A Double-Vessel Coronary Artery Bypass Grafting Porcine Model using Autologous Internal Mammary Veins

Summary

This study successfully established three double-vessel coronary artery bypass grafting (CABG) porcine models using autologous internal mammary veins (IMVs). Because the native LAD and LCX were not ligated, this model theoretically preserves native coronary flow and may provide a technical platform for future studies of competitive-flow-related vein graft changes.

Abstract

The saphenous vein is one of the most commonly used conduits in coronary artery bypass grafting (CABG). However, the high long-term failure rate limits its clinical efficacy. Although hemodynamic factors are widely believed to drive vein graft failure (VGF), the exact underlying mechanisms remain unclear. Currently, the rat common carotid artery interposition vein graft model serves as the primary animal model for investigating VGF. However, substantial differences in cardiovascular physiology and hemodynamics between rats and humans limit the clinical translation of research findings. Pigs represent an ideal animal model for cardiovascular research because their cardiovascular anatomy and physiology closely resemble those of humans. In this study, three double-vessel CABG porcine models were established using autologous left and right internal mammary veins (IMVs), with one graft anastomosed from the aorta to the left anterior descending coronary artery (LAD) and the other from the aorta to the left circumflex coronary artery (LCX). Intraoperative ultrasonography confirmed flow in both IMV grafts in a representative animal, whereas postoperative computed tomography angiography (CTA) clearly demonstrated patency of the aorta-to-LAD IMV graft. Therefore, this study describes a technically feasible approach for establishing a large-animal CABG model for future studies of VGF.

Introduction

The saphenous vein remains one of the most important conduit sources for coronary artery bypass grafting (CABG) because of its availability, length, and technical versatility¹. However, saphenous vein grafts exhibit a failure rate of up to 61% at 10 years after CABG². This increases the need for repeat revascularization and is associated with a higher risk of in-hospital mortality. In recent years, accumulating evidence has suggested that hemodynamic factors, particularly competitive flow and abnormal wall shear stress, are major contributors to late graft failure^3,4,5. However, the lack of suitable animal models has created a bottleneck for related research. At present, most preclinical studies of vein graft failure (VGF) still rely primarily on small animals, especially rats, mice, and rabbits, because these models are inexpensive and technically accessible, whereas large-animal graft models remain relatively limited⁶. The most commonly used method for establishing small animal vein graft models involves transecting the common carotid artery and connecting the two stumps with an autologous inferior vena cava^7,8,9. However, due to the substantial differences in heart rate and blood pressure between small animals and humans¹⁰, findings derived from small-animal models may not fully reflect the pathophysiological mechanisms in humans.

Pigs are ideal models for cardiovascular surgery because their hearts closely resemble human hearts in cardiac size, coronary anatomy, and surgical handling^11,12. In addition, porcine and human coronary arteries are highly similar in both anatomic and hemodynamic characteristics, and pigs have been shown to recapitulate the pathological phenotype of vein graft disease^13,14. Therefore, performing CABG with vein grafts in a porcine model may provide a superior animal model for investigating VGF.

In this study, three on-pump double-vessel CABG models in Bama miniature pig models were established using bilateral autologous internal mammary veins (IMVs). One IMV graft was constructed from the aorta to the left anterior descending coronary artery (LAD), and the other from the aorta to the left circumflex coronary artery (LCX). In one representative model, intraoperative ultrasonographic assessment confirmed the patency of both vein grafts, and postoperative computed tomography angiography (CTA) demonstrated the patency of the aorta-to-LAD IMV graft. Notably, the target native coronary arteries were not ligated in this model. Therefore, this model is most suitable for investigating the effects of competitive flow in the target coronary arteries on graft hemodynamics and graft failure. However, competitive flow in the target coronary arteries was not directly measured in the present study. Thus, this study mainly demonstrates the technical feasibility of model establishment.

Protocol

The animal experiments in this study were approved by the Institutional Animal Care and Use Committee (IACUC) of Fuwai Hospital, Chinese Academy of Medical Sciences (Approval No. 0110-1-10-ZX(X)-07). All procedures were performed in strict compliance with animal welfare regulations and ethical guidelines to ensure adherence to relevant standards. The reagents and the equipment used are listed in the Table of Materials. The purpose of establishing this model was to provide a potential platform for investigating the effect of competitive flow on VGF. Therefore, after completion of coronary artery bypass grafting, the native coronary arteries were not ligated proximal to the anastomotic sites.

Perform all procedures in accordance with institutional biosafety and animal welfare regulations. Handle sharps, electrosurgical devices, anticoagulated blood, CPB circuits, and biological materials using appropriate personal protective equipment. Confirm adequate grounding before using the electrosurgical unit. Monitor ACT carefully after systemic heparinization and before CPB initiation. Ensure complete de-airing of all cannulas and extracorporeal lines before initiating CPB to reduce the risk of air embolism.

1. Preparation of animals for CABG

1. Use healthy male Bama miniature pigs, typically 35–40 kg and 10–12 months old, and allow them to acclimate to the housing environment for 1 week prior to surgery.
2. Perform baseline examination, including body weight recording, complete blood count, serum biochemistry, echocardiography, and CTA.

2. Anesthesia and monitoring

1. Withhold feed for 8–12 h and water for 2–4 h before anesthesia.
2. Induce anesthesia through intramuscular injection of ketamine (10 mg/kg) and midazolam (1 mg/kg) (following institutionally approved protocol).
3. Maintain anesthesia using inhaled isoflurane (2%–3%) along with an infusion of dexmedetomidine (1 µg/kg/h) and propofol (1–2 mg/kg/h).
4. Confirm adequate anesthesia by verifying relaxed jaw tone and the absence of a pain response to toe pinch.
5. Make a 4–6 cm incision on the neck to expose the jugular vein and carotid artery.
6. Establish venous access via the jugular vein using a 5 F triple-lumen central venous catheter for central venous pressure (CVP) monitoring and drug administration.
7. Establish carotid artery access using a 20 G arterial catheter for real-time monitoring of blood pressure and hemodynamic parameters.
8. Establish femoral artery access using a 20 G arterial catheter for lower limb blood pressure and oxygen saturation monitoring.
9. Perform orotracheal intubation using a 6.5–8 mm endotracheal tube. Confirm that the airflow is unobstructed and provide 100% oxygen.
10. Make a 2–3 cm incision in the lower abdomen to expose the bladder wall. Secure the bladder to the edges of the incision with fine sutures, and then create a bladder fistula. Insert a 10 F Foley catheter into the bladder, inflate the balloon with 5 mL of sterile water, and gently pull the catheter until the balloon rests against the bladder wall. Connect the urinary catheter to a collection bag for urine drainage and monitoring.
    NOTE: Because the urethra of male pigs is long and curved, it is difficult to insert the urinary catheter. Therefore, a bladder fistula needs to be created to drain the urine for early postoperative urine output monitoring. The catheter should be removed as early as possible, preferably within 24–48 h after surgery, once the pig is awake, hemodynamically stable, and no longer requires continuous urine monitoring.
11. Continuously monitor electrocardiogram, invasive arterial pressure, SpO₂, end-tidal CO₂, temperature, and urine output.

3. Surgical exposure

1. Place the pig in the supine position.
2. Shave and disinfect the entire anterior chest and upper abdomen with povidone-iodine. Then, drape the surgical area.
3. Make a midline incision from the mid-cervical region to below the xiphoid process with an electrosurgical unit (ESU).
4. Perform a median sternotomy along the midline from the xiphoid process upward using a sternal saw. Cauterize the sternal cut edges with an ESU and apply bone wax to the marrow cavity to achieve hemostasis.
5. Maintain the chest open with a sternal retractor.

4. Harvest of two autologous IMV conduits

1. Administer 300 U/kg of heparin for systemic anticoagulation to prevent thrombosis during the procedure.
2. Dissect the surrounding tissue of the IMV with an ESU. Transect the side branches with scissors and achieve hemostasis using the ESU.
3. Clamp the distal end of the left IMV with a hemostatic clamp. Make an incision with a scalpel just proximal to the clamp. Insert a blunt flushing needle through the incision and secure it with a 5-0 nonabsorbable polypropylene suture. After ligation, completely transect the distal end of the left IMV.
4. Ensure that the harvested vein conduit is of adequate length (approximately 7–8 cm). Clamp the proximal end of the left IMV with a hemostatic clamp. Transect the IMV distal to the clamping site, and ligate the proximal end with a 5-0 nonabsorbable polypropylene suture. A successfully harvested IMV should be 7–8 cm in length, free of obvious spasm or twisting, and without visible side-branch bleeding.
   NOTE: The IMV has a thin wall and is prone to spasm. Direct grasping, excessive traction, and high-pressure distension should be avoided. The conduit should be handled by the surrounding tissue whenever possible and stored immediately in ice-cold heparin-papaverine saline after harvest.
5. Place the left IMV into ice-cold heparin-papaverine normal saline (30 mg papaverine and 2,500 U heparin dissolved in 500 mL normal saline).
6. Harvest the right IMV using the same procedure.

5. Establishment and initiation of cardiopulmonary bypass (CPB)

1. Open the pericardium longitudinally and suspend it with traction sutures.
2. Ensure activated clotting time (ACT) > 480 s.
3. Place two concentric purse-string sutures using 5-0 nonabsorbable polypropylene sutures. Establish central arterial cannulation with an 18 F arterial cannula. After thorough de-airing, connect the arterial cannula to the arterial line of the cardiopulmonary bypass circuit.
4. Establish venous cannulation with a 24 F venous cannula in the right atrium and connect it to the venous line.
5. Initiate CPB. Slowly establish arterial inflow, followed by venous drainage. Increase pump flow over the next several minutes according to systemic arterial pressure, venous return, reservoir level, and global perfusion parameters.
   NOTE: Because Bama miniature pigs have a relatively small blood volume, the CPB circuit should be adequately primed with 2 L of lactated Ringer’s solution and 500 mg of methylprednisolone. If excessive hemodilution occurs, blood transfusion may be considered as needed.

6. Aortic cross-clamping and cardioplegic arrest

1. Place an antegrade cardioplegia cannula in the aortic root through a purse-string suture. Connect the cardioplegia cannula to the cardioplegia line.
2. Cross-clamp the ascending aorta at a position between the arterial cannula and the cardioplegia access site.
3. Induce cardiac arrest with 4 °C cold modified St. Thomas solution (10–15 mL/kg). Apply ice slush to the cardiac surface for rapid cooling and myocardial protection.
   NOTE: The St. Thomas solution was prepared according to Pfizer Hospital US Plegisol, NDC 00409-7969-05: each 100 mL contained sodium chloride 643 mg, potassium chloride 119.3 mg, magnesium chloride hexahydrate 325.3 mg, and calcium chloride dihydrate 17.6 mg in water for injection, with 10 mL of 8.4% sodium bicarbonate added to each 1,000 mL immediately before use.

7. Distal anastomosis of IMV grafts

1. Inject 4 °C heparin-papaverine normal saline (prepared as described in step 4.5) into the graft through a blunt flushing needle to check for leakage, trim the free end, and place the 8-0 nonabsorbable polypropylene suture.
2. Open the LCX with microsurgical scissors. Insert an intraluminal shunt.
3. Using an 8-0 nonabsorbable polypropylene suture, perform an end-to-side anastomosis between one end of the IMV graft and the LCX with a parachute suture technique.
4. Remove the shunt. Inject heparinized autologous blood into the IMV graft to distend the vessel to expel any trapped air and to check for any leakage at the anastomotic sites and side branches. After injection of heparinized autologous blood, the graft should distend smoothly without focal narrowing, twisting, or leakage from the side branches or distal anastomosis. Complete the anastomosis between the IMV graft and the LCX.
   NOTE: The heparinized autologous blood is directly obtained from the CPB circuit. The total volume of heparinized autologous blood should be at least 50 mL, and the exact volume for each injection should be adjusted according to graft distension and leakage from the grafts or anastomotic sites.
5. Use the same method to completely anastomose one end of the other IMV graft to the side of the LAD.

8. Proximal anastomosis of IMV grafts

1. Remove the cardioplegia cannula. Create an opening at that site using a 3.5 mm punch.
2. Inject room-temperature heparin-papaverine normal saline (with the proportions of heparin, papaverine, and normal saline as described in step 4.5) into the IMV graft anastomosed to the LAD through a blunt flushing needle. After the IMV graft is distended, partially clamp it and transect the end connected to the blunt flushing needle. Further trim the free end with tissue scissors.
   NOTE: Avoid using 4 °C heparin-papaverine normal saline in this step to reduce graft spasm. The specific injection volume of heparin-papaverine normal saline should be determined by the amount required to maintain the distension of the IMV graft.
3. Trim a segment of the arterial catheter and connect it to the left ventricular vent. After connection, insert the arterial catheter into the aorta through the punched opening.
4. Process the IMV graft anastomosed to the LCX in the same manner as described in step 8.2.
5. Create an opening on the left side of the aortic root using a 3.5 mm punch.
6. Perform an end-to-side anastomosis of the free end of the IMV graft, anastomosed to the LCX to the opening on the left side of the aortic root, and leave the anastomosis incomplete.
7. Insert the left heart vent catheter into the aortic root through this anastomotic opening.
8. Perform an end-to-side anastomosis of the free end of the IMV graft, distally anastomosed to the LAD to the other opening in the aortic root.
9. Remove the left heart vent catheter. Clamp both IMV grafts with microsurgical hemostatic clips. Complete the anastomoses of both IMV grafts to the aorta.
   NOTE: Before reperfusion, both IMV grafts should lie without tension or kinking, and the proximal and distal anastomoses should show no obvious leakage.

9. Reperfusion, weaning from CPB, and decannulation

1. Release the aortic cross-clamp and reperfuse the heart.
2. Place an additional 8-0 nonabsorbable polypropylene sutures at the anastomotic sites or along the IMV grafts as needed to achieve hemostasis.
3. Wean from CPB once the pig is hemodynamically stable and the heart has recovered adequate function.
4. Decannulate the aorta and right atrium, and secure hemostasis at all cannulation sites.
5. After separation from CPB, assess both grafts using intraoperative ultrasonography according to the institutional standard protocol. Use color Doppler imaging to identify blood-flow signals within the aorta-to-LAD and aorta-to-LCX grafts, and record the graft location, flow direction, and qualitative patency. If available, perform transit-time flow measurement (TTFM) for quantitative graft-flow assessment.

10. Hemostasis and chest closure

1. Obtain meticulous hemostasis at proximal aortic anastomoses, distal coronary anastomoses, internal mammary vein harvest beds, aortic and atrial cannulation sites, and the sternotomy edges.
2. Insert two drainage tubes.
3. Reapproximate the sternum and close muscle, fascia, subcutaneous tissue, and skin in layers.
4. Transfer the pig to a monitored postoperative recovery.

11. Postoperative care and follow-up

1. Maintain thermal support continuously using heating pads or forced-air warming blankets to keep the pig’s core body temperature at 37.0–38.5 °C.
2. Record the pig model’s fluid intake and output, level of consciousness, heart rate, arterial blood pressure, central venous pressure, complete blood count, and blood gas results daily.
3. Provide mechanical ventilation support using 100% oxygen in the early postoperative phase to guarantee stable gas exchange and prevent hypoxia-induced pulmonary vasoconstriction. Wean the animal from the ventilator and remove the endotracheal tube once the pig resumes strong, regular spontaneous breathing, demonstrates a protective swallowing reflex, and achieves satisfactory arterial blood gas results.
4. Postoperative antimicrobial prophylaxis: Administer cefuroxime sodium (3–5 mg/kg) every 8–12 h for 48–72 h after surgery. Assess the animals daily for signs of infection. Inspect the sternotomy incision and drainage-tube sites daily for abnormal exudate or abscess formation.
5. Assess the animal’s signs of pain every 2–4 h using standard porcine behavioral pain scales. Monitor for common indicators of post-sternotomy pain, including vocalization, a hunched posture, reluctance to move, teeth grinding, or social isolation. Administer opioids or non-steroidal anti-inflammatory drugs (NSAIDs) based on the animal’s behavior to ensure adequate pain relief and smooth recovery.
6. Promptly adjust vasoactive drugs (e.g., dopamine, epinephrine) and fluid support to maintain a stable arterial blood pressure (>70 mmHg).
7. Assess postoperative graft patency by CTA on postoperative day 1 and postoperative day 28 according to the institutional standard imaging protocol.

Results

Three Bama miniature pigs, P1, P2, and P3, underwent the double-vessel CABG procedure. All three animals survived for more than 7 days. Figure 1 illustrates the key surgical steps, including median sternotomy, harvesting of the bilateral autologous IMVs, pericardiotomy to expose the major vessels, establishment of CPB, delivery of cardioplegic solution through the aorta, cooling of the heart with ice slush, distal and proximal anastomoses for double-vessel CABG, weaning from CPB, ultrasonographic assessment of graft pate...

Discussion

In this study, three double-vessel CABG porcine models were established using bilateral autologous IMVs. Of the two IMV grafts, one was used to construct a bypass from the aorta to the LCX, and the other was used to construct a bypass from the aorta to the LAD. Although the saphenous vein is the standard clinical venous conduit for CABG, IMVs were selected because the saphenous veins of Bama miniature pigs were too short to provide two free grafts without tension for aorta-to-LAD and aorta-to-LCX bypass construction. Sev...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
10-degree aortic cross-clamp	Sinoview	CP40431-19	CABG Surgery
45-degree aortic cross-clamp	Sinoview	CP40044-18	CABG Surgery
Affinity Fusion Oxygenation System	Medtronic	BB841	Cardiopulmonary bypass
Anesthesia machine	Mindray	A9	Anesthesia and others
Arterial cannula	Medtronic	18Fr	Cardiopulmonary bypass
Atracurium	Hengrui Pharmaceutical	-	Anesthesia and others
Atraumatic flat forceps	SureMed	GF04021-25	CABG Surgery
Atraumatic flat forceps	SureMed	GF04016-25	CABG Surgery
Balanced handle pen-stylemicrosurgical forceps	Sinoview	FC12010-21	CABG Surgery
Bama miniature pigs	Institute of Zoology, ChineseAcademy of Sciences, NorthernLarge Animal Research Facility	-	Experimental animals
Belzer UW Cold Storage Solution	Bridge to Life Ltd.	1000 ml/bag	CABG Surgery
Black-handle extreme-sharp scissors	Sinoview	SC35101-23UC	CABG Surgery
Blood gas analyzer	Ediagnosis	PT1000	Anesthesia and others
Blunt Fill Needle	BD	305180	Flush and distend IMV grafts
Bone Wax	Ethicon	W31G	Hemostasis
Cardiopulmonary bypass circuit	Medtronic	B-HL-159	Cardiopulmonary bypass
Central venous catheter	Baihe Medical	-	Anesthesia and others
Curved forceps	SureMed	GC01002-12	CABG Surgery
Curved forceps	SureMed	GC01002-16	CABG Surgery
Disposable blood microembolus filter	Sansin	FAF-2	Cardiopulmonary bypass
Disposable blood reservoir filter	Sansin	FCR300K	Cardiopulmonary bypass
Disposable cardioplegia delivery system	Medtronic	XP41	Cardiopulmonary bypass
Dopamine	Jiuan Pharmaceutical	-	Anesthesia and others
Electrosurgical unit	Medtronic	VLFT10FXGEN	CABG Surgery
Endotracheal tube	Yaxin Medicine	YS-0000	Anesthesia and others
Epinephrine	Jinyao Pharmaceutical	-	Anesthesia and others
Fine dissecting forceps	SureMed	GC01090-20	CABG Surgery
Gold-handle ultra-sharp scissors	Sinoview	SC35001-23SC	CABG Surgery
Heart-lung machine	LivaNova	S5	Cardiopulmonary bypass
Heparin	North China Pharmaceutical	-	Anesthesia and others
Ice bucket	SureMed	GQ13018-00D	CABG Surgery
Infusion pump	Sino MDT	SN-C8	Anesthesia and others
Intraluminal shunt	Medtronic	31200	CABG Surgery
Intravenous catheter	KDL	16G-26G	Anesthesia and others
Isoflurane	Lunan Pharmaceutical	-	Anesthesia and others
Isoproterenol	Harvest Pharmaceutical	-	Anesthesia and others
Ketamine	Hikma Pharmaceuticals	0143-9509-10	Anesthesia and others
Lactated Ringer's Solution	Kelun Pharmaceutical	-	Anesthesia and others
Large basin	SureMed	GQ13033-00D	CABG Surgery
Laryngoscope	Hanfeiyl	TD-C-III	Anesthesia and others
Lidocaine hydrochloride injection	Kelun Pharmaceutical co.,Ltd	H20057816	CABG Surgery
Magnesium sulfate for injection	Zdjt Pharmaceutical co.,Ltd	H20051792	CABG Surgery
Medical electric sternum saw	Jingdong xiji	HF-X01	CABG Surgery
Medium basin	SureMed	-	CABG Surgery
Medium-sized sternum retractor	SureMed	GR04130-00	CABG Surgery
Midazolam	Hikma Pharmaceuticals	0641-6220-10	Anesthesia and others
Modified St. Thomas Solution	Self-made	-	Anesthesia and others
Multiparameter monitor	Mindray	Benoversion N17	Anesthesia and others
Needle passer for purse-string sutures	SureMed	GR04074-00	CABG Surgery
Norepinephrine	Harvest Pharmaceutical	-	Anesthesia and others
Papaverine hydrochloride	Sigma-Aldrich	P3510	Store IMV conduits
Pediatric sternum retractor	SureMed	GR04114-00	CABG Surgery
Pen-style microsurgical needle holder	Sinoview	NH11300-21	CABG Surgery
Potassium chloride injection	Kelun Pharmaceutical co.,Ltd	H42021164	CABG Surgery
Propofol	Hikma Pharmaceuticals	0641-6194-10	Anesthesia and others
Protamine Sulfate	Youcare Pharmaceutical	-	Anesthesia and others
Purse-string suture introducer	SureMed	GR04074-00	CABG Surgery
Resano atraumatic magic forceps	Sinoview	FC25501-23S	CABG Surgery
Right-angle forceps	SureMed	GC01110-14	CABG Surgery
Right-angle forceps	SureMed	GC01089-18	CABG Surgery
Small basin	SureMed	-	CABG Surgery
Sodium acetate Ringer's injection	Duo Rui Pharmaceutical co.,Ltd	H20163331	CABG Surgery
Sodium bicarbonate injection	Kelun Pharmaceutical co.,Ltd	H20043739	CABG Surgery
St. Thomas Solution	Pfizer Hospital US	00409-7969-05	Cardioplegia
Sternal retractor (medium size)	SureMed	GR04130-00	CABG Surgery
Straight forceps	SureMed	GC01001-12	CABG Surgery
Straight forceps	SureMed	GC01001-16	CABG Surgery
Suture 5-0 Prolene BB	Ethicon	-	CABG Surgery
Suture 8-0 Prolene	Ethicon	-	CABG Surgery
Suture Prolene Blum 4-0 SH 36	Ethicon	-	CABG Surgery
Sutures 2-0 Prolene Blu M SH	Ethicon	-	CABG Surgery
Sutures BB 4-0 Prolene	Ethicon	-	CABG Surgery
Temperature probe	3M	-	Anesthesia and others
Tonsil forceps	SureMed	GC09009-20D	CABG Surgery
Tungsten carbide ring-handled needle holder	SureMed	GN01013-22K	CABG Surgery
Tungsten carbide ring-handled needle holder	SureMed	GN01010-22K	CABG Surgery
UW Solution	Belzer	-	Anesthesia and others
Venous cannula	Medtronic	28Fr, 32Fr	Cardiopulmonary bypass
Ventilator	Mindray	SV300	Anesthesia and others
Weighted pen-style needle holder	Sinoview	NH10400-23	CABG Surgery