Multi-channel system for beat to beat QT interval variability
View Patent ↗A PC-based ECG software program that in real time, acquires, analyzes and displays QTV and PQ interval variability (PQV) in each of the independent channels that constitute the 12-lead conventional and/or Frank X, Y, Z lead ECG. The system also analyzes and displays the QTV and PQV from QT and PQ interval signals that are derived from multiple channels and from singular value decomposition such that the effect of noise and other artifacts on the QTV and PQV results are substantially reduced compared to existing single-channel methods. Moreover, this invention also provides certain new parameters of T-wave (and QRS and P-wave) morphology, that in initial studies have improved clinical diagnostic utility and/or reproducibility and reliability compared to known existing parameters of T-wave morphology. Finally, it also provides a method for determining the beat-to-beat variability these T, QRS and P-wave morphologic parameters.
1. A method for analyzing electrocardiograph signals from a plurality of ECG leads comprising the steps of:
sensing analog fluctuations in voltage simultaneously from the plurality of ECG leads, the fluctuations in voltage resulting from electrical activity of a heart and defining a plurality of analog signals;
converting such signals having an analog value to digital values corresponding substantially to the analog value of the signals;
analyzing the digital values of the record in real-time by:
identifying a time of each R wave of a heartbeat;
defining individual signal averaged templates for the T wave and the QRS wave for a series of heartbeats by segmenting each heartbeat of the series of heartbeats at:
i. the beginning and the end of the QRS wave; and
ii. the beginning and the end of the T wave;
utilizing the defined individual templates to determine alteration values for individual T waves and QRS waves of an individual heartbeat, the alteration values comprising shifts in time of the T wave and QRS wave as error functions for the heartbeat; and
assessing changes in QT interval for each heartbeat using the T wave template, the QRS wave template, and the series of heartbeats to determine beat-to-beat variability of the QT intervals of the heartbeats.
2. The method of claim 1 further comprising the step of recording the digital values in a record before the step of analyzing the digital values of the record.
3. The method of claim 1 , further comprising the step of constructing a singular value decomposition from at least two converted digital values.
4. The method of claim 1 , further comprising the steps of:
iteratively refining the template by adjusting the template based on a plurality of more recently received beat data and;
iteratively assessing the time variation of each beat as it is received to the iteratively refined template.
5. The method of claim 1 , further comprising the steps of
defining a norm for each wave as an estimate of the noise of matching for each wave of a selected beat; and
selecting only selected ones of the beats for averaging on the basis of the similarity in the QT signal value and of the beat quality as assessed by the norm.
6. A system for analyzing electrocardiograph signals from a plurality of ECG leads comprising:
means for sensing analog fluctuations in voltage simultaneously from the plurality of ECG leads, the fluctuations in voltage resulting from electrical activity of a heart and defining a plurality of analog signals;
means for converting such signals having an analog value to digital values corresponding substantially to the analog value of the signals;
means for analyzing the digital values of the record in real-time by:
identifying a time of each R wave of a heartbeat;
defining individual signal averaged templates for the T wave and the QRS wave for a series of heartbeats by segmenting each heartbeat of the series of heartbeats at:
i. the beginning and the end of the QRS wave; and
ii. the beginning and the end of the T wave;
means for utilizing the defined individual templates to determine alteration values for individual T waves and QRS waves of an individual heartbeat, the alteration values comprising shifts in time of the T wave and QRS wave as error functions for the heartbeat; and
means for assessing changes in QT interval for each heartbeat using the T wave template, the QRS wave template, and the series of heartbeats to determine beat-to-beat variability of the QT intervals of the heartbeats.
7. The system of claim 6 , wherein the system is included in an implantable device.
8. The system of claim 6 , wherein the means for assessing changes in QT interval develops an output signal that is provided to one of a group consisting of means for monitoring the condition of the patient's heart; means for monitoring the progression of disease in the patient's heart; means for controlling the rhythm of the patient's heart; means for raising an alarm when predetermined limits are exceeded; and means for controlling a drug dispensing pump.