Abstract

BACKGROUND:

Angioplasty and stenting using nitinol stents is a recognized treatment option for intracranial atherosclerosis.

OBJECTIVE:

To identify procedure-related factors that may affect patient safety and technical outcome.

METHODS:

In this prospective study of 57 consecutive patients, the primary end points were intraprocedural technical problems, periprocedure morbidity, and complications. Major periprocedure complication was defined as all stroke or death at 30 days. Technical failure was defined as the inability to complete the procedure because of technical or safety problems. Procedure failure was defined as a procedure outcome of technical failure or major periprocedure complication. Secondary end points were procedure-related factors that may affect patient safety and technical outcome.

RESULTS:

Procedure failure rate was 12.3% (7/57) (major periprocedure complication rate, 5.3% [3/57]; technical failure rate, 7% [4/57]). Initial failure in tracking of balloon or stent occurred in 20 patients, other technical problems occurred in 11 patients, including kinking or trapping of balloon catheter (2 cases), difficulty in unsheathing of stent (3 cases), forward migration of stent during deployment (4 cases), trapping of nose cone after stent deployment (1 case), fracture of delivery system (2 cases), and guidewire fracture (1 case). Unfavorable vascular morphology signified by the presence of 2 or more reverse curves along the access path was found to associate with initial failure in the tracking of instruments (OR = ∞), and occurrence of other technical problems (OR = 25).

CONCLUSION:

Procedure-related factors could be identified and lead to improvements in patient safety and technical outcome. Tortuous vascular morphology is a key factor to be overcome.

Intracranial atherosclerotic stenosis is responsible for approximately 8% to 10% and up to 33% of ischemic strokes in the United States and Asia, respectively.13 The scientific basis leading to the use of intracranial angioplasty and stenting as a therapeutic option could be found recently in the literature.46 A matched comparison between medically treated patients in the Warfarin Aspirin Symptomatic Intracranial Disease study and stent-treated patients in the National Institutes of Health intracranial stent registry concluded that stent placement might offer benefit in patients with 70% to 99% stenosis.7 Randomized controlled trials comparing angioplasty and stenting with the best medical therapy in patients with symptomatic intracranial stenosis are currently in progress.8 The use of conservative angioplasty and the Wingspan system as a self-expanding nitinol stent specifically developed for intracranial atherosclerotic stenosis has brought down the periprocedure stroke or death rate from 9.5% (95% confidence interval 7.0% to 12.0%) to 4.5%.9,10 To date, there are many published studies on the clinical outcome and clinical factors affecting procedure outcome; however, there are hardly any studies in detail on the effect of device feature and procedure-related factors on the procedure outcome.914 The objective of the current study was to identify procedure-related factors that may affect patient safety and technical outcome.

METHODS

Study Design

This was a prospective single-center, single-arm study approved by the institutional review board. An informed consent was signed by the patient. All patients who received angioplasty and stenting with a self-expanding nitinol stent for intracranial atherosclerosis were recruited. The inclusion criteria for angioplasty and stenting were as follows: (1) patients presented with symptomatic ischemia stroke or transient ischemic attack, there was no limit on the timing between the last symptomatic event and the stent procedure; (2) patients had minor degree of ischemic stroke with potentially salvageable cerebral function, mentally sound enough to give their own consent and cooperate during the procedure, with National Institute of Health Stroke Scale (NIHSS) score ⩽8, and baseline modified Rankin Scale ⩽3; (3) intracranial stenosis confirmed on digital subtraction angiography (DSA); (4) location of intracranial stenosis corresponding to the vascular territory of ischemic event; (5) degree of intracranial stenosis was ≥70% for patients presenting with a first episode of cerebral ischemia; (6) degree of intracranial stenosis was ≥50% for patients with recurrent cerebral ischemia despite medical therapy; and (7) diameter of vessel immediately adjacent to stenosis ≥2 mm. For patients presenting with a first episode of cerebral ischemia, we followed the recommendation of the Warfarin Aspirin Symptomatic Intracranial Disease study in that stenosis ≥70% was used as an inclusion requirement. However, for those patients with recurrent cerebral ischemia despite medical therapy, the requirement for degree of stenosis as an inclusion criterion was lowered to ≥50%, because it was believed that these patients might benefit from the stenting procedure since the protection from medical therapy alone was probably inadequate for them.

The primary end points were technical problems encountered during the procedure, and periprocedure morbidity and complications. Major periprocedure complication was defined as all stroke or death at 30 days after the procedure. Technical failure was defined as the inability to complete the procedure of angioplasty and stenting at the site of stenosis because of technical or safety problems. Procedure failure was defined as a procedure outcome of technical failure or major periprocedure complication. Secondary end points were procedure-related factors that may affect patient safety and technical outcome.

Preprocedure Assessment

All patients presenting with acute stroke or transient ischemic attacks to the institution were investigated with noncontrast computed tomography and transcranial Doppler (TCD). Some patients, particularly those with potentially salvageable brain function, were investigated with MRI (diffusion-weighted imaging and magnetic resonance angiography). Patients fulfilling all the following preliminary selection criteria were then investigated with computed tomographic angiography (CTA): (1) stroke mechanism pertaining to intracranial atherosclerosis; (2) NIHSS score 8 or less; (3) area of infarction less than one-third of the territory of the intracranial artery; and (4) abnormally high flow velocity within intracranial artery detected on TCD (≥100 cm/s for basilar artery, ≥180 cm/s for middle cerebral artery, ≥160 cm/s for internal carotid artery) or signal void defect detected on magnetic resonance angiography. Those patients with significant intracranial stenosis detected on CTA were further investigated with DSA. The degree of vascular stenosis before stenting was measured at DSA and calculated with one minus the ratio of the diameter of the stenotic lumen to the diameter of the parent vessel. The diameter of the stenotic lumen was measured at the smallest dimension of a plane of the lumen taken at the most stenotic site of the lesion. The diameter of the parent artery was measured at the largest dimension of a plane of the artery taken at a normal segment proximal to the stenosis.

The Procedure and Instruments

Oral dual antiplatelet therapy with aspirin 80 to 160 mg daily plus clopidogrel 75 mg daily was given at least 4 days before stenting. During the procedure, unfractionated heparin was administered intravenously as a 2000 units bolus and at an hourly dose of 500 units to aim at prolongation of activated partial thromboplastin time to 1.5 to 2 times the baseline. It takes less than an hour to obtain results of activated partial thromboplastin time in the authors' institution. The arterial sheath was removed at 4 hours after completion of the procedure. After the procedure, aspirin 100 mg and clopidogrel 75 mg per oral daily were prescribed for 3 months, and oral aspirin 100 mg daily was continued for life. All the procedures were performed by the same team composed of an interventional neuroradiologist with 8 years of experience in neurovascular intervention (S.Y.) and an interventional neurologist with 1 year of experience in neurovascular intervention (T.L.). As a standard for all these procedures, a 6F guiding catheter was placed at the cervical internal carotid artery (Guider, Boston Scientific Corporation [BSC], Natick, Massachusetts). Other instruments were only limited to a microguidewire of 160 cm or 300 cm long (Transend Floppy 160 cm or 300 cm, BSC), microcatheter (Excel 14, BSC), angioplasty balloon catheter (Gateway, BSC), and Wingspan Stent System (BSC). Angioplasty of the stenotic lesion was performed with an undersized angioplasty balloon not greater than 80% of the native vessel diameter.1012 Selection of stent size was based on an oversize of the native diameter of the target vessel by 0.5 to 1.0 mm and an extended stent length by 3 mm on either side of the lesion.10

The procedure of angioplasty and stenting was the same as what had been described,1012 except for the following step that was practiced in the first 45 cases. The angioplasty balloon catheter (Gateway) was introduced directly with a 160-cm microwire (Transend Floppy). After angioplasty was performed, the 160-cm microwire was exchanged for a 300-cm microwire (Transend Floppy 300) through the balloon catheter, and the subsequent stenting procedure was performed over the 300-cm-long wire. After a major complication occurred as a result of such a technique, the rest of the cases were performed in the standard fashion.1012 Time duration of balloon inflation was not greater than 10 seconds each time to reduce the duration of brain ischemia.

Grading System for Assessment of Morphology of the Access Vascular Path

The morphology of the vascular access path of each patient was assessed with a standardized grading system that signified the number of reverse curves along the path. A reverse curve was defined as a catheter path that consists of an inferiorly pointing vector. The location of the reverse curve was attributed to 1 of 3 anatomic regions along the vascular access path: (1) aortic arch; (2) neck vessel, from aortic arch to skull base; and (3) intracranial vessel, from skull base to proximal end of vascular stenosis (Figure 1). The vascular morphology was classified into grade 0, 1, 2, or 3 when there was no reverse curve, 1 reverse curve, 2 reverse curves, or 3 reverse curves along the vascular access path, respectively.

Figure 1

A, radiograph showing a reverse curve of the vascular access path at the aortic arch. The downward vector of the reverse curve is shown with an arrow. B, radiograph showing a reverse curve of the vascular access path at the cervical internal carotid artery and 2 reverse curves of the vascular access path at the intracranial internal carotid artery. The downward vectors of the reverse curves are shown with arrows.

Figure 1

A, radiograph showing a reverse curve of the vascular access path at the aortic arch. The downward vector of the reverse curve is shown with an arrow. B, radiograph showing a reverse curve of the vascular access path at the cervical internal carotid artery and 2 reverse curves of the vascular access path at the intracranial internal carotid artery. The downward vectors of the reverse curves are shown with arrows.

Intraprocedural Observation

Events of patient morbidity, procedure-related complications, and technical problems were observed prospectively. For patient morbidity, signs of cerebral ischemia or focal neurological deficit were observed. For complications, events of guidewire perforation, vascular dissection, or intracranial hemorrhage were observed. For technical problems, problems that arose at the following 5 check points of the technical process were observed: (1) tracking of angioplasty catheter and stent system to the site of stenosis, (2) unsheathing of stent system, (3) precision in stent placement, (4) retrieval of delivery system, and (5) integrity of instruments.

Analysis of Factors Affecting the Occurrence of Technical Problems

Technical problems were categorized into (1) initial failure in tracking of instruments and (2) other procedural problems. The correlation between the classification of vascular morphology and the occurrence of technical problems was analyzed by means of odds ratio, relative risk, and the Fisher exact test. The correlation between the occurrence of technical problems and factors other than vascular morphology, such as age, sex, and location of stenosis, was studied with both univariate and multivariate analysis. The χ2 test and Fisher exact test were used for univariate analysis of the factors of sex and location vs the outcomes of tracking failure and other procedural problems; t tests were used for univariate analysis of age distribution and degree of stenosis vs the 2 outcomes. Logistic regression models were used for multivariate analysis.

To study the possible effect of the learning curve of the operative team on the occurrence of technical problems and intraoperative transient ischemic events, the whole group of patients was divided into an initial-half group and a latter-half group based on chronological order; the incidence of technical problems and intraoperative transient ischemic events in each of the 2 groups was observed.

RESULTS

Patient Demographics

During the period of enrollment of study subjects from January 2006 to November 2008, 2750 patients presenting with symptomatic ischemic stroke or transient ischemic attack were admitted and investigated with CT and TCD; 1386 were investigated with MRI, 351 were investigated with CTA, 162 were investigated with DSA, and 103 were excluded after DSA because the degree of stenosis on DSA did not fulfill the requirement of ≥70% for those with first presentation and ≥50% for those with recurrent event; 2 patients were excluded because the vessel diameter was <2 mm. Fifty-seven patients were finally recruited for the current study. There were 45 men and 12 women. Average patient age was 64.1 ± 10.8 years. Forty-two patients presented with stroke, and 15 presented with transient ischemic attack. The median score of NIHSS was 3, the mode was 2, and the range was 0 to 8.

Timing of Procedure and Lesion Characteristics

The stenting procedure was performed within 30 days after the onset of the ischemic event in 32 patients; it was performed beyond 30 days after the onset of the event in 25 patients. Average timing of stenting procedure was 91.2 ± 257.3 days after the ischemic event. The average degree of stenosis at the lesions was 72.8 ± 11.1%. The lesion was located at the middle cerebral artery in 33 cases, internal carotid artery in 16 cases, vertebral artery in 4 cases, basilar artery in 3 cases, and involved both the middle cerebral artery and the internal carotid artery at their junction in 1 case.

Technical Problems Encountered During the Procedure and Their Solutions

The technical problems encountered during the procedures and the suggested solutions as well as technical and patient outcomes are outlined in Table 1. Tracking of angioplasty catheter (Gateway) and stent system (Wingspan) to the site of stenosis was unsuccessful in 20 patients with the use of a 6F guiding catheter (Guider, BSC) and Transend 300 microwire (35.5%, 20/57) as a standard, without the use of an additional supportive wire or long sheath. Of these 20 patients, tracking of the instruments became successful in 14 patients when an additional supportive guidewire was used (V18, BSC). Of the other 6 patients, tracking became successful in 3 patients when a 6F long sheath was used (Cook Shuttle sheath, Cook Medical Incorporation, Bloomington, Indiana); tracking became successful in 3 patients when a long sheath was used together with an additional supportive wire. Therefore, the rate of successful tracking with optional use of an additional supportive wire or a long sheath was 100% (57/57).

TABLE 1

Technical Problems Encountered During the Procedure

Technical difficulty related to balloon catheter (Gateway) occurred in 2 patients (3.5%, 2/57). In one, kinking of the balloon catheter occurred at the tortuous vascular segment after removal of the microwire, which subsequently lead to a fatal complication described in the next section. In the other patient, the balloon catheter could not be advanced beyond the high-grade stenosis at M1-M2 junction of the middle cerebral artery and lead to a technical failure. In this study, the longest length of Gateway balloon used for each patient was 9 mm in 21 patients and 15 mm in 36 patients. The longest length of balloon catheters used in the 2 cases with balloon-navigation problems was 9 mm and 15 mm, respectively. There was no correlation between balloon length and balloon-navigation problems.

Difficulty in unsheathing of the stent delivery system (Wingspan) occurred in 3 patients (5.26%, 3/57). In one of these patients, unsheathing difficulty was due to jamming of the stent sheath as a result of vascular tortuosity, which caused gripping of the outer sheath between the inner core and the vessel wall; excessive and sustained pulling on the outer sheath was required for unsheathing. Unsheathing was eventually completed but delayed, and there were stretching and elongation of the outer sheath. In the other 2 patients, unsheathing difficulty was due to bending of the nose cone. Bending of the nose cone caused kinking of the distal tip of the sheath that covered the nose cone, the kinked sheath gripped onto the inner core and resisted unsheathing (Figure 2). In one of them, the nose cone of the inner core was bent after it entered a side branch of the vessel. After the nose cone was repositioned into another branch, so that the path of the nose cone was straightened, unsheathing was subsequently successful (Figure 3). In the other one, unsheathing was eventually completed but delayed, and there was stretching and elongation of the outer sheath. Forward displacement of the stent during stent deployment at M1 segment occurred in 4 patients (7%, 4/57), it was due to technical error in 2 patients and to vascular tortuosity in 2 patients (Figure 4). In one of them, an additional stent was required to fully cover the stenotic lesion. In 1 patient, the nose cone of the inner core was trapped between the microwire and the stent during removal of the delivery system because of the compression of the nose cone onto the stent struts by the microwire as a result of vascular tortuosity (1.75%, 1/57). In this patient, the microwire was removed to relieve its compression on the nose cone; afterward, the delivery system was successfully removed. During manipulation of instruments across vascular tortuosity, fracture of the metallic cannula of the inner core occurred in 2 patients (3.5%, 2/57). In one of them, fracture occurred during tracking of the instrument, the stent delivery system was withdrawn over the microwire, and the stent was reloaded into a microcatheter (Renegade Hi-Flo, BSC); the stent was deployed with a microcatheter of 0.018 microwire (V18, BSC). In the other patient, fracture occurred after the stent was positioned at the stenosis, stent unsheathing was performed with the metallic cannula of the inner core secured with an artery forceps. The longest length of Wingspan stent used for each patient was 9 mm in 7 patients, 15 mm in 29 patients, and 20 mm in 21 patients. The longest length of Wingspan stent used in the 9 cases with stent deployment problems was 15 mm in 7 patients and 20 mm in 2 patients. There was no correlation between stent length and stent deployment problems.

Figure 2

Diagram showing the mechanism of the unsheathing difficulty due to a bent nose cone. The bend causes a kink at the sheath tip that grips onto the inner core and resists unsheathing. The mechanism was revealed in one of the retrieved systems.

Figure 2

Diagram showing the mechanism of the unsheathing difficulty due to a bent nose cone. The bend causes a kink at the sheath tip that grips onto the inner core and resists unsheathing. The mechanism was revealed in one of the retrieved systems.

Figure 3

Angiography of a case in which difficulty in unsheathing of the stent occurred when the nose cone was bent when it was placed into an inferior division of M2 (open arrow). The problem was resolved when the bending of the nose cone was eliminated with repositioning of the nose cone to a straight path (arrow).

Figure 3

Angiography of a case in which difficulty in unsheathing of the stent occurred when the nose cone was bent when it was placed into an inferior division of M2 (open arrow). The problem was resolved when the bending of the nose cone was eliminated with repositioning of the nose cone to a straight path (arrow).

Figure 4

A, radiograph showing the position of a stent before stent deployment, the proximal end of the stent (arrow) was located to the left (from the reader's perspective) of the calcified falx cerebri (straight line). B, radiograph showing the position of a deployed stent, after stent deployment, the proximal end of the stent (arrow) was located to the right (from the reader's perspective) of the calcified falx cerebri (straight line). Forward migration of the stent position occurred because of vascular tortuosity.

Figure 4

A, radiograph showing the position of a stent before stent deployment, the proximal end of the stent (arrow) was located to the left (from the reader's perspective) of the calcified falx cerebri (straight line). B, radiograph showing the position of a deployed stent, after stent deployment, the proximal end of the stent (arrow) was located to the right (from the reader's perspective) of the calcified falx cerebri (straight line). Forward migration of the stent position occurred because of vascular tortuosity.

Guidewire fracture occurred in 1 patient during withdrawal of balloon catheter across a sharply angulated vascular segment (1.75%, 1/57) (Figure 5). The balloon catheter with the fractured wire inside its lumen was removed, and the procedure repeated.

Figure 5

A, angiography of a case in which a sharp angulation (arrow) was present just proximal to the carotid siphon. B, radiograph showing successful advancement of an angioplasty balloon catheter across the sharp angulation (arrow) over a microwire. C, radiograph showing fracture of the microwire at the location of sharp angulation (arrow), which occurred during an attempt to withdraw the angioplasty catheter while the microwire was forced to stay.

Figure 5

A, angiography of a case in which a sharp angulation (arrow) was present just proximal to the carotid siphon. B, radiograph showing successful advancement of an angioplasty balloon catheter across the sharp angulation (arrow) over a microwire. C, radiograph showing fracture of the microwire at the location of sharp angulation (arrow), which occurred during an attempt to withdraw the angioplasty catheter while the microwire was forced to stay.

Apart from the technical problem of instrument tracking, the other technical problems occurred in 10 patients. There were 2 patients with 2 problems.

Procedure-Related Morbidity and Complications

The events of procedure-related morbidity and complications and subsequent patient outcome are outlined in Table 2. Apart from the episodes of ischemic events and headache that resulted in technical failure, there was 1 case of intracerebral hemorrhage due to arterial dissection and guidewire perforation at the M1 segment of the middle cerebral artery. In this case of highly tortuous vascular morphology, the balloon catheter (Gateway) was introduced directly over a 160-cm-long Transend Floppy wire for angioplasty of a high-grade M1 stenosis, afterward, the 160-cm wire was removed for exchange with a 300-cm wire to prepare for the stenting procedure. However, kinking of the balloon catheter occurred at the tortuous vascular segment after removal of the 160-cm wire, and the 300-cm wire could not get through the kinked catheter. The balloon catheter was therefore removed, and the M1 lesion that had been dilated was recannulated with a Transend Floppy microwire that led to vascular dissection. The true lumen was subsequently successfully cannulated and a Wingspan was placed across the stenotic and dissected segment, resulting in a good angiographic outcome. Afterward, the patient reported headache and became confused. Computed tomography confirmed the presence of subarachnoid hemorrhage that was probably due to guidewire perforation at M1. The patient subsequently died.

TABLE 2

Events of Procedure-Related Morbidity and Complications

Major Periprocedure Complication

One patient died 1 day after arterial dissection and perforation at the procedure. Within 30 days after the procedure, another patient died of pneumonia, and a third patient had an ischemic stroke. The major periprocedure complication rate was 5.3% (3/57).

Technical Failure

Technical failure occurred in 1 patient because of failure in advancing the angioplasty balloon catheter beyond the 87% stenosis at the M1-M2 junction of the middle cerebral artery. This patient was subsequently treated with double-antiplatelet therapy; he presented with atrial fibrillation 1 year afterward and died of a major ischemic stroke. The procedure was terminated in 3 patients before successful stent placement for patient safety. Two of these 3 patients with a stenosis of 83% and 90%, respectively, developed transient ischemic attack and presented with drowsiness, dysphasia, and hemiparesis or eye deviation during passage of angioplasty balloon catheter or the stent system across the stenotic lesion. The third patient with 87.2% stenosis reported the acute onset of severe headache and loss of vision when the system was being advanced to the ophthalmic segment of the internal carotid artery. These 3 patients fully recovered from their symptoms after removal of the instruments and termination of the procedure. Follow-up computed tomography did not show evidence of new infarction. The overall technical failure rate was therefore 7% (4/57). These 3 patients were subsequently treated with double-antiplatelet therapy; 2 of them presented with transient ischemic attack at 4 months and 3 years, respectively; one of these patients had been well up to the follow-up at 2 years.

Morphology of the Access Vascular Path

The findings of vascular morphology along the access path and the results of tracking instruments in patients with different morphology were outlined in Table 3. Ten of 57 patients had grade 2 or 3 vascular morphology, or 2 or 3 reverse curves along the vascular access path; tracking of instruments through a standard 6F Guider in these patients was always unsuccessful. It was noted that a reverse curve in catheters might occur in aortic arch that apparently did not have excessive downward looping, because a reverse curve in catheters might form within the relatively large superior-inferior space of the aortic arch.

TABLE 3

Morphology of Vascular Access Path

The Effect of Vascular Morphology on Occurrence of Technical Problems

The correlation between vascular morphology and technical problems is shown in Table 4. There were infinitefold greater odds of occurrence of initial tracking failure in patients with grade 2 or 3 vascular morphology and 25-fold greater odds of occurrence of other procedural problems in patients with grade 2 or 3 vascular morphology. There was a 4.76-fold greater probability of occurrence of initial tracking failure in patients with grade 2 or 3 vascular morphology and 8.23-fold greater probability of occurrence of other procedural problems in patients with grade 2 or 3 vascular morphology. Therefore, initial failure in tracking instruments and other procedural problems were much more likely to occur in patients with grade 2 or 3 vascular morphology.

TABLE 4

Correlation Between Unfavorable Vascular Morphology and Occurrence of Technical Problemsa

The Effect of Other Factors and Occurrence of Technical Problems

There was no statistically significant correlation between sex, age, location of stenosis, or degree of stenosis to the outcomes of tracking failure or other procedural problems (Table 5).

TABLE 5

Correlation Between Other Factors and Occurrence of Technical Problems

The Effect of the Learning Curve of the Operative Team and the Occurrence of Technical Problems and Intraoperative Transient Ischemic Events

The 57 patients were divided into an initial-half group of 28 consecutive patients, and a latter-half group of 29 patients. The incidence of initial tracking difficulty in the initial group and the latter group was 10 and 10, respectively; the incidence of other technical problems in the initial group and the latter group was 4 and 7, respectively; and the incidence of transient ischemic attack leading to procedure suspension was 1 and 3, respectively. These results showed that the occurrence of technical problems and transient ischemic attack were unrelated to the learning curve.

DISCUSSION

In the current study, the observed procedure-related technical problems reflected the in vivo characteristics and behavior of the Gateway and Wingspan system during performance of the angioplasty and stenting procedure, and served as a reference to future improvements in the device features of Wingspan, as well as a reference to the development of other self-expanding nitinol devices that consist of an over-the-wire delivery system.

Vascular Morphology and Procedure Outcome

In the current study, unfavorable vascular morphology was found to be a key factor affecting initial success in tracking of instruments and the occurrence of procedure-related technical problems. The finding is in line with that of a multicenter study on Wingspan stent system reported by Fiorella et al, in which tortuous carotid anatomy had precluded delivery of the Wingspan stent in 1 patient.11 The knowledge of vascular tortuosity as a limitation to instrument tracking for intracranial endovascular procedures encourages the development of guiding sheaths or catheters that help to straighten the access vascular path and reduce the resistance of passage of instruments. Some of the newer access tools, such as the Neuron catheter (Penumbra Inc., Alameda, California), which allows intracranial placement, may effectively reduce the number of reverse curves and therefore help to eliminate some of the technical problems encountered in the current study. In the study by Jiang et al on the use of balloon-mount stent for intracranial atherosclerotic stenosis, severe vascular tortuosity was correlated with stent failure, which was defined as a residual stenosis >30%.14 In the current study on self-expanding stents, there was no correlation between vascular tortuosity and poststenting residual stenosis.

A Grading System for Assessment of Vascular Morphology

A grading system has been proposed for the assessment of vascular morphology, using the number of reverse curves as a quantifiable parameter for objective observation of vascular tortuosity along the vascular access path. The use of a standardized grading system for assessment allows objective analysis of the vascular morphology and its association with the procedure outcome. Knowledge generated from such analysis provides objective evidence on which newer techniques or instruments are developed. The use of such a grading system also allows objective comparison of morphology between different cases and the evaluation of the effect of new techniques and catheters on the change in vascular morphology. New guiding catheters like the Neuron do make stenting procedures much easier, but they do not necessarily solve all the problems; objective evaluation on how they have changed the vascular morphology and how they have improved the technical outcome in comparison with the old catheters are still necessary. Therefore, the development of new catheters should not stop us from further studies on the topic, and the use of an objective grading system may be helpful for such studies.

Causes of Technical Problems

The cause of failure in tracking was due to tortuous vascular morphology of the access vascular path, which caused resistance in forward advancement of the instruments and backward migration of the guiding catheter. The cause of jamming of the outer sheath during unsheathing of the stent system in highly tortuous vessels was due to gripping of the outer sheath between the microwire and the vascular wall. Unsheathing failure as a result of nose cone bending was due to the gripping of the outer sheath between the nose cone and the vascular wall. In the 3 cases with unsheathing problems, the stent delivery system had been retracted to eliminate all redundancy before unsheathing of the outer catheters.

Forward displacement of the stent system during stent deployment occurred as a technical error, when unsheathing of the stent was performed right after advancement of the delivery system to the stenotic site, without slight retraction of the stent delivery system to eliminate a forward pressure on the system. Forward displacement of the stent system during stent deployment also occurred as a result of highly tortuous vascular morphology in 2 cases. In these 2 cases, although the stent delivery system had been retracted to eliminate all redundancy or forward pressure, straightening, and thus forward displacement of the inner core of the system occurred during unsheathing as a result of a change in friction between the outer sheath and the vessel wall.

Other Wingspan Studies

The clinical and angiographic periprocedure outcomes of several recent studies on endovascular stenting of intracranial atherosclerotic stenosis with Wingspan are shown in Table 6. Major periprocedure complication rates as represented by stroke or death rates at 30 days in these studies varied from 4.5% to 9.6%. The major periprocedure complication rate in the present series was 5.3%. There were 3 technical deviations in the procedures of the current study compared with what was described in the other series. The first one was skipping the use of a microcatheter to introduce a long exchange microwire. Such a technique had led to a fatal complication of arterial dissection and perforation. If the use of a microcatheter was not skipped, the fatal complication could have been avoided, and the major complication rate would have been 3.5%. Another deviation was a short inflation time of the angioplasty balloon of not more than 15 seconds, as opposed to a slow and graded inflation of the balloon for at least 120 seconds.11 The short inflation time did not result in a suboptimal angioplasty result or complication. A third deviation was the use of local anesthesia in the current study instead of general anesthesia. Procedures for Wingspan placement had been performed under general anesthesia in the other series.10,12 The advantage of not using general anesthesia was that the patient's neurological status could be monitored during the procedure, so that signs and symptoms of cerebral ischemia could be detected early. In the current study, intraprocedural ischemic events occurred in 3 patients; these were detected immediately and were reversible without any neurological sequelae. If general anesthesia were used for the procedures, the procedures of these 3 patients could have been completed, but there would also be an increased risk of stroke due to cerebral ischemia that was undetected until it caused irreversible brain damage. Without general anesthesia, a high degree of patient cooperation during the procedure was required. From the experience of the current study, cooperation could be obtained with reasonable education and communication. Patient movement or motion degradation of DSA images was not a problem in the current study. In the current study, there was no evidence showing that complications were more likely to occur without general anesthesia. In the only case of major procedure-related periprocedural complication, the arterial perforation was directly due to the procedure of guidewire cannulation of a stenotic lesion that had been dilated with a balloon, rather than due to patient movement. The procedure of guidewire cannulation of a stenotic lesion that had been dilated with a balloon is a well-known contraindication that should have been avoided, and it was a result of the faulty selection of the instrument in this particular case.

TABLE 6

Periprocedure Clinical and Angiographic Outcomes of Wingspan Stenting for Intracranial Atherosclerotic Stenosis

Clopidogrel Resistance

Aspirin and clopidogrel resistance are emerging clinical entities with potentially severe consequences such as recurrent myocardial infarction, stroke, or death. The mechanism of resistance remains incompletely defined, but there are specific clinical, cellular, and genetic factors that influence therapeutic failure. In the current study, clopidogrel resistance has not been tested. In a study of 1477 patients with acute coronary syndrome, 21% had genetic evidence of clopidogrel resistance (CYP2C19*2 polymorphism) that resulted in a 53% increase in the relative risk of death from cardiovascular causes or myocardial infarction or stroke. There was a 3-fold increase in stent thrombosis among those with the CYP2C19*2 polymorphism, which had been reported to occur in 30% of whites, 40% of blacks, and 55% of East Asians.15 The benefit of tailored antiplatelet therapy has yet to be validated in large randomized trials. In the future, an individualized therapy based on platelet tests and/or genetic testing may arise and hopefully help to improve patient outcome.

Limitation and Conclusion

The limitation of this study was that it essentially dealt with the procedure-related and device-related technical problems, factors leading to these problems, and probable solutions to these problems. The study on the relation between these problems and long-term clinical and angiographic outcome was not within the scope of the current study.

Procedure-related factors affecting patient safety and technical outcome could be identified and lead to improvements in patient safety and technical outcome. Tortuous vascular morphology was a key factor to be overcome.

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ABBREVIATIONS

    ABBREVIATIONS
  • BSC

    Boston Scientific Corporation

  • CTA

    computed tomographic angiography

  • DSA

    digital subtraction angiography

  • NIHSS

    National Institute of Health Stroke Scale

  • TCD

    transcranial Doppler