Waveform Capture? All You Need is a Smartphone

Abstract

HeartWare assist device (HVAD) monitor provides flow and power waveform information which has been shown to respond to changes in physiological loading conditions, cardiac contractility and aortic valve status. Instantaneous point data is recorded every 15 minutes into the controller logfile. Because some phenomena are of short duration or need an immediate intervention (such as suction or tamponade), significant changes may not be captured within the logfile. We present a simple method to capture the displayed waveforms via a smartphone photo followed by re-digitization for data extraction. Waveform recording provides an opportunity for teaching or research. During an interesting event, a photo of the screen of the HVAD monitor is taken. The photographer will take care to capture the border of the waveform screen as reference. The second step is the restitution of parallel lines using the smartphone application TurboScan (picksoft, V.3.0.2). This will use the border of the screen to straighten the whole picture. Loss of quality can happen during this stage if an extreme angle is used. To reconstruct the axis, we feed the picture in WebPlotDigitalizer (Atomeris, V.4.2). Using the built-in VAD-screen scale, the software will output a table of calibrated values corresponding to the flow or power trace. Using an R-script (3.6.1) written within R-studio (V.12.1355), we can reproduce flow and power waveforms identical to that displayed from the HVAD controller with sampling frequency of data up to 100Hz. This can be used as an algorithm input for further waveform analysis (waveform, rhythm, PI) or for illustration purposes. Our illustrative case shows a photo taken during a normal VAD-clinic appointment and reconstituted using our technique. This technique is cheap, easy to use at the bedside or clinic and represents an opportunity to capture interesting waveform events for teaching or illustration purposes or subsequent algorithm development.