Perspectives of coronary excimer laser angioplasty: multiplexing, saline flushing, and acoustic ablation control

Bubble formation, pressure wave generation, and cavitations constitute major factors influencing the outcome of clinical Excimer laser angioplasty. Thus, the rationale of this study was to determine the extent of pressure waves occurring during excimer laser ablation and to discuss possibilities that allow a less traumatic plaque removal in the coronary circulation.

Conventional and experimental Xenon-Chlorid-Excimer lasers emitting light at a wave-length of 308 nm and a pulse duration of 115 ns were used for testing of signals. Whereas the conventional excimer laser light source transmits light through all fibers of a 1.7 mm laser catheter simultaneously, the prototype excimer laser divides the laser beam into several areas of uniform energy fluence by scanning the beam from one section to the other using the intermission between two laser discharges. Hydrophones consisting of piezoelectric films detected the acoustic signals, which were obtained on normal arterial wall and atherosclerotic plaque.

Multiplexing decreases maximum pressures for both normal arterial wall and calcified plaque significantly, whereas pressure rise time remains comparable. During ablation of pure blood, a linear increase of peak pressures of 1 MPa at 10 mJ/mm2 to 7.5 MPa at 50 mJ/mm2 is found. Contrast media intensifies the extent of pressure wave formation. At 20 mJ/mm2, 60% contrast media added to blood results in an increase of maximum pressures from 1.5 MPa up to 5 MPa. Dilution with saline solution is effective; however, high concentrations of > 90% are required to achieve a significant pressure wave reduction.

Peak pressures of several thousand kPa occur during excimer laser ablation of contrast media, blood, calcified plaque, and normal arterial wall in a decreasing order. Multiplexing and saline flushing are capable of reducing the intensity of the generated acoustic signals during tissue ablation. It has to be taken into consideration, however, that high concentrations of saline solution are necessary to achieve a significant reduction of peak pressures.