INDIANAPOLIS – A retrospective analysis has shed some light on the prevalence of carotid artery stent fracture, but ultimately underscores how little is known about the durability of carotid stents.
No accepted standard currently exists for carotid artery stent surveillance specific to fracture identification. In addition, the etiology of these fractures is unknown, as is their clinical relevance, Dr. Anthony Nigliazzo said at the annual meeting of the Midwestern Vascular Surgical Society.
He presented a retrospective analysis of 91 patients who received 107 carotid artery stents from January 2002 through December 2009 at the Michigan Vascular Center in Flint, a group that has significant carotid artery stenting (CAS) experience, including 14 CAS trials.
Two vascular surgeons and two radiologists independently reviewed anteroposterior and lateral cervical x-rays taken at a median follow-up of 28 months to evaluate for stent fractures. Because the reviewers did not all agree, a peer review consensus conference was held to determine whether fractures had occurred, Dr. Nigliazzo explained. Information from duplex ultrasounds obtained at 30 days, 6 months, and 1 year was also used to determine flow velocities and to correlate with a fracture diagnosis.
“We found this was a very difficult thing to do, not only in diagnosing stent fractures, but we really didn’t find a good correlation between our ultrasound findings and those patients” who developed fracture, he said.
Ultimately, the experts agreed that 4 of the 107 stents (3.7%) were fractured. Only one of the fractures had any evidence of restenosis, and none had clinical sequelae or were symptomatic at the time of identification.
When the team asked outside expert Dr. Michael Dake, a pioneer in endovascular stent development from Stanford (Calif.) University Medical Center, to review the same films, however, the fracture rate reached 7.7% for the 91 patients and 107 stents.
Overall, Dr. Nigliazzo said that the prevalence of carotid artery stent fracture appears to be low, but added that “the true incidence of stent fracture remains elusive.”
Part of the difficulty in making the diagnosis is that some fractures could not be seen on certain x-ray projections, and many stents had significant deformities. One such deformity – called “fish scaling,” in which layers of an open-cell stent protrude – make it appear that a fracture is present when it is not. Although vessel angulation greater than 45 degrees and calcification have been identified as risk factors for stent fracture, this was not apparent in the analysis, said Dr. Nigliazzo, a senior resident with the department of surgery at Michigan State University in Flint.
He noted that reported prevalence rates of carotid stent fracture vary widely, from 1.9% to 29%. “We believe this magnifies the difficulty in identifying stent fractures and the different modalities that investigators are using,” he said.
The researchers, led by Dr. Robert G. Molnar, who is with the Michigan Vascular Center and is chief of vascular surgery at McLaren Regional Medical Center, also in Flint, called for further research to determine the ideal methods for long-term CAS surveillance. For the time being, they recommended obtaining anteroposterior/lateral and oblique images for poststent fracture surveillance. One attendee cautioned that this type of surveillance may be “overkill” until it’s known whether clinical sequelae are associated with stent fracture.
Dr. Nigliazzo responded that the argument can go both ways, and highlighted a recent prospective Italian study reporting that stent fracture was significantly associated with restenosis (J. Vasc. Surg. 2010;51:1397-405).
Limitations of the current study include its retrospective design, the analysis of only 33% of the 272 patients who received stents during the study period, and the fact that x-ray quality varied with patient anatomy, calcifications, and angulation.
The cohort had a mean age of 71.6 years and was mostly male (61%). Overall, 45% had received a carotid stent after carotid endarterectomy whereas 15% did so after radiation. Only 4% were classified as low risk according to entry criteria for the CREST and CARESS trials.
The study was funded by the McLaren Foundation and the Michigan Vascular Center. The authors reported no conflicts of interest.