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How can hypertension is related to... Um, uh... Hypertróphy of the cardiac muscle. Yes.

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Tell me about hypertension and how it's caused it and what are the mechanism.

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Hypertension means persistently elevated pressure in the systemic arteries. Blood pressure is determined mainly by:
[ \text{Blood pressure} = \text{Cardiac output} \times \text{Systemic vascular resistance} ]
So hypertension develops when the heart pumps more blood, the small arteries become more constricted or stiff, the body retains excess salt and water, or a combination of these occurs.

How normal blood pressure is controlled

  • Short term: Baroreceptors in the carotid sinus and aortic arch sense pressure changes and adjust sympathetic nervous-system activity.
  • Long term: The kidneys regulate salt and water balance. The renin-angiotensin-aldosterone system (RAAS) increases vessel constriction and sodium retention when activated. - Frameworks for Internal Medicine, BP regulation section, lines 7507-7513

What causes hypertension?

1. Primary (essential) hypertension

This accounts for about 90% to 95% of adult cases. There is no single identifiable cause. It results from an interaction between:
  • Family/genetic susceptibility
  • High sodium intake in salt-sensitive people
  • Excess body weight and insulin resistance
  • Physical inactivity
  • Alcohol excess
  • Chronic stress and increased sympathetic activity
  • Aging and arterial stiffness
  • Kidney tendency to retain sodium and water
A central mechanism is that the kidneys may need a higher arterial pressure to excrete enough salt and water. This resets the long-term blood-pressure level upward. - Guyton and Hall Textbook of Medical Physiology, primary hypertension section, pp. 245-246
Mechanism in simple sequence:
Genetic/lifestyle factors
        ↓
Sympathetic activation + kidney sodium retention + RAAS activation
        ↓
More blood volume + vasoconstriction
        ↓
Higher cardiac output and/or higher peripheral resistance
        ↓
Persistent hypertension
Obesity can activate the sympathetic nervous system, including renal sympathetic nerves. This impairs renal salt excretion and contributes to chronic hypertension. - Guyton and Hall Textbook of Medical Physiology, p. 246

2. Secondary hypertension

This is hypertension due to an identifiable underlying condition, sometimes treatable or curable. It affects roughly 5% to 10% of people with hypertension. - Frameworks for Internal Medicine, lines 7474-7485
Important causes include:
  • Kidney disease or renal artery narrowing
  • Primary aldosteronism: excess aldosterone causes sodium and water retention
  • Pheochromocytoma: excess catecholamines cause intense vasoconstriction
  • Thyroid disease, Cushing syndrome, hyperparathyroidism
  • Obstructive sleep apnea
  • Coarctation of the aorta
  • Pregnancy-related hypertension
  • Drugs/substances: NSAIDs, oral contraceptives, glucocorticoids, decongestants/stimulants, cocaine, excess alcohol
Secondary causes are especially considered when hypertension starts young, becomes suddenly severe, is resistant to treatment, or causes early target-organ damage. - Frameworks for Internal Medicine, lines 7488-7497

How hypertension causes cardiac-muscle hypertrophy

This is the connection you asked about earlier.
With systemic hypertension, the left ventricle must pump blood against a persistently higher pressure. This is called increased afterload.
High arterial pressure
        ↓
Left ventricle must generate greater force to eject blood
        ↓
Chronic pressure overload
        ↓
Cardiac muscle cells enlarge
        ↓
Left ventricular hypertrophy (usually concentric)
The muscle thickens initially as an adaptation: a thicker ventricular wall can generate more force and reduce wall stress. But over time it becomes harmful:
  • The ventricle becomes stiff and does not relax well.
  • Filling during diastole is impaired, causing diastolic dysfunction.
  • Oxygen demand rises but blood supply may not keep up, causing demand ischemia.
  • Fibrosis can develop.
  • The patient is at increased risk of heart failure, atrial fibrillation, ventricular arrhythmias, stroke, and sudden cardiac death.
Chronic hypertension causes pressure overload and ventricular hypertrophy, commonly on the left side of the heart. - Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 521
Even prolonged mild hypertension can produce left ventricular hypertrophy. - Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 521
So, the short answer is:
Hypertension increases the work the left ventricle must do. In response, cardiac muscle cells enlarge, causing left ventricular hypertrophy. At first this is compensatory, but later it can lead to a stiff, poorly functioning heart.
Persistent high blood pressure is also a major risk factor for stroke, myocardial infarction, heart failure, and kidney failure. - Frameworks for Internal Medicine, lines 7500-7504
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