Coherent signal rejection in ECG

• US 7,894,885 B2
• Filed: 05/02/2007
• Issued: 02/22/2011
• Est. Priority Date: 05/02/2007
• Status: Active Grant

• Current Assignee: Biosense Webster Incorporated (Johnson & Johnson)
• Original Assignee: Biosense Webster Incorporated (Johnson & Johnson)
• Inventors: Bartal, Meir, Razansky, Daniel
• Primary Examiner(s): Layno; Carl H
• Assistant Examiner(s): Stice; Paula J
• Application Number:
  US11/743,195
• Publication Number:
  US 20080275353A1
• Time in Patent Office: 1,392 Days
• Field of Search: None
• US Class Current: 600/509
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: G06F 2218/02 Preprocessing
• CPC Class Codes: H04B 15/005 Reducing noise, e.g. humm, from the supply

Abstract

A method for monitoring an electrocardiogram (ECG) signal of a subject, includes digitally sampling an average signal from at least a first ECG electrode, determining an average interference frequency, and digitally sampling and buffering a raw ECG signal from at least a second ECG electrode. The method further includes: filtering the raw ECG signal to generate a residual signal; calculating, based on the residual signal, a first amplitude and a first phase shift of a primary interference signal at the average interference frequency and a second amplitude and a second phase shift of one or more harmonic interference signals at respective multiples of the average interference frequency; and digitally subtracting the primary interference signal and the one or more harmonic interference signals from the raw ECG signal so as to generate and output a clean ECG signal.

Claims

1. A method for monitoring an electrocardiogram (ECG) signal of a subject, comprising:

digitally sampling an average signal from ECG electrodes attached to the subject, the average signal comprising a Wilson Central Terminal (WCT) signal;

processing the WCT signal with a band-pass filter to establish a band-pass filter signal, the band-pass filter signal having a line interference component;

processing the band-pass filter signal with a frequency meter and determining a frequency of the line interference component;

determining an average interference frequency of the WCT signal based on the frequency of the line interference component;

digitally sampling and buffering a raw ECG signal from another ECG electrode attached to the subject;

calculating a moving average of the raw ECG signal;

calculating a residual signal using the moving average of the raw ECG signal wherein the residual signal comprises frequency components at and above the average interference frequency;

calculating, based on the residual signal, a first amplitude and a first phase shift of a primary interference signal at the average interference frequency and a second amplitude and a second phase shift of one or more harmonic interference signals at respective multiples of the average interference frequency; and

digitally subtracting the primary interference signal and the one or more harmonic interference signals from the raw ECG signal so as to generate and output a clean ECG signal.

2. The method according to claim 1, and comprising using an artifact processor for imposing a limit on a rate of change in the first amplitude over time prior to subtracting the primary interference signal from the raw ECG signal.

3. The method according to claim 2, wherein the limit on the rate of change in the first amplitude over time is a first limit and further comprising imposing a second limit on a rate of change in the second amplitude over time prior to subtracting the one or more harmonic interference signals from the raw ECG signal.

4. The method according to claim 1, wherein filtering the raw ECG signal comprises applying to the raw ECG signal a moving average filter, and wherein generating the residual signal comprises subtracting an output of the moving average filter from the raw ECG signal.

5. The method according to claim 1, wherein calculating the first amplitude and the first phase shift of the primary interference signal comprises finding a correlation between the residual signal and a periodic function having a frequency equal to the average interference frequency.

6. The method according to claim 1, wherein calculating the second amplitude and the second phase shift of the one or more harmonic interference signals comprises finding a correlation between the residual signal and a periodic function having a frequency equal to a multiple of the average interference frequency.