Congenital Heart Disease

Congenital Heart Disease (CHD)

What is congenital heart
disease (CHD)?



Congenital heart disease (CHD) is malformation of the heart or the large blood
vessels near the heart. "Congenital" speaks only to time, not to causation. It
means "born with" or "present at birth."

Alternative names for CHD
include: congenital heart defect, congenital heart malformation, congenital
cardiovascular disease, congenital cardiovascular defect, and congenital
cardiovascular malformation.

How
common is congenital heart disease?



Congenital heart disease is the most frequent form of major birth defects in
newborns affecting close to 1% of newborn babies (8 per 1,000). This figure is
an underestimate since it does not include some common problems, namely:

• 
  
  

  Patent ductus arteriosus in
  preterm babies (a temporary condition)




• 
  
  

  Bicuspid (two cusps) aortic
  valve (the aortic valve usually has three cusps or flaps)




• 
  
  

  
  
  Mitral valve prolapse (drooping of a heart valve)




• 
  
  

  Peripheral pulmonary sten

When is the diagnosis of
congenital heart disease (CHD) usually made?



Although all types of CHD (by definition) are present at birth and therefore
were present before birth, few cases of CHD come to light until birth or
beyond. The diagnosis of CHD is made by one week of age in 40-50% of cases.
And 50-60% of all cases is diagnosed within the newborn period (the first
month of life after birth). The remaining cases are not diagnosed until
after that time.

Why are most cases of CHD
not a problem before birth?



The circulation of blood in the fetus (the fetal circulation) differs from
that after birth. The fetal circulation derives oxygen and nutrients from
the mother through the placenta. The fetal circulation also has important
communications (shunts) between the upper heart chambers and the great blood
vessels near the heart. Consequently, most types of CHD are well tolerated
during fetal life. Even such a severe form of CHD as left heart hypoplasia
(in which the entire left side of the heart is underdeveloped) is
compensated for by the fetal circulation.

The fetal circulation:
The three major features of the fetal circulation are:

1. 
   
   

   The maternal circulation
   through the placenta brings oxygen and nutrients to the fetus and
   removes carbon dioxide from the fetal circulation.




2. 
   
   

   The foramen ovale is a
   hole located in the septum (wall) between the two upper heart chambers
   (the right and left atria). The foramen allows blood to shunt from the
   right atrium to the left atrium.




3. 
   
   

   Another shunt, the ductus
   arteriosus, allows deoxygenated blood to flow from the pulmonary artery
   into the aorta and through it to the body.

The circulation after
birth: The placenta is removed and the lungs have to take over
oxygenating the blood. Major circulatory changes occur after birth.

These changes include:

• 
  
  

  The maternal circulation
  can no longer bring oxygen and remove carbon dioxide from the baby's
  circulation




• 
  
  

  The foramen ovale closes
  (or is restricted) and can no longer act as a shunt between the two
  atria (the two upper chambers) of the heart




• 
  
  

  The ductus arteriosus
  closes and no longer provides a communication between the pulmonary
  artery and aorta

Once these changes occur, the
fetal circulation is a thing of the past and the full impact of various
congenital heart defects is felt. These defects become evident, cause signs
and symptoms and so may be diagnosed. Further changes occur in the
cardiovascular system during infancy and childhood as, for example, in the
pressure relationships between the right and left ventricles. These changes
serve to bring more cases of CHD to light.

What causes congenital
heart defects?



Congenital heart disease can have diverse causes. The causes include
environmental factors (such as chemicals, drugs or infections), certain
maternal diseases, chromosome abnormalities, genetic diseases, and unknown
(idiopathic) factors.

Environmental factors
sometimes are at fault. For example, if a mother catches German

measles (rubella) during pregnancy, the infection can impair the
development of her unborn baby's heart (and other organs). If the mother
consumes alcohol during pregnancy, the fetus can suffer from

fetal alcohol syndrome (FAS) including CHD.

Exposure to certain
medications during pregnancy can also cause CHD. An example is retinoic acid
(brand name Accutane) which is used for
acne.
Other examples are anticonvulsant drugs, specifically the hydantoins (such
as Dilantin) and valproate.

Certain diseases in the
mother can increase the risk of developing CHD in the fetus. The infants of
women with

diabetes mellitus, especially those women under less than optimal blood

glucose control during pregnancy, are at increased risk for CHD. And
women who have the genetic disease

phenylketonuria (PKU) and do not stay on their special diet during
pregnancy tend also to have babies with CHD (and many other problems as
well).

Chromosome disorders can
cause congenital heart disease. (The chromosomes contain the genetic
material, the DNA, with each person normally having 46 chromosomes, 23
chromosomes from each parent). About 3% of all children with CHD have a
detectable chromosome abnormality.

A common chromosome
abnormality causing CHD is Down's syndrome (trisomy 21, that is, an extra
chromosome # 21. About half of children with

Down syndrome have CHD.

Other autosomal (non-sex)
chromosome abnormalities associated with CHD include trisomy 13 (Patau
syndrome) and trisomy 18 (Edwards syndrome). Although less common than Down
syndrome, these trisomies carry an even higher risk of CHD.

A sex chromosome abnormality
with only one X chromosome (45,X) causes

Turner syndrome and a 40% risk of CHD.

Genetic factors can cause CHD.
About 5% of CHD babies have an identifiable genetic disease. Genetic
diseases associated with an increased risk of CHD include Apert syndrome,
Carpenter syndrome, Conradi syndrome, Crouzon syndrome, cutis laxa, Cornelia
de Lange syndrome, Ellis-van Creveld syndrome, Holt-Oram (cardiac-limb)
syndrome, Kartagener syndrome, Meckel-Gruber syndrome,

Noonan syndrome Pallister-Hall syndrome, Rubinstein-Taybi syndrome,
Scimitar syndrome, Smith-Lemli-Opitz syndrome, thrombocytopenia-absent
radius (TAR) syndrome, Treacher Collins syndrome, and Williams syndrome,
etc. (The point here is not for you to learn all the entities just listed
but to know that there are many genes capable of contributing to CHD).

Idiopathic: in the
majority of children with CHD, the cause of the CHD is totally unknown. It
is idiopathic (cause unknown).A number of syndromes of unknown origin are
associated with CHD including:

• 
  
  

  Alagille syndrome (arteriohepatic
  dysplasia)




• 
  
  

  Asplenia syndrome (no
  spleen)




• 
  
  

  CHARGE association
  (CHARGE is an acronym for Coloboma, Heart, Atresia choanae, Retardation,
  Genital anomalies, and Ear anomalies)




• 
  
  

  CHILD association (CHILD
  is an acronym for Congenital Hemidysplasia, Ichthyosiform erythroderma,
  and Limb Defects)




• 
  
  

  DiGeorge sequence
  




• 
  
  

  FAVS spectrum (FAVS is an
  acronym for Facio-Auriculo-Vertebral Spectrum)




• 
  
  

  Mullibrey nanism (Mullibrey
  is an acronym for MUscle, Liver, BRain, and EYe)




• 
  
  

  Polysplenia syndrome
  (multiple spleens)




• 
  
  

  VATER association (VATER
  is an acronym for Venticular septal defect or Vertebral defect, Anal,
  TracheoEsophageal, and Renal anomalies)