Author + information
- Received January 15, 1997
- Revision received June 26, 1997
- Accepted August 14, 1997
- Published online November 15, 1997.
- Christopher J White, MD, FACCA,*,
- Stephen R Ramee, MD, FACCA,
- Tyrone J Collins, MD, FACCA,
- J.Stephen Jenkins, MDA,
- Alvaro Escobar, MDA and
- Dinesh Shaw, MDA ()
- ↵*Dr. Christopher J. White, Chairman, Department of Cardiology, Ochsner Clinic, 1514 Jefferson Highway, New Orleans, Louisiana 70121.
Objectives. We assessed the safety and efficacy of stent placement in patients with poorly controlled hypertension and renal artery stenoses, which are difficult to treat with balloon angioplasty alone.
Background. Preliminary experience with stent placement suggests improved results over balloon angioplasty alone in patients with atherosclerotic renal artery stenosis.
Methods. Balloon-expandable stents were placed in 100 consecutive patients (133 renal arteries) with hypertension and renal artery stenosis. Sixty-seven of the patients had unilateral renal artery stenosis treated and 33 had bilateral renal artery stenoses treated with stents placed in both renal arteries.
Results. Angiographic success, as determined by quantitative angiography, was obtained in 132 (99%) of 133 lesions. Early clinical success was achieved in 76% of the patients. Six months after stent placement, the systolic blood pressure was reduced from 173 ± 25 to 147 ± 23 mm Hg (p < 0.001); the diastolic pressure from 88 ± 17 to 76 ± 12 mm Hg (p < 0.001); and the mean number of antihypertensive medications per patient from 2.6 ± 1 to 2.0 ± 0.9 (p < 0.001). Angiographic follow-up at a mean of 8.7 ± 5.0 months in 67 patients revealed restenosis (>50% diameter narrowing) in 15 (19%) of 80 stented vessels.
Conclusions. Renal artery stenting is an effective treatment for renovascular hypertension, with a low angiographic restenosis rate. Stent placement appears to be a very attractive therapy in patients with lesions difficult to treat with balloon angioplasty such as renal aorto-ostial lesions and restenotic lesions, as well as after a suboptimal balloon angioplasty result.
Percutaneous transluminal balloon angioplasty is an accepted treatment for selected renal artery stenoses causing renovascular hypertension or renal insufficiency, or both [1–6], and is the treatment of choice for discrete lesions caused by fibromuscular dysplasia [2, 7–10]. Less satisfactory results have been reported for atherosclerotic renovascular stenoses [3, 11, 12], particularly the very proximal renal aorto-ostial stenoses [13–17].
Results after renal artery stent placement have demonstrated superior hemodynamic and angiographic outcomes when compared with published results with balloon angioplasty alone [18–21]. Detailed quantitative studies involving coronary artery angioplasty have documented that the major determinant of long-term patency is early gain in lumen diameter [22, 23]. If the same principle applies to the renal arteries, it would be expected that stent placement would result in improved patency and enhanced clinical success by achieving a greater lumen diameter than with balloon dilation alone.
The purpose of this investigation was to assess the early and 6-month results of renal artery stent placement in a consecutive series of patients with poorly controlled hypertension and renal artery stenoses that were difficult to treat with balloon angioplasty alone.
1.1 Patient Selection
The patients enrolled in this study represent a consecutive series of all patients treated with renal artery stents from June 1992 through December 1994 at the Ochsner Clinic (Table 1). Patients were considered candidates for renal stent placement if they had poorly controlled hypertension (systolic >150 mm Hg or diastolic >90 mm Hg or both) while receiving medical therapy, in the presence of a significant (>50% diameter stenosis by visual estimation on angiography) renal artery aorto-ostial lesion or restenosis lesion or after a suboptimal balloon angioplasty result. All patients gave written informed consent before undergoing the procedure.
For the purposes of this study, chronic renal insufficiency was defined as a serum creatinine level >1.5 mg/dl. Ostial lesions were defined by their proximity (≤1 cm) to the aorta. Restenosis lesions were those that had recurred (>50% diameter stenosis) after a previous successful balloon angioplasty procedure, and suboptimal angioplasty results were those with ≥30% residual stenosis or a large dissection after balloon dilation.
1.2 Stent Placement
Vascular access using the brachial approach was preferred when the origin of the renal artery was cranially oriented. A 7.5F, 90-cm long vascular sheath (Daig) with a multipurpose angiographic catheter as the introducer was inserted through the brachial artery; 3,000 to 5,000 IU of heparin was administered; and the target renal artery was selectively engaged with the multipurpose introducer catheter. Baseline angiography was performed and the lesion was crossed with a steerable 0.035-in. (0.089-cm) guide wire. Predilation of the lesion with a conventional angioplasty balloon (4 to 8 mm in diameter and 2 cm in length) was performed to ensure that full expansion of the lesion was possible.
The long vascular sheath was advanced across the dilated lesion and the balloon catheter was withdrawn. A nonarticulated balloon-expandable stent (Palmaz 104, 154 or 204 Johnson & Johnson Interventional Systems) was mounted on a balloon whose nominal inflation diameter was 10% to 15% larger than the visually estimated reference artery diameter. The balloon-mounted stent was advanced over the guide wire to the lesion site remaining within the shelter of the vascular sheath. The sheath was pulled back into the aorta, uncovering the stent at the lesion site. Contrast injections through the vascular sheath were used to position the stent precisely. The stent was then deployed by inflating the balloon to 6 to 8 atm. Additional inflations with the same or larger balloons or with higher pressures were performed or additional stents were placed, or both, to optimize the angiographic result before final angiography was performed.
For the femoral approach, an 8F vascular sheath was placed percutaneously in the femoral artery, after which 3,000 to 5,000 IU of heparin was administered. An 8F renal angioplasty guiding catheter was advanced to the renal artery and baseline angiography was performed. The remainder of the procedure was analogous to the brachial approach.
Patients were given 325 mg of aspirin per day, at least 1 day before the procedure. Antihypertensive medications were held immediately after the procedure and the patients were observed for 18 to 24 h before resuming or adjusting the medications. Patients were placed on warfarin for 1 to 3 months after stent placement, titrated to achieve an international normalized ratio of 2.0 to 2.5.
1.4 Quantitative Angiography
Quantitative assessment of the angiographic images before and after stent placement was performed using commercially available software (ImageComm). Quantitative measurements included the minimal lumen diameter (MLD) of the reference segment and target lesion, including a determination of the percent diameter stenosis at the lesion site. The reference segment was defined as the nearest visually normal segment of the renal artery on angiography. Measurements were performed at baseline, after stent placement and at follow-up.
Patients had blood pressure measurements and renal function tests performed before hospital discharge and 6 months after the procedure. Follow-up angiography was planned at 6 months after the procedure or earlier if there was clinical suspicion of restenosis.
1.6 Outcome Criteria
Angiographic success was defined as achieving <30% final diameter stenosis for all treated lesions in any given patient. Clinical success was defined as normalization of the blood pressure (systolic ≤150 mm Hg and diastolic ≤90 mm Hg) while the patient received the same or fewer medications without a major procedural complication. Major complications included stent-related death, myocardial infarction, bleeding requiring transfusion or vascular surgery repair, renal failure requiring dialysis therapy, emergency renal artery bypass surgery or stent thrombosis within 30 days of the procedure. Angiographic restenosis was defined as >50% diameter stenosis at the site of stent placement.
1.7 Statistical Analysis
Discrete variables are presented as percentages, and comparisons among the groups were made with the Pearson chi-square test. Continuous variables are expressed as the mean value ± SD. The two-tailed, unpaired ttest was used for comparisons between the groups. Analysis of longitudinal data was made with the two-tailed, paired ttest when the repeated measures involved two observations and repeated measures analysis of variance for more than two observations on the same subject. Contrast with the Bonferroni correction was used to adjust for multiple comparisons. A p value <0.05 was accepted as representing statistical significance. All calculations were performed using JMP software, version 3.2 (SAS Institute, Inc.).
2.1 Procedural Results
A total of 149 balloon-expandable stents were placed in 133 renal arteries of 100 patients, 44 of whom also had chronic renal insufficiency (serum creatinine >1.5 mg/dl). Stents were placed in 107 ostial lesions (80.5%), 10 restenosis lesions (7.5%) and 16 arteries (12%) after a suboptimal balloon angioplasty result. Thirty-three patients with bilateral renal artery stenoses had stents placed in both arteries, whereas 67 patients with unilateral lesions were treated with stents, five of whom had solitary (single) kidneys. Single stents were placed in 117 arteries (88%), and tandem stents were placed in 16 (12%).
2.2 Angiographic Results
Angiographic success was obtained in 132 (99%) of 133 renal arteries (Figs. 1 and 2). ⇓⇓The single angiographic failure had a residual stenosis of 36%, as measured by quantitative angiography, which was visually underestimated by the operator at the time of the procedure. For all vessels, the mean reference vessel MLD was 5.0 ± 1.1 mm and the mean lesion MLD was 1.2 ± 0.6 mm, yielding an average baseline stenosis of 75.3 ± 11.1% (range 43% to 99%). After stent placement, the lesion MLD was 4.8 ± 1.0 mm and the percent stenosis after stent placement was 1.3 ± 15.7% (range −54.8% to 36.4%). The average (nominal) inflated diameter of the balloons used to deploy the stents was 5.7 ± 0.9 mm (range 4 to 8), and the mean maximal inflation pressure was 9.4 ± 2.6 atm (range 6 to 18).
2.3 Clinical Outcome
Clinical success was obtained in 76% of the patients. The baseline blood pressure was significantly reduced before hospital discharge (Fig. 3). The average number of antihypertensive medications per patient was reduced from 2.6 ± 1 at baseline to 2.0 ± 0.9 at 6 months (p < 0.001).
Renal function after stent placement showed a small decline in blood urea nitrogen and no change in serum creatinine (Fig. 4). In the 44 patients with baseline chronic renal insufficiency, the preprocedural creatinine level was 2.4 ± 1.6 mg/dl and the postprocedural creatinine level was not significantly changed at 2.5 ± 1.8 mg/dl (p = 0.59). However, in nine patients (22.5%) with baseline chronic renal insufficiency (mean creatinine level of 1.8 ± 0.1 mg/dl [range 1.6 to 2.0]) creatinine levels became normalized after stent placement (1.4 ± 0.1 mg/dl [range 1.2 to 1.5]) and in two patients with normal renal function levels became slightly abnormal after stent placement (mean creatinine 1.7 ± 0.1 mg/dl).
One major complication, subacute stent thrombosis, occurred 3 days after stent placement in this series of patients. Two patients experienced transient contrast nephropathy without need for dialysis. There were no guide wire perforations or emergency renal artery bypass procedures. There were seven access-site complications, including groin hematomas in five patients, one femoral artery pseudoaneurysm that resolved with external compression using duplex ultrasound guidance and one brachial artery occlusion that occurred after sheath removal and was resolved with balloon dilation from a femoral access site. One patient had a sudden ischemic cardiac death 2 days after hospital discharge, which was determined to be unrelated to the stent placement.
Procedural difficulties encountered and subsequently resolved included failure to deploy a stent on the initial attempt in two patients. In one patient, the balloon developed a leak and the stent could not be deployed. The partially expanded stent was withdrawn on the balloon, and a second stent was successfully placed. In another patient an undeployed stent became embolized from the balloon catheter but remained on the guide wire at the level of the common iliac artery. The stent was retrieved through the vascular sheath with a loop snare, and a second stent was successfully deployed in the renal artery.
Late complications (>30 days from stent placement to 6-month follow-up) included non–stent-related death in two patients. One patient died of complications of heart failure 2 months after stent placement, and one patient died of complications of a myocardial infarction 4 months after stent placement.
Six months after stent placement, the mean systolic blood pressure was reduced from 173 ± 25 to 146 ± 20 mm Hg (p < 0.01) and the mean diastolic pressure from 88 ± 17 to 77 ± 12 mm Hg (p < 0.01) (Fig. 3). Angiographic follow-up at a mean of 8.7 ± 5.0 months in 67 patients revealed restenosis (>50% diameter narrowing) in 15 (18.8%) of 80 stented vessels. At the follow-up visit, patients with angiographic restenosis tended to have a higher systolic blood pressure (155 ± 15 vs. 145 ± 21 mm Hg [p = 0.09]) than those without restenosis, but there was almost no difference in diastolic blood pressure (75 ± 14 vs. 77 ± 12 mm Hg [p = 0.78]).
Quantitative angiographic measurements revealed significant differences in the immediate post-stent MLD for patent vessels (4.9 ± 0.9 mm) compared with restenotic lesions (4.3 ± 0.7 mm) (p = 0.025) and in the late loss (post-stent MLD minus follow-up MLD) for restenosis vessels (3.0 ± 1.4 mm) compared with patent vessels (1.3 ± 0.9 mm) (p < 0.001) (Table 2).
This series of consecutive patients demonstrates the safety and efficacy of renal stent placement for lesions considered difficult to treat with balloon angioplasty. Our technical success in 99% of lesions, clinical success in 76% of patients and only one major stent-related complication compare very favorably with published results of balloon angioplasty for renal artery stenosis [1–6]and are consistent with previous published reports for renal artery stent placement [18–21].
The 6-month outcomes in our patients demonstrated sustained benefit with regard to lower blood pressure and fewer antihypertensive medications required. An angiographic restenosis rate of 18.8%, in the two-thirds of patients undergoing follow-up angiography, is encouraging considering the difficulty in convincing asymptomatic patients to undergo repeat angiography, which may have resulted in a bias favoring angiographic follow-up in patients with clinical evidence of restenosis.
Our 6-month angiographic restenosis rate is comparable to the 16% to 25% restenosis rate in previous studies [18, 20]and is significantly better than the 39% restenosis rate in a comparable group of 28 patients treated with renal stents in a multicenter study by Rees et al. . There may be several reasons for this discrepancy in the latter study, including 1) their use of 20-mm long, articulated stents (stents with 1-mm gaps in their center) versus our use of nonarticulated stents, 95% of which were ≤15 mm; and 2) their underdeployment of stents as they attempted to match the reference artery size, whereas we used slightly oversized stents with regard to the reference artery diameter.
The benefit of endolumen stent placement comes from the stent’s ability to scaffold the endolumen surface of the dilated lesion and to resist the inherent elastic recoil of the dilated artery to maximize the lumen area. The ability of the stent to overcome the elastic recoil of the stented vessel is an advantage over balloon dilation alone, and results in a larger early gain in the MLD.
We attempted to use slightly oversized stents compared with the reference vessel diameter. The nominal size of the balloon used to deploy the stents (5.7 ± 0.9 mm) was larger than that of the quantitatively measured reference vessel (5.0 ± 1.1 mm, p < 0.001). However, the final lumen diameter after stent placement (4.8 ± 1.0 mm) was slightly smaller than the reference vessel diameter. This reflects incomplete expansion of the stent at the balloon inflation pressures used for deployment (9.4 ± 2.6 atm).
The only procedural variable that was related to angiographic restenosis in our patients was the post-stent MLD. There was no difference among patients with or without restenosis regarding the nominal balloon diameter or maximal inflation pressure used for stent deployment. Therefore, safely achieving the lowest residual stenosis after stent deployment by employing higher inflation pressures or larger balloons to more fully expand a suboptimally dilated stent should be the goal when placing renal stents.
For the total group of patients, there was a slight improvement in blood urea nitrogen but no significant change in serum creatinine after stent placement, nor was there a significant difference in the baseline or follow-up serum creatinine levels for the groups with or without renal insufficiency. It is noteworthy, however, that nine patients (22.5%) with mild baseline renal insufficiency did not have normalized renal function after the stent procedure.
3.1 Study Limitations
The limitations of this investigation are that it was not a randomized study, so no direct comparison with balloon angioplasty is possible; and that follow-up angiography was not performed in all patients. However, at the time of this study, we were unwilling to randomize this group of patients because we believed balloon angioplasty alone was an unattractive choice for treatment of this subset of renal artery lesions.
3.2 Indications for Stent Placement
These data suggest that elective stent placement is the procedure of choice for patients with difficult lesions for balloon angioplasty alone. Determining the benefit of primary stent placement for other renal artery lesions currently adequately treated with balloon angioplasty will require a randomized trial.
The issue of preserving or improving renal function with percutaneous renal artery revascularization is an important one. The natural history of renal artery stenosis is progressive in nature [24–26]. Given the low restenosis rate obtained in our study, renal stent placement may prevent progressive renal artery stenosis and subsequent loss of renal function. Previous reports of renal angioplasty as well as stent placement have documented improvement in renal function in some patients with renal failure, but this has not been predictable [4, 5, 12, 18–21]. A separate issue is whether treating more moderate stenoses of the renal arteries (50% to 70% diameter stenosis) in patients with normal renal function and without hypertension will prevent loss of renal function in the long term. This will require a prospective, randomized study.
We have demonstrated excellent angiographic and clinical results of stent placement for renal artery stenosis in a consecutive series of patients with poorly controlled hypertension and lesions difficult to treat with balloon angioplasty alone. To obtain the best results every effort should be made to optimize stent expansion and minimize residual vessel stenosis. Stent placement appears to be a very attractive therapy for renovascular hypertension in patients with lesions difficult to treat with balloon angioplasty alone, such as ostial lesions and restenotic lesions, as well as after a suboptimal angiographic result after balloon dilation alone.
☆ To discuss this article on-line, visit the ACC Home Page at www.acc.org/membersand click on the JACC Forum
- Received January 15, 1997.
- Revision received June 26, 1997.
- Accepted August 14, 1997.
- The American College of Cardiology