Fetal Heart Flashcards
(42 cards)
What is the best time to do a fetal exam?
18-22 weeks
What is the approximate size and heart rate of a 20-week fetal heart?
- Size: Comparable to an American quarter
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Usual fetal heart rate at 20 weeks:
- 120–160 bpm (beats per minute)
- Normal range can extend from 100–180 bpm
What are the types of fetal arrhythmias and their heart rate ranges?
- Tachycardia: Heart rate between 180–300 bpm (too fast)
- Bradycardia: Sustained heart rate below 100 bpm (too slow)
- Fetal arrhythmias can lead to non-immune fetal hydrops
How does the embryonic cardiovascular system develop and when does the heart begin to function?
- Origin: Cardiovascular system (heart, vessels, blood cells) forms from the mesoderm
- First functional system in the embryo
- Blood circulation begins at \~3 weeks post-conception (5 weeks menstrual age)
- Heartbeat can be detected by ultrasound around this time
- Cardiogenic cords (paired tubes) fuse around day 22 to form the heart tube, which begins beating the same day
- By the 6th menstrual week, the heart is fully formed and placental circulation begins
When does the fetal heart become a four-chambered structure, and where does fetal circulation begin?
- By 11 menstrual weeks, the embryonic heart becomes a four-chambered pump
- Fetal circulation begins at the placenta
What are the four main shunts in fetal circulation and their purpose?
Purpose: To bypass the liver and non-functioning fetal lungs, directing oxygenated blood from the placenta to vital organs
The four fetal circulation shunts are:
1. Placenta – where oxygen and nutrient exchange occurs
2. Ductus Venosus – bypasses the liver to deliver oxygenated blood to the heart
3. Foramen Ovale – allows blood to flow from the right atrium to the left atrium, bypassing the lungs
4. Ductus Arteriosus – connects the pulmonary artery to the aorta, further bypassing the lungs
What are the four key ultrasound views used to assess normal fetal cardiac anatomy?
Four Chamber View (4CH HT)
* Shows the right and left atria and right and left ventricles
* Most important view—detects many cardiac anomalies
Left Ventricular Outflow Tract (LVOT)
* Assesses flow from the left ventricle into the aorta
Right Ventricular Outflow Tract (RVOT)
* Assesses flow from the right ventricle into the pulmonary artery
3 Vessel Views:
* 3VV (3 Vessel View): Evaluates arrangement and size of the pulmonary artery, aorta, and superior vena cava
* 3VTV (3 Vessel Tracheal View): Adds trachea for spatial orientation of vessels and airway
What are the key components of a sonographic exam of the fetal chest?
- Check thoracic bones for integrity and symmetry
- Compare chest size to abdomen size
- Evaluate lungs for echogenicity and structure
- Identify and assess diaphragm; confirm heart is in the chest and stomach is in the abdomen
- Assess the great vessels
- Evaluate the fetal heart for structure and function
What is the role of the foramen ovale in fetal circulation and what happens to it after birth?
- The foramen ovale allows blood to flow from the right atrium to the left atrium, bypassing the fetal lungs
- About 40% of fetal blood passes through it into the left atrium
- After birth, it normally closes and seals within the first 24 hours as part of the transition to neonatal circulation
What are the optimal fetal positions and key components of a complete fetal heart ultrasound exam?
- Best fetal position: Supine (spine down) or side-lying
- Poor visibility if fetus has spine up
- First, confirm the heart is on the left side and correctly positioned in the chest
Complete cardiac evaluation includes:
* Four chambers
* Valves
* Connections to great vessels (aorta and pulmonary artery)
* Three vessel heart view (3VV) – PA, AO, SVC
* Three vessel tracheal view (3VTV) – PA, AO, SVC, trachea
What is Roy Filly’s 4 Chamber Heart System and how does it guide fetal heart evaluation?
- Step 1: Locate the stomach in a cross-sectional view of the fetal abdomen
- Step 2: Scan upward to the chest; the apex of the heart should point in the same direction as the stomach
- Step 3: Identify the spine in cross-section at the level of the heart
- Step 4: Find the descending aorta (vessel in front of spine)
- Step 5: The left atrium is always located anterior to the descending aorta
What is the 4 chamber heart view?
- Heart is located in the left chest
- Occupies about 1/3 of the chest cavity
- Apex points \~45° toward the left anterior chest wall
- Right and left ventricles are equal in size
- Foramen ovale flap opens into the left atrium
- Moderator band seen in right ventricular apex
- Atrioventricular valves separate atria and ventricles
- Left ventricular blood flow reaches the apex of the heart
What are the four fetal heart valves that can be visualized on ultrasound, and where are they located?
- Tricuspid valve – between the right atrium and right ventricle
- Mitral (bicuspid) valve – between the left atrium and left ventricle
- Pulmonic valve – between the right ventricle and pulmonary artery
- Aortic valve – between the left ventricle and aorta
What cardiac anomalies can be detected in the four-chamber view of the fetal heart?
- Single ventricle
- Chamber abnormalities: hypertrophy, hypoplasia, atresia
- Tricuspid or mitral valve atresia
- Atrial or ventricular septal defects
- Cardiomyopathy
- Endocardial cushion defects
- Aortic or pulmonary stenosis
- Ebstein’s anomaly
What are key features to evaluate in the ventricles during a basic fetal cardiac exam?
- Ventricles should be equal in size
- Interventricular septum should be intact
- Moderator band helps identify the right ventricle
What is an echogenic intracardiac focus (EIF), and when is it considered normal or concerning?
- EIF is a microcalcification within the papillary muscle of the heart, often seen in the left ventricle
- Found in up to 5% of pregnancies
- Considered a normal variant if seen alone with no other abnormalities
- EIF in the right ventricle or with other findings may increase the risk of aneuploidy (e.g., Down syndrome)
What are the key outflow tracts of the fetal heart and their corresponding chambers?
- Right ventricle → Pulmonary artery (PA) → to the lungs (oxygen-poor blood)
- Left ventricle → Aorta (AO) → to the body (oxygen-rich blood)
These outflow tracts are essential for evaluating proper fetal heart structure and blood flow direction.
What does the Left Ventricular Outflow Tract (LVOT) view demonstrate in fetal cardiac ultrasound?
- Connection between the aorta and left ventricle
- Left atrium
- Aortic root
- Aortic valve
- Ventricular septum
- Technique: Imaged by tilting the probe toward the fetal head
What does the Right Ventricular Outflow Tract (RVOT) view show in fetal cardiac ultrasound?
- Pulmonary artery in long axis, extending anteriorly in axial section
- Pulmonic valve between the right ventricle and pulmonary artery
- Visualization of the right ventricle
What does the 3-vessel view (3VV) in fetal ultrasound evaluate and what vessels are seen?
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Purpose: Evaluates alignment, size, and number of the great vessels
Vessels visualized (from left anterior to right posterior):
- Pulmonary artery (largest)
- Aorta (middle size)
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Superior vena cava (SVC) (smallest)
* Alignment: In a straight line, decreasing in size from left to right
* Clinical use: Helps detect abnormalities in the outflow tracts and vascular anatomy
What are the additional fetal heart views shown in this image, and how are they identified?
Aortic Arch View:
* Obtained by rotating 90° from the 3-vessel view (3VV)
* “Candy cane” appearance
* Shows the aortic arch arising from the center of the heart
Ductal Arch View:
* Appears like a hockey stick
* Seen from the anterior chest wall
* Represents the ductus arteriosus connecting the pulmonary artery to the descending aorta
What anomalies can be detected using outflow tract views in fetal cardiac ultrasound?
- Transposition of the great vessels
- Tetralogy of Fallot
- Double-outlet right ventricle
- Pulmonary stenosis
How common are fetal cardiovascular abnormalities and how are they typically detected?
- Cardiovascular abnormalities are among the most common congenital defects
- Occur in about 1 in 100 live births
- Most can be detected during a routine OB ultrasound
Important associations to remember:
* Aorta arises from the left ventricle
* Pulmonary artery arises from the right ventricle
What are the main categories of congenital cardiac abnormalities in the fetus?
Septal Defects
* Ventricular septal defect (VSD)
* Atrial septal defect (ASD)
* Atrioventricular septal defect (AVSD)
Conotruncal Anomalies
* Tetralogy of Fallot
* Transposition of the great arteries
* Persistent truncus arteriosus
* Double-outlet right ventricle
Single Ventricle Anomalies
* Hypoplastic heart syndromes
* Tricuspid atresia
* Double-inlet left ventricle
Disproportionate Ventricular Size
* Ebstein’s anomaly
* Coarctation of the aorta
Positional Abnormalities
* Situs abnormalities
* Ectopia cordis
Cardiac Wall Abnormalities
* Cardiomyopathy
* Cardiac tumors
* Fetal pericardial effusion
Heart Rate/Rhythm Abnormalities
* Fetal supraventricular tachycardia
* Atrial flutter
* Premature ventricular contractions
* Premature atrial contractions
* Atrioventricular block
