Motion Artifact Reduction in Ambulatory ECG Monitoring: An Integrated System Approach Iñaki Romero, Torfinn Berset, Dilpreet Buxi, Lindsay Brown, Julien Penders Imec / Holst Centre High Tech Campus 31, Eindhoven, The Netherlands Corresponding author: Julien.Penders@imec-nl.nl Sunyoung Kim, Nick van Helleputte, Hyejung Kim, Chris Van Hoof, Firat Yazicioglu Imec Kapeldreef 75, Leuven, Belgium ABSTRACT Recent advances in low-power micro-electronics are revolutionizing ECG monitoring. Wearable patches now allow comfortable monitoring over several days. Achieving reliable and high integrity recording however remains a challenge, especially under daily-life activities. In this paper we present a system approach to motion artifact reduction in ambulatory recordings, including: selection of electrode configuration, algorithms for motion artifact filtering, custom analog front-ends and integration in wearable electrode patches. A three (bipolar) lead configuration is selected based on literature. Two algorithm methods are tested. The first method applies ICA for de-noising multi-lead ECG recordings. The second method is an adaptive filter that uses skin/electrode impedance as the measurement of noise. A custom ultra-low-power ECG analog front-end read-out is reported for the recording of 3-lead ECG and skin/electrode impedance at only 40 μW. Finally a wireless patch is presented, which records 3-lead ECG, 1-lead electrode tissue impedance and 3D-acceleration, thus providing the necessary data to test and implement motion artifact algorithms. Algorithms, circuits and system provide a platform for reliable ECG monitoring on-the-move. Categories and Subject Descriptors J.3.4 [Computer applications]: Life & medical sciences–Health. General Terms Algorithms, Measurement, Design, Experimentation. Keywords Wearable sensors, ECG patch, motion artifact reduction, ultra- low-power electronics. 1. INTRODUCTION Integrated wearable sensors enable continuous, reliable and long- term monitoring of vital signs and physiological signals on-the- move. In the area of cardiac activity monitoring, recent advances in low-power micro-electronics have revolutionized the concept of ECG monitoring. Holter systems have tremendously improved, and now achieve up to 3 days continuous monitoring. Recently a variety of wearable systems have also been introduced in an attempt to reduce size, improve comfort and extend the duration of monitoring. Product concepts and prototypes of ECG patches have been introduced by several companies and research groups such as: Curvus, Corventis, iRhythm, Toumaz and Delta. Previously we also reported an ultra-low-power ECG platform [14] and a low-power wireless ECG necklace [15], illustrated in Figure 1. The main specifications of a selection of these systems are compared in Table 1. Wearable and wireless devices allow delocalizing ECG monitoring from hospitals to home environments. Achieving reliable and high integrity recording however remains a challenge in ambulatory conditions due to the high level of noise introduced by motion artifacts. For Holter systems, motion artifacts often Table 1: Comparison of the main specifications of selected wearable ECG systems Device Piix (Corventis) [1] iRhythm [2] Imec ECG necklace [3] Sensor modalities ECG (1-lead), Respiration , Skin Temperature, body fluids, accelerometer ECG (1-lead) ECG (1-lead), respiration (derived from ECG), accelerometer Analog front-end Not disclosed Not disclosed imec ULP 1-ch ECG ASIC [9] ADC resolution 10-bits 10-bits 12-bits Functionality Event detection (Arrhythmia) None Beat-to-beat HR and HRV, seizure detection Wireless Connectivity Event sent to z-link; and downloaded for off-line analysis None Real-time interface to mobile phone (using dongle) Power consumption 40 mW Not disclosed 3 mW (data streaming); 7 mW (embedded data processing) Form factor Patch (160 mm x 60 mm) Patch (123 mm x 53 mm) Necklace (60 mm x 40 mm) + lead wires to disposable electrodes Usability Disposable Recycle Re-usable Figure 1: imec ECG necklace [4]