Terminology                                                                                          

Sequential Segmental Analysis

To understand the anatomy and blood flow pattern in complex disease it is necessary to systematically assess the venous (systemic & pulmonary) return to the heart, the cardiac chambers & the great vessels.

This is done by first determining the atrial arrangement (situs) and the connecting veins. Then the ventricular arrangement is assessed and the connection to the atria (atrio-ventricular connection). Finally the great arterial arrangement is assessed and the connection to the ventricles.

Situs (Atrial Arrangement)

The right and left atria are identified morphologically by their respective atrial appendages. The RA has a triangular, broad based appendage whilst the LA has a narrow, finger like appendage. Almost invariably 2 atria are present although sometimes there may be a common atrial  chamber if the atrial septum is absent. There are 4 possible atrial arrangements situs solitus, situs inversus, right isomerism and left isomerism.

The atrial arrangement can be identified echocardiographically by the relationship of the aorta and IVC to the spine although sometimes the appendages can be viewed directly (TEE). In situs solitus the Ao lies to the left of the spine and the IVC to the right. The arrangement is the reverse in situs inversus. In right isomerism both vessels lie on the same side with the aorta posterior whilst in left isomerism, as shown on the right, the aorta lies anterior.

Another method is to assess the bronchial tree. The right main bronchus is shorter than the left and takes off at a more acute angle from the carina. The reverse is true in situs inversus, there are two symmetrical short main bronchi in right isomerism and two longer bronchi in left isomerism.

The normal arrangement (situs solitus) is shown in the bronchogram on the right.

Situs Solitus

This is the normal arrangement in most patients with the organs on their appropriate sides.

Situs Inversus

This is sometimes know as a mirror image arrangement. It is found in Kartagener's syndrome. Usually, but not always, the abdominal situs is also mirror imaged.

Right Isomerism

This is often known as asplenic syndrome. The lungs are both tri-lobed (right morphology) with short main bronchi. The atria are both of right sided morphology. 2 sinus nodes may occur. Cardiac problems include anomalous pulmonary venous return, septation & abnormal cardiac positions. Infections are a serious risk as the spleen is frequently absent.
 

Left Isomerism

This is often known as polysplenic syndrome. The lungs are both bi-lobed (left morphology) with long main bronchi. The atria are both of left sided morphology. No true sinus node exists and the p wave morphology is often variable. Cardiac problems include anomalies of systemic venous return, septation & abnormal cardiac positions. The IVC is incomplete & continues as the hemi-azygos vessel. The liver is usually central and polysplenia common.

Ventricular Morphology

The right ventricle is distinguished by its triangular shape, heavy apical muscle bands and septal attachments of the valve leaflets. In contrast the left ventricle is banana shaped with a smooth wall and valvar attachments only to the free wall. Clearly the commonest situation is when two, well formed ventricles are present. True “single” ventricles do exist but it is usually possible to identify a rudimentary ventricle attached to the side of the main ventricle. The surgical outcome is better in those with a dominant LV.
 

Atrio-Ventricular Connection

The AV connection may be biventricular, when the atria are connected to both ventricles, univentricular when connected to just one ventricle or a common connection.

Biventricular Connection

If two adequate sized ventricles are present then they may each be connected to the appropriate atrium ie. RA to RV, LA to LV (concordant connection) or they may be connected to the opposite atrium ie. RA to LV, LA to RV (discordant connection) as in the picture opposite where the smooth walled LV lies on the right and the trabeculated RV lies on the left.

Univentricular Connection

When there is only a single dominant ventricle for the atria to connect to then they may both drain into the ventricle This is described as a double inlet ventricle.

Alternatively only one atrium may be connected to the ventricle with the other connection being absent. This is the case for example in tricuspid atresia.

Common Connection

An AV connection is described as common when the atria are connected to both ventricles by a single valve - most often seen in a complete atrio-ventricular septal defect.

Overriding Connection

An atrium or artery may be connected to more than one ventricle. If a valve overhang across the ventricular septum into another ventricle it is described as over-riding. The commonest situation is tetralogy of Fallot when the aortic root overrides the ventricular septum. If part of the valve apparatus inserts into the other ventricle then it is described as straddling

Arterial Morphology

The definition of an aorta is an artery that gives rise to the coronary arteries and the brachio-cephalic vessels. In contrast the pulmonary artery branches into two but does not give rise to any vessels. Clearly the commonest situation is when two, well formed arteries arise from the ventricular mass.
 

Ventricular-Arterial Connection

When the aorta is connected to the LV & the pulmonary artery to the RV the connection is described as concordant. This is the normal situation.

Transposed Connections

If the aorta is connected to the RV & the pulmonary artery to the LV then the connection is discordant. This is most commonly seen in transposition of the great arteries.
 

Double Outlet Connections

If both great arteries arise from a single ventricle (invariably the RV) the connection is described as double outlet. The great arteries may be normally related to each other or mal-positioned (“TGA”).

The situation is still described as double outlet even if both vessels are not completely over a single ventricle. If more than 50% of an artery overrides a ventricle it is said to be committed to it.
 

Single Outlet Connections

One vessel only may arise from the heart. This may be because a vessel is absent (invariably the pulmonary artery) as is the case with the drawing on the left or because the two vessels have fused to form a common outlet as seen in the drawing of a truncus on the right.

Cardiac Position

The cardiac position is independent of the connections and hence the cardiovascular physiology.
Laevocardia is the normal cardiac position with the heart in the left side of the chest, dextrocardia implies the heart is predominantly in the right hemi-thorax, whilst in mesocardia the heart lies in the midline. Similarly the direction the apex points (as judged by echocardiography) is described as laevoversion, dextroversion or mesoversion. It is important to note the position of other organs eg. in the picture there is dextrocardia but the stomach is in the normal place.
 

This page was last edited 16/2/2004

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