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A complication of hypertension is a medical consequence of high blood pressure. It can be a condition that develops or an event that occurs. Complications of hypertension can result from either chronic or acute sustained elevations of blood pressure. They consist of initial and secondary manifestations. The initial ones are changes in blood vessels and/or tissue of the heart. The secondary ones are adverse effects in the tissues of organs where the changes in blood vessels occur. The reason for those changes is alterations in blood flow.
Pathogenesis of complications of hypertension
The various steps in the development of the complications of hypertension are complex and not fully known. But the initial event of those involving changes in blood vessels appears to be damage to the endothelium. After that initial damage subsequent changes might be one of the forms of arteriosclerosis or acute mechanical disruption of the wall of an artery(s).
An understanding of the pathogenesis of the complications of hypertension is not clear-cut, nor is it complete. Even though the incidence of complications is less with treatment and control of blood pressure, the risk of them occurring is still greater in a person with hypertension than in a person who does not have it. Such is the case even if both persons have comparable blood pressure levels.
Other facts that belie high pressure in arteries alone as the cause of the complications are the following:
- The arteriosclerotic component of many of the complications and the many risk factors for arteriosclerosis
- The occurrence of the same conditions and events in some individuals who do not have hypertension
Hypertensive target organ damage
A discussion of the complications of hypertension would be remiss without some mention of target organ damage. The term refers to injury to specific organs in the body that is the presumed result of elevated blood pressure.
The main organs affected are the endothelium, heart, brain, kidneys and eyes. Except for certain complications of the heart, the initial injury to blood vessels precedes secondary damage to the organs those blood vessels supply.
The heart is the only organ in which high blood pressure can directly affect its tissues without causing blood vessel injury first. The presumed reason is the direct connection between the left ventricle and the arteries. Muscle fibers of the heart are under increased tension much like smooth muscle in arteries in a person with hypertension. This might be the case during systole and/or diastole. The increased strain on the muscle cells of the heart appears to be involved in causing damage to the myocardium per se. This explanation is more theory than proven fact at this point in time though. Furthermore, if it is correct, it is probably a simplification.
In fact, some early research has shown that endocardial dysfunction precedes the development of some forms of left ventricular pathology, including LVH – one of the complications of hypertension. The process involves injury to the endocardium followed by a flow of events involving the release of mediators, similar to what happens in the pathogenesis of an atheromatous plaque. This is not surprising inasmuch as endocardial cells are very similar to endothelial cells and since some scholars consider the two to be one and the same.
Complications of hypertension and organ effects
Heart complications of hypertension
Complications of hypertension involving the heart are the major cause of death and morbidity from hypertension. Complications of hypertension affecting the heart can begin in the coronary arteries or the heart muscle per se. When they involve the arteries the outcome is coronary artery disease due to atherosclerosis. Consequences of it can be:
When high blood pressure causes a complication affecting primarily the myocardium (heart muscle) the most common complications are either or a combination of the following:
- Left ventricular systolic dysfunction
- Left ventricular diastolic dysfunction
- Congestive heart failure
- Left ventricular hypertrophy
- Ventricular (originating from the left or right ventricle) arrhythmias
- Sudden death
Brain complications of hypertension
The most common complications of hypertension involving the brain are stroke and impaired cognition. The strokes can be either ischemic or hemorrhagic. Ischemic strokes result from occlusion of an artery in the brain due to atherosclerosis, degenerative small vessel disease or emboli. Hemorrhagic strokes result from the rupture of an artery in the brain. The cognitive impairment might be due to vascular dementia. But there is also an increased incidence of Alzheimer’s disease in people with chronic poorly controlled high blood pressure.
A more acute complication which can occur with malignant hypertension is hypertensive encephalopathy. The pathophysiology is the seepage of fluid into the brain due to breaching of the blood brain barrier by the high blood pressure.
Complications of hypertension affecting the kidneys are common and are rising in prevalence worldwide. The main type is chronic kidney disease. The main form is nephrosclerosis – a term which means hardening of the kidneys. It begins as arteriosclerosis involving the small arteries and afferent arterioles of the kidney. Scarring of the glomeruli and shrinkage of the kidneys often follow. End-stage renal failure is sometimes the end result. Severely elevated blood pressure might lead to acute kidney injury by causing disruptive damage to both blood vessels and glomeruli of the kidneys.
The medical term for complications of hypertension involving the eyes is hypertensive retinopathy. It is damage to the blood vessels in the retinae of the eyes caused by high blood pressure.
There are different stages and degrees of pathology. The first change that usually occurs is vasoconstriction to reduce flow. The first actual pathology develops when the increased pressure causes endothelial damage. Ensuing damage might lead to breaks and leakage of plasma into the vessel walls. Blood clot formation and narrowing of the lumens of vessels might also occur. Depending on the events and the degree of blood pressure elevation any or a combination of the following may result:
- Ischemia to the nerve fibers of the retina resulting in swelling and thickening of the nerves
- Leakage of plasma into the retina
- The formation of exudates due to the accumulation of lipid in the retina
- Retinal hemorrhages from blood seepage
- Microaneurysms – areas of swelling in small vessels due to weakening of their walls
- Retinal artery or vein occlusions
- Swelling and blurring of the margins of the optic nerve
- Damage to the macula (the portion of the retina that enables sharp central vision) from ischemia ± the previously mentioned pathologic processes
Depending on the severity, the end result of hypertensive retinopathy might be a reduction in vision.