Abstract
A method to estimate the speed and direction of wave propagation of cardiac excitation in optical mapping and the utility are presented in this paper. Optical mapping has been widely used in arrhythmia studies where an isolated animal heart is stained with a membrane voltage-sensitive dye. We developed an optical mapping system consisting of a high-speed CMOS camera with high spatial resolution and advanced our understanding of the basic mechanisms of arrhythmia. Conduction velocity, the local velocity of the propagation of cardiac excitation, depends on cardiac tissue properties, fiber orientation, wave-front curvature, past activity, and drug effects. Conduction velocity is important to analyze the dynamics of cardiac electrical activity and must be estimated accurately by the accurate determination of depolarization times. However, it is difficult to obtain depolarization times correctly in optical mapping data because optical mapping has low temporal resolution. Taking advantage of the high spatial resolution in optical mapping, we extracted wavefronts from each frame of an optical mapping to obtain depolarization times and estimate conduction velocity by polynomial fitting to the times and positions of the wavefronts. Our method was applied to simulated data, epicardial activation during pacing and spiral wave reentry, which is known as one of the mechanisms to occur and maintain tachyarrhythmia, and estimated vector fields. For simulated data, the calculated velocity agreed well with the actual simulated velocity. In cardiac wave propagation during pacing, our method was able to estimate not only the mean conduction velocity, but also instantaneous conduction velocity. In spiral wave reentry, we quantitatively analyzed the delay of conduction velocity near the spiral wave reentry core and the relationship between conduction velocity and fiber orientation. Our method will be useful for the quantitative analysis of complex arrhythmia in optical mapping.
