Identification of photoproducts liberated by in vitro argon laser irradiation of atherosclerotic plaque, calcified cardiac valves and myocardium.
To determine how laser light effects alterations in cardiovascular tissue, photoproducts liberated as the result of argon laser irradiation of atherosclerotic plaque, myocardium and calcified aortic valve leaflets were analyzed by gas chromatography, gas chromatography-mass spectrometry and absorbance spectroscopy. The products formed in gas phase are those expected when proteins and porphyrins are pyrolyzed--light hydrocarbon fragments, carbon monoxide and water vapor. The laser-generated products dissolved in solution are those expected when a protein chain or porphyrin ring is degraded in a thermal reaction, namely protein fragments and nitrogen heterocyclic ring fragments. These photoproducts are those typical of combustion or thermal degradation, and indicate that the fundamental nature of laser irradiation of coronary plaque, myocardium and calcified valve leaflets is thermal rather than photochemical. Thermal degradation of myocardium is more extensive than thermal degradation of atherosclerotic arteries or calcified valves because the red hue of myoglobin-containing myocardium enhances the absorption of the blue-green argon laser light. In contrast, the yellow-white hue of both atherosclerotic plaque and calcified aortic valve leaflets allows less complete absorbance of the argon laser light, leading to a lesser amount of converted heat and, therefore, less complete thermal degradation.