Renal artery stenosis: duplex US after angioplasty and stent placement

The Role of Sonography in Renal Artery Stenosis Evaluation and Stent Placement

A literature review has been conducted to demonstrate the role of duplex sonography in evaluating renal artery stenosis (RAS) as a screening method for patients prior to percutaneous transluminal renal artery stent (PTRAS) placement. The review also evaluates the role of ultrasound surveillance following PTRAS and establishes the overall influence of ultrasound on defining stent efficacy for managing hemodynamically significant renovascular disease. Recent studies have narrowed criteria for intervention through duplex sonographic assessment of RAS to better predict patient benefit and response to stent placement. Studies using sonographic parameters evaluating patients for renal artery stenosis, criteria-dependent stent placement, and postintervention follow-up have shown improved patient response, helping ensure effective and appropriate care in RAS management.

Renal artery stenting with noninvasive duplex ultrasound follow-up: 3-year results from the RENAISSANCE renal stent trial

OBJECTIVE

The multicenter, single-arm RENAISSANCE trial evaluated outcomes in patients with progressive atherosclerotic renal artery stenosis (ARAS) treated with the Express Renal Premounted Stent System (Boston Scientific, Natick, MA).

BACKGROUND

Renal artery stenting may prevent the morbidity and mortality of surgical revascularization and high restenosis rates of percutaneous renal angioplasty (PTRA). Renal artery duplex ultrasonography (DUS) offers an alternative to traditional invasive poststenting angiographic surveillance, though concordance with angiography for in-stent restenosis has yet to be validated independently.

METHODS

RENAISSANCE enrolled 100 patients (117 lesions) with de novo or restenotic ostial atherosclerotic lesions <or=15 mm long in vessels >or=4.0 and <or=7.0 mm diameter with diameter stenosis >or=70%. The primary endpoint, 9-month binary restenosis, was compared to an objective performance criterion (OPC) of 40% for published PTRA results. Follow-up was conducted through 3 years.

RESULTS

Technical and procedural success was both 99%. Follow-up angiography, triggered clinically or by ultrasonography, revealed 21.3% binary restenosis at 9 months, which was superior to the OPC (P < 0.0001). Concordance between ultrasonography and angiography for detection of binary restenosis at 9 months was 87%. Peak systolic velocity and renal-to-aortic ratio were both significantly improved compared to baseline at 9 months and 2 years. The major adverse event (defined as device- or procedure-related death, target lesion revascularization or significant embolic event) rate was 10.5% at 9 months and 20.9% at 3 years.

CONCLUSIONS

RENAISSANCE demonstrates that renal artery stenting is superior to the prespecified OPC at 9 months, and also shows that DUS can accurately identify in-stent restenosis.

Advances in vascular imaging

Advances in vascular surgery have mirrored advances in diagnostic imaging. Indeed, the endovascular revolution has been made possible largely by advances in computed tomography, magnetic resonance imaging, and vascular ultrasound. As technology allows better noninvasive vascular diagnosis, conventional angiography, once the gold standard for the diagnosis of vascular disease, is now reserved largely for intervention. This article discusses the current state of vascular imaging. Specific emphasis is placed on the comparative clinical utility of different imaging modalities in the detection and management of vascular disease.

Enhanced flow velocity after stenting of renal arteries is associated with decreased renal function

BACKGROUND

Atherosclerotic renal artery stenosis (RAS) is frequently treated by angioplasty and stent placement. Duplex sonography is an established noninvasive technique for patient follow-up. There is lack of evidence that routine monitoring of asymptomatic patients with stable blood pressure is needed.

METHODS

Renal duplex sonography was performed in 64 patients who had received percutaneous angioplasty and stenting of an atherosclerotic RAS. Duplex sonographic diagnosis was made by a combination of direct flow measurement in the renal artery and evaluation of intrarenal resistive indices. Renal function was determined by serum creatinine and calculated glomerular filtration rate (GFR).

RESULTS

With a mean follow-up of 28 months after angioplasty, a flow velocity of >2.0 m/s was detected within the stented arteries in 11/64 patients. While the initial blood pressure and GFR as well as the influence of angioplasty on these parameters were not different, the decrease in renal function over time was significantly higher in patients with flow enhancement (annual GFR decrease, 8.0 ml/min vs. 0.8 ml/min; p < 0.05).

CONCLUSION

Follow-up duplex sonography in patients after renal artery stenting detected an unexpectedly high rate of in-stent restenosis associated with enhanced loss of renal function. Routine duplex sonographic follow-up may detect patients at risk of more rapidly declining renal function.

Renal artery stent revascularization with embolic protection in patients with ischemic nephropathy

A prospective analysis of renal artery stent revascularization with distal embolic protection in a high-risk patient population with ischemic nephropathy is presented. A total of 63 patients (median age 70.2 years, range 54-86 years) had significant atherosclerotic stenosis of 83 renal arteries documented on pre-procedural imaging. All patients had baseline chronic renal insufficiency with a documented deterioration in renal function in the 6 months before revascularization. The endovascular technique used in all patients involved primary passage of an embolic filter into the distal main renal artery followed by primary stent deployment with a balloon expandable stainless steel stent. The filter baskets were recaptured and contents submitted for pathological analysis. At 6 months post-intervention, 97% of patients demonstrated stabilization or improvement in renal function. Only 3% of patients had an inexorable decline in renal function, unchanged by the intervention. After a mean follow up of 16.0 months (6-27), 94% of patients demonstrated stabilization or improvement in renal function. One patient suffered an acute post-procedural deterioration in renal function. In total, 60% of the filter baskets contained embolic material. This study confirms the technical feasibility of renal artery stent deployment with adjuvant embolic protection. The excellent results for renal preservation at 6 months post-intervention also suggest that a distal embolic protection device may improve the impact of percutaneous renal revascularization on progressive deterioration in renal function. The postulated mechanism is through the prevention of atheromatous embolization and the embolic yield from the distal filters supports this hypothesis. Patients most likely to receive the greatest benefit are those with mild baseline chronic renal insufficiency and a recent decline in renal function.

Technology insight: Clinical role of magnetic resonance angiography in the diagnosis and management of renal artery stenosis

Noninvasive modalities, including duplex ultrasonography, renal scintigraphy, CT angiography and magnetic resonance angiography (MRA), may usefully contribute to diagnosis and treatment planning in patients with suspected renal artery stenosis. Important technical developments have increased the accuracy and feasibility of MRA for the detection of renal artery stenosis. A number of different MRA techniques can be applied to the study of renal arteries, but contrast-enhanced MRA represents the most valuable approach; several studies corroborate the high diagnostic accuracy of this technique, especially for the detection of atherosclerotic renal artery stenosis. A combined MRA protocol, which might include angiographic information provided by contrast-enhanced technique in addition to renal flow information derived from phase-contrast imaging, could help in classifying patients appropriately. Limitations of renal MRA include low accuracy in the evaluation of renal fibromuscular dysplasia and in the assessment of patients who undergo stenting of the renal arteries. This review describes the MRA techniques applied to the study of renal artery stenosis, including the technical features of current approaches and forthcoming developments. An overview of the clinical role of MRA, in conjunction with the other diagnostic modalities, in the identification and management of patients with renal artery stenosis, is also presented.

The role of ultrasound in renal insufficiency: the essentials

Sonography is the best screening modality to evaluate patients presenting with renal insufficiency. Ultrasound findings can be normal in patients with renal disease, especially in prerenal azotemia and acute parenchymal renal disease. Echogenic kidneys indicate the presence of parenchymal renal disease; the kidneys may be of a normal size or enlarged. Small kidneys suggest advanced stage chronic kidney disease. Uncommonly, cystic disease of the kidney, especially adult type polycystic kidney disease may be the cause of the patient's renal insufficiency with bilaterally enlarged kidneys containing multiple cysts of various sizes. If hydronephrosis is present, the level and cause of the obstruction should be sought. When ultrasound cannot diagnose the level and cause of obstruction, other imaging modalities, including CT and MRI may be useful. When renovascular disease (arterial stenosis or venous thrombosis) is suspected, spectral and color Doppler can be useful in detecting abnormalities.

Correlation between noninvasive and endovascular Doppler in patients with atherosclerotic renal artery stenosis: A pilot study

Considerable interest exists in using endovascular techniques for assessing the renal circulation. The vasomotor response of the renal circulation in patients with hypertension and severe atherosclerotic renal artery stenosis was evaluated. Sixteen patients (5 men and 11 women) with a mean age of 73.2+/-7.1 years (range, 59-82 years) underwent noninvasive renal duplex ultrasonography and endovascular flow wire evaluation. The flow wire was positioned in the main renal artery distal to the stenosis and used to examine the reactivity of the renal circulation in response to intra-arterial papaverine before and after percutaneous revascularization. Resistive index was computed as (MPV - EDV)/MPV, where MPV is the maximum peak velocity and EDV is the end-diastolic velocity. Renal flow reserve was defined as the ratio of peak hyperemic response to baseline flow. Intervention was technically successful in 18/18 arteries. Heart rate (69+/-11 vs. 65+/-10 beats/min; P=NS) and systolic blood pressure (168+/-19 vs. 163+/-24 mm Hg; P=NS) remained constant following injection of intrarenal papaverine, while diastolic blood pressure decreased (77+/-13 vs. 65+/-11 mm Hg; P<0.006). Papaverine injection resulted in significant increases in average peak velocity (APV; 148% of baseline; P=0.0003), MPV (146% of baseline; P=0.001), and EDV (161% of baseline; P=0.0026), but had no effect on the endovascular resistive index (0.81+/-0.12 vs. 0.84+/-0.08; P=NS). Renal artery stenting produced no effect on APV or EDV, but a small increase in MPV (123% of baseline; P<0.05). In contrast, renal stenting resulted in a significant increase in the endovascular resistive index (0.77+/-012 vs. 0.84+/-0.08; P=0.003), pulsatility index (1.84+/-0.61 vs. 2.23+/-0.70; P<0.014), and renal flow reserve (1.49+/-0.44 vs. 1.86+/-0.73; P<0.0071). A correlation was found between the noninvasive and endovascular measures diastolic/systolic ratio (r=0.73; P<0.0009) and resistive index (r=0.63; P<0.0053). Patients with atherosclerotic renal artery stenosis have preserved vasomotor response to papaverine, as well as marked increases in renal flow and resistive index following successful renal artery stenting. Endovascular flow wire measurements are safe, easy to perform, and correlate well with noninvasive Doppler measurements.

Endovascular treatment of an occluded axillofemoral bypass graft

Unsuspected subclavian or axillary disease may cause failure of axillofemoral bypass grafts. A 52-year-old woman who underwent left axillofemoral bypass grafting 5 years ago presented with 24 h of left foot pain. Routine duplex ultrasonography 2 months previously demonstrated velocities throughout the graft > 80 cm/s. Emergent angiography revealed thrombotic occlusion of the axillofemoral bypass graft. Both rheolytic thrombectomy and pulse spray thrombolysis using tissue plasminogen activator were used to restore graft patency. Arterial pressure waveform and pressure remained damped throughout the graft; a 50 mmHg gradient was found from the descending thoracic aorta to the mid-left subclavian artery. Angiography revealed a 70% diameter stenosis at the origin of the left subclavian artery. Following balloon angioplasty and stent placement, the pressure gradient was eliminated. In conclusion, careful evaluation of arterial inflow to bypass grafts is critical for ensuring long-term graft patency.

Segmental Waveform Analysis in the Diagnosis of Peripheral Arterial Occlusive Diseases

The duplex exam is widely used in the diagnosis of peripheral arterial occlusive disease. It presents some drawbacks, however, such as calcified plaques, sequential stenosis, and time-consuming examinations. A type of waveform analysis, referred to in this study as segmental analysis, was conducted to try to find solutions to these problems. Parameters of waveform analysis (peak systolic velocity, acceleration time, pulsatility, and resistance indices) taken at the common femoral and popliteal arteries in 177 arterial segments (aortoiliac and femoropopliteal) were compared to angiography results in a prospective manner. The statistical analysis showed an accuracy rate above 95% for all parameters in defining hemodynamic-significant (stenosis and occlusions) lesions in both segments. Also, a combination of measurements (parallel tests) was used to differentiate between hemodynamic-significant stenosis and occlusions, showing sensitivity and specificity rates between 84.8% and 94.8%. Findings from this study show that the hemodynamics of an arterial segment can be evaluated by segmental waveform analysis. It can also be used as a screening test for peripheral arterial occlusive diseases alone or combined with the standard duplex color exam.

Sonographic follow-up after visceral artery stenting

OBJECTIVE

The aim of this study was to evaluate the sonographic features of stents and the flow parameters of the visceral arteries after stent implantation.

METHODS

Since 1996, 34 stenoses of the visceral arteries (2 mesenteric, 4 celiac trunk, and 28 renal arteries) in 28 patients have been treated with metallic stent implantation in the Department of Radiology of Szeged Medical University. All these patients were regularly followed sonographically. For the diagnosis of restenosis, previously published criteria were used.

RESULTS

All the mesenteric and celiac stents could be visualized, but none of the renal stents were clearly seen sonographically. The flow parameters could be established in all cases. Sonographic examination revealed 1 occlusion, 2 restenoses, and 1 stent displacement. All these abnormalities were confirmed by other imaging modalities.

CONCLUSIONS

Sonography is a useful tool in the follow-up of patients after visceral artery stenting. Despite the fact that none of the renal artery stents were visualized directly, the flow parameters could be evaluated, and the pathologic changes were found.

Multidetector CT angiography with perfusion analysis in the surveillance of renal artery stents

PURPOSE

To evaluate 4 perfusion parameters obtained by multidetector computed tomographic angiography (CTA) in the follow-up of patients after renal artery stenting.

METHODS

Thirty-three consecutive patients (20 women; mean age 64.3+/-10.7 years) with renal artery stents were included in this prospective pilot trial. CTA was performed in 21 patients on a 4-row scanner and in 12 patients on a 16-row scanner. Volume maximum intensity projections and curved planar reconstructions were used for morphological analysis. The initial contrast test bolus was used for perfusion imaging by placing 2 additional regions of interest in the cortex of each kidney. The maximum relative attenuation values (Hounsfield units [HU max]), the time-to-peak values, an attenuation ratio, and a time-to-peak ratio for each side were calculated.

RESULTS

Over a mean follow-up of 3.4+/-1.7 years, restenosis was detected in 4 (12.1%) of the 33 stents; in all 66 main renal arteries, 5 (7.5%) significant flow obstructions were detected. Interobserver agreement for all morphological parameters was excellent (kappa>0.8). Mean relative HU max for the cortical region of stented arteries was 63.7+/-29.7 (mean HU ratio 0.37+/-0.12); the mean TTP max was 32.9+/-7.4 seconds (mean ratio 0.76+/-0.10). None of the perfusion parameters differed significantly between patients with and without significant flow obstructions (p>0.05).

CONCLUSIONS

Despite the excellent morphological information provided by multidetector CTA in the follow-up of renal stents, this modality does not provide hemodynamic information. Unfortunately, none of the evaluated perfusion parameters added any useful information in the follow-up after renal artery stenting.

Current issues in the diagnosis and management of patients with renal artery stenosis: a cardiologic perspective

Renal artery stenosis most often is caused by atherosclerosis. Although patients with renal artery stenosis can be managed conservatively, renal revascularization may be indicated, particularly in patients with refractory hypertension on a multidrug regimen and patients with declining renal function. Duplex ultrasonography of the renal arteries and magnetic resonance angiography are currently the most efficient noninvasive methods for the evaluation of renal artery stenosis. Selective digital subtraction renal arteriography remains the gold standard for the definitive diagnosis. In selected patients undergoing coronary studies and angiography immediately after the coronary procedure can be efficient. Atherosclerotic renal artery lesions, which commonly affect the renal artery ostium, can be treated safely and effectively with balloon-expandable stents. Successful angioplasty commonly results in improved control of hypertension, but an overall benefit on renal function and/or patient survival has not been shown. Generally the risk/benefit ratio of renal artery stenting seems favorable, but further randomized studies are needed for evidence-based decision making. All patients with atherosclerotic renal artery stenosis should receive rigorous secondary prevention measures including platelet inhibitors, statins, and beta-blockers.

Long-term follow-up after renal artery stenting

BACKGROUND

Renal artery stenosis may cause secondary arterial hypertension and lead to end-stage renal disease. Percutaneous transluminal angioplasty with stent implantation (PTRAS) allows effective and consistent treatment with a high technical success rate. The present trial focuses on the morphological and clinical results as assessed at a long-term follow-up (FU) visit. The main goals were assessment of the restenosis rate and evaluation of arterial hypertension and renal function.

PATIENTS AND METHODS

40 patients who had undergone successful stenting of a main renal artery were prospectively enrolled. At the FU visit, all patients underwent a risk-factor assessment, evaluation of arterial blood pressure and serum creatinine, and multi-detector computed tomography angiography (CTA).

RESULTS

Median FU was 3.3 years. Hyperlipidemia was present in 67.5% of the patients, current cigarette smoking in 35% and diabetes mellitus in 15%. All patients still suffered from arterial hypertension but, compared with the pre-interventional situation, arterial hypertension was improved in 37.5%. Serum creatinine was increased in 25% of patients, mean creatinine level was 1.3 +/- 0.4 mg/dl. Hemodynamically relevant restenosis was detected by observer 1 in five patients and by observer 2 in six patients, giving restenosis rates of 12.5% and 15%, respectively, after the median FU period. Both observers detected three additional relevant stenoses in the contralateral main renal arteries.

CONCLUSIONS

PTRAS gives excellent morphological long-term results. However, the clinical long-term outcome regarding arterial hypertension and renal function is only moderate.

Guidelines for the Reporting of Renal Artery Revascularization in Clinical Trials

Although the treatment of atherosclerotic renal artery stenosis with use of percutaneous angioplasty, stent placement, and surgical revascularization has gained widespread use, there exist few prospective randomized controlled trials (RCTs) comparing these techniques to each other or against the standard of medical management alone. To facilitate this process as well as help answer many important questions regarding the appropriate application of renal revascularization, well-designed and rigorously conducted trials are needed. These trials must have clearly defined goals and must be sufficiently sized and performed so as to withstand intensive outcomes assessment. Toward this end, this document provides guidelines and definitions for the design, conduct, evaluation, and reporting of renal artery revascularization RCTs. In addition, areas of critically necessary renal artery revascularization investigation are identified. It is hoped that this information will be valuable to the investigator wishing to conduct research in this important area.

Color Doppler ultrasound guidance during renal angioplasty and stenting

PURPOSE

To investigate whether an imaging technique combining color Doppler ultrasonography and selective renal artery digital subtraction angiography reduces contrast requirements in patients with progressive renal insufficiency undergoing renal artery angioplasty and stenting.

METHODS

Eight patients (5 men; mean age 58 years) with renal artery stenosis and renal insufficiency underwent percutaneous transluminal angioplasty and stenting under color Doppler ultrasound guidance.

RESULTS

Color Doppler ultrasound imaging yielded the information necessary for verifying catheter position, stent placement and expansion, and hemodynamics after revascularization. The combined imaging technique considerably reduced contrast requirements to only 10 mL in each case. No worsening of renal function was seen in any patient.

CONCLUSIONS

The combined imaging procedure uses low doses of contrast agent and is especially suited to patients with renal dysfunction undergoing percutaneous renal revascularization.

Guidelines for the reporting of renal artery revascularization in clinical trials

Although the treatment of atherosclerotic renal artery stenosis with use of percutaneous angioplasty, stent placement, and surgical revascularization has gained widespread use, there exist few prospective randomized controlled trials (RCTs) comparing these techniques to each other or against the standard of medical management alone. To facilitate this process as well as help answer many important questions regarding the appropriate application of renal revascularization, well-designed and rigorously conducted trials are needed. These trials must have clearly defined goals and must be sufficiently sized and performed so as to withstand intensive outcomes assessment. Toward this end, this document provides guidelines and definitions for the design, conduct, evaluation, and reporting of renal artery revascularization RCTs. In addition, areas of critically necessary renal artery revascularization investigation are identified. It is hoped that this information will be valuable to the investigator wishing to conduct research in this important area.