ULTRASOUND OF THE FETAL HEART - Normal


 

For the detailed scanning protocol

 

A 10 step approach

Step 1: Check the heart is beating

Step 2: M-mode heart rate - should be between 120 and 180 beats per minute

Hover your cursor over images to see highlighted anatomy or pathology

Step 3: SITUS


 Heart Orientation  Situs
The heart should be angled 45degrees to the left and occupy approximately 1/3 of the chest. Confirm that the heart is on the fetal left.

 

Step 4: 4 CHAMBER VIEW AND VALVES

                                                                                             

 

4 chamber heart
 

Valves
4 chamber heart.
  • LA= Left Atrium
  • LV= Left ventricle
  • RA= Right Atrium
  • LV left Ventricle
The transverse view should only contain 1 rib. If you can only get a 4 chamber view with more than this it could be a sign of cardiac pathology. The heart should occupy approximately 1/3 of the chest. The apex is orientated 45 degrees to the left. The right ventricle contains the moderator band.
  • The atrio-ventricular valves should arise from the crux of the heart as an offset cross.
  • The Foramen ovale is clearly seen.
  • The atria should be of equal size and the ventricles 

 

  • 4 chamber view scan plane:scan plane
 

This image shows the scan planes to obtain:

  • 4 CHAMBER VIEW
  • LVOT
  • RVOT

From the 4chamber view, by angling cranially rather than sliding the probe the outflow tracts are easily seen. 

 

VALVES visible on the 4 chamber view

 4 chamber

Atrioventricular Valves opening and closing
Angle the probe cephalad to get the 4 chamber view of the fetal heart.
The valvular movement should simulate birds wings.

Pulmonary Vein Drainage

 

Pulmonary Vein drainage
When assessing the 4 chamber heart with CDI it is important to assess the pulmonary veins draining into the left atrium as above.

 

STEP 5: Left Ventricular Outflow Tract  LVOT

 

 Left ventricular outflow tract  LVOT

SCAN PLANE LVOT

The LVOT is seen by scanning through the right chest wall. The aorta arises from the left ventricle and  is just above and between the AV valves. The aortic valve moves freely. 

Left Ventricular Outflow Tract:
(Aortic Root) It should always be assessed in both B Mode and colour imaging. No branching should be seen in this view.


STEP 6: Right Ventricular Outflow tract - RVOT

 RVOT  

Right ventricular outflow tract

RVOT

The probe is angled cephalically from the LVOT view and a slight rotation of the probe to the right fetal shoulder. The pulmonary artery is superior to the aorta and it arises from the right ventricle.


Right Ventricular Outflow Tract:
(Pulmonary Trunk

 

Pulmonary Arteries

 

 Pulmonary arteries  Pulmonary arteries colour
Look for the RVOT to branch into the left and right Pulmonary arteries. The RPA is posterior to the Aorta and the LPA is superior to the right.

 

STEP 7: 3 Vessel view - PAV view

 PAV view  3 vessel view
3 vessel or PAV  or SAP view
  • P = Pulmonary artery exiting the right ventricle
  • A = Ascending aorta
  • V or S =Superior Vena Cava 
These should be in order of descending size. (otherwise suspect coarctation of the aorta)
If the aorta and pulmonary artery are not in perpendicular planes, suspect transposition

STEP 8: INTERVENTRICULAR SEPTUM

 

False Positive Ventricular Septal Defect

 

 

 Ventricular Septum

 

 

Beware of false positives with the interventricular septum:
The part of the interventricular septum closest to the crux of the heart is the membranous portion and naturally tapers. If your angle is poor, it may be invisible simulating a venticular septal defect(VSD). Note the descending aorta is on the left.
To avoid this, ideally, the integrity of the interventricular septum should be confirmed from a perpendicular approach.

STEP 9: AORTIC ARCH

 Aortic Arch  sagittal view aortic arch
Demonstrate the aortic arch as it leaves the left ventricle.
It will have a 'walking stick' curve.
Sagittal View of the Aortic Arch

 

 

STEP 10:  DUCTAL ARCH

 

 Ductal Arch  Ductus arteriosus
The ductal arch demonstrates the correct orientation and communication between the Aorta and the pulmonary trunk.
It will have a flatter curve like a 'hockey stick'.
Ductal Arch

 

 

 

Ultrasound of the Fetal Heart -Protocol

Role of Ultrasound

  1. To confirm normal anatomy to the best of our ability.
  2. To progress, or elaborate on, known foetal heart pathology.

Limitations

  • Fetal lie and large maternal habitus will inhibit the scan.
  • With patience, the difficulties posed by foetal postion can usually be overcome.

Equipment Selection

  • Depending on the gestational age and maternal habitus, a curvilinear probe between 3-9Mhz.A linear probe may be used on thin patients.
  • If 3rd trimester with very large maternal habitus, a 2.5Mhz annular array may be needed.
  • Low dynamic range B-mode
  • High PRF colour and doppler settings with low persistance.
(most machines will have an adequate factory preset, fetal heart setting)

 

 

Scanning Technique

1st Step: Check the heart is beating

2nd Step: M-mode heart rate - should be between 120 and 180 beats per minute

3rd Step:    Situs- check which is the left side of fetus then do a dual image in a tranverse axial plane of the fetus with firstly the thorax showing the heart apex orientated to the left at an angle of approximately 45degrees. The transverse section should only contain 1 rib. The second image showing the stomach on the left ensuring the left and right side is labelled.

4th Step: Four Chamber View- Angling cephalad from a transverse axial view of the abdomen.

The heart should occupy approximately 1/3 of the chest.The ventricles should be of similar size and the atria should be of similar size. The moderator band is in the right ventricle. The left ventricle extends more apically.
Assess the AV valves (atrioventricular) ie The tricuspid valve on the right is more apical than the mitral (on the left)valve insertion onto the interventricular septum. (the "offset cross" appearance)
Watch ,in real time, the opening and closing of the valves in systole and diastole.
The pulmonary venous connections can be identified.

5th and 6th Step Outflow Tracts

5th Step:      LVOT

From the 4chamber view, angle further cephalad to see the Left ventricle and the aorta (Left outflow tract) in the same view.
The aorta will be coursing to the right posterior direction.It should be assessed in colour Doppler also looking for any stenosis.
6th Step: RVOT From the LVOT view, the probe is angled further towards the head and slightly towards the fetal left shoulder.
This show the pulmonary trunk heading directly posteriorly towards the spine. It will divide into the pulmonary arteries.
Image and look in bmode and Colour Doppler.

7th Step: 3 Vessel View This view is a slightly oblique, axial view.

It cuts the upper part of the arches and transversally the Superior Vena Cava.

    This is an image with
  1. A full length view of the Pulmonary Artery (P) which arises from the right ventricle.
  2. A cross section of the ascending aorta (A)
  3. The superior vena cava (V)

It is commonly labelled PAV on the image.
It is important to have the 3 vessels in line with each other in order of largest (P) to smallest (V).
The aorta and pulmonary artery must be perpendicular to each other, otherwise there is a serious heart defect such as transposition of the great vessels.

8th Step: Interventricular Septum
IVS (inter-ventricular Septum):
Should be assessed when the foetus is in a decubitus position so the ultrasound beam is perpendicular to the septum.
This will avoid anisotropy and a false positve for septal defect.
It should be assessed in both Bmode and Colour Doppler.

9th Step: Aortic Arch

The 'arches' are best assessed when the foetus is prone.


Aortic Arch: Turn the probe 90degrees to a para-sagittal plane on the foetus.
The Aortic arch arises from the centre of the heart and is commonly referred to as a "cane".
Coarctations may be visualised in this view.

10th Step: Ductal Arch

 

This is the ductus arteriosis: The junction between the pulmonary trunk and the aorta.
Utilise a similar scan plane to the aortic arch.
The ductal arch is referred to as a "hockey stick" appearance, with the arch arising from the anterior of the heart. Bmode and colour assessment.

 


 

Common Pathology

 

For fetal heart pathology

 


 

Basic Hard Copy Imaging


A foetal heart series should include the following minimum imaging:

  • Situs and orientation
  • 4 Chambers
  • Inter-ventricular septum
  • Left Ventricular outflow tract
  • Right ventricular outflow tract
  • 3 vessel view
  • Aortic arch V's ductal arch
  • Document the normal anatomy. Any pathology found in 2 planes, including measurements and any vascularity.

 

REFERENCES

  • Callen PW. Ultrasonography in Obstetrics and Gynecology, Fourth Edition. W.B.Saunders Company, 2000.
  • Nyberg DA, Kapur RP, Mahony B, Pretorius DH. Ultrasound of Fetal Anomalies. Mosby,Inc., 1995.
  • FOETAL HEART ULTRASOUND    “How,Why and When” June 2007 Catherine Fredouille, MD, Jean-Eric Develay-Morice, MD, Ultrasonographer
 


 

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