Renal Denervation

Definition

Renal denervation (RDN) is a catheter-based procedure that ablates the renal sympathetic nerves to reduce blood pressure by suppressing sympathetic outflow to the kidney. FDA-approved in November 2023 as an adjunctive treatment for patients with uncontrolled hypertension in whom lifestyle modifications and antihypertensive medications do not adequately control blood pressure. (sources/rnd-aha-2024, rating: high)

Key Concepts

Physiological Basis

• Renal sympathetic nerves regulate BP through three level-dependent mechanisms (sources/rnd-aha-2024, rating: high):
  • Low activation: renin release
  • Moderate activation: sodium reabsorption (antinatriuresis)
  • High activation: increased renal vascular resistance
• Knowledge of renal nerve physiology dates to mid-1800s; percutaneous methods developed after work with direct electrical stimulation and complete surgical denervation

Device Types and Mechanisms

Three main RDN systems have been studied (sources/rnd-aha-2024, rating: high):

• Earlier RF prototypes (Symplicity Flex monoelectrode, Vessix bipolar) caused incomplete denervation — now superseded
• More extensive denervation (incorporating branching/accessory renal arteries in addition to main arteries) in newer protocols improves outcomes

Efficacy — Drug-Naive / Washout Patients

• 6 RCTs with ambulatory SBP endpoints at 2–3 months (sources/rnd-aha-2024, rating: high):
  • SPYRAL OFF-MED Pivotal (n=331, Spyral): −4.7 mmHg 24h SBP vs −0.6 mmHg sham (p<0.01)
  • RADIANCE-HTN SOLO (n=146, Paradise): −8.5 mmHg daytime SBP vs −2.2 mmHg sham (p<0.01)
  • RADIANCE II (n=150, Paradise): −7.9 mmHg vs −1.8 mmHg sham (p<0.01); office SBP −5.5 mmHg in both SOLO and RADIANCE II
  • REDUCE HTN: REINFORCE (n=51, Vessix): No difference
  • TARGET BP OFF-MED (n=106, Peregrine): No difference at 8 weeks; lower medication burden at 12 months
• Summary: majority of trials positive; BP reduction equivalent to approximately 1 additional antihypertensive drug

Efficacy — Patients on 1–5 Antihypertensives

• Results more variable due to medication protocol heterogeneity (sources/rnd-aha-2024, rating: high):
  • SPYRAL ON-MED pilot (n=80): RDN superior by 7.4 mmHg 24h SBP (p<0.01)
  • SPYRAL ON-MED Expansion (n=257): No significant difference — unexpectedly large sham arm reduction (4.5 mmHg) from protocol-violating medication intensification in sham arm (29.9% vs 17.3%; p=0.02)
  • TARGET BP I (n=301, Peregrine): Modest but significant −3.2 mmHg at 3 months (p=0.049)

Efficacy — Resistant Hypertension (RH)

• RH defined as BP above goal on ≥3 drugs (complementary mechanisms, including diuretic) or at goal on ≥4 drugs; prevalence ≈19.7% of treated hypertensive adults; 2× CVD risk (sources/rnd-aha-2024, rating: high)
• 10 sham-controlled RCTs; early trials with Symplicity Flex (unipolar) negative (SYMPLICITY HTN-3, Desch, ReSET) — attributed to incomplete denervation and medication intensification in sham arms
• DENERHTN (standardised triple therapy + adherence monitoring): −5.9 mmHg daytime SBP (95% CI −11.3 to −0.5; p=0.03)
• RADIANCE-HTN TRIO (standardised triple-pill): −4.5 mmHg daytime SBP (95% CI −8.5 to −0.3; p=0.02)
• RADIOSOUND-HTN (only head-to-head trial): Ultrasound-based RDN (Paradise, −13.2 mmHg daytime) > radiofrequency main-artery alone (−6.7 mmHg) or main+branch (−8.3 mmHg) at 3 months (p=0.04)
• Unipolar RF vs spironolactone: RDN inferior or equivalent (DENERVHTA, Prague-15)
• Global SYMPLICITY Registry (3 years, no sham control): office SBP −16.5±28.6 mmHg; 24h ambulatory SBP −8.0±20.0 mmHg — sustained but uncontrolled data

Overall Response Rate

• 60–70% of patients achieve a meaningful ≥5 mmHg reduction in office or daytime ambulatory SBP within 2–3 months of ultrasound RDN (sources/rnd-aha-2024, rating: high)
• 24% of RDN patients achieve target daytime/home BP <135/85 mmHg vs 12% sham, with lower medication burden in the RDN arm
• Higher baseline BP is the most consistent predictor of greater BP reduction; no other clinical predictor reliably validated

Patient Selection Framework

Indications (sources/rnd-aha-2024, rating: high):

• Sustained, uncontrolled hypertension confirmed with 24h ABPM or appropriate home BP (to exclude white-coat hypertension)
• True resistant hypertension (≥3 drugs including diuretic above goal, or ≥4 drugs to maintain goal)
• Uncontrolled BP despite medication intolerance, non-adherence, or inability to escalate therapy

Absolute contraindications:

• Pregnancy
• Fibromuscular dysplasia
• Stented renal artery
• Renal artery aneurysm
• Significant renal artery stenosis (>50%)
• Known kidney or adrenal-secreting tumour

Limited data / use with caution:

• Stage 1 hypertension
• Isolated systolic hypertension
• Stage 4–5 CKD
• Single kidney
• Kidney transplant recipients

Mandatory pre-procedure workup:

• Serum creatinine + urinalysis (eGFR ≥40 mL/min/1.73m² required in most RCTs)
• Universal screening for primary aldosteronism (present but often undiagnosed; normal K⁺ does not exclude it)
• Based on clinical suspicion: hormonal testing (Cushing, phaeochromocytoma, thyroid, hyperparathyroidism), imaging (RAS, fibromuscular dysplasia, aortic coarctation)

Safety Profile

• Procedure via femoral artery access; duration ≈1 hour (sources/rnd-aha-2024, rating: high)
• Procedural risks: same as standard femoral arterial access (haemorrhage, infection, arterial dissection, thromboembolism, AV fistula, pseudoaneurysm, contrast, radiation)
• Serious adverse events <1% (renal artery dissection, access site complications, death)
• Most common adverse event: pain lasting >2 days post-procedure (12%)
• No deleterious effect on kidney function — including in moderate-to-severe CKD and systolic HF
• Renal artery stenosis post-procedure: estimated incidence 0.2%/year; similar to natural rate in hypertensive patients; greatest risk within first 6 months
• 3-year Global SYMPLICITY Registry: no late safety signals
• Reinnervation: Animal models show partial/full reinnervation with persistent BP reduction — functional significance in humans unclear; theoretical concern remains

Response Variability and Durability

• Factors associated with attenuated response: lower baseline BP, higher arterial stiffness, anatomical variants (accessory arteries), development of comorbidities, aging, medication changes (sources/rnd-aha-2024, rating: high)
• Some patients exhibit partial response or return to baseline values over time
• Proposed but unvalidated predictors of greater response: higher sympathetic activity markers (BP variability, resting heart rate, renin), orthostatic hypertension

Shared Decision-Making and Patient Expectations

• ≈30% of medicated patients and 35–40% of unmedicated patients globally are interested in RDN (sources/rnd-aha-2024, rating: high)
• Patient expectation gap: >96% expect ≥10 mmHg SBP reduction; actual outcomes are 5–10 mmHg; 40% in Germany expect to stop all medications post-RDN
• A 10 mmHg BP reduction is associated with 10–20% decline in CV morbidity/mortality; RDN's 5–10 mmHg reduction could yield similar benefit — no completed CVD outcomes trial
• Multidisciplinary team (hypertension specialist + trained proceduralist: interventional radiologist, interventional cardiologist, or vascular surgeon) required for candidate selection and post-procedure follow-up
• Physician concerns: invasive procedure, limited long-term data, continued medication reliance

Contradictions / Open Questions

• Inconsistent RCT efficacy: Early trials (SYMPLICITY HTN-3, REDUCE HTN:REINFORCE, TARGET BP OFF-MED) negative; newer trials with better technique, drug surveillance, and sham control largely positive — creates uncertainty about generalising across device types (sources/rnd-aha-2024, rating: high)
• No CVD outcomes data: All RCT endpoints are BP-based; no completed trial demonstrates reduction in MI, stroke, or death
• Spironolactone vs RDN: Two trials (DENERVHTA, Prague-15) show unipolar RF RDN inferior or equivalent to spironolactone as 4th agent — optimal sequencing unclear; MRA + RDN combination not studied (sources/rnd-aha-2024, rating: high; sources/HT-AHA-2025, rating: very high)
• Reinnervation in humans: Animal models show reinnervation with persistent effect; human durability data limited to registry observational data
• Responder identification: No clinical or biomarker predictor reliably identifies prospective responders
• Cost-effectiveness: Unknown vs generic pharmacotherapy, which is now very low cost

Connections

• Related to entities/Hypertension (primary disease entity; RDN as adjunctive treatment)
• Related to concepts/ASCVD-Risk-Assessment (resistant hypertension as high CVD risk state)
• Related to concepts/Cuffless-BP-Monitoring (BP monitoring approach in RDN candidates)
• Related to sources/HT-AHA-2025 (2025 AHA hypertension guideline: RDN COR 2b)

Sources

• sources/HT-AHA-2025
• sources/rnd-aha-2024