Optical properties of normal, diseased, and laser photocoagulated myocardium at the Nd:YAG wavelength

Abstract

Laser photocoagulation of the myocardium effectively destroys arrhythmogenic foci. The purpose of this study was 1) to compare the optical properties of canine myocardium before and after photocoagulation, 2) to compare the canine model with clinical cases by measuring the optical properties of human myocardium, and 3) to assess the optical properties of human myocardial scar and epicardial fat tissue. Measured optical properties were the absorption coefficent, μ_a; scattering coefficient, μ_s; and scattering anisotropy factor, g. Optical measurements were performed at 1064 nm wavelength on thin plane parallel tissue slices using the integrating sphere method with glass hemispheres on either side of the sample. The study showed 1) an increase of the scattering coefficient by 40% and a two‐ to threefold increase in reduced scattering coefficient as a result of photocoagulation; 2) that the μ_a (0.035 ± 0.024 mm⁻¹) and μ_s (17.9 ± 3.8 mm⁻¹) of human myocardium were not significantly different from μ_a (0.043 ± 0.021 mm⁻¹) and μ_s (17.3 ± 2.2 mm⁻¹) of canine myocardium, whereas the human g (0.964 ± 0.005) was slightly different from the canine g (0.974 ± 0.008); and 3) that the μ_a (0.021 ± 0.016 mm⁻¹) of epicardial fat and μ_s (13.8 ± 1.1 mm⁻¹) of myocardial scar were significantly lower than those of normal myocardium. A dynamic model of laser‐tissue interaction incorporating these changes and inhomogeneities is necessary to better describe light distribution during laser photocoagulation.