Renal Artery Stenosis

Renovascular hypertension is the systemic hypertension due to narrowing of the renal arteries. From a haemodynaemic point of view, a proximal stenosis is significant when there is a pressure gradient across the stenosis.

RAS has two main aetiologies: atherosclerosis and fibromuscular dysplasia.

Caring for Australasians with Renovascular Diesease ( CARI ) guidelines, the following classification has been devised based ont he likelihood of progression:

• Less than 50 % stenosis - insignificant
• 50 - 70 % stenosis - moderate
• more than 70 % stenosis - severe

Indication for screening RAS:

• Refractory hypertension ( > 160/100 mmHg and resistant to more than 4 antihypertensives )
• A greater than 40 % rise in serum creatinine level after the commencement of ACE inhibitor / ARB therapy.
• Progressive and rapid decline in renal function with other causes excluded.
• Proven episodes of pulmonary oedema and normal baseline left ventricular function.

Which Imaging tools to be used?

• Duplex ultrasonography - least invasive but subsequent tests are required due to high rate of false positive and negative results.
• Intra-arterial digital substraction angiography - definitive tool to diagnose the presence RAS.
• CT angiography - it is an accurate, minimally invasive screening test especially suited to the diagnosis of RAS due to fibromuscular dysplasia.
• Gadolinium enhanced MR angiography - highly sensitive in detecting atherosclerotic RAS and has significantly higher accuracy than any other modality in excluding the disease. However, the use of gadolinium is contraindicated in patients with GFR less than 30ml/min due to risk of nephrogenic systemic sclerosis.

Management:

Medical Therapy - In unilateral RAS, angiotensin converting enzyme inhibitors and angiotensin receptor blockers are useful for their ability to improve blood pressure and their overall cardiovascular benefit. a small initial rise in serum creatinine ( less than 30 % ) is transient and acceptable.

In bilateral RAS, ARB and ACEI are considered contraindicated. Acute renal failure occurs in about 30 % of patients but is usually reversible. In some patients, ACEI/ARB has high benefits, such as congestive cardiac failure patient, ACEI and ARB should be initiated in hospital setting.

Endovascular Treatment - There has been no difference in either blood pressure reduction and renal decline after 12 months when medical therapy has been compared with endovascular therapy.
Disappointly, the adverse event rate in those undergoing angioplasty has ranged from 10 - 25 %.

It seems reasonable to restrict renovascularisation to those patients with high grade stenosis ( > 70 % ) and with specific clinical problems:

• Refractory hypertension ( > 160 mmHg ) and resistant to more than four antihypertensive agents
• > 30 % rise in creatinine level on commencement of ACEI
• Progressive vascular renal decline
• Recurrent, unexplained pulmonary oedema with normal left ventricular function on echocardiography