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1 Department of Radiology, CHUM—Notre-Dame Hospital, 1560 Sherbrooke St.
E., Montreal, QC H2L 4M1, Canada.
2 Department of Radiology, CHUV, University of Lausanne, 46 rue du Bugnan,
Lausanne 1011, Switzerland.
3 Department of Medicine, CHUM—Notre-Dame Hospital, Montreal, QC H2L 4M1,
Canada.
4 Department of Nuclear Medicine, CHUM—Notre-Dame Hospital, Montreal, QC
H2L 4M1, Canada.
5 Department of Biostatistics, Montreal Heart Institute, University of Montreal,
5000 Bélanger St., Montreal, QC H1T 1C8, Canada.
Received November 18, 2002;
accepted after revision April 23, 2003.
Partially supported by Canadian Health Institute of Research grant MA15225.
G. Soulez was supported by a grant from Fonds de la Recherche en Santé
du Qúebec. S. D. Qanadli was supported by a grant from the
Société Française de Radiologie.
Abstract
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SUBJECTS AND METHODS. Seventy-four hypertensive patients underwent clinical examination, Doppler sonography, and renal scintigraphy before and after receiving captopril in preparation for renal revascularization. The patients were evaluated for the status of hypertension 3 months after the procedure. The predictive values of the findings of clinical examination, Doppler sonography, renal scintigraphy, and angiography were assessed.
RESULTS. For prediction of a favorable therapeutic outcome, abnormal results from renal scintigraphy before and after captopril administration had a sensitivity of 58% and specificity of 57%. Findings of Doppler sonography had a sensitivity of 68% and specificity of 50% before captopril administration and a sensitivity of 81% and specificity of 32% after captopril administration. Significant predictors of a cure or reduction of hypertension after revascularization were low unilateral (p = 0.014) and bilateral resistive (p = 0.016) indexes on Doppler sonography before (p = 0.009) and after (p = 0.028) captopril administration. On multivariate analysis, the best predictors were a unilateral resistive index of less than 0.65 (odds ratio [OR] = 3.7) after captopril administration and a kidney longer than 93 mm (OR = 7.8). The two best combined criteria to predict the favorable therapeutic outcome were a bilateral resistive index of less than 0.75 before captopril administration combined with a unilateral resistive index of less than 0.70 after captopril administration (sensitivity, 76%; specificity, 58%) or a bilateral resistive index of less than 0.75 before captopril administration and a kidney measuring longer than 90 mm (sensitivity, 81%; specificity, 50%).
CONCLUSION. Measurements of kidney length and unilateral and bilateral resistive indexes before and after captopril administration were useful in predicting the outcome after renal angioplasty. Renal scintigraphy had no significant predictive value.
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Renal scintigraphy is widely used to detect renal artery stenosis although the sensitivity of the technique varies [11]. An abnormal finding on a captopril (Capoten, Squibb, Montreal, QC, Canada) renogram before renal angioplasty has been reported to be a good predictor of reduced hypertension after the procedure [11, 12], but these results have not been reproduced by other researchers [13, 14]. Doppler sonography is a good screening test for detecting renal artery stenosis [15, 16], and several researchers have found a correlation between the resistive index value and the therapeutic response after revascularization [17–19]. However, inconsistent study results have been reported concerning the strength of this correlation and the value of the resistive index threshold for identifying patients who could benefit from revascularization [17–19]. The goal of our study was to compare the value of Doppler sonography and renal scintigraphy for predicting reduction of hypertension after renal revascularization and to identify imaging findings that can be used to predict the clinical outcome.
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Our study population was composed of 35 patients with no previous imaging studies who had clinically suspected renovascular hypertension, 53 patients with abnormal findings on renal Doppler sonography, 23 with such findings on renal scintigraphy, 11 with such findings on MR angiography, and 17 patients with such findings on catheter angiography. After inclusion in the study, all patients were scheduled for renal Doppler sonography and renal scintigraphy before and after receiving captopril in preparation for renal angioplasty.
Five patients were excluded from the study because their examinations were not completed before angioplasty. Four patients refused to undergo angiography. Thirteen patients were excluded from the study by their referring physician before angiography because no stenosis was shown on noninvasive imaging (MR angiography in nine patients, Doppler sonography and scintigraphy in four patients). Eight patients were excluded because their clinical condition deteriorated to the point that angiography was contraindicated. Twenty-eight patients were excluded because on catheter angiography, their renal artery stenosis was found to be insufficiently severe (< 60% in diameter) to indicate angioplasty. Therefore, 81 patients with complete examinations underwent angiography and renal angioplasty, with or without renal artery stenting. Of these, three patients died of unrelated causes before their clinical follow-up appointments, and four patients were lost to follow-up after renal angioplasty, leaving 74 patients in our study population. The protocol for our study was approved by the ethics and research committees of our institution. All patients included in the study signed an informed consent form.
Our final study population was composed of 39 women (53%) and 35 men (47%) with a mean age ± a standard deviation of 65 ± 9 years. The mean duration of hypertension before angioplasty was performed was 10 ± 11 years. Twenty-five patients (34%) had bilateral renal artery stenosis.
Doppler Sonography
Doppler sonography was performed on an HDI-5000 (ATL, Bothell, WA) or a
Spectra scanner (Diasonics, Milpitas, CA) by one of three investigators. All
the patients except one were asked to discontinue use of
angiotensin-converting enzyme inhibitor 2–5 days before undergoing
Doppler sonography (depending on the half-life of the medication). The kidneys
in all patients were measured on sonography. The proximal renal artery was
first evaluated using direct color-flow Doppler sonography and then by
spectral Doppler sonography at an angle of insonation of less than 60°.
Maximum velocities in the proximal renal arteries and the aorta were measured.
Intrarenal Doppler sonography was then performed. Doppler waveforms were
obtained from segmental arteries at the superior, mid (anterior and
posterior), and inferior portions of the kidney. Intrarenal Doppler sonography
was repeated 1 hr after the patient had received an oral dose of 25 mg of
captopril, a protocol that was based on the recommendations for a radionuclide
study [8]. The operators used
the waveform pattern and acceleration measurement (provided it was
reproducible) to select the most abnormal Doppler tracing for each kidney
before and after captopril administration. Morphologic Doppler spectral
tracings were classified into normal and abnormal categories on the basis of
eight patterns drawn from previously described criteria
[21,
22].
Early systolic acceleration was measured from the steepest portion of the initial systolic rise on the spectral waveform, as has previously been described [22]. Thresholds for abnormal (positive) results were set at 390 cm/sec2 for acceleration and 0.06 sec for acceleration time for baseline (before captopril) examination and 440 cm/sec2 for acceleration and 0.09 sec for acceleration time after captopril examination [21]. Results from an intrarenal Doppler study were considered positive if either the quantitative (acceleration and time of acceleration) or morphologic (pattern recognition) findings were abnormal. Resistive index measurements were performed for each kidney by averaging two or three measurements obtained in the segmental arteries from the upper, middle, and lower poles. In patients undergoing unilateral revascularization, the resistive index measurement of the kidney to be revascularized was considered. In patients undergoing bilateral revascularization, the Doppler (resistive index, acceleration, and acceleration time) measurements obtained in the kidney with the more severe renal artery stenosis were considered, provided that the length of the kidney was at least 80 mm. We also calculated a bilateral resistive index value, which represented an average of resistive index measurements of both kidneys, as previously described by Radermacher et al. [19]. Because one patient underwent Doppler sonography without cessation of angiotensin-converting enzyme inhibitor, we analyzed the results of the sonography before captopril administration in 73 patients and after captopril in 74 patients.
Renal Scintigraphy
The protocol consisted of performing baseline (without captopril) and
captopril-enhanced technetium-99m mercaptoacetyltriglycine renal scintigraphy
using a same-day 25-mg captopril protocol as recommended by the Working Party
Group on Determining the Radionuclide of Choice
[23]. Patients were instructed
to be well hydrated before the examination, and all but three patients were
asked to forgo angiotensin-converting enzyme inhibitors for 2–5 days
before renal scintigraphy (depending on the half-life of the medication). A
large field-of-view gamma camera was positioned beneath the patient to obtain
standard posterior views of the kidneys. Images were stored in a 64 x 64
word-mode pixel matrix. Time–activity curves were generated. Data were
acquired for a minimum of 30 min.
After the baseline study, an oral dose of 25 mg of captopril was administered, and patients were instructed to drink 300–500 mL of water. The captopril-stimulated study was initiated 60 min after captopril administration. Renographic curves were generated from regions of interest assigned to the whole kidney after exclusion of the pelvis and calices and were compared before and after administration of captopril. The renographic curves then were classified as one of five categories according to guidelines of the Society of Nuclear Medicine [24]. The time to maximum activity and the ratio of activity at 20 min to maximum activity were calculated. Relative uptake was measured during the 1–2 min interval after injection of the radiopharmaceutical.
The criterion for positive results on the renogram was a change of 0.15 or greater in the ratio of activity at 20 min to maximum activity, a change in the renographic curve, an increase of the time to maximum activity of at least 2 min or 40%, or a change in relative uptake greater than 10%. The criterion for negative results on the renogram obtained after the captopril administration was a normal upslope with peak activity occurring earlier than 6 min after the captopril was injected. In patients undergoing bilateral revascularization, we analyzed the scintigraphic measurements obtained in the kidney with the most severe renal artery stenosis. Because three patients did not stop taking angiotensin-converting enzyme inhibitors before undergoing scintigraphy, we analyzed the results of scintigraphy in 71 patients.
Renal Angiography and Angioplasty
Catheter angiography and renal revascularization procedures were performed
on two digital subtraction systems (DFP-2000, Toshiba Medical Systems,
Otawara-Shi, Japan; Angiostar, Siemens, Erlengen, Germany). A femoral approach
was used in all but one patient who was imaged using a left axillary approach.
An abdominal aortogram was obtained first; if necessary, this image was
supplemented by a corresponding selective renal angiogram before angioplasty
was performed. All patients had atherosclerotic stenosis that narrowed the
renal artery by at least 60%.
Two radiologists independently reviewed all arteriograms before and after angioplasty performed with or without stenting. Stenosis was measured with high-precision calipers. In patients with bilateral renal artery stenosis, the most severe area of stenosis was measured, provided that the kidney in which the stenosis was located was at least 80 mm long. In cases in which differences in the degree of stenosis measured by investigators exceeded 10%, discrepancies were resolved by consensus. Renal revascularization was performed according to recognized standards of practice. Stenting was performed if a residual transstenotic gradient greater than 10 mm Hg or a residual stenosis greater than 30% was observed after angioplasty. Stenting procedures were performed with balloon-expandable Palmaz stents (Cordis, Miami, FL). The criteria for technical success of the procedure were a transstenotic gradient of less than 10 mm Hg and a residual stenosis that narrowed the renal artery by less than 30%.
Evaluation of Hypertension and Clinical Response
All blood pressure measurements were obtained after a 10-min period of
rest. Three successive measurements were obtained, and the mean of the last
two measurements was recorded for analysis. Baseline blood pressure and
antihypertensive treatment regimen had been noted before angioplasty. After
angioplasty, antihypertensive medication was adjusted by the referring
physician to obtain blood pressure values of less than 140/90 mm Hg, if
possible. Patients were asked to limit sodium intake to 100 mmol per day and
to lose weight if their body mass index was above normal range.
The therapeutic effect of angioplasty was evaluated 3 months after revascularization by measuring the blood pressure and noting the drug regimen. The clinical response after revascularization was defined as follows: a cure was considered to have occurred if a patient's systolic blood pressure was lowered to less than 140 mm Hg and diastolic blood pressure to less than 90 mm Hg without the use of antihypertensive medication, and an improvement was considered to have occured if a patient's systolic or diastolic blood pressure was lowered by more than 15% without an increase in the dosage of antihypertensive medication and if a patient's systolic blood pressure was lowered to less than 160 mm Hg and diastolic blood pressure was lowered to less than 110 mm Hg. For statistical analyses, clinical success of revascularization included patients with cured or improved hypertension. Any results other than those described were considered indications of clinical failure. Clearance of the creatinine was calculated before and 3 months after angioplasty, using the Cockcroft and Gault formula [25].
Data Analysis
We correlated the clinical response observed 3 months after
revascularization with the results of renal scintigraphy and Doppler
sonography. We performed a univariate analysis of clinical data, such as age,
sex, and duration of hypertension in our patients, and imaging findings before
and after captopril administration for such factors as abnormal intrarenal
Doppler sonographic results, unilateral and bilateral resistive index values,
variation of unilateral and bilateral resistive index values, acceleration
measured on intrarenal Doppler sonography, abnormal scintigraphic results,
relative uptake and variation in relative uptake, ratio of activity at 20 min
to maximum activity and variation in this ratio, value of time to maximum
activity and variation in this time, scintigraphic curve category and
variation in the category, degree of angiographic stenosis measured,
unilateral versus bilateral stenosis, and value of baseline transstenotic
gradient. Because the maximum systolic velocity in the proximal arteries was
measured in only 35 of 74 patients, we did not analyze this variable in our
study.
Data were analyzed using statistical software programs (SAS release 6.12, SAS Institute, Cary, NC). Categorical variables were tested by a chisquare test and continuous values, by a Student's t test. Continuous variables with abnormal distributions were tested by a Wilcoxon's rank sum test. A stepwise forward logistic regression analysis, including all variables with a p value of less than 0.20, was conducted. Only variables fitted into the model with a p value of 0.05 or less were retained. Potential confounding clinical variables such as sex, age, and duration of hypertension were systematically introduced into the model.
Sensitivity and specificity for predicting clinical success after revascularization were calculated for each imaging modality. Receiver operating characteristic (ROC) curves were generated to calculate the best threshold values associated with a better therapeutic outcome. Sensitivity, specificity and global accuracy were calculated with different threshold values and different combinations of criteria in order to maximize the prediction of therapeutic success after revascularization.
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The mean systolic and diastolic blood pressure before treatment was 165 ± 22 mm Hg and 83 ± 12 mm Hg, respectively. Significant lowering of the mean systolic (152 ± 17 mm Hg, p = 0.0001) and diastolic (79 ± 10 mm Hg, p = 0.002) blood pressure values was observed 3 months after revascularization. No variation in the clearance of the creatinine before (59 ± 25 mL/min) and after angioplasty (57 ± 24 mL/min) was found. The clinical success rate was 50%, with six (8%) of 74 patients cured and 31 (42%) of 74 improved.
For the whole study population, the mean baseline (before captopril administration) value of the unilateral resistive index (0.65 ± 11) was significantly lower than the bilateral resistive index (0.68 ± 0.08) (p = 0.04). Mean values of the unilateral resistive index (0.61 ± 0.12, p = 0.002) and the bilateral resistive index (0.66 ± 0.08, p = 0.005) after captopril were significantly lower than those before captopril.
For predicting therapeutic improvement after angioplasty, the sensitivity of positive results on intrarenal Doppler sonography before captopril administration was 68% (25/37), and the specificity of negative results on intrarenal Doppler sonography before captopril administration was 50% (18/36). Similarly, the sensitivity and specificity values for Doppler sonography after captopril were 81% (30/37) and 32% (12/37), respectively. Scintigraphy after captopril administration had a sensitivity of 58% (21/36 patients with clinical success) and a specificity of 57% (20/35 patients with clinical failure) for predicting therapeutic improvement after angioplasty.
Table 1 summarizes the results of univariate analysis of clinical and imaging parameters for predicting therapeutic success. We listed only the parameters with a significance level of 0.20 or less, positive results on intrarenal Doppler or scintigraphy, pertinent angiographic criteria (degree of renal artery stenosis and transstenotic gradient), and the clinical parameters that we systematically introduced into the multivariate model.
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No clinical parameter could be used to predict a favorable outcome after angioplasty. Intrarenal Doppler sonographic findings that were considered positive on the basis of pattern recognition and positive findings on scintigraphy after captopril administration were not associated with clinical success after revascularization. We noted a trend toward longer acceleration time measurements on intrarenal Doppler tracings before (0.18 ± 0.31 sec) and after captopril (0.22 ± 0.39 sec) in the successful treatment group as compared with the group in whom treatment failed (0.08 ± 0.06 sec and 0.10 ± 0.07 sec, respectively), but these differences were not significant (p = 0.063 and p = 0.067, respectively). Unilateral and bilateral resistive index measurements before and after captopril administration were significantly lower in patients whose treatment was a clinical success than in patients whose treatment was a clinical failure. The best predictors of clinical success were the unilateral resistive index after captopril (p = 0.009), unilateral resistive index before captopril (p = 0.014), bilateral resistive indexes before captopril (p = 0.016), and bilateral resistive index values after captopril (p = 0.029). No significant scintigraphic or angiographic predictor was found.
We used a multivariate analysis and ROC curve analysis to find the best threshold values. The best parameters for predicting therapeutic success after angioplasty were the presence of a unilateral resistive index after captopril less than 0.65 (p = 0.03, OR = 3.7, 95% confidence interval [CI] = 1.12–12.6), and a kidney longer than 93 mm (p = 0.002, OR = 7.8, CI = 2.1–29.4).
Areas under ROC curves generated for resistive index and kidney size measurements are summarized in Table 2. For resistive index measurements, two threshold values were selected to maximize either the sensitivity or the specificity. The ROC curve fitted for unilateral resistive index measurement after captopril is presented in Figure 1. Areas under the curves for the different resistive index measurements were quite similar. Thresholds below 0.70 or 0.75 should be selected for unilateral and bilateral resistive measurements before captopril administration. Thresholds below 0.65 or 0.70 are better suited for unilateral resistive index measurement after captopril administration. When applying these thresholds as a single criterion to select patients before angioplasty, we found that global accuracy values were quite low (56–66%). Using the length of the kidney as a single criterion presented a good sensitivity of 83% and a fair specificity of 57%.
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Sensitivity, specificity, and global accuracy values of combined criteria are listed in Table 3. The most sensitive combined criteria for predicting a favorable therapeutic outcome after angioplasty were the presence of a bilateral resistive index before captopril administration of less than 0.75 and a kidney longer than 90 mm (sensitivity, 81% and specificity, 50%). The most specific criteria were the presence of a unilateral resistive index after captopril of less than 0.65 and a kidney longer than 90 mm. Finally, the selection of patients presenting a unilateral resistive index after captopril administration of less than 0.70 and a bilateral resistive index before captopril administration of less than 0.75 was fairly sensitive (76%) and specific (58%).
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The value of captopril renal scintigraphy in identifying patients who can benefit from angioplasty is controversial. Several noncontrolled studies have shown an association between positive findings on captopril scintigraphy and an improvement of hypertension after angioplasty, with a sensitivity of 92% (range, 84–100%) and a specificity of 78% (range, 62–100%) [15, 26–28]. Other studies have shown that captopril renal scintigraphy was not useful for patient selection before angioplasty [13, 29, 30]. In a prospective comparative study, van Jaarsveld et al. [8] confirmed that a positive result on scintigraphy was not a predictor of clinical improvement after angioplasty.
As previously reported, resistive index measurements play an important role in patient selection [17–19]. Radermacher et al. [19] reported an impressive sensitivity of 94% and a fair specificity of 53% in predicting improvement of hypertension after renal artery stenosis treatment when a bilateral resistive index of less than 0.80 was used for patient selection. In our study, bilateral resistive index thresholds below 0.70 or 0.75 before captopril administration were appropriate for patient selection, depending on whether the intention was to maximize the sensitivity or the specificity. Using a bilateral resistive index threshold of less than 0.75 before captopril, our sensitivity (91%) was similar to that reported by Radermacher et al., but our specificity (31%) was lower. Consequently, our results differ somewhat from those of Radermacher et al. Because we performed our bilateral resistive index measurement before captopril after the cessation of angiotensin-converting enzyme inhibitors, we expected to find higher values of resistive index. This discrepancy could be explained by our patient population. Indeed, only six (8%) of 74 patients in our series had a resistive index greater than 0.80 compared with 35 (27%) of 131 in the series by Radermacher et al.
When resistive index measurements are performed only in the stenotic kidney, lower values should be expected. Frauchiger et al. [17] and Cohn et al. [18] found that a unilateral resistive index threshold of 0.70 was useful in selecting patients for angioplasty. These findings are consistent with the results of our series.
Our results clearly indicated that captopril administration significantly decreased the resistive index. We also found lower values in unilateral resistive index than in the bilateral index. However, for predicting therapeutic improvement after angioplasty, the accuracy values of unilateral and bilateral resistive index measurements before and after captopril were not substantially different. Furthermore, the predictive values of these resistive indexes were not sufficiently high to be used as the sole selection criteria for patients who could benefit from angioplasty.
Kidney size proved to be a valuable predictive factor in the multivariate analysis when used in association with resistive index measurement. In fact, applying selection criteria that combined the criterion of a kidney longer than 99 mm with a criterion of either a bilateral resistive index measured before captopril administration or a unilateral restive index measured after captopril administration was predictive of therapeutic success either before or after captopril administration. Consequently, by applying appropriate resistive index thresholds, this combination of criteria could be used in patients who receive angiotensin-converting enzyme inhibitors as well as those who do not. The criterion of the 70- to 90-mm kidney length has already been reported in previous studies for patient selection for renal revascularization, chiefly as a tool in predicting the evolution of the renal function rather than the lowering of hypertension [31]. Renal size can be influenced by body height or body mass. Consequently, the kidney length criterion should be adapted to suit the body habitus of a particular patient. We did not calculate an indexed kidney length because it would be cumbersome to use clinically.
Depending on the clinical setting, a sensitive combination of criteria may be used in patients who present a low procedural risk during angioplasty, such as those with a precaptopril bilateral resistive index of less than 0.75 and a kidney longer than 90 mm. Using these criteria in our population, 66% (48/73) of our population would have been treated, with a clinical success rate of 63% (30/48) and a rate of exclusion from successful treatment of 10% (7/73). Conversely, in patients who present a high procedural risk of complications, more specific criteria, such as a postcaptropril unilateral resistive index of less than 0.65 and a kidney longer than 90 mm, should be preferred. With these criteria, 43% (32/74) of our population would have been treated, with a clinical success rate of 75% (24/32) and a rate of exclusion from successful treatment of 18% (13/74).
In patients presenting an intermediate risk, criteria combining a postcaptopril unilateral resistive index of less than 0.70 and a precaptopril bilateral resistive index of less than 0.75 could be used. Applying these criteria in our population, 59% (43/73) of our patients would have been treated with a clinical success rate of 65% (28/43), and 12% (9/73) of our population would have been excluded from a successful treatment. A limitation of these latter combined Doppler sonographic criteria is that resistive measurements must be performed before and after captopril administration. Furthermore, angiotensin-converting enzyme inhibitors must be withheld before performing the Doppler sonography, thus making the examination more cumbersome.
Despite differences observed in the clinical results and discrepancies in the resistive index values used for selecting patients for renal revascularization in published series [17–19], evidence indicates that physiologic evaluation of the kidney is helpful in predicting the clinical response. In several randomized studies in which such physiologic screening of the kidneys was not performed, results failed to show there was any significant clinical benefit of renal revascularization over medical treatment [8–10]. These studies recruited hypertensive patients on the basis of angiographically determined stenosis, and two of the studies included patients in whom the degree of renal artery stenosis was low as 50% [8, 10]. The absence of correlation between the degree of angiographically determined stenosis and the clinical response found in our study further justifies the need for functional evaluation of the kidneys as a tool for planning treatment.
No clear physiologic explanation allows understanding of the association among the resistive index, the influence of captopril, and the therapeutic outcome. Resistive index is a complex integration of arterial compliance, arterial pulsatility, and peripheral resistance [32]. Some researchers have shown a relationship between resistive index and the peripheral arterial resistance by performing renal embolization in animal models [33]. Others have used pharmacologic manipulation in animal studies to highlight the influence of arterial compliance and pulsatility on resistive index [34]. These observations help us understand the progression of atherosclerosis and the reasons that resistive index increases with age.
Patients with an increased resistive index are more likely to present with irreversible intrarenal vascular lesions that preclude any chance of clinical improvement after renal artery stenosis correction. Because captopril modifies both the arterial compliance and the peripheral resistance [35], one could hypothesize that captopril can lower the resistive index only in patients with compliant vascular beds that can respond to renal artery stenosis treatment. This hypothesis is not supported by the results of our study. Apparently, captopril-induced decrease in the resistive index occurs in all patients, including those who receive no therapeutic benefit from angioplasty. Because our results showed that resistive index thresholds were influenced by captopril, the drug regimen of patients being considered for angioplasty should be taken into account when interpreting Doppler sonographic results.
One of the shortcomings of our study is the lack of systematic angiographic or Doppler sonographic follow-up to verify the continued patency of the treated arteries. However, we obtained a high technical success rate using strict criteria that should guarantee a low restenosis rate. Furthermore, restenosis seldom appears within 3 months of angioplasty or stenting, the time interval that we used to measure the clinical outcome. On the other hand, late recurrence of hypertension could have been ignored in our series. Several patients with bilateral stenosis underwent unilateral angioplasty because of renal atrophy on the contralateral side; some may have had no improvement in blood pressure control because of the remaining atrophic kidney.
Another limitation of our research is the difficulty in attributing improvement in hypertension to either revascularization or medical treatment; moreover, a placebo effect following renal intervention could be observed. Further validation of the role of functional screening could be obtained by randomly assigning patients to receive either medical or interventional therapy. Finally, the quality of Doppler sonographic studies is operator dependent, which may hamper the reproducibility of our results. The differences observed between resistive indexes in the group in whom treatment was successful and the group in whom treatment failed are quite small. Therefore, it is important to use a rigorous technique during resistive index measurement to minimize variability.
MR angiography and CT angiography are more accurate than Doppler sonography for detection of renal artery stenosis [36], but Doppler sonography with resistive index measurement proved to be a good tool with which to select patients who could benefit from angioplasty. The best way to investigate these patients before angioplasty may be to combine a noninvasive anatomic imaging examination, such as MR angiography or CT angiography, with Doppler sonography.
Because our follow-up period was so short, we did not study the correlation between the long-term evolution of ischemic nephropathy after angioplasty and the various Doppler and scintigraphic criteria. This clinical problem needs to be investigated in the future.
In summary, sonographic measurements of kidney length and of the resistive indexes before and after captopril administration were more useful than findings of renal scintigraphy for predicting the clinical outcome of patients after renal angioplasty. Angiotensin-converting enzyme inhibitors influence the resistive index thresholds used in patient selection for renal angioplasty.
Acknowledgments
We thank Andrée Cliche and Vicky Thiffauly for their outstanding
research assistance and Ginette Bleau for her secretarial assistance.
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