Methodology for automated QT variability measurement
First Claim
1. A method for analyzing electrocardiograph signals to determine beat-to-beat QT interval variability, said method comprising:
- a) sensing fluctuations in voltage resulting from electrical activity of a heart over a predetermined time period as signals having an analog value;
b) converting said signals having an analog value to digital values defined as x(n), where n is a sample number by sampling said analog signal with a fixed digitization interval Δ
t;
c) analyzing said digital values, said analyzing comprising;
i) identifying a time of each R wave of a heartbeat using a peak detection algorithm, wherein Ti is defined as a time location for beat i;
ii) defining a template QT interval, φ
(n) for a heartbeat defined as beat number k, by selecting a beginning of a QRS complex, n0, and an end point of a T wave, n1, for said heartbeat wherein;
φ
(n)=x(n) from n=n0 to n=n1 ;
iii) determining a QT interval for all other heartbeats by finding an optimally time-altered version of a T wave of each beat i that substantially matches a template T wave of beat wherein a QT interval determined for beat i is defined as QTi.
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Abstract
A method for analyzing electrocardiograph signals to determine risk of malignant arrhythmias, that involves: sensing fluctuations in voltage resulting from electrical activity of a heart over a time period of about 256 seconds as signals having an analog value; converting such signals having an analog value to digital values corresponding substantially to the analog value of the signals; recording the digital values in a record; analyzing the digital values of the record by: identifying a time of each R wave of a heartbeat; defining a template QT interval for a heartbeat by selecting a beginning of a QRS complex and an end of a T wave for the heartbeat; determining an alteration value selected from the group consisting of an elongation of a heartbeat in time and a compression of a heartbeat in time as an error function for the heartbeat; performing a binary search to determine a minimal value for the error function; and assessing changes in QT interval for each heartbeat using the entire T wave.
175 Citations
16 Claims
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1. A method for analyzing electrocardiograph signals to determine beat-to-beat QT interval variability, said method comprising:
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a) sensing fluctuations in voltage resulting from electrical activity of a heart over a predetermined time period as signals having an analog value; b) converting said signals having an analog value to digital values defined as x(n), where n is a sample number by sampling said analog signal with a fixed digitization interval Δ
t;c) analyzing said digital values, said analyzing comprising; i) identifying a time of each R wave of a heartbeat using a peak detection algorithm, wherein Ti is defined as a time location for beat i; ii) defining a template QT interval, φ
(n) for a heartbeat defined as beat number k, by selecting a beginning of a QRS complex, n0, and an end point of a T wave, n1, for said heartbeat wherein;
φ
(n)=x(n) from n=n0 to n=n1 ;iii) determining a QT interval for all other heartbeats by finding an optimally time-altered version of a T wave of each beat i that substantially matches a template T wave of beat wherein a QT interval determined for beat i is defined as QTi. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method for analyzing electrocardiograph signals, said method comprising:
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a) sensing fluctuations in voltage resulting from electrical activity of a heart over a time period of about 256 seconds as signals having an analog value; b) converting said signals having an analog value to digital values corresponding substantially to said analog value of said signals; c) recording said digital values in a record; d) analyzing said digital values of said record, said analyzing comprising; i) identifying a time of each R wave of a heartbeat; ii) defining a template QT interval for a heartbeat by selecting a beginning of a QRS complex and an end of a T wave for said heartbeat; iii) determining an alteration value selected from the group consisting of an elongation of a heartbeat in time and a compression of a heartbeat in time as an error function for said heartbeat; iv) performing a search to determine a minimal value for said error function; v) assessing changes in QT interval for each heartbeat using said entire T wave; and
utilizing a region of said QT template from n=Tk +n.sub.∇
to n=n1, where n.sub.∇
comprises a preset delay, to match all heartbeats to said QT template wherein;
i) comprises identifying a time for each R wave using a peak detection algorithm wherein Ti are time locations; and
ii) comprises selecting a beginning of a QT interval and an end of a QT interval for said heartbeat, wherein k is said heartbeat, so a QT template is φ
(n), where n is a sample number such that;
space="preserve" listing-type="equation">φ
(n)=x(n) from n=n.sub.0 to n=n.sub.1where x(n) is one of said signals, and n0 and n1 are said beginning of said QT interval and end of said QT interval, respectively;
said QT template comprises N=n1 -n0 points and said template QT interval duration comprises N Δ
t where Δ
t is a digitization interval; and
said digitization interval comprises about 1 msec.
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Specification