Surgical Technique for the Implantation of a Wireless Telemetry Device on Pigs' Backs

Summary

A new surgical technique was developed for implanting telemetry devices in pigs that allows continuous monitoring without discomfort. The device is placed on the back, minimizing irritation and infection risk.

Abstract

Telemetry devices are essential for preclinical cardiovascular research, allowing for continuous monitoring of physiological parameters like electrocardiogram, temperature, and respiration in experimental animals without causing disruption. Traditional methods, such as intra-abdominal placement, can cause discomfort, particularly in pigs due to their habit of lying prone. To address this issue, a novel surgical technique was developed for implanting wireless telemetry devices in pigs, aimed at improving animal comfort and maintaining signal quality. This study involved 40 Yorkshire pigs (20-30 kg). The telemetry device was implanted in the back. A 2 inch incision was made lateral to the spine, followed by blunt dissection to create a pocket under the latissimus dorsi fascia. The pocket was treated with a vancomycin solution to prevent infection before device insertion. The leads were secured, and the site was closed in layers. All pigs showed strong, continuous telemetry signals after surgery. Over the 180-day follow-up period, only two cases of infection occurred: One was managed with antibiotics, and the other required device removal. No significant bleeding or loss of telemetry signal was observed, and all animals survived to the end of the study. This new technique offers a reliable method for implanting telemetry devices in pigs, reducing discomfort and infection risk while providing high-quality physiological data. It holds promise for broader use in preclinical cardiovascular research, improving both animal welfare and data reliability.

Introduction

Telemetry devices play a pivotal role in advancing the understanding of cardiovascular physiology, particularly in studies using an animal model of myocardial infarction. By enabling the continuous monitoring of physiological signals, including vital parameters and electrocardiogram (ECG) readings, these devices offer invaluable insights into the dynamic changes occurring during cardiac events. In preclinical studies, where animal models like pigs are instrumental in mimicking human cardiovascular responses, telemetry devices have become indispensable tools¹. The ability to record ECG continuously in unrestrained, freely moving animals provides a nuanced perspective on the impact of myocardial infarction, allowing researchers to capture real-time alterations in cardiac function.

In studies involving animal models of myocardial infarction, implantable telemetry devices offer distinct advantages. They facilitate the measurement of critical parameters such as heart rate with minimal disruption to the animals' natural behavior, eliminating potential confounding factors introduced by external devices².

These devices often come with a manual with instructions for their surgical implantation, but different studies and animal models may require implantation techniques different from those in the manual. Traditional telemetry implantation sites, such as intra-abdominal or neck placement, present drawbacks in porcine models used in extended cardiovascular studies, including potential discomfort, interference with femoral access, restricted movement, and increased infection risk^1,2,3. Therefore, an alternative approach was needed that was compatible with long-term monitoring in unrestrained pigs.

Compared to traditional intra-abdominal placement, which can cause discomfort, or neck placement, which has had lower success rates in pigs in some other studies, this dorsal approach aims to improve welfare while maintaining data quality.

The primary goal of this study was to develop and validate a novel surgical technique for implanting wireless telemetry devices in the backs of pigs to ensure animal comfort and reliability. The aim was to harness the benefits of continuous ECG monitoring over an extended period (up to 180 days). This technique was developed in response to the limitations observed with traditional implantation methods (e.g., intra-abdominal, inguinal, and neck placements), which in pigs are associated with substantial risk of discomfort, limited mobility, interference with vascular access, and infection. We developed this novel dorsal approach to enhance animal welfare, reduce postoperative complications, and maintain reliable signal quality during long-term monitoring in unrestrained animals.

Protocol

All animal procedures were approved by The Texas Heart Institute's Institutional Animal Care and Use Committee (IACUC). Animals were implanted with the EMKA easyTEL+L-EEEETA digital system (https://www.emkatech.com/product/easytel-large-animals/).

1. Preoperative preparations for experimental animals

1. Use Yorkshire pigs of either sex weighing between 20 kg and 30 kg. Do not feed the pigs 12-24 h before the start of anesthesia but allow access to water.

2. Sedation and anesthesia

1. Administer Telazol (tiletamine and zolazepam; 2-6 mg/kg intramuscular [IM]) and atropine sulfate (0.02-0.05 mg/kg IM). Allow 10-15 min for the drugs to induce sedation, then transport the pig to the preparation room. Confirm adequate anesthetization by the absence of jaw tone and lack of response to toe pinch. Apply an ophthalmic ointment to both eyes to prevent corneal drying during anesthesia.
2. Place a face mask to administer oxygen and isoflurane at 3% until adequate jaw tone relaxation permits endotracheal intubation.
3. Intubate the pig with direct vision of the vocal folds. Connect the pig to a volume ventilator and maintain anesthesia by isoflurane inhalation (0.5%-3.0%) in O₂ (40%-100%).
4. Place an intravenous (IV) catheter in an ear vein. Shave the area over the lateral auricular vein and disinfect it with 70% isopropyl alcohol followed by povidone-iodine solution. Insert a 20- to 22G catheter into the vein, using aseptic technique, then secure the catheter with medical tape and flush it with sterile saline to confirm patency.
5. Administer buprenorphine (Buprenex; 0.005-0.015 mg/kg IM), flunixin meglumine (1.1-2.2 mg/kg IV or IM), and ceftiofur (Naxcel; 3-5 mg/kg IM).
6. Shave the chest, upper back, lower back, and the distal portions of all four limbs, specifically the areas over the anterior aspect of the hooves, using electric clippers to fully expose the skin for electrode placement. Clean all shaved areas with sterile gauze soaked in 70% isopropyl alcohol, wiping in a circular motion from the center outward to remove debris and oils in preparation for sterile draping. Place adhesive ECG electrodes on all four limbs, ensuring firm skin contact to minimize signal artifacts.

3. Surgical procedure

1. In the operating room, place the pig on the table in the ventral position. Maintain anesthesia with isoflurane inhalation (0.5%-3.0%). Start IV infusion of plasmalyte at 10-15 mL/h.
2. Surgical site preparation
   1. Clean the intended surgical incision site on the left upper back and the surrounding shaved area (approximately 15 cm x 15 cm) with sterile gauze soaked in 70% isopropyl alcohol. Wipe from the center outward until no visible dirt or debris remains on the gauze. Allow the alcohol to air-dry completely.
   2. Perform a sterile surgical scrub using povidone-iodine scrub solution and sterile gauze. Apply the scrub using firm, circular motions, starting at the incision line and moving outward in expanding circles. Continue scrubbing for at least 5 min, using fresh gauze as needed.
   3. Apply povidone-iodine solution with sterile gauze or sponge sticks, again moving from the center outward. Allow this final paint layer to air-dry completely; do not wipe it off.
   4. Isolate the prepared surgical area with sterile surgical drapes.
3. Identify the anatomical landmarks for the incision. These landmarks form a triangle comprising the spine (upper border), the scapula (left border), and the lower border of the trapezius muscle (right border; Figure 1).
4. Using a number 10 blade, make a 2 inch longitudinal incision approximately 2 inches laterally from the spine.
5. After the epidermis has been incised, use an electrocautery to advance through the subcutaneous tissue and then divide the trapezius muscle. Take special care to divide all of the fascial layers.
6. Once the inner fascial layer has been divided, use blunt dissection with the index and middle finger to create a pocket in this layer. Check that the tip of the scapula is within reach of the fingertips. After dissection, the tip of the scapula will be palpable at the extent of the pocket (Figure 2).
7. Check that the telemetry device can fit in the pocket with minimum tension on the skin incision. Remove the device from the pocket.
8. Mix vancomycin (1 g) with 50 mL of 0.9% saline and place approximately 10 mL of the mixture in the pocket for 1-2 min. Remove excess solution with a gauze pad.
9. Use a 14 Fr angiocath to place wires as shown in Figure 2.
   1. Insert angiocath, going lateral to medial, outer to inner orientation. Direct the needle under the muscle toward the pocket. Advance the needle until only a third of its body remains visible. Remove the needle and thread the lead through the catheter, going from the tip of the catheter to the catheter hub.
   2. Leave between 1 and 2 inches of lead exposed. Sufficiently exposed lead prevents it from being lost in the subcutaneous tract during placement of other leads. Remove the catheter.
   3. Insert one colored lead (yellow, red, green, or blue), followed immediately by its corresponding contralateral transparent lead on the opposite side of the pocket. Insert each pair together, one pair at a time, to match their arrangement on the telemetry device and prevent confusion during placement. The colored and transparent leads form a differential pair for each ECG channel, enabling bipolar signal acquisition and reducing electrical noise. Repeat this process sequentially for all lead pairs. Insert the black ground lead last. This approach ensures consistent lead orientation and accurate signal transmission (Figure 3).
   4. Once all leads are placed, pull the wires so the tips of the leads are barely under the skin. Ensure that no leads are visible at the skin level (Figure 3).
10. Collect all wires into a loop, using the hand as a guide, and tie them into a bundle with heavy silks.
11. Place the device and lead bundle in the pocket. Ensure that the device sits flat and is oriented correctly. One side of the device is labeled with the instruction: This side facing out.
12. Position the device within the pocket so that its lateral edge lies at least 1-2 cm medial to the palpable caudal edge of the scapula. Before proceeding, gently manipulate the pig's left forelimb through its range of motion to confirm that the device does not significantly impinge on or rub against the scapula.
13. Make sure device readings are transmitted to the receiver and computer (Figure 4).
    NOTE: Successful transmission is defined as a transmission that accurately measures heart rate, assesses rhythm, and identifies QRS complexes. The raw signal may not be perfectly isoelectric or artifact-free.
14. Ensure hemostasis. Close the muscle layer with 1-0 Vicryl. Apply the vancomycin mixture on top of the muscle layer. Allow 1-2 min for absorption.
15. Close the subcutaneous layer with 2-0 Vicryl. Staple the incision and apply tissue glue.

4. Post -operative care

1. Monitor and record vital signs-heart rate, respiratory rate, and temperature-hourly, beginning at the time of intensive care unit admission. Continuously assess the pig until extubation criteria are met, including spontaneous respiratory effort while on the ventilator, presence of a chewing reflex, and the ability to maintain sternal recumbency. Extubation should be based on these clinical indicators and supported by arterial blood gas measurements.
2. Continue hourly monitoring after extubation; reduce to every 4 h once the pig demonstrates physiological stability. Ensure the pig is never left unattended during recovery. A trained veterinary technician must remain present at all times throughout the recovery period.
3. House the pigs individually in adjacent pens that permit visual but not physical contact with conspecifics, and do not return the pig to group housing until it has fully recovered.
4. Administer postoperative analgesia, which include buprenorphine (0.05-0.1 mg/kg IM or PO) every 6-12 h or as directed by the attending veterinarian, and flunixin meglumine (1.1-2.2 mg/kg IV, IM, or PO) administered every 6-8 h as needed.
5. Administer antimicrobial prophylaxis beginning with Naxcel (ceftiofur; 3-5 mg/kg IM) once daily for 24 h, starting the day after surgery, followed by Baytril (enrofloxacin; 2.5-5.0 mg/kg PO, BID) for up to 14 days.
6. Maintain aseptic postoperative care by applying iodine spray to the incision site every 8 h until complete wound healing and staple removal at postoperative day 14. Apply triple antibiotic ointment to the incision site as needed.

Results

The data presented in Table 1 show the reliability and safety of the surgical technique for dorsal implantation of telemetry devices in pigs. Successful ECG transmission was recorded in all 40 pigs (100%), confirming that the positioning of the device and lead configuration consistently enabled effective long-term signal acquisition. The absence of major bleeding events (0%; defined as ≥10 mL of blood loss) indicates the safety of the fascial pocket dissection and careful handling of vascular structures....

Discussion

A device-implantation procedure is described as a new invasive telemetric method of continuous ECG monitoring. This method ensures reliable recordings in animal experiments. Although the user manual for the EMKA device⁴ describes a surgical procedure for implanting the device in the abdomen of large animals such as dogs and pigs, intra-abdominal placement was not considered desirable because pigs typically lie on their abdomen, resulting in pressure on the peritoneum that could cause pain or disco...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
1 cc syringe	Vetone	V1 670097
10 cc syringe	Medline	SYR110010
12 cc syringe	Vetone	V1 670065
20 cc syringe	Nipro	JD+20L
20G needle	Medline	SYR100205
3 cc syringe	Nipro	JD+03L-NIJ
ACT cartridge	Medtronic	402-03
Alcohol	Vetone	V1 500205
Anesthesia circuit	Fisher & Paykel	RT210
Angiocath 14 Fr	BD	382269
Atropine sulfate	Vetone	V1 510221
Bariatric drape	Medline	DYNJP3105
Blade 10	Medline	MDS15010
Blade 11	Medline	MDS15011
Buprenorphine	PAR Pharmaceuticals	3003408B
Camera cover	Aspen Surgical	LT-C02
Cautery pen	Medline	ESPB3000
Cautery pen scratch pad	Medline	DYNJ01208
Coflex 2" tape	Vetwrap	1404BK
Curos cap protector	3M	CFF1-270
ECG electrodes	Medline	MDSM618305
EMKA easyTEL+L-EEEETA digital system	EMKA
Endotracheal tube	Jorvet	J0615J
Flunixin meglumine	Merck	65707
Injection cap	ICU Medical	C1000
Introducer catheter 5F	Abbott	406101
Introducer catheter 6F	Abbott	407845
Isoflurane	Vetone	MWI502017
IV Catheter Extension Set	Baxter	2C8612
IV Pump Set SmartSite	BD Alaris	2420-0007
Light cover	Medline	DYNJLHS2
Naxcel (ceftiofur)	Zoetis	25434
Needle counter	Medline	DYNJNC20F
Percutaneous entry needle	Cook	G00272
Permahand silk 2-0	Ethicon	C012D
PlasmaLyte	Baxter	2B2544
Povidone-iodine paint sticks	Aplicare	ORF20025S
Pressure monitoring transducer 1x1	Edwards Lifesciences	PX260
Pressure tubing 84"	Edwards Lifesciences	50P184
Saline	Baxter	2F7124
Shoe covers	Medline	NON29858
Skin stapler	Covidien	8886803712
Specimen cup	Medline	DYND30389
Sponge, 4"×4", X-ray detectable	Covidien	441002
Sponge, lap	Medline	MDS241518
Surgeon's cap	CardinalHealth	4359
Surgical gloves	Medline	MSG9065
Surgical gowns	Medline	DYNJP2001S
Surgical mask	Halyard	6211580
Table cover	Medline	DYNJP2311
Telazol	Zoetis	10004135
Tissue adhesive	3M	1469SB
Vancomycin	Fresenius Kabi	402254G
Vicryl 1	Ethicon	J480H
Vicryl 2-0	Ethicon	J869H