Secondary Hypertension

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Diagnosis | Management

Definition

Secondary hypertension is a form of high blood pressure with an identifiable underlying cause, differentiating it from primary (essential) hypertension, which has no clear cause. Secondary hypertension can result from a variety of conditions, including renal disease, endocrine disorders, and certain medications.

Aetiology

Secondary hypertension can be caused by various conditions, including:

• Diabetes Mellitus: Causes damage to the kidney's filtering system, leading to hypertension.
• Polycystic Kidney Disease: Cysts in the kidneys impair normal kidney function, resulting in increased blood pressure.
• Cushing's Syndrome: Excess cortisol production leading to increased blood pressure.
• Phaeochromocytoma: An adrenal gland tumour that causes overproduction of adrenaline and noradrenaline, leading to hypertension.
• Thyroid Disorders: Both hyperthyroidism and hypothyroidism can contribute to elevated blood pressure.
• Hyperparathyroidism: Overproduction of parathyroid hormone causes a rise in calcium levels, leading to increased blood pressure.
• Aortic Coarctation: A congenital narrowing of the aorta that leads to high blood pressure, particularly in the upper body.
• Obstructive Sleep Apnoea: Recurrent episodes of airway obstruction during sleep, causing intermittent hypoxia and increased blood pressure.
• Obesity: Excess body weight increases the workload on the heart and blood vessels, contributing to hypertension.
• Pregnancy: Conditions like pre-eclampsia can cause secondary hypertension during pregnancy.
• Medications: Certain drugs, such as oral contraceptives, NSAIDs, and corticosteroids, can elevate blood pressure.
• Primary Aldosteronism: Overproduction of aldosterone leads to salt and water retention, raising blood pressure.

Pathophysiology

The pathophysiology of secondary hypertension involves increased cardiac output, elevated systemic vascular resistance, or both. The underlying conditions contributing to secondary hypertension often lead to an imbalance in the regulatory mechanisms of blood pressure, such as:

• Renal Dysfunction: Impaired kidney function leads to fluid retention and increased blood pressure.
• Endocrine Disorders: Hormonal imbalances, such as excess cortisol or aldosterone, lead to increased blood pressure through fluid retention and vasoconstriction.
• Vascular Abnormalities: Structural abnormalities like aortic coarctation increase resistance in the arterial system, leading to higher blood pressure.

Risk Factors

Risk factors for secondary hypertension include:

• Existing kidney, artery, heart, or endocrine disorders.
• Obesity and sedentary lifestyle.
• Family history of hypertension or related disorders.
• Use of certain medications (e.g., oral contraceptives, corticosteroids).
• Obstructive sleep apnoea.

Signs and Symptoms

Secondary hypertension may not have distinct symptoms, especially in the early stages. However, when symptoms occur, they can include:

• Headache: Particularly in the mornings and often located at the back of the head.
• Chest Pain: A sign of possible heart strain due to high blood pressure.
• Shortness of Breath: Often related to heart failure or pulmonary congestion.
• Dizziness: Can occur with severe hypertension or associated with fluctuations in blood pressure.
• Visual Disturbances: Such as blurred vision, which can indicate hypertensive retinopathy.

Investigations

Diagnostic investigations for secondary hypertension include:

• Urinalysis: To check for haematuria, proteinuria, or signs of renal dysfunction.
• Urine Albumin:Creatinine Ratio: To assess proteinuria, which can indicate kidney damage.
• Blood Tests: Including HbA1c, U&Es (urea and electrolytes), and lipid profile (cholesterol levels).
• Fundoscopy: To check for hypertensive retinopathy, which indicates the impact of hypertension on the eyes.
• 12-Lead ECG: To assess for signs of left ventricular hypertrophy or other cardiac abnormalities.
• Q-Risk Assessment: To evaluate cardiovascular risk. If the risk is 10% or more, consider starting a statin.
• Imaging: Depending on the suspected cause, imaging studies like renal ultrasound, CT scan, or MRI may be indicated.

Diagnosis

Diagnosis of secondary hypertension involves confirming elevated blood pressure and identifying the underlying cause:

• If clinic blood pressure is between 140/90 mmHg and 180/120 mmHg, arrange 24-hour ambulatory blood pressure monitoring (ABPM) or home blood pressure monitoring (HBPM) to confirm hypertension.
• Classify hypertension into stages based on the following:
  • Stage 1 Hypertension: Home BP ≥135/85 mmHg or ABPM ≥135/85 mmHg.
  • Stage 2 Hypertension: Home BP ≥150/95 mmHg or ABPM ≥150/95 mmHg.
  • Stage 3 Hypertension: Home BP ≥180/120 mmHg or ABPM ≥180/120 mmHg.
• Further tests should be conducted based on the suspected underlying cause to confirm secondary hypertension.

Management

Management of secondary hypertension involves treating the underlying cause and controlling blood pressure through a stepped approach:

1. Lifestyle Modifications

• Encourage weight loss, regular physical activity, a healthy diet (such as the DASH diet), and reduced salt intake.
• Advise smoking cessation and moderation of alcohol consumption.

2. Pharmacological Management

Medications commonly used to manage hypertension include:

• ACE Inhibitors (ACEi): E.g., Ramipril. First-line for patients under 55 years old without diabetes, particularly in non-black populations.
• Angiotensin Receptor Blockers (ARBs): E.g., Losartan. Use if ACE inhibitors are not tolerated (e.g., due to cough).
• Calcium Channel Blockers (CCBs): E.g., Amlodipine. Preferred in patients over 55 years old or those of black African or African-Caribbean descent.
• Thiazide-like Diuretics: E.g., Indapamide. Used if CCBs are not tolerated or as part of combination therapy.
• Beta-blockers: E.g., Bisoprolol. Consider for patients with coexisting conditions such as heart failure or atrial fibrillation.
• Alpha-blockers: E.g., Doxazosin. Used in resistant hypertension or when other medications are not suitable.

3. Stepped Approach to Treatment

Follow the NICE guidelines for a stepped approach to managing hypertension:

• Step 1:
  • Offer an ACEi or ARB if under 55 years old and not of black African or African-Caribbean descent.
  • Offer a CCB if over 55 years old or of black African or African-Caribbean descent.
  • If a CCB is not tolerated, offer a thiazide-like diuretic (e.g., Indapamide).
• Step 2:
  • If BP is not controlled with an ACEi/ARB, add a CCB or thiazide-like diuretic.
  • If BP is not controlled with a CCB, add an ACEi/ARB or thiazide-like diuretic.
• Step 3:
  • If BP is not controlled with two drugs, use a combination of ACEi/ARB + CCB + thiazide-like diuretic.
• Step 4 (Resistant Hypertension):
  • If BP remains uncontrolled, consider adding a fourth antihypertensive, such as a low-dose spironolactone (if potassium is ≤4.5 mmol/L) or an alpha-blocker like doxazosin (if potassium is >4.5 mmol/L).
  • Review patient adherence and consider seeking specialist advice.

References

1. National Institute for Health and Care Excellence (NICE) (2024) Hypertension in adults: diagnosis and management. Available at: https://www.nice.org.uk/guidance/ng136 (Accessed: 26 August 2024).
2. British Hypertension Society (2024) Guidelines for the Management of Hypertension. Available at: https://bhs.org.uk (Accessed: 26 August 2024).
3. British National Formulary (BNF) (2024) Antihypertensive therapy. Available at: https://bnf.nice.org.uk/ (Accessed: 26 August 2024).

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