Optical Imaging Measurement of Intravascular Solution Efficacy Trial

Peripheral artery disease (PAD) affects anywhere from 8-12 Million people in the United
States. Many of these people go on to develop claudication, rest pain, and tissue loss.
During the workup for these disease states many imaging modalities are conducted including
Pulse Volume Recording, Duplex Ultrasound, Angiography, and IVUS, but an emerging catheter
based imaging has been developed that may supplement the current modalities used.

Intravascular optical coherence tomography (iOCT) is based on near-infrared light system.
The light reflects off plaque and other objects within vessels and the signals are processed
into a series of axial images (A-scans) at different positions along the artery to generate
a two-dimensional dataset (B-scans). These images are created at an extremely fine
resolution of 10-15 μm, which has allowed iOCT to be used in many research settings
including PAD and coronary artery disease. OCT has been approved for clinical use in the
coronary territory by the FDA in May 2010. Since then many centers have been using iOCT in
the daily clinical practice. However, it's still not widely in the clinical management of
patients with PAD. There is hope that the high resolution capabilities of iOCT may help
before and after an intervention to predict outcomes or correct errors in stent deployment.

The iOCT procedure for lower extremity PAD is fairly straightforward. An introducer is
placed into the femoral artery. After which a wire is placed past the lesion of interest and
the iOCT catheter is inserted. The catheter is then attached to an automated pullback
device. Next an optical medium is needed to displace the erythrocytes. Due to the high
resolution of the iOCT this is necessary for a cleaner image to analyze. At the time of
injection of the optical medium a sensor triggers the catheter to be withdrawn (distal to
proximal) at anywhere from 10-25 mm/sec. The images are captured and processed and arterial
plaque can be characterized.

The greatest strength of the iOCT catheter is its high resolution images but the problem is
that the imaging signal is substantially attenuated by blood. In order to remedy this
complication techniques such as proximal balloon occlusion and continuous infusion of a
fluid have been used to acquire improved iOCT images. In the continuous infusion methods,
different mediums have been injected such as contrast, dextran, and even an oxygen-carrying
substitute in hopes of improving decreasing the attenuation by blood.

In order the overcome the attenuation of red blood cells during iOCT imaging, we are
proposing a novel approach involving CO2 injection to clear the erythrocytes. Currently CO2
is used as medium for digital subtraction angiography in patients with renal insufficiency
and was first used in humans by Hawkins in 1982. The other alternative for angiography,
iodinated contrast medium, is nephrotoxic and thus is avoided in these patients for fear of
exacerbating the patient's acute or chronic problem. Another group where CO2 angiography is
employed is history of a contrast allergy. Although this technique is usually used under
these circumstances, Kerns et al reports conducting CO2 angiography in as high as 20% of
their patients with abdominal and lower extremity studies.

In addition to the benefits of patients with allergies and renal insufficiency, CO2 is
extremely safe in a variety of arterial and venous applications. It is 20 times as soluble
as room air and is expired through the lungs in a first-pass-type effect. The current
contraindication to CO2 digital subtraction angiography is that the cerebral arterial
circulation should never be exposed to CO2 because of possible neurotoxicity. Relative
contraindications include use in the presence of a large arteriovenous shunt, with nitrous
oxide anesthesia, and used cautiously in patients with chronic obstructive pulmonary
disease.

Dextran has been used in the past in the critical care setting of human as a volume expander
with the rare side effects of anaphylaxis and nephrotoxicity. It has also been used in human
coronary arteries with iOCT as a blood displacement medium. Finally it has been used with
iOCT in a proximal occlusion model. The main complaint in the final study was a burning
sensation that lasted < 10s.

Iodinated contrast is the current gold standard for infrainguinal angiography imaging in
patients without renal insufficiency and has also been used with iOCT to improve image
quality in human coronary arteries as well as carotid arteries. The current debate in the
literature for iOCT medium is between iodinated contrast and dextran and CO2 may offer a
superior method of iOCT imaging during lower extremity occlusive disease interventions.

Inclusion Criteria:

- Age greater than or equal to 18 years

- English speaking

- Scheduled to undergo an infrainguinal angiogram and/or endovascular procedure as
determined by a vascular surgery specialist

- Superficial Femoral Artery diseased segment

Exclusion Criteria:

- Acute or Chronic Renal insufficiency with Cr >1.5

- Chronic obstructive pulmonary disease

- Congestive heart failure (American Heart Association C lass III or IV)

- Acute limb ischemia, defined by a significant change in symptoms (one category on the
Rutherford scale within the previous 14 days)

- Concurrent oral anticoagulant therapy that cannot be safely withheld