The Principles and Basis of Congenital Heart Diseases
Posted: Saturday, July 03, 2010
by Funom Theophilus Makama
D Chosen 1
The exact incidence of congenital heart disease in children is approximately 8:1000 to 10:1000 live births. Congenital heart disease is the major cause of death in the first year (other than premature ones). Depending on the defect, the sexes are affected differently. Heart defects are found in a much higher percentage of stillbirths, spontaneous abortions, and low-birth-weight infants, especially those small for age.
Etiology
The etiology of most congenital heart defects is not known. However, several factors are associated with a higher than normal incidence of the disease. These include prenatal factors such as maternal rubella or other viruses, such as coxsackie-virus, during pregnancy, poor nutrition in the mother, maternal alcoholism, maternal age over 40 years, maternal insulin- dependent diabetes, and maternal ingestion of lithium salts.
Several genetic factors are also implicated in Congenital Heart disease. There is an increased risk of congenital heart disease in the child who has siblings with a heart defect. Has parent with congenital heart disease, has a chromosomal aberration, such as Down's syndrome, or is born with other non-cardiac congenital anomalies.
Types of defects
Congenital heart defects are usually divided into two types, based on the alteration is circulation: acyanotic, in which there is no mixing of un-oxygenated blood in the systemic circulation. Cyanotic; in which un-oxygenated blood enters the systemic circulation, regardless of, if cyanosis is clinically evident.
Clinical manifestations depend on the severity of the defect and the amount of pulmonary blood flow. In acyanotic defects, no associated signs and symptoms may be apparent if the defect is small and the heart is able to compensate for the extra workload.
Altered Hemodynamics
To understand the physiology of heart defects, it is necessary to review the role of pressure gradients and flow resistance to blood circulation. Blood flows as a result of pressure gradients existing in different parts of the body, like any fluid, blood flows from an area of high pressure to one of low pressure. The rate of flow is directly proportional to the pressure gradient (that is, the higher the pressure gradient, the greater the rate of flow) and inversely proportional to the resistance (that is, the higher the resistance, the less the rate of flow). Normally the pressure on the right side of the heart is lower than on the left side, and the resistance in the pulmonary circulation is less than in the systemic circulation. Likewise, vessels entering or exiting from these chambers have corresponding pressures. Therefore, if there is an abnormal connection between the heart chambers, such as a septal defect, blood flows from an area of higher pressure (left side) to one of lower pressure (right side). This directional flow of blood is termed left-to-right shunt. If the hole is small, the amount of blood shunted to the atrium or ventricle may be minimal. In this instance no un-oxygenated blood flows directly into the left side of the heart, therefore, the term acyanotic defect is used.
Severe acyanotic defects are potentially cyanotic as a result of pulmonary vascular changes. Eisenmeng's complex (syndrome) refers to the clinical situation in which a left-to-right shunt becomes a right-to-left shunt because of progressive increase in pulmonary vascular resistance. With increasing pulmonary vascular thickening the resistance in the pulmonary circulation can exceed that in the systemic circulation, causing a reversal of blood flow from the right to the left ventricle.
Cyanotic heart defects may be the result of anomalies that cause a change in pressure so that the blood is shunted from the right to the left side of the heart, hence termed right-to-left shunt, because of either increased pulmonary vascular resistance or obstruction to blood flow through the pulmonic valve/artery. Cyanosis may also occur because of a defect that allows direct communication between the pulmonary and systemic circulations, such as truncus arteriosus or transposition of the great vessels.
There is more to congenital heart defects but a clue such as this is the basis to understanding such anomalies in newly born children.
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Top-level comments on this article: (2 total)this could possibly be a term paper - well thought out and clear. Thanks!
Between 8 and 10 out of a thousand is quite a high incidence. I wonder if it has increased over the past 100 years?
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