Wireless Telemetry Device Implantation in a Fontan Ovine Model for Continuous and Long-Term Hemodynamic Monitoring

So our lab conducts clinical translational research focused on congenital heart disease, and we have developed several large animal models to evaluate the performance of tissue-engineered vascular grafts, as well as study the late physiological changes associated with the fontan circulation. Freely moving large animals, close post-operative hemodynamic monitoring, as well as long-term data collection, unlike humans, can pose significant challenges. With our protocol, we are able to obtain long-term and realtime hemodynamic data, which allows us to study the late term physiological changes, as well as initiate goal-directed therapies in our animals, ultimately improving their survival.

[Narrator] Position the sheep in the right lateral decubitus on the operating table and secure the left front limb inflection using a slip knot tie to expose the chest. Make a five centimeter longitudinal skin incision above the left carotid artery and internal jugular vein, approximately seven centimeters cranial to the thoracic inlet. Using electrocautery, dissect through the subcutaneous fat, connective tissue, and platysma muscle to expose the neck vessels. Using a combination of blunt and sharp dissection, clear the connective tissue circumferentially from the left carotid artery and internal jugular vein. Now, pass a double looped 2-O silk tie around both vessels, proximal and distal to the cannulation site for temporary vessel ligation. Then make a six centimeter longitudinal incision at the base of the left neck between the scapula and cervical spine. Using a combination of electrocautery and blunt dissection, dissect through the subcutaneous fat and connective tissue to create a six by four centimeter pocket extending toward the spine. Then insert the telemetry device into the subcutaneous pocket, and secure it in place using a 2-0 silk suture. Tunnel the telemetry device antenna under the subcutaneous tissue, and secure it in place using a 2-0 silk suture. Now ,make one centimeter counter skin incisions at the base of the neck, lower left chest, and upper right chest, for placement of the electrocardiogram leads. Tunnel subcutaneously to connect these incisions to the device body pocket, and guide the leads to their intended positions. Place the positive electrocardiogram electrode in the subcutaneous tissue to the left of the lower sternum, removing the silicone tubing, encasing the tip of the steel wire underneath. Place the negative electrode in the subcutaneous tissue to the right of the upper sternum. Prepare the pressure catheters using gel before cannulation. Create a subcutaneous tunnel from the lateral device pocket to the medial neck incision and thread the two pressure catheters through using a 6-O polypropylene suture, place a purse string stitch around the cannulation site on both vessels, and secure it with a plastic tourniquet. Then, tighten the proximal and distal 2-O silk tourniquets around the carotid artery, carefully incise into the vessel at the center of the purse string stitch using a number 11 blade scalpel, and slightly dilate with the tip of a curved hemostat. Insert the pressure catheter for the left ventricular pressure channel into the thoracic ascending aorta. Loosen the proximal silk tourniquet to allow catheter passage, then tighten the purse string suture around the catheter. Repeat the previous steps to cannulate the left internal jugular vein using the pressure catheter for the blood pressure channel, and advance it into the thoracic superior vena cava. Confirm the position of catheter tips in the thoracic superior vena cava and descending aorta using fluoroscopy. Finally, reapproximate the platysma muscle using a 2-O absorbable suture. Close the skin with deep dermal sutures using 3-O absorbable sutures, and subcuticular region with 4-O absorbable sutures. Wireless telemetry device implantation allowed for continuous monitoring of several cardiovascular parameters, including heart rate, arterial pressure and inferior vena cava or superior vena cava pressure. For instance, hemodynamic trends in one sheep following the fontan procedure showed a peak in heart rate around day three, while inferior vena cava pressure exhibited a mild but sustained elevation in pressure from the time of surgery until post-operative day 21. Variations in venous pressures were observed minute to minute, though overall trends appeared to show an acute increase in both abdominal inferior vena cava and thoracic superior vena cava pressures following the establishment of the fontan circulation. Invasive pressure measurements of the thoracic superior vena cava showed mean values fluctuating between two and four millimeters of mercury, corresponding closely with the telemetry device readings, which averaged around 1.1 millimeters of mercury. Abdominal inferior vena cava pressure was consistently higher during recumbent, and dropped significantly whenever the sheep transitioned to a standing position.