ABSTRACT & COMMENTARY

By Jeffrey Zimmet, MD, PhD

SOURCE: Choi JC, et al. Early outcomes after carotid artery stenting compared with endarterectomy for asymptomatic carotid stenosis. Stroke 2014 Nov 25. pii: STROKEAHA.114.006209. [Epub ahead of print]

Although carotid artery stenting (CAS) is a less invasive means of carotid revascularization, multiple trials have demonstrated an increased risk of post-procedural stroke in patients with symptomatic carotid stenosis, as compared to carotid endarterectomy (CEA). Because of the lower annual stroke hazard associated with asymptomatic severe carotid stenosis (approximately 2%), carotid revascularization is recommended by current guidelines only in selected patients and when the procedural risk of morbidity and mortality is estimated to be less than 3%. Randomized clinical trial data comparing CAS to CEA for asymptomatic patients are lacking. Nevertheless, the application of CAS to this population in the United States has been growing steadily over the past decade.

Using retrospective data from the University Health System Consortium (UHC)’s clinical database, Dr. Anthony Kim and colleagues from the University of California, San Francisco department of neurology analyzed rates of in-hospital death and postoperative stroke following CEA and CAS performed on asymptomatic patients. For the study period from January 2010 to December 2012, the authors identified 17,716 patients with asymptomatic carotid stenosis treated with CEA and 3962 treated with CAS at 186 University Health System Consortium hospitals. Compared with CEA patients, those patients treated with CAS were more likely to be younger and black, and to have high-risk comorbidities, including coronary artery disease, peripheral artery disease, chronic kidney disease, and heart failure. Balancing this out, however, was a lower likelihood of having hypertension, hyperlipidemia, and smoking. Just 61% of patients in the CAS group and 59% in the CEA group were considered high risk for CEA by standard definitions (age > 80, history of coronary artery disease, congestive heart failure, or chronic lung disease).

In the unadjusted analysis, CAS patients compared with CEA patients were more likely to develop in-hospital death or postoperative stroke (4.0% vs 1.5%; P < 0.001). After logistic regression analysis adjusting for age, race, sex, and multiple comorbidities, the odds of stroke or death after CAS remained significantly higher than after CEA (odds ratio 2.5; 95% confidence interval, 2.1-3.1; P < 0.001). Similar results were obtained using propensity score matching. Other expected benefits of the less-invasive procedure did not materialize, as the postoperative myocardial infarction (MI) rate and early readmission for MI rate was not significantly different between the two groups.

Analysis of hospital-level and physician-level information yielded several interesting results. At the physician level, a link between higher operator volumes and improved outcomes was seen with CEA but not with CAS. Low annual procedure volumes for CAS may be partly responsible for this observation; median annual procedure volumes were only 1.5 for CAS, as compared with 3 for CEA. While rates of in-hospital death and postoperative stroke were < 3% for all specialties performing CEA, adverse event rates for CAS were > 3% for most specialties (vascular surgeons, neurosurgeons, radiologists, general surgeons, and neurologists), with the exception of cardiologists, who composed 22.8% of the total group and had an adverse event rate of 2.6%.

Hospitals for which CAS composed a greater proportion of carotid revascularization procedures had greater odds of inducing postoperative stroke or in-hospital death than those where CAS was less common, even after adjustment for patient-level variables.

The authors argue that "widespread prophylactic use of CAS for asymptomatic carotid stenosis is not justified without additional evidence of clear benefit, and provide further justification for additional randomized clinical trial data for this indication."

COMMENTARY

Currently in the United States, more than 90% of carotid revascularization procedures are performed in asymptomatic patients. The proportion of asymptomatic patients in the United States treated by CAS has increased from 3% in 1998 to 13% in 2008, and, further, to more than 18% in this analysis. This steady increase has been in spite of the lack of high-level evidence supporting the use of CAS in this population.

In the current study, CAS, as compared with CEA, was associated with more than a two-fold higher rate of in-hospital death and stroke, even after adjustm with several methods to adjust for confounding. In each group, the death/stroke rates exceeded the commonly accepted 3% threshold to justify any intervention. At the very least, randomized clinical trials are warranted to fully explore this question and to inform future practice.

The low per-physician and per-hospital annual CAS procedure volumes were a surprising and somewhat disturbing aspect of this study. Whether practitioners who perform only one or two procedures annually should continue to do so is questionable, especially in the already-controversial asymptomatic population.