Method of enhancing the signal-to-noise ratio (SNR) of measured electrocardiogram (ECG) signals and a cardiac device for use in detecting heartbeats

• US 9,295,428 B2
• Filed: 08/22/2013
• Issued: 03/29/2016
• Est. Priority Date: 09/21/2012
• Status: Active Grant

• Current Assignee: Biotronik SE & Company KG
• Original Assignee: Biotronik SE & Company KG
• Inventors: Lian, Jie, Garner, Garth, Mssig, Dirk
• Primary Examiner(s): Koharski, Christopher D
• Assistant Examiner(s): So, Elizabeth K
• Application Number:
  US13/973,418
• Publication Number:
  US 20140088399A1
• Time in Patent Office: 950 Days
• US Class Current: 1/1
• CPC Class Codes: A61B 5/282 Holders for multiple electrodes for introduction into the body A61B5/287
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/327 Generation of artificial ECG signals based on measured signals, e.g. to compensate for missing leads
• CPC Class Codes: A61B 5/332 Portable devices specially adapted therefor
• CPC Class Codes: A61B 5/333 Recording apparatus specially adapted therefor
• CPC Class Codes: A61B 5/341 Vectorcardiography [VCG]
• CPC Class Codes: A61B 5/366 Detecting abnormal QRS complex, e.g. widening
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths

Abstract

A method of enhancing the signal-to-noise ratio (SNR) of measured electrocardiogram (ECG) signals is provided. The method includes the steps of providing at least three cardiac input signals derived from the measured ECG signals S₁ and forming a first estimate U₁ S₂ from each of at least three pairs of input signals. Moreover, the method includes the steps of forming a second estimate U₂ S₃ from each of at least three input signals; comparing S₄ the polarity and the amplitude of a first and second estimate U₁, U₂ to at least one threshold T; generating S₅ a composite signal X, wherein the polarity and the amplitude of the composite signal X depend on the result of the comparison; and using S₆ the generated composite signal X to produce an output signal with enhanced signal-to-noise ratio (SNR). Furthermore, a corresponding cardiac device is also provided.

Claims

1. A method of enhancing the signal-to-noise ratio (SNR) of measured electrocardiogram (ECG) signals, the method comprising the steps of:

providing at least three cardiac input signals derived from the measured ECG signals;

forming a first estimate U₁ from each pair of the at least three cardiac input signals;

forming a second estimate U₂ from each of at least three cardiac input signals;

comparing the polarity and the amplitude of a first and second estimate U₁, U₂ to at least one threshold T;

generating a composite signal X, wherein the polarity and the amplitude of the composite signal X depend on the result of the comparison; and

using the generated composite signal X to produce an output signal with enhanced signal-to-noise ratio (SNR),

wherein within the step of comparing, the first and second estimate U₁ and U₂ are compared to an upper threshold UT and a lower threshold LT, wherein the upper threshold UT and the lower threshold LT are different values.

2. The method of claim 1, wherein the first estimate U₁ is a differential signal Ũ

and the second estimate U₂ is an averaged signal Ū

formed by using a weighted moving average filter.

3. The method of claim 1, wherein the lower threshold LT and the upper threshold UT are symmetric around the baseline of the measured electrocardiogram (ECG) signals and/or predefinable by a user and/or automatically adjusted based on the moving average of the peaks of the absolute amplitudes of previously measured QRS complexes that are detected within the previously measured electrocardiogram (ECG) signals.

4. The method of claim 1, wherein a composite signal X=0 is generated if the corresponding first estimate U₁ is lower than the lower threshold LT and the corresponding second estimate U₂ is greater than the upper threshold UT or if the corresponding first estimate U₁ is greater than the upper threshold UT and the corresponding second estimate U₂ is lower than the lower threshold LT.

5. The method of claim 1, wherein if a first and second estimate U₁, U₂ are both greater than or equal to the lower threshold LT and both lower than or equal to the upper threshold UT, a corresponding composite signal X=U₁ is generated if the absolute value of the corresponding second estimate U₂ is greater than the absolute value of the corresponding first estimate U₁, or a corresponding composite signal X=U₂ is generated if the absolute value of the corresponding first estimate U₁ is greater than or equal to the absolute value of the corresponding second estimate U₂.

6. The method of claim 1, wherein a composite signal X equal to the arithmetic mean of a corresponding first and second estimate U₁, U₂ is generated if the corresponding second estimate U₂ is greater than or equal to the lower threshold LT and lower than or equal to the upper threshold UT while the corresponding first estimate U₁ is either greater than the upper threshold UT or lower than the lower threshold LT or if a corresponding first estimate U₁ is greater than or equal to the lower threshold LT and lower than or equal to the upper threshold UT while the corresponding second estimate U₂ is either greater than the upper threshold UT or lower than the lower threshold LT.

7. The method of claim 1, wherein if a first and second estimate U₁ and U₂ are both greater than the upper threshold UT or both lower than the lower threshold LT a corresponding composite signal X=U₂ is generated, if the absolute value of the corresponding second estimate U₂ is greater than the absolute value of the corresponding first estimate U₁, or a corresponding composite signal X=U₁ is generated, if the absolute value of the corresponding first estimate U₁ is greater than or equal to the absolute value of the corresponding second estimate U₂.

8. A cardiac device for use in detecting heartbeats, to which at least three external sensing electrodes are attachable to provide at least three analog voltage input signals, the cardiac device comprising:

an electrocardiogram (ECG) sensing unit for use in producing digital signals from the analog voltage input signals, comprising;

a multiplexer; and

a plurality of signal processing units;

a controller having interconnected parts including a programmable microprocessor, a battery, a memory, a system clock, wherein the battery supplies power to the cardiac device; and

a further processing unit being designed to execute the method of claim 1.

9. The cardiac device of claim 8, wherein the cardiac device comprises a rounded head with a length of d₁ and a rounded tail with a length of d₂, wherein d₁ is smaller than d₂.

10. The cardiac device of claim 9, wherein d₁ and d₂ follow the equation (d₁+d₂)/d₂≈

d₂/d₁ and wherein d₂/d₁≈

(1+√

5;

)/2≈

1.6.

11. The cardiac device of claim 8, wherein the cardiac device has an asymmetric geometry and resembles a spiral shape, wherein the bottom contour of the cardiac device has a shape that approximates the Fibonacci spiral while the top contour of the cardiac device follows a spiral shape that is rounded at the head and the tail of the cardiac device.

12. The cardiac device of claim 11, wherein the at least three external sensing electrodes are respectively located in the top of the head of the cardiac device, in the bottom of the cardiac device and at the end of the tail of the cardiac device.

13. The cardiac device of claim 8, wherein the cardiac device has an egg-oval shape that is symmetric to a first centerline C1, wherein the head of the cardiac device is wider than the tail of the cardiac device.

14. The cardiac device of claim 13, wherein the cardiac device comprises at least four external sensing electrodes, wherein two of the external sensing electrodes are respectively located with the greatest distance possible from one another, in the tail and the head of the cardiac device, at the intersection points of the first centerline C1 with the circumference of the cardiac device, wherein the other two of the external sensing electrodes are located in the top and bottom of the cardiac device, positioned at the intersection points of a line L1 with the circumference of the cardiac device, wherein the line L1 is orthogonal to the first centerline C1, preferably crossing the center of gravity of the cardiac device.