CardioVascular and Interventional Radiology
9 Springer-Verla9 New York, Inc. 1999
CLINICAL
Cardiovasc Intervent Radiol (1999) 22:89-95
INVESTIGATIONS
Aortic Bifurcation Reconstruction: Use of the Memotherm Self-Expanding Nitinol Stent for Stenoses and Occlusions J. Graeme Houston, 1 Peter T. McCollum, 2 Peter A. Stonebridge, 2 Zahid Raza, 2 J. William Shaw 1 ~Directorate of Clinical Radiology, Dundee Teaching Hospitals NHS Trust, Ninewells Hospital & Medical School, Dundee DD1 9SY, Scotland 2Department of Vascular Surgery, Dundee Teaching Hospitals NHS Trust, Ninewells Hospital & Medical School, Dundee DD1 9SY, Scotland
Abstract Purpose: To assess the technical success, initial clinical outcome, and intermediate follow-up of the Memotherm nitinol self-expanding stent in aortic bifurcation reconstruction. Methods: Thirty-three patients (13 male, 20 female), mean age 64 years, were treated, who had symptoms classified by the Surgical Vascular Society/International Society of Cardiovascular Surgery (SVS/ICVS) classification as grade 2 in 11 (33%), grade 3 in 19 (58%) and grade 4 in 3 (9%) patients. Lesions were classified according to severity and type. Indications for placement of a Memotherm nitinol self-expanding stent were failed angioplasty in 14 (42%), chronic occlusions in 12 (37%), and complex stenoses in seven (21%) patients. Results: Sixty-seven stents were technically successfully placed in 66 aorto-iliac segments in 33 patients, with one major complication. Initial clinical outcome was improvement in 25 (81%), no change in four (13%), and a worsening in two (6%) patients by Rutherford criteria. Mean early ankle/brachial pressure index (ABI) gain was 0.27 for occlusions and 0.05 for stenoses. Clinical follow-up was obtained in all patients, with retrospective angiographic follow-up in 28 (85%) at a mean of 16 months (range 12-26 months). The decrease in ABI and the decrease in angiographic luminal diameter at follow-up was determined as the "late loss." The mean ABI late losses were -0.06, 0.00, and 0.09, and the mean angiographic late losses were 6.7%, 10% and 14% for occlusions, stenoses, and normal segments respectively. Primary clinical patency was 96%, primary Correspondence t o :
Dr. J.G. Houston
angiographic patency was 89%, and secondary angiographic patency was 93%. Conclusion: The high technical success of stent placement, the low complication rates for aortic bifurcation reconstruction using the Memotherm self-expanding stent, and high clinical and angiographic patency maintained at intermediate follow-up support their use in aortic bifurcation reconstruction. Key words: Aorta, transluminal angioplasty--Arteries-Stents and prostheses Percutaneous balloon angioplasty has proved efficacious in the treatment of focal iliac artery stenoses. However, results for treatment of long segment disease or chronic occlusions have been mixed [1-3]. Lesions involving the aortic bifurcation have been treated by "kissing balloon" angioplasty [4]. The use of "kissing stents" has previously been used to describe bilateral iliac stents [5]. These stents may be deployed with their proximal margin either at the common iliac origin or projecting into the distal aorta. We have applied the term "aortic bifurcation reconstruction" to the technique of deploying bilateral common iliac stents projecting symmetrically upward for a variable distance into the aorta, thus creating a new bifurcation at a higher level. The purpose of this paper is to evaluate retrospectively a group of patients with aorto-iliac stenosis or occlusion, treated by insertion of bilateral Memotherm stents (Bard, Crawley, UK).
Materials and Methods This retrospective study examined the patients treated by this technique, between 1994 and 1996, in terms of lesion type, indi-
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J.G. Houston et al.: Aortic Bifurcation Reconstruction
TYPE A
TYPE B
TYPE C
UNILATERAL
BILATERAL
AORTIC
Fig. 1. Classification of aorto-iliac atheromatous disease.
Table 1. Distribution of lesion morphology Type
A B C
Description
Unilateral ostial Bilateral ostial Distal aorta
Total
No. of patients
Occlusions
Stenoses Significant (75%-99%)
Insignificant (30%-75%)
Minimal (0-30%)
6 23 4
4 8 0
2 25 8
0 13 0
6 0 0
33
12
35
13
6
cation, technical success, early clinical outcome, and intermediate clinical and angiographic follow-up. All patients who had placement of bilateral common iliac artery self-expanding Memotherm stents, involving positioning of the proximal stent ends at a higher level than the aortic bifurcation, were included in the study. Reconstructions using other types of self-expanding stents and patients with separate aortic or iliac stents were excluded. Thirty-three patients (13 male, 20 female), mean age of 64 years (range 44-82 years) were included. Twenty-six patients (78%) were smokers, seven (21%) patients were diabetic, and 11 (33%) had ischemic heart disease. The clinical indication for intervention based on the classification of the Surgical Vascular Society/International Society of Cardiovascular Surgery (SVS/ISCVS) [6] included mild claudication (grade 2) in 11 (33%) patients, severe claudication (grade 3) in 19 (58%) patients, and rest pain (grade 4) in three (9%) patients. Diagnostic angiography was performed as intraarterial studies in 29 patients using the femoral arterial approach, while four patients had intravenous digital subtraction examinations performed. Diagnostic angiography included full runoff examination. Three patterns of underlying aortoiliac atheromatous disease were identified (Fig. 1). All had in common the involvement of at least one common iliac origin by an aortic or iliac disease process, such that treatment by a discrete aortic or common iliac stent, if indicated, was not considered feasible. The distribution of the underlying lesions is detailed in Table 1.
Indications for Stenting The radiologic indications for intervention were stenoses (diameter reduction > 75% or a pressure gradient of greater than 10 mmHg, without pharmacologic augmentation) and chronic occlusions. The average stenosis requiring intervention was 87% (range 65%-95%) with a mean length of 37 mm (range 15-90 ram). The mean occlusion length was 56 mm (range 15-110 ram). In the context of
preserving the aortic bifurcation, treatment of type A lesions did involve placing stents in common iliac arteries that had minimal (diameter reduction < 30%) stenosis. The radiologic indications for stenting were an unsatisfactory post-angioplasty appearance due to recoil (residual diameter reduction > 30%) and residual intraarterial pressure gradient (>10 mmHg, no pharmacologic augmentation) in 14 patients (42%), primary stent placement (stent placement followed by balloon dilatation without thrombolysis) in chronic occlusions in 12 patients (37%), and complex elongated stenoses (greater than 5 cm in length) in seven patients (21%).
Stenting Technique A previously described standardized technique was employed throughout [7]. Chronic occlusions were all treated by primary stent placement. Occlusions were first crossed with a guidewire, and a subsequent 5 Fr diagnostic catheter allowed multiple oblique angiograms to be performed. A long (30 cm) 7 Fr sheath (Arrow, Kimal, Uxbridge, UK) was used, the sheath and dilator being passed through the occlusion, performing a "Dotter" dilatation. The aortic ends of the stents were aligned side by side, normally projecting 10-15 mm into nonsignificantly stenosed aorta below the origin of the inferior mesenteric artery. Both stents were deployed simultaneously following withdrawal of the sheath. Following replacement of the sheath dilator, the sheath was advanced through the stent, allowing shielded positioning of the balloon used for post-stent dilatation. Stenotic segments were predilated [balloon size and stent diameter (1 mm greater than the balloon) and length assessed by cutaneous radiopaque measure]. Balloon angioplasty was performed after stent deployment (second balloon, same diameter as stent) to insure adequate stent dilatation.
J.G. Houston et al.: Aortic Bifurcation Reconstruction
Completion angiograms (minimum of two obliques) were performed to confirm a successful angiographic result (Figs. 2-4). At the time of stent deployment pressure measurements were not routinely in use in our institution. All patients were given antiplatelet therapy, starting 24 hr before the procedure and continued indefinitely (unless contraindicated). This was normally aspirin 75 mg daily. Heparin was administered as a 3000-unit bolus before stent deployment and continued subcutaneously for 24 hr, 5000 units 6-hourly, commencing 6 hr after uncomplicated sheath removal. Immediate ankle/brachial pressure index (ABI) was performed within 24 hr.
Follow-Up For the purpose of follow-up, classification of the aortic bifurcation was considered as two aorto-iliac segments (one segment for each patient limb). At follow-up, pre-intervention segments were separated into occlusions, stenoses > 30%, and stenoses < 30% (lumen diameter reduction). (Stenoses < 30% were considered "normal" segments.) This allowed assessment of any significant stenosis in a pre-intervention "normal" segment (type A lesions). Patient follow-up consisted of clinical assessment of ABI at 3 months, 6 months, 12 months, and annually thereafter. Intraarterial digital subtraction angiography [3 Fr pigtail catheters (Merck, Alton, UK), anteroposterior, right, and left anterior oblique projections using pump injection of 20 ml at 8 ml/sec of Iopamidol 300 (Merck)] was performed on 28 of the 33 patients (85%) with a follow-up period of at least 12 months (mean 16 months, range 12-26 months). The final ABI was performed on the day of angiographic follow-up. Fully informed consent was obtained in accordance with the policy of our institution. There were five patients lost to angiographic follow-up (3 deaths, 1 major cerebrovascular accident, and 1 patient who declined angiography).
Outcome Measures and Statistical Analysis Technical acceptability of stent deployment was assessed in terms of satisfactory release of the stent in position, and complications. Technical success of stent deployment was defined by a residual stenosis of <30%. Pre-intervention assessment of runoff vascular segment patency was defined for the profunda femoris, superficial femoral/popliteal segment, and the number of trifurcation vessels patent from origin to ankle level. Patency of runoff vessels was defined as less than 75% stenosis for any vessel. The immediate clinical outcome was defined according the SVS/ISCVS criteria on a scale of - 1 to + 3 for symptoms [6]. The ABI early gain was defined as the difference between preprocedural and 24-hr postprocedural ABI. The angiographic early gain was defined as the difference between the preproceduraI and postprocedural maximal stenosis expressed as a percentage of the estimated native luminal diameter as demonstrated on the optimally angulated digital subtraction images. The intermediate follow-up ABI late loss was defined as the difference between the 24-hr ABI and the ABI at the time of angiographic follow-up. The intermediate follow-up angiographic late loss was defined as the difference between the postprocedural and the follow-up maximal stenosis expressed as a percentage of the maximal stent diameter. Clinical patency loss was defined as a reduction in ABI of >0.15 at follow-up compared with the 24-hr postprocedural ABI.
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Angiographic patency loss was defined as a stenosis of >50% of the maximal stent diameter at follow-up. Primary clinical, and primary and secondary angiograpbic patency were calculated separately on both a patient and a limb basis. It is of note that this is not on an intention-to-treat basis but on the basis of a successful procedure having been carried out. For comparison of parameters such as ABI, Student's t-test was used (p < 0.05 level of significance), while a log-rank test was used to compare differences in patency and possible predictors.
Results Technical Success and Complications Sixty-seven stents were used for the 33 procedures (a combined common iliac/external iliac occlusion measuring 110 m m long required two stents), mean diameter 8.8 mm (range 7-10 ram), mean length 65 mm (range 4 0 - 9 0 mm). Satisfactory deployment and accurate positioning were achieved with all 67 stents. Technical success in stent placement was achieved in 65 of 66 (98%) limbs and in 32 of 33 (97%) patients. The runoff assessment showed patent profunda femoris arteries in 65 of 66 (98%) limbs, patent superficial femoral/popliteal segments in 44 of 66 (66%) limbs. There were three patent trifurcation vessels to the ankle in 15 (23%), two patent vessels in 35 (53%), one patent vessel in eight (12%), and no patent vessels in five (12%) limbs. Early in the series, one delivery system problem was encountered (the tip of the delivery system avulsed but was successfully retrieved using a gooseneck snare). Minor complications were limited to three groin hematomata. One major complication was encountered (morbidity rate 3%). Thrombosis in an external iliac artery distal to a common iliac stent occurred and was attributed to an underlying stenosis that had been overlooked. The patient was initially treated conservatively and later had successful femoro-femoral bypass surgery. There were no procedure-related mortalities and 30-day mortality was 3% (one patient suffered a fatal myocardial infarction at day 20).
Immediate Results Immediate clinical outcome was improvement in 27 of 33 (81%) patients ( + 3 in 10, + 2 in 7, +1 in 8), no improvement in four (13%) and a worsening ( - 1 ) in two (6%) patients. The mean (SD) ABIs before the intervention were 0.57 (0.21), 0.7 (0.21), and 0.91 (0.1), and ABIs immediately after the intervention were 0.86 (0.23), 0.76 (0.24), and 0.92 (0.11) for occlusions, significant, and insignificant stenoses respectively. There was a statistically significant gain in ABI for occlusions (p = 0.001) and significant stenoses (p = 0.03), but not for insignificant stenoses (p = 0.2). Angiographic early gain and ABI early gain are given in Table 2.
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J.G. Houston et al.: Aortic Bifurcation Reconstruction
Fig. 2. Type A lesion: unilateral occlusion. A Recanalized with re-entry point involving the contralateral common lilac ostium; B after stent placement. Fig. 3. Type B lesion: bilateral elongated common lilac stenoses. A Poor result of angioplasty; B after stent placement. Fig. 4. Type C lesion: eccentric aortic stenosis close to aortic bifurcation. A Before stent placement; B after stent placement.
J.G. Houston et al.: Aortic Bifurcation Reconstruction
Table 2. Clinical and angiographicearly gain
Occlusions Significantstenoses Insignificant stenoses
n
ABI early gain
Angiographic early gain (%)
I2 35 19
0.28 (0.23) 0.08 (0.18) 0.03 (0.18)
93 (7) 80 (1l) 37 (16)
ABI = ankle/brachialpressure index Values are the mean _+ SD
Follow-Up The results of ABI and angiographic late loss are shown in Table 3. There was no statistically significant difference between the 24-hr and the final follow-up ABI for occlusions (p = 0.22), stenoses (p = 0.13), and normal (p = 0.38) segments. At angiographic follow-up there were three restenosed segments (stenoses of 80%, 60%, and 55%). Only the segment with an 80% restenosis had a pressure gradient greater than 10 mmHg. This was treated by atherectomy (Simpson Atherocath, Boston Scientific, St. Albans, UK), and angioplasty due to the focal eccentric nature of the intimal hyperplasia. The other restenoses had no gradient and were asymptomatic. The restenoses all occurred in segments with a pre-intervention hemodynamicatly significant stenosis (75%-99% or significant pressure gradient). While one was type A (unilateral stenosis), the other restenoses were type B (bilateral stenoses). On a patient basis, the primary clinical patency rate was 96%, the primary angiographic patency rate was 89%, and secondary angiographic patency was 93%. On a limb basis, the primary clinical patency was 98%, primary angiographic patency 95%, and secondary angiographic patency 96.5%.
Discussion Balloon angioplasty for stenoses and occlusions is reported with technical success of 80%-90% for stenoses, 75%100% for occlusions and cumulative patency rates of 65%95% after 5 years for stenoses [8] and 76%-78% after 2 years for occlusions [9-12]. Stent placement for poor angioplasty result [13-16] and primary stenting for occlusions have been increasingly performed with results similar to that for angioplasty overall [ 17-21 ]. Atheromatous lesions affecting the aortic bifurcation require consideration of bilateral "kissing balloon" angioplasty if the lesion is bilateral (type B), or if protection of the contralateral common iliac origin is required to reduce post-angioplasty compromise of the ostium by plaque (type A or C). The classification described allows separation of these lesion types before intervention and for follow-up. While balloon angioplasty at the aortic bifurcation [4] is reported to have a technical success of 95% with acceptable durability in follow-up extending to 53 months, this is the first report of the technical
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success and intermediate follow-up of the Memotherm selfexpanding stent in aortic bifurcation reconstruction. The increasing use of stents to treat suboptimal angioplasty results or primary stent placement for occlusions [20] requires evaluation at the aortic bifurcation in terms of the appropriate stent, technical success, and the long-term patency. The use of primary stenting in ulcerated plaques and complex eccentric stenoses is practised [22], while the risks of distal embolization in angioplasty of occlusions are well recognized [3, 12]. Stent placement at a common iliac origin or both common iliac origins, without aortic extension (type A and B), demands accurate placement to avoid compromise of a common iliac origin. The use of balloon-expandable stents confers greater accuracy of placement in this situation, due to minimal stent shortening. Consideration of bilateral common iliac stent placement to include the distal aorta is appropriate. In this situation self-expanding stents appear more appropriate due to their flexibility, but only if significant shortening does not occur. In addition the available lengths are an advantage for longer lesions. If the lesion involves the distal aorta in close proximity to the common iliac origin (type C), this may preclude safe aortic stent placement. The immediate clinical outcome of improvement in 81% of patients corresponds with the results of other studies on peripheral stenting [12]. (Assessment of immediate clinical outcome per limb was not recorded.) In this retrospective study the lack of reliable data on failed procedures due to failure to recanalize occlusions has resulted in the follow-up angiographic patency being higher than that for occlusions in the iliac segment as previously reported. The patency rates we observed in this smaller study are similar to that of 86.5% for Wallstents at 2 years [23], but better than that reported for knitted tantalum Strecker stent reconstruction of the aortic bifurcation at 12 and 18 months, which resulted in a cumulative primary patency of 71% and 63% respectively [5]. The results of this study need to be reflected in a larger study. It is of interest that the loss of patency, in our study, was in stenotic segments, with no loss of patency in the previously occluded segments or minimally stenosed ("normal") segments. There were no restenoses in type C lesions, although the numbers are too small to allow useful conclusions on lesion type. The reduction in the lumen of the normal segments did not result in any loss of patency. However, any restenosis in a previously hemodynamically insignificantly stenosed vessel is of concern. Therefore, type A lesions are worthy of careful consideration, as the minimally stenosed segments showed the highest level of angiographic late loss in this study. The practice of stenting these lesions must be based on the higher risk of ostium compromise due to atheroma remodeling, contralateral proximal stent compromise of the minimally stenosed origin, or risk of distal embolization. The numbers of such segments in this study are too low for a useful conclusion regarding this issue.
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J.G. Houston et al.: Aortic Bifurcation Reconstruction
Table 3. Clinical and angiographic follow-up
Segment
Occlusions Stenoses Normal
n
12 42 12
ABI late loss
Angiographic late loss (%)
6 months
12 months
Final
Final
0.02 (0.11) -0.07 (0.16) 0.07 (0.16)
-0.04 (0.23)
-0.06 (0.24) 0.00 (0.08) 0.01 (0.09)
6.7 (7.0) 10 (17) 14 (15)
-0.03 (0.15) 0.01 (0.08)
Values are the mean _+ SD
There was no clear correlation between clinical loss of patency (ABI loss > 0.15) and angiographic loss of patency. This is likely to be due to coincident superficial femoral/ popliteal or runoff vessel disease. Due to the low restenosis rate and small patient numbers, useful analysis of possible predictors of angiographic loss of patency such as lesion length, resultant vessel diameter, superficial femoral or runoff vessel patency, and continued smoking, was not possible. The comparisons of segments with and without angiographic loss of patency, and these parameters showed no clear correlation, or significance on statistical analysis. This is of interest given the finding of run-off vessel patency as a predictor of iliac stent reocclusion [24] and the lack of support of this predictor by other studies [12, 20]. The options for aortic bifurcation reconstruction include conservative management, surgery, and percutaneous transluminal angioplasty with or without stent placement. The 30-day procedural mortality rate (3%) and morbidity rate (3%) in our study compare favorably with a recent meta-analysis of aortic bifurcation graft surgery for aorto-iliac disease from 1970 to 1996 [25], in which aggregated operative mortality was 4.6% in the older studies (before 1975) and 3.3% in the more recent studies. The aggregated procedure-related morbidity was 13.1% in the older studies (before 1970) and 8.3% in the more recent studies. Because of differences in reporting, and length of follow-up available, patency rates are difficult to compare with surgical results. The meta-analysis reported a 5-year limb-based clinical patency of 91% for claudication and 87.5% for ischemia. Although, only at a mean follow-up of 16 months was our limb-based clinical patency 98% (predominantly for claudication). In conclusion, although results from the intermediate follow-up data in this small study group do not unequivocally support the replacement of aortofemoral bypass surgery by percutaneous revascularization in all patients with aortic bifurcation insufficiency, the procedure-related mortality and morbidity are lower. The technique appears to have good early clinical outcome with relatively low loss of clinical and angiographic patency at intermediate follow-up. The technique offers an alternative for cases of aortic bifurcation atheromatous disease, where the result of balloon angioplasty for stenoses is suboptimal or high risk, and for cases of occlusion.
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