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Anti-Interventional Bias
Submit responseAnti-Interventional Bias
To the Editor: The publication and explicit editor’s endorsement of the findings of the seriously flawed STAR(1) (STent placement and blood pressure and lipid-lowering for the prevention of progression of renal dysfunction caused by Atherosclerotic ostial stenosis of the Renal artery) renal intervention trial, in my opinion, was unbalanced. This trial rivals the DRASTIC trial(2) as the most poorly designed and deceptive renal interventional trial ever published. How this manuscript got by the scrutiny of your expert content reviewers as well as the Annals’ Editors without even inviting a counterbalancing editorial is disconcerting to those perhaps expecting more objectivity.
As an interventionalist who performs renal intervention, I welcome additional evidence to guide appropriate utilization of renal artery intervention in patients with renovascular disease. There are patients suffering the clinical consequences of renal ischemia (nephropathy, refractory hypertension, or flash pulmonary edema) who have failed medical therapy, that benefit from renal intervention, but most reasonable clinicians in this field would acknowledge that further refinement in patient selection would be helpful to increase the percentage of positive responders.
The STAR trial(1) had a valid hypothesis to test, “is renal stenting with best medical therapy better treatment than best medical therapy alone in patients with renal artery stenosis and impaired renal function”? Unfortunately, strategic errors in the conduct of the trial led to glaring flaws in the methodology which generated inappropriate conclusions that misinformed readers.
Specifically, the authors designed a trial that 1) systematically over-estimated the severity of renal artery stenosis because they enrolled patients based upon non-invasive angiography and 2) the interventionalists may not have been adequately skilled. Because the renal artery stenosis severity was systematically overestimated, their patients had milder renal artery narrowing than anticipated. Why would anyone expect patients with mild renal artery narrowing to respond (the treatment group) to revascularization? Furthermore, why would anyone expect patients with mild renal disease (the control group) to deteriorate from ischemic nephropathy? The investigators failed to objectively determine the severity of renal artery narrowing with intravascular ultrasound or translesional pressure gradients as recommended in the AHA/ACC guidelines for treatment of mild to moderate lesions(3). The authors were aware of this shortcoming and acknowledged that lesion severity in “both” groups was overestimated by non-invasive imaging. However, the impact of overestimating the severity of the renal artery narrowing for ischemic nephropathy was critical to answering the questions raised by this trial. Renal revascularization therapy is not expected to benefit non-ischemic kidneys. The control group, also with overestimated lesion severity, will have a lower rate of progression to renal failure than expected, ensuring that conservative therapy will always prevail.
The authors point out their concern over the serious complications that were related to the renal interventions, but did not ensure that the interventionalists were well qualified for to perform this procedure. Rather than document a minimal skill level for the interventionalists by requiring a track record for quality and success in renal stent cases, they simply enlisted senior radiologists (10 years of experience). Interventionalists, like surgeons, have widely varying skill levels, and renal stent placement is a demanding technical skill. The interventionalists in this trial had more problems than would be expected (4% failure rate to successfully deliver the renal stent and more renal artery perforations) in a reasonable quality interventional practice. The expert reviewers should have been skeptical of the quality of renal stenting performed in this trial, which certainly would have been voiced in a balancing editorial.
In this intention to treat analysis, one-third of the patients randomized to stent therapy were not treated due to the lack of significant stenosis. The failure of the expert content reviewers and the journal editors to understand the impact of relying on an “intention to treat” analysis, when one-third of the study subjects failed to receive their allocated treatment, and that revascularization of “mild” RAS would be very unlikely to improve non-ischemic nephropathy, is hard to believe. The end result is that renal stenting was compared to medical therapy in patients very unlikely to benefit from revascularization because the lesions (in both groups) were milder than expected and patients were more likely to encounter a complication due to the uncertain skill level of the interventionalists.
The authors’ conclusion that “our findings favor a conservative therapeutic approach to patients with atherosclerotic renal artery stenosis, focused on cardiovascular risk factor management without stenting”, disserves clinicians trying to understand the appropriate role for renal revascularization in their clinical practice. The question to be answered is “how should responsible physicians select patients who are most likely to benefit from renal stenting”? This trial doesn’t answer that question, and does more harm than good by misinforming the physician in the trenches about treatment choices in patients with renal artery stenosis and worsening renal function.
Christopher J. White, MD Ochsner Clinic Foundation New Orleans, LA 70121
References:
1. Bax L, Woittiez AJ, Kouwenberg HJ, Mali WP, Buskens E, Beek FJ, Braam B, Huysmans FT, Schultze Kool LJ, Rutten MJ, Doorenbos CJ, Aarts JC, Rabelink TJ, Plouin PF, Raynaud A, van Montfrans GA, Reekers JA, van den Meiracker AH, Pattynama PM, van de Ven PJ, Vroegindeweij D, Kroon AA, de Haan MW, Postma CT, Beutler JJ. Stent placement in patients with atherosclerotic renal artery stenosis and impaired renal function: a randomized trial. Ann Intern Med. 2009;150(12):840-848, W150-841.
2. van Jaarsveld B, Krijnen P, Pieterman H, Derkx F, Deinum J, Postma C, Dees A, Woittiez A, Bartelink A, Man in 't Veld A, Schalekamp M. The effect of balloon angioplasty on hypertension in atherosclerotic renal artery stenosis. N Eng J Med. 2000;342:1007-1014.
3. Hirsch AT, Haskal ZJ, Hertzer NR, Bakal CW, Creager MA, Halperin JL, Hiratzka LF, Murphy WR, Olin JW, Puschett JB, Rosenfield KA, Sacks D, Stanley JC, Taylor LM, Jr., White CJ, White J, White RA, Antman EM, Smith SC, Jr., Adams CD, Anderson JL, Faxon DP, Fuster V, Gibbons RJ, Halperin JL, Hiratzka LF, Hunt SA, Jacobs AK, Nishimura R, Ornato JP, Page RL, Riegel B. ACC/AHA 2005 guidelines for the management of patients with peripheral arterial disease (lower extremity, renal, mesenteric, and abdominal aortic): executive summary a collaborative report from the American Association for Vascular Surgery/Society for Vascular Surgery, Society for Cardiovascular Angiography and Interventions, Society for Vascular Medicine and Biology, Society of Interventional Radiology, and the ACC/AHA Task Force on Practice Guidelines (Writing Committee to Develop Guidelines for the Management of Patients With Peripheral Arterial Disease) endorsed by the American Association of Cardiovascular and Pulmonary Rehabilitation; National Heart, Lung, and Blood Institute; Society for Vascular Nursing; TransAtlantic Inter-Society Consensus; and Vascular Disease Foundation. J Am Coll Cardiol. 2006;47(6):1239-1312.
Conflict of Interest:
Principal investigator for a carotid stent trial funded by Boston Scientific Corporation, a manufacturer of renal stents.
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Author's response
Submit responseSir, with interest we read the letters from drs Mann and Jovin.
What our study showed is that in patients with impaired renal function and atherosclerotic renal artery stenosis (ARAS), stent placement goes with costs and complications for at best uncertain benefit. For this category of patients the treatment with stents remains subject of research. We want to stress that we focused our study on impaired renal function and ARAS and, therefore do not make statements about other categories of patients with for instance renovascular hypertension, therapy refractory hypertension or congestive heart failure.
As we discussed in our article, the lower event rate than anticipated has reduced the power of our study and we might therefore be dealing with a chance finding. In the mean time the ASTRAL study from the UK, including more than 800 patients, found similar results and was neither able to show any effect in predefined subgroup analysis such as severe renal dysfunction, severe or bilateral renal artery stenosis (PA Kalra, World Congress of Nephrology, May 2009, Milan, Italy).
It is of note that the enumeration by Mann of patients unlikely, a priori, to benefit from stent placement is simplistic and not correct as the different categories stated largely overlap.
In both letters poor patient selection for not using functional stenosis tests and including patients with a stenosis 50-70% is suggested as an explanation for the negative results. The hypothesis that patients with more severe ARAS would be the ones to benefit more from stent placement has however not been demonstrated in terms of renal function. In fact, in patients with ARAS and impaired renal function, the severity of the stenosis is not correlated with renal function (1), and is neither a predictor of progression of renal failure nor a predictor of outcome after revascularization (2-4). Yet in our study majority (67%) of the patients had a stenosis >70% to the most affected kidney. When we designed our study back in 1999, a reduction in luminal diameter of 50% or more (corresponding to a surface reduction >70%) was widely considered as clinically significant (5). Although our insight on the relationship between stenosis severity and degree of renin release by the post-stenotic kidney and renovascular hypertension may have improved in the last decade, the use of functional tests have not been proven to predict favorable outcome after stent placement as far as renal function is concerned. This underscores the fact that the pathophysiology of renal failure in this group of patients is extremely complex. In addition to reduced blood flow, renal function in these patients is also the dependent on presence of small vessel disease, glomerulosclerosis and renal fibrosis.
Although there may be some criticism about our study it shows that indiscriminate widespread introduction of stent placement without proper scientific evaluation is unjustified, costly and dangerous for patients.
References
1. Farmer CK, Cook GJ, Blake GM, Reidy J, Scoble JE. Individual kidney function in atherosclerotic nephropathy is not related to the presence of renal artery stenosis. Nephrol Dial Transplant 1999;14(12):2880-4.
2. Suresh M, Laboi P, Mamtora H, Kalra PA. Relationship of renal dysfunction to proximal arterial disease severity in atherosclerotic renovascular disease. Nephrol Dial Transplant 2000;15(5):631-6.
3. Cheung CM, Wright JR, Shurrab AE, Mamtora H, Foley RN, O'Donoghue DJ, Waldek S, Kalra PA. Epidemiology of renal dysfunction and patient outcome in atherosclerotic renal artery occlusion. J Am Soc Nephrol 2002;13(1):149-57.
4. Wright JR, Shurrab AE, Cheung C, Waldek S, O'Donoghue DJ, Foley RN, Mamtora H, Kalra PA. A prospective study of the determinants of renal functional outcome and mortality in atherosclerotic renovascular disease. Am J Kidney Dis 2002;39(6):1153-61.
5. Leertouwer TC, Gussenhoven EJ, Bosch JL, van Jaarsveld BC, van Dijk LC, Deinum J, Man In 't Veld AJ. Stent placement for renal arterial stenosis: where do we stand? A meta-analysis. Radiology 2000;216(1):78-85.
Conflict of Interest:
None declared
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A Questionable Trial
Submit responseTo the Editor:
I would make the following comments regarding the manuscript, Stent Placement in Patients With atherosclerotic Renal Artery Stenosis and Impaired Renal Function by Bax L, Arend-Jan JW, Kouwenberg HJ et al. Ann Intern Med 2009; 150:840-848.
First, the authors used 50% or greater stenosis as the definition of clinically significant stenosis. Most workers in the field agree that unless the stenosis is 75% or greater, it is not of clinical significance (1). Second, in an attempt to reduce the sample size, the authors used an enormous effect size of a 60% relative risk reduction (RRR) i.e. 50% renal failure in the medication group to 20% in the stent group. This is an unrealistic goal. Even commonly accepted practices, such as the use of angiotensin-converting enzyme inhibitors (ACE inhibitors) in diabetic nephropathy, only achieve a RRR of 21% for all renal events compared to placebo (2).
References
1. Renovascular hypertension: Balancing the controversies in diagnosis and treatment . Garovic VD, Kane GC, Schwartz GL. Cleve Clin J Med 2005; 72(12):1135-1144.
2. Effects of a fixed combination of peridopril and indapamide on macrovascular and microvascular outcomes in patients with Type 2 diabetes mellitus (the ADVANCE trial): a randomized controlled trial. ADVANCE collaborative group. Lancet 2007;370:829-840.
Conflict of Interest:
None declared
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Resonse to "In Defense of Renal Artery Stenting”
Submit responseI read the article “In Defense of Renal Artery Stenting” and the authors stated, “Having personally observed many patients who, following renal artery angioplasty +/- stenting, experienced rapid amelioration of problems such as refractory hypertension, congestive heart failure and renal insufficiency, it is inconceivable to us, and to many others, that stenting is of no benefit. Unfortunately, there is also no doubt that it is overused, often employed in cases unlikely to benefit.”My mother had a CVA after a biliary stent was implanted. She was having renal failure due to polypharmacy. She was admitted to the hospital on 5 medications, 3 of which were interacting with each other. Her numbers got better when they got her on the right medications and treated her dehydration and anemia yet they stented her anyway. If they would have waited, her creatinine levels would have returned to acceptable levels. However, I bet that the doctor who put in the stent, in his mind believes it was his procedure that did the trick.
I’m quickly summarizing my findings. I’ve studied her medical records and researched her case for two years, so I’m very sure of what really happened. My point is, often doctors are in denial. Often the patient gets better in spite of the procedure although it looks like they got better because of the procedure.
References
1. Liesbeth Bax, Arend-Jan J. Woittiez, Hans J. Kouwenberg, Willem P.T.M. Mali, Erik Buskens, Frederik J.A. Beek, Branko Braam, Frans T.M. Huysmans, Leo J. Schultze Kool, Matthieu J.C.M. Rutten, Cornelius J. Doorenbos, Johannes C.N.M. Aarts, Ton J. Rabelink, Pierre-François Plouin, Alain Raynaud, Gert A. van Montfrans, Jim A. Reekers, Anton H. van den Meiracker, Peter M.T. Pattynama, Peter J.G. van de Ven, Dammis Vroegindeweij, Abraham A. Kroon, Michiel W. de Haan, Cornelis T. Postma, and Jaap J. Beutler Stent Placement in Patients With Atherosclerotic Renal Artery Stenosis and Impaired Renal Function: A Randomized Trial Ann Intern Med 2009; 150: 840-848
Conflict of Interest:
None declared
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In defense of renal artery stenting
Submit responseWhen the results of a randomized trial disagree with clinical experience and prior publications, its validity merits critical examination. In the STAR trial, assessing the efficacy of renal artery stenting, Bax et al reported no benefit, and recommended avoiding stenting in patients with renal artery stenosis (1). This could lead to denial of the procedure, by physicians and by managed care organizations, to patients who truly need the procedure.
Having personally observed many patients who, following renal artery angioplasty +/- stenting, experienced rapid amelioration of problems such as refractory hypertension, congestive heart failure and renal insufficiency, it is inconceivable to us, and to many others, that stenting is of no benefit. Unfortunately, there is also no doubt that it is overused, often employed in cases unlikely to benefit.
Why did this randomized trial show no benefit? First, among the subjects randomized to the stenting group and included in the intention-to -treat analysis, 40 of 64 (62.5%) were unlikely, a priori, to benefit because: (1) 12 had stenoses of <50% and were not even stented, (2) 22 had 50-70% stenosis, which usually is not hemodynamically significant, (3) even some stenoses of 70-90% are not hemodynamically significant (2), and (4) in 6 others, stenting was not performed for various reasons. Unfortunately, hemodynamic significance of the stenoses was not assessed. Second, all subjects were required to have a treated blood pressure <140/90 on entry, excluding patients with resistant hypertension, who are more likely to have true renovascular hypertension and ischemic nephropathy. Third, there is a major unmentioned bias: patients strongly believed to have true renovascular hypertension, who would be the most likely to benefit, are generally referred for stenting rather than being entered into a randomized study which could deny them the procedure. There is no easy answer for this problem, and in such situations, a randomized trial might be the wrong type of study.
Extrapolation of the results of this study to patients with unequivocal renovascular hypertension and ischemic nephropathy is unwarranted, and wrong. Clearly there are cases where the wisdom of stenting is unclear, but this study did not address that important question.
The overuse of renal artery angioplasty and stenting clearly merits condemnation. However, the benefit of the procedure in appropriate patients should not be withheld based on this trial. Instead, clarification of the indications for stenting is needed.
References:
1. Bax L, Woittiez A-JJ, Kouwenberg HJ, et al. Stent placement in patients with atherosclerotic renal artery stenosis and impaired renal function. A randomized trial. Ann Intern Med 2009;150:840-848.
2. Simon G. What is critical renal artery stenosis? Implications for treatment. Am J Hypertens 2000; 13: 1189-1193.
Conflict of Interest:
None declared
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A Study With Shortcomings
Submit responseWe read with interest the randomized trial on renal artery stenting by Bax et al (1). We agree that randomized trials are ultimately the way to prove or disprove the usefulness of renal artery angioplasty and stenting in the treatment of renal artery stenosis. However, we are concerned that, because of several issues, this particular paper will do neither.
First, the abstract is inconsistent in and of itself. The results section which should essentially reflect a non significant reduction in the primary endpoint and no significant difference in the secondary endpoint is not adequately summarized in the abstract and the conclusions section of the abstract does not reflect the fact that, despite the unusually high number and severity of procedure-related complications in the stenting group, the mortality was not different between the two groups. Since the abstract is the most widely disseminated part of any paper, these shortcomings are very unfortunate.
Second, as acknowledged by the authors and the editor’s notes, the study was underpowered because the rate of events in the control group was lower than anticipated. This impairs the study’s ability to detect a real difference between renal artery stenting and medical therapy (2), although it is noteworthy that the point estimate of the hazard ratio for the primary endpoint (0.73) favors stenting. Moreover, the evidence for renal revascularization therapy to halt progression of renal insufficiency is not solid and, as such, choosing an increase in creatinine as the primary endpoint was not a good choice.
Third, there was no physiologic assessment of the significance of the renal artery stenosis, a widespread problem of current randomized trials of renal stenting (3). Indeed, patients with renal stenosis severity of as low as 50% were included, when the evidence suggests that stenoses below 70% are not hemodynamically significant (4). This and the fact that inclusion criteria contained no stringent requirement of therapy with at least three antihypertenisves as required by the ACC/AHA guidelines (5) may also have biased the study results toward showing no benefit with renal stenting.
In summary, every piece of evidence that contributes to our better understanding of the optimal therapy of renal artery stenosis is welcome, but only if the evidence is clear. Unfortunately, the study by Bax et al, will raise more questions than it will provide answers and will make it harder for other investigators to obtain support for future trials addressing the issue.
References
1. Bax L, Woittiez AJ, Kouwenberg HJ, Mali WP, Buskens E, Beek FJ, Braam B, Huysmans FT, Schultze Kool LJ, Rutten MJ, Doorenbos CJ, Aarts JC, Rabelink TJ, Plouin PF, Raynaud A, van Montfrans GA, Reekers JA, van den Meiracker AH, Pattynama PM, van de Ven PJ, Vroegindeweij D, Kroon AA, de Haan MW, Postma CT, Beutler JJ. Stent Placement in Patients With Atherosclerotic Renal Artery Stenosis and Impaired Renal Function: A Randomized Trial. Ann Intern Med. 2009; 150: 840-8. PMID: 19414832
2. Szczech LA, Coladonato JA, Owen WF Jr. Key concepts in biostatistics: using statistics to answer the question "is there a difference?". Semin Dial. 2002;15:347-51. PMID: 12100461
3. Schwarzwälder U, Zeller T. Critical review of indications for renal artery stenting: Do randomized trials give the answer? Catheter Cardiovasc Interv. 2009 Apr 7. [Epub ahead of print] PMID: 19434748
4. Schönberg SO, Bock M, Kallinowski F. Just a correlation of hemodynamic impact and morphologic degree of renal artery stenosis in a canine model. J Am Soc Nephrol 2000; 11: 2190-2198. PMID: 11095642
5. Hirsch AT, Haskal ZJ, Hertzer NR, et al. ACC/AHA 2005 guidelines for the management of patients with peripheral arterial disease (lower extremity, renal, mesenteric, and abdominal aortic): executive summary of a collaborative report from the American Association for Vascular Surgery/Society for Vascular Surgery, Society for Cardiovascular Angiography and Intervention, Society for Vascular Medicine and Biology, Society of Interventional Radiology, and the ACC/AHA Task Force on Practice Guidelines for the Management of Patients with Peripheral Arterial Disease) endorsed by the American Association of Cardiovascular and Pulmonary Rehabilitation; National Heart, Lung, and Blood Institute; Society for Vascular Nursing; TransAtlantic Inter-Society Consensus; and Vascular Disease Foundation. J Am Coll Cardiol 2006;47:1239-1312. PMID: 16545667
Conflict of Interest:
None declared
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Benefit from renal stenting requires expert operators with expert skills
Submit responseSTAR TRIAL REPLY
The results of the STAR Trial reported by Bax et al (1) emphasize the importance of operator skill as well as volume when performing endovascular interventions is any benefit is to be gained. In this study over a period of more than five years over 20 authors in 10 participating centers managed to recruit 46 patients for stenting, this is an average of less than one stented patient per year per center. It may therefore be unsurprising that the procedural morbidity and mortality was so high. Any individual operator with a 2/46 procedural mortality from stenting (which is a mortality rate of 4.3% and not 3% as reported in the discussion), and a similar incidence of false aneurysm and over 10% incidence of renal artery injury should really examine their technique and consider retraining, no matter their previous length of experience.
For the record my personal experience of 81 renal stent procedures, mostly for ostial stenosis, performed over a similar period (Sept 2000- January 2006) there were no procedure related deaths, no femoral false aneurysms and only one significant renal artery injury. It is interesting to note that in the same study we found that in patients where the Palmaz Corinthian stent was used the mean creatinine rose on follow-up after stenting, but fell after stenting with the rapid exchange Express system (2).
References
1. Liesbeth Bax, Arend-Jan J. Woittiez, Hans J. Kouwenberg, Willem P.T.M. Mali, Erik Buskens, Frederik J.A. Beek, Branko Braam, Frans T.M. Huysmans, Leo J. Schultze Kool, Matthieu J.C.M. Rutten, Cornelius J. Doorenbos, Johannes C.N.M. Aarts, Ton J. Rabelink, Pierre-François Plouin, Alain Raynaud, Gert A. van Montfrans, Jim A. Reekers, Anton H. van den Meiracker, Peter M.T. Pattynama, Peter J.G. van de Ven, Dammis Vroegindeweij, Abraham A. Kroon, Michiel W. de Haan, Cornelis T. Postma, and Jaap J. Beutler Stent Placement in Patients With Atherosclerotic Renal Artery Stenosis and Impaired Renal Function: A Randomized Trial Ann Intern Med 2009; 150: 840-848
2. Nallamshetty L, Chong CC, Patel H, Greco B, Hartnell GG. Technical Factors in Renal Artery Stenting: Effects on Contrast Volume, Fluoroscopy Time, and Post Procedure Creatinine. 92nd Scientific Assembly and Annual Meeting RSNA, Chicago, November 29th 2006
Conflict of Interest:
None declared
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Stenting of renal arteries
Submit responseTO THE EDITOR: The findings of Bax and coworkers (1) did not surprise me. Previously, I have reported that reduction of main renal artery diameter (stenosis) must be at least 80% – probably, 85% or greater– to be hemodynamically significant, that is, to trigger renin release and to result in impairment of renal function (2). It appears that the majority of patients in the study of Bax et al. had atherosclerotic renal artery stenosis (ARAS) less than 85% (Table 1); impairment of their renal function was probably due to causes other than ARAS. Stenting of main renal arteries with less than 85% stenosis is not expected to impact patients’ BP or renal function.
For fuller understanding of the findings of Bax and coworkers, it would be helpful to know what the comparative outcome, with or without stenting, of patients with greater than 85% stenosis was. Future studies of this type of intervention should enroll patients with at least 85% ARAS.
References
1. Bax L, Woittiez A-JJ, Kouwenberg HJ, Mali WPTM, Buskens E, Beek FJA, Braam B, Huysmans FTM, et al. Stent placement in patients with atherosclerotic renal artery stenosis and impaired renal function. A randomized trial. Ann Int Med. 2009; 150: 840-848.
2. Simon G. What is critical renal artery stenosis? Implications for treatment. Am J Hypertens 2000; 13: 1189-1193.
Conflict of Interest:
None declared
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To stent or not to stent Renal Artery Stenosis?
Submit responseThe results of this study by Bax et al are in concordance with some of the earlier studies which failed to show a benefit of stenting atherosclerotic renal artery stenosis (ARAS)(1,2). However, one of the limitations in the previous studies and this study by Bax et al is that they failed to identify patients with a ARAS > 50% with a Renal Resistive Index (RRI) of < 80%. This subset of patients, have been hypothesized to benefit maximally from renal artery stenting (3,4). One needs to be aware that no single diagnostic test reflects anatomical and functional stenosis. A combination of MRA or CT angio, Captopril renal scan, Ultrasound of the kidney with renal doppler to identify patients with a > 50% stenosis and a RRI of < 80% is important (5). In a study done by Tanemoto et al has shown the benefit of measuring the peak gradient across the stenosis prior to intervention (4). Intervention in this selected group of patients with a hemodynamically significant ARAS may show a benefit when compared to patients who receive maximal medical treatment. Results of the “Renal Athersosclerotic reVascularization Evaluation” (RAVE) and the “Comparison of Best Medical Treatment Versus Best Medical Treatment Plus Renal Artery Stenting” (RADAR) studies would help address some of these limitations.
References
1.Mistry, S., et al., Angioplasty and STent for Renal Artery Lesions (ASTRAL trial): rationale, methods and results so far. J Hum Hypertens, 2007. 21(7): p. 511-5.
2.Nordmann, A.J., et al., Balloon angioplasty or medical therapy for hypertensive patients with atherosclerotic renal artery stenosis? A meta- analysis of randomized controlled trials. Am J Med, 2003. 114(1): p. 44- 50.
3.Schwarzwalder, U. and T. Zeller, Critical review of indications for renal artery stenting: Do randomized trials give the answer? Catheter Cardiovasc Interv, 2009.
4.Tanemoto, M., et al., Hemodynamic index of atheromatous renal artery stenosis for angioplasty. Clin J Am Soc Nephrol, 2009. 4(3): p. 651 -5.
5.Radermacher, J., et al., Use of Doppler ultrasonography to predict the outcome of therapy for renal-artery stenosis. N Engl J Med, 2001. 344(6): p. 410-7.
Conflict of Interest:
None declared