Coarctation of the aorta as a cause of arterial hypertension. Diagnostic criteria for renovascular arterial hypertension.
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coarctation of the aorta arterial hypertension pathophysiology diagnosis treatment
Harrison's Principles of Internal Medicine, Twenty First Edition
Page 7664
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renovascular hypertension diagnostic criteria renal artery stenosis
Harrison's Principles of Internal Medicine, Twenty First Edition
Page 7693
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Coarctation of the Aorta as a Cause of Arterial Hypertension
Overview
Coarctation of the aorta (CoA) is the most common congenital cardiovascular cause of hypertension, according to Harrison's Principles of Internal Medicine (p. 7664). Its incidence is 1–8 per 1,000 live births. It is usually sporadic but occurs in 35% of children with Turner's syndrome.
Pathophysiology of Hypertension in CoA
Hypertension in CoA arises through two main mechanisms:
- Mechanical obstruction — the narrowing creates a pressure gradient: elevated pressure proximal to the coarctation (upper limbs/head) and reduced pressure distal (lower limbs/renal circulation).
- Neurohormonal activation — reduced renal perfusion distal to the coarctation activates the renin-angiotensin-aldosterone system (RAAS), further sustaining systemic hypertension even after the obstruction is relieved.
Clinical Features & Diagnosis
| Feature | Details |
|---|---|
| Femoral pulses | Diminished and delayed ("radio-femoral delay") |
| Blood pressure gradient | Systolic BP higher in right arm vs. legs; may also differ between right and left arms depending on coarctation location |
| Murmur | Blowing systolic murmur in the posterior left interscapular area |
| Collateral vessels | Rib notching on chest X-ray (from intercostal collaterals); "figure 3" sign of the aortic knuckle |
| Age at presentation | Severe lesions: neonatal/infancy; mild lesions: young adulthood |
Confirmatory imaging:
- Thoracic and abdominal CT angiography — gold standard for anatomy
- MRI/MRA — excellent for anatomy and hemodynamic assessment, avoids radiation
- Echocardiography — Doppler gradient across the coarctation site; also identifies associated defects (bicuspid aortic valve in ~50%)
- Cardiac catheterization — if intervention is planned
Complications
- Persistent/recurrent hypertension after repair — even when anatomically corrected in infancy, up to 30% of patients develop subsequent hypertension and are at risk for accelerated coronary artery disease and cerebrovascular events (Harrison's, p. 7664).
- Aortic dissection or rupture
- Intracranial aneurysm (especially in association with bicuspid aortic valve)
- Heart failure
Treatment
| Approach | Indication |
|---|---|
| Balloon angioplasty ± stenting | Adults and older children; preferred for discrete native or recurrent coarctation |
| Surgical repair | Neonates/infants; complex anatomy |
| Antihypertensive therapy (RAAS blockade) | Adjunct for residual hypertension; ACE inhibitors / ARBs target the neurohormonal component |
Diagnostic Criteria for Renovascular Arterial Hypertension
Definition
Renovascular hypertension (RVH) results from stenosis of one or both renal arteries, most commonly due to:
- Atherosclerosis (~90% of cases; older patients, diffuse vascular disease)
- Fibromuscular dysplasia (FMD) (~10%; young to middle-aged women)
When to Suspect RVH — Clinical Clues
- Resistant hypertension (uncontrolled on ≥3 drugs including a diuretic)
- Severe hypertension with onset before age 30 (FMD) or after age 55 (atherosclerosis)
- Sudden-onset or rapidly accelerating hypertension
- Flash pulmonary edema without clear cardiac cause
- Unexplained deterioration in renal function — especially acute rise in creatinine after starting an ACE inhibitor or ARB (bilateral RAS or RAS in a solitary kidney)
- Abdominal bruit (epigastric/flank)
- Asymmetric kidney size (>1.5 cm difference)
- Diffuse atherosclerosis in other vascular beds
Diagnostic Work-up
1. Functional/Biochemical Tests
| Test | Comment |
|---|---|
| Plasma renin activity (PRA) | Elevated in many cases but unreliable — affected by timing, medications, sodium intake; does NOT reliably predict response to revascularization (Harrison's, p. 7693) |
| Captopril-stimulated PRA | Historical; superseded by imaging |
| Captopril renography | Scintigraphy showing asymmetric perfusion after ACE inhibition; moderate sensitivity/specificity |
Activation of the renin-angiotensin system is a key pathogenic step, but it is transient — renin levels therefore cannot be relied upon alone for diagnosis (Harrison's, p. 7693).
2. Non-Invasive Vascular Imaging
| Modality | Key Criteria / Comments |
|---|---|
| Doppler Renal Ultrasound | Peak systolic velocity (PSV) >200 cm/s predicts hemodynamically significant stenosis (>60% lumen occlusion); some trials require >300 cm/s to reduce false positives. Renal Resistive Index (RRI) predicts kidney viability. Operator- and institution-dependent. (Harrison's, p. 7693) |
| CT Angiography (CTA) | High sensitivity/specificity for anatomic stenosis; excellent spatial resolution; requires iodinated contrast (caution in CKD) |
| MR Angiography (MRA) | Avoids ionizing radiation; gadolinium-based contrast (caution: nephrogenic systemic fibrosis in advanced CKD); good for FMD detection |
| Captopril Renal Scintigraphy | Functional assessment; asymmetric reduction in tracer uptake post-captopril is suggestive |
3. Invasive (Confirmatory + Therapeutic)
| Modality | Role |
|---|---|
| Catheter-based renal arteriography | Gold standard for anatomy; performed when revascularization is planned |
| Translesional pressure gradient | Gradient >20 mmHg (mean) or >10% systolic at rest = hemodynamically significant |
| Fractional flow reserve (FFR) | Used in some centers to confirm functional significance |
Diagnostic Criteria Summary
A diagnosis of renovascular hypertension requires:
- Hypertension (often resistant or of the characteristics above)
- Anatomically significant renal artery stenosis (≥60–70% luminal narrowing on imaging, or PSV >200–300 cm/s on Doppler)
- Evidence of functional significance (lateralizing renin, asymmetric renal function, positive captopril renography, or pressure gradient at catheterization)
- Improvement in BP or renal function after revascularization (retrospective confirmation)
Management Implications
- FMD — percutaneous transluminal angioplasty (PTA) without stenting is the treatment of choice; excellent response.
- Atherosclerotic RAS — medical therapy (RAAS blockade, statins, antiplatelet) is first-line for most; revascularization reserved for resistant hypertension, flash pulmonary edema, or deteriorating renal function (CORAL and ASTRAL trials showed no benefit of routine stenting).
- Bilateral RAS / solitary kidney — ACE inhibitors and ARBs must be used cautiously (risk of acute kidney injury); monitor closely.
Sources: Harrison's Principles of Internal Medicine, 21st Edition, pp. 7664, 7693.
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