A Novel Porcine Model of Bilateral Hindlimb Bypass Graft Surgery Integrating Transit Time Flowmetry

Abstract

Background: Bypass graft surgery is a key surgical intervention for ischemic heart disease (coronary bypass graft surgery) and critical limb ischemia (peripheral bypass graft surgery). Graft occlusion remains a significant clinical problem for both types. Further research into the pathobiological mechanisms of graft occlusion are needed in order to design targeted therapeutic strategies.

Methods: Three Large White female pigs (mean weight 52.3 +/- 4.4 kg) received general anaesthesia prior to surgery. The external jugular vein was harvested bilaterally, and a bilateral femoral peripheral arterial bypass was performed, with the superficial femoral artery permanently ligated. The grafts were interrogated immediately post operatively on-table using Medistim MiraQ transit time flowmetry system (Medistim, Oslo, Norway) to assess graft performance. On postoperative day three, the pigs were returned to the operating room, and the grafts were interrogated once again using transit time flowmetry.

Results: Six out of six (100%) successful bilateral EJV to femoral artery bypass grafts were performed. All pigs were successfully recovered, and returned to the operating room at postoperative day 3. The wounds were re-opened and the grafts were inspected. Postoperative graft assessment was performed with transit time flowmetry using the Medistim MiraQTM system (Medistim, Oslo, Norway), demonstrating all grafts were patent (100%).

Conclusion: This model may serve as a platform to gain further mechanistic insight into graft failure pathobiology. By combining a bilateral graft model with gold-standard transit time flowmetry, longitudinal experimentation of targeted therapeutic interventions to combat graft failure may be further studied with improved objectivity.

Keywords: Atherosclerosis; Bypass; Cardiovascular; Graft failure; Thrombosis.

Fig. 1

Positioning of the pig in dorsal recumbent position. a) Ultrasound-guided marking of bilateral femoral arteries) and b) landmarks for dissection of bilateral external jugular veins, at the intersection of a triangle made by the sternal notch, ramus of the mandible, and shoulder joint

Fig. 2

a) Exposure of the left external and internal jugular veins, b) harvested EJV conduit. Great care was taken to avoid injuring the carotid artery and vagus nerve, which lie in close proximity to the IJV. A total conduit length of approximately 5-8cm of vein was prepared. The proximal and distal ends of this length were clamped, ligated with Vicryl ties and divided. The EJV conduit was removed carefully inspected for defects, and reversed (Figure 2)

Fig. 3

a) Right femoral artery dissected, looped and clamped, with arteriotomy performed. The arterial lumen was flushed with heparinized saline and inspected prior to graft anastomosis. B) Proximal anastomosis of EJV conduit to femoral artery

Fig. 4

(a) Completed anastomosis. (b) Patent bypass graft at postoperative day three. Patency was confirmed by a palpable pulsatile graft, and verified with transit time flowmetry

Fig. 5

Graft performance was objectively assessed both intraoperatively and at postoperative day 3 using a Medistim MiraQ^™ probe (left). In this figure demonstrating a right femoral bypass graft, a 5 mm probe was used, showing a mean graft flow rate of 30mL/min with a pulsatility index of 1.3, which are both within acceptable limits for a vein bypass graft

Fig. 6

TTFM probe size, mean graft flow, and pulsatility index for each graft, immediately following anastomosis (Day 0) and postoperative day 3 (Day 3)