NICU to Nursery: Cardiac Assessment of the Neonate by Nancy Braudis.
Basic Cardiac Anatomy and Physiology.
The right side of the heart receives venous blood from the body through the superior and
inferior vena cava, which enter the right atrium.
Blood flows through the trike tricuspid valve into the right ventricle.
Blood leaves the right ventricle through the pulmonary valve into the main pulmonary artery.
The pulmonary artery divides into right and left pulmonary arteries to transport deoxygenated
blood from the right side of the heart to the right and left lungs.
The pulmonary arteries branch further into the pulmonary capillary bed where oxygen and
carbon dioxide exchange occurs.
The four pulmonary veins, two from the right lung and two from the left lung, carry oxygenated
blood from the lungs to the left side of the heart.
The oxygenated blood flows from the left atrium through the mitral valve, and into the left
ventricle, and out through the aortic valve, and into the aorta, and to the body.
This picture shows the individual heart valves.
The heart valve openings are protected by flaps of tissue called leaflets or cusps that
are attached to the papillary muscles by the chordae tendinae.
The papillary muscles are extensions of the heart muscle that pull the cusps together
and downward at the onset of ventricular contraction.
As the pressure increases in the ventricles, the valves close and the papillary muscles
prevent the valves from opening.
The branch of the circulation that supplies oxygen and other nutrients to the cells of
the heart is called the coronary circulation.
The major coronary arteries are the right coronary artery and the left coronary artery.
The left coronary artery originates from a single opening behind the left cusp of the
aortic valve and divides into the left anterior descending artery and the circumflex artery.
The right coronary artery originates from an opening behind the right cusp of the aortic
valve.
And divides into three major branches, the conus, the right marginal branch, and the
posterior descending branch.
After flowing through an extensive network of capillaries, blood from the coronary arteries
drain into the cardiac veins.
The veins follow into the great cardiac vein and coronary sinus.
Blood empties from the coronary sinus into the right atrium.
Electrical impulses originate in the sinoatrial node, located at the junction of the right
atrium and superior vena cava.
Each electrical impulse generated from the SA node travels through the right and left
atrium, causing the atria to contract.
The impulse then travels to the atrioventricular node, AV node, then to the bundle of His,
and finally, through the right and left bundle branches of the ventricles, causing the ventricles
to contract.
Clinical Presentation of Heart Disease in Newborns.
Children with congenital heart disease often present in one of three pathophysiological
states.
Low cardiac output, this occurs when there is a heart defect that obstructs the flow
of blood from the heart or when the heart muscle is unable to pump effectively.
Congestive heart failure, this often occurs when there is a heart defect that causes an
increase in blood flow to the lungs.
Cyanosis, this occurs when there is a heart defect that causes a decrease in blood flow
to the lungs.
On admission, a full cardiac assessment should be completed.
This includes a comprehensive history that should identify if there was a prenatal diagnosis
or any significant birth and genetic history.
A complete set of vital signs should be done as a baseline and a set of blood pressures
in all four extremities should be done to evaluate for any gradient within the aorta.
The physical exam includes evaluation of general color, body temperature, evaluation of heart
sounds, and the presence of any murmurs.
Assessment of the liver will indicate if there is an overload of fluid on the right side
of the heart, and the quality and strength of pulses.
Diagnostic tests should include a chest radiograph and electrocardiogram.
Other tests may include an echocardiogram or a cardiac catheterization.
Signs of low cardiac output in infants and children include pale or modeled skin color,
tachycardia, altered conduction within the heart.
Irritability, cool and clammy skin, or decreased level of consciousness.
Decreased urine output.
Point of clarification.
Six to eight wet diapers per day is considered normal.
Anything less may be considered decreased urine output.
Capillary refill greater than three seconds, metabolic acidosis, hypoglycemia, and increased
serum lactate.
Other signs include weak pulses, temperature instability, or apnea.
There may also be evidence of organ dysfunction, such as kidney or liver failure.
Late signs include hypotension, cyanosis, anuria, and altered mental status.
Interventions to improve low cardiac output include correcting the heart rate and restoring
normal conduction within the heart.
Administration of fluids.
Correcting acid-base imbalance and electrolyte abnormalities.
And using medications to improve the function of the heart and to reduce the stress on the
body.
Congestive heart failure occurs when the heart cannot deliver enough blood to meet the demands
of the body.
The heart attempts to compensate by increasing the heart rate, thickening the walls of the
heart to contract more effectively or dilating the heart to increase the volume of blood
within the heart to improve cardiac output.
Congestive heart failure occurs in 30% of infants and children with congenital heart
disease.
And occurs in over 75% of children with complex heart disease.
The causes of congestive heart failure include volume overload of the heart, pressure overload
of the heart, and heart muscle dysfunction.
Some of the clinical signs of congestive heart failure include tachypnea, retractions, nasal
flaring, diaphoresis, pulmonary edema, irritability, change in responsiveness, fatigue, poor feeding,
failure to thrive.
Tachycardia, cool skin, decreased urine output, an enlarged liver, periorbital edema, pulmonary
effusions, and ascites.
Interventions for congestive heart failure include medications, such as diuretics, to
eliminate excess fluid.
Limiting fluid administration.
And improved nutrition to maximize calories.
Other interventions include respiratory support to reduce the work of breathing and temperature
control.
Cyanosis occurs when neonates are unable to tolerate the changes that occur when the blood
flow within the heart changes after birth.
Cyanosis may also occur in infants and children with congenital heart defects that cause a
decrease in blood flow to the lungs.
Cyanosis, respiratory or cardiac?
When cyanosis occurs with respiratory disease, the cyanosis usually decreases with crying.
Improves with oxygen administration.
And there are usually signs of respiratory distress.
When cyanosis occurs with cardiac disease, the cyanosis usually increases with crying
because the demand of oxygen increases, but the body is unable to deliver sufficient oxygen.
Cyanosis with cardiac disease does not usually improve significantly with the administration
of supplemental oxygen.
And the infants usually breathe fast, but do not have evidence of respiratory distress.
Tests that can help in the diagnosis of respiratory or cardiac disease include a 12-lead electrocardiogram,
a chest radiograph, and a hyperoxia test that involves evaluating the oxygen content of
the blood with and without supplemental oxygen.
Signs of cyanosis with congenital heart disease include bluish discoloration of skin and mucous
membranes, increased respiratory rate and effort, irritability or lethargy.
Other signs include decreased blood flow to the body, decreased urine output, and metabolic
acidosis.
Long-term effects of chronic cyanosis include an increased hematocrit.
Thickening of the blood, increased risk of clot formation, clubbing of fingers, and an
increase in the release of oxygen to the tissues.
Interventions to reduce cyanosis include the administration of supplemental oxygen and
maintaining a high hematocrit to maximize oxygen carrying capacity.
Point of clarification.
If the infant becomes anemic, packed red blood cells may be transfused to maintain a high
hematocrit and limit the impact of cyanosis.
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