What is the mechanism of secondary hypertension?

Mechanisms of Secondary Hypertension

Secondary hypertension occurs in approximately 10% of hypertension cases and is characterized by specific identifiable underlying causes that lead to elevated blood pressure through distinct pathophysiological mechanisms. 1

Primary Pathophysiological Mechanisms

Secondary hypertension can arise from various mechanisms depending on the underlying cause:

Endocrine Mechanisms

• Primary Aldosteronism: Excessive aldosterone production leads to sodium and water retention, potassium excretion, and subsequent blood pressure elevation 1
• Pheochromocytoma: Catecholamine excess causes vasoconstriction and increased cardiac output 1
• Cushing's Syndrome: Cortisol excess enhances vascular sensitivity to vasoconstrictors and promotes sodium retention 1
• Thyroid Disorders: Hyperthyroidism increases cardiac output and systolic blood pressure 1
• Hyperparathyroidism: Elevated calcium levels lead to vasoconstriction 1

Renal Mechanisms

• Renovascular Disease: Renal artery stenosis activates the renin-angiotensin-aldosterone system, causing vasoconstriction and sodium retention 1
• Renal Parenchymal Disease: Impaired sodium excretion, activation of the renin-angiotensin-aldosterone system, and increased sympathetic activity 1

Other Mechanisms

• Obstructive Sleep Apnea: Intermittent hypoxia activates sympathetic nervous system and causes endothelial dysfunction 1
• Medication/Substance-Induced: Various mechanisms including sodium retention (NSAIDs, corticosteroids), sympathetic activation (decongestants), and direct vasoconstriction 1
• Coarctation of Aorta: Mechanical obstruction increases pressure proximal to the narrowing 1

Clinical Indicators Suggesting Secondary Hypertension

• Early onset hypertension (before age 20) 2
• Late onset hypertension (after age 50) 2
• Severe or resistant hypertension requiring multiple medications 1
• Sudden deterioration in previously controlled blood pressure 1
• Target organ damage disproportionate to hypertension duration 1
• Specific clinical features (hypokalemia, abdominal bruits) 1, 2

Diagnostic Approach

Screening tests for secondary hypertension should include:

• Basic screening:

  • Blood tests: electrolytes, renal function, thyroid function, glucose 1
  • Urinalysis and urinary albumin-to-creatinine ratio 1
  • 12-lead ECG 1

• Specific testing based on suspected cause:

  • Plasma aldosterone/renin ratio for primary aldosteronism 1
  • Renal imaging for parenchymal disease or renovascular disease 1
  • Sleep studies for obstructive sleep apnea 1
  • Hormone testing for endocrine disorders 1

Treatment Principles

Treatment should target the underlying cause whenever possible:

• Endocrine causes: Surgical intervention (adrenalectomy) or specific medications (mineralocorticoid receptor antagonists) 1
• Renovascular disease: Angioplasty for fibromuscular dysplasia, medical therapy for atherosclerotic disease 1
• Obstructive sleep apnea: CPAP therapy, weight loss 1
• Medication-induced: Discontinuation of offending agents 1

Common Pitfalls to Avoid

• Failing to screen appropriate patients for secondary causes 1
• Continuing medications that contribute to hypertension 1
• Inadequate dosing of diuretics in resistant hypertension 1
• Not referring complex cases to specialists 1

Secondary hypertension, while less common than essential hypertension, represents an important subset of cases where identifying and addressing the underlying cause can significantly improve blood pressure control and reduce cardiovascular risk.