Editors' ChoiceCardiology

Personalized printing for stroke prevention, hand in glove

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Science Translational Medicine  17 Jan 2018:
Vol. 10, Issue 424, eaar7516
DOI: 10.1126/scitranslmed.aar7516

Abstract

3D-printed patient-specific left atrial appendage occluders overcome anatomic variability to personalize stroke prevention.

Atrial fibrillation (AF) is the most common arrhythmia (electrical conduction abnormality) in the human heart. During AF, disorganized cardiac contractions allow blood clots to form in a pouch-like region of the heart called the left atrial appendage (LAA). These clots can travel to the brain where they cause devastating strokes. The risk of stroke can be reduced by taking anticoagulants (blood thinners), but this comes at the expense of increased bleeding. An alternative approach is to occlude the LAA with a device delivered surgically or via a catheter. However, because the LAA shape is highly variable, one-size-fits-all devices tend to incompletely occlude the pouch, leaving the stroke risk unchanged. In a recent report, Robinson and colleagues set out to build personalized soft LAA occluding devices customized to a patient’s anatomy.

Starting with patient-specific noninvasive computed tomography (CT) images, the team used computer-aided design to isolate the LAA surface and create a custom occluder with a 0.5 mm thick shell recessed 1 mm from the LAA surface. They added a chimney-like valve to the design to allow inflation and mechanical stabilization of the hollow occluder after implantation. Using the design, they created high-resolution three-dimensional (3D)–printed molds for casting and curing a silicone polymer blend, first in two halves that were later bonded together to create the closed volume occluder with an integrated valve. The device was dip-coated in polycarbonate urethane and cured to create a clot-resistant surface.

By delivering fluid from a syringe pump into the valve port in vitro, they found that the device could withstand more than ten times normal LAA pressures (~20 kPa versus < 2 kPa) and hold two times more volume than a typical LAA. They next created a custom cauliflower-shaped LAA model that mimics the most complex category of human LAA shapes. When this model was placed under pulsatile flow, the one-size-fits-all spherical occluders allowed substantial fluid leakage into the LAA whereas custom cauliflower-shaped occluders did not. Last, the occluder was combined with a purse-string suture and collapsed into an 18 French catheter (6 mm diameter) surgical deployment system. This allowed the entire workflow, from cardiac CT imaging to custom occluder fabrication and implantation, to be tested in a canine model. After deployment in vivo, the hollow occluder was filled with a biocompatible elastomer, which was cured over several hours, allowing time for adjusting fill volume and positioning.

Although the study included only one animal, it nevertheless establishes the feasibility of the workflow for creating soft, inflatable personalized devices for LAA occlusion from CT images. Future work will need to perform longer term evaluations in vivo to determine whether devices become endothelialized, are stable across time, and whether the LAA undergoes remodeling after occlusion. Nevertheless, as the population ages and the prevalence of AF and stroke continue to grow, hand in glove atrial appendage occluders offer an exciting gateway to personalized medical devices.

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