increased significantly at forces less than or equal to 20 gm (ANOVA, p < 0.05); however, at higher forces VE began to decrease. PT and TD both decreased with increasing probe force. Comparing the two probe systems revealed that VR and VE were significantly greater (ANOVA, p < 0.0001 and - < 0.005, respectively) but TD was not significantly smaller (ANOVA, p < 0.10) for the thermal-optical system compared to the thermal system. Within the range of energy settings evaluated, increasing mechanical force consistently enhanced vaporization up to 30gm of pressure when using the thermal-optical probe. Using the thermal probe system, this effect occurred abruptly when the power was increased. Thus, mechanical force seems to enhance laser recanalization, however, if much force is applied vaporizatioin efficiency starts to drop.