Experimental validation of alternating transillumination for imaging intramural wave propagation

Current techniques to map intramural activation patterns in ex vivo cardiac tissue have limited spatial resolution. Here, we report on the experimental validation of a novel optical technique that was recently proposed to resolve the size and depth of intramural wave fronts using alternating transillumination (AT). AT was achieved by simultaneously mapping the epi- and endocardial surfaces with two synchronized CCD cameras and rapidly alternating LED illumination between both surfaces. Optical phantoms were made based on tissue optical properties measured using a hybrid optical spectrometer. Spherical fluorescent sources (Scarlet microspheres, Invitrogen, UK) of varying sizes were embedded at known depths in the phantoms. Coronary-perfused procine left ventricular slab preparations were stained with DI-4-ANBDQBS (n=3) and paced at known intramural depths. In phantoms we were able to reliably estimate the depth of the center of fluorescent sources (9.6±5.4% error), as well as their transmural extent (15.7±11.5% error). In ventricular slabs we were able to localize the sites of origin of intramural excitation waves with a precision of ±1.6 mm. Transmural conduction velocities were, for the first time, measured optically from the surfaces and found to be 21.0±12.4 cm/s. In conclusion, alternating transillumination is a promising technique for reliable reconstruction of depth and expansion rate of intramural activation wave fronts in cardiac tissue.