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Chronic kidney disease is common among patients undergoing carotid revascularization, and while moderate renal dysfunction generally has little impact on outcomes, severe renal insufficiency is associated not only with increased short-term mortality and stroke in those who receive carotid artery stenting (CAS) but also with dramatically reduced 5-year survival regardless of whether patients receive CAS or carotid endarterectomy (CEA).

The findings from a retrospective series were published online June 20, 2011, ahead of print in the Archives of Surgery.

Investigators led by Mark G. Davies, MD, PhD, of the Methodist DeBakey Heart and Vascular Center (Houston, TX), reviewed a database of 921 patients who underwent carotid revascularization at a single center between 1996 and 2006. Carotid stenosis was required to be at least 80% if patients were asymptomatic and at least 50% if they were symptomatic.

Patients Stratified by Renal Function

Renal function was evaluated using the Modification of Diet in Renal Disease formula, with overall mean glomerular filtration rate (GFR) estimated to be 69.5 mL/min/1.73 m². Patients’ renal function status was classified as:

• Normal function (GFR ≥ 60 mL/min/1.73 m²): 604 patients
• Moderate renal insufficiency (GFR < 60 but ≥ 30 mL/min/1.73 m²): 262 patients
• Severe renal insufficiency (GFR < 30 mL/min/1.73 m²): 55 patients

Seven patients were undergoing dialysis at the time of intervention.

Of the 921 patients revascularized, 81% received CEA and 19% CAS. The latter were more likely than surgical patients to have a history of MI or congestive heart failure (P < 0.001 for both). Stratified by renal function, the percentages of patients receiving each procedure were:

• Normal function: 84% CEA vs. 16% CAS
• Moderate renal insufficiency: 77% CEA vs. 23% CAS
• Severe renal insufficiency: 76% CEA vs. 24% CAS

At 30 days, overall mortality was 1.1%, while stroke occurred in 3.04% of patients, MI in 1.30%, and major adverse events (MAE; composite of ipsilateral stroke, MI, and death) in 4.3%.

When results were stratified by level of renal function, most outcomes, including stroke and MAE, were similar across the spectrum. Only mortality differed significantly (table 1).

Table 1. CAS and CEA: 30-Day Outcomes by Renal Function

Analyzed according to type of procedure, there were no differences in any 30-day outcomes among the 3 levels of renal function for those who underwent CEA. However, in the CAS group, rates of mortality, stroke, and the combination of death and stroke were all higher in patients with severe renal insufficiency (table 2).

Table 2. CAS: 30-Day Outcomes by Renal Function

Without considering the different levels of renal function, comparison of the 2 procedures at 30 days showed that CAS yielded higher rates of mortality (2.9% vs. 0.7%; P = 0.01) and MI (3.5% vs. 0.8%; P = 0.005) as well as a trend toward increased stroke (5.3% vs. 2.5%; P = 0.07).

Over a mean follow-up of 4.5 years, 28% of patients died, 5% experienced an ipsilateral stroke, 10% suffered an MI, and 35% had a major adverse event.

When normal renal function was compared with moderate insufficiency, the only difference that emerged was a higher survival rate for patients with normal function who underwent CEA. On the other hand, when normal function was paired with severe insufficiency, patients with the latter status generally had far worse outcomes irrespective of the chosen revascularization method. The only exception was stroke rates, which were similar across renal function groups for CEA (table 3).

Table 3. Freedom from Events at 5 Years

According to the authors, a limitation of the study for comparing CEA with CAS is “a potential unequal distribution of patients toward one modality based on the preconceived notion that one modality was safer for high-risk patients. During our study period, 1996 to 2006, CAS was often seen as the ‘less invasive’ and therefore safer operation for patients deemed as medically high risk,” they note.

Nonetheless, Dr. Davies and colleagues point to one disparity between the 2 strategies in regard to renal function. “When undergoing CEA, both short-term and long-term outcomes for freedom from stroke are similar among patients, regardless of degree of renal function,” they write. “However, when undergoing CAS, patients with severe renal insufficiency exhibit higher rates of stroke during both the perioperative period as well as during long-term analysis.”

Data Not Strong Enough to Influence Revascularization Choice

“The authors seem to make the claim—not directly but indirectly—that endarterectomy is better in patients with renal dysfunction,” said Hitinder S. Gurm, MD, of the University of Michigan Medical School (Ann Arbor, MI), in a telephone interview with TCTMD. “But I think that’s an overstatement given that only 13 patients with severe renal dysfunction underwent stenting.”

In addition, he pointed out, 20% of CAS patients did not receive successful embolic protection, and all procedures were performed at least 5 years ago—both factors suggesting that this series does not represent contemporary standards for carotid stenting.

“For long-term risk, I think these data are fairly corroborative of earlier studies suggesting that the worse the renal function, the worse the long-term survival,” Dr. Gurm commented, noting that 5 years after revascularization more than two-thirds of patients with severe renal insufficiency had died.

“So the question one has to ask [about patients with renal insufficiency]—especially if they are asymptomatic—is whether there is any value in trying to do either endarterectomy or stenting,” he said. “That should be discussed at the time the procedure is being planned. I’m not sure that abnormal renal function as such is a contraindication to intervention. For a given patient, it’s all about risk versus benefit.”

Unfortunately, early studies of medical therapy vs. CEA excluded subjects with severe renal dysfunction, and no randomized trials have compared CAS with medical therapy, Dr. Gurm observed, “so we don’t really know how patients with severe renal dysfunction will do on medical therapy alone.” 

The current study emphasizes that physicians should take renal function into account, he concluded, “but I don’t think it’s in a position to help them choose one therapy over another based on renal dysfunction—that would be premature.”

Study Details

Among the overall cohort, comorbidity rates were high: 27% had a prior MI, 12% congestive heart failure, 87% hypertension, 9% atrial fibrillation, 10% chronic obstructive pulmonary disease, 32% diabetes, and 11% hypothyroidism. In addition, 73% of patients had a history of tobacco use.

CAS patients were implanted with self-expanding monorail carotid stents (Wallstent, Boston Scientific, Natick, MA; Precise, Cordis, Warren, NJ; or Acculink, Guidant, Santa Clara, CA). All CAS patients were given clopidogrel (75 mg/dL) and aspirin (81 mg) beginning 3 days before the intervention. After stenting, clopidogrel was continued for 1 month, and aspirin was continued for life.

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