ODESSA Trial Looks Inside Drug-Eluting Stents With Optical Coherence Tomography (OCT)

related stories:
Overview of
Drug-Eluting Stents

Interview with Marc D. Feldman, MD about OCT

Volcano Corp Announces First Human Use of the Volcano Optical Coherence Tomography (OCT) Imaging Catheter

October 22, 2008 / Washington, DC -- A new imaging technology, Optical Coherence Tomography (OCT) popped up in a number of presentations and evening symposia at this year's Transcatheter Cardiovascular Therapeutics meeting (TCT 2008). OCT is very new: one of the two currently available systems was first used in humans only five months ago.

OCT image from ODESSA
Trial, showing covered and
uncovered struts of a
drug-eluting stent

OCT is a catheter-based system which provides a high resolution image of the inner artery surfaces (10 microns) and can easily show if stents have been covered by the body's endothelial cells. Theoretically, as long as metal stent struts remain uncovered, healing is delayed and the risk of blood clotting (stent thrombosis) inside the artery is higher. Antiplatelet therapy keeps the blood slippery and minimizes this risk while the cells gather and cover the metal struts.

Until the development of OCT, there was no direct way to see if struts had been covered, except through pathology specimens (in fact pathologist Renu Virmani was one of the early voices of concern regarding the delayed healing around stents that she had seen in specimens).

But OCT allows viewing the interior surfaces of the artery and stent in an awake patient. The imaging is done in the cath lab, over the same type of wire as balloons, stents, IVUS, etc. devices are delivered.

The assessment of strut coverage in stents was the goal of the ODESSA Trial (Optical coherence tomography for DES SAfety). Presented last Tuesday by Dr. Giulio Guagliumi of Ospedali Riuniti di Bergamo, Italy, the goal of this trial was to determine whether OCT could accurately measure strut coverage and stent malapposition in long lesions (greater than 20mm) that required overlapping stents. Overlapping stents are associated with an increased incidence of uncovered struts.

Although the number of patients (77) and stents (189) was small, the actual number of struts analyzed was 53,047. The stents were further divided in to four groups: sirolimus-eluting (SES) or CYPHER stents, paclitaxel-eluting (PES) or TAXUS stents, zotarolimus-eluting (ZES) or ENDEAVOR stents, and bare-metal stents (BMS). Also measured was the amount of neo-intimal hyperplasia (NIH): the amount of tissue regrowth inside the stent. Too much NIH and restenosis occurs: the stent closes up. Too little NIH may result in delayed healing and increased stent thrombosis, especially late stent thrombosis which can occur a year or more after implantation.

The results of ODESSA showed that OCT could indeed accurately measure strut coverage and NIH, and thus has a place in further clinical trial research. An interesting data point, was confirmation of the differences in the currently available DES. Medtronic has touted the safety advantage of its zotarolimus-eluting Endeavor stent and, in fact, the ODESSA results showed that at six months, virtually all the struts of the Endeavor stent were covered -- the healing was even more complete than with bare metal stents, which reinforces reports of little or no very late stent thrombosis with the Endeavor.

At the same time, an inverse relationship was observed between strut coverage and growth of NIH -- the Endeavor had the highest NIH growth of the DES (also called Late Loss) while the Cypher stent had the least Late Loss, but the highest number of uncovered struts. The clinical significance of these data is beyond the scope of the ODESSA Trial, but the author report clinical events were low overall with no statistically significant difference.

6 month Follow-up	% uncovered or malapposed		% of Intimal Hyperplasia
	OL	non-OL	OL
SES (Cypher)	8.70	7.90	19.3
PES (Taxus)	8.30	2.30	31.5
ZES (Endeavor)	0.05	0.01	45.2
BMS (Liberte)	1.80	0.50	57.8

Reviewing the ODESSA Trial for the American College of Cardiology's Cardiosource, Dr. Dharam J Kumbhani of the Cleveland Clinic concluded: "While the OCT findings are unique and interesting, the clinical significance of these findings is unclear. Moreover, even in this small study, the investigators had to analyze more than 50,000 struts. Hence, until this methodology is standardized, automated, and validated, its applicability in routine practice is limited."

Angioplasty.Org expects to see the use of OCT increase in future clinical trials and may, at some future time, be useful in determining when it is safe for DES patients to stop dual antiplatelet therapy.

Reported by Burt Cohen, October 22, 2008 (updated)