R-r interval analysis for ecg waveforms to assess autonomic response to vagus nerve simulation

An assessment system for vagus nerve stimulation therapy treatment for congestive heart failure in a subject implanted with a neurostimulator configured to deliver a periodic stimulation signal having a plurality of ON-periods and OFF-periods, each ON-period being defined as time between an initiating pulse and a terminating pulse of a plurality of stimulation pulses delivered to the subject, each OFF-period being defined as a time between consecutive ON-periods, the assessment system comprising:

• a wand assembly in communication with the neurostimulator and configured to generate a delivery detection signal indicating delivery of the stimulation signal;
• a lead assembly configured to acquire an ECG signal of the subject over the plurality of ON-periods and OFF-periods;
• a data acquisition system coupled to the wand and lead assemblies and configured to capture each of the delivery detection signal and the ECG signal;
• and
• a processor and a non-transitory computer-readable memory storing instructions that, when executed by the processor, cause the assessment system to:
• record the ECG signal over at least one successive pair of ON- and OFF-periods including, for each pair of ON- and OFF-periods, synchronizing a start of the recorded ECG signal to provide a first portion of the recorded ECG signal corresponding to the ON-period and a second portion of the recorded ECG signal corresponding to the OFF-period;
• determine a heart rate dynamic response from the ECG signal, including:
• detecting each QRS complex in each of the first and second portions of the recorded digital ECG signal;
• identifying each potential R-wave in each QRS complex in each of the first and second portions of the recorded ECG signal;
• verifying each identified R-wave in each of the first and second portions of the recorded ECG signal;
• and
• determining an R-R interval between each pair of successive verified R-waves;
• and
• determine an instantaneous heart rate for each determined R-R interval to determine heart rate dynamics for assessment of autonomic engagement in response to the vagus nerve stimulation treatment.