Coordinated cardiac conduction plays an important role in cardiogenesis, not only for initiating rhythmic contractions of cardiac myocytes for efficient blood pumping, but also for maintaining normal cardiac development. Optical mapping (OM), which u...
Coordinated cardiac conduction plays an important role in cardiogenesis, not only for initiating rhythmic contractions of cardiac myocytes for efficient blood pumping, but also for maintaining normal cardiac development. Optical mapping (OM), which uses fluorescent voltage-sensitive dyes to measure membrane potential is currently the most effective method for electrophysiology studies in early embryonic hearts due to its noninvasiveness and large field-of-view. OM has two major limitations: 1) it projects signals from part of a 3D sample to a 2D map therefore the electrophysiological information is incomplete, orientation-dependent and ignorant of 3D topology of the sample; 2) it requires excitation-contraction (EC) uncoupling drugs to stop the contraction of the heart, yet EC-uncouplers may affect calcium handling, ion channel kinetics and action potential characteristics. This dissertation focuses on overcoming the limitations of OM and improving cardiac conduction imaging in embryonic hearts. First, OM was integrated with optical coherence tomography (OCT), which is capable of capturing the 3D topology of the looped embryonic heart. A 3D conduction velocity correction algorithm was developed. This eliminated underestimation bias in 2D conduction velocity calculation and provided more accurate 3D corrected conduction velocity measurements. Second, 4D OM in the embryonic heart was achieved with light-sheet fluorescence microscopy. We built a fast light-sheet system that illuminated the sample with a sheet of light generated by a cylindrical lens and collected OM signals from an orthogonal direction. OM data from multiple slices throughout the looping stage quail embryonic hearts were acquired. With this imaging system, complete, orientation independent, four-dimensional transmembrane potentials were demonstrated. Next, correction of motion artifacts in freely beating embryonic hearts was demonstrated using a B-spline nonrigid registration algorithm. Activation maps and conduction velocity measurements calculated from motion-corrected and the motion-free recordings are comparable. Finally, cardiac neural crest cells (CNCCs) were ablated in quail embryos as a congenital heart disease (CHD) model. Structural and functional defects at early and late stages were detected. This model will be applied in the investigation of how abnormalities in the conduction system arises. The imaging tools and CHD model developed here will significantly benefit the investigation of both normal and abnormal developmental cardiac electrophysiology.