Editors' ChoiceCardiology

Probing the entire vascular system

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Science Translational Medicine  13 Jan 2021:
Vol. 13, Issue 576, eabg1762
DOI: 10.1126/scitranslmed.abg1762

Abstract

Microscopic endovascular probes that navigate by blood flow and an external magnetic field may increase the capabilities of vascular catheterization.

Endovascular catheters are critical for medical practice, facilitating diagnostic and interventional procedures such as coronary arterial stenting or embolization of bleeding arteries. However, standard catheters are too large to navigate smaller or more tortuous blood vessels. Furthermore, their navigation requires manual push-based advancement and tip adjustment, with potential for traumatic injury to the blood vessels.

Pancaldi and colleagues recently developed a novel endovascular probe that addresses many deficiencies of standard catheters. The new probes are microscopic (40 to 350 μm in diameter), magnetic, flexible, tethered, and non-thrombogenic. They are deployed within the blood vessel via a saline pump and then depend on natural blood flow for navigation, which can be achieved even within tortuous vasculature. Unlike standard catheters, this navigation does not require contact pressure on vessel walls and thus reduces the potential for vessel perforation. As demonstrated in fabricated fluidics systems and ex vivo rabbit ears, the flow velocity and application of an external magnetic field at vessel bifurcations deformed the probe’s head to choose which vascular path to take. The probes could be linked to sensors to assess flow characteristics and temperature or to microtubes to inject dye locally, showing the potential of this technology for interventional applications.

This approach addresses the need for miniaturized endovascular catheters that leverage natural blood flow for navigation. However, because the system relies on blood flow, it must be deployed upstream of the target area. Yet, most current clinical catheter applications involve going against the normal blood flow (e.g., accessing the coronary arteries via a femoral artery) to minimize the invasiveness of the procedure and damage to critical vascular structures. Even so, this technology may be complementary to existing catheters and fill a specific niche for more distal, smaller arterial applications, particularly within the brain vasculature. Furthermore, this approach may allow specific embolization of distal vessels that are bleeding or are feeding a tumor rather than a major arterial branch, decreasing the morbidity of such procedures. Another apparent limitation is that the vasculature map must be known in order to magnetically guide the probe along the appropriate bifurcations. Presumably, this would require repetitive injection of a radiopaque contrast dye for visualization and may be challenging in a three-dimensional microscopic clinical situation dissimilar from the translucent ex vivo rabbit ears demonstrated in this work. Ultimately, even with these limitations, this technology represents an impressive step toward achieving miniaturized endovascular catheters for previously impossible but sorely needed clinical applications.

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