The Underuse of Carotid Interventions in Veterans With Symptomatic Carotid Stenosis
Published Online: July 24, 2014
Salomeh Keyhani; Eric Cheng; Susan Ofner; Linda Williams, and Dawn Bravata
Stroke is the fourth leading cause of death and a leading cause of disability among adults in the US.1 Approximately 10 to 15% of ischemic strokes are attributable to atherosclerosis of the internal carotid arteries. 2 Carotid stenosis is categorized as either symptomatic or asymptomatic. Patients with recent (less than 6 months) ischemic stroke or transient ischemic attack (TIA) in the vascular distribution of a partially blocked carotid artery are defined as having symptomatic carotid stenosis, and patients who have not had either a TIA or stroke in the distribution of the stenotic artery are defined as having asymptomatic carotid stenosis.3
Carotid endarterectomy (CEA) is the only surgical intervention proven in randomized controlled trials (RCTs) to reduce the risk of stroke.4-9 Carotid artery stenting (CAS) is a newer, less invasive, percutaneous procedure that involves angioplasty of the carotid stenosis and placement of a stent to open the stenotic area.10,11 For persons with symptomatic severe (>70%) carotid stenosis, the absolute risk reduction for CEA is 17% over 2 years (8.5% per year).12 This translates to an annualized number-needed-to-treat (NNT) of about 12, among the lowest annualized NNT reported for any secondary stroke intervention. In other words, CEA is highly effective at reducing the risk of subsequent stroke and is recommended in the management of patients with symptomatic severe carotid stenosis. Carotid stenting has never been compared to medical therapy. However, a large RCT that compared carotid stenting to CEA showed that patients undergoing either procedure had similar rates of a primary outcome consisting of stroke, myocardial infarction, or death during the periprocedural period, or ipsilateral stroke within 4 years of randomization.13 A recent meta-analysis concluded that these procedures should be considered “complementary rather than competing modes of therapy” and patient selection may play a role in who would benefit from either modality of intervention.14
Although a number of studies have examined the appropriate use of CEA among patients who have received intervention in the Medicare program,3,15-17 very few studies have examined the underuse of this procedure in patients with stroke—those who stand to benefit the most from revascularization. To our knowledge only 1 study, published more than 15 years ago, examined the use of carotid intervention in a cohort of veterans which demonstrated underuse of CEA in both symptomatic and asymptomatic populations.18 Given the large and well-accepted clinical benefit in stroke reduction, the appropriate receipt of revascularization in this high-risk population is particularly of interest.
In this study, we examined the use of carotid intervention among patients with an acute ischemic stroke in the Veterans Health Administration (VA) and determined factors associated with receipt of intervention. We specifically hypothesized that access to vascular surgery services at the VA medical center (VAMC) where patients were admitted for the management of their stroke may be associated with receipt of intervention.
As part of the VA Stroke Special Study conducted in 2007, a multidisciplinary team with members drawn from the VA Office of Quality and Performance, the VA Stroke Quality Enhancement Research Initiative (QUERI), the VA Office of Patient Care Services, and the VA Office of Nursing Services was assembled to develop stroke quality measure specifications and to develop the data collection methodology. 19-21 Data from the VA Stroke Special Study pertaining to carotid imaging use was used in this study. Data on availability of carotid intervention services (CEA or CAS) was obtained from the National VA SAS databases. Data on receipt of carotid intervention in the Medicare program was obtained from the Medpar and physician supplier files. We examined whether any eligible veteran received CEA using International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code 38.12 from the Medpar file and CPT code 35301 from outpatient data. Similarly, we identified patients who received CAS using ICD-9-CM codes 00.61 and 00.63 and CPT codes 37215 and 37216 6 months post stroke in the Medicare program.3,22
A national cohort of all veterans (N = 5721) admitted to a VAMC between October 1, 2006, and September 30, 2007, with a primary discharge diagnosis of ischemic stroke were identified from VA administrative data using a modified high specificity algorithm of ICD-9-CM.23 A sample of 5000 medical records was obtained by including all veterans at small-volume centers (≤55 patients in fiscal year 2007) and an 80% random sample of veterans at high-volume centers (>55 patients in fiscal year 2007). Trained nurse abstractors confirmed a diagnosis of ischemic stroke in 3987 patients and then proceeded with a chart review of 307 data elements among the confirmed patients. Data elements especially relevant to this study from chart review include results of carotid studies, receipt of carotid intervention, comorbid conditions, code status, and stroke characteristics. Inter-rater reliability was greater than 70% for over 90% of data elements.
Among the 3987 patients, 3014 received at least 1 carotid imaging test (Figure). We excluded the following patients: those with a code status of do not resuscitate/ do not intubate (N = 338) or who were discharged to hospice (N = 20), because these patients would likely be too ill to receive CEA or CAS; patients with posterior circulation stroke (N = 926) because the carotid stenosis would be classified as asymptomatic (see assessing side of stroke, below); patients who had atrial fibrillation (N = 280) because the original randomized controlled trials excluded such patients; and patients with missing data on carotid stenosis (N = 2). That left 1717 patients for the analyses.
The American Academy of Neurology recommends CEA for severe (70%-99%) symptomatic stenosis and considers CEA as only moderately useful for symptomatic patients with 50%-69% stenosis.12 Current guidelines do not recommend surgery for patients with less than 50% stenosis. 12 Similarly, the American Heart Association and the American Stroke Association guideline recommends carotid intervention for patients at average or low surgical risk who experience nondisabling ischemic stroke or transient cerebral ischemic symptoms, within 6 months of the event, if the stenosis of the lumen of the ipsilateral internal carotid artery is more than 70% as documented by noninvasive imaging or more than 50% as documented by catheter angiography, and the anticipated rate of perioperative stroke or mortality is less than 6%.10 We considered patients appropriate for intervention if they had documented carotid stenosis between 50% and 99% and had had a stroke in the distribution of the carotid artery. Among the 1717 patients with data on carotid imaging, 388 had stenosis of 50%-99% in at least 1 artery. However, we only had data on side of stroke for 253 (65%) of these patients and could not conclusively evaluate underuse of carotid intervention in patients without data on the side of stroke. Therefore, the main sample for the analyses included 253 patients with documented severe carotid stenosis and a stroke in the distribution of the carotid artery (Figure).
The key outcome measure was not receiving guidelinerecommended carotid intervention within 6 months of hospital discharge for acute ischemic stroke for patients with severe symptomatic carotid stenosis. The main independent variables included age, race, stroke severity based on the retrospective National Institutes of Health (NIH) Stroke Scale, comorbid conditions, and availability of vascular surgery at the VAMC where the patient was admitted for stroke. Among the 130 hospitals in the VA, 84 hospitals have vascular surgery services.
Because the vast majority of patients (>76%) in the VA receive CEA as the method for carotid revascularization, and because a recent meta-analysis suggested CEA and CAS are comparable14, we examined the combined receipt of carotid intervention rather than these procedures separately. First, we determined the proportion of eligible patients who received carotid intervention in the VA. We also examined receipt of carotid intervention up to 6 months post stroke in the Medicare program for patients aged ≥65 years.
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