System for cardiac condition characterization using electrophysiological signal data
A system for heart performance characterization and abnormality detection includes an interface for receiving signal data representing an electrical signal indicating electrical activity of a patient heart over multiple heart beat cycles. A signal processor uses the received signal data in calculating at least one of, (a) a first signal characteristic value substantially comprising a ratio of a time interval from S wave to T wave, to a time interval from Q wave to S wave and (b) a second signal characteristic value substantially comprising a ratio of a T wave base voltage from a peak of a T wave to a zero base reference voltage, to an R wave base voltage from a peak of an R wave to a zero base reference voltage. A comparator compares at least one of the first and second characteristic values with a threshold value to provide a comparison indicator. A patient monitor in response to the comparison indicator indicating a calculated signal characteristic value exceeds the threshold value, generates an alert message associated with the threshold.
1. A system comprising:
an interface configured to receive signal data representing an electrical signal indicating electrical activity of a patient heart over a plurality of heart beat cycles;
a signal processor for configured to:
determine a time interval from an S wave to a T wave based on the signal data;
determine a time interval from a Q wave to an S wave based on the signal data;
calculate a first comparison value comparing the time interval from the S wave to the T wave to the time interval from the Q wave to the S wave; and
determine a cardiac condition based on the first comparison value; and
a patient monitor configured to, in response to said determination of the cardiac condition, generate an alert message associated with the cardiac condition.
2. A system according to claim 1 , wherein
the time interval from the S wave to the T wave and the time interval from the Q wave to the S wave occur within a single heart cycle.
3. A system according to claim 1 , wherein
said signal data is digitally sampled data.
4. A system according to claim 1 , wherein
said signal processor is further configured to determine, based on the received signal data,
a second comparison value comparing a maximum magnitude (peak to peak) voltage value for a T wave to a maximum magnitude (peak to peak) voltage value for an R wave and
a third comparison value comparing a time interval from a Q wave to an R wave to a time interval from an R wave to and S wave, and
wherein said signal processor is further configured to determine the cardiac condition based on the first comparison value, the second comparison value and the third comparison value.
5. A system according to claim 1 , wherein
said signal processor is further configured to calculate from the received signal data a signal characteristic value comprising,
ratio
=
A
R
_
ma
x
(
T
QR
+
T
RS
)
A
T
_
ma
x
T
ST
where,
A R — max is substantially maximum magnitude (peak to peak) voltage value for an R wave,
T QR is substantially a time interval from Q wave to R wave,
T RS is substantially a time interval from an R wave to an S wave,
A T — max is substantially a maximum magnitude (peak to peak) voltage value for a T wave and
T ST is substantially a time interval from S wave to T wave.
6. A system according to claim 1 , wherein
said signal processor is configured to calculate a weighted sum of different calculated ratios of parameters derived from the received signal.
7. A system according to claim 6 , wherein
individual weights of said weighted sum are at least one of,
(a) adaptively controlled by a processor and
(b) time varying.
8. A system according to claim 6 , wherein
said weighted sum of different calculated ratios of parameters is of the form,
∑
i
∈
Ratio
selection
μ
i
Ratio
i
wherein Ratio i is the i-th calculated ratio, and μ i is a weight associated with the i-th calculated ratio.
9. A system according to claim 1 , wherein
the determination of the cardiac condition based on the first comparison value comprises comparing the first comparison value to a threshold value,
wherein said signal processor is configured to derive said threshold value from recorded electrical signal data for said patient.
10. A system according to claim 1 , wherein
the determination of the cardiac condition based on the first comparison value comprises comparing the first comparison value to a threshold value,
wherein said signal processor is configured to derive said threshold value from recorded electrical signal data for a population of patients.
11. A system according to claim 10 , wherein
said population of patients has similar demographic characteristics including at least two of, (a) age, (b) weight, (c) gender and (d) height, to those of said patient.
12. A system according to claim 1 , wherein
the determination of the cardiac condition based on the first comparison value comprises comparing the first comparison value to a threshold value,
wherein said signal processor is configured to dynamically adjust said threshold value in response to a determined sensitivity of arrhythmia detection.
13. A system according to claim 1 , wherein
said signal processor is configured to:
calculate a standard deviation of said first comparison value over a plurality of heart cycles, and
determine the cardiac condition based on the standard deviation of the first comparison value.
14. A system according to claim 1 , wherein
said signal processor is configured to:
calculate a signal variability of said time intervals determined over a plurality of heart cycles and
determine the cardiac condition based on the signal variability and the first comparison value.
15. A system according to claim 14 , wherein
said signal variability is calculated over a plurality of heart cycles and is of the form,
Signal
Variability
=
max
(
X
-
Mean
(
X
)
)
Mean
(
X
)
where X is said first comparison value.
16. A system according to claim 1 , including
a repository of predetermined mapping information, associating ranges of the first comparison value with corresponding medical conditions, wherein
said cardiac condition is determined based on the first comparison value and the predetermined mapping information.
17. A system according to claim 16 , wherein
said predetermined mapping information associates ranges of the first comparison value with particular patient demographic characteristics and with corresponding medical conditions, and said system is configured to use patient demographic data including at least one of age weight, gender and height in comparing the first comparison value with said ranges.
18. A system according to claim 1 , wherein said signal processor is further configured to determine, based on the received signal data,
a second comparison value comparing a T wave base voltage from a peak of a T wave to a zero base reference voltage, to an R wave base voltage from a peak of an R wave to a zero base reference voltage,
wherein said signal processor is further configured to determine the cardiac condition based on the first comparison value and the second comparison value.
19. A method comprising:
receiving signal data representing an electrical signal indicating electrical activity of a patient heart over a plurality of heart beat cycles;
determining a time interval from an S wave to a T wave based on the signal data;
determining a time interval from a Q wave to an S wave based on the signal data;
calculating a first comparison value comparing the time interval from the S wave to the T wave to the time interval from the Q wave to the S wave; and
determining a cardiac condition based on the first comparison value
in response to said determination of the cardiac condition, generating an alert message associated with the cardiac condition.