Investigation into Electrocardiogram Motion Artifact Reduction, 10-9191

Principal Investigator
David A. Tong

Inclusive Dates: 04/01/2000 - Current

Background - The electrocardiogram (ECG) is the body-surface manifestation of the electrical potentials produced by the beating heart. The magnitude, conduction, and duration of these potentials are detected by placing electrodes on the patient's skin. The ECG is the most prescribed diagnostic procedure in medicine and is routinely used to diagnose heart disease, identify irregular cardiac rhythms (arrhythmias), evaluate the effects of drugs, and monitor surgical procedures. Motion artifact is the noise introduced to the ECG signal that results from electrode motion. More specifically, movement of the electrode or lead wire produces skin deformation around the electrode site. The skin deformations change the impedance and capacitance of the skin around the sensing electrode. The impedance and capacitance changes are sensed by the ECG electrode and result in artifacts that are manifest as large amplitude signals on the ECG. The presence of motion artifact can result in misdiagnosis, can prolong procedure duration, and may lead to delayed or inappropriate treatment decisions.

Approach - The hypothesis of this project is that since electrode motion is the catalyst for motion artifact, measuring electrode motion and using the measurements in an adaptive filtering system to remove the noise reduces the amount of motion artifact in the ECG. The technical approach is divided into two phases. The Phase I objective is to determine if a correlation exists between electrode motion and the amount of noise induced into the ECG signal (i.e., motion artifact). This phase will concentrate on 1) developing a prototype ECG lead with attached motion sensor to simultaneously record the ECG and electrode motion and 2) developing a data-acquisition system using a graphical programming language and an off-the-shelf analog-to-digital converter. If a correlation can be demonstrated in Phase I, the Phase II objective will be to develop and evaluate adaptive filtering algorithms to remove the motion artifact.

Accomplishments - Institutional Review Board approval has been obtained, which allows the research team to collect physiologic data from human subjects. The data-acquisition system and single- and dual-axis motion sensors have been developed. Data have been collected from one subject and used to demonstrate a correlation between the sensor signal and the artifact seen in the ECG. The illustration below shows the motion sensor placement on the ECG electrode. It is envisioned that the motion sensor electronics can be miniaturized and incorporated into the black clip for manufacturing.

The white patch is the ECG electrode attached to the patient's skin, while the black clip attached to the ECG electrode is used to acquire the ECG signal. The motion sensor is attached to the black clip.
(a)	(b)
Time-frequency plots for the signals obtained from the motion sensor (a) and ECG (b). The frequency characteristics of motion artifact are outlined in both plots. The prominent bands of red in B are harmonics of the heart rate. Amplitudes increase from light green to dark red.

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