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Thermal Effects and Histologic Changes from Nd:YAG Laser Irradiation on Normal and Diseased Aortic Tissue Using a Novel Angioplasty Catheter with a Mobile Optical Fiber: An in Vitro Assessment

Although various laser angioplasty devices are currently being examined, thermal damage and perforation of the vessel wall remains the major acute complication of vascular laser recanalization. Consequently, the aim of this study was to investigate the thermal effects and histologic changes from laser irradiation (Nd:YAG, 1064 nm) on normal and diseased aortic tissue using a novel angioplasty device. During laser emission the coaxially guided optical fiber tip was positioned in reference to the end hole of the metallic capped probe as follows: (1) at the end hole (metal-cap position), (2) protruding 10 mm from that end hole (bare-fiber position), (3) withdrawn 5 mm into the metal cap's lumen (hot-tip position). In total, 96 laser impacts (25 joule: 5 W, 5 s, each) were produced on normal and atherosclerotic aorta in air through a 0.2-mm-core-diameter silica quartz fiber, with direct contact on the intimal surface of the target tissue by both the fiber and the metal cap and by either the fiber or the metal cap (n = 32 each). Tissue temperature was measured by means of special sensors positioned opposite the irradiated intimal spot in direct contact with the adventitial surface. Morphohistologic evaluation of lesions was performed and injury indexes were determined. Thermal injury (on normal aorta) for the metal-cap position was 0.063 ± 0.02 versus 0.42 ± 14 and 0.13 ± 0.03 for bare-fiber and hot-tip position, respectively (p< 0.001). In the metal-cap position of the optical fiber tip the metal cap appears to act as a "heat sink" to decrease the lateral spread of thermal injury and thereby reduce the risk of perforation and enhance the safety of tissue ablation for potential vascular laser recanalization.