Assessment system with wand detection cable synchronizing ECG recording
An assessment system is provided for a subject patient implanted with a neurostimulator configured to deliver a stimulation signal having a plurality of ON-periods and OFF-periods. The assessment system includes a wand assembly configured to generate a delivery detection signal indicating delivery of an initiating pulse. The assessment system also includes a processor and a memory associated with the wand. The memory stores instructions that, when executed by the processor, cause the assessment system to record an ECG signal over at least one successive pair of ON- and OFF-periods and determine changes in heart rate dynamics to indicate autonomic response to the stimulation. The wand assembly includes a programming device configured to wirelessly communicate with the neurostimulator and a cable connector configured to form a surface contact with the programming device. The cable connector includes a detection circuit configured to indirectly detect a time of the initiating pulse.
1. A method of assessing vagus nerve stimulation in congestive heart failure treatment of a subject patient, the method comprising:
detecting a delivery of a stimulation signal from an implantable neurostimulator device in the subject patient, wherein detecting the delivery of the stimulation signal is performed by a wand assembly in communication with the implantable neurostimulator device; and
synchronizing a start of a recording of an ECG response signal with the delivery of the stimulation signal delivery based upon the detection of the delivery of the stimulation signal by the wand assembly.
2. The method of claim 1 , wherein the detecting includes indirectly detecting a communication transmission between a wand of the wand assembly and the neurostimulator.
3. The method of claim 2 , wherein the indirectly detecting includes detecting the communication transmission with a parallel capacitor and resistor of a detection circuit.
4. The method of claim 3 , wherein the detection circuit includes an inductor, and wherein the indirectly detecting includes detecting, by the inductor, a pulse indicating a time of an initiating pulse of the stimulation signal.
5. The method of claim 4 , wherein the indirectly detecting includes detecting a voltage induced across the inductor by the pulse, the induced voltage exceeding a threshold to indicate the time of the initiating pulse.
6. The method of claim 5 , wherein the detection circuit includes a low pass filter, and wherein the indirectly detecting includes defining the threshold by the low pass filter.
7. The method of claim 1 , wherein the synchronizing includes identifying an ON-period and an OFF-period of the stimulation signal and distinguishing first portions of the ECG response signal corresponding to the ON-period from second portions corresponding to the OFF-period.
8. The method of claim 7 , further comprising:
detecting each QRS complex in each of the first portions and the second portions of the recorded ECG signal;
identifying each potential R-wave in each QRS complex;
determining a time interval between each pair of successive R-waves; and
determining an instantaneous heart rate for each determined time interval.
9. The method of claim 1 , further comprising:
acquiring, by a lead assembly, an analog ECG signal of the subject patient over a plurality of ON-periods and OFF-periods of the stimulation signal, and wherein the detecting includes generating, by the wand assembly, an analog delivery detection signal indicating delivery of the stimulation signal; and
capturing and converting, by a data acquisition system coupled to the wand and lead assemblies, each of the analog ECG signal and the analog delivery detection signal to a digital ECG signal and a digital delivery detection signal.
10. The method of claim 1 , wherein the wand assembly includes a programming device configured to wirelessly communicate with the implantable neurostimulator device and a cable connector configured to form a surface contact with the programming device, the cable connector including a detection circuit; and
wherein the detecting includes indirectly detecting a time of an initiating pulse of the stimulation signal via the detection circuit.