Congenital Cardiac Defects with Obstruction to Systemic Blood Flow by Patricia Lincoln.
Hello, my name is Trish Lincoln.
I'm the Clinical Nurse Specialist in the Cardiac ICU at Children's Hospital, Boston.
Today's lecture will provide information on the most common congenital heart defects and
their surgical repairs.
The heart defects that I will be discussing are those with obstruction to systemic blood
flow.
Introduction and Pathophysiology.
What will happen with congenital heart defects that cause an obstruction to systemic blood
flow?
The blood in the heart is unable to flow out to the body.
This occurs due to a restriction, underdevelopment, or a defect in a valve, vessel, or chamber
on the left side of the heart.
The pressure in the left side of the heart increases.
As pressure increases in the left atrium, the pulmonary veins returning the blood from
the lungs are unable to empty into the left atrium.
Since the pulmonary veins are unable to empty, pulmonary congestion results.
Pulmonary congestion increases right ventricular workload.
As the right ventricle, it tends to pump against the increased pressure in the lungs.
The signs and symptoms of obstruction to systemic blood flow depend on the severity of the lesion
and degree of obstruction.
If the obstruction is mild, the patient may have no symptoms.
Diagnosis is made on auscultation of a murmur that occurs as blood flows through the area
of obstruction.
If the obstruction to systemic blood flow is severe, the patient may present with congestive
heart failure and low cardiac output.
Signs and symptoms of congestive heart failure and decreased cardiac output.
With small-to-moderate obstruction to systemic blood flow, these patients may be slightly
pale or dusky.
If it's a baby, they may have difficulty with feeding.
And peripheral pulses will be decreased, especially in the lower extremities.
If there is severe obstruction to systemic blood flow, these patients will have very
decreased peripheral and central pulses.
There may be delayed cap refill.
The patient will be dusky in color.
They probably will experience respiratory distress, and urine output will be decreased.Aortic
Stenosis.
The defect with obstruction to systemic blood flow that I will be discussing is aortic stenosis.
The aortic valve is located between the left ventricle and the aorta.
Aortic stenosis occurs when the aortic valve is unable to open properly and completely.
It is difficult for blood to flow forward from the left ventricle to the aorta.
Aortic stenosis occurs for a number of reasons.
The aortic valve may only have two leaflets instead of three leaflets.
The valve leaflets may be partially fused together.
The leaflets may be too thick to open all the way, or the valve may have been damaged
by an infection.
There are three types of aortic stenosis.
The first type, valvular aortic stenosis, which is present in 75% of the aortic stenosis
cases.
The cusps may be fused or abnormally formed, bicuspid, small, thickened, or misshaped.
If the valve tissue itself is thick and rigid, calcification may be occurring.
In the second type, supravalvular aortic stenosis, there is usually an hourglass constriction
located at the sinus of Valsalva.
This type of aortic stenosis is often associated with Williams syndrome.
In the third type of aortic stenosis, it is subvalvular or subaortic aortic stenosis.
This occurs in about 10% of the cases.
In subvalvular or subaortic aortic stenosis, there is a short or long segment of membranous
diaphragm present in the ventricular outflow tract, or there may be a fibrous ring present
that encircles the left ventricular outflow tract.
There are two approaches to the repair of aortic stenosis, commissurotomy and valvuloplasty,
which is an excision of the fibrous ring or bands or a splitting of muscle bundles around
the valve, or the second approach, valvulotomy, which is a dilation of the valve annulus with
a finger or instrument.
Post-operative concerns following repair of aortic stenosis are aortic insufficiency.
If the valve does not close properly, the pressure in the aorta during diastole, the
resting phase of the heart when the coronaries are perfused, will be decreased.
This may decrease blood flow through the coronary arteries, the blood vessels that supply the
heart with its needed nutrients.
Aortic regurgitation.
If the valve is not competent, there will be back flow from the aorta through the valve.
This will decrease the pressure in the coronary arteries, and the heart muscle may not receive
adequate blood flow.
Left ventricular dysfunction or hypertrophy.
The heart muscle has had to pump against an obstruction and may be overworked and not
contract well.
Arrhythmias, especially heart block.
This may be caused by left ventricular dysfunction, increased pressure on the left side of the
heart, or heart muscle damage from decreased coronary blood flow.
Hypertension.
High pressure in the aorta may add undue stress on the newly repaired aortic valve.
Also, congestive heart failure and/or pulmonary congestion.
These are related to the presence of severe systemic obstruction during the preoperative
period in the patient that is now post-operative.
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