Figure 1. 3-D reconstruction of cardiac electrical activity in isolated porcine RV wall. The slab was paced at 400 ms BCL on the epicardium and was stained with the NIR voltage-sensitive dye JPW-5034. The epicardium was scanned with a 50 mW diode laser (685nm) in 196 points and optical signals were recorded from the endocardium (biaxial scanning). Reconstruction was achieved by using our multiplicative tomography algorithm. The picture shows the activation front 6 ms after stimulation.
Optical imaging utilizing voltage-sensitive dyes has become a powerful tool for the analysis of cardiac excitation. Until recently, it has been primarily used for fluorescence surface recordings, where only the subsurface layers beneath the epicardial surface were shown to contribute to the optical signal. However, the myocardial wall can be up to 1 cm thick and imaging of the heart electrical activity throughout the thickness of the ventricular muscle would greatly add to the understanding of the mechanisms underlying cardiac arrhythmias.
Our research focuses on the development of novel algorithms for the three-dimensional reconstruction of cardiac electrical activity from optical signals. We have developed hybrid electrical-optical models for the synthesis of optical signals emanating from typical activation patterns in the myocardial wall (forward problem). These hybrid models have provided better insights in the genesis and interpretation of optical signals and also provided the basis for the solution of the inverse problem: reconstruct 3-D activity from 2-D images. We are currently applying techniques from diffusive optical tomography involving matrix inversion and regularization. We have also developed a novel multiplicative algorithm based on biaxial laser scanning. These methods have been validated computationally and are currently being tested in vitro.
3D reconstruction of a propagating wave initiated at 3 mm under the epicardial surface in an 8 mm thick right ventricular wall (biaxial scanning method).
3D reconstruction of the electrical wave in a 12 mm thick left ventricular wall of a pig heart with a non-conducting ischemic region (biaxial scanning method).
3D reconstruction of the electrical wavefront in a 10 mm thick right ventricular wall of a pig heart, following point epicardial stimulation (alternating trans-illumination method).
