Renovascular Hypertension

Hypertension caused by narrowing of one or both main renal arteries (or segmental branches), reducing renal perfusion and activating the renin and angiotensin system.

• Two main causes: atherosclerotic stenosis (about 90%, usually ostial, older patients with vascular disease) and fibromuscular dysplasia (about 10%, mainly women aged 15 to 50, mid to distal artery).
• Accounts for about 1 to 5% of all hypertension, and a larger share of resistant hypertension, malignant hypertension and hypertension with diffuse atherosclerosis.
• Mechanism: reduced perfusion pressure, renin release, angiotensin II vasoconstriction and aldosterone driven sodium retention. With bilateral disease or a solitary functioning kidney, glomerular filtration depends on angiotensin II, giving flash pulmonary oedema, volume dependent hypertension and ischaemic nephropathy.

• Onset before age 30 (fibromuscular dysplasia) or after age 55 (atherosclerosis), sudden worsening of controlled hypertension, resistant hypertension, malignant hypertension.
• Recurrent flash pulmonary oedema with preserved left ventricular function; unexplained renal impairment; asymmetric kidney size (difference greater than 1.5 cm).
• Systolic or continuous abdominal or flank bruit; hypokalaemia from secondary aldosteronism.
• Creatinine rise greater than 30% within 2 weeks of starting an ACE inhibitor or ARB.
• Evidence of atherosclerosis at other sites (coronary, carotid, peripheral).
• Differential diagnosis: essential hypertension, primary aldosteronism, phaeochromocytoma, chronic kidney disease, aortic coarctation, other secondary causes.
• Complications: flash pulmonary oedema, ischaemic nephropathy and end stage kidney disease, malignant hypertension, stroke, renal artery dissection or aneurysm.

• Renal duplex ultrasonography: peak systolic velocity greater than 200 cm/s and renal to aortic velocity ratio greater than 3.5 indicate stenosis of 60% or more. A resistive index greater than 0.8 in the renal parenchyma predicts poor benefit from revascularisation.
• CT angiography (contrast risk when eGFR is less than 30) or MR angiography (use gadolinium with caution when eGFR is less than 30). Fibromuscular dysplasia shows a "string of beads" pattern.
• Catheter angiography confirms: stenosis of 70% or more, or 50 to 70% with a translesional pressure gradient greater than 20 mmHg systolic (or 10 mmHg mean).
• Plasma renin and aldosterone (raised renin with normal or raised aldosterone), potassium, creatinine and eGFR, urinalysis, renal ultrasound for kidney size (less than 7 to 8 cm suggests little recoverable function).
• Fibromuscular dysplasia: image neck, intracranial and abdominal vessels, because aneurysm and dissection occur at other sites.

• Blood pressure target less than 130/80 mmHg.
• Medical therapy for atherosclerotic stenosis:
  • Ramipril 2.5 mg daily titrated to 10 mg, or losartan 25 to 100 mg daily. Check creatinine and potassium at 1 to 2 weeks. Accept a creatinine rise up to 30%; stop if it rises further, particularly with bilateral stenosis or a solitary kidney.
  • Add amlodipine 5 to 10 mg daily, chlorthalidone 12.5 to 25 mg daily (furosemide 40 to 120 mg daily if eGFR is less than 30), and bisoprolol 2.5 to 10 mg daily if needed.
  • Atorvastatin 40 to 80 mg daily, aspirin 75 to 100 mg daily, smoking cessation.
• Revascularisation indications for atherosclerotic disease (benefit over medical therapy is limited for most patients):
  • Recurrent flash pulmonary oedema or acute heart failure.
  • Resistant hypertension despite maximal tolerated therapy.
  • Progressive renal function loss with bilateral stenosis or a solitary functioning kidney.
  • Technique: balloon angioplasty with stent for ostial lesions; restenosis occurs in about 10 to 20%. Surgical bypass if endovascular treatment fails or anatomy is unsuitable.
  • Avoid revascularisation with a small atrophic kidney (less than 7 cm), resistive index greater than 0.8, or advanced irreversible renal failure.
• Fibromuscular dysplasia: balloon angioplasty without a stent is the first choice. Blood pressure is cured or improved in most patients, with cure in about one third to one half. Surgery for complex branch disease or failed angioplasty. Aspirin 75 to 100 mg daily afterwards.
• Special groups: pregnancy (stop ACE inhibitors and ARBs; use labetalol 100 to 400 mg two to three times daily, nifedipine retard 10 to 20 mg twice daily, or methyldopa 250 to 500 mg 8-hourly); children (specialist care, angioplasty for fibromuscular dysplasia); renal impairment (limit contrast, hydrate); elderly (slower titration, check postural BP).
• Red flags: acute pulmonary oedema, malignant hypertension, rapid creatinine rise after an ACE inhibitor, anuria with a solitary kidney.
• Follow up: BP, creatinine and potassium every 3 to 6 months; duplex ultrasonography at 6 and 12 months after stenting, then yearly; annual lipid and glucose checks.