Heart rate determination based on VAD current waveform
The present disclosure provides for methods and systems for determining heart rate of a patient. Based on motor current signals of a ventricular assist device (VAD), each of first, second and third events in the measured current signal may be detected, the first event being indicative of a rise or fall in the current signal, the second event being indicative of a rise or fall in the current signal in the opposite direction as the first event, and the third event being indicative of a rise or fall in the current signal in the same direction as the first event. A timer counter may be initiated upon detection of the first event, and an elapsed time may be measured upon detection of the third event. Heart rate may be determined based on the elapsed time of the timer counter.
1. A method of determining heart rate of a patient having an implantable blood pump, comprising:
measuring a motor current signal of the implantable blood pump, the implantable blood pump being in fluid communication with a ventricle of the patient's heart;
detecting a first event in the measured current signal, the first event being indicative of one from the group consisting of a rise in the current signal and a fall in the current signal;
initiating a timer counter when detecting the first event;
detecting a second event in the measured current signal, the second event being indicative of one from the group consisting of a rise in the current signal and a fall in the current signal in the opposite direction as the first event;
detecting a third event in the measured current signal, the third event being indicative of one from the group consisting of a rise in the current signal and a fall in the current signal in the same direction as the first event;
measuring an elapsed time of the timer counter when detecting the third event;
filtering the motor current signal to create a filtered signal, and having the first, second, and third events be detected using a combination of the unfiltered motor current signal and the filtered signal; and
determining the heart rate of the patient based on the elapsed time of the timer counter.
2. The method of claim 1 , wherein detecting the second event is initiated after the first event is detected, and wherein detecting the third event is initiated after the second event is detected.
3. The method of claim 1 , wherein the first event and the third event are rises in current signal and the second event is a fall in current signal.
4. The method of claim 1 , wherein detecting the rise in current signal occurs when the unfiltered current signal exceeds the filtered current signal by a first predetermined amount, and wherein detecting the fall in current signal occurs when the unfiltered current signal is less than the filtered current signal by a second predetermined amount.
5. The method of claim 4 , wherein the first predetermined amount and the second predetermined amount are equal.
6. The method of claim 1 , wherein the filtered signal is a running average of the motor current signal.
7. The method of claim 1 , wherein detecting the first, second and third events is repeatedly performed, and wherein the method includes measuring a plurality of elapsed times, and wherein the heart rate is determined based on an average of the plurality of elapsed times.
8. The method of claim 1 , further comprising:
initiating a second counter timer when detecting the second event;
detecting of a fourth event in the measured current signal after detecting the third event, the fourth event being indicative of one from the group consisting of a rise in the current signal and a fall in the current signal in the same direction as the second event; and
measuring an elapsed time of the second timer counter when detecting the fourth event.
9. The method of claim 1 , further comprising:
repeatedly determining the heart rate to obtain a plurality of heart rate values over a predetermined amount of time; and
determining a statistical variability of the plurality of heart rate values indicative of heart rate variability.
10. The method of claim 9 , wherein determining a statistical variability of the plurality of heart rate values comprises determining a standard deviation of the heart rate values.