Understanding Secondary Hypertension

Hypertension, or persistent high blood pressure (BP), is a major risk factor for the development of cardiovascular (CV) complications such as stroke, coronary heart disease, and kidney damage. It leads to premature disability and death, and in Singapore, 23 people die from cardiovascular disease every day. Furthermore, over one in three Singaporeans between the ages of 18 and 74 suffer from hypertension. The association between hypertension and the risk of CV events has been consistently demonstrated across age groups and ethnicities, extending from high BP levels to relatively low levels.

What is Secondary Hypertension?

Primary hypertension is the most common type of high BP that develops due to lifestyle factors such as diet, exercise and stress. Secondary hypertension is caused by an underlying medical condition or factor that is often linked to identifiable causes affecting the kidneys, arteries, heart, or endocrine (hormonal) system.

Common Causes of Secondary Hypertension

Several conditions can lead to secondary hypertension, the most common of
which include:

• Kidney problems
  Examples include chronic kidney disease, renal artery stenosis (narrowing of the arteries supplying the kidneys), and congenital polycystic kidney disease.
• Obstructive Sleep Apnonea
  A sleep disorder in which there is interrupted breathing during sleep, leading to reduced oxygen intake and increased BP.
• Congenital Heart Defects
  Some heart defects present at birth, such as coarctation of the aorta (a narrowing of the main artery supplying arterial blood to the body), can cause hypertension.
• Hormonal Disease
  Disorders such as primary aldosteronism (excessive production of the aldosterone hormone by the adrenal glands), pheochromocytoma (a rare adrenal gland tumor), and hyperthyroid disorders (where there is excessive production of the thyroid hormone) can also cause secondary hypertension.
• Medication and Substance Abuse
  Certain medications, like nonsteroidal anti-inflammatory drugs (NSAIDs), nasal (nose) decongestants, and even excessive consumption of alcohol or overuse of illegal drugs, can raise BP.

Who is More Susceptible to Secondary Hypertension?

Secondary hypertension is more likely to be present in the following situations:

• Resistant hypertension – the persistence of hypertension despite the concurrent use of adequate doses of three antihypertensive medication from different classes, including a diuretic
• An acute rise in BP in an individual with previously stable levels
• An individual under 30 years old who does not have a family history of hypertension and has no other risk factors for hypertension
• Malignant or accelerated hypertension, i.e., patients with severe hypertension and signs of end-organ damage such as retinal hemorrhages, papilledema, heart failure, neurologic disturbances, or acute kidney injury
• Young age of onset (less than 30 years old)

Detecting Secondary Hypertension

To determine if an individual has secondary hypertension, a routine clinical evaluation should be conducted. This process includes the following:

• Understanding the individual’s clinical and family history
• A full standard physical examination
• Laboratory investigations, including: a. Urinalysis for haematuria/albumin and testing for albuminuria b. Measurement of serum concentrations of electrolytes (sodium, potassium, calcium, chloride, bicarbonate) creatinine, urea, eGFR (calculated glomerular filtration rate), fasting glucose and fasting lipids (cholesterol, triglycerides)
• 12-lead ECG
• Chest x-ray

These individuals should also undergo a thorough medical evaluation, which may include blood tests, imaging studies (such as ultrasound or CT scans), and sometimes specialised tests to evaluate hormone levels or kidney function.

How should Secondary Hypertension be Treated?

The treatment of secondary hypertension focuses on addressing the underlying cause. This could involve medication to control BP, treating the primary condition (such as surgery for renal artery stenosis or addressing sleep apnea), or adjusting medications that may be contributing to high BP.

Individuals with or suspected to have secondary hypertension may be referred to a hypertension specialist or clinic, particularly if they:

• Have conditions needing emergency or urgent treatment, e.g., malignant hypertension, hypertensive heart failure, or other impending complications
• Have hypertension that is difficult to manage, e.g., unusual fluctuating BP, or resistant hypertension
• Are pregnant
• Are a young child
• Require further tests, treatment or surgery, e.g., removal of an adrenal tumour, corrective surgery for the narrowing of the aorta, or continuous positive airway pressure (CPAP) therapy for sleep apnoea

By understanding secondary hypertension and its underlying causes, you can take an active role in your health. Early diagnosis and treatment of the root cause can significantly improve BP control and reduce your risk of future complications.

Article is contributed by Dr Low Lip Ping, Chairman Emeritus of the Singapore Heart Foundation, and Consultant Cardiologist at the Mt Elizabeth Medical Centre.