Ethan Balk, MD, MPH; Gowri Raman, MD; Mei Chung, MPH; Stanley Ip, MD; Athina Tatsioni, MD; Alvaro Alonso, MD; Priscilla Chew, MPH; Scott J. Gilbert, MD; Joseph Lau, MD
Note: The full report is Available at http://www.effectivehealthcare.ahrq.gov/reports/final.cfm.
Disclaimer: The authors of this report are responsible for its content. Statements in the report should not be construed as endorsement by the Agency for Healthcare Research and Quality or the U.S. Department of Health and Human Services.
Grant Support: This project was funded under contract no. 290-02-0023 from the Agency for Healthcare Research and Quality, U.S. Department of Health and Human Services.
Potential Financial Conflicts of Interest: None disclosed.
Requests for Single Reprints: Ethan Balk, MD, MPH, Tufts-New England Medical Center, Box 63, 750 Washington Street, Boston, MA 02111; e-mail, firstname.lastname@example.org.
Current Author Addresses: Drs. Balk, Raman, Chung, Ip, Tatsioni, and Lau and Ms. Chew: Tufts-New England Medical Center, Box 63, 750 Washington Street, Boston, MA 02111.
Dr. Alonso: Tufts-New England Medical Center, Box 235, 750 Washington Street, Boston, MA 02111.
Dr. Gilbert: Tufts-New England Medical Center, Box 391, 750 Washington Street, Boston, MA 02111.
Balk E., Raman G., Chung M., Ip S., Tatsioni A., Alonso A., Chew P., Gilbert S., Lau J.; Effectiveness of Management Strategies for Renal Artery Stenosis: A Systematic Review. Ann Intern Med. 2006;145:901-912. doi: 10.7326/0003-4819-145-12-200612190-00143
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Published: Ann Intern Med. 2006;145(12):901-912.
Atherosclerotic renal artery stenosis is increasingly common in an aging population. Therapeutic options include medical treatment only or revascularization procedures.
To compare the effects of medical treatment and revascularization on clinically important outcomes in adults with atherosclerotic renal artery stenosis.
The MEDLINE database (inception to 6 September 2005) and selected reference lists were searched for English-language articles.
The authors selected prospective studies of renal artery revascularization or medical treatment of patients with atherosclerotic renal artery stenosis that reported mortality rates, kidney function, blood pressure, cardiovascular events, or adverse events at 6 months or later after study entry.
A standardized protocol with predefined criteria was used to extract details on study design, interventions, outcomes, study quality, and applicability. The overall body of evidence was then graded as robust, acceptable, or weak.
No study directly compared aggressive medical therapy with angioplasty and stent placement. Two randomized trials compared angioplasty without stent and medical treatments. Eight other comparative studies and 46 cohort studies met criteria for analysis. Studies generally had poor methodologic quality and limited applicability to current practice. Overall, there was no robust evidence. Weak evidence suggested no large differences in mortality rates or cardiovascular events between medical and revascularization treatments. Acceptable evidence suggested similar kidney-related outcomes but better blood pressure outcomes with angioplasty, particularly in patients with bilateral disease. Improvements in kidney function and cure of hypertension were reported among some patients only in cohort studies of angioplasty. Available evidence did not adequately assess adverse events or baseline characteristics that could predict which intervention would result in better outcomes.
The evidence from direct comparisons of interventions is sparse and inadequate to draw robust conclusions.
Available evidence does not clearly support one treatment approach over another for atherosclerotic renal artery stenosis.
Is medical therapy as effective as revascularization for atherosclerotic renal artery stenosis?
This systematic review found no trials that compared aggressive medical therapy and angioplasty with stent in adults with atherosclerotic renal artery stenosis. Some evidence suggested similar kidney outcomes but better blood pressure outcomes with angioplasty, particularly in patients with bilateral renal disease. Weak evidence suggested no large differences in mortality or cardiovascular events between medical and revascularization treatments. No evidence directly compared adverse event rates between treatments.
Available evidence comparing benefits and harms of modern treatments for atherosclerotic renal artery stenosis is sparse and inconclusive.
Renal artery stenosis is defined as narrowing of the renal artery lumen. Atherosclerosis, which usually involves the ostium and proximal third of the main renal artery and the perirenal aorta, accounts for 90% of cases of renal artery stenosis (1). Atherosclerotic renal artery stenosis is increasingly common in aging populations, particularly elderly people with diabetes, hyperlipidemia, aortoiliac occlusive disease, coronary artery disease, or hypertension. Atherosclerotic renal artery stenosis is a progressive disease that may occur alone or in combination with hypertension and ischemic kidney disease (1). Although the prevalence of atherosclerotic renal artery stenosis is poorly defined, it may vary from 30% among patients with coronary artery disease identified by angiography (2) to 50% among elderly people or those with diffuse atherosclerotic vascular diseases (3). In the United States, 12% to 14% of patients in whom dialysis is initiated have been found to have atherosclerotic renal artery stenosis (4).
Most authorities consider blood pressure control, preservation or salvage of kidney function, and prevention of flash pulmonary edema to be important treatment goals for patients with atherosclerotic renal stenosis. Treatment options include medication alone or revascularization of the stenosed artery or arteries. Combination therapy with multiple antihypertensive agents, often including angiotensin-converting enzyme inhibitors or angiotensin-receptor blockers, calcium-channel blockers, and β-blockers, is frequently prescribed. Some clinicians also use statins to decrease low-density lipoprotein cholesterol levels and antiplatelet agents, such as aspirin or clopidogrel, to reduce the risk for thrombosis. The current standard for revascularization in most patients is percutaneous transluminal angioplasty with stent placement across the stenosis. Angioplasty without stent placement is less commonly used. Revascularization by surgical reconstruction is generally done only in patients with complicated renal artery anatomy or in those who require pararenal aortic reconstructions for aortic aneurysms or severe aortoiliac occlusive disease.
The American College of Cardiology and the American Heart Association recently published guidelines for management of patients with peripheral arterial disease, including renal artery stenosis (5-6). Although these guidelines provide recommendations about which patients should be considered for revascularization, considerable uncertainty remains about which intervention provides the best clinical outcomes. Among patients treated with medical therapy alone, experts are concerned about the risk for deterioration of kidney function and worsening cardiovascular morbidity and mortality. Revascularization procedures may provide immediate improvement in kidney function and blood pressure, but they are invasive interventions that could result in substantial morbidity or death, and because of the risk for restenosis the durability of their benefits is questioned.
Although evidence regarding the optimal management of atherosclerotic renal artery stenosis appears uncertain, a Medicare claims analysis found that the rate of percutaneous renal artery revascularization has rapidly increased between 1996 and 2000, with the number of interventions increasing from 7660 to 18 520 (7). To determine which patients, if any, with atherosclerotic renal artery stenosis would most benefit from angioplasty with stent placement, as opposed to continued aggressive medical treatment, the National Institutes of Health has sponsored the large, multicenter Cardiovascular Outcomes in Renal Atherosclerotic Lesions (CORAL) trial. Participants are currently being enrolled in the trial, and results should be reported in 2010. Meanwhile, the Agency for Healthcare Research and Quality, under Section 1013 of the Medicare Modernization Act, commissioned a review asking key questions related to the effectiveness of aggressive medical therapy compared with renal artery angioplasty with stent placement. However, because no published evidence directly compared angioplasty with stent placement and aggressive medical treatment with currently available drugs, the review covered direct comparisons of revascularization, including angioplasty with or without stent placement and surgery, and various medical regimens and indirect comparisons of angioplasty (with stent placement) and surgical interventions, various medical therapies, and natural history (8).
To identify articles relevant to several key questions, we searched the MEDLINE database from inception to 6 September 2005 for studies involving adults with atherosclerotic renal artery stenosis. The Figure shows the search and selection process. The full technical report (Available at http://www.effectivehealthcare.ahrq.gov/reports/final.cfm) provides a more detailed description of the study methods. We also reviewed reference lists of related systematic reviews, selected narrative reviews, and primary articles, and we invited domain experts to provide additional citations. We combined search terms for renal artery stenosis, renal hypertension, and renal vascular disease, and we limited the search to English-language articles of studies in adult humans that had relevant research designs. We included peer-reviewed primary studies of adult patients treated for atherosclerotic renal artery stenosis and excluded studies that evaluated patients with renal artery stenosis in the setting of a transplanted kidney, renal artery aneurysm requiring repair, aortic disease requiring invasive intervention, or concurrent cancer or patients who had had previous surgical or angioplasty interventions for renal artery stenosis. We included only studies that reported outcomes of interest (mortality rate, kidney function, blood pressure, and cardiovascular events) at 6 months or more after the initial intervention. We excluded studies in which more than 20% of patients had renal artery stenosis due to other causes. We categorized studies according to whether they evaluated medical treatment, angioplasty, or surgical revascularization or were natural history studies, and by whether they directly compared interventions.
*Prospective study; enrolled 10 or more patients; study duration at least 6 months. †Prospective study; angioplasty included stent placement; enrolled 30 or more patients; study duration at least 6 months; patients recruited in 1993 or later; patients did not have previous angioplasty. ‡One study has data both for direct comparison of medical treatment to angioplasty and for natural history. §Any study design; enrolled 10 or more patients; study duration at least 6 months. Studies with surgical intervention must have recruited patients in 1993 or later. ∥Any study design; enrolled 10 or more patients; study duration at least 6 months; patients recruited in 1993 or later. ¶Any study design; enrolled 100 or more patients (10 or more if the study was prospective); study duration at least 6 months; patients recruited in 1993 or later.
We used different eligibility criteria for studies of different interventions, based on the varying number of studies available for each intervention and the relevance of the intervention to current practice. We included all direct comparisons of medical treatment with angioplasty and all uncontrolled (cohort) studies of medical treatment that had at least 10 patients in each group, regardless of study design. For angioplasty, surgical, or natural history studies, we included only those in which at least some patients were recruited in 1993 or later, after the publication of the Fifth Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure. These guidelines marked a substantial change from previous guidelines in treatment recommendations for hypertension, including more aggressive blood pressure targets (9). In addition, at this time point, angiotensin-converting enzyme inhibitors began to be used more routinely in the treatment of patients with severe hypertension. We included only angioplasty studies that used stent placement, were prospective, and had at least 30 patients and retrospective surgery studies that included at least 100 patients. Any prospective surgery study that otherwise met criteria was eligible.
Data from each study were extracted by one of the authors and confirmed by another. The extracted data included information about patient samples, interventions, outcomes, adverse events, study design, quality, and applicability. We used predefined criteria to grade study quality as good, fair, or poor; study applicability as high, moderate, or low; and the strength of the overall body of evidence as robust, acceptable, or weak (Appendix Table). Each included study was graded by at least 2 of the authors.
Because the study designs, participants, interventions, and reported outcome measures varied markedly, we focused on describing the studies, their results, their applicability, and their limitations and on qualitative synthesis rather than meta-analysis.
The Agency for Healthcare Research and Quality formulated the initial study questions but did not participate in the literature search; determination of study eligibility criteria; data analysis or interpretation; or preparation, review, or approval of the manuscript for publication.
Available evidence was neither adequate nor sufficiently applicable to current practice to clearly support one treatment approach over another for the general population with atherosclerotic renal artery stenosis. Only 2 randomized trials directly compared angioplasty and medical treatment alone (Table 1). Weak evidence based on few study participants suggested no large differences in mortality rates or cardiovascular events between patients treated medically only and those receiving angioplasty (Table 2). Randomized, controlled trials; other comparative studies; and cohort studies reported similar overall changes in kidney function after angioplasty as with medical therapy alone. However, improved kidney function over time after the intervention was reported among some patients only in cohort studies of angioplasty. Acceptable evidence showed that combination antihypertensive treatment decreased blood pressure substantively but that angioplasty may result in better blood pressure control, particularly in people with bilateral disease. Cure of hypertension (achievement of blood pressure control without medication) was reported only among several patients treated with angioplasty. Available evidence did not adequately assess net harm due to adverse events and complications of medical treatment or angioplasty, but important complications after revascularization occur in a small percentage of patients and all drugs have associated adverse events.
Almost two thirds of the studies that we reviewed were of poor methodologic quality; none was deemed to be of good quality. More than half of the studies had limited applicability to patients commonly seen in practice or to modern management strategies. All studies implicitly or explicitly included only patients with generally stable blood pressure, kidney function, and cardiovascular status. Thus, they were not applicable to patients with acute decompensation due to progressive atherosclerotic renal artery stenosis. No study directly compared angioplasty with stent placement and “aggressive” medical treatment with currently available antihypertensive, antiplatelet, and lipid-lowering agents.
Overall, we reviewed 55 studies (Table 1). Nine studies (in 11 publications) directly compared medical treatment with revascularization (Table 3) ((10-20)). Of these, 2 randomized trials compared angioplasty without stent placement with medical treatment ((10-11)). A third randomized trial compared angioplasty without stent placement at the start of the trial with angioplasty delayed by 3 months in half of the remaining patients and medical treatment alone in the other patients ((12-14)). The remaining 7 comparative studies (including 1 of a nonrandomized subgroup from a randomized trial [(10)]) compared multiple types of revascularization with a variety of medical treatment for a wide range of durations (6 months to 7 years).
Twenty-five prospective cohort studies that each included at least 30 patients who received angioplasty primarily after 1993 reported “long-term” outcomes 6 months or more after angioplasty ((21-45)). Four cohort studies evaluated angiotensin-converting enzyme inhibitors or “triple therapy” (treatment with 3 classes of antihypertensive agents) ((46-49)). An additional 8 natural history studies evaluated cohorts of patients who usually received some medical treatment that was not clearly described ((18), (50-56)). Long-term outcomes of interest were reported for 4 surgical cohorts that each included at least 100 patients who received angioplasty mostly after 1993 ((57-60)). Thirty-seven studies reported on adverse events ((10-14), (16-17), (21-22), (24-25), (27), (29-36), (39-46), (49), (57-65)).
One small randomized, controlled trial of angioplasty versus medical treatment (55 patients) ((10)), 4 other comparative studies ((10), (17-19)), and 30 cohort studies of various interventions reported on mortality ((18), (22-30), (32-36), (39), (41-44), (47), (49), (51-52), (55-60)). About half of the studies reported mortality data at 2 years or less. Seven studies (primarily surgical studies) reported mortality data for patients followed for at least 5 years ((17), (19), (51), (57-60)). Studies were generally too small to detect anything but large differences in mortality rates, and no large differences in mortality rates were found. Mortality rates greater than 40% within 6 years occurred mostly in studies of patients with high-grade stenosis (>75%) or bilateral disease.
The 2 randomized, controlled trials of angioplasty versus medical treatment ((10-11)) and the 7 other studies that directly compared revascularization and medical treatment ((10), (12-18), (20)) mostly found no clinically or statistically significant differences in kidney-related outcomes. Among 22 cohort studies of angioplasty (18 with stent placement, 4 with or without stent placement), 2 reported statistically significant improvements in kidney function ((25), (37)), 2 reported statistically significant deterioration ((34), (39)), and 18 reported no statistically significant changes ((21-24), (26-28), (30), (32-33), (35-36), (38), (40-42), (44-45)). Within these studies, 8% to 51% of patients were categorized as having improved kidney function and up to 31% had worsened kidney function. Mean changes in kidney function were generally small; the largest improvement found was a mean increase in glomerular filtration rate from baseline (0.9 mL/s [54 mL/min]) of 0.13 mL/s (8 mL/min) over 3 to 23 months ((37)). Among 3 surgical cohort studies, kidney function improved in 43% of patients in 1 study and worsened in 10% to 28% across the studies ((58-60)). In comparison, 2 cohort studies of medical treatment ((47), (49)) and 7 cohort studies of natural history ((18), (50-55)) reported progressive decreases in kidney function.
The 2 randomized trials of angioplasty versus medical treatment ((10-11)), the 8 other comparative studies ((10), (12-20)), all 25 angioplasty cohort studies ((21-45)), all 4 medical cohort studies ((46-49)), 3 natural history cohort studies ((18), (53), (56)), and 2 surgical cohort studies ((58-59)) reported blood pressure outcomes. Both trials of angioplasty versus medical treatment and most of the other comparative studies found some evidence of greater improvement in blood pressure after angioplasty than medical treatment. Plouin and colleagues ((11)) found that both systolic and diastolic blood pressures were reduced by 6 mm Hg more after angioplasty than medical treatment alone, but only the change in diastolic blood pressure was statistically significant. In addition, after angioplasty, patients required almost half as many antihypertensive drugs. Webster and associates ((10)) found that among patients with bilateral disease, a substantially greater, statistically significant reduction in blood pressure occurred after angioplasty than with medical treatment alone (net decrease, 26/10 mm Hg); however, no statistically significant difference was found in blood pressure among patients with unilateral disease. Among the cohort studies, medical treatment or natural history (mostly medical treatment alone) resulted in decreases of 20 to 50 mm Hg in systolic blood pressure and 8 to 42 mm Hg in diastolic blood pressure, whereas in studies of angioplasty with stent placement, patients had decreases of 6 to 32 mm Hg in systolic blood pressure and 0 to 17 mm Hg in diastolic blood pressure after revascularization. Almost all studies of angioplasty with stent placement reported that some patients (up to 18%) were cured of hypertension.
In a trial of 55 patients randomly assigned to angioplasty without stent or antihypertensive treatment alone, Webster and associates ((10)) found no differences in event rates for congestive heart failure, stroke, or myocardial infarction across 54 months of follow-up. Similarly, in a trial of 52 patients receiving surgical revascularization or medical treatment alone, near-identical percentages of participants had a stop point event that included cardiovascular events ((20)). The reporting of cardiovascular outcomes in cohort studies ((47), (56), (58)) was inadequate to allow cross-study comparisons. No study of medical interventions reported cardiovascular outcomes.
Adverse events were reported in 37 studies, including the 2 randomized trials of angioplasty and medical treatment and 1 retrospective comparative trial ((10-14), (16-17), (21-22), (24-25), (27), (29-36), (39-46), (49), (57-65)). Rates of adverse events between interventions were not directly compared. Adverse events reported in angioplasty studies included death by 30 days in up to 3% of patients, transient deterioration of kidney function in 1% to 13%, renal artery or parenchymal injury in up to 5%, and periprocedural cardiovascular events in up to 3%. Other adverse events reported were hemorrhage, hematomas, and renal artery occlusion. Seventeen studies of angioplasty with stent placement showed restenosis rates that ranged from 10% to 21% during follow-up of 3 to 40 months ((22-23), (26-31), (33-35), (37-41), (43)). Only Ramos and colleagues ((37)) noted a statistically significantly higher rate of restenosis among patients who had undergone stent placement for ostial lesions compared with those with nonostial lesions (27% vs. 8%). Adverse events related to blood pressure medications (angiotensin-converting enzyme inhibitors, β-blockers, and hydralazine) included orthostatic hypotension, central nervous system symptoms, digestive symptoms, the Raynaud phenomenon, and various other symptoms.
The studies of diagnostic tests were inadequate to determine whether any such tests may predict long-term outcomes or guide best treatment approaches (Table 4). Weak evidence suggests that patients with bilateral disease may preferentially benefit from angioplasty over medical treatment alone. A variety of other clinical factors may be predictive of poorer outcomes with angioplasty or medical treatment alone; however, evidence is insufficient to suggest whether other factors can assist in decisions about preferred treatment.
Webster and associates (10) found different relative effects of angioplasty and medical treatment according to whether patients had unilateral or bilateral disease. Patients with bilateral stenosis had much larger, statistically significant decreases in blood pressure after angioplasty than with medical treatment, in contrast to patients with unilateral stenosis, who had similar changes in blood pressure regardless of the type of intervention (Table 3). The Dutch Renal Artery Stenosis Intervention Cooperative Study, which compared early revascularization with delayed or no revascularization, found a similar difference in diastolic blood pressure reduction but not in creatinine clearance (12-14). A single trial comparing surgical revascularization with medical treatment reported that among patients with an elevated serum creatinine concentration (177 to 354 µmol/L [2 to 4 mg/dL]), those who had surgical procedures were less likely to die or have uncontrollable hypertension than were those treated medically (P = 0.01; no other data reported) (20). This was in contrast to their overall finding of no difference in outcomes between interventions. No other associations were reported between baseline factors and relative difference in outcomes based on treatment choice.
Among the reviewed studies, 4 diagnostic tests have been evaluated to determine their value in predicting outcomes in patients with atherosclerotic renal artery stenosis; however, each test was evaluated in only 1 study. The Dutch Renal Artery Stenosis Intervention Cooperative Study found that neither the captopril test nor renography (scintigraphy) predicted kidney function, blood pressure, or dose of antihypertensive drugs after angioplasty or medical treatment (12-14). Two cohort studies disagreed on the predictive value of baseline resistance index greater than 80%. In one study, patients with an elevated resistance index were most likely to benefit in terms of kidney function and blood pressure control after angioplasty with stent placement (44), whereas in another study, patients with an elevated resistance index were more likely to have worsening kidney function and less likely to have improved blood pressure or reduced use of antihypertensive medication after surgery or angioplasty with or without stenting (36). One natural history study reported that nonspiral flow on magnetic resonance angiography predicted statistically significantly worse kidney function outcomes (54).
Acceptable evidence, primarily from cohort studies, showed that poorer kidney function ((17), (19), (26), (30), (34-38), (41), (44), (58-60)) or concomitant cardiovascular disease ((17), (19), (28), (34-35), (44), (58)) predicted higher mortality rates and poorer clinical outcomes among patients who had angioplasty (with or without stent placement). Evidence was weak owing to sparseness of data or disagreement among studies on other baseline factors and outcomes (Table 4), including the presence of bilateral disease among patients having revascularization ((25), (27), (34), (37), (39-40), (45)) or among those enrolled in natural history studies (55-56); the degree of kidney function ((20), (51)) and cardiovascular disease ((17), (19), (52)) in patients enrolled in medical treatment studies; and percentage of artery stenosis ((17), (19), (28), (34-35), (44), (52), (58)), age, and sex ((10), (17), (19), (34-35), (52)), regardless of intervention or type of study.
No study that met eligibility criteria reported analyses of whether periprocedural interventions, such as different drugs or different approaches, affected complications or long-term outcomes in patients undergoing revascularization. Two prospective cohort studies reported no difference in blood pressure and kidney-related outcomes between patients who had stents placed and those who did not (Table 4) ((21), (42)).
Overall, the evidence is not sufficiently robust to determine the comparative effectiveness of angioplasty (with or without stenting) and medical treatment alone. Only 2 randomized trials with long-term outcomes and a third randomized trial that allowed substantial crossover of treatment after 3 months directly compared angioplasty and medical treatment. However, no randomized trial evaluated angioplasty with stent placement, the revascularization technique that is currently most commonly used. Furthermore, the randomized trials did not evaluate enough patients or did not follow patients for a sufficient duration to allow definitive conclusions to be made about clinical outcomes, such as mortality and cardiovascular or kidney failure events.
Some acceptable evidence from comparison of medical treatment and angioplasty suggested no difference in long-term kidney function but possibly better blood pressure control after angioplasty, an effect that may be limited to patients with bilateral atherosclerotic renal artery stenosis. The evidence regarding other outcomes is weak. Because the reviewed studies did not explicitly address patients with rapid clinical deterioration who may need acute intervention, our conclusions do not apply to this important subset of patients.
Although use of angioplasty to improve blood flow to the kidneys holds appeal, the treatment of atherosclerotic renal artery stenosis is probably considerably more complicated. The challenge lies in the substantial overlap between etiologic factors of aortorenal vascular disease and parenchymal kidney disease. The disease conditions that result in atherosclerotic narrowing of the renal arteries, namely diabetes mellitus, dyslipidemia, and elevated blood pressure, are also independently associated with direct kidney injury. Thus, in many cases, revascularizing the renal artery fails to improve hypertension or kidney function, which may be mediated not only by macrovascular atherosclerotic renal artery stenosis but also by underlying microvascular kidney disease. Further evaluation of the role of atherosclerotic renal artery stenosis in hypertension and kidney dysfunction is needed to determine whether intervention should be directed toward improving kidney perfusion through angioplasty with stent placement or more aggressively targeting the underlying factors of parenchymal kidney disease with combination medical therapy.
The ongoing CORAL trial is enrolling patients with atherosclerotic renal artery stenosis with at least 60% narrowing and systolic hypertension for which they are receiving 2 or more antihypertensive medications (66). Patients with advanced chronic kidney disease (serum creatinine concentration ≥ 265 µmol/L [≥3.0 mg/dL]), those with very small kidneys, and certain patients with cardiovascular disease are being excluded. This trial, whose results are expected to be reported in 2010, will probably address many of the deficiencies in current evidence about revascularization versus medical treatment alone. It also might provide useful evidence about the value of different diagnostic tests to determine which intervention would be best for individual patients; whether particular baseline characteristics could suggest which intervention would be best; the value of co-interventions at the time of angioplasty; the value of alternative methods of performing angioplasty with stent placement or of using different types of stents; and the effect of different combinations of antihypertensive medications with other interventions, such as lipid-lowering and antiplatelet drugs. However, if no further trials of sufficient size and duration are done, the findings of the CORAL trial may be applied to patients with less or more severe atherosclerotic renal artery stenosis than those included in the trial. This potentially incorrect extrapolation may result in inappropriate treatment of patients, misallocated resources, and worse patient outcomes. Given the limitations in the quality and applicability to current practice of published studies, it is unclear whether the differences between participants in the published studies and those being enrolled in the CORAL trial will help with extrapolation of the results to patients who were not eligible for the CORAL trial.
Another lesson from our review is that researchers should consider how to improve and standardize definitions of atherosclerotic renal artery stenosis and severity of disease. These considerations should be based on how these definitions and classifications might be associated with clinical outcomes. The CORAL trial and other studies of atherosclerotic renal artery stenosis should use the current suggested methods for estimating kidney function, including preferential use of estimated glomerular filtration rate and stage of chronic kidney disease over serum creatinine concentration alone. The community of clinicians and professional organizations involved in performing renal artery angioplasty should also consider how to improve procedural techniques with the goal of improving clinical outcomes. The methods to achieve these goals may require quality improvement and other types of studies.
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