Surgical Implant Procedure and Wiring Configuration for Continuous Long-Term EEG/ECG Monitoring in Rabbits

Using continuous EEG and ECG recordings, the goal of the study is to simultaneously monitor electrical activity in both the brain and the heart. This provides a platform to enable us to examine the multisystem cascade of events that surround cardiac arrhythmias, epileptic seizures, and ultimately leading up to sudden death. This recording system acquires EEGs and ECGs 24/7 from multiple unrestrained rabbits during various physiologic states and surrounding rare episodic events.

It facilitates continuous recordings without the need for direct supervision, is affordable, provides immediate data directly to the researcher, and does not require the replacement of third party owned batteries. The development of a custom-made, hardwired recording setup was built to facilitate the rabbit to move freely in its natural housing environment. The wires are encased to protect them from being bitten.

Thus, the wire harness and tunneling all electrodes under the skin enable continuous recordings during various physiological states. With our system, we amassed a great deal of high quality data that enables us to investigate the prevalence, substrate, and triggers for abnormal electrical activity in the brain and the heart. It also enables us to evaluate the concordance between EEG and ECG abnormalities, which may lead to sudden death.

To begin, obtain the complementary plug for the port alon with the swivel retaining nine preconnected wires on each side. Using wire cutters, trim the wires to five centimeters on the smaller swivel side, and strip five millimeters of the wire coating off the ends. Slide a two centimeter piece of small shrink tubing over each wire of the complementary plug.

Solder the wires thoroughly. For each wire, slide the shrink tubing over the soldered connections. Using a heat gun, shrink the tubing to affix it securely in place.

Then pass a long piece of large shrink tubing over the plug, sliding it to cover the entire length of the wire bundle. On the larger swivel side, strip five millimeters of wire coating from the end of each wire using a wire stripper and slide a piece of metal sheathing greater than 45 centimeters long over the wire bundle. Next, attach the wires from the larger side of the swivel to the cut electrode wires.

Affix small shrink tubing over each connection and use a heat gun to secure the tubing in place. Now slide the metal sheathing over the newly connected wires and swivel. After stretching the metal sheathing, mark the location on the nylon sheathing for reference.

Then slide a one centimeter piece of 15 millimeter outer diameter rubber tubing over the nylon sheathing and wire bundle. Place a three centimeter piece of large shrink tubing over the rubber tubing and affix it. Add two pieces of one centimeter long heat-shrink tubing over the unstretched metal sheathing at 20 and 24 centimeter distances from the plug.

To begin, assemble all the wire harness required for the procedure. After positioning the anesthetized rabbit, make four small marks using a sterile tip marker at the intended electrocardiogram or ECG electrode placement sites. Make a longitudinal incision measuring 2.5 to 3.5 centimeters on the rabbit's right flank.

Using hemostats, perform dissection ventrally to create a subdermal pocket, ensuring that the pocket extends to the four marked locations. Using the non needle end of the 3-0 monofilament suture, tie three sets of surgical knots around the base of the ECG electrode. Pass the needle attached to the ECG electrode through the subdermal pocket and exit at the corresponding marked location.

Apply gentle traction to position the ECG electrode at the marked location. Release the traction and palpate the area to verify that the electrode remains in place. To secure the electrode, pass the 3-O monofilament suture and needle through the rabbit's skin adjacent to the electrode exit site.

Pull the suture partially through the skin and tie a standard surgical knot. From the incision on the rabbit's flank, bluntly dissect toward the inferior angle of the scapulae and then to the base of the head. After turning the rabbit to a prone position, use a sterile tip marker to place five small dots at the intended electroencephalogram or EEG electrode placement sites.

Make a small transverse incision on the head measuring 1.5 centimeters between the anterior aspects of the base of the ears. Bluntly, dissect caudally and cranially from the incision until a subdermal pocket is formed. Insert large forceps into the incision on the flank before spreading the forceps open and lifting the skin at the site marked for the port.

Uses six millimeter punch biopsy tool to create a circular hole at the marked site. After covering the wire plug with plastic or rubber, push the plug side of the port through the hole made by the punch biopsy. Next, press the skin down to the base of the port so that it is taut.

Place a rubber gasket over the port and push it down until it sits flush against the skin. Tuck excess wire into the subdermal pocket on the back and flank. Now gently bring the skin together and close all incision sites using simple interrupted stitches.

Apply an acrylic mixture to the outside of the port, creating a small dome that seals the port site to the skin. After the acrylic solidifies, place sterile gauze over the incision site on the flank and loosely wrap the rabbit with vet wrap. Pass the wire harness through a hole located at the top center of the rabbit's cage.

Plug the DIN connectors into the appropriate monitoring device and affix a retractor cable to the top inside of the cage near the hole for the wire harness. Extend the retractor cable wire that has a plastic clip on the end and attach the clip to the wire harness at the location between the two pieces of shrink tubing. Finally, connect the plug on the wire harness to the plug on the rabbit's back and record the signal from the monitoring device.

Stable EEG and ECG signals were recorded from a three-month-old rabbit using chronically implanted electrodes that retained their positioning without rejection or infection. High resolution data of heart rate variability and cardiac metrics were observed to cycle every 30 minutes. EEG and ECG signals captured during grooming demonstrated robust signal stability despite rabbit movement maintaining high signal quality for analysis.

Pro-convulsant drug administration induced distinct theta bursts in the occipital EEG leads, which were recorded alongside normal sinus rhythm ECG signals. Higher doses of the pro-convulsant triggered seizures, with EEG showing preictal theta bursts, chronic artifacts, and ictal tonic period signals. ECG demonstrated T wave abnormalities indicative of hypoxia during the ictal tonic period, returning to pre ictal normalcy post seizure.