Methodology for automated QT variability measurement

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 Δt; 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 T i 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, n 0 , and an end point of a T wave, n 1 , for said heartbeat wherein: φ(n)=x(n) from n=n 0 to n=n 1 ; 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 QT i .

Claim 2

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 Δt; 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 T i 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, n 0 , and an end point of a T wave, n 1 , for said heartbeat wherein: φ(n)=x(n) from n=n 0 to n=n 1 ; 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 QT i .

Claim 17

A method for analyzing electrocardiograph signals, said method comprising: 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=T k +n.sub.∇ to n=n 1 , 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 T i 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: φ(n)=x(n) from n=n.sub.0 to n=n.sub.1 where x(n) is one of said signals, and n 0 and n 1 are said beginning of said QT interval and end of said QT interval, respectively; said QT template comprises N=n 1 -n 0 points and said template QT interval duration comprises N Δt where Δt is a digitization interval; and said digitization interval comprises about 1 msec.

Claim 18

A method for analyzing electrocardiograph signals, said method comprising: 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=T k +n.sub.∇ to n=n 1 , 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 T i 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: φ(n)=x(n) from n=n.sub.0 to n=n.sub.1 where x(n) is one of said signals, and n 0 and n 1 are said beginning of said QT interval and end of said QT interval, respectively; said QT template comprises N=n 1 -n 0 points and said template QT interval duration comprises N Δt where Δt is a digitization interval; and said digitization interval comprises about 1 msec.