Evaluation of calcified mitral valves after Er,Cr:YSGG irradiation using Optical Coherence Tomography

Abstract

Mitral valve is responsible to control the left atrium-ventricle blood flux. Mitral stenosis is a disease that occurs in consequence of calcification and fibrosis on the cuspids of the valve. Diagnosis can be performed using echocardiography.Many treatments are possible, and one of them is commissurotomy (surgical approach).High intensity laser irradiation may be a new strategy for this surgical technique[1], and the optical coherence tomography (OCT) may contribute to the valve evaluation[2], asit provides higherspatialresolutionin exchange of lower penetrationthan ultrasonography. In this way, the aim of this study is to evaluate laser irradiation effectsincalcified mitral valvesusing OCTand digital processing.To that, it was conducted an ex-vivostudywith four human mitral valvessamples,obtained from valve replacement surgeries in the Heart Institute.The samples were splitin four groups: scalpel cut, laser cut, scalpel debridement and laser debridement.Cutting and debridement procedures were performed in calcified regions of the valves, usinga disposable scalpelbladeand anEr,Cr:YSGG laser(Waterlase; Biolase Inc., CA, USA), emitting at 2780 nm. The laser parameters were set at power = 1.6W, frequency = 20 Hz, energy density = 28.3J/cm2,pulse duration = 700 μs, 15% of water and 15% of air.The imaging was performed using a spectraldomain OCT system(Callisto110C1;ThorLabs Inc., NJ, USA).It was acquired10 B-scans per sample, 5 inprocedures regions and 5 in sound regions. The Optical Attenuation Coefficient (OAC) was calculated by comparing a beer-lambert like equation to exponential fittings of the A-scans[3].The distribution and normality of variances were tested using Shapiro-Wilk test,and statistical comparison was performed using one-way ANOVA and Tukey’s post hoc. All tests considered a level of significance of 5%.The FigureAshows a representative B-scan of a visibly calcified region, where a pattern of higher intensities can be observed.Thispattern is related tomorphological and optical changes, mainly a refractive index change, due to calcium presence in the valve tissue.This B-scan was acquired only to understand the calcified tissue aspect, as the procedures regions does notpresent visibly largecalcium stones.The Figure Bshowsthe statisticalanalysis, where the sound OAC values, as a mean of all sound regions, presented a significant statistical difference in comparison to scalpel groups, while no difference waspresentedin relation to laser groups. Higher OAC values are related to anaugmentation of the light backscatteringdue to calcium refractive index, leading to a change of lightpropagation in tissue-calcium interfaces.This finding indicates thatthe laser procedures promoted a better removal of calcified tissue than the scalpelmethods, which can be related to tissue-ablation interaction.Furthermore, the statistical difference between scalpel cut group and both laser groups suggests that the scalpel needs more wear interaction with the tissue, such as in the debridement procedure, being unable to significatively remove the calcification in a single cut.This study points the Er,Cr:YSGG and the OCT as potential techniques for the calcified tissue removal and evaluation,respectively, duringmitral valvessurgeries, although further studieswith higher sample numbermust be performed.