A wearable cardiac monitor for long-term data acquisition and analysis

Abstract

A low-power wearable ECG monitoring system has been developed entirely from discrete electronic components and a custom PCB. This device removes all loose wires from the system and minimizes the footprint on the user. The monitor consists of five electrodes, which allow a cardiologist to choose from a variety of possible projections. Clinical tests to compare our wearable monitor with a commercial clinical ECG recorder are conducted on ten healthy adults under different ambulatory conditions, with nine of the datasets used for analysis. Data from both monitors were synchronized and annotated with PhysioNet's waveform viewer WAVE (physionet.org) [1]. All gold standard annotations are compared to the results of the WQRS detection algorithm [2] provided by PhysioNet. QRS sensitivity and QRS positive predictability are extracted from both monitors to validate the wearable monitor.

Fig. 1

“L”-shaped wearable cardiac monitor. Clearly visible are the battery, MSP430 and eight spansion FLASH chips as well as the five electrode buttons used to connect the monitor to wet electrodes.

Fig. 2

Electrode and surrounding circuitry with switching network. This switching network allows for configurability of the electrodes without sacrificing power consumption.

Fig. 3

Instrumentation and configurable gain stage including ground drive circuity. The overall system gain is configured during user setup to be between 400 and 950. The output of amplified ECG signal passes through a simple low-pass filter before digitization by the built-in ADC of the MSP430.

Fig. 4

Timeline of the clinical protocol. Boxes labeled C signify calibration of the continuous blood pressure monitor. All boxes labeled C are 1 min long except for calibration after the running portion, which was 2 min to allow the patient extra rest. Lying down, sitting, standing, walking and running all lasted 5 min. The green blocks indicate light movement, yellow blocks indicate moderate movement, red indicate heavy movement and blue indicate rest.