What are the indications for renal artery stenting?

Indications for Renal Artery Stenting

Renal artery stenting should be considered in patients with hemodynamically significant renal artery stenosis who have specific high-risk clinical features after optimal medical therapy has failed. 1

Primary Indications

Renal artery stenting may be considered in patients with hemodynamically significant atherosclerotic renal artery stenosis (RAS) defined as:

• Severe stenosis (≥70% diameter stenosis) OR
• Moderate stenosis (50-69%) with post-stenotic dilatation and/or significant trans-stenotic pressure gradient

High-Risk Clinical Features Warranting Stenting

1. Recurrent flash pulmonary edema/heart failure despite maximal medical therapy 1
2. Resistant hypertension defined as:
   • Uncontrolled BP despite ≥3 maximally tolerated antihypertensive medications (one being a diuretic) 1
   • Intolerance to optimal medical therapy 1
3. Rapidly declining renal function in the presence of:
   • Bilateral renal artery stenosis 1
   • Unilateral stenosis in a solitary functioning kidney 1
4. Unstable angina despite maximal medical therapy 1

Etiological Considerations

Fibromuscular Dysplasia

• Percutaneous transluminal renal angioplasty (PTRA) without stenting is the treatment of choice 1
• Higher success rates and better outcomes compared to atherosclerotic RAS

Atherosclerotic RAS

• Primary stenting (rather than angioplasty alone) is the preferred approach 1
• Higher risk of restenosis compared to fibromuscular dysplasia
• Should be performed in experienced centers 1

Hemodynamic Assessment Criteria

For moderate stenosis (50-69%), confirmation of hemodynamic significance is required using one of the following:

• Resting systolic translesional gradient ≥20 mmHg or mean gradient ≥10 mmHg 1
• Hyperemic systolic gradient ≥20 mmHg or mean gradient ≥10 mmHg 1
• Renal fractional flow reserve ≤0.8-0.9 1

Assessment of Kidney Viability

Before proceeding with stenting, kidney viability should be assessed 1:

Parameter	Signs of Viability	Signs of Non-viability
Kidney size	>8 cm	<7 cm
Renal cortex	Distinct cortex (>0.5 cm)	Loss of corticomedullary differentiation
Renal resistance index	<0.8	>0.8

Important Caveats and Pitfalls

1. Avoid stenting in patients with small (<7 cm) non-viable kidneys as revascularization is unlikely to provide benefit 1

2. Avoid stenting in patients with well-controlled hypertension on current medical therapy 1

3. Avoid stenting in patients with incidentally discovered RAS without clinical manifestations 1

4. Careful monitoring of renal function is required when using RAS blockers in patients with bilateral stenoses or stenosis to a solitary functioning kidney, as they can cause acute renal failure 1

5. Intravascular ultrasound should be considered for optimal stent sizing to avoid undersizing (leads to restenosis) or oversizing (risks vessel rupture) 1

6. Post-procedure follow-up should include:

   • Initial assessment at 1 month
   • Subsequent follow-up every 12 months
   • Monitoring of blood pressure, renal function, and duplex ultrasound 1

Clinical Outcomes After Stenting

In appropriately selected patients, renal artery stenting can lead to:

• Significant reduction in systolic blood pressure 2, 3
• Reduction in number of antihypertensive medications 3, 4
• Preservation of renal function in a substantial proportion of patients 4
• Improvement in left ventricular structure and function 4

However, it's important to note that large randomized trials have not demonstrated clear benefits in hard endpoints like mortality or major cardiovascular events, which is why patient selection based on the above criteria is critical.