Congenital Cardiac Defects with Decreased Pulmonary 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.
This lecture will provide information on the most common congenital heart defects and their
surgical repair.
I will be discussing the defects with decreased pulmonary blood flow.
Introduction and Pathophysiology.
What will happen with congenital heart defects that cause a decrease in pulmonary blood flow?
The decrease in pulmonary blood flow occurs as blood shunts right to left at either the
atria level or ventricular level through a hole in the septum because the blood is unable
to leave the heart due to an obstruction or defect in a valve, vessel, or chamber on the
right side of the heart.
In defects with decreased pulmonary blood flow, there is an obstruction to blood flow
on the right side of the heart.
The blood must find another exit from the right side of the heart either through an
opening at the atrial level, a patent foramen ovale still present from uterine life, or
an atrial septal defect, or an opening at the ventricular level-- a ventricular septal
defect.
Because deoxygenated blood from the right side of the heart is mixing with oxygenated
blood returning from the lungs on the left side of the heart, the patient is cyanotic.
Children that are cyanotic for a few years have problems related to their cyanosis.
These children may develop clubbing of their fingernails.
This is related to overgrowth of capillaries in the fingers in an attempt to bring more
oxygen to the tips of the fingers.
These children maybe polycythemic, having hematocrits in the 50-70% range.
Because of the increased amount of red blood cells in the blood, the amount of circulating
clotting factors are decreased, and the clotting factors that are available do not work well
in a cyanotic environment.
This patient is at risk for hemorrhage, especially in the post-operative period.
The elevated hematocrit also has the patient at risk for the development of blood clots
and infections, specifically bacterial endocarditis.
The blood vessels in the lungs may become damaged by shearing forces and stress from
the extra red blood cells and sluggish circulation, causing higher pressure in the lung blood
vessels.
The biggest risks for the cyanotic patient are hypercyanotic spells.
Hypercyanotic spells occur when the body needs more oxygen, and there is less oxygen available.
A cyanotic baby or child that cries often and is very irritable may be having a hypercyanotic
spell.
If the patient is stressed and the body needs more oxygen, that may trigger a spell.
A spell may also occur spontaneously, or with feeding, bathing, or intravenous insertion.
During anesthesia induction, a spell may occur as blood shunts right to left through the
VSD, due to a decrease in systemic vascular resistance.
Treatment for hypercyanotic spells include providing supplemental oxygen to the patient.
Place the child in a knee-chest position, lying the child down and bringing their knees
bent up to their chest.
In doing this, the large muscles of the legs contract and force more blood back to the
heart.
This increases preload on the right side of the heart and possibly forces blood through
the spasming right ventricular outflow tract.
That same large muscle contraction increases afterload on the left side of the heart, making
it more difficult for blood to shunt right to left in the heart.
Morphine may be administered to relax the patient, and hopefully relax the right ventricular
outflow tract.
Volume is administered to increase preload.
The patient may require intubation to provide oxygen and ventilation.
The hypercyanotic spell may be so severe that the patient will experience cardiac arrest
and need emergency heart surgery.
The defects associated with decreased pulmonary blood flow that I will be discussing are Tetralogy
of Fallot, and transposition of the great arteries.
Tetralogy of Fallot.
Patients diagnosed with Tetralogy of Fallot are at the greatest risk for a hypercyanotic
spell.
Tetralogy of Fallot is a combination of four congenital heart defects-- a ventricular septal
defect; pulmonary stenosis, which is a narrowing or obstruction involving the pulmonary valve
and/or the right ventricular outflow tract; an overriding aorta, which occurs because
the aortic outflow tract does not have a well-developed pulmonary outflow tract to balance against
in utero; and right ventricular hypertrophy, which develops as the right ventricle attempts
to pump against an obstructed or narrowed pulmonary valve.
Children diagnosed which Tetralogy of Fallot will be cyanotic as the deoxygenated blood
on the right side of the heart is unable to get through the area of obstruction in the
pulmonary outflow tract, and flows across the ventricular septal defect to the left
side of the heart and out to the body.
The greater the amount of obstruction in the pulmonary outflow tract, or the greater the
degree of pulmonary stenosis, the more cyanotic the patient will be.
The surgical repair for Tetralogy of Fallot involves the closure of the ventricular septal
defect with Dacron or pericardium, and removal of the muscle bundles from around the pulmonary
valve, or right ventricular outflow tract.
Also, the right ventriclular outflow tract or passage out of the right ventricle is opened
and widened using a patch.
Post-operative concerns after repair of Tetralogy of Fallot are a residual ventricular septal
defect, which is evaluated by checking right atrial pulmonary artery saturations for an
increase in the pulmonary artery saturation.
A residual right ventricular outflow tract obstruction, which is evaluated as the pulmonary
artery line is removed.
An increase in systolic pulmonary artery pressure of 10 millimeters of mercury or greater with
pulmonary artery line removal may indicate a residual obstruction or right ventricular
dysfunction.
Another post operative concern is right ventricular dysfunction, which would be evidenced by low
cardiac output state and congestive heart failure signs and symptoms.
The most common arrhythmia experienced after repair of Tetralogy of Fallot is junctional
ectopic tachycardia.
In junctional ectopic tachycardia, the rate is regular with a normal-looking QRS.
The ventricular rate usually ranges from 170 to the high 200s.
However, the atrial rate is slower, and it is difficult to see the P waves.
Junctional ectopic tachycardia may be triggered by catecholamine release associated with a
high heart rate that accompanies fever, pain, or dopamine use.
Transposition of the Great Arteries.
In transposition of the great arteries, the pulmonary artery arises from the morphologic
left ventricle, and the aorta arises from the morphologic right ventricle.
This results in two parallel circulations with mixing occurring at the ductal level
across the patent ductus arteriosis, and at the atrial or ventricular level through an
atrial septal defect or ventricular septal defect.
The patient is profoundly cyanotic.
Transposition of the great arteries accounts for 10% of all congenital heart disease.
There's a 75% male predominance in transposition of the great arteries.
Repair of transposition of the great arteries is accomplished with the arterial switch operation.
In the arterial switch operation, both great vessels-- the aorta and the pulmonary artery--
are resected.
The coronary arteries, with some extra tissue, are removed from the root of the aorta on
the right ventricle.
The pulmonary artery is sutured into its correct position on the right ventricle.
The aorta is sutured into its correct position on the left ventricle.
And the coronary arteries are reattached to the aorta.
Postoperative concerns following an arterial switch operation are decreased left ventricular
function, as the left ventricle has been pumping against the low pressure pulmonary system,
and now must support systemic circulation.
Another concern is coronary artery spasm or occlusion.
There are many suture lines involved in the reattachment of the great vessels and the
reimplantation of the coronary arteries.
The suture lines may interfere with the flow through the coronary arteries.
Also, there may be swelling along the suture lines.
And that may affect flow through the coronary arteries.
Also, manipulation of the coronary arteries may cause coronary artery spasm.
These arteries are the blood supply for the myocardium.
So anything that impedes the flow through these vessels could impact the function of
the heart.
As the child grows and the coronaries are stretched more, there is a risk of late occlusion
of the coronary arteries.
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