A three-tier Rescue stent improves outcomes over balloon occlusion in a porcine model of noncompressible hemorrhage

A porcine model of thoracic aortic aneurysms created with a retrievable drug infusion stent graft mirrors human aneurysm pathophysiology

Objective

Aneurysm pathophysiology remains poorly understood, in part from the disparity of murine models with human physiology and the requirement for invasive aortic exposure to apply agents used to create aneurysm models. A retrievable drug infusion stent graft (RDIS) was developed to isolate the aortic wall intraluminally for drug exposure. We hypothesized that an RDIS could deliver aneurysm-promoting enzymes to create a porcine model of thoracic aneurysms without major surgical exposure.

Methods

Retrievable nitinol stent graft frames were designed with an isolated drug delivery chamber, covered with polytetrafluoroethylene, and connected to a delivery wire with a drug infusion catheter installed to the outer chamber. Institutional Animal Care and Use Committee-approved Yorkshire pigs (n = 5) underwent percutaneous access of the femoral artery, baseline aortogram and stent placement in the thoracic aorta followed by 30-minute exposure to a cocktail of elastase, collagenase, and trypsin. After aspiration of excess drug, stent retrieval, and femoral artery repair, animals were recovered, with angiograms at 1 and 4 weeks followed by explant. Histological analysis, in situ zymography, and multiplex cytokine assays were performed.

Results

The RDIS isolated a segment of anterior aorta angiographically, while the center lumen preserved distal perfusion during drug treatment (baseline femoral mean arterial pressure, 70 ± 14 mm Hg; after RDIS, 75 ± 12; P = .55). Endovascular induction of thoracic aneurysms did not require prior mechanical injury and animals revealed no evidence of toxicity. Within 1 week, significant aneurysmal growth was observed in all five animals (1.4 ± 0.1 cm baseline to 2.9 ± 0.7 cm; P = .002) and only within the treated region of the aorta. Aneurysms persisted out to 4 weeks. Aneurysm histology demonstrated loss of elastin and collagen that was otherwise preserved in untreated aorta. Proinflammatory cytokines and increased matrix metalloproteinase activity were increased significantly within the aneurysm.

Conclusions

An RDIS achieves isolated drug delivery while preserving distal perfusion to achieve an endovascular porcine model of thoracic aneurysms without major surgery. This model may have value for surgical training, device testing, and to better understand aneurysm pathogenesis. Most important, although the RDIS was used to simulate aortic pathology, this tool offers intriguing horizons for focused therapeutic drug delivery directly to aneurysms and, more broadly, focused locoregional drug delivery to vessels and vascular beds.

A self calibrating, magnetic sensor approach accurately positions an aortic damage control stent in a porcine model

Objectives

Non-compressible torso hemorrhage remains a high mortality injury, with difficulty mobilizing resources before exsanguination. Previous studies reported on a retrievable stent graft for damage control and morphometric algorithms for rapid placement, yet fluoroscopy is impractical for the austere environment. We hypothesized that magnetic sensors could be used to position stents relative to an external magnet placed on an anatomic landmark, whereas an electromagnet would allow self-calibration to account for environmental noise.

Methods

A magnetic sensor alone (MSA) and with integrated stent (MSIS) were examined in a porcine model under anesthesia. A target electromagnet was placed on the xiphoid process (position 0 cm). Sensors were placed in the aorta and measurements obtained at positions 0 cm, +4 cm, and +12 cm from the magnet and compared with fluoroscopy. Sensors were examined under conditions of tachycardia/hypertension, hypotension, vibration, and metal shrapnel to simulate environmental factors that might impact accuracy. General linear models compared mean differences between fluoroscopy and sensor readings.

Results

Both sensors were compatible with a 10 French catheter system and provided real-time assessment of the distance between the sensor and magnetic target in centimeters. Mean differences between fluoroscopy and both magnetic sensor readings demonstrated accuracy within ±0.5 cm for all but one condition at 0 cm and +4 cm, whereas accuracy decreased at +12 cm from the target. Using the control as a reference, there was no significant difference in mean differences between fluoroscopy and both MSA or MSIS readings at 0 cm and +4 cm for all conditions. The system retained effectiveness if the target was overshot.

Conclusion

Magnetic sensors achieved the highest accuracy as sensors approached the target. Oscillation of the electromagnet on and off effectively accounts for environmental noise.This approach is promising for rapid and accurate placement of damage control retrievable stent grafts when fluoroscopy is impractical.

Level of evidence

Not applicable.

A dumbbell rescue stent graft facilitates clamp-free repair of aortic injury in a porcine model

Objective

Noncompressible torso hemorrhage is a high-mortality injury. We previously reported improved outcomes with a retrievable rescue stent graft to temporize aortic hemorrhage in a porcine model while maintaining distal perfusion. A limitation was that the original cylindrical stent graft design prohibited simultaneous vascular repair, given the concern for suture ensnarement of the temporary stent. We hypothesized that a modified, dumbbell-shaped design would preserve distal perfusion and also offer a bloodless plane in the midsection, facilitating repair with the stent graft in place and improve the postrepair hemodynamics.

Methods

In an Institutional Animal Care and Use Committee-approved terminal porcine model, a custom retrievable dumbbell-shaped rescue stent graft (dRS) was fashioned from laser-cut nitinol and polytetrafluoroethylene covering and compared with aortic cross-clamping. Under anesthesia, the descending thoracic aorta was injured and then repaired with cross-clamping (n = 6) or dRS (n = 6). Angiography was performed in both groups. Operations were divided into phases: (1) baseline, (2) thoracic injury with either cross-clamp or dRS deployed, and (3) recovery, after which the clamp or dRS were removed. Target blood loss was 22% to simulate class II or III hemorrhagic shock. Shed blood was recovered with a Cell Saver and reinfused for resuscitation. Renal artery flow rates were recorded at baseline and during the repair phase and reported as a percentage of cardiac output. Phenylephrine pressor requirements were recorded.

Results

In contrast with cross-clamped animals, dRS animals demonstrated both operative hemostasis and preserved flow beyond the dRS angiographically. Recovery phase mean arterial pressure, cardiac output, and right ventricular end-diastolic volume were significantly higher in dRS animals (P = .033, P = .015, and P = .012, respectively). Whereas distal femoral blood pressures were absent during cross-clamping, among the dRS animals, the carotid and femoral MAPs were not significantly different during the injury phase (P = .504). Cross-clamped animals demonstrated nearly absent renal artery flow, in contrast with dRS animals, which exhibited preserved perfusion (P<.0001). Femoral oxygen levels (partial pressure of oxygen) among a subset of animals further confirmed greater distal oxygenation during dRS deployment compared with cross-clamping (P = .006). After aortic repair and clamp or stent removal, cross-clamped animals demonstrated more significant hypotension, as demonstrated by increased pressor requirements over stented animals (P = .035).

Conclusions

Compared with aortic cross-clamping, the dRS model demonstrated superior distal perfusion, while also facilitating simultaneous hemorrhage control and aortic repair. This study demonstrates a promising alternative to aortic cross-clamping to decrease distal ischemia and avoid the unfavorable hemodynamics that accompany clamp reperfusion. Future studies will assess differences in ischemic injury and physiological outcomes.

Clinical Relevance

Noncompressible aortic hemorrhage remains a high-mortality injury, and current damage control options are limited by ischemic complications. We have previously reported a retrievable stent graft to allow rapid hemorrhage control, preserved distal perfusion, and removal at the primary repair. The prior cylindrical stent graft was limited by the inability to suture the aorta over the stent graft owing to risk of ensnarement. This large animal study explored a dumbbell retrievable stent with a bloodless plane to allow suture placement with the stent in place. This approach improved distal perfusion and hemodynamics over clamp repair and heralds the potential for aortic repair while avoiding complications.

A retrievable, dual-chamber stent protects against warm ischemia of donor organs in a model of donation after circulatory death

BACKGROUND

Ischemic injury during the agonal period of donation after circulatory death donors remains a significant barrier to increasing abdominal transplants. A major obstacle has been the inability to improve visceral perfusion, while at the same time respecting the ethics of the organ donor. A retrievable dual-chamber stentgraft could potentially isolate the organ perfusion from systemic hypotension and hypoxia, without increasing cardiac work or committing the donor.

METHODS

Retrievable dumbbell-shaped stents were laser welded from nitinol wire and covered with polytetrafluoroethylene. Yorkshire pigs were assigned to either agonal control or dumbbell-shaped dual-chamber stentgraft. A central lumen maintained aortic flow, while an outer visceral chamber was perfused with oxygenated blood. A 1-hour agonal phase of hypoxia and hypotension was simulated. Stents were removed by simple sheath advancement. Cardiac monitoring, labs, and visceral flow were recorded followed by recovery of the animal to a goal of 48 hours.

RESULTS

Cardiac stress did not increase during stent deployment. Visceral pO2 and flow were dramatically improved in stented animal relative to control animals. Five of 7 control animals were killed after renal failure complications, whereas all stent animals survived. Histology confirmed increased ischemic changes among control kidneys compared to stented animals.

CONCLUSION

A dual-chamber stent improved outcomes after a simulated agonal phase. The stent did not increase cardiac work, thus respecting a key ethical consideration. The ability of a dual-chamber stent to prevent ischemia during organ recovery may become a powerful tool to address the critical donor organ shortage.

Assessment of mechanical and biocompatible performance of ultra-large nitinol endovascular devices fabricated via a low-energy laser joining process

Nitinol is an excellent candidate material for developing various self-expanding endovascular devices due to its unique properties such as superelasticity, biocompatibility and shape memory effect. A low-energy laser joining technique suggests a high potential to create various large diameter Nitinol endovascular devices that contain complex geometries. The primary purpose of the study is to investigate the effects of laser joining process parameters with regard to the mechanical and biocompatible performance of Nitinol stents. Both the chemical composition and the microstructure of the laser-welded joints were evaluated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). In vitro study results on cytotoxicity demonstrated that the joining condition of 8 Hz frequency and 1 kW laser power showed the highest degree of endothelial cell viability after thermal annealing in 500°C for 30 min. Also, in vitro study results showed the highest oxygen content at 0.9 kW laser power, 8 Hz frequency, and 0.3 mm spot size after the thermal annealing. Mechanical performance test results showed that the optimal condition for the highest disconnecting force was found at 1 Hz frequency and 1 kW power with 0.6 mm spot size. Two new endovascular devices have been fabricated using the optimized laser joining parameters, which have demonstrated successful device delivery and retrieval, as well as acute biocompatibility.