Application of information theory to eliminate redundant part of electrocardiogram or vectorcardiogram is described. Operation of medical equipment to obtain three dimensional study of patient is discussed. Use of fast Fourier transform to accomplish data compression is explained

Bennett, W. P.

Conover, M. F.

Hayden, W. L.

English

NASA Technical Reports Server

July: 1972	 B72-10391 
NASA TECH BRIEF 
Manned Spacecraft Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Compression and R-Wave Detection of ECG/VCG Data 
T 
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0 S
Digitized ECG Wave Form 
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The problem: 
When electrocardiograms (ECG'S) and vectorcardio-
grams (VCG's) are digitally processed, as is often the case 
in many fields of study today, a great mass of data is 
transmitted and stored on magnetic tape. Because cardiac 
cycles are quite redundant, the changes in an ECG or 
VCG wave form are the primary elements used for 
analysis. A reliable method of eliminating the repetitive 
part of the data from data processing would save 
important time in computer processing, storage and 
transmission of digital cardiac data. 
The solution: 
Information theory is used to eliminate the redundant 
part of an ECG or VCG wave form from data trans-
mission and computer storage. 
How it's done: 
An ECG measures the electrical impulses generated by 
the heart; electrodes placed on the arms, legs, and chest,
are connected in sequence to a galvanometer from which 
the signals are read and recorded. A VCG uses several 
electrodes simultaneously on the front, back, and side 
of the patient's torso to get a three dimensional study of 
the heart's electrical activity. In both cases the wave form 
(see figure) is primarily sinusodial. Once digitized for 
computer compatibility, the amount of data needed to 
analyze the ECG/VCG wave forms can be reduced by a 
transformation alogrithm. When used for this purpose a 
Fast Fourier Transform reduces the data needed to 
analyze the wave form by a factor of sixteen with a re-
constructed root-mean-square error of only six percent. 
The Fast Fourier Transform accomplishes the data 
compression by changing the usual time domain represen-
tation of the signal to one of frequency representation. 
A representation of the ECG or VCG signal requires less 
data in the frequency domain than in the original time 
domain. A Hadamard Transform may also be used in a 
similar manner to yield a data compression factor of 
eleven.
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights. 
https://ntrs.nasa.gov/search.jsp?R=19720000390 2020-03-17T03:37:26+00:00Z
Digital processing of cardiac data depends on computer 
recognition of a complete cardiac cycle (heart beat). The 
most prominent factor in a cardiac cycle is the R-wave 
(see figure). The R-wave can be determined in real time 
by a Peakedness Parameter technique which simply and 
reliably detects the R-peak regardless of the variabilities 
of ECG/VCG signal characteristics. A peakedness para-
meter is defined using the millivolt differences between 
the digital data points making up the rapidly rising and 
falling R-wave. In order to reduce the effect of random 
noise, millivolt differences are taken between data 
points eight samples apart. In the figure, the differences 
between data points (curve slope) are at first positive, 
i.e., rising, then negative on any positive peak. The 
peakedness parameter is defined as: 
Peakedness = max. negative slope - max. positive slope 
Accordingly, the peakedness parameter is a negative 
number and the largest negative values will always occur 
on the R-Peak of the wave form. A pointed or peaked 
wave produces a large peakedness value; conversely, a 
more rounded wave produces a much smaller value. An 
appropriate threshold value is compared against each 
peakedness calculation. A peakedness calculation ex-
ceeding this threshold value is a sure detection of the 
R-wave.
Notes: 
1. This technique may be used as a real time patient 
monitor in large hospitals and may be of interest to 
designers and users of biomedically oriented computer 
software. 
2. The following documentation may be obtained from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: NASA CR-i 15177 (N71-35323), 
Final Project Report Investigation of Data 
Compression Techniques 
3. Technical questions may be directed to: 
Technology Utilization Officer 
Manned SpacedraftCenter 
Code JM7 
Houston, Texas 77058 
Reference B72-10391 
Patent status: 
No patent action is contemplated by NASA. 
Source: Waldo L. Hayden, Marshall F. Conover and,

William P. Bennett of

TRW Systems Goup, TRW Inc.

under contract to
Manned Spacecraft Center

(MSC-14126,14127) 
B72-l0391
	
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Compression and R-wave detection of ECG/VCG data

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