Renal Artery Stenosis

1. Clinical Overview

Summary

Renal artery stenosis (RAS) is a narrowing of one or both renal arteries, leading to renal hypoperfusion, activation of the renin-angiotensin-aldosterone system (RAAS), and secondary hypertension. RAS represents the most common secondary cause of hypertension, accounting for 1-5% of all hypertensive patients and 10-20% of those with resistant hypertension. [1,2] The two principal aetiologies are atherosclerotic disease (approximately 90% of cases) and fibromuscular dysplasia (FMD, approximately 10%), each with distinct pathophysiology, demographics, and therapeutic implications. [3]

The clinical significance of RAS extends beyond hypertension to include ischaemic nephropathy, cardiovascular destabilisation syndromes such as recurrent flash pulmonary oedema (Pickering syndrome), and progressive chronic kidney disease. [4,5] However, landmark trials including ASTRAL (2009) and CORAL (2014) have fundamentally altered the management paradigm, demonstrating that for atherosclerotic RAS, optimal medical therapy is non-inferior to revascularisation in most patients, with selected exceptions for specific clinical presentations. [6,7]

Recognition of RAS requires high clinical suspicion in specific populations: elderly patients with diffuse atherosclerotic disease and resistant hypertension, young women with hypertension and abdominal bruit suggesting FMD, patients developing acute kidney injury following ACE inhibitor or ARB initiation, and those with recurrent flash pulmonary oedema. [8,9]

Key Facts

Clinical Pearls

• Flash Pulmonary Oedema (Pickering Syndrome): Recurrent, sudden-onset severe pulmonary oedema in hypertensive patient - pathognomonic for bilateral RAS or RAS in solitary kidney. High index of suspicion required. [10]
• ACE Inhibitor/ARB Test: Acute rise in creatinine (> 30% increase) after starting ACEi/ARB suggests bilateral RAS or RAS in solitary kidney - efferent arteriolar dilatation removes compensatory mechanism maintaining GFR. [11]
• Abdominal Bruit: Epigastric or flank systolic-diastolic bruit present in approximately 50% of significant RAS - listen carefully, but absence does not exclude diagnosis. [12]
• Resistant HTN Screening: RAS is a key secondary cause to exclude in resistant hypertension (BP uncontrolled despite 3+ drugs including diuretic at optimal doses). [13]
• Size Discrepancy: Kidney length difference > 1.5-2.0 cm on ultrasound suggests chronic unilateral RAS with ipsilateral atrophy. [14]
• CORAL Trial Impact: Renal artery stenting + medical therapy NOT superior to medical therapy alone for atherosclerotic RAS - changed practice paradigm from interventional to medical-first approach. [7]
• FMD vs Atherosclerotic: FMD responds excellently to angioplasty alone (no stent needed), whereas atherosclerotic RAS rarely benefits from revascularisation. [3,15]
• Bilateral Disease: Carries worse prognosis - higher risk of refractory hypertension, ischaemic nephropathy, and flash pulmonary oedema. [16]

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2. Epidemiology

Prevalence & Demographics

The true prevalence of RAS is difficult to ascertain as many cases are asymptomatic and discovered incidentally. Prevalence varies significantly depending on the population studied. [17]

Age and Sex Distribution

Risk Factors by Aetiology

Atherosclerotic RAS Risk Factors

• Age: > 50 years, particularly > 60 years
• Sex: Male predominance
• Smoking: Most significant modifiable risk factor
• Diabetes mellitus: Accelerated atherosclerosis
• Dyslipidaemia: Elevated LDL, low HDL
• Hypertension: Both cause and consequence
• Known atherosclerotic disease: PAD, CAD, cerebrovascular disease
• Chronic kidney disease: Bidirectional relationship
• Family history: Premature cardiovascular disease

Fibromuscular Dysplasia Risk Factors

• Sex: Female (90%)
• Age: Typically presents age 20-50 years
• Genetic predisposition: Familial clustering observed, but no single gene identified [18]
• Ethnicity: More common in Caucasians
• Associated conditions: Cervical artery dissection, intracranial aneurysms (7-10%)
• Smoking: May exacerbate but not causative

Geographic and Ethnic Variations

Atherosclerotic RAS prevalence is higher in developed nations with higher rates of cardiovascular disease risk factors. Ethnicity influences both prevalence and severity, with African-American and Hispanic populations at higher risk for severe, resistant hypertension secondary to RAS. [1]

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3. Pathophysiology

Renal Artery Anatomy

The renal arteries arise from the abdominal aorta at approximately L1-L2 vertebral level, immediately below the superior mesenteric artery. Each renal artery divides into segmental branches supplying distinct renal zones. The renal arteries are end-arteries with minimal collateral circulation, making the kidney vulnerable to ischaemia from stenotic lesions.

Atherosclerotic lesions: Typically affect the proximal renal artery or ostium (within 1 cm of the aortic origin), often as "spill-over" from aortic atherosclerotic plaque. Lesions are eccentric, calcified, and progressive.

FMD lesions: Primarily affect the mid-to-distal renal artery (sparing the ostium), with the classic "string of beads" appearance on angiography representing alternating zones of fibromuscular thickening and aneurysmal dilatation. Medial fibroplasia is the most common subtype (80-90% of FMD cases). [3,18]

Renin-Angiotensin-Aldosterone System (RAAS) Activation

The central pathophysiological mechanism in RAS is inappropriate RAAS activation in response to renal hypoperfusion. [19]

Renal Artery Stenosis
         ↓
Reduced Renal Perfusion Pressure
         ↓
Juxtaglomerular Cells Sense ↓ Pressure
(Baroreceptor mechanism)
         ↓
↑ Renin Release
         ↓
Angiotensinogen → Angiotensin I (Renin)
         ↓
Angiotensin I → Angiotensin II (ACE)
         ↓
    ┌────────────┬────────────┬────────────┐
    ↓            ↓            ↓            ↓
Vasoconstriction  Aldosterone   Sympathetic  ADH Release
(Systemic)        Release       Activation   
    ↓            ↓            ↓            ↓
↑ Peripheral     Na⁺/H₂O      ↑ Cardiac    H₂O
Resistance       Retention     Output       Retention
         ↓            ↓            ↓            ↓
         └────────────┴────────────┴────────────┘
                      ↓
              HYPERTENSION
              (Secondary, Volume-Dependent)

Molecular and Cellular Mechanisms

Angiotensin II Effects: [19,20]

• Vascular: Direct vasoconstriction via AT1 receptors on vascular smooth muscle → increased systemic vascular resistance
• Renal: Preferential efferent arteriolar vasoconstriction → maintains GFR despite reduced perfusion (compensatory but maladaptive)
• Cardiac: Myocardial hypertrophy, fibrosis, and remodelling
• Adrenal: Stimulates aldosterone secretion from zona glomerulosa
• Central nervous system: Enhances sympathetic outflow, stimulates thirst and ADH release
• Oxidative stress: Increases NADPH oxidase activity → reactive oxygen species → endothelial dysfunction
• Pro-inflammatory: Upregulates inflammatory cytokines and adhesion molecules

Aldosterone Effects:

• Sodium and water retention via ENaC channels in collecting duct
• Potassium excretion (hypokalaemia in 15-30% of cases)
• Volume expansion and hypertension
• Myocardial and vascular fibrosis

Nitric Oxide Dysfunction: [20]

• Reduced NO bioavailability due to oxidative stress and peroxynitrite formation
• Impaired endothelium-dependent vasodilation
• Contributes to endothelial dysfunction, vascular remodelling, and hypertension

Atherosclerotic vs Fibromuscular Dysplasia: Comparative Pathophysiology

• alternating stenosis/dilatation | | Progression | Progressive in 50% over 5 years | Usually stable, rarely progresses | | Bilateral | 30-40% | 50-60% | | Associated conditions | Systemic atherosclerosis (CAD, PAD, CVA) | Cervical artery FMD, intracranial aneurysms | | Treatment response | Poor response to revascularisation | Excellent response to angioplasty (60-80%) | | Pathology | Foam cells, smooth muscle proliferation, calcification | Medial fibroplasia, smooth muscle hyperplasia |

Compensatory Mechanisms and the ACE Inhibitor Effect

In unilateral RAS, the contralateral kidney can compensate through pressure natriuresis, maintaining overall sodium balance and volume homeostasis. However, in bilateral RAS or RAS in a solitary kidney, this compensatory mechanism is lost, leading to:

1. Uncompensated volume expansion: No escape mechanism for sodium and water excretion
2. Flash pulmonary oedema: Rapid fluid accumulation due to combined hypertension and volume overload [10]
3. Severe hypertension: Unopposed RAAS activation

The ACE Inhibitor Paradox:

In RAS, GFR is maintained by efferent arteriolar vasoconstriction mediated by angiotensin II. ACE inhibitors or ARBs remove this compensatory mechanism by:

• Dilating the efferent arteriole
• Reducing intraglomerular pressure
• Acutely dropping GFR (> 30% increase in creatinine)

This is diagnostic of bilateral RAS or RAS in a solitary kidney and represents a haemodynamically significant lesion. [11]

Ischaemic Nephropathy

Chronic renal ischaemia from RAS leads to irreversible structural kidney damage: [21]

• Glomerular: Sclerosis, obsolescence
• Tubular: Atrophy, loss of tubular mass
• Interstitial: Fibrosis, chronic inflammation
• Vascular: Arteriolosclerosis, hyalinosis

Once ischaemic nephropathy is established with significant fibrosis and nephron loss, revascularisation is unlikely to restore renal function - explaining the neutral findings of CORAL and ASTRAL trials. [6,7]

Cardiac Destabilisation Syndromes

Flash Pulmonary Oedema (Pickering Syndrome): [10]

Mechanism:

1. Bilateral RAS → unopposed RAAS activation
2. Volume expansion without compensatory natriuresis
3. Severe hypertension → increased LV afterload → diastolic dysfunction
4. Rapid shift of fluid from intravascular to alveolar space
5. Sudden onset dyspnoea, often nocturnal

Characteristics:

• Recurrent episodes (differentiates from typical APO)
• Rapid onset (less than 1 hour)
• Disproportionate to cardiac function
• Often with preserved ejection fraction
• Associated with bilateral RAS (80-90% of cases)

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4. Clinical Presentation

Suggestive Clinical Features

RAS is often asymptomatic until complications develop. Clinical suspicion should be heightened in specific scenarios.

Classic Clinical Scenarios

Scenario 1: Atherosclerotic RAS

Patient: 68-year-old male, ex-smoker, known PAD Presentation: BP 190/110 mmHg despite amlodipine, ramipril, indapamide Examination: Epigastric bruit, absent left pedal pulses, carotid bruit Investigations: Creatinine 145 μmol/L (previously 110), K⁺ 3.2 mmol/L Think: Atherosclerotic RAS in high-risk patient with resistant HTN

Scenario 2: Fibromuscular Dysplasia

Patient: 35-year-old woman, non-smoker, no family history Presentation: New-onset hypertension BP 175/100 mmHg, headaches Examination: Epigastric bruit, otherwise normal cardiovascular exam Investigations: Normal renal function, no proteinuria Think: FMD - young woman with HTN and bruit

Scenario 3: Flash Pulmonary Oedema (Pickering Syndrome)

Patient: 72-year-old woman with CKD, resistant HTN Presentation: Third admission in 6 months with sudden nocturnal dyspnoea, pulmonary oedema Examination: BP 210/110 mmHg, bibasal crackles, no peripheral oedema Investigations: Echo - EF 55%, normal LV function; BNP mildly elevated Think: Bilateral RAS causing flash pulmonary oedema - preserved EF, recurrent episodes

Scenario 4: ACE Inhibitor-Induced Acute Kidney Injury

Patient: 60-year-old male with hypertension Presentation: Started on ramipril 2 weeks ago, now feeling unwell Examination: BP 160/95 mmHg (improved from 180/105) Investigations: Creatinine risen from 95 to 145 μmol/L (53% increase) Think: Bilateral RAS or RAS in solitary kidney - ACEi unmasked haemodynamically significant lesion

Red Flag Features Requiring Urgent Investigation

• Flash pulmonary oedema: Recurrent episodes - bilateral RAS until proven otherwise
• Acute kidney injury on ACEi/ARB: Creatinine rise > 30% - suggests bilateral disease
• Rapidly progressive renal failure: CKD progression > 5 mL/min/year - ischaemic nephropathy
• Malignant hypertension: BP > 180/120 with end-organ damage - hypertensive emergency
• Refractory hypertension: Uncontrolled on 4+ agents - exclude secondary causes

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5. Clinical Examination

General Inspection

• Appearance: Signs of chronic illness, atherosclerotic disease
• Body habitus: Obesity (metabolic syndrome), cachexia (severe renovascular disease)
• Skin: Nicotine staining (smoking), xanthomata (dyslipidaemia)

Cardiovascular Examination

Abdominal Examination

• Abdominal aortic aneurysm: Palpable expansile pulsatile mass - associated atherosclerosis
• Hepatomegaly: Right heart failure from hypertensive heart disease
• Renal mass: Palpable kidney (rare) - polycystic kidney disease differential
• Renal bruit: Listen in epigastrium and flanks, systolic-diastolic character

Fundoscopy

Assess for hypertensive retinopathy (Keith-Wagener classification):

• Grade I: Arteriolar narrowing, increased tortuosity
• Grade II: AV nipping
• Grade III: Flame haemorrhages, cotton-wool spots, exudates
• Grade IV: Papilloedema (malignant hypertension)

Fluid Status Assessment

• Pulmonary oedema: Bibasal crackles, tachypnoea (flash pulmonary oedema)
• Peripheral oedema: Ankle/sacral oedema (volume overload)
• JVP: Elevated (fluid overload, right heart failure)

Signs of Underlying Aetiology

Atherosclerotic disease:

• Absent peripheral pulses
• Carotid/femoral bruits
• Previous vascular surgery scars
• Diabetic stigmata (retinopathy, neuropathy)

Fibromuscular dysplasia:

• Often normal examination apart from hypertension and bruit
• Young woman with no other vascular risk factors
• Possible cervical bruit (carotid FMD)

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6. Differential Diagnosis

Differential Diagnosis of Secondary Hypertension

Differentiating RAS from Primary Aldosteronism

Both can present with resistant hypertension and hypokalaemia.

Differentiating Atherosclerotic RAS from FMD

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7. Investigations

The diagnostic approach to RAS involves clinical suspicion, non-invasive screening, and confirmatory imaging. The goal is to identify haemodynamically significant stenosis (≥60-70% luminal narrowing) that may benefit from intervention.

First-Line Screening Investigations

Biochemistry

Renal Ultrasound

• Kidney size: Discrepancy > 1.5-2.0 cm suggests unilateral RAS with chronic ischaemia
• Cortical thinning: Chronic ischaemic changes
• Hydronephrosis: Excludes obstructive uropathy
• Echogenicity: Increased in chronic kidney disease

Limitations: Cannot reliably visualise renal arteries; not a definitive diagnostic test for RAS

Non-Invasive Imaging Modalities

Duplex Ultrasound (Renal Artery Doppler)

Advantages:

• Non-invasive, no contrast, no radiation
• Functional assessment (resistive index)
• Can assess accessory renal arteries

Disadvantages:

• Operator-dependent
• Technically difficult in obesity, bowel gas
• Cannot assess distal vessels or FMD lesions
• Time-consuming

Clinical Use: First-line screening in many centres, particularly in CKD where contrast-based imaging poses risks [14]

Computed Tomography Angiography (CTA)

Advantages:

• Excellent sensitivity and specificity
• Detects calcification (atherosclerotic disease)
• Assesses accessory arteries and aorta
• Fast acquisition
• Widely available

Disadvantages:

• Iodinated contrast - nephrotoxicity risk (particularly in CKD)
• Radiation exposure
• Artefact from calcification may overestimate stenosis severity

Clinical Use: Preferred in patients with adequate renal function, particularly for atherosclerotic RAS

Magnetic Resonance Angiography (MRA)

Advantages:

• No ionising radiation
• Excellent for FMD ("string of beads" well visualised)
• Assesses kidney perfusion and anatomy
• Multi-planar imaging

Disadvantages:

• Gadolinium risk in severe CKD (eGFR less than 30): nephrogenic systemic fibrosis (rare but serious)
• Overestimates stenosis severity (flow turbulence)
• Contraindicated with some metallic implants
• Longer acquisition time, claustrophobia
• More expensive

Clinical Use: Preferred for FMD, young patients, or when avoiding radiation/iodinated contrast

Gold Standard: Renal Angiography

Catheter-based selective renal angiography remains the gold standard for definitive diagnosis.

Technique:

• Femoral or radial arterial access
• Selective catheterisation of renal arteries
• Iodinated contrast injection
• Digital subtraction angiography (DSA)

Advantages:

• Highest sensitivity and specificity (100%)
• Allows pressure gradient measurement across stenosis (> 20 mmHg = haemodynamically significant)
• Enables simultaneous intervention (angioplasty ± stenting)
• Visualises collateral circulation

Disadvantages:

• Invasive procedure
• Contrast nephropathy risk
• Arterial access complications (haematoma, dissection, pseudoaneurysm)
• Atheroembolic disease risk (cholesterol emboli)
• Radiation exposure
• Expensive

Clinical Use: Reserved for patients in whom revascularisation is planned or when non-invasive tests are inconclusive

Diagnostic Criteria

Haemodynamically Significant Stenosis:

• Anatomic: ≥60-70% luminal diameter reduction on angiography
• Functional: Peak systolic velocity > 180-200 cm/s on Duplex ultrasound, or renal-to-aortic ratio > 3.5
• Pressure gradient: > 20 mmHg trans-stenotic pressure gradient on catheter angiography

Grading of Stenosis:

• Mild: less than 50% diameter stenosis
• Moderate: 50-70% diameter stenosis
• Severe: 70-99% diameter stenosis
• Occlusion: 100% - no flow

Functional Assessment

Resistive Index (RI) on Duplex ultrasound:

• Formula: RI = (PSV - EDV) / PSV
• Normal: less than 0.70
• Abnormal: > 0.80 suggests irreversible parenchymal disease - poor response to revascularisation
• Clinical significance: Helps predict which patients will NOT benefit from revascularisation [14]

Captopril Renography (Historical)

Radionuclide renography with captopril challenge was previously used but has been largely superseded by modern imaging techniques due to low sensitivity (60-75%) and specificity (60-90%).

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8. Classification and Staging

Aetiology-Based Classification

Atherosclerotic RAS (90%)

• Proximal/ostial lesions: Most common - within 1 cm of aortic origin
• Eccentric plaque: Lipid-rich core, fibrous cap, calcification
• Progressive: 50% progress over 5 years; 5-10% progress to occlusion
• Associated disease: Systemic atherosclerosis

Fibromuscular Dysplasia (10%)

• Medial fibroplasia (80-90%): "String of beads"
• alternating stenosis and aneurysmal dilatation
• Perimedial fibroplasia (10-15%): Smooth, concentric stenosis
• Intimal fibroplasia (less than 5%): Smooth, focal stenosis - more common in children
• Medial hyperplasia (1-2%): Smooth, long-segment stenosis

Anatomic Classification

• Unilateral: 60-70% of cases
• Bilateral: 30-40% of cases - worse prognosis, higher risk of flash pulmonary oedema
• Solitary kidney: High risk of renal failure and flash pulmonary oedema

Severity Classification (Angiographic)

Functional Classification (Clinical Presentation)

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9. Management

The management of RAS has been fundamentally transformed by the ASTRAL (2009) and CORAL (2014) trials, which demonstrated that for atherosclerotic RAS, optimal medical therapy is non-inferior to revascularisation for most patients. [6,7] Medical therapy is now first-line for atherosclerotic RAS, with selected exceptions. Fibromuscular dysplasia, in contrast, responds excellently to percutaneous angioplasty. [15,18]

Management Algorithm

Suspected Renal Artery Stenosis
              ↓
      Clinical Suspicion:
      - Resistant HTN
      - Flash pulmonary oedema
      - AKI on ACEi/ARB
      - Onset less than 30 or > 55 years
              ↓
   First-Line Screening
   - Duplex US / MRA / CTA
   (Choice depends on local expertise, renal function)
              ↓
         ┌────┴────┐
         ↓         ↓
     Negative   Positive (≥60-70% stenosis)
         ↓         ↓
  Consider other   Determine Aetiology
  secondary causes        ↓
                   ┌──────┴───────┐
                   ↓              ↓
           Atherosclerotic       FMD
                   ↓              ↓
          MEDICAL THERAPY    ANGIOPLASTY
          (First-line)       (Curative in 60-80%)
          - Statins               ↓
          - Aspirin          Excellent outcomes
          - BP control       No stent needed
          - Smoking          
          - Diabetic control      
                   ↓
      Revascularisation only if:
      - Flash pulmonary oedema (recurrent)
      - Rapidly progressive CKD despite medical Rx
      - Refractory HTN (> 4 drugs, non-adherence excluded)
      - Acute kidney injury (bilateral or solitary kidney)
                   ↓
          Renal Angiography
          ± Angioplasty/Stenting

Medical Management (First-Line for Atherosclerotic RAS)

The CORAL trial demonstrated that optimal medical therapy alone is non-inferior to medical therapy + renal artery stenting for cardiovascular and renal outcomes in atherosclerotic RAS. [7] Medical therapy is therefore first-line.

Antihypertensive Therapy

ACE Inhibitor/ARB Controversy:

• Unilateral RAS: ACEi/ARB are SAFE and may be beneficial by reducing proteinuria and protecting the contralateral kidney [11]
• Bilateral RAS or solitary kidney: ACEi/ARB are CONTRAINDICATED due to risk of acute renal failure
• Unknown laterality: Use with caution; monitor creatinine closely (check at 1-2 weeks); stop if rise > 30%

Blood Pressure Targets:

• General target: less than 130/80 mmHg (individualised to patient tolerance)
• Resistant HTN: Aim for less than 140/90 mmHg initially, then optimise further
• Avoid over-aggressive BP lowering: Risk of renal hypoperfusion in severe bilateral disease

Cardiovascular Risk Reduction

Monitoring on Medical Therapy

Revascularisation: Indications and Techniques

Indications for Revascularisation (Selected Patients Only)

The ASTRAL and CORAL trials showed no benefit of routine revascularisation for atherosclerotic RAS. [6,7] However, specific clinical scenarios may benefit:

CORAL Trial (2014): [7]

• Design: RCT, 947 patients with atherosclerotic RAS and HTN or CKD
• Intervention: Renal artery stenting + medical therapy vs medical therapy alone
• Primary outcome: Composite of cardiovascular and renal events
• Result: No significant difference (HR 0.94, 95% CI 0.76-1.17, p=0.58)
• Conclusion: Routine stenting not beneficial for atherosclerotic RAS

ASTRAL Trial (2009): [6]

• Design: RCT, 806 patients with atherosclerotic RAS
• Intervention: Revascularisation + medical therapy vs medical therapy alone
• Primary outcome: Renal function (creatinine)
• Result: No significant difference in renal function, BP, or cardiovascular events
• Conclusion: Revascularisation provides no additional benefit over medical therapy

Revascularisation Techniques

Percutaneous Transluminal Renal Angioplasty (PTRA):

• Technique: Balloon dilatation of stenotic segment
• Use: First-line for FMD (no stent needed)
• Success rate in FMD: Technical success > 95%; clinical improvement (cure/improvement HTN) 60-80% [15,18]
• Atherosclerotic RAS: High restenosis rate (30-50%) without stenting

Renal Artery Stenting:

• Technique: PTRA followed by stent deployment
• Use: Atherosclerotic ostial lesions (elastic recoil prevention)
• Success rate: Technical success > 95%; clinical benefit limited per CORAL [7]
• Restenosis rate: 10-20% at 6-12 months
• Not recommended: Routine use in atherosclerotic RAS (CORAL/ASTRAL evidence)

Surgical Revascularisation:

• Techniques: Aorto-renal bypass, renal artery endarterectomy, extra-anatomic bypass
• Indications: Complex anatomy unsuitable for endovascular approach, failed PTRA/stenting, concurrent aortic surgery
• Rarely performed: Endovascular techniques have largely replaced surgical options
• Morbidity: Higher than endovascular; reserved for exceptional cases

Complications of Revascularisation

Management of Specific Presentations

Flash Pulmonary Oedema (Pickering Syndrome)

Acute Management:

1. Oxygen: High-flow to maintain SpO₂ > 94%
2. CPAP/NIV: If respiratory distress
3. IV diuretics: Furosemide 40-80 mg IV bolus, then infusion if needed
4. IV nitrates: GTN infusion for afterload reduction
5. Blood pressure control: IV agents (labetalol, hydralazase) - avoid over-aggressive lowering
6. Monitor fluid balance: Strict input/output

Long-Term Management:

• Medical optimisation: CCBs, beta-blockers, diuretics (AVOID ACEi/ARB)
• Fluid restriction: 1.5 L/day
• Sodium restriction: less than 6 g/day
• Consider revascularisation: If recurrent episodes despite medical therapy [10]
• Imaging: Confirm bilateral RAS (CTA/MRA)

Fibromuscular Dysplasia

First-Line: Percutaneous angioplasty (NO stent)

• Success rate: 60-80% cure or improvement in hypertension [15,18]
• Technique: Balloon angioplasty alone; stenting reserved for complications (dissection, elastic recoil)
• Outcomes: Excellent long-term patency (> 90% at 5 years)

Medical therapy: If angioplasty unsuccessful or not suitable

• Standard antihypertensive therapy
• Lower threshold for ACEi/ARB (less risk than atherosclerotic bilateral disease)

Screening for associated FMD:

• Cervical artery imaging: MRA neck - FMD in 40-50% of renal FMD patients [18]
• Intracranial aneurysm screening: MRA brain - 7-10% prevalence

Acute Kidney Injury on ACEi/ARB

Immediate Management:

1. Stop ACEi/ARB immediately
2. Assess volume status: IV fluids if hypovolaemic; diuretics if volume overloaded
3. Monitor U&E: Daily until stabilisation
4. Exclude other causes: Obstruction (ultrasound), acute tubular necrosis, interstitial nephritis

Investigation:

• Renal imaging: Duplex US/CTA/MRA to assess for bilateral RAS
• If bilateral RAS confirmed → avoid ACEi/ARB long-term

Definitive Management:

• Bilateral RAS: Medical therapy without ACEi/ARB; consider revascularisation if progressive
• Unilateral RAS: May cautiously re-trial ACEi/ARB after renal function stabilisation

Special Populations

Pregnancy

• RAS is a rare cause of hypertension in pregnancy
• Avoid: ACEi/ARB (teratogenic), statins
• Safe antihypertensives: Labetalol, nifedipine, methyldopa
• Delivery planning: Severe HTN may necessitate early delivery

Chronic Kidney Disease (Advanced)

• Contrast caution: High risk of contrast-induced nephropathy
• Revascularisation: Unlikely to benefit if advanced irreversible parenchymal disease (RI > 0.80) [14]
• Medical therapy: Avoid ACEi/ARB in bilateral disease; careful BP management

Elderly and Frail

• Medical therapy preferred: Higher procedural risk
• BP targets: Individualised - avoid over-aggressive lowering
• Polypharmacy: Simplify regimen for adherence

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10. Complications

Complications of Untreated/Undertreated RAS

Complications of Medical Therapy

Complications of Revascularisation

Procedure-Related (see section 9):

• Renal artery dissection: 2-5%
• Contrast-induced nephropathy: 5-15%
• Atheroembolic disease: 2-5%
• Access site complications: 2-10%

Late Complications:

• Restenosis: 10-20% within 6-12 months
• Stent fracture: 2-5%
• No clinical benefit in most atherosclerotic RAS patients (CORAL/ASTRAL) [6,7]

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11. Prognosis & Outcomes

Natural History

Atherosclerotic RAS

• Progression: 50% of stenoses progress over 5 years [2]
• Severe stenosis (> 60%): 5-10% progress to complete occlusion
• Renal function: Slow decline in many patients; 10-15% develop ESRD
• Cardiovascular events: High risk - 20-30% 5-year event rate (MI, stroke, death) due to systemic atherosclerosis

Fibromuscular Dysplasia

• Progression: Rarely progressive; most remain stable [18]
• Renal function: Usually preserved
• Hypertension: Persists if untreated; excellent response to angioplasty (60-80% cure/improvement) [15]

Outcomes with Medical Therapy

CORAL Trial Results (medical therapy arm): [7]

• Blood pressure control: Achieved in majority with median 3 antihypertensive drugs
• Renal function: Stable in 50%; slow decline in 30%; rapid decline in 20%
• Cardiovascular events: 15% 5-year event rate (similar to stenting arm)
• Survival: 88% 5-year survival

Key Message: Optimal medical therapy achieves satisfactory outcomes in most patients with atherosclerotic RAS.

Outcomes with Revascularisation

Fibromuscular Dysplasia

• Technical success: > 95% for PTRA [15,18]
• Clinical success: 60-80% cure or significant improvement in hypertension
• Complete cure: 30-40%
• Improved but still requires medication: 30-40%
• No benefit: 20-30%
• Patency: > 90% long-term patency (5 years)
• Renal function: Usually preserved or improved

Atherosclerotic RAS

• Technical success: > 95% for stenting
• Clinical benefit: CORAL trial showed NO significant benefit vs medical therapy alone [7]
• Blood pressure: Minimal additional BP reduction over medical therapy
• Renal function: No improvement; similar decline to medical therapy alone
• Cardiovascular events: No reduction vs medical therapy
• Restenosis: 10-20% at 6-12 months

CORAL Primary Outcome: [7]

• Renal artery stenting + medical therapy: 35.1% event rate
• Medical therapy alone: 35.8% event rate
• HR 0.94 (95% CI 0.76-1.17), p=0.58 - NO SIGNIFICANT DIFFERENCE

Prognostic Factors

Favourable Prognosis

• Unilateral disease
• Fibromuscular dysplasia
• Young age
• Normal baseline renal function
• Kidney size > 9 cm
• Resistive index less than 0.80
• No proteinuria

Poor Prognosis

• Bilateral disease or solitary kidney with RAS
• Atherosclerotic aetiology
• Elderly with comorbidities
• Baseline CKD (eGFR less than 30 mL/min)
• Small kidneys (less than 8 cm) - irreversible parenchymal damage
• Resistive index > 0.80 - predicts poor response to revascularisation [14]
• Proteinuria > 1 g/day
• Severe calcification

Renal Survival

Cardiovascular Outcomes

Patients with RAS have high cardiovascular risk due to:

• Systemic atherosclerosis (if atherosclerotic aetiology)
• Chronic hypertension and LVH
• Chronic kidney disease
• Endothelial dysfunction

5-Year Cardiovascular Event Rate: 20-30% (MI, stroke, cardiovascular death) [2,7]

Risk Reduction: Optimal medical therapy (statins, antiplatelets, BP control, smoking cessation) is essential.

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12. Prevention & Screening

Primary Prevention (Atherosclerotic RAS)

As RAS is predominantly a manifestation of systemic atherosclerosis, primary prevention targets cardiovascular risk factors:

1. Smoking cessation: Most important modifiable risk factor
2. Hypertension control: Target less than 130/80 mmHg
3. Lipid management: Statins for high-risk patients (QRISK > 10%)
4. Diabetes control: HbA1c less than 53 mmol/mol (7%)
5. Healthy lifestyle: Mediterranean diet, regular exercise, weight management
6. Antiplatelet therapy: In established cardiovascular disease

Secondary Prevention

For patients with diagnosed RAS:

1. Cardiovascular risk reduction: Statin, aspirin, BP control, smoking cessation
2. Monitor renal function: 3-6 monthly U&E, eGFR, urinalysis
3. Slow progression: Optimal medical therapy slows stenosis progression
4. Screen for other vascular beds: Carotid Doppler, peripheral pulses, ECG

Screening for RAS

Who to screen:

1. Resistant hypertension: Uncontrolled BP on ≥3 drugs including diuretic
2. Flash pulmonary oedema: Recurrent unexplained APO
3. Onset of hypertension: Age less than 30 or > 55 years
4. Acute kidney injury: On ACEi/ARB initiation (> 30% creatinine rise)
5. Unexplained renal impairment: Progressive CKD without clear cause
6. Abdominal bruit: Systolic-diastolic bruit in hypertensive patient
7. Known atherosclerotic disease: PAD, CAD, AAA - particularly if resistant HTN

Screening modality:

• First-line: Duplex ultrasound (if expertise available) or CTA/MRA (depending on renal function)
• Second-line: Renal angiography if high suspicion and non-invasive tests inconclusive

Who NOT to screen:

• Well-controlled hypertension on 1-2 drugs
• No clinical features suggesting RAS
• Advanced CKD unlikely to benefit from intervention (eGFR less than 20, small kidneys less than 8 cm, RI > 0.80)

Screening for FMD-Associated Conditions

In patients with renal artery FMD, screen for:

1. Cervical artery FMD: MRA neck - present in 40-50% [18]
2. Intracranial aneurysms: MRA brain - present in 7-10%
3. Other vascular beds: Carotid, vertebral, iliac arteries

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13. Key Guidelines & Evidence

Major Society Guidelines

AHA/ACC 2017 Key Points: [1]

• Optimal medical therapy is recommended for all patients with RAS
• Revascularisation NOT routinely recommended for atherosclerotic RAS (Class III, Level of Evidence A)
• Revascularisation may be considered for:
  • Recurrent flash pulmonary oedema (Class IIa, Level of Evidence B)
  • Rapidly progressive CKD with bilateral RAS (Class IIb, Level of Evidence C)
  • Fibromuscular dysplasia with haemodynamically significant stenosis (Class I, Level of Evidence B)

Landmark Trials

CORAL Trial (Cardiovascular Outcomes in Renal Atherosclerotic Lesions): [7]

• Design: Multicentre RCT, 947 patients, median follow-up 43 months
• Population: Atherosclerotic RAS ≥60% stenosis + HTN on ≥2 drugs or CKD (eGFR 20-90 mL/min)
• Intervention: Renal artery stenting + medical therapy vs medical therapy alone
• Primary outcome: Composite of cardiovascular death, MI, stroke, HF hospitalisation, progressive renal insufficiency, need for renal replacement therapy
• Results:
  • "Primary outcome: 35.1% (stenting) vs 35.8% (medical), HR 0.94 (95% CI 0.76-1.17), p=0.58"
  • No difference in BP control, renal function, or mortality
• Conclusion: Routine stenting provides NO additional benefit over optimal medical therapy alone

ASTRAL Trial (Angioplasty and Stenting for Renal Artery Lesions): [6]

• Design: Multicentre RCT, 806 patients, median follow-up 34 months
• Population: Atherosclerotic RAS
• Intervention: Revascularisation (PTRA ± stenting) + medical therapy vs medical therapy alone
• Primary outcome: Renal function (serum creatinine)
• Results:
  • No significant difference in creatinine, BP, cardiovascular events, or mortality
  • Higher complication rate in revascularisation group
• Conclusion: Revascularisation provides no benefit over medical therapy

Systematic Reviews and Meta-Analyses

• Cochrane Review (2014): Revascularisation vs medical therapy for RAS - no benefit in BP, renal function, or cardiovascular outcomes [2]
• Meta-analysis of RCTs: Consistent finding that routine revascularisation does not improve outcomes in atherosclerotic RAS [2]

Evidence Summary

Strong Evidence (Level I):

• Optimal medical therapy is first-line for atherosclerotic RAS (CORAL, ASTRAL)
• Routine revascularisation does NOT improve outcomes in atherosclerotic RAS (CORAL, ASTRAL)
• Statins reduce cardiovascular events in atherosclerotic disease
• Smoking cessation slows atherosclerotic progression

Moderate Evidence (Level II):

• Percutaneous angioplasty is effective for FMD (observational studies, registries)
• Flash pulmonary oedema may benefit from revascularisation (observational data)
• Resistive index > 0.80 predicts poor response to revascularisation

Weak Evidence (Level III-IV):

• Rapidly progressive CKD may benefit from revascularisation (case series)
• Acute renal artery occlusion may benefit from urgent revascularisation (case reports)

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14. Exam-Focused Sections

Common Exam Questions

Written Exams (MCQ/SBA)

1. What percentage of renal artery stenosis cases are caused by atherosclerosis?

   • Answer: 90%

2. What is the gold standard imaging modality for diagnosing renal artery stenosis?

   • Answer: Renal angiography (selective catheter angiography)

3. What is the typical presentation of flash pulmonary oedema in renal artery stenosis?

   • Answer: Recurrent, sudden-onset APO with preserved ejection fraction, associated with bilateral RAS

4. According to the CORAL trial, what is the first-line management of atherosclerotic RAS?

   • Answer: Optimal medical therapy (statins, antiplatelets, BP control)

5. What percentage of patients with fibromuscular dysplasia achieve cure or improvement of hypertension with percutaneous angioplasty?

   • Answer: 60-80%

6. What investigation finding suggests bilateral RAS or RAS in a solitary kidney?

   • Answer: Acute rise in creatinine (> 30%) after starting ACE inhibitor or ARB

7. What resistive index on Duplex ultrasound predicts poor response to revascularisation?

   • Answer: > 0.80

8. What is the classic angiographic appearance of FMD?

   • Answer: "String of beads"

• alternating stenosis and aneurysmal dilatation in mid-distal renal artery

Clinical Scenarios (PACES/OSCE)

Scenario 1: Elderly man with resistant hypertension and abdominal bruit

• Diagnosis: Atherosclerotic RAS
• Investigations: Duplex US/CTA, U&E, lipids
• Management: Medical therapy first-line (statins, antiplatelets, BP control); consider imaging for confirmation

Scenario 2: Young woman with new-onset hypertension and epigastric bruit

• Diagnosis: Fibromuscular dysplasia
• Investigations: MRA (preferred in young patient - no radiation)
• Management: Percutaneous angioplasty (curative in 60-80%)

Scenario 3: Patient with recurrent flash pulmonary oedema and hypertension

• Diagnosis: Bilateral RAS (Pickering syndrome)
• Investigations: CTA/MRA to confirm bilateral disease
• Management: Medical therapy optimisation; consider revascularisation if recurrent despite optimal Rx

Viva Points

Opening Statement: "Renal artery stenosis is a narrowing of one or both renal arteries, leading to renal hypoperfusion and activation of the renin-angiotensin-aldosterone system, causing secondary hypertension. It is the most common cause of secondary hypertension, accounting for 1-5% of all cases. The two principal aetiologies are atherosclerosis (90%) and fibromuscular dysplasia (10%)."

Key Facts to Mention:

• Prevalence: 1-5% general hypertensive population; 10-20% resistant hypertension
• Pathophysiology: Renal hypoperfusion → RAAS activation → hypertension and volume overload
• Clinical clues: Resistant HTN, onset less than 30 or > 55 years, abdominal bruit, flash pulmonary oedema, AKI on ACEi
• Investigations: Duplex US/CTA/MRA screening; angiography gold standard
• Haemodynamic significance: ≥60-70% stenosis
• Management paradigm shift: CORAL trial (2014) - medical therapy first-line for atherosclerotic RAS
• Medical therapy: Statins, antiplatelets, BP control (CCB, beta-blockers, diuretics); AVOID ACEi/ARB in bilateral disease
• Revascularisation: FMD - excellent response (60-80%); atherosclerotic - no benefit in most (CORAL/ASTRAL)
• Exceptions for revascularisation: Flash pulmonary oedema, rapidly progressive CKD, FMD

Common Follow-Up Questions:

1. "Why doesn't stenting work for atherosclerotic RAS?"

   • Answer: CORAL and ASTRAL trials showed no benefit. Likely because the problem is not just the stenosis but the underlying ischaemic nephropathy with irreversible parenchymal damage (fibrosis, glomerulosclerosis). Opening the artery doesn't reverse established kidney damage. Additionally, patients have systemic atherosclerosis, so cardiovascular risk remains high regardless of local intervention.

2. "When would you consider revascularisation?"

   • Answer: Selected cases only: (1) Fibromuscular dysplasia - first-line treatment; (2) Recurrent flash pulmonary oedema despite medical therapy; (3) Rapidly progressive CKD with bilateral RAS despite optimal medical therapy; (4) Acute kidney injury in bilateral disease or solitary kidney.

3. "Why do ACE inhibitors cause renal failure in bilateral RAS?"

   • Answer: In RAS, GFR is maintained by efferent arteriolar vasoconstriction mediated by angiotensin II, which increases intraglomerular pressure. ACE inhibitors block angiotensin II formation, causing efferent arteriolar dilatation, reducing intraglomerular pressure, and acutely dropping GFR. In bilateral disease, both kidneys are affected, leading to acute renal failure.

4. "What is flash pulmonary oedema and why does it occur?"

   • Answer: Flash pulmonary oedema (Pickering syndrome) is sudden-onset pulmonary oedema in bilateral RAS. It occurs because: (1) Bilateral RAS → unopposed RAAS activation → volume expansion without escape mechanism; (2) Severe hypertension → increased LV afterload → diastolic dysfunction; (3) Rapid fluid shift to alveolar space. Characteristic features are recurrent episodes and preserved ejection fraction.

5. "What imaging would you request and why?"

   • Answer: First-line: Duplex ultrasound (non-invasive, no contrast/radiation) or CTA (excellent sensitivity/specificity, fast) or MRA (no radiation, good for FMD). Choice depends on local expertise and renal function. CTA preferred if good renal function and atherosclerotic suspected. MRA preferred for FMD (young patients, "string of beads" well visualised). Duplex if CKD (avoid contrast). Gold standard: Renal angiography - reserved for patients where revascularisation planned.

Common Mistakes to Avoid

❌ Mistake 1: Routinely recommending revascularisation for atherosclerotic RAS

• Correct: Medical therapy is first-line (CORAL evidence); revascularisation only in selected cases

❌ Mistake 2: Using ACE inhibitors in bilateral RAS

• Correct: AVOID ACEi/ARB in bilateral RAS or solitary kidney (risk of acute renal failure)

❌ Mistake 3: Missing flash pulmonary oedema as presentation of bilateral RAS

• Correct: Recurrent APO with preserved EF → think bilateral RAS (Pickering syndrome)

❌ Mistake 4: Not screening high-risk populations (resistant HTN, flash APO, AKI on ACEi)

• Correct: High index of suspicion in specific populations; screen with non-invasive imaging

❌ Mistake 5: Treating FMD the same as atherosclerotic RAS

• Correct: FMD responds excellently to angioplasty (60-80%); atherosclerotic RAS benefits from medical therapy

❌ Mistake 6: Forgetting to measure both arms' BP and examine peripheral pulses

• Correct: Assess for diffuse atherosclerotic disease (carotid bruit, absent pulses, BP asymmetry)

❌ Mistake 7: Ordering gadolinium MRA in severe CKD (eGFR less than 30)

• Correct: Risk of nephrogenic systemic fibrosis; use non-contrast MRA or alternative imaging

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15. Patient / Layperson Explanation

For Patients

What is renal artery stenosis?

Renal artery stenosis is a narrowing of the blood vessels (arteries) that supply blood to your kidneys. When your kidneys don't receive enough blood, they release hormones that raise your blood pressure. This creates a vicious cycle: narrowed arteries → less blood to kidneys → hormones released → high blood pressure.

Why does this happen?

There are two main causes:

1. Atherosclerosis (fatty deposits) - This is the most common cause (9 out of 10 cases). It's the same process that causes heart attacks and strokes. Fatty material builds up in the artery walls, narrowing them. This typically affects older people (over 55 years) who smoke, have diabetes, high cholesterol, or other blood vessel problems.

2. Fibromuscular dysplasia (abnormal artery wall) - This is less common (1 out of 10 cases). The artery wall develops abnormal bands of tissue that narrow the artery. This typically affects younger women (ages 20-50) and has a characteristic "string of beads" appearance on X-rays. The cause is unknown but may be genetic.

What are the symptoms?

Often there are no specific symptoms - many people are diagnosed when their doctor investigates high blood pressure. Clues that might suggest renal artery stenosis include:

• High blood pressure that's hard to control even with multiple medications
• Sudden episodes of fluid on the lungs (flash pulmonary oedema) - you wake up at night gasping for breath
• Worsening kidney function, especially after starting certain blood pressure medications (ACE inhibitors or ARBs)
• New high blood pressure at an unusual age (under 30 or over 55 years)
• Whooshing sound (bruit) in your abdomen when the doctor listens with a stethoscope

How is it diagnosed?

Your doctor will first assess your risk and symptoms. If renal artery stenosis is suspected:

1. Blood tests: Check kidney function, potassium levels
2. Ultrasound scan (Duplex ultrasound): Uses sound waves to look at blood flow in your kidney arteries - painless, no needles or dye
3. CT or MRI scan (CTA or MRA): More detailed pictures of your kidney arteries using X-rays or magnets - may need dye injection
4. Angiogram: The most accurate test - a thin tube is inserted into an artery (usually in your groin or wrist) and dye is injected to take detailed X-rays. This is reserved for cases where treatment is being considered.

How is it treated?

Treatment depends on the cause and how severe it is.

For atherosclerosis (fatty deposits) - the most common type:

Modern research (CORAL and ASTRAL trials) has shown that medication is just as good as procedures for most people. So the first-line treatment is:

1. Blood pressure tablets: You'll likely need 3-4 different types (e.g., calcium channel blockers like amlodipine, diuretics like indapamide, beta-blockers like bisoprolol). Important: ACE inhibitors (like ramipril) and ARBs (like losartan) may worsen kidney function if you have narrowing in both kidney arteries, so your doctor will monitor you closely.

2. Cholesterol tablets (statins): To slow down the fatty deposit build-up

3. Aspirin: A blood thinner to protect your heart and blood vessels

4. Lifestyle changes:

   • Stop smoking (most important!)
   • Healthy diet (low salt, Mediterranean-style)
   • Regular exercise
   • Weight loss if overweight
   • Control diabetes if you have it

Balloon/stent procedure: Only recommended in specific situations:

• Recurrent flash pulmonary oedema (fluid on lungs)
• Rapidly worsening kidney function despite medication
• Fibromuscular dysplasia (see below)

For fibromuscular dysplasia:

Balloon angioplasty is the preferred treatment. This involves:

• A thin tube (catheter) inserted into an artery (usually your groin)
• A balloon is inflated to widen the narrowed artery
• No stent is usually needed
• Success rate: 6-8 out of 10 people have their blood pressure cured or greatly improved

What's the outlook?

With good treatment, most people do well:

• Atherosclerosis: Blood pressure can be controlled with medication in most people. Kidney function often stays stable or declines slowly. You'll need regular monitoring (blood tests every 3-6 months, blood pressure checks).

• Fibromuscular dysplasia: Excellent outlook, especially with angioplasty. The condition usually doesn't get worse over time.

Important: Renal artery stenosis is often part of wider blood vessel disease (if caused by atherosclerosis), so protecting your heart, brain, and other organs with medication and lifestyle changes is crucial.

Questions to ask your doctor:

1. Which type of renal artery stenosis do I have?
2. Is it affecting one kidney or both?
3. What are my treatment options?
4. How often do I need monitoring?
5. Can I take ACE inhibitors or ARBs safely?
6. Am I suitable for a balloon procedure?

Living with renal artery stenosis:

• Take medications as prescribed
• Monitor your blood pressure at home
• Attend regular check-ups
• Maintain a healthy lifestyle
• Report any new symptoms (sudden breathlessness, swelling, reduced urine output)

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