Optical Coherence Tomography (OCT) guided Percutaneous Transluminal Angiography (PTA) in lesions below the knee: a proof of concept study

The golden standard imaging modality for Percutaneous Transluminal Angioplasty
(PTA) is Digital Subtraction Angiography (DSA) using an iodine contrast agent.
This imaging modality is able to visualize the approximate diameter of the
vessel where the contrast agent is injected, thus enabling the surgeon to
estimate the size of the stenosis in the vessel wall. This technique however
has its shortcomings. Firstly, DSA does not allow objective measurement of the
vessel diameter. This means the surgeon must estimate the vessel diameter,
causing interobserver variability and difficulties in selecting the correct
balloon size or stent. Secondly, DSA does not give the surgeon sufficient
information on the morphology and shape of the plaque or stenosis in the
vessel. This information could change operative decision making it might
influence the decision to use or not use a stent, and the type of stent that
might have to be used. DSA uses iodinated contrast to visualize the vessels,
making it hazardous to use in patients with kidney failure with an eGFR below
29 ml/min/1.73m2 , as the risk of inducing acute kidney failure is increased in
these patients.

Optical Coherence Tomography (OCT) is an intravascular imaging modality that is
able to provide objective information, visualizing the quality of the vessel
wall, the morphology of the stenosis and the diameter of the vessel. Using a
catheter that is positioned within the affected blood vessel, OCT visualizes
the vessel wall by emitting near-infrared light to provide high-definition,
cross-sectional and three-dimensional image of the vessel microstructure. The
tip of the catheter is placed distal of the stenosis and, while administering a
bolus of iodine contrast agent, the tip of the catheter will be pulled back
while making images to visualize the structures of the vessel wall and
stenosis. While this is performed, a simultaneous image is made using DSA. This
enables the surgeon to assess the quality of the vessel wall and the morphology
and stability of the plaque while correlating the image made with the DSA to
the OCT images. Furthermore, it allows for objective measurement of the
diameter of the vessel, thus allowing the surgeon to select the correct balloon
size without guessing as the vessel wall can objectively be measured. If a
stent needs to be placed in the vessel, OCT provides information on the correct
size and can be used to ensure correct placement of this stent. OCT does not
require the use of additional contrast agent, enabling it to be used in
patients with reduced kidney function. Intravascular ultrasonography has also
been proposed to this end; however, OCT has a 10-fold greater spatial
resolution compared to intravascular ultrasonography. OCT is already being used
in the field of Cardiology, and this study aims to make the first steps with
this technique in the field of Vascular Surgery.

The advantages of OCT have improved patient outcomes in PCI procedures, where
it is part of the standard practice in both acute and chronic myocardial
infarction. PTA has comparable limitations to PCI using merely DSA. However,
this has not been studied outside of the coronary arteries thus far. The first
steps need to be taken to study the safety and efficacy of OCT within the
peripheral vascular system. This study will be the first step, using OCT in a
small population of patients undergoing PTA to provide the first proof of its
viability and its effectiveness in the peripheral vessels. This study will
focus on below the knee (BTK) arteries, as these are most comparable of all
peripheral vessels compared to coronary vessels.

This proof-of-concept study aims to prove the safety and usability of OCT in
BTK lesions. Furthermore, it aims to provide information on the discrepancy
between objective measurement of the vessel diameter using OCT versus the
estimated vessel diameter based on DSA, as well as the effect this extra
information has on intraoperative decision-making regarding the surgical
endpoint.

This will be a proof of principle study. It will be a one-armed trial wherein
patients will be their own control, thus the measurements as described will not
need a control group to provide the information required to achieve the stated
objectives. This study will be conducted between January 1, 2023, and January
1, 2025, in the Zuyderland MC. 20 patients will undergo PTA guided by DSA. When
the surgeon has located the stenosis within the blood vessel, OCT will e
utilized to measure the vessel diameter. After the procedure, the surgeon will
assess the OCT measurements and discuss whether their intraoperative
decision-making would have been altered knowing these measurements. Patients
will be followed until 6 weeks after the procedure, which is adequate to detect
adverse events caused by the procedure. This is also the current standard
clinical practice. As this is the first prospective study using OCT in BTK
arteries, a validation in a small patient group is necessary as a step-up to
larger studies.

The OCT system uses iodinated contrast during measurements, the same substance
as is already being used during PTA in order to make DSA images. OCT uses
4ml/sec during the measurement. The amount of contrast fluid is determined by
the length of the lesion. The contrast is injected in the vessel at the site of
interest. Although iodinated contrast is known to cause risk of acute kidney
failure, the amount used for the OCT measurement is minimal compared to the
amount used for DSA. The use of the agent is therefore justified. There are no
additional risks for participating subjects. Subjects undergo a PTA, which they
would undergo regardless of study participation. During this procedure, a
catheter is inserted into the artery. The additional OCT measurement is
performed using this catheter. This means that merely an extra measurement is
made using this catheter, which has no additional risks for the test subject.
No radiation is used.