Segmental Approach to congenital heart diseases
Congenital heart defects have various forms and can occur in many different combinations. Majority of patients with congenital heart defects survived into adulthood as a result of surgical palliations and intervention which may cause physiologic and anatomic changes. Even without intervention during early life, cardiac structure grows and evolves with the patients. Sequential segmental analysis of the heart enables complex congenital heart malformations to be described in a simple fashion. Most congenital heart malformations occur with normal connections of the cardiac chambers, but the chambers should be analyzed sequentially before the specific lesions are highlighted.
All hearts, normal or abnormal, are formed of three segments – the atria, the ventricular mass, and the arterial trunks. The sequential approach begins by determining the position of the atrial chambers. Thereafter, the atrioventricular connection and the ventriculoarterial connection and relations are analyzed. Philosophy of segmental analysis is founded on morphology. Chambers of the heart should be called what they were rather than where they were. Chambers are recognized according to their morphology. Each chamber had morphological characteristic that identified it no matter where it was in relation to the rest of the heart.
Sequential segmental analysis using echocardiography
Sequential segmental analysis using echocardiography should include following:
- I: Cardiac position and apex orientation
- II: Atrial arrangement
- III: Atrioventricular connection
- IV: Ventriculoarterial connections
- V: Associated malformations and function of segments.
Cardiac position and apex orientation
There are four possible atrial arrangements:
- usual atrial arrangement (or situs solitus, when morphological right atrium on the right and morphological left atrium on the left)
- mirror-image arrangement (situs inversus, when morphological right atrium on the left and morphological left atrium on the right),
- left or right atrial isomerism(there are bilaterally right or left atrial morphologies) (Figure 2).
Morphological features of left atrium
- tubular narrow based appendage
- limited pectinate muscle
- and no terminal crest.
Morphological features of right atrium
- broad base appendage
- extensive pectinate muscle
- presence of terminal crest.
Differentiation on echocardiographyOn echocardiogram, the morphological right or left atrium is best differentiated by their appendages. The right atrium has a triangular appendage and left atrium has a narrow tube-like appendage (Figure 3).
When aorta is to the left and IVC is to the right of the spine, there is abdominal situs solitus and corresponding atrial situs solitus. When aorta is to the right and IVC is to the left of the spine, correspond to situs inversus. In isomerism, the great vessels lie to the same side of the spine. In left isomerism, the inferior vena cava lies posterior to aorta and is interrupted and continued via a hemi-azygos vein in majority of cases. In right isomerism, the IVC is anterior to the aorta.
Atrioventricular connectionAtrioventricular connection can either be biventricular or univentricular connection. With biventricular connection, it can either be concordant when morphologic right atrium empties into the morphologic right ventricle and morphological left atrium empties into morphologic left ventricle or discordant when morphological right atrium empties to morphological left ventricle and morphological left atrium empties to morphological right ventricle (Figure 6).
When there is atrial isomerism, the connection is described as ambiguous. In contrast, univentricular atrioventricular connection describes hearts where only one ventricle is connected to the atrial chamber. The majority of hearts with univentricular atrioventricular connection have two ventricles but markedly different in size. There are three possible junction arrangements: double inlet, absent left-sided and absent right-sided atrioventricular connections. Depending on the morphology of the ventricle, it can be a dominant right ventricle, a dominant left ventricle, or morphologically indeterminate ventricle (Figure 7a-c).
In bi-ventricular heart, the valve usually follows the ventricle. Tricuspid valve connects to right ventricle and mitral valve connects to left ventricle. A common valve guards both right- and left-sided atrioventricular junctions, irrespective of its morphology.
Features of morphological right ventricle
The morphological right ventricle has following features that distinguish it from the morphological left ventricle:
- Coarse trabeculations at apex
- Moderate band
- More apically positioned septal leaflet attachment of tricuspid valve as compared to mitral valve
- Tethering of the septal leaflet to the septum (Figure 8).
Features of Morphological Left ventricle
The characteristics of morphologic left ventricle are
- Smooth trabeculation at apex
- No moderate band
- No septal attachment of the mitral valve
- Higher (basal) insertion of the mitral valve compared to tricuspid valve
The feature of solitary and indeterminate ventricle
- Coarse trabeculation than the morphological right ventricle
- There is no other chamber in the ventricular mass
A valve overrides when the atrioventricular junction is connected to ventricle on both sides of a septal structure (Figure 10). The degree of override determines the atrioventricular connections. The heart where one AV valve confined to the ventricle and the other AV valve overrides more than 50% will be described as double inlet ventricle (Figure 10). A valve straddles when its tension apparatus is attached to both sides of a septum within the ventricular mass. When the valve straddles, it usually overrides.
Atrioventricular valve morphology can influence type of atrioventricular connection.
Ventricular topology describes the spatial relationship of one ventricle to the other. There are two topologic patterns that are mirror images of each other. Right and left hand topology. Right hand topology is the normal pattern. Determination of ventricular topology requires first identification of the morphologic right ventricle. If the palmar surface of right hand can be placed on the septal surface, thumb in the inlet and the fingers toward the outlet and the wrist is at the apex, then this is the right –hand pattern. If only the left hand palm can be placed on the septal surface of the right ventricle in the same manner, then this will be described as left hand topology. Ventricular topology allows analysis of the atrioventricular junction in hearts with isomeric arrangement of atrial appendages.
There are four possible ventriculoarterial connections: concordant (connection to appropriate ventricle), discordant (connection to inappropriate ventricle), double-outlet (one arterial trunk and more than 50% of the other arterial trunk are connected to the same ventricle, be it of right ventricle, left ventricle or indeterminate morphology) and single outlet (common or solitary arterial trunk). The aorta and pulmonary trunk are distinguished by their branching patterns and origins of the coronary arteries. Pulmonary artery branches into left and right pulmonary arteries. Aorta has coronary arteries taking off from its root and head and neck vessels from aortic arch. A common arterial trunk has a single arterial valve and always gives rise directly to the coronary arteries, at least one pulmonary artery and the majority of systemic arteries. A solitary arterial trunk exists when there are no identifiable intrapericardial pulmonary arteries and collateral arteries arising form the descending aorta supply the lungs (Figure 11-13).
The majority of patients with congenitally malformed hearts will have usual chamber combinations. It is the associated malformations plays major role in patients’ clinical presentation. Anomalies of atrial, ventricular and great arteries must be carefully searched for and haemodynamic effect of the lesions must be assessed.
In summary, all hearts can be considered in three segments: the atrial chambers, the ventricular mass and the great arteries. Sequential segmental analysis means to identify the component parts of the heart by their morphology and describe the interconnections in a sequential manner.