Automated analysis of determinants of wavefront propagation and block during fibrillatory conduction in the rabbit heart: A study using high resolution laser imaging and stereoscopic shape reconstruction

An automated analysis technique was applied to images of disorganized fibrillatory activation in a cryoablated rabbit heart obtained with a laser imaging system to evaluate proposed mechanisms responsible for wavefront propagation block. A laser imaging system was used which provides high spatial and temporal resolution images of cardiac activation from a heart stained with a voltage-sensitive dye. A stereoscopic camera system was developed for use in conjunction with the laser imaging system to allow for three-dimensional shape reconstruction of the surface of the heart to enable accurate geometric measurements. An automated analysis technique was developed which identifies actively depolarizing wavefronts and tracks their movement. Multiple measurements along the length of the wavefront outline of the shape and movement of the wavefront were obtained. The anisotropic properties of the heart were quantified and used to adjust the measured properties into their equivalent isotropic state so that measurements obtained at different orientations relative to the longitudinal axis could be compared. Three properties that have been proposed as determinants of wavefront propagation block were examined. Refractoriness was measured in the form of potential at activation and compared to the incidence of propagation or block. It was found, in agreement with theory and previous studies, that as the activation potential increased the propagation incidence decreased. Wavefront curvature was also evaluated. It was found that as the wavefront became more convex the propagation incidence dropped. The orientation of propagation was also evaluated. It was found that the propagation incidence for propagation oriented in the transverse direction was lower than for propagation oriented in the longitudinal direction. Binary logistic regression analysis showed that all three properties were statistically significant determinants of propagation block. Activation potential was shown to have the most influence on whether a point on a wavefront propagated or blocked, followed by wavefront curvature, and lastly by orientation of propagation with respect to the longitudinal axis.