The Arterial Trunk: Part Four

The Arterial Trunk: Morphology of the Pediatric Heart: How to Identify the Various Structures of the Heart in the Presence of Congenital Heart Disease, for Echocardiographers. Part Four
The Great Arteries
It is advisable that you read the first three installments of this series for important background information. As an echosonographer, the ability to identify the various structures of the heart is critical if you are going to provide adequate information to both the pediatric cardiologist as well as the pediatric surgeon.

Which atria connect to which ventricle? Which ventricles connect to each great artery? What types of venous connections are there? The best way to do an echo is to take each structure one at a time, identify that structure and determine where that structure begins and terminates.

Embryologically, the great arteries (pulmonary artery – PA, and the aorta – AO) begin as a common trunk that is attached to the ventricular mass with a “ring” of tissue that will later form the truncal cushions of the semilunar valves. This primordial trunk will begin to septate, or begin to form two separate arteries that twist rightward (d-looping) until the appropriate arteries merge with their respective ventricles.

If the venous connections are normal (inferior vena cava – IVC, superior vena cava – SVC and, the pulmonary veins), connecting to the appropriate atria, and the atria connect in a normal fashion to the appropriate ventricles, but the AO and PA are “switched” or transposed, this is a d-transposition of the great arteries.

If the venous connections are normal and connect to the heart appropriately, but the ventricles are transposed, this is known as an l-transposition, or “corrected transposition.”

Four things may happen to the arterial trunk. These are known as “truncus arteriosis defects.”

Truncus Arteriosis Defects
Where there are a two fully septated arteries that connect normally to the ventricular mass, this is a normal configuration.

There may be a “merged” PA and AO (common trunk) or a PA and AO that override a two ventricle structure with an incomplete ventricular septum (a large primum VSD). In this presentation, the semilunar valves also merge into a multi-leaflet common valve that may have two, three, four, or five leaflets. Most commonly, the valve is a four leaflet type of valve.

There may be a single truncal artery (typically of aortic morphology) where the pulmonary arteries arise distally from the aortic valve apparatus in the ascending or descending portion of the truncal artery with a large primum VSD.

There is a fourth type of configuration in which there is a common arterial trunk where the aortal portion is separated from the pulmonary artery, but connected by a PDA (patent ductus arteriosis) and a large primum VSD. This is known as a truncus arteriosis with an interrupted aortic arch.

Further adding to the mix, there may be a right sided aortic arch or left sided (normal) aortal aortic arch.

As an echosonographer, you must identify all of the structures of the heart: the atria, ventricles, venous connections and the type of truncal connections present. Further, you will need to identify the number of leaflets present in the semilunar valve apparatus, whether the arch is right or left sided, and where the pulmonary artery connections arise.


Ken Heiden RDCS