Simultaneous widefield voltage and interferometric dye-free optical mapping quantifies electromechanical waves in human iPSC-cardiomyocytes

Coupled electro-mechanical waves define heart’s function in health and disease. Genetic abnormalities, drug-triggered or acquired pathologies can disrupt and uncouple these waves with potentially lethal consequences. Optical mapping of electrical waves using fluorescent dyes or genetically-encoded sensors in human induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) offers mechanistic insights into cardiac conduction abnormalities. Interferometric dye-free/label-free wave mapping (without specific sensors) presents an alternative, likely capturing the mechanical aspects of cardiac conduction. Because of its non-invasive nature and spectral flexibility (not restricted to a specific excitation wavelength), it is an attractive chronic imaging tool in iPSC-CMs, as part of all-optical high-throughput platforms. In this study, we developed simultaneous widefield voltage and interferometric dye-free optical imaging methodology that was used: 1) to validate dye-free optical mapping for quantification of cardiac wave properties in human iPSC-CMs; 2) to demonstrate low-cost optical mapping of electromechanical waves in hiPSC-CMs using recent near-infrared (NIR) voltage sensors and orders of magnitude cheaper miniature CMOS cameras; 3) to uncover previously underexplored frequency- and space-varying parameters of cardiac electromechanical waves in hiPSC-CMs. We find similarity in the frequency-dependent responses of electrical (NIR fluorescence imaged) and mechanical (dye-free imaged) waves, with the latter being more sensitive to faster rates and showing steeper restitution and earlier appearance of wave-front tortuosity. During regular pacing, the dye-free imaged conduction velocity and the electrical wave velocity are correlated; both modalities being sensitive to pharmacological uncoupling and both dependent on gap-junctional protein (connexins) determinants of wave propagation. We uncover strong frequency-dependence of the electromechanical delay (EMD) locally and globally in hiPSC-CMs on a rigid substrate. The presented framework and results offer new means to track the functional responses of hiPSC-CM inexpensively and non-invasively for counteracting heart disease and aiding cardiotoxicity testing and drug development.