The congenital cardiovascular defects make up the largest category of the human congenital malformations, accounting for about 20% of all congenital anomalies observed in liveborn infants. The percentage in stillborns is much higher. The incidence of congenital heart defects (CHD) has been estimated to be 6 to 8 per 1000 births.
The cause of most cardiovascular malformations is not well understood. However, a few can be attributed to specific genetic or environmental factors. It has been estimated that about 4% of cardiovascular defects can be ascribed to single gene mutations, another 6% to chromosomal aberrations such as monosomies and trisomies, and 5% to exposure to specific .teratogens. The remaining 85% of the cardiovascular defects are caused by multifactorial inheritance, ie, by a
complex interplay between genetic and environmental factors.
The teratogens known to cause CHD are rubella virus, thalidomide, vitamin A, and alcohol, etc. There is evidence that maternal diabetes and hypertension also cause congenital cardiac defects.
Most of the congenital cardiovascular defects are well tolerated during intrauterine life because gaseous exchange is occurring in placenta and pulmonary circulation has not begun. After birth, however, the pulmonary circulation starts and the impact of congenital heart defects become evident. Some of these defects produce very little disability, others are incapacitating, while still others are incompatible with extrauterine life. The cyanosed child is also called a blue baby.
Those cardiovascular anomalies which cause shunting of oxygenated blood into the deoxygenated blood produce a clinical condition called cyanosis, which consists of a dark bluish or purplish discolouration of the skin and mucous membranes. The Cyonosis results from excessive concentration of reduced hemoglobin in the blood. A considerable number of congenital cardiovascular defects can be corrected surgically.
The number of reported congenital cardiac defects is very large. The cardiac anomalies of clinical significance can be grouped as under:
1) Anomalies of position.
2) Atrial septal defects (ASD).