Open-Source Solution Could Lower Cost of Optical Cardiography

An open-source solution for multiparametric optical mapping of the heart’s electrical activity, developed by an international research team, could further understanding of the mechanisms underlying cardiac arrhythmias. The 3D models of the mapping system components and the source code for the data analysis have been made openly available by the researchers at the Moscow Institute of Physics and Technology (MIPT) and The George Washington University (GW), to enable other research groups to benefit from the new solution.

Researchers can download specific pieces of a mapping system they want to replicate or the entire system, which supports specialized optical equipment including cameras, lenses, and mirrors. Courtesy of The George Washington University.

The researchers developed an open-source and expansible system that simultaneously tracks cardiac electrical excitation and intracellular calcium dynamics. Every system component, excluding cameras, lenses, and pumps, was 3D printed. Since the designs of all components are open source, any laboratory can use the designs to create a similar tool. The researchers calculated that this could save other labs about $20,000, compared with commercially available products. This approach also allows easy customization and rapid, inexpensive prototyping, providing optical mappers and other investigators with an alternative that could mitigate the overall cost of optical mapping systems and catalyze new study protocol development.

Excitation propagation in a mouse heart with simultaneous use of voltage-sensitive dye RH237 (a, left) and calcium-sensitive dye Rhod2AM (a, right). Action potential and calcium transient recordings of whole mouse heart (b) and rat cardiac slice (c). Courtesy of Brianna Cathey et al./Scientific Reports.

The functioning of the system was demonstrated by optical mapping of whole mouse hearts and rat cardiac slice preparations, to simultaneously record voltage and calcium signals. The custom-designed electrocardiogram (ECG) electrode holder improved the quality of the recorded pseudo-ECG traces.

Along with the designs for the system components, the team open-sourced the code of their MATLAB-based RHYTHM software for signal processing. While a previously released version of this software allowed for analysis of action potential duration, generation of activation, and phase maps, the updated version, RHYTHM 1.2, analyzes several additional parameters of voltage and calcium recording.

Optical mapping is currently the leading technique for investigating the mechanisms behind arrhythmias. A number of intracellular parameter changes can be tracked this way using high-speed cameras, but the high cost of the equipment and the technical challenges of monitoring multiple parameters at the same time and processing the associated signals have prevented widespread use of optical mapping in the biological community, the researchers said.

“Our laboratory maintains an open data policy,” said professor Igor Efimov of GW, who also heads the Human Physiology Lab at MIPT. “Not many research teams nowadays can afford the expensive equipment for optical mapping. Now they can use our designs to re-create an affordable system just like the one we used. And they can process the data with RHYTHM. A further advantage of our tool is that it offers the freedom to design new experiments on diverse samples.”

The research was published in Scientific Reports (https://doi.org/10.1038/s41598-018-36809-y).