Variations in rates of appropriate and inappropriate carotid endarterectomy for stroke prevention in 4 Canadian provinces

Background

Carotid endarterectomy (CE), when performed on appropriate patients, reduces the incidence of stroke, yet there are marked variations in rates of this procedure. We sought to determine reasons for the variation in CE rates in 4 Canadian provinces.

Methods

We identified all CEs performed in 4 Canadian provinces between January 2000 and December 2001, inclusive. From chart review and expert assessment, we determined the proportion of these procedures that were appropriate, inappropriate or of uncertain appropriateness, using the RAND/UCLA Appropriateness Method. We sought to determine the variation in rates by province and whether the variation was due to differences in type of hospital, surgical specialty or surgical volume.

Results

Overall, 1656 (52.3%) of the 3167 CEs studied were performed for appropriate indications. The proportions of appropriate procedures were 78.2% (176/225) in Saskatchewan, 58.7% (481/819) in Alberta, 49.1% (350/713) in Manitoba and 46.0% (649/1410) in British Columbia (p < 0.001 across provinces). Rates of appropriate procedures per 100 000 population ranged from 44.3 in Manitoba to 16.2 in Saskatchewan (p < 0.001 across provinces). CEs were more likely to be appropriate when performed by a neurosurgeon compared with all other surgeons (74.4% v. 49.4% were appropriate; p < 0.001), when performed by surgeons doing fewer than 31 procedures over 2 years compared with surgeons doing more than 31 (70.1% v. 49.5% were appropriate; p < 0.001) and when performed in hospitals doing fewer than 135 procedures per year compared with hospitals doing more than 135 (63.4% v. 49.1% were appropriate; p < 0.001). Overall, 10.3% of procedures were done for inappropriate reasons.

Interpretation

Our findings suggest some overuse (for inappropriate or uncertain indications) but also some underuse (low population rates in some regions). High rates of CE are associated with lower rates of appropriateness for both surgeons and hospitals. That 1 in 10 CEs is done inappropriately suggests the need for preoperative assessment of appropriateness.The efficacy of carotid endarterectomy (CE) to prevent stroke is well established.^1,2,3,4Clinical trials have shown that CE reduces the 5-year risk of stroke by 16.0% when performed because of symptomatic lesions causing more than 70% stenosis.⁵ The risk reduction is more modest (4.6% and 5.9%, respectively) in cases of symptomatic moderate (50% to 69%) stenosis or asymptomatic stenosis (> 60%).^4,5 However, concerns remain regarding the effectiveness of the procedure outside of clinical trials, when the potential benefit may be reduced.^6,7 Although national societies have issued guidelines on indications for CE,^8,9 in some cases CE is performed on patients who do not meet these guidelines.The RAND/UCLA (University of California at Los Angeles) Appropriateness Method,^10,11 developed in response to concerns about possible unnecessary use of procedures, is perhaps the most respected approach to defining appropriate care, combining best evidence and expert opinion.¹² The first study of the appropriateness of CE, published in 1988, showed that only one-third of procedures were appropriate.¹³ A Canadian study in 1997 showed similar results.¹⁴The role of health system factors in choosing patients appropriately for CE is not well explored. Administrative databases allow only limited appreciation of the decision-making process that leads to the operating room.Our objectives were to describe the variation in appropriateness of CE in 4 Canadian provinces, to document rates of appropriate CE in the provinces and to explore potential explanatory factors, such as hospital type, surgeon specialty and number of CEs performed each year per surgeon and per hospital.