Renal Artery Stenosis

1. Epidemiology
   1. Renal Artery Stenosis is the most common cause of secondary Hypertension (1-5%)
   2. Responsible for as much as 25% of Hypertension refractory to medications
2. Types
   1. Atherosclerotic Renal Artery Stenosis (90%)
   2. Fibromuscular Dysplasia (10%): Also associated with ruptured aneurysms and dissections
      1. Medial fibroplasia (most common FMD type, has string of beads appearance on imaging)
      2. Perimedial fibroplasia
      3. Intimal fibroplasia
      4. Adventitial fibroplasia
3. Evaluation: Diagnostic Clues
   1. Hypertension
      1. Recent onset of Hypertension
      2. No Family History of Hypertension
      3. Hypertension onset under age 30 or over 55 years
      4. Hypertension with Hypokalemia and Hyponatremia (Hyperaldosterone state)
      5. Hypertension resistant to therapy
         1. Increased Blood Pressure on Diuretic
         2. Excellent response to ACE Inhibitor
         3. ACE Inhibitor increases Serum Creatinine
   2. Comorbid vascular disease
      1. Retinopathy
      2. Systolic or diastolic abdominal bruit
      3. Long History of Tobacco use
      4. Coronary Artery Disease
      5. Cerebrovascular Disease
      6. Peripheral Vascular Disease
   3. Renal dysfunction
      1. Especially Serum Creatinine rise on ACE Inhibitors
      2. Recurrent pulmonary edema
      3. Asymmetric or bilaterally small Kidneys
4. Labs: Diagnosis (rarely used - imaging is gold standard)
   1. Plasma renin assay before and after ACE Inhibitor
      1. Morning Sample
      2. Unusual to be <3ng/ml/hour in renal vascular disease
5. Imaging: Diagnosis
   1. Renal artery duplex sonography (Preferred test where experienced operators)
      1. Efficacy
         1. Test Sensitivity markedly reduced in Obesity and if significant overlying bowel gas
         2. Operator dependent for accurate results (requires experienced technician)
         3. Test Sensitivity: 84-98%
         4. Test Specificity: 62-99% (Better Specificity than MRA)
      2. Diagnostic Criteria
         1. Peak systolic velocity in renal artery >1.8 to 2.0 m/sec
         2. Renal artery to aortic velocity ratio >3.5
      3. Renal resistive index (RRI) has prognostic value pre-operatively
         1. RRI<80 predicts best Hypertension improvement with revascularization
   2. Magnetic Resonance Angiography (MRA)
      1. Consider preferred Screening Test if sonographer not experienced with RAS screening
      2. Precaution: Gadolinium-Induced Nephrogenic Systemic Fibrosis (nearly always fatal)
         1. Consider alternative screening in renal insufficiency (esp. where Serum Creatinine >2.5)
      3. Efficacy
         1. Overestimates extrarenal stenosis
         2. Test Sensitivity: 90-100%
         3. Test Specificity: 76-94%
   3. CT Angiography
      1. Precautions
         1. Do not use if renal insufficiency due to Intravenous Contrast material
         2. Significant radiation exposure
      2. Efficacy
         1. Test Sensitivity: 89-100%
         2. Test Specificity: 82-100%
   4. Arteriogram
      1. Gold standard but invasive
   5. Radionuclide renal scan with and without ACE Inhibitor (Captopril Renography)
      1. Test Sensitivity: 80-100%
      2. Safe even in renal insufficiency
         1. However not reliable in poor Renal Function or bilateral Renal Artery Stenosis
      3. May help stratify those who will have greatest benefit from RAS intervention
6. Management: Medical
   1. See Prevention of Kidney Disease Progression
   2. Hypertension control
      1. ACE Inhibitor or Angiotensin Receptor Blocker
         1. Expect some increase in Serum Creatinine
         2. Stop if Serum Creatinine increases 20% in first 4 days of starting (or 30% later)
      2. Diuretics (e.g. Chlorthalidone or Hydrochlorothiazide)
   3. Hyperlipidemia control (goal LDL 70-100)
      1. StatinAntiHyperlipidemics (e.g. Simvastatin)
   4. Maximize Diabetes Mellitus management
7. Management: Surgical interventions for revascularization
   1. Indications
      1. Refractory Hypertension on 3 or more medications including a Diuretic
      2. Progressive Azotemia
      3. Acute Renal Failure with ACE Inhibitor (or ARB) with comorbid Congestive Heart Failure
      4. Recurrent flash pulmonary edema
      5. Bilateral Renal Artery Stenosis
      6. Stenosis of solitary Kidney
      7. Renal resistive index <0.80
   2. Contraindications (Relative): Factors favoring conservative therapy
      1. Good Hypertension control on 1 or 2 agents
      2. Normal Renal Function
      3. Advanced renal atrophy (<7.5 cm)
      4. Renal resistive index >0.80 (predicts poor Hypertension response to revascularization)
      5. Significant Proteinuria
   3. Procedures
      1. Surgical Revascularization
         1. Rarely used now unless undergoing concurrent open AAA repair
      2. Percutaneous transluminal renal Angioplasty
         1. Stenting has replaced PTRA in most centers due to recoil and recurrent stenosis
      3. Renal artery stenting (preferred)
   4. Efficacy
      1. Small study suggests outcomes from medical management is equivalent to surgical management
         1. Stenting confers risk (including mortality from massive Cholesterol emboli)
         2. Bax (2009) Ann Intern Med 150(12): 840-8
8. Prognosis: Five year survival in atherosclerotic Renal Artery Stenosis
   1. Unilateral Renal Artery Stenosis: 96% five year survival
   2. Bilateral Renal Artery Stenosis: 74% five year survival
   3. Stenosis or Occlusion of solitary Kidney: 47% five year survival
   4. End-stage renal disease on Hemodialysis: 18% five year survival (50% two year survival)
9. References
   1. Shetty (2007) 29th Annual CV Conference, HealthPartners, St. Paul, MN
   2. Hartman (2009) Am Fam Physician 80(3): 273-9