Characteristics and mechanism of myocardium tissue laser ablation: in-vitro study for transmyocardial laser revascularization

To investigate the optimum laser condition for transmyocardial laser revascularization, ablation characteristics of porcine myocardium tissue have been measured in vitro in the spectral region from UV to near IR (230 - 1064 nm). In experiments, a nanosecond, tunable optical parametric oscillator and a Q-switched Nd:YAG laser (the fundamental band and its 2nd, 3rd, and 4th harmonics) were used for ablation. Measurement of ablation hole depth and diameter, and histological analysis with an optical microscopy were performed. It was found that the ablation efficiency increased and the thermal damage threshold of the tissue decreased with decreasing the wavelength. However, at relatively high fluences (approximately 5 J/cm2), unexpected deep ablation was obtained with a 1064-nm laser light, where not thermal but acoustic damage was observed near the walls of the ablation holes. Because intense laser- induced plasma was observed in this case, the shock wave would contribute to removal and/or damage of the tissue.