Present Status and Technique of Renal Artery Denervation (RDN)

Renal artery denervation is a catheter-based interventional therapy for resistant or uncontrolled hypertension that targets the sympathetic nerves surrounding the renal arteries. By ablating these nerves, the procedure reduces renal sympathetic activity, leading to a sustained fall in blood pressure.

1. Physiological Basis

Hypertension is partly mediated by renal sympathetic overactivity. Renal nerves regulate:

• Renin release
• Sodium reabsorption
• Renal vasoconstriction
• Central sympathetic activation

Denervation interrupts these pathways → reduction in systemic sympathetic tone and BP.

Associated pathophysiologic system:

• Renin–Angiotensin–Aldosterone System (RAAS)

2. Indications (Current Clinical Use)

Primary indication

Resistant hypertension

Defined as BP above target despite:

• ≥3 antihypertensive drugs
• including a diuretic
• optimal doses

Related condition:

• Resistant Hypertension

Potential/expanding indications

Studies are exploring RDN in:

• Uncontrolled hypertension on fewer drugs
• Heart Failure
• Atrial Fibrillation
• Chronic Kidney Disease
• Obstructive Sleep Apnea
• Metabolic syndrome

These are investigational.

3. Present Status (Evidence Evolution)

Initial enthusiasm

Early trials:

• SYMPLICITY HTN‑1 Trial
• SYMPLICITY HTN‑2 Trial

Showed large BP reductions (~30 mmHg).

Major setback

The randomized sham-controlled:

• SYMPLICITY HTN‑3 Trial

showed no significant difference vs sham procedure.

Reasons identified:

• Incomplete denervation
• Operator variability
• Inadequate ablation pattern
• Medication adherence issues

Second-generation trials (improved design)

Modern trials with better catheters and sham control demonstrated benefit:

• SPYRAL HTN‑OFF MED Trial
• SPYRAL HTN‑ON MED Trial
• RADIANCE‑HTN SOLO Trial
• RADIANCE‑HTN TRIO Trial

Results:

• Office BP reduction: ~5–10 mmHg
• 24-hr ambulatory BP reduction: ~3–7 mmHg

Clinically meaningful and durable.

Current Guideline Position

Guidelines such as:

• European Society of Cardiology
• European Society of Hypertension

recommend:

✔ Consider RDN in true resistant hypertension
✔ Only in experienced centers
✔ After exclusion of secondary hypertension

4. Devices Used

Two main technologies exist.

Radiofrequency ablation

Example system:

• Symplicity Spyral Renal Denervation System

Mechanism:
Multiple RF ablations around the renal artery.

Ultrasound ablation

Example:

• Paradise Ultrasound Renal Denervation System

Mechanism:
Circumferential ultrasound energy → uniform nerve ablation.

Advantage: more complete denervation.

5. Technique of Renal Artery Denervation

Step-by-Step Procedure

1. Vascular access

• Usually femoral artery access
• 6F or 7F guiding catheter

2. Renal angiography

• Identify renal artery anatomy
• Exclude stenosis, accessory arteries

Requirements:

• Diameter ≥4 mm
• Length ≥20 mm

3. Catheter positioning

The denervation catheter is advanced into the renal artery distal segment.

4. Ablation

Energy is delivered in multiple spiral lesions.

Key procedural principles:

• Distal → proximal pattern
• Include branch arteries
• Circumferential ablation

Typical:

• 4–6 ablations per artery
• Duration ~60 seconds each (RF)

5. Bilateral treatment

Both renal arteries are treated.

6. Post-procedure angiography

Confirm:

• No dissection
• No thrombosis
• No significant spasm

6. Procedural Outcomes

Average BP reduction:

Office BP ↓ 10–15 mmHg
Ambulatory BP ↓ 5–8 mmHg

Benefits:

• Sustained reduction
• Reduced medication burden
• Good safety profile

7. Complications

Rare but include:

• Renal artery dissection
• Renal artery stenosis
• Access site hematoma
• Transient renal spasm

Incidence < 2–3% in modern trials.

8. Ideal Patient Selection

Best candidates:

• True resistant hypertension
• High sympathetic tone
• Preserved renal function
• Favorable renal artery anatomy

Avoid in:

• eGFR < 30 ml/min
• Multiple small renal arteries
• Renal artery stenosis

9. Key Exam Points (SS/DM Cardiology)

High-yield facts:

• Target = renal sympathetic nerves in adventitia
• Depth of nerves = 2–5 mm from lumen
• Denervation requires distal + branch ablation
• Best evidence from SPYRAL and RADIANCE trials
• BP fall modest but clinically meaningful

✅ In one line:
Renal artery denervation is a minimally invasive catheter-based therapy that reduces sympathetic renal nerve activity and lowers blood pressure in resistant hypertension, with modern trials demonstrating modest but significant benefit.