Use of Excitation Emission Matrices to Reveal Spectral Changes Caused by Radiofrequency Ablation of Cardiac Tissue

New diagnostic catheters can be developed by delivering and acquiring light through a small fiberoptic bundle. This can provide useful real time feedback guidance to observe tissue damage caused by thermal injury used to treat cardiac fibrillation. Yet, little is known about the exact spectral changes caused by radiofrequency ablation (RFA) in different types of cardiac tissue. We hypothesized that the most sensitive optical ranges for characterizing thermal injury can be revealed by comparing spectral information from different areas of the heart before and after RF ablation. Freshly excised porcine hearts were used to acquire and analyze excitation emission matrices (EEMs, 300-600nm) from ventricular muscle, endocardium of the left atria, and aorta. Each type of tissue exhibited distinct EEMs that underwent highly reproducible changes in fluorescence absorption and reflectance upon RF ablation. Specifically, RFA resulted in a reduction of the NADH fluorescence peak in ventricular muscle EEMs (360/460nm excitation/emission maxima). It also led to a broadening and fusing of collagen and elastin fluorescence peaks in the aorta and it had a combined effect on left atrial tissue. RFA led to an increase in specular and diffuse reflectance (seen as higher amplitude and width of the EEM diagonal line) in all three tissue types. Thermal coagulation of heme-containing proteins, including different forms of myoglobin, led to a weaker absorption in the Soret band range (410-430nm). The latter was particularly noticeable in ventricular tissue but was also significant in the left atrial tissue. EEMs can provide a wealth of quantitative information, including types of optical measurements and specific wavelength ranges that can help to develop new diagnostic tools, including hyperspectral imaging techniques, to probe for spectral changes during RF ablation of different parts of the heart.