LAA Closure: the LAA is the windsock-like structure shown to originate from the left atrium (3 o’clock). [Image: Wikipedia]

According to a recent paper by Kevin R. King, with the UC San Diego Department of Medicine and Bioengineering, atrial fibrillation, or AF, is the most common arrhythmia in the human heart. When this occurs, disorganized cardiac contractions allow blood clots to form in a region of the heart called the left atrial appendage, or LAA – a pouch of tissue about the size of the thumb located off the left atrium. If these clots make their way up to the brain, a stroke occurs. Blood thinners can be taken to reduce stroke risk, but the patient will have increased bleeding, so another option is to occlude (close) the LAA with an occluder, a small, elastomeric balloon delivered through a catheter or surgery. However, standard one-size-fits-all devices won’t help: the shape of the LAA varies, so the device may not totally close it up.

As we know, 3D printing technology is often used to build personalized, patient-specific medical devices, models, and implants. In his paper, King mentions another report, which is centered on the efforts of a group of researchers with the Dalio Institute of Cardiovascular Imaging at New York–Presbyterian Hospital and Weill Cornell Medicine who are working to develop 3D printed, personalized soft LAA occluding devices that are customized to a specific patient’s anatomy.

Together, the researchers – Sanlin S. Robinson, Seyedhamidreza Alaie, Hannah Sidoti, Jordyn Auge, Lohendran Baskaran, Kenneth Avilés-Fernández, Samantha D. Hollenberg, Robert F. Shepherd, James K. Min, Simon Dunham, and Bobak Mosadegh – used their combined expertise in the areas of biomedical engineering, cardiology, manufacturing, and materials to develop a soft, 3D printed, patient-specific occluder, then published a paper about their efforts in Nature Biomedical Engineering.

Sanlin Robinson [Image: Nature Biomedical Engineering]

“While our ultimate goal is to make an occluder that can be delivered to the left atrial appendage (LAA) percutaneously, in this paper we focused on a clinically relevant surgical approach that allowed us to test the efficacy of the patient-specific design without the added complications of catheter delivery and deployment,” Robinson wrote. “This decision occurred while our engineering team was attending the 4th International Symposium on the Left Atrial Appendage in NYC—a clear example of how attending conferences in fields outside of engineering can often stimulate new thoughts on how to execute interdisciplinary research.”

LAA occluder devices inserted through a catheter look like circular, mini umbrellas, and self-expand inside the LAA in order to prevent blood from flowing into the appendage. While they come in multiple sizes to fit more people, the devices do have some issues, such as the metal hooks used to anchor the device perforating the thin tissue.

The abstract for the paper reads, “3D printing has been used to create a wide variety of anatomical models and tools for procedural planning and training. Yet, the printing of permanent, soft endocardial implants remains challenging because of the need for haemocompatibility and durability of the printed materials. Here, we describe an approach for the rapid prototyping of patient-specific cardiovascular occluders via 3D printing and static moulding of inflatable silicone/polyurethane balloons derived from volume-rendered computed tomography scans. We demonstrate the use of the approach, which provides custom-made implants made of high-quality, durable and haemocompatible elastomeric materials, in the fabrication of devices for occlusion of the left atrial appendage—a structure known to be highly variable in geometry and the primary source of stroke for patients with atrial fibrillation. We describe the design workflow, fabrication and deployment of patient-specific left atrial appendage occluders and, as a proof-of-concept, show their efficacy using 3D-printed anatomical models, in vitro flow loops and an in vivo large animal model.”

Patient-specific left atrial appendage occluder. (a) This elastomeric device can be completely evacuated and inflated to large volumes. (b) We use CT image slices from the patient’s heart to get their exact LAA geometry, from this we design a personalized LAA occluder that matches their morphology upon implantation into the appendage. [Image: Nature Biomedical Engineering]

The team used CT images of a person’s heart and a CAD program to isolate the surface of the LAA with a 0.5 mm thick shell, adding a valve for inflation and mechanical stabilization to the design. As with many objects we hear about, the occluder itself wasn’t 3D printed, but the molds to create it were: the researchers 3D printed high-resolution molds of the design for casting, filling them with a soft silicone polymer blend so the resulting hollow occluder would conform to the walls of the appendage once it was implanted.

“To demonstrate the feasibility of this workflow, as well as the functionality and performance of the occluder, we implanted our device into a large animal model 2 weeks after receiving the animal’s CT scan,” Robinson explained.

Once the 3D printed occluder was implanted, the researchers filled it with liquid epoxy until it expanded and filled up the space; it then hardened after 24 hours to secure the occluder, which will stop the blood from flowing into the LAA and negating the risk of blood clot formation inside.

Robinson said, “While we did not perform a chronic study, we expect after 30-45 days the atrial facing wall of the occluder to become covered with endothelial and smooth muscle cells, essentially sealing the appendage from the rest of the left atrium.”

While more experiments will be necessary to validate the 3D printed occluder’s long-term performance, Robinson believes that it was a significant first step in 3D printed patient-specific endovascular devices.

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