Risk Factors and Angiographic Technical Considerations to Guide Carotid Intervention

Article Outline

• Abstract
• Introduction
• Methods
• Results
• Discussion
• References
• Copyright

Carotid angioplasty and stenting (CAS) with embolic protection is currently accepted as treatment for patients considered to be at high risk for carotid endarterectomy (CEA). The purpose of this study was (1) to determine what proportion of patients treated with CEA would be categorized as “high” risk by currently accepted criteria, (2) to characterize preoperative angiographic findings in patients with carotid stenosis, and (3) to determine the potential technical challenges of CAS in these patients. Consecutive patients who underwent CEA from January 1999 through August 2004 prior to introduction of CAS at our institution were identified. Demographics, indications, perioperative complications, and deaths were reviewed. Published guidelines defining high risk for CEA were applied, and preoperative angiograms were examined for technical limitations to CAS. Two hundred and seventy-nine CEAs were performed in 259 patients for asymptomatic carotid occlusive disease (57%), transient ischemic attacks (35%), or stroke (8%) during the study period. Of these, 35.5% (n = 99) would have met one or more high-risk criteria. Overall risks of perioperative stroke, myocardial infarction, and death were 1.1%, 2.2%, and 0.4% (n = 279), respectively, with a combined major complication rate of 3.3%. No difference in major complication rates was observed between standard-risk and high-risk patients. Preoperative angiograms were available for review in 83.5% of CEAs (n = 233). The distribution of aortic arch configurations included types I (3.5%), IIa (39.5%), IIb (54.5%), and III (1.3%). Aortic arch anomalies were observed in 15.5% (n = 35) of angiograms. There were 77.7% (n = 181) with one or more angiographic findings that would have increased the technical difficulty of CAS, but only 17.6% had relative angiographic contraindications to CAS. A significant proportion of patients with carotid stenosis previously managed with CEA would be categorized as high risk and considered potential candidates for CAS by currently accepted criteria. Based on preoperative angiography, technically challenging factors, some of which limit the ability to perform CAS, are common and should be anticipated when planning CAS.

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Introduction 

Carotid endarterectomy (CEA) has been shown to reduce risk of stroke in patients with both symptomatic and asymptomatic carotid stenosis and is currently considered standard therapy.¹, ², ³, ⁴ Several studies comparing carotid artery stenting (CAS) and CEA have demonstrated similar short-term efficacy and risk profiles.⁵, ⁶, ⁷, ⁸ This has led to expanding interest in CAS⁹ despite existing data that are heterogeneous in terms of patient selection criteria, employment of cerebral protection, and stent placement.

Available randomized studies comparing CEA and CAS have limited patient inclusion criteria based on symptoms¹⁰, ¹¹, ¹² or perceived risk.⁸ A number of these trials have been industry-sponsored,⁶, ⁸ and the variety of stent and embolic protection devices utilized make direct comparisons challenging. While angiographic findings such as aortic arch anatomic factors, presence of intracranial occlusive and/or aneurysmal disease, and plaque characteristics potentially impact the technical feasibility of CAS and have been used as exclusion criteria in previous randomized trials,⁵, ⁸ published angiographic findings from the CAS literature are limited in detail. The at-large population of patients with carotid stenosis warranting intervention remains poorly defined in terms of modern risk factors and anatomic data as determined by angiography. The purpose of this study was (1) to determine which patients would have been characterized as high risk by currently accepted criteria and examine their outcomes relative to standard-risk patients, (2) to characterize the preoperative angiographic findings in patients with carotid stenosis, and (3) to determine the frequency of potential technical challenges for CAS.

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Methods 

We retrospectively reviewed electronic medical records and cerebrovascular angiograms for all patients who underwent CEA at the Veterans Affairs Hospital (Nashville, TN) from January 1999 through August 2004. This study period immediately predates the introduction of CAS at our institution. Approval from our institutional review board was obtained prior to initiation of medical record and image reviews.

Medical records for all patients who had CEA during the study period were reviewed for demographic information, comorbid conditions, risk factors for CEA, survival status, and complications within the first 30 days following CEA. Determination of high-risk status for CEA was based on previously published criteria⁶, ⁷, ⁸, ⁹ and included severe pulmonary disease, severe cardiac disease (New York Heart Association class III or IV congestive heart failure or unstable angina), age >80, total occlusion of the contralateral internal carotid artery (ICA), recurrent carotid stenosis, history of neck radiation or ipsilateral radical neck dissection, and known previous contralateral recurrent laryngeal nerve injury. Major perioperative complications were defined as perioperative stroke, myocardial infarction (MI), or death.

All available preoperative cerebrovascular angiograms in patients undergoing CEA were reviewed for percent ipsilateral and contralateral ICA stenosis, ipsilateral common carotid artery (CCA) stenosis, aortic arch anatomy, intracranial occlusive or aneurysmal disease, ipsilateral external carotid artery (ECA) occlusion, CCA or ICA tortuosity, and length of stenotic lesion. Extent of carotid stenosis was measured using the North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria.¹³ Aortic arch anatomy was classified based on segment of origin for the target branch vessel as previously described:¹⁴ a horizontal line was drawn across the superiormost aspect of the inner aortic arch curve as viewed in the left anterior oblique position; a vertical line was then drawn which bisected the arch into left and right halves. Segment I was defined as the quadrant to the patient's left and above the horizontal line, segment II as the segment to the patient's right and above the horizontal line, and segment III as the segment to the patient's right and below the horizontal line. Segment II was further subdivided by a diagonal line bisecting it into IIa (superior) and IIb (inferior). Tortuosity was defined as ICA angulation >70°. Angiographic data were collected independently of demographic and outcome data in order to avoid potential interpretation bias.

CEAs were performed under general anesthesia and routinely included patch angioplasty. Patients were monitored in the immediate postoperative period in the surgical intensive care unit. Evaluation for acute MI with serial electrocardiograms and cardiac troponin I levels was performed selectively in patients manifesting clinical signs of MI including chest pain, hypotension, arrhythmia, ST segment changes, shortness of breath, or respiratory failure. MI was defined as elevation of troponin levels above baseline (>1.5 ng/mL) and/or evidence of new ventricular wall motion abnormality on postoperative echocardiogram. Postoperative neurological examinations were performed daily until time of discharge, with subsequent routine examinations at 1 month, 6 months, and annually thereafter. Stroke was defined as postoperative onset of a neurological deficit that persisted for greater than 24 hr and/or evidence of new stroke on cross-sectional brain imaging.

Patients lost to follow-up prior to the end of the 30-day perioperative period were excluded from the study. Multiple CEAs in the same patient were treated as individual events, and aortic branch vessels were classified based on the target vessel for each CEA. Summary data are presented as mean ± standard deviation. Continuous numeric data were compared using the t-test, while nominal data were analyzed using the χ² or Fisher's exact test. All statistical analyses were performed using the Statistical Package for the Social Sciences software (SPSS, Chicago, IL).

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Results 

Two hundred seventy-nine CEAs were performed in 259 patients and constitute the study population. Mean patient age was 68.3 ± 9.2 years (range 46-86), and 99.3% of patients were males. Of the 279 CEAs performed, 99 (35%) were high risk as defined by currently accepted criteria. Mean ages for standard-risk and high-risk patients were 65.5 ± 8.6 and 70.6 ± 9.4 years, respectively (p < 0.001, t-test). Asymptomatic carotid stenosis was the indication for CEA in 57% of patients (n = 159). Of the remaining symptomatic patients (n = 120), 34.8% had transient ischemic symptoms and 8.2% had permanent stroke as their respective indications for CEA. Four CEAs (1.4%) were performed for recurrent carotid stenosis.

Of the 99 CEAs performed in high-risk patients, 20 (7.2%) had multiple high-risk criteria (Table I). Severe pulmonary disease (12.9%), cardiac disease (11.1%), contralateral ICA occlusion (8.6%), and age >80 (7.9%) were the most commonly observed risk factors.

Table I. High-risk criteria among patients undergoing CEA (n = 279)

A major complication (defined as stroke, MI, or death) was observed in 3.3% (n = 9) of CEAs in the perioperative period (Table II). Overall incidence of perioperative stroke was 1.1% (n = 3), and rates were 1.1% in standard-risk and 1.0% in high-risk patients, respectively (p = 0.712, Fisher's exact test). Incidence of perioperative MI was 2.2% overall (n = 6), 2.2% in standard-risk patients, and 2.0% in high-risk patients (p = 0.638, Fisher's exact test). A single perioperative death occurred in a standard-risk patient who also had a perioperative MI. Aggregate risk for any major complication was similar for the standard-risk (3.3%, n = 6) and high-risk (3.0%, n = 3) groups (p = 0.891, χ²). No major complications occurred in the 22 patients >80 years of age. Overall risk for any complication was 17.6% (n = 49). Other complications observed but not included in the aggregate major complication end point included transient cranial nerve injury (7.5%, n = 21), wound hematoma (3.6%, n = 10), arrhythmia (1.4%, n = 4), wound infection (n = 2, 0.7%), seizure (0.4%, n = 1), acute congestive heart failure (0.4%, n = 1), respiratory failure (0.4%, n = 1), and permanent cranial nerve injury (0.4%, n = 1). Two patients required reoperation within the perioperative period, both for bleeding.

Table II. Major complications following CEA by risk status (n = 279)

Preoperative angiograms were available for review for 233 CEAs (83.5%). The distribution of aortic arch configurations included types I (3.5%), IIa (39.5%), IIb (54.5%), and III (1.3%) (Fig. 1). Aberrant aortic arch anatomy was observed in 35 patients (15.5%). Of the patients with available angiograms, 171 (73.4%) had at least one angiographic finding that would have potentially increased the technical difficulty of CAS but only 17.6% had findings considered relative contraindications to CAS (Table III).

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• Fig. 1 

  Distribution of aortic arch classification. Adapted from: Schneider PA, Bohannon WT, Silva MB. Carotid Interventions. Boca Raton, FL: Marcel Dekker, 2005.¹⁴

Table III. Angiographic technical limitations among patients undergoing CEA (n = 233)

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Discussion 

Although several early randomized trials comparing CAS with CEA were terminated due to high periprocedural complication rates,¹², ¹⁵ ongoing experience and technological developments such as cerebral protection devices were followed by additional trials showing comparable early results between the two techniques.⁵, ⁶, ⁷, ⁸, ¹⁶, ¹⁷ While the reported incidence of fatal stroke at 3 years following CAS has been comparable to CEA,⁵, ¹⁸ longer-term outcomes remain to be determined. Approval for CAS as primary therapy for carotid stenosis outside clinical trials in the United States by the Centers for Medicare and Medicaid Services (CMS)⁹ has created increased interest in this therapy across specialties, however, and resulted in widespread clinical implementation. While analysis of the NASCET data yielded seven patient characteristics that more than doubled the risk of perioperative stroke or death following CEA,¹ only one of these factors (contralateral carotid occlusion) was included among the high-risk criteria in the Stenting and Angioplasty with Protection in Patients at High Risk for Endarterectomy (SAPPHIRE) trial, from which most currently accepted high-risk criteria are borrowed.⁸ Although anatomic information obtained from angiography plays an especially important role in both patient selection and determination of technical feasibility for CAS, these data are sparsely reported and remain poorly defined for patients with carotid stenosis. The primary goals of our study were validation of currently accepted high-risk criteria for CEA in our own patient population and further characterization of cerebrovascular anatomy in the at-large carotid stenosis population with attention directed toward angiographic findings that potentially impact patient selection for and/or technical feasibility of CAS.

Patient benefit derived from CEA is dependent upon a low incidence of procedure-related complications and death,¹, ², ³ but the applicability of these data to institutions outside those participating in large randomized trials has been justifiably questioned due to their rigorous patient, institution, and physician selection standards.¹⁹, ²⁰ Although 35% of the patients in this study would have qualified as high risk for CEA by currently accepted standards, with some patients meeting criteria which would have resulted in exclusion from prior randomized trials of CEA (age >80,¹, ², ³ severe cardiac disease,³, ¹³ or previous ipsilateral CEA³, ¹³), we failed to detect a difference in major postoperative complications in high- versus standard-risk patients. The appropriateness of currently accepted high-risk criteria for CEA, in terms of both validity as selection criteria for CAS as well as accuracy in predicting CEA-related major complications, may therefore warrant further consideration.

Age >80 has been previously proposed as a preoperative risk factor for CEA in symptomatic patients²¹ and was included among high-risk criteria in a previous trial in addition to our study.⁸ A significant difference in age was observed between our standard- and high-risk groups (65 vs. 75 years, respectively), but no major complications occurred in the 22 CEAs performed in patients >80 years old. A similar finding was made in NASCET, which failed to detect an age-related difference in perioperative complications following CEA in a group of over 1,000 patients.¹ A correlation between advanced age and CAS-related complications, however, has been observed,¹⁵, ¹⁸, ²², ²³, ²⁴ suggesting that advanced age would be more appropriately considered a risk factor for CAS, with CEA being the preferred therapy in the elderly.

The current study's findings are similar to those of Mozes et al.,²⁵ who demonstrated similar stroke and mortality rates between patients categorized as high-risk and low-risk based on the SAPPHIRE trial criteria. In contrast to our own findings, however, they observed an increased incidence in non-Q wave MI in high-risk patients (3.1% vs. 0.9%). Early postoperative cardiac troponin I elevation has been shown to be predictive of both MI and short-term mortality in vascular surgery patients,²⁶ and a higher incidence of troponin elevation with CEA in comparison with CAS has been demonstrated.²⁷ One limiting factor of the current study was lack of routine postoperative surveillance of cardiac isoenzymes in all patients, which may have reduced the detection of postoperative cardiac events, especially non-Q wave MIs which did not lead to other early sequelae that were clinically apparent.

A second factor that potentially impacted the detection of postoperative complications in this study was the lack of pre- and postoperative patient evaluation by an independent neurologist. Several prospective trials examining carotid intervention have included routine patient evaluation by a neurologist and/or standardized scoring systems for stroke events (such as the National Institutes of Health Stroke Scale).², ⁴, ⁵, ⁸, ²⁸, ²⁹ While impossible to implement in a retrospective study, such measures theoretically would have helped to reduce bias and improve both sensitivity and standardization in the detection and reporting of perioperative neurological events.

Cerebrovascular angiograms in our study detected findings that would potentially limit the technical success of CAS in 73.4% of patients, and angiographic findings commonly considered as relative contraindications to CAS were observed in 17.6% of patients. The observed frequency of adverse anatomic factors is consistent with previous reports³⁰ but discordant with the high reported technical feasibility rates for CAS,¹⁸, ²², ²³, ²⁴, ³¹, ³² suggesting that some reported factors may not be clinically meaningful barriers to successful CAS.

Our interest in describing findings from carotid arteriograms in this patient population was in part stimulated by the scarcity of previously published anatomic data, and the list of technical limitations was therefore intentionally made inclusive in nature. The technique that we currently utilize for CAS involves “parking” a guidewire in the ECA at the time of advancement of our cerebral protection device across the carotid lesion in order to minimize trauma to the plaque; we therefore regard ECA occlusion as a technical limitation. However, this finding may not represent a significant impairment for those utilizing alternative methods. Severe carotid calcification has been categorized as an adverse angiographic finding when considering CAS,³⁰, ³³ but we did not include this factor among technical limitations due to difficulty in objectively grading its severity. Further prospective investigation to determine which anatomic factors truly impact CAS technical success and/or complication rates is planned at our institution, where an active CAS program has been under way since the end point of this study's period of investigation.

The predominantly male study population is representative of the overall patient gender distribution at the study institution, a Veterans Affairs medical center, and may make it difficult to generalize the findings to other, more heterogeneous patient populations outside the Veterans Affairs system. The widespread application of preoperative arteriography in this study is an additional institution-specific factor prompted by perceived variability of carotid duplex results from our hospital's vascular laboratory, which is not independently accredited. While these arteriograms provided excellent anatomic information, less invasive methods of preoperative imaging (such as duplex and/or computed tomographic angiography) offer decreased risk and are more often preferred if available and of adequate quality.

In conclusion, CAS offers promise as a less invasive alternative to CEA that avoids risk of cranial nerve injury and can be performed with minimal or no sedation, but long-term outcomes and appropriate criteria for choosing CAS for an individual patient are still being determined. Currently accepted high-risk criteria for CEA may not accurately reflect outcomes at all centers, and caution should be used in applying these criteria to guide intervention outside of clinical trials. Based on preoperative angiography, technically challenging factors, some of which limit the ability to perform CAS, are common and should be anticipated when planning CAS. Prospective investigation is warranted to further characterize the impact of these technical limitations on the success of CAS.

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