Abnormal Heart Development

Learning Objectives:

Define and be able to use the following clinical terms: cyanosis, stenosis, atresia,

hypoplasty, hypertrophy, persistent, patent, secondary effect.

Discuss the prevalence and diagnosis of congenital heart defects. How common

are they, and how are they detected?

Explain the developmental cause of the following disorders and their effect on

circulation: patent ductus arteriosus, persistent truncus arteriosus, transposition of

the great arteries, atrial and ventricular septal defects, atrioventricular canal defect,

tricuspid atresia, aortic and pulmonary stenosis, Tetralogy of Fallot, and hypoplastic

left heart syndrome.

Describe the treatment of hypoplastic left heart syndrome. What is the purpose of

each treatment step?

Body

Right atrium

Lungs

Left atrium

Review of adult circulation

Superior,

inferior

vena cava

Tricuspid valve

Right ventricle

Left ventricle

Pulmonary artery

Pulmonary veins

Mitral valve

Body

Aorta

Two right-to-left shunts are used in fetal heart

Fetal lungs are not fully developed and cannot handle the full amount of blood

entering the pulmonary artery

The foramen ovale (present in the interatrial septum) shunts blood from the right

atrium to the left atrium

The ductus arteriosus connects the pulmonary and aortic arteries, directing blood

away from the lungs

A third shunt, the ductus venosus, bypasses the liver. It is not involved in right-left

shunting.

Congenital heart malformations are the most common birth defect

1 in 100 births 25% of all congenital defects

Septal defects account for 50% of congenital heart disease cases

Heart defects are classified as either cyanotic or acyanotic

Cyanosis = bluish skin. Caused by too much deoxygenated hemoglobin

Major disorders that we will cover today:

Patent ductus arteriosus Transposition of the Great Arteries Septal defects

Atrial septal defects Ventricular septal defects Atrioventricular canal defects

Obstruction (Atresia/stenosis)

Tricuspid/mitral valve atresia Aortic/Pulmonary stenosis

Hypoplasia

Persistent truncus arteriosus Hypoplastic left heart syndrome

Cause of congenital heart defects is unknown in most cases.

15% of cases can be attributed to genetic factors

Known risk factors:

Maternal diabetes, obesity, phenylketonuria Maternal smoking Rubella infection

Diagnosis of some severe defects can be made by prenatal ultrasound.

Infant diagnosis is usually by presence of murmur upon stethoscope examination, presentation of cyanosis or abnormal pulse oximetry result.

Pulse oximetry non-invasive measurement of oxygen saturation levels. Used to screen for heart defects at 24-

48 hours after birth. Does not rule out all defects.

At one-week checkup, physician will check for cyanosis,

tachypnea, poor perfusion, weak pulse to screen for

latent defects.

Undiagnosed congenital heart defects contribute to sudden death during childhood

and adolescence, adult heart disease.

Athletes have heightened risk of sudden

cardiac death.

Marc-Vivien Fo soccer player for Cameroon. Collapsed during match in

2003 due to hypertrophic cardiomyopathy.

Patent ductus arteriosus (PDA):

Ductus arteriosus normally closes immediately after birth Default state is closed; ductus remains open in fetus due to high prostaglandin

levels secreted by placenta.

Common in premature infants. Small PDA is asymptomatic. Risk of endocarditis. Large PDA is life-threatening and requires closure. High pressure blood from aorta will flow backwards into lungs and cause pulmonary

hypertension. Untreated PDA will eventually cause congestive heart failure.

Treatment: Indomethacin therapy or surgical closure. Some catheter devices used.

Normal Patent ductus arteriosus

Persistent truncus arteriosus:

Outflow tract fails to divide into pulmonary and aortic channels A VSD is usually present Treatment = surgery

VSD is closed, and the pulmonary arteries are connected to the right ventricle Still a high rate of survival even without surgery

Normal Persistent truncus arteriosus

Transposition of the Great Arteries:

Aorta and pulmonary artery are reversed aorta connects to RV, pulmonary artery connects to LV

Usually co-occurs with VSD or patent ductus arteriosus Caused by failure of aorticopulmonary septum to spiral as it grows Fatal unless another defect is present that allows systemic and pulmonary blood to

mix

Treatment: Surgical reversal of the vessels, closure of septal defects

Normal Transposition of the Great Arteries

Atrial septal defects (ASD):

Results in a common atrium Due to higher pressure of the left atrium, blood flows from the left to the right atrium More than normal amounts of blood are diverted to the lungs, resulting in

pulmonary hypertension

Additional blood causes hypertrophy and increased blood pressure of the right atrium

Increase in right atrium blood pressure results in blood moving back toward the left atrium and cyanosis

Treatment = surgical closure of the septum - may result in right ventricular failure

Ventricular septal defects (VSD):

70% are in membranous septum; 30% muscular Due to higher pressure of the left ventricle, blood flows from the left to the right

ventricle

Excessive blood is diverted to the lungs, resulting in pulmonary hypertension Results in hypertrophy and increased blood pressure of the right ventricle Increase in right ventricle blood pressure eventually results in blood moving back

toward the left ventricle

Most heal on their own in the first few years of life, but surgery can be used

Normal Membranous VSD

Atrioventricular canal defect:

Caused by a defect in endocardial cushion formation/fusion Usually co-occurs with other septal defects Often associated with Down Syndrome Results in increased blood flow toward the lungs and back to the atria.

Increased blood in the lungs leads to pulmonary hypertension, and in the atria leads to congestion of blood in the veins that drain into the atria

Treatment = surgery to reconstruct the septa and valves Generally done 3-6 months after birth

Tricuspid valve atresia:

Tricuspid valve does not develop and stops the flow of blood from the right atrium to the right ventricle

Stenosis (narrowing) may also occur Causes an underdeveloped right ventricle and pulmonary artery An ASD and VSD are needed to keep the baby alive Mitral valve atresia can occur, but is less prevalent Treatment = surgery

Tricuspid atresia Normal

Aortic/Pulmonary Stenosis:

Occurs when the outflow tract is partitioned asymmetrically Atresia occurs when the stenosis is so extreme that blood flow is completely

blocked

Usually leads to death in the early fetal period The ventricle pumping blood through the affected artery becomes thickened Treatment = surgery to replace the heart valve

Aortic stenosis Pulmonary stenosis

Tetralogy of Fallot:

Compound disorder involving 4 malformations: Pulmonary stenosis primary defect; severity determines overall severity Overriding aorta aorta straddles both ventricles Ventricular septal defect below overriding aorta Right ventricular hypertrophy - secondary effect of pulmonary stenosis

Most common cyanotic heart defect Affected individuals have tet spells transient, rapid-onset periods of hypoxia

during exertion due to spasm of pulmonary valve

Treatment = surgical widening of pulmonary stenosis, repair VSD

Hypoplastic left heart syndrome (HLHS):

Left side of the heart (left atrium and ventricle, mitral valve, aortic semilunar valve) does not develop completely

Hypoplastic left ventricle cannot pump the necessary amount of blood to the body The only way for babys to survive with HLHS is failure of the two fetal shunts to close Blood from the right ventricle travels through the ductus arteriosus to the body Blood returning from the lungs accesses the right side of the heart through the foramen ovale

HLHS detection:

May initially go undetected due to the open shunts If it goes undetected, the ductus arteriosus closes completely 1 - 2 after birth

Usually results in death HLHS can be detected about 18 weeks into pregnancy with an ultrasound If detected, a prostaglandin is given to keep the ductus arteriosus open

This is temporary measure 3 options:

1. Do nothing

2. Heart transplant

3. Begin a series of three operations to rebuild the heart

The 1st 2 choices have a 95% mortality rate by 1 month The 3rd choice has an over 60% survival rate at 5 years

The operation to correct HLHS has 3 steps:

1. Norwood operation - done in the 1st week of life

2. Hemi-Fontan operation - done between 4 to 6 months of age

3. Fontan operation - done between 18 to 36 months of age

Norwood Operation: Goal to connect the aorta to the right ventricle The ductus arteriosus connecting the aortic and pulmonary arteries is closed The main pulmonary artery is separated from the left and right pulmonary arteries The aortic artery is separated from the left ventricle The aortic artery is connected to the pulmonary artery, allowing blood from the heart to enter the body via the right ventricle A BT (Blalock-Taussig) shunt is introduced, which connects the aorta and pulmonary artery, allowing some blood to be directed to the lungs If an ASD is not present, one will be artificially created The heart pumps mixture of oxygenated and deoxygenated blood to the body

Norwood operation

Hemi-Fontan/Glenn Operation: Goal - reduce the workload of the right ventricle The superior vena cava (SVC) is connected to the pulmonary artery

The SVC loses connection with the right atrium The BT shunt is removed Deoxygenated blood from the SVC moves to the lungs, becomes oxygenated,

empties into the left atrium, moves to the right atrium, then to the right ventricle mixes with deoxygenated blood from the inferior vena cava (IVC), and is sent to the body

Norwood Operation Hemi-Fontan Operation

Fontan Operation: Goal send all deoxygenated blood to the lungs The IVC is connected to the pulmonary artery A wall called a baffle is built in the right atrium, separating the right atrium from the vena cava Deoxygenated blood from the SVC and IVC moves to the lungs, becomes oxygenated, empties into the left atrium, moves to the right atrium, then to the right ventricle and is sent to the body

Hemi-Fontan Operation Fontan Operation