Abstracts

Rationale: In patients undergoing evaluation for epilepsy surgery, localizing the epileptogenic focus may require invasive electro-encephalography (EEG) using depth electrodes or subdural grid electrodes. Unfortunately, certain risks are associated with the use of invasive EEG, such as infection and hemorrhage. A less invasive method that allows the acquisition of high-quality EEG would be of interest. Intravascular EEG, measured by recording from electrodes introduced through venous or arterial catheterization of the brain, has been proposed as an alternative to invasive EEG. In recent papers it has been shown that intravascular EEG has comparable signal quality as invasive EEG. In this work we describe the acquisition of intra-arterial EEG during the intracarotid amobarbital test in a single patient. Methods: The study was approved by the ethical committee of Ghent University Hospital. The patient was a 25-year old woman suffering from refractory epilepsy undergoing presurgical evaluation. Brain MRI showed left mesial temporal sclerosis. To evaluate the lateralization of memory and language function, she was scheduled for an intracarotid amobarbital test. After giving written informed consent, the patient was asked to start taking aspirin 160mg/day from 7 days before the test. Before the procedure, a standard 9-channel EEG was attached. The patient was fully heparinized for the procedure. The left carotid artery was first catheterized, after verifying normal vascular anatomy using fluoroscopy. A guidewire (Silverspeed) and micro-catheter (Echelon) were advanced up to the proximal M1 segment of the left medial cerebral artery, and the guidewire tip was placed approximately 1cm distal to the tip of the micro-catheter. The proximal end of the guidewire was connected to the EEG amplifier. Subsequently, amobarbital (100mg) was injected into the left internal carotid artery and memory and language testing was performed according to the standard protocol. This was then repeated on the right side. EEG was recorded continuously from 9 scalp electrodes and 1 intra-arterial electrode during the entire procedure. Results: During baseline recording, the intra-arterial EEG showed a signal amplitude that was approximately 2-3x higher than the signal amplitude of the scalp EEG. Shortly after the intracarotid injection of amobarbital, delta waves with high amplitude were observed on the intra-arterial EEG. These delta waves were also seen on the scalp EEG, with lateralization to the injected side. No clear epileptiform discharges were observed on the intra-arterial or scalp EEG. After approximately 5 minutes the EEG pattern returned to normal on the scalp and intra-arterial channels. Figures 1 and 2 demonstrate the EEG immediately after injection of amobarbital into the right internal carotid artery, and after complete recovery. The patient did not experience any side effects from the procedure. Conclusions: Intra-arterial EEG was recorded during the intracarotid amobarbital test in a patient with left mesial temporal sclerosis. High-amplitude delta waves were observed for approximately 5 minutes immediately after amobarbital injections. The signal quality of the intravascular EEG was comparable to conventional invasive EEG. Funding: None.