Atrial septal defect (ASD) review for nursing students!
In this review you will learn about the congenital heart defect known as atrial septal defect (ASD). This is a topic you will see on your pediatric nursing lecture exams and possibly the NCLEX exam.
After reviewing these notes, don’t forget to take the quiz that contains atrial septal defect NCLEX questions and to watch the lecture.
Atrial Septal Defect Lecture
Atrial Septal Defect (ASD) NCLEX Review
What is an atrial septal defect (ASD)? It’s a congenital heart defect characterized by a hole in the interatrial septum (atrial septum). This hole allows blood to flow from the left atrium to the right atrium (the atria are the upper chambers of the heart).
It’s important to remember that there should NOT be a connection of blood flow between the two atria after birth. However, in utero there is a connection between the atria, but this is through the foramen ovale (discussed more below).
According to CDC.gov, 1 in every 770 babies born in the United States each year are born with an atrial septal defect.
Why is an ASD a problem?
If the defect if larger enough (small ASDs usually don’t cause many issues), it creates a right-to-left shunt of blood that can lead to INCREASED LUNG BLOOD FLOW. This is a problem because it can lead to:
- Heart failure
- Pulmonary hypertension….if not treated this can lead to an irreversible condition can Eisenmenger Syndrome (this is rare but can happened overtime)
Types of ASDs: types depend on the location of the hole
- Ostium Secundum: a hole is found in the MIDDLE of the atrial septum….MOST COMMON!
- Ostium Primum: a hole is found near the location of the atrioventricular valves (tricuspid and mitral)…the bottom part of the atrial septum
- Sinus Venosus: a hole is found near the superior vena cava and right atrium.
Pathophysiology of an Atrial Septal Defect
To understand an ASD, you must first understand the NORMAL blood flow of the heart!
Therefore, how should blood flow NORMALLY in the heart without an ASD?
Blood flow starts on the RIGHT SIDE of the heart
- The goal of the right side is to get the UNOXYGENATED blood to the LUNGS!
The un-oxygenated blood (this is blood that has been “used-up” by your body that needs to be resupplied with oxygen) enters to the heart through the SUPERIOR AND INFERIOR VENA CAVA.
Blood enters into the RIGHT ATRIUM
Then it is squeezed through the TRICUSPID VALVE
Blood then enters into the RIGHT VENTRICLE
Then it is squeezed into the PULMONIC VALVE
Blood is then shot-up through the PULMONARY ARTERY and then enters into the lungs for some oxygen
Left Side of the Heart
- The goal of the left side of the heart is to get the richly, oxygenated blood to the body to feed the brain, tissue, muscles, organs etc.
Blood enters from the lungs through the PULMONARY VEIN that has just been refreshed with oxygen to go into the LEFT ATRIUM
Down through the BICUSPID VALVE (also called mitral valve)
Then blood is squeezed into the LEFT VENTRICLE
Up through the AORTIC VALVE
Lastly up through the AORTA, where it pumped throughout the body
Blood flow through the Atria in a Fetus’ Heart
Now in a baby’s heart, who is still in the womb, there is a natural opening in the septum called the formen ovale (O-VALLEY).
This opening allows blood from the right atrium to flow into the left atrium. WHY is this needed in a fetus’ heart?
While a baby is in utero, blood doesn’t need to pass through the lungs because they don’t work yet….the placenta is providing the oxygen. So, this opening allows the blood on the right side to bypass the lungs.
However, after birth the formen ovale will close. It does this when the baby starts breathing own its own. There is a layer of tissue that will seal the opening as the pressure changes in the heart after the baby starts breathing.
As the baby breathes (hence uses the lungs) the pressure in the right side of the heart decreases (in the womb the pressure was the same on the right and left side of the heart).
Therefore, in a normal heart, the pressure is higher on the left side when compared to the right. The purpose for this pressure difference is: The left side needs more pressure to pump all that oxygenated blood throughout the body, while the right side just needs to pump unoxygenated blood to the lungs.
***Now, in some people the formen ovale does not seal shut after birth, and this is called a patent formen ovale (PFO). This “usually” doesn’t cause any issues. However, some patients are at a higher risk for stroke.
Therefore, there are really two types of holes that can occur in the atrial septum: a PFO or an ASD. A hole that has occurred during the formation of the atrial septum in utero is called an ASD (these tend to be larger than a PFO), and the other type occurs AFTER birth when a natural structure (the foramen ovale) fails to CLOSE, which is a PFO.
How is the blood flow altered in a patient with an atrial septal defect?
It’s important to remember large ASDs really are the ones that cause major changes of blood flow rather than a small one. Smaller ASDs don’t allow much blood to shunt from left-to-right…hence not leading to major problems/complications:
Blood enters the heart the same way, but now there is a connection between the right and left atrium. Because of this a LEFT-to-RIGHT shunt of blood will occur.
This is where blood from the left side of the heart (this is arterial blood that is oxygenated….it’s already been on the right side of the heart and to the lungs) will RE-ENTER the right side of the heart.
WHY is this shunting occurring? The pressure in the left side of the heart is higher, so the blood will flow to a lower pressure gradient…hence the right side.
Why is this an issue? This allows too much blood to enter the right side of the heart, which will in turn pump too much blood to the lungs. The lungs will not be able to handle this extra blood volume. In turn, the arteries that feed the lungs will become damaged and narrow. This is called pulmonary hypertension. In addition, many babies and children will have frequent respiratory infections because of lung congestion from the pulmonary hypertension and heart failure.
Furthermore, the right side of the heart will become overwhelmed as well because of the extra blood volume it must pump and the extra pressure it must pump against to get the blood on the right side to the lungs. Heart failure will eventually occur.
Other complications of an ASD: arrhythmias can occur like the atrial type (flutter, fibrillation), STROKE (WHY? clots can sometimes form in the veins, and when this happens these clots usually go to the lungs, but if there is a hole in the atrial septum this can allow for the clot to enter circulation and travel to the brain. When this occurs it will stop blood flow to that specific area of the brain and cause a CVA (stroke).
- Eisenmenger Syndrome: happens later on in life when untreated. This is a reversal of blood shunting from left-to-right to right-to-left. This will occur due to the extensive pulmonary hypertension in a condition called Eisenmenger syndrome.
- With this new change in blood shunting, unoxygenated blood (remember it’s leaving the right side and hasn’t went to the lungs yet) will start to enter circulation because it crosses over through the hole into the left side and goes into the systemic circulation rather than to the lungs. Due to this, cyanosis and clubbing can start to be seen.
Signs and Symptoms of an Atrial Septal Defect
*Signs and symptoms depend on the size of the hole, and usually do NOT present at birth but later in childhood…may be even into adulthood. Furthermore, the larger the defect the early the signs and symptoms will appear. An ASD is usually found because a heart murmur is noticed (which is then further investigated with an echocardiogram). If the hole is large and not found early it can lead to major damage to the lungs and heart and eventually Eisenmenger Syndrome.
The signs and symptoms are going to be related to left-to-right shunting along with the heart failure/pulmonary hypertension….which is usually with LARGE ASDs.
Heart Failure (low cardiac output) and pulmonary hypertension: difficulty breathing, fatigues with ease, fluid build-up (congested lungs, edema in extremities, sweating that’s clammy and occurs with activity like crying, activity, feeding etc.)….activity intolerance, decreased cardiac output, excess fluid volume
Often experiences lung infections (due to lung congestion from fluid)…risk for infection
Low growth rate (inability to eat and burns calories due to difficulty breathing and increased workload on the heart)
Extra heart sounds: midsystolic murmur (systolic ejection murmur at the 2nd intercostal space at the upper left sternal border (WHY a murmur? This is due to increased blood flow through the pulmonic valve). The murmur is quiet at the beginning of systole, increases mid-systole and then decreases at the end of systole….it will end before S2. In addition a wide, fixed splitting of s2 may be present due to the slowness of the pulmonic valve closing.
Nursing Interventions and Treatment for Atrial Septal Defect
Diagnosed with echocardiogram (this is an ultrasound of the heart and is non-invasive….it can show if there is shunting of blood and if structures of the heart have been affected)
Monitor the defect (small ASDs may not cause problems but will be monitored), may need medications like diuretics to remove extra fluid due to heart failure, surgery to close the hole…open heart (done before school age) or heart cath performed to close
- Nutrition: many patients have decreased growth because of the decrease cardiac output (heart failure)…calculating caloric intake, weights, educated about nutrition, patient may be a candidate for a feeding tube “risk for imbalance nutrition”
- heart rhythm: at risk for dysrhythmias, monitor rhythm, heart sounds, signs of heart failure “decreased cardiac output”, “activity intolerance”
- respiratory: monitor lungs sounds for crackles (indicate fluid overload), education about risk of frequent respiratory infections (vaccines to prevent, especially childhood vaccines) “risk for infection)
Atrial Septal Defect Facts | Congenital Heart Defects | NCBDDD | CDC. Retrieved from https://www.cdc.gov/ncbddd/heartdefects/atrialseptaldefect.html
Atrial Septal Defects – National Library of Medicine – PubMed Health. Retrieved from https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0023507/