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Vascular and Interventional Radiology |
1 From the Division of Angiology (I.B., K.v.A., D.D.D., M.B., F.M.) and the Department of Radiology (J.T.), University Hospital, Freiburgstrasse, 3010 Bern, Switzerland. Received June 30, 1999; revision requested August 16; final revision received November 26; accepted December 7. Address correspondence to I.B. (e-mail: iris.baumgartner@insel.ch).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Between January 1994 and April 1998 the authors prospectively followed up 163 consecutive patients with 200 atherosclerotic renal arterial lesions after primary PTRA or primary stent placement. Duplex ultrasonography was performed 1 day and 3, 6, and 12 months later.
RESULTS: The primary 12-month PTRA patency rates were 34% (21 of 33 atherosclerotic lesions) for ostial stenoses, 65% (20 of 60) for proximal stenoses, and 83% (five of 30) for truncal stenoses (
2 value, 15.63; P < .001). The corresponding stent patency rates were 80% (four of 21), 72% (nine of 34), and 66% (five of nine), respectively (2 value, 4.11; not significant). Significant stent-related reduction in risk of restenosis was limited to the ostial stenoses (P = .002).
CONCLUSION: Renal arterial stent placement considerably improves patency in ostial stenoses, but compared with the technically successful PTRA, it does not significantly improve primary patency in proximal and isolated truncal renal arterial stenoses.
Index terms: Renal angiography, 961.122 • Renal arteries, stenosis or obstruction, 961.721 • Renal arteries, transluminal angioplasty, 961.1282, 961.1286 • Renal arteries, US, 961.12989 • Stents and prostheses, 961.1268, 961.1286
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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Because ostial lesions represent bulky plaques along the aortic wall that encroach the origin of the renal artery (21,22), the mechanisms of balloon PTRA, such as stretching and cracking of the interna and media and remodeling of the plaque, are impeded. Stent placement provides a luminal scaffolding that virtually eliminates recoil, a factor of paramount importance in ostial lesions. According to data in the literature (1,2,7,12), true ostial stenoses located within 5 mm from the aortic lumen represent 11%–40% of atherosclerotic renovascular lesions. The definition of ostial stenosis varies in published series, however, and includes proximal (close to the ostium or pseudotruncal) stenosis in some studies (4,17,20).
The aim of this prospective, nonrandomized observational study was to compare the patency results of balloon PTRA and stent-assisted PTRA in atherosclerotic ostial, proximal, and isolated truncal renal arterial stenoses.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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Ostial lesions were defined as stenoses located within 5 mm of the aortic lumen and caused by atherosclerotic disease of the aorta (Figs 2, 3a) (21). Nonostial lesions were defined as (a) proximal renal arterial stenoses located within 5–10 mm of the aortic lumen (Figs 2, 3b) and (b) isolated truncal renal arterial stenoses located more than 10 mm distally and clearly separated from the aortic lumen (Figs 2, 3c) (22). Larger stenoses (>5 mm) were classified according to the most proximal location. A stenosis of 60% or greater caused by the aortic wall was considered to be ostial, even when it extended more than 5 mm into the renal artery. A stenosis was classified as proximal when there was an aortic cuff, with the stenosis separated more than 5 mm from the contrast material–enhanced aortic lumen (Fig 2).
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Transstenotic pressure measurements were used to estimate the success of the balloon dilation. Stent insertion was performed when a transstenotic pressure gradient higher than 10 mm Hg and/or an angiographic residual stenosis of more than 60% in diameter remained after PTRA. Balloon-expandable Palmaz stents (Johnson & Johnson Interventional Systems, Warren, NJ), with an unexpanded length of 10, 15, or 20 mm, were fitted individually; no additional sheaths were used for stent placement. For ostial lesions, we attempted to have approximately 0.5–1.0 mm of the stent protrude into the aorta. The stents were deployed with inflation of 5–7-mm balloons at up to 12 atm.
Complete technical success after PTRA or stent placement was defined as an estimated residual stenosis of less than 50% according to angiographic results and a transstenotic pressure gradient lower than 10 mm Hg. Thus, transstenotic pressure measurements were obtained before the intervention when the relevance of a stenosis was in question. Pressure measurements were not performed in cases of high-grade stenosis. Postintervention measurements were performed in 89% (178 of 200) of stenotic lesions; in 11% (n = 22) of the lesions, these measurements were not obtained because of technical or anatomic reasons.
The patients were admitted 1 day before the interventional procedure. The patients with a serum creatinine level of 115 µmol/L or higher or diabetes mellitus received additional intravenous fluids (1,500 mL of isotonic saline [0.9%] within 12 hours) to guarantee sufficient hydration. Monitoring of patients was limited to electrocardiographic monitoring during the interventional procedure and manual blood pressure measurements before and up to 24 hours after the procedure. Bed rest for 10 hours was required after the procedure, and compression bandages were removed the next day. Aspirin (100 mg daily) was prescribed routinely for at least 12 months in all the treated patients.
Clinical complication was defined as the occurrence of at least one of the following: death, myocardial infarction, renal function deterioration of more than 15%, or unexpected start of dialysis within 30 days after endovascular intervention. Other events included hemorrhagic complications, which were defined as bleeding that necessitated transfusion, the need for vascular surgery, or procedural difficulties (ie, those related to the puncture site, dilation site, or area distal to the dilation site).
Follow-up
Patients were required to undergo follow-up studies, including duplex ultrasonography (US), 1 day and 3, 6, and 12 months after the procedure. Follow-up visits were scheduled prospectively. The most frequent reasons for missed follow-up visits were death, coexistent morbidity, and long-distance travel in the older age group of patients. The primary end point of the study was US (9,23) and/or angiographic evidence of the first restenosis, which was defined as at least 60% stenosis.
All US examinations were performed with a 2.5–4.5-MHz phased-array transducer (128/XP 10; Acuson, Mountain View, Calif). The abdominal aorta was evaluated to determine whether there was aneurysmal or occlusive disease, and then the aortic peak systolic velocity was measured at or above the level of the superior mesenteric artery. The degree of renal arterial stenosis was determined according to previously validated criteria on the basis of the renal arterial peak systolic velocity and the renal aortic ratio (24–27). The degree of narrowing was classified as follows: less than 30% diameter reduction when the peak systolic velocity was less than or equal to 180 cm/sec and the renal aortic ratio was less than 3.5, moderate (30%–60%) stenosis when the peak systolic velocity was greater than 180 cm/sec and the renal aortic ratio was less than 3.5, hemodynamically significant (>60%) stenosis when the peak systolic velocity was greater than 180 cm/sec and the renal aortic ratio was greater than 3.5, and occlusion when there was no flow detectable (28).
Direct renal arterial assessment was supplemented by using analysis of segmental Doppler waveforms, with an absent early systolic peak indicating more than 60% stenosis (29). Duplex US was supplemented by intraarterial digital subtraction angiography when there was greater than 60% restenosis, which occurred in 79 (13%) of 611 assessments, or when US assessment was insufficient; 43 (7%) of 611 renal arteries were not assessable at any time (ie, 3-, 6-, and 12-month US examination results were unreliable). Insufficient US assessment was defined as the inability to directly detect Doppler signals from the main renal artery (ostial, middle, or distal) and/or interpret indirect intrarenal Doppler waveforms, as defined by Stavros and Harshfield (29). All US examinations were performed by two of the authors (I.B. and M.B.).
Improvement of arterial hypertension was defined as a decrease in the systolic and/or diastolic blood pressure of more than 20 mm Hg or a reduced necessity for antihypertensive drugs. Patients were evaluated for renal function response after the interventional procedure if their serum creatinine level was 115 µmol/L or more before the intervention. Response was classified as improved renal function (decrease in serum creatinine level of 15% or more), no change (serum creatinine ± 14%), or deterioration of renal function (increase in serum creatinine level of 15% or more). Because patients with bilateral renal arterial stenosis underwent combined interventional procedures, no assessments of subgroups were performed. Response was classified with consensus by two authors (I.B., M.B.) by obtaining blood pressure measurements in patients in the sitting position and serum creatinine measurements after each duplex US examination and using additional available data (eg, blood pressure diary, general practitioner visits).
Statistical Analyses
Values are expressed as the mean ± one SD. Estimates for the cumulative primary patency rates were calculated by using life-table analysis. The 95% CIs were calculated according to the normal approximation of the binomial distribution. For analysis of continuous blood pressure (in millimeters of mercury) and serum creatinine level (in micromoles per liter) data, two-tailed nonparametric tests were used to assess the differences over time (Wilcoxon signed rank test). Categorical data are presented as rates, which were compared by using contingency tables (2 test). A P value less than .05 was considered to be indicative of statistical significance. The STATVIEW software package, version 4.5 (SAS Institute, Cary, NC) was used for all calculations.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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2 value, 15.63; P < .001), which essentially was based on a higher rate of restenoses in the ostial lesions (2 value, 13.26; P < .001). The corresponding patency rates achieved with stent placement in 64 renal arteries were 80% (four of 21 atherosclerotic lesions; 95% CI: 97%, 63%) for ostial stenoses, 72% (nine of 34; 95% CI: 91%, 53%) for proximal stenoses, and 66% (five of nine; 95% CI: 90%, 41%) for truncal stenoses. In contrast to the results seen after balloon PTRA, there was no statistically significant difference in patency between ostial, proximal, and truncal stenoses (2 value, 4.11; not significant). Life-table graphs are shown in Figures 4–6.
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The three renal arterial occlusions and 10 stenoses within the accessory renal arteries were analyzed separately. Two renal arterial occlusions were primarily treated with stent placement. One artery was shown to be patent 9 months after the intervention. An early reocclusion appeared twice in the second renal arterial occlusion; however, long-term patency was achieved after intraarterial lysis and insertion of a second stent. The third renal arterial occlusion showed a restenosis 4 and 6 months after PTRA. Five stenoses in accessory renal arteries were characterized to be of ostial origin. Three of these lesions were treated by using PTRA, and all three were shown to be restenosed within 3 months of follow-up. Two ostial lesions in accessory renal arteries were primarily treated with stent placement, and both were shown to be patent at 12-month follow-up. The remaining five stenoses were classified to be proximal lesions. All five of these arteries remained free of restenosis within 12 months of follow-up, three after PTRA and two after stent placement.
During the study period, the percentage of primary stent placements performed increased from 9% (three of 34 interventional procedures) in 1994 to 53% (31 of 59) in 1998, whereas the material used—that is, balloons and/or stents—and the group of interventionalists performing the renal interventional procedures remained unchanged.
Complications
Among the 188 patients who underwent 232 primary catheter treatments or attempted catheter treatments for renal arterial stenosis, there were three (1.6%)deaths within 30 days. None of these deaths was related to the interventional procedure. Within 30 days of the primary intervention, deterioration of renal function, based on a greater than 15% increase in the serum creatinine level, was measured in 20 (10.6%) patients; within 3 months, one patient became dependent on dialysis; and immediate dialysis was required in three patients. In the patients who developed renal failure, there was no clear relationship between the preprocedural serum creatinine level and either the volume (15—120 mL; median, 53 mL) or type of contrast material used.
With regard to renal function, there was no statistically significant difference between balloon PTRA or stent-assisted PTRA. The rate of complications directly related to PTRA was 3.1% (bleeding requiring transfusion [n = 2], femoral pseudoaneurysm [n = 1], atheroembolization with small segmental renal infarction [n = 1]). The rate of complications associated with stent placement was 8.6% (bleeding requiring transfusion [n = 1], acute renal arterial occlusion [n = 1], femoral pseudoaneurysm [n = 2], peripheral atheroembolization [n = 1], stent dislocation [n = 1]).
Clinical Outcome
The mean (± SD) blood pressure values before balloon PTRA or stent placement and after the procedure at the end of follow-up are shown in Figure 7. The mean decrease in systolic blood pressure was 12 mm Hg (95% CI: 8 mm Hg, 15 mm Hg), and the mean decrease in diastolic blood pressure was 4 mm Hg (95% CI: 1 mm Hg, 6 mm Hg). The mean number of antihypertensive drugs prescribed before PTRA or stent placement and after the procedure at the end of follow-up was 2.2 ± 1.0 or 2.1 ± 1.1, respectively (not significant). Overall, a decrease in the systolic and/or diastolic blood pressure of more than 20 mm Hg and/or a reduced necessity for antihypertensive drugs was achieved in 70 (43%) of 163 patients, and an increase in the systolic and/or diastolic blood pressure of more than 20 mm Hg and/or an increased necessity for antihypertensive drugs was seen in 19 (12%) patients.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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Coronary stents, by virtue of their capability to serve as mechanical scaffolds that have been shown to lower the rate of restenosis and reduce the need for additional percutaneous interventions (30,31), have engendered widespread enthusiasm for stent placement. Although stents are used in more than half of all coronary catheter interventions (14), to our knowledge, it has not been proved whether the application of stents in renal arteries is generally beneficial. Although there are numerous historic series, the analysis of data in these studies is troublesome. The definition of ostial renal arterial lesions is either discrepant (6,9) or missing (1,7,28), or the reported patency rates after PTRA do not include the location of the lesions (1,6,7,9). The patency rates after stent placement initially reported ranged from 61% (13) to 75% (14) and were not superior to the results achieved with PTRA. More favorable results have been seen in subsequent series, all of which have been restricted to ostial lesions. Blum and colleagues (16) reported a notable patency rate of 84.5% at 60 months after stent placement. Their series included 63 ostial lesions after unsatisfactory PTRA and 10 restenoses. van de Ven (20) et al reported a 6-month patency rate of 52% with technically successful PTRA compared with a patency rate of 86% with stent placement.
Our results in atherosclerotic ostial stenoses are in accordance with the data of van de Ven et al (20). In our study, the calculated 6-month patency rate was 58% with PTRA and 79% with stent placement. The results of PTRA in nonostial lesions—that is, the calculated 12-month patency rates of 65.3% in proximal stenoses and 82.6% in truncal renal arterial stenoses—are similar to the data reported by Weibull et al (patency rate of 65% for most lesions within 10 mm from the aortic lumen) (6), Plouin et al (patency rate of 81% for most lesions defined as truncal) (7), and Tullis et al (patency rate of 82% for nonostial lesions) (28). This prospective series, which included 200 atherosclerotic renal arterial stenoses, however, is, to our knowledge, the first study in which technically successful primary PTRA and primary stent placement have been directly compared in nonostial (ie, proximal and truncal) renal arterial stenoses. The patency achieved with PTRA in the ostial lesions was 31% lower than that achieved in the proximal lesions and 48% lower than that achieved in the truncal renal arterial stenoses (P < .001). These results were not unexpected, but up-to-date analysis of the anatomic location of the lesions was lacking (4,5,7,10,12).
We showed that the stent-related reduction in relative risk of restenosis within 12 months was 70% in the ostial stenoses (P = .002), whereas it was 20% and not statistically significant in the proximal stenoses. The isolated truncal lesions showed tendentiously better results with PTRA, but the difference was not statistically significant. Thus, although the scaffolding properties of stents are favorable in ostial stenoses, stents may provoke a proliferative response (eg, intimal hyperplasia) in nonostial lesions and thus erase the net benefit.
Although van de Ven et al (20) reported a similar rate of complications with PTRA and stent procedures in their randomized trial, there was a slightly higher stent-related complication rate in our series. In accordance with the complications reported in the literature—that is, perirenal or puncture site hematomas that necessitate transfusion—atheroembolization, femoral pseudoaneurysm, and acute vessel closure are common (32–34). With the exception of two cases of perirenal bleeding due to a wire perforation, none of the complications were related to a learning curve, as suggested by Beek et al (34). Deterioration of renal function was most common and, as mentioned by Martin et al (35), the most easily avoidable complication encountered.
The clinical outcomes in this series—that is, arterial hypertension and renal function deterioration—were significantly improved independent of the technique used. It was beyond the scope of this study to assess the clinical outcomes in correlation with the locations of the stenoses or the techniques used, particularly because there were a considerable number of bilateral renal arterial stenoses treated with a combination of PTRA and stent placement. Moreover, other variables, such as the morphologic features of the stenoses, nonischemic nephropathy, or long-standing arterial hypertension, would have had to have been included for such analysis.
The main limitation of our study was that treatment with either PTRA or stent placement was not randomly assigned. Although a bias in favor of PTRA or stent placement cannot be excluded, there are arguments that may equalize it. First, the results in ostial lesions were in accordance with the data of van de Ven et al (20) in their randomized trial. Second, there were fewer postprocedural residual stenoses in the group of stenotic arteries treated with stent placement, meaning that even if all the stents placed in proximal and truncal stenoses had been most negatively selected, this would not have resulted in a disadvantageous early result.
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FOOTNOTES |
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Author contributions: Guarantor of integrity of entire study, I.B.; study concepts and design, I.B.; definition of intellectual content, I.B., F.M.; literature research, M.B.; clinical studies, J.T., D.D.D., I.B., K.v.A.; data acquisition, K.v.A., I.B.; data analysis, I.B., J.T.; statistical analysis, I.B.; manuscript preparation, I.B.; manuscript editing, D.D.D.; manuscript review, F.M.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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