ULTRASOUND OF THE FETAL HEART

–  Check the heart is beating , Do the M-Mode image, get the fetal hear rate. make sure the heart is in the left side by showing the stomach in transverse section and the 4ch heart in transverses section.

–  M-mode heart rate – should be between 120 and 180 beats per minute

Hover your cursor over images to see highlighted anatomy or pathology

 

 –  SITUS 

The heart should be angled 45 degrees to the left and occupy approximately 1/3 of the chest.

 Step 4: 4 CHAMBER VIEW AND VALVES

                                  
                                                       

4 Chambers heart.	LVOT & 4CH.H         Valves.
LA= Left Atrium LV= Left ventricle RA= Right Atrium LV left Ventricle The prominant papillary muscles make the right ventricle appear to be a much smaller chamber.	The atrio-ventricular valves should arise from the crux of the heart as an offset cross. The Foramen ovale is clearly seen.

 

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

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

  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 ventricular septal defect(VSD)

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)

To avoid this, ideally, the integrity of the interventricular septum should be confirmed from a perpendicular approach.

 

 

A = Ascending aorta

    V = Vena Cava (superior)

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

To avoid this, ideally, the integrity of the interventricular septum should be confirmed from a perpendicular approach.

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’.

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) To avoid this, ideally, the integrity of the interventricular septum should be confirmed from a perpendicular approach.

                                    Role of Ultrasound

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

Limitations ; Fetal lie and large maternal habitus will inhibit the scan.

• With patience, the difficulties posed by fetal postion can usually be overcome.

Equipment Selection

• Depending on the gestational age and maternal habitus, a curvilinear probe between 3-5 MHz.
• If 3rd trimester with very large maternal habitus, a 2.5 MHz annular array may be needed.
• Low dynamic range B-mode
• High PRF colour and Doppler settings with low persistence.

(most machines will have an adequate factory preset, fetal heart setting)

–   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 hearts axis towards the left and the second image showing the stomach on the left ensuring the left and right side is labelled.

–  Four Chamber View– Angling cephalad from a transverse axial view of the abdomen.

The ventricles should be of similar size and the atria should be of similar size.
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.

–   LVOT & RVOT.

From the 4 chamber 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.

– 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 B-mode and Color Doppler.

-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.

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.

– IVC-Interventricular Septum
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’.(inter-ventricular Septum):
Should be assessed when the fetus is in a decubitus position so the ultrasound beam is perpendicular to the septum.
This will avoid anisotropy and a FALSE POSITIVE FOR SEPTAL DEFECT.
It should be assessed in both B-mode and Color Doppler.

– DO the Aortic Arch

The ‘arches’ are best assessed when the fetus is prone.

Aortic Arch: Turn the probe 90 degrees to a para-sagittal plane on the fetus.
The Aortic arch arises from the center of the heart and is commonly referred to as a “cane”.
Coarctations may be visualized in this view.

– do the Ductal Arch ; This is the Ductus arteriosis: The junction between the pulmonary trunk and the aorta.

Utilize 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. B-mode and colour assessment.

Basic Hard Copy Imaging ; A fetal 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.

Twins kissing each other.

     Thanks for reading.

Steve Ramsey, PhD.    Calgary, Alberta- Canada.