Novel Percutaneous Approach for Deployment of 3D Printed Coronary Stenosis Implants in Swine Models of Ischemic Heart Disease

Summary

We describe a novel, cost-effective, and efficient technique for percutaneous delivery of three-dimensionally printed coronary implants to create closed-chest swine models of ischemic heart disease. The implants were fixed in place using a mother-and-child extension catheter with high success rate.

Abstract

Minimally invasive methods for creating models of focal coronary narrowing in large animals are challenging. Rapid prototyping using three-dimensionally (3D) printed coronary implants can be employed to percutaneously create a focal coronary stenosis. However, reliable delivery of the implants can be difficult without the use of ancillary equipment. We describe the use of a mother-and-child coronary guide catheter for stabilization of the implant and for effective delivery of the 3D printed implant to any desired location along the length of the coronary vessel. The focal coronary narrowing was confirmed under coronary cineangiography and the functional significance of the coronary stenosis was assessed using gadolinium-enhanced first-pass cardiac perfusion MRI. We showed that reliable delivery of 3D printed coronary implants in swine models (n = 11) of ischemic heart disease can be achieved through repurposing mother-and-child coronary guide catheters. Our technique simplifies the percutaneous delivery of coronary implants to create closed-chest swine models of focal coronary artery stenosis and can be performed expeditiously, with a low procedural failure rate.

Introduction

Ischemic heart disease continues to be the number one cause of death in the United States¹. Large animal models have been used experimentally to understand and characterize mechanisms driving coronary artery disease (CAD) and associated complications (including myocardial infarction, arrhythmic events, and heart failure), as well as for testing of new therapeutics or diagnostic modalities. Results from these studies have helped to broaden the understanding, diagnosis, and monitoring of ischemic heart disease and to advance clinical practice². Several animal models including rabbits, dogs, and swine have been used. However, coronary stenoses, particularly discrete lesions, occur very rarely in these animals and are difficult to induce reproducibly³. Prior work described the creation of artificial coronary stenoses using ligation, occluders, or external clamps. Recently, we described how to use 3D printing technology to manufacture coronary implants that can be used to percutaneously create discrete artificial coronary narrowing⁴. Using computer-aided design software, we designed coronary artery implants as hollow tubes with varying inner and outer diameters as well as implant length and then fabricated them using commercially available additive materials. The implants are smooth, hollow, 3D printed tubes with rounded edges. We designed a library of implant sizes with a range of inner diameter, outer diameter, and length. The outer diameter of the implant is based on the size of the coronary guide catheter. The inner diameter is based on the size of a deflated coronary angioplasty balloon. We varied the length of the implant to tailor the desired severity of perfusion. However, safe percutaneous delivery of such devices can be challenging due to the lack of wires and catheters manufactured specifically for large animal use. In contrast, an extensive collection of catheters, wires, and supportive equipment are available for clinical use in human coronary arteries. In this work, we show how to repurpose a clinical grade mother-and-child coronary guide catheter for the delivery of the 3D printed coronary implants.

The GuideLiner catheter (Figure 1A) was developed for percutaneous coronary intervention (PCI) to allow for deep catheter seating and increased support for complex cases⁵. In our investigation, the GuideLiner catheter was chosen due to familiarity of use and availability, but similar catheters, where available, may also be considered. Considered a "mother-and-child" guide catheter (Figure 1B), the device fits inside a typical coronary guide catheter ("mother") and is a coaxial flexible tube ("child"). This catheter can be inserted over a guidewire and effectively lengthens the reach of a typical coronary guide catheter by extending beyond the end of the coronary guide. The GuideLiner or a similar mother-and-child catheter can be used as added support for deployment of the 3D printed coronary implants. Because the implants are mounted over angioplasty balloons to be inserted as a unit over a coronary wire into the vessel (Figure 1B,1C), the catheter offers additional support to deliver the implant to the desired site. By positioning the mother-and-child catheter just proximal to the balloon, the implant remains at the desired location during balloon deflation and retraction. Despite having some firmness to its structure, the mother-and-child catheter's unique ability to be advanced deep into coronary arteries over a guidewire and the radiopaque marker at the catheter tip were essential characteristics for implantation.

Our assembled delivery apparatus consisted of a typical coronary guide catheter, the mother-and-child catheter, and a 3D printed implant fixed onto a deflated coronary angioplasty balloon (Figure 1B). As a functional delivery unit, the mother-and-child catheter not only provided stable additional support for the delivery of the equipment but was also uniquely applied as a shearing device to keep the implants in place during deflation and removal of the balloon. The radiopaque marker at the catheter tip served as a positioning guide for the assembled apparatus and sits proximal to the angioplasty balloon. These characteristics allowed for precise deployment of the flow-limiting implants. The process was designed to be reproducible, efficient, and humane for the animal subjects.

In our application, the mother-and-child percutaneous delivery technique was used to create swine models with focal coronary stenosis for evaluation of contrast-enhanced stress cardiac perfusion magnetic resonance imaging (MRI). However, the technique may be employed in other investigations including vascular systems outside the coronary vessels.

Protocol

We conducted the experiments according to the guidelines by the Animal Welfare Act, the National Institutes of Health, and the American Heart Association on Research Animal Use. Our Institutional Animal Care and Use Committee approved the animal study protocol.

1. Preprocedural preparation of 3D printed coronary stenosis implants

1. Using tweezers, dip-coat the printed implants in a 25% heparin solution to prevent thrombus formation and allow to air dry for 24 h.

2. Preprocedural preparation of animal subjects

1. Have male Yorkshire swine (SNS Farms, 30–45 kg) arrive at the institution 1 week prior to the experiment date and allow them to acclimate.
2. Keep the swine in a fasting state after midnight the day prior to the procedure.

3. Procedural anesthesia

1. Sedate the swine with intramuscular ketamine (10 mg/kg) and intravenous midazolam (1 mg/kg).
2. Ventilate the animals with an oxygen-isoflurane (1–2%) mixture.
3. Perform endotracheal intubation once the animal subject is sedated.
4. Infuse intravenous (IV) rocuronium (2.5 mg/kg/h) and give additional boluses (1–3 mg/kg IV every 20–30 min) when needed to achieve diaphragmatic immobilization.
5. Maintain a surgical plane of anesthesia throughout the procedure by checking for awakening, movements, wide fluctuation in vital signs, and other signs of distress or discomfort throughout the duration of the experiment. We monitored the swine for roughly 6 h under anesthesia.

4. Vascular access

1. Using the Seldinger technique, insert the arterial and venous sheaths into the bilateral femoral arteries and veins of the subjects.
2. Flush all catheter ports continuously with heparinized normal saline.

5. Preprocedural medication administration

1. Administer amiodarone intramuscularly (1.5 mg/kg), lidocaine intravenously (2 mg/kg), and esmolol intravenously (1 mg/kg) as needed for prophylaxis against arrhythmia. Give repeat dosages of amiodarone, lidocaine, and esmolol as needed throughout the course of the experiment to suppress ventricular rhythms and control heart rate response.
2. After vascular access is obtained, administer heparin (5,000–10,000 units) to keep an activated clotting time (ACT) >300 s. Check the ACT every hour during the course of the experiment and give additional intravenous heparin as needed to maintain the ACT goal.

6. Hemodynamic monitoring

1. Use a single lateral electrocardiography (ECG) chest lead for recording changes in ST segment, T-waves, and heart rate during the entire experimental period.
2. Use a pressure transducer to record continuous femoral arterial pressure throughout the procedure.
3. Attach a pulse oximeter to the animal's ear or lip for continuous pulse oximetry recordings.

7. Preparation of implant delivery equipment

1. Prior to performing coronary angiography, insert a deflated NC Trek over-the-wire coronary balloon through a mother-and-child catheter of the desired size such that the balloon tip extends beyond the tip of the catheter.
2. Mount the 3D printed implant onto the deflated angioplasty balloon such that the implant is positioned between the markers of the balloon and close to the proximal marker (Figure 1B).
3. Inflate the balloon with an insufflator to 2–3 atm in order to fix the implant onto the balloon. Verify that the implant is positioned closer to the proximal half of the balloon so it will be closest to the mother-and-child catheter when ready for removal (Figure 1B).

8. Coronary angiography and deployment of coronary implant

1. Position the fluoroscopic C-arm in the anteroposterior (AP) projection.
2. Attach a control valve (see Table of Materials) to a left or right coronary guide catheter (see Table of Materials).
3. Introduce the guide catheter over a J-tipped wire through the right femoral artery sheath and, under fluoroscopic guidance, advance the catheter to the aortic root.
4. Selectively (or nonselectively) engage the catheter into the left main coronary artery (LMCA) and inject 5 mL of iodinated contrast under fluoroscopy to visualize the left coronary system.
5. Position the guide catheter towards the LMCA for the second angiogram (Figure 2). If coronary artery engagement proves difficult, due in part to the short aortic arch of the swine, consider performing non-selective angiograms as long as they provide adequate visualization of the vessels.
6. Once engaged within, or positioned near the LMCA, under fluoroscopy, advance a 0.014", 300 cm coronary wire (see Table of Materials) into the LMCA and further advance the wire to the distal left anterior descending artery (LAD) or left circumflex coronary artery (LCX) if desired (Figure 3).
7. Under fluoroscopic guidance, insert the previously assembled mother-and-child catheter with the inflated coronary angioplasty balloon and implant over the coronary wire and advance to the desired location along the coronary vessel. Inject 5 mL of iodinated contrast to visualize a discrete narrowing at the desired location where the coronary implant should be deployed (Figure 4).
8. Once the implant is in position, advance the mother-and-child catheter to the proximal marker of the inflated balloon.
9. Deflate the balloon and retract it through the mother-and-child catheter. This process allows the mother-and-child catheter to shear the implant off the balloon as it is retracted and fixes the position of the implant in the designated segment of the vessel.
10. Remove the balloon, mother-and-child catheter, and coronary wire.
11. Perform final angiograms to document the location of the new artificial stenosis within the vessel. When feasible, angiograms should be performed in two orthogonal views to acquire visual estimation of stenosis severity. A final angiography (Figure 5) can also be performed with subselective positioning of the mother-and-child catheter in the proximal vessel, which provides excellent opacification with minimal contrast.
12. Immediately transfer the animal to the MR suite to undergo cardiac stress perfusion MRI using gadobutrol (0.1 mM/kg) injected at a rate of 2 mL/sec.
    NOTE: The stress agent used was a 4 min infusion of adenosine at 300 µg/kg/min. The imaging protocol included 1) cine imaging (field of view [FOV] = 292 x 360 mm, matrix size = 102 x 126, repetition time [TR] = 5.22 ms, echo time [TE] = 2.48 ms, slice thickness = 6 mm, pixel bandwidth = 450 Hz, flip angle = 12˚); 2) first-pass perfusion at rest and at peak adenosine vasodilator stress using a spoiled gradient echo sequence (FOV = 320 x 320 mm, matrix size = 130 x 130, TR = 2.5 ms, TE = 1.1 ms, slice thickness = 10 mm, pixel bandwidth = 650 Hz, flip angle = 12˚; and 3) late gadolinium enhancement imaging using an ECG-gated, segmented, spoiled gradient-echo phase-sensitive-inversion-recovery sequence (FOV = 225 x 340 mm, matrix size = 131 x 175 mm, TR = 5.2 ms, TE = 1.96 ms, slice thickness = 8 mm, inversion time (TI) = optimized to null the myocardium, pixel bandwidth = 465 Hz, flip angle = 20˚). An illustrative first-pass perfusion image is shown in Figure 6.
13. After completion of the MRI protocol, euthanize the swine by an infusion of sodium pentobarbital (100 mg/kg).
14. Perform a lateral thoracotomy, excise the heart, and dissect the ex vivo heart to expose the coronary vessels. Note the location of the implant in relationship to either the diagonal branches (LAD territory) or obtuse marginal branches (LCX territory), and retrieve the implants.
15. Using blunted and curved Metzenbaum scissors, open the coronary vessel and inspect the vessel for gross injury (see Figure 7). Photograph the heart tissue for gross pathology and stain with triphenyltetrazolium chloride to exclude myocardial infarction (see Figure 8).

Results

After initial optimization of the procedure, the intervention component was completed within 30 min. The implants were successfully delivered in all 11 subjects (100%). The implant was retrieved at the autopsy in all 11 subjects (100%). Using the diagonal branches (along the LAD) or obtuse marginal branches (along the LCX) as positional markers, we found the position of the implant at fluoroscopic-guided deployment and at autopsy to be consistent in 10 of the 11 (91%) subjects where the implant was retrievable. In one su...

Discussion

In this work, we focused on a novel percutaneous deployment strategy for coronary stenosis-inducing implants and showed that a mother-and-child catheter can be repurposed for effective percutaneous delivery of 3D printed coronary implants. Discrete artificial coronary stenoses of variable severity can be created quickly in swine models with a high success rate and in a minimally invasive manner using standard human percutaneous coronary interventional techniques and equipment. These implants were shown to be safe in the ...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
3D-Printed coronary implants	Study Site Manufactured
Amiodarone IV solution	Study Site Pharmacy
Amplatz Left-2 (AL-2) guide catheter (8F)	Boston Scientific, Marlborough, Massachusetts, USA
Balance Middleweight coronary wire (0.014” 300cm)	Abbott Laboratories, Abbott Park, Illinois, USA
COPILOT Bleedback Control valve	Abbott Laboratories, Abbott Park, Illinois, USA
Esmolol IV solution (1 mg/kg)	Study Site Pharmacy
Formlabs Form 2 3D-printer with a minimum XY feature size of 150 µm	Formlabs Inc., Somerville, Massachusetts, USA
Formlabs Grey Resin (implant material)	Formlabs Inc., Somerville, Massachusetts, USA
Gadobutrol 0.1 mmol/kg	Gadvist, Bayer Pharmaceuticals, Wayne, NJ
GuideLiner catheter (6F)	Vascular Solutions Inc., Minneapolis, Minnesota, USA
Heparin IV solution	Surface Solutions Laboratories Inc., Carlisle, Massachusetts, USA
Ketamine IM solution (10 mg/kg)	Study Site Pharmacy
Lidocaine IV solution	Study Site Pharmacy
Male Yorkshire swine (30-45 kg)	SNS Farms
Midazolam IV solution	Study Site Pharmacy
NC Trek over-the-wire coronary balloon	Abbott Laboratories, Abbott Park, Illinois, USA
Oxygen-isoflurane 1-2% inhaled mixture	Study Site Pharmacy
Rocuronium IV solution	Study Site Pharmacy
Sodium Pentobarbital IV solution (100mg/kg)	Study Site Pharmacy
Triphenyltetrazolium chloride stain	Institution Pathology Lab