Contingent cardio-protection for epilepsy patients
Disclosed are methods and systems for treating epilepsy by stimulating a main trunk of a vagus nerve, or a left vagus nerve, when the patient has had no seizure or a seizure that is not characterized by cardiac changes such as an increase in heart rate, and stimulating a cardiac branch of a vagus nerve, or a right vagus nerve, when the patient has had a seizure characterized by cardiac changes such as a heart rate increase.
1. A method of treating a patient having epilepsy comprising:
receiving at least one body data stream;
analyzing the at least one body data stream using a seizure detection algorithm to detect a first condition where an epileptic seizure event has occurred and a second condition where the epileptic seizure event is not present;
receiving a cardiac signal of the patient;
analyzing the cardiac signal to determine the patient's heart rate;
based on a first determination that the first condition is present, determining whether the epileptic seizure event is characterized by a decrease in the patient's heart rate from a reference value or a normative value;
applying a first electrical signal to a vagus nerve of the patient based on the first determination that the first condition is present and that the epileptic seizure event is characterized by the decrease in the patient's heart rate from the reference value or the normative value; and
applying a second electrical signal to the vagus nerve of the patient based on a second determination that the second condition is present.
2. The method of claim 1 , wherein the first electrical signal is a pulsed electrical signal that blocks action potential conduction in the vagus nerve.
3. The method of claim 1 , wherein the second electrical signal is not a vagus nerve conduction blocking electrical signal.
4. The method of claim 1 , wherein the first electrical signal is a pulsed electrical signal that blocks action potential conduction in the vagus nerve and the second electrical signal is not a vagus nerve conduction blocking electrical signal.
5. The method of claim 1 , wherein determining the first condition comprises:
determining a first heart rate of the patient prior to detecting of an onset of the epileptic seizure event;
determining a second heart rate of the patient in response to detecting the onset of the epileptic seizure event using the seizure detection algorithm;
comparing the first heart rate and the second heart rate; and
determining that the epileptic seizure event is characterized by the decrease in the patient's heart rate based on the second heart rate is less than the first heart rate.
6. The method of claim 5 , wherein determining the first heart rate comprises determining a heart rate during a non-seizure period.
7. The method of claim 1 , wherein applying the first electrical signal comprises applying a high frequency pulsed electrical signal to a target site of the vagus nerve, such that at least a fraction of axons in the vagus nerve are incapable of supporting action potential propagation across the target site.
8. The method of claim 1 , wherein applying the second electrical signal comprises applying an electrical signal according to a programmed duty cycle having at least a programmed on-time and a programmed off-time.
9. The method of claim 8 , further comprising interrupting the applying of the second electrical signal based on a determination that the patient has had the epileptic seizure event characterized by the decrease in the patient's heart rate.
10. The method of claim 1 further comprising:
sensing the patient's heart rate in response to providing the first electrical signal, and modifying the first electrical signal to maintain the patient's heart rate between an upper heart range threshold and a lower heart rate range threshold.
11. The method of claim 1 , wherein at least one of the first electrical signal and the second electrical signal is a microburst electrical signal characterized by having a number of pulses per microburst from 2 pulses to about 25 pulses, an interpulse interval of about 2 msec to about 50 msec, an interburst period of at least 100 msec, and a microburst duration of less than about 1 second.
12. The method of claim 1 , wherein the second electrical signal is selected from 1) an electrical signal that generates action potentials in at least a population of nerve fibers of the vagus nerve, and 2) a subthreshold electrical signal that does not generate action potentials in a population of the fibers of the vagus nerve.
13. The method of claim 1 , further comprising issuing a warning that the patient has had the epileptic seizure event characterized by the decrease in the patient's heart rate.