Congenital Heart Defects

Fetal circulation and transition to postnatal cirulation overview:

In order to fully understand congential heart disease, you must first have a sound knowledge of the fetal circulation. 

Key points to remember:

• The fetus receives oxygenated blood from the placenta. 
• Pulmonary pressure is higher in utero; therefore, blood flow through the pulmonary circulation is minimal during gestation
• Patent fetal shunts allow the fetal blood flow during gestation: ductus venosus, foramen ovale, and ductus arteriosus
• Dramatic changes occur after birth to allow transition to post-natal ciruculation
• Developmental defects occuring during early gestation give rise to congenital heart defects
• Some of the congential heart defects are considered "duct dependent" and require continuation of the ductus arteriosus after birth.

Now for a little fun before we go much further enjoy this short video on fetal circulation http://www.youtube.com/watch?v=3IkAnVZpO5Y

Congenital Heart Defects

Congenital heart disease is so named because the defects are present at birth.  Some of the defects may cause problems in the neonatal period while other may cause problems later in life.  Risk factors associated with the development of heart defects are multifactoral.  Congenital heart disease affects approximately 6-21 per 1000 live births and can be categorized as cyanotic or acyanotic.   

So, now lets starts with the cyanotic heart lesions...

Cyanotic Lesions

Heart defects which alter the flow of blood from right to left are considered cyanotic because blood is shunted away from the lungs.  Therefore, de-oxygenated or mixed blood is ciruclated throughout the body.  Cyanotic heart disease can be secondary to vavlular defects, structural defects, or blood vessel abnormalities.  Cyanotic heart defects should be considered as a diagnosis in neonates who present with cyanosis and/or respiratory distress.  A quick test to determine if cyanotic CHD is a likely diagnosis is the hyperoxia test.  If your neonate's oxygen level fails to rise despite delivery of 100% FiO2, then cyantoic CHD must be considered.  Cyanotic heart defects are considered ductal dependent and will require the patency of the ductus arteriosus for survival.  In these infants, prostaglandin E1 is a critical componenet of initial management.

With that in mind, let us move on to some of the more common cyanotic heart defects. If you are like me, you need an easy way to remember the lesions which cause cyanosis.  One way to remember five of the cyanotic lesions is by stating the "5 T's":

1.)  Truncus arteriosus
Truncus arteriosus occurs when there is a single vessel carrying blood away from the right and left ventricles.  Normally, there are two pathways out of the heart (the pulmonary artery and the aorta).  This lesion is considered cyanotic because de-oxygenated blood from the right ventricle is allowed to mix with oxygenated blood from the left ventricle via a VSD before being sent to the lungs, carotid arteries, and the rest of the body via the single vessel.  There are three types of truncus arteriosus.  In this defect,  too much blood is sent to the lungs; therefore, patients may exhibit signs and symptoms of congestive heart failure.

Key points to remeber about truncus arteriosus:

• There is a single blood vessel leaving the R and L ventricles instead of 2
• There is an associated VSD which allows for mixing of blood
• There are three types of truncus arteriosus
• Patients will experience CHF if too much blood is sent to the lungs
• All neonates with truncus arteriosus should be evaluated for chromosome 22 microdeletion
• EKG is usually normal
• Mild tacypnea or cyanosis may be only indicator
• Supplemental oxygen should be avoided unless severe hypoxia is present because it will decrease pulmonary vasculature resistance further
• Digoxin and Lasix are used to treat tachypnea s/t increased pulmonary blood flow

2.)  Transposition of the great arteries
Transposition of the great arteries is one of the more common cyanotic heart defects.  In this defect, the aorta arises from the right ventricle and the pulmonary artery arises from the left ventricle.  Transposition fo the great vessels can be classified as d-transposition (d-TGA) or L-transposition (L-TGA) depending on the location of the aorta in relation to the pulmonary arteries.  L-TGA is a rare condition and is also considered acyanotic; therefore, will not be discussed at length in this section. 

TGA can also be further classified as:

Other cyanotic heart defects:

1.) Pulmonary Atresia
Pulmonary atresia is a defect in the pulmonary valve which hinders blood flow out of the right ventricle into the pulmonary artery.  In this type of CHD, pulmonary blood flow is restricted and blood must flow to the lungs via alternate pathways such as an atrial septal defect (ASD) or patent ductus arteriosus (PDA).  Infants may or may not have a ventricular septal defect (VSD).  Infants without a VSD will present with severe hypoxia when the ductus arteriosus closes because blood flow to the lungs via the alternate pathway is blocked.  These infants will require prostaglandin E1 until surgical correction can be performed.  Balloon valvuloplasty is performed to the pulmonary valve in order to increase the blood flow out of the right ventricle.  Surgical correction of pulmonary atresia includes the b-directional Glenn and Fontan procedures.

Key points about pulmonary atresia:

• The affected valve is the pulmonary valve
• Blood flow to the lungs is restricted
• Ductal dependent
• Symptoms such as cyanosis, tachypnea, or increased work of breathing may present within the first few hours after birth or several days after birth
• Holosystolic murmur may be heard
• Hepatomegaly secondary to tricuspid reguritation and right ventricular dysfunction
• Chest Xray may show cardiomegaly with right ventricle enlargement

•  **Mild to moderate aortic stenosis can be considered an acyanotic defect. 
  
  
  
  3.) Coarctation of the Aorta
  Coarctation of the aorta occurs as a result of narrowing in the aorta, most commonly just beyond the aortic arch.  Coarctation is considered duct dependent when aortic arch interruption is present or when the extent of obstruction leads to left ventricular failure or decreased lower body perfusion at the time of ductal closure.  Coarctation is commonly associated with left heart diease, bicuspid aortic valve stenosis, and VSD.  Aortic arch interruption is associated with VSD, aortic pulmonary window, truncus arteriosus, or transposition of the great vessels.
  
  Key points about coarctation of the aorta:
• Infants with coarctation will have higher blood pressures in the upper extremities than in the lower extremities
• Occurs more often in boys, but 10% of girls with Turner's syndrom will have coarcation
• Coarctation can occur as an isolated defect or in association with transposition of the great vessels, double outlet right ventricle, or single ventricle defects
• Infants may present with diminshed leg pulses
• Early signs of CHF should raise concern about associated defects
• Precordial hyperactivity, gallop rhythm, and hepatomegaly may be present with significant obstruction
• EKG and chest xray usually normal
• ECHO can usuallly define extent of obstruction
• Right to left shunting indicative of severe obstruction
• Those in CHF or with signs of poor perfusion should receive prostaglandin E1
• Those with aortic arch interruption must have surgical correction of defect
• Uncomplicated coarctation can be repaired in early childhood

Additional reference for cyanotic heart defects:
Zahka, K.G., & Erenberg, F. (2011). Congenital defects. In R.J. Martin, A.A. Fanaroff, & M.C. Walsh (Eds.), Neonatal-Perinatal medicine: Diseases of the fetus and infant (pp. 1245-1265). St. Louis, MO: Elsevier-Mosby.

Acyanotic Lesions

Now, moving right along, let's discuss the ACYANOTIC congenital heart defects.  Acyanotic heart defects are those which are characterized by left to right shunting and a lack of cyanosis.  The acyanotic heart defects include functional murmurs, pulmonary stenosis, VSD, ASD, endocardial cushion defect, PDA, aortopulmonary window, and L-transposition of the great arteries.

1.)  Murmurs
Heart murmurs are the product of turbulent blood flow across normal heart valves.  The presence and/or intensity of heart murmurs can be affected by anemia, fever, or infection.  The Kansas University Medical Center (KUMC) presents a complete table of functional murmurs and indicated the peripheral pulmonary stenosis (PPS) murmur is most often encountered in the pre-term population.  The Univeristy of Chicago also offers an explanation of heart murmurs and why the PPS affects preterm neonates. 

And, for you auditory learners http://depts.washington.edu/physdx/heart/demo.html

2.) Pulmonary Stenosis
Pulmonary stenosis occurs when there is a narrowing of the pulmonic valve.  Pulmonary stenosis differs from pulomary atresia or critical pulmonary stenosis because the tricuspid valve remains normal with a normal right ventricle.  Pulmonary stenosis can be catergorized as valvular, subvalvular, or peripheral. Pulmonary stenosis can also be associated with other congenital heart defects.

Key points about Pulmonary Stenosis:

• Pulmonary valve is narrowed - tricuspid valve is normal
• Right ventricle is normal size
• Peripheral pulmonary steonsis (PPS) can cause systolic murmur - may be continuous, softer, and higher pitched
• Cyanosis may be present if occurs with significant R-L shunting via a PFO, ASD, or VSD (critical PS)
• CXR reveals prominence of right, main, or left pulmonary arteries
• ECHO is diagnostic

3.) Ventricular Septal Defects (VSD)
Ventricular septal defects are lesions found between the right and left ventricles and are classified according to the location of teh defect.  The VSD becomes apparent as the pulmonary pressure decreases and blood begins to be shunted in a L-R fashion across the septal defect.  The murmur associated with a VSD varies according to type and size of defect.  A large VSD may not produce an audible murmur because of lack of resistance to flow.  VSDs are common with may of the congenital heart defects.  A large VSD may cause CHF and an increased risk of pulmonary vascular disease.

4.)  Atrial Septal Defects (ASD)
Atrial septal defects are lesions located between the right and left atria.  An ASD allows blood to be shunted in a L-R fashion from the left atrium to the right atrium which, in turn, increases the amount of blood in the pulmonary circulation.  An untreated ASD may increase the risk of developing CHF, pulmonary hypertension, and atrial arrhythmias.

5.) Endocardial Cushion Defect
An endocardial cushion defect can also be referred to as an atrioventricular septal defect, atrioventricular canal defect, or persistent ostium primum.  Endocardial cushion defects are most commonly seen in patients with Down syndrome.  Complete defects cause CHF and pulmonary vascular obstructive disease while partial defects may remain asymptomatic.

6.) Patent Ductus Arteriosus (PDA)
The ductus arteriosus is a fetal shunt critical during gestation for the proper flow of fetal circulation.  After birth, the ductus arteriosus should close within 48 hours in full term neonates and by 72 hours in preterm neonates.  Failure of the ductus arteriosus to close by 72 hours is classified as patent ductus arteriosus.  A small PDA may not cause any problems while a large PDA will cause significant L-R shunting.  A large PDA, left untreated, increases the risk of neonates developing Eisenmenger's syndrome.  The PDA is a common occurence among neonates.  During the course of your career, it is likely that you will encounter the PDA more than any other congenital heart defect.  It is imperative that you have a sound knowledge of the PDA and how to treat the PDA effectively.  Therefore, I have added a few more sites to help increase your PDA knowledge base. Enjoy!!

http://emedicine.medscape.com/article/891096-overview

http://www.merckmanuals.com/professional/pediatrics/congenital_cardiovascular_anomalies/patent_ductus_arteriosus_pda.html#v1096387

 7.) Aortopulmonary Window
Aortopulmonary window (AW) is a defect between the ascending aorta and main pulmonary artery which mimics a PDA. AW can occur with an interrupted aortic arch or TOF.  The neonate with AW may present with signs and symptoms of CHF within the first few weeks of life.  The EKG is usally normal, but the CXR will show cardiomegaly and increased pulmonary vasculature.  Surgical closure usually provides excellent outcomes. 

8.) L-Transposition of the great arteries (L-TGA)
L-TGA is a rare condition and is considered congenitally corrected transposition.  Ventricle inversion has occured in L-TGA along with transposition of the great vessels.  The systemic and pulmonary circulations remain normal; therefore, cyanosis does not occur.

Additional reference for acyanotic heart defects:
Zahka, K.G., & Erenberg, F. (2011). Congenital defects. In R.J. Martin, A.A. Fanaroff, & M.C. Walsh (Eds.), Neonatal-Perinatal medicine: Diseases of the fetus and infant (pp. 1245-1265). St. Louis, MO: Elsevier-Mosby.