1. A method of operating an implantable medical device (IMD) comprising a neurostimulator coupled to an electrode assembly, said neurostimulator adapted to deliver a stimulation signal at a plurality of intensity parameter levels at predefined increments, said method comprising: monitoring a heart rate of a patient implanted with the IMD; delivering to the patient a first set of stimulation signals at a first frequency, wherein said delivering comprises incrementally increasing the intensity parameter level by the predefined increment for subsequent stimulation signals until bradycardia is detected; detecting tachycardia or a transition heart rate response in response to the stimulation signal having a first intensity parameter level one predefined increment below a second intensity parameter level at which bradycardia is detected; based on detecting tachycardia in response to the stimulation signal having the first intensity parameter level, delivering to the patient a second set of stimulation signals at a second frequency lower than the first frequency, wherein said delivering the second set of stimulation signals comprises incrementally increasing the intensity parameter level by the predefined increment for subsequent stimulation signals until bradycardia is detected; and based on detecting the transition heart rate response in response to the stimulation signal having the first intensity parameter level, identifying the stimulation signal resulting in the transition heart rate response as corresponding to a neural fulcrum zone.