Seizure Detection and Automatic Magnet Mode Performance Study

The purpose of this study is to confirm cardiac-based seizure detection in Cyberonics Model 106 VNS Therapy System.

Prospective, observational, unblinded, multi-site study designed to collect data on patients implanted with a Model 106 VNS Therapy System from baseline through an EMU stay of up to 5 days. After the EMU stay, patients will continue follow-up for safety for approximately two years or until final regulatory approval of the product.

Eligibility Criteria:
Inclusion Criteria:

* Patients with a clinical diagnosis of medically refractory epilepsy dominated by partial seizures suitable for implantation with the Model 106 VNS Therapy System.
* Patients with a history of increased heart rate (tachycardia) associated with seizure onset based on clinical data obtained from medical history, admission/hospital charts, or prior neurophysiologic evaluations.
* Patients willing to undergo an EMU evaluation for a period of at least three days with activation of the AMM feature during that time.
* Patients having an average of ≥ 3 seizures per month based upon diary or patient reporting for the 3 months prior to the screening visit.
* Patients must have peak-peak R-wave amplitude greater than or equal to 0.40 mV on ECG measured from the proposed electrode location in the neck to the proposed generator location in the chest via surface ECG electrodes in 7 different body positions.
* Patients must be at least 18 years old.
* Patients must be in good general health and ambulatory.
* Patient must be willing and able to complete informed consent.

Exclusion Criteria:

* Patients have had a bilateral or left cervical vagotomy.
* Patients currently use, or are expected to use, short-wave diathermy, microwave diathermy, or therapeutic ultrasound diathermy.
* A VNS Therapy System implant would (in the investigator's judgment) pose an unacceptable surgical or medical risk for the patient.
* Patients expected to require full body magnetic resonance imaging.
* Patients have a history of VNS Therapy.
* Patients have a documented history of clinically meaningful bradycardia (heart rate less than 50 bpm) associated with seizures.
* Patients with a significant psychiatric disorder, significant cognitive impairment, history of major depression, or suicidality as defined by DSM IV-TR that in the investigator's judgment would pose an unacceptable risk for the patient or prevent the patient's successful completion of the study.
* Patients with a history of status epilepticus within 3 months of study enrollment.
* Patients prescribed drugs specifically for a cardiac or autonomic disorder that in the investigator's opinion would affect heart rate response unless the patient has ictal tachycardia while taking said drugs. These include, but are not limited to, beta adrenergic antagonists ("beta blockers").
* Patients with known clinically meaningful cardiovascular arrhythmias as well as patients with clinically meaningful cardiovascular arrhythmias determined by a 24-hour Holter recording obtained at the screening visit.
* Patients dependent on alcohol or narcotic drugs as defined by DSM IV-TR within the past 2 years.
* Patients with a history of only psychogenic or pseudo seizures.
* Women who are pregnant. Women of childbearing age must take a pregnancy test.
* Patients currently enrolled in another investigational study.