eMedicine Specialties > Radiology > Genitourinary
Renal Artery Stenosis/Renovascular Hypertension: Follow-up
Updated: Oct 2, 2009
Intervention
Interventions appropriate for patients with RAS/RVHT include medical therapy, percutaneous transluminal angioplasty (PTA), vascular stent placement, intravascular ultrasonography-guided atherectomy, and surgical revascularization.44,45,46,9
Medical therapy
Treatment with antihypertensive drugs is indicated, and optimal blood pressure control is essential. ACE inhibitors should be avoided. Other risk factors that should be addressed include atherosclerosis, smoking, and hyperlipidemia. Definitive therapy for the underlying cause should always be considered to prevent the development of ischemic nephropathy. In patients with diffuse atherosclerosis, the complication rate with both surgery and angioplasty is relatively high. Medical therapy may be preferred to other treatments.
Percutaneous transluminal angioplasty
PTA has become the procedure of choice for the treatment of symptomatic stenoses. Patency rates after PTA are strongly dependent on the size of the vessel treated and the quality of inflow and outflow through the vessel. RAS is an established cause of either RVHT or chronic renal insufficiency. Because of the excellent results obtained with renal angioplasty, it is the most commonly performed procedure for patients with symptomatic RAS.11,47
Previously, angioplasty was considered to be contraindicated for patients with a solitary or transplanted kidney. This is no longer the case, and angioplasty is now considered the procedure of choice for treatment of RAS in these patients.
Technical success is achieved in more than 90% of patients; patency rates are 90-95% at 2 years for MFP and 80-85% for atherosclerosis. Restenosis requiring repeat angioplasty has been reported in fewer than 10% of patients with AD and in 8-30% with atherosclerotic stenosis. Improvement in blood pressure control with fewer antihypertensive medications is achieved in 30-35% of patients with fibromuscular lesions and in 50-60% of patients with atherosclerotic lesions. A success rate of 83% has been reported with PTA in RAS associated with renal transplantation.
Vascular stent placement
Vascular stenting is considered complementary to PTA.
Many vascular stents are now available. Some stents are metallic and are either self-expanding or balloon expandable. The US Food and Drug Administration (FDA) has approved a few of these for peripheral coronary procedures and for transjugular intrahepatic portosystemic shunt (TIPS) procedures.
The ultimate role of stents in the treatment of vascular disease is not yet established, but these devices have already had a dramatic impact on the practice of interventional radiology.10 In studies from both the US and Europe, stenting of smaller vessels has resulted in an unacceptably high incidence of thrombosis. These problems are being addressed in the development of new stent materials and coatings.
Intravascular stents placed during angioplasty may be helpful in the prevention of restenosis and the management of RAS. Early results suggest that stenting may prove useful in patients with ostial disease, in those in whom restenosis occurs after PTA, and in those with complications (eg, renal artery dissection) resulting from PTA. Primary renal artery stenting in patients with atherosclerotic RAS has a high technical success rate and a low complication rate.
Intravascular ultrasonography-guided atherectomy
In a single reported case, hypertension secondary to AD was successfully diagnosed with intravascular sonography, and intravascular sonography-guided renal atherectomy was curative.
Surgical revascularization
Currently, surgical revascularization is reserved for patients in whom the main renal artery appears completely occluded and in whom the surviving renal parenchyma is vascularized by collaterals. Surgical revascularization might also be used when an ostial stenosis is present with a buttressing atheroma on either side of the ostium. Some of these lesions may also be amenable to percutaneous vascular stent placement.
Several surgical options are available. The stenotic segment may be excised and the artery resutured directly onto either the aorta or surviving stump. A vein graft may be transplanted or the kidney resected and reimplanted in the iliac fossa with the renal artery anastomosed to the iliac artery. Another novel method involves a splenectomy and anastomoses of the splenic artery to the renal artery when RAS involves the left kidney. The underlying diagnosis determines the results of this surgery. With advanced diffuse atherosclerosis, surgery may become less feasible because the certainty that the RAS is the cause of the hypertension is less and the prognosis may be determined by comorbidities.
A potential complication is the release of cholesterol emboli during the surgery; however, 80-90% of patients undergoing operation for atherosclerotic RAS benefit with cure or improvement. The perioperative mortality rate is less than 5%. In patients with AD, the cure rate is as high as 80%, and morbidity rates are low. However, similar results can be achieved with the minimally invasive renal angioplasty technique, with considerably less morbidity, mortality, and expense. In patients with diffuse atherosclerosis, the complication rate with both surgery and angioplasty is relatively high.48
Measurement of renin activity
Antihypertensive therapy may increase or decrease plasma renin levels. Nonsteroidal anti-inflammatory drugs can also decrease plasma renin levels. The baseline plasma renin activity is elevated in 50-80% of patients with RVHT. Measuring the increase in the baseline plasma renin activity 1 hour after the administration of 25-50 mg of the ACE inhibitor captopril can increase the predictive value of baseline plasma renin activity. In patients with RAS, the baseline plasma renin activity is significantly increased, perhaps as a result of the cessation of the normal suppressive effect of high angiotensin II levels on renin secretion in the ischemic kidney.
The sensitivity and specificity of the captopril renin test are 75-100% and 60-95%, respectively. A major limitation is the need to discontinue antihypertensive therapy, including the use of ACE inhibitors, beta blockers, and diuretics, because these agents can affect the baseline plasma renin activity. The sensitivity of the test is also low, and its predictive value is lower than that of a captopril renogram.
Ischemic kidneys release higher levels of renin in their veins. Renal venous sampling can be used to measure renin levels so as to compare the venous drainage from each kidney; the resulting data can be used to predict the degree of renal ischemia and the potential success of surgical revascularization. A 1.5-fold increase in renin level in the ischemic kidney is a positive result and suggests that revascularization may be successful in the treatment of elevated blood pressure.
Renin secretion in the contralateral kidney is suppressed, as evidenced by the fact that the levels of renin in the renal artery, the infrarenal inferior vena cava, and the renal vein are similar. Approximately 10% of healthy patients have a ratio above 1.5, and fewer than 20% have a ratio below 1.1. The accuracy of the measurements may improve by prior administration of an ACE inhibitor, which increases renin secretion on the affected side.
False-negative and false-positive results occur frequently. Although more than 90% of patients with unilateral RAS and increased renin levels in the affected renal vein have a positive response to angioplasty or surgery, approximately 50% of patients with nondiagnostic findings also benefit from revascularization. As a result, most clinicians rely on the clinical index of suspicion rather than renin measurements in the renal vein to estimate the physiologic significance of RAS. However, these renin measurements may still be useful in patients with bilateral RAS, in whom measurements may determine the side that most contributes to the hypertension.
Medicolegal Pitfalls
- Patients with moderate to severe renal insufficiency are at significant risk for contrast–induced acute tubular necrosis and atheroembolic renal failure, which could result in permanent or temporary dialysis. These complications must be discussed with the patient and put into perspective before any invasive procedure (eg, surgery, angiography, or angioplasty) is performed.
- Contrast nephropathy typically manifests as a transient increase in the serum creatinine level 3-6 days after the administration of iodinated contrast material.
- Contrast nephropathy is reported in as many as 40% of patients with underlying renal failure.
- Most patients with contrast nephropathy ultimately recover renal function.
- Porter reviewed results from nearly 300 patients with contrast nephropathy and concluded that fewer than 10% required permanent dialysis.49
See also the Medscape topic Medical Malpractice and Legal Issues.
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Further Reading
Keywords
renal artery stenosis, renovascular hypertension, RAS, RVHT, atheromatous renal artery stenosis, renal artery fibrosing lesions, intimal fibroplasia, medial fibrosis with microaneurysms, subadventitial fibroplasia, fibromuscular hyperplasia, segmental mediolytic arteriopathy, renal ischemia, renin-angiotensin-aldosterone activation, arterial dysplasia, medial fibroplasia, MFP
