Accurately quantifying embryonic cardiac electrophysiology is important not only for understanding the complex interplay between the conduction system and development of other cardiac tissues, but also for assessing how the conduction system is altered in disease and how this alteration, in turn, can cause congenital heart defects. Optical mapping (OM) using fluorescent voltage-sensitive dyes is a powerful tool for measuring electrical activities of early intact beating embryonic hearts with a large field-of-view. However, conventional OM provides a two-dimensional (2-D) representation of a three-dimensional (3-D) sample, and thus information acquired is incomplete and dependent upon the orientation of the sample, which makes it hard to compare one heart to another. To overcome this limitation, volumetric OM using light-sheet microscopy has been developed. However, the methods for calculating conduction velocity (CV) from volumetric data are lacking. Here, we extend this approach to measure 3-D CV. First, the activation time for each voxel is determined by fitting the upstroke of the action potential trace in time. From this, we find the spatial gradient of activation time. Finally, CV is calculated based on this spatial gradient of activation time. This approach was validated using a 3-D simulated digital phantom, and embryonic quail hearts at looping stages. The conduction patterns in looping hearts are consistent with previously observed features: conduction is faster in the ventricle region and slower at the atrioventricular junction and outflow tract; the inner curvature of the ventricle has slower conduction than the outer curvature.
Shan Ling, Matthew McPheeters, Shi Gu, Michiko Watanabe, Michael W. Jenkins, and Andrew M. Rollins, "Three-dimensional mapping of conduction velocity in early embryonic hearts (Conference Presentation)," Proc. SPIE 10472, Diagnosis and Treatment of Diseases in the Breast and Reproductive System IV, 104720Q (Presented at SPIE BiOS: January 28, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2290028.5751477423001.
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