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TRAINING COURSE
Year : 2021  |  Volume : 6  |  Issue : 2  |  Page : 141-147

Congenital heart defects: A morphological approach


Cardiac Morphology, Royal Brompton Hospital; National Heart & Lung Institute, Imperial College London, London, UK

Date of Submission06-May-2021
Date of Acceptance31-May-2021
Date of Web Publication30-Jun-2021

Correspondence Address:
Siew Yen Ho
Royal Brompton and Harefield NHS Foundation Trust, Sydney Street, London SW3 6NP
UK
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2470-7511.320323

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  Abstract 


Congenitally malformed hearts are often perceived as too complex for the general practitioner. By using a descriptive method, each malformed heart can be analyzed systematically without reference to presumptions of what went wrong during cardiac embryogenesis. The basis of this method, systemic segmental approach, is reviewed followed by examples of the common malformations.

Keywords: Atrial isomerism; Atrioventricular; Segmental analysis; Univentricular; Ventriculo-arterial


How to cite this article:
Ho SY. Congenital heart defects: A morphological approach. Cardiol Plus 2021;6:141-7

How to cite this URL:
Ho SY. Congenital heart defects: A morphological approach. Cardiol Plus [serial online] 2021 [cited 2021 Nov 28];6:141-7. Available from: https://www.cardiologyplus.org/text.asp?2021/6/2/141/320323




  Introduction Top


Congenital malformations of the heart are varied, ranging from the “simple” to the most complex comprising multiple defects. To facilitate diagnosis, practitioners have developed ways of analyzing the heart in systematic fashion over many years.[1],[2],[3],[4] While the segmental approach described by van Praagh in 1972, followed by Shinebourne et al. from 1976, and modified hybrid versions used in different institutions are essentially comparable, the terminologies and concepts often differ. Some relate back to what might have gone wrong during embryonic development while others are more descriptive. Given the penchant of busy clinicians to use shorthand and acronyms, nomenclature of congenital heart defects acquired an unwarranted reputation of being too complex and difficult for the beginner in the field. This article summarizes an approach based entirely on morphology and reviews several examples of congenital heart defects.


  Morphologic Approach Top


Based entirely upon recognition of the morphology of the cardiac chambers, this approach is not dependent on prior knowledge or presumptions of embryology. As is obvious in the human heart, right and left heart chambers are not located strictly in right and left positions.[5] Indeed, the chambers in the malformed heart may be abnormally located in relation to one another. Therefore, instead of location, morphologic distinction between right and left cardiac chambers is key. As discussed in the first article in this series, each cardiac chamber has characteristic morphologic features.[5] [Figure 1] summarizes the key features of each chamber. Not all distinctive features are present or detectable on imaging the malformed heart. The identification of a chamber may have to be inferred in few instances.

When describing a heart in a patient, it is important to note the position and orientation of the heart. Then, the analysis begins by following the flow of the blood from the great mediastinal veins to the atria and through the atrioventricular valves to the ventricles then to the great arteries via the arterial valves. Thus, the atria, ventricles, and great arteries are three fundamental segments interposed by two junctions [Figure 2].
Figure 1: The morphologic features of cardiac chambers and great arteries.

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Figure 2: The three segments of the heart and the junctions across which they connect are analyzed sequentially.

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This approach is known as sequential segmental analysis (SSA). Having determined the intrinsic morphology of each chamber, it considers the connections across the atrioventricular junctions and those across the ventriculo-arterial junctions [Figure 2].[3],[6] Connection refers to the anatomic linkage between atrial and ventricular chambers and between ventricular chambers and great arteries. “Connection” of adjoining chambers is usually, but not always, synonymous with “drainage.” In certain rare physiologies, drainage is abnormal even though the connection is normal.

Importantly, this approach provides the basic framework, but analysis is not complete until account is taken of all the associated malformations and listed. Majority of hearts have usual connections and spatial relations of the chambers but the associated lesions such as a large ventricular septal defect (VSD) or severe stenosis of the pulmonary valve that will dictate the clinical course.

Sequential segmental analysis 1: Atrial arrangement

The first step in SSA is the determination of atrial arrangement (also known as “situs” in Latinate terminology). According to the morphology of the atrial appendages, there are four variants of arrangement of atria [Figure 3]. Hearts with usual arrangement (“situs solitus”) are by far the most common. These have the atrial appendages in their normal positions. However, when the morphologic right atrial appendage is on the left side while the morphologic left atrial appendage is on the right side, the arrangement is described as mirror-imaged of usual (“situs inversus”).
Figure 3: The four variants of atrial arrangement.
al arrangement.


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The other two variants of arrangement of the atrial appendages are right and left isomerism. As the description implies, these hearts have bilateral morphologic right and left appendages, respectively. Arrangement of the atrial appendages frequently corresponds to arrangement of the branching pattern of the main bronchi and their relation to the pulmonary arteries. Although previously described as syndromes of visceral heterotaxy, the correlation between isomeric arrangement of the atrial appendages and arrangement of the abdominal organs and status of the spleen is not consistent.

To help diagnosis using imaging, inference can be made from the spatial relationships of the abdominal great vessels and the spine. Usually, the abdominal aorta descends in front or slightly to the left of the spine with the inferior caval vein to the right of the spine and anterior to the aorta. This pattern is reversed in patients with mirror imagery of the normal. There is usually right isomerism when both venous and arterial trunks are to the same side of the spine with the aorta in posterior position. Majority of left isomerism have interruption of the suprarenal portion of the inferior caval vein resulting in blood from the lower body draining via an azygos or hemiazygos vein into a superior caval vein. The enlarged vein will be on the same side of the spine as the aorta but posterior.

Sequential segmental analysis 2: Atrioventricular junctions

Examination of the atrioventricular junction distinguishes between biventricular and univentricular atrioventricular connections. Biventricular atrioventricular connections describe the arrangement whereby each atrium is connected to its own ventricle, albeit that one ventricle may be hypoplastic or the atrioventricular valve is imperforate. By contrast, univentricular atrioventricular connections describe hearts where only one ventricle is connected to the atrial mass.

Biventricular atrioventricular connections

When the atrial appendages are lateralized (either usual arrangement or mirror-imaged arrangement), there are two variations of biventricular atrioventricular connections, i.e., concordant and discordant [Figure 4]A. The atria are connected to the appropriate ventricles, when the atrioventricular connections are concordant. Discordant connections occur when the atria are connected to inappropriate ventricles. In cases with isomeric arrangement of the atrial appendages, the atrioventricular connections are described as ambiguous since the atrioventricular junctions are neither entirely concordant nor discordant [Figure 4]B. In these, the spatial relations of the ventricles relative to one another are noted.
Figure 4: Biventricular atrioventricular connections. They occur with either usual and mirror-imaged atrial arrangements (A) or with isomeric arrangements of the atrial appendages (B).
RA: Right atrium; LA: Left atrium; RV: Right ventricle; LV: Left ventricle


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Univentricular atrioventricular connections

This term describes hearts in which the atria are connected primarily to one ventricle. Most frequently, a second ventricle is present. Lacking an inlet portion and usually smaller, it is described as a rudimentary ventricle. Univentricular atrioventricular connections can exist in combination with any of the four variants of atrial arrangement. There are two major groups of univentricular atrioventricular connections [Figure 5]. One is double inlet and the other is absence of an atrioventricular connection.
Figure 5: Univentricular atrioventricular connections. These can occur with any of the four variants of atrial arrangement in combination with any of the three variants of ventricular morphology.
RV: Right ventricle; LV: Left ventricle


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Double inlet describes both atrial chambers connecting to the same ventricle. Most frequently, the receiving ventricle is large and of left ventricular morphology, recognized by its fine apical trabeculations. Accompanying the large or dominant ventricle, there is usually a rudimentary right ventricle in the anterior part of the ventricular mass. Occasionally, the dominant ventricle is of right morphology while the rudimentary left ventricle is located on the diaphragmatic aspect of the ventricular mass. It may be very small or even slit like. Very rarely, the receiving ventricle is of indeterminate morphology with very coarse trabeculations. This is a solitary ventricle, the truly univentricular heart.

Absence of an atrioventricular connection describes hearts in which only one atrium is connected to the ventricular mass [Figure 5]. In these hearts, either the right- or the left-sided atrium ends blindly in a muscular floor at the atrioventricular junction, without any remnant of a valve. Absent right atrioventricular connection usually exists with the left-sided atrium opening to a dominant morphologic left ventricle. Again, in these cases, a rudimentary right ventricle is in the anterior part of the ventricular mass. On the other hand, absent left atrioventricular connection usually occurs with the right-sided atrium connected to a dominant right ventricle while the rudimentary morphologic left ventricle is sited on the diaphragmatic aspect of the ventricular mass.

While consideration of the atrioventricular connections is a vital step in sequential analysis, the morphology of the atrioventricular valves should also be noted. For example, is there any straddling and overriding, any stenosis, etc. Furthermore, the proportion of straddling and overriding may change the type of atrioventricular connection from a biventricular form to a univentricular form and vice versa. An imperforate valve should be distinguished from absence of an atrioventricular connection. The imperforate valvar membrane between atrial and ventricular chambers renders a connection, thereby making biventricular atrioventricular connection instead.

Sequential segmental analysis 3: Ventriculo-arterial junctions

When two identifiable great arteries are present, and each arises from one ventricular chamber, the ventriculo-arterial connections are either concordant or discordant. When both great arteries arise from the same ventricle, this situation is described as double outlet from the morphologically right, left, or indeterminate ventricle.

Occasionally, the blind origin of one of the great arteries cannot be traced back to a specific ventricle. When this occurs, as in some cases with aortic atresia or pulmonary atresia, the term single outlet is used. Single outlet is also used to describe the connection existing in settings of common arterial trunk or solitary arterial trunk where there is only one arterial valve [Figure 1].

The morphology of the arterial valves should be noted. The proportion of overriding of an arterial valve needs to be considered in assigning the ventricle to which the major part of the valve is connected to.


  Associated Malformations Top


Finally, list all the associated malformations to complete the analysis. Most often, these are the lesions mainly causing the clinical presentation. These could be septal defects, valvar abnormalities, coronary abnormalities, anomalies of systemic and pulmonary venous connections, aortic arch anomalies, anomalies of pulmonary arteries, position of the heart and apex, etc.

Indeed, segmentally, majority of malformed hearts have usual atrial arrangement with concordant atrioventricular connections and ventriculo-arterial connections, but this cannot be assumed. The systematic analysis does not assume anything is normal until proven. This considerably reduces the risk of missing a vital piece of the jigsaw when putting together a summary of the malformation examined.


  Examples of Congenital Heart Malformations Top


Congenital heart defects are the most common congenital malformations with an incidence estimated at 4/1000–50/1000 in a review of published data[7] and an incidence of 1 in 130–145 live births in the UK.[8] Presented below are some examples of common defects presenting with dominant left to right shunt (VSD, atrial septal defect [ASD], atrioventricular septal defect [AVSD], and patent arterial duct [PDA]), cyanotic heart defects (tetralogy of Fallot and complete transposition), and obstructive defects (aortic arch coarctation).

Ventricular septal defect

Whether presenting in isolation or as an integral part of a combination of lesions, VSDs can be classified into three groups according to the composition of their borders [Figure 6]. The most common is perimembranous defect with a fibrous posterior-inferior border highlighting its proximity to the atrioventricular conduction bundle. By contrast, a muscular defect is surrounded completely by muscle distancing it from the immediate vicinity of the conduction bundle. The third type is the doubly committed and juxta-arterial defect that has the conjoined aortic and pulmonary valves at its superior border. Its posteroinferior border may be muscular or extend to become perimembranous.
Figure 6: Right ventricular perspective of the three types of ventricular septal defects classified according to their borders.
Muscular defects (yellow) are located anywhere in the ventricular septum. Perimembranous defects (orange) have the atrioventricular conduction bundle (red) in the posteroinferior margin. Doubly committed and juxta-arterial defects (green) have the aortic and pulmonary valves forming the superior border.


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Atrial septal defect

Shunting at atrial level mostly occurs through a hole in the oval fossa owing to a deficiency in the flap valve (septum primum) that normally covers the fossa floor completely. Although often referred to as a secundum ASD, it is a deficient septum primum, i.e., defect within the oval fossa.[9] The flap valve has one or more holes or resembles a fishnet. Interatrial connections outside the confines of the rim of the oval fossa are named in relation to their locations [Figure 7]. The orifices of the superior and inferior caval veins are related to the superior and inferior sinus venosus defects, respectively, usually with the respective caval vein opening to both atria. Often, these are associated with partial anomalous connection of a pulmonary vein. Coronary sinus defects can be due to apertures in the partition between the sinus and the left atrium or are direct interatrial communications at the site of the orifice of the coronary sinus when the partition is absent.
Figure 7: Right atrial perspective of the locations of different types of defects giving interatrial communications.
SCV: Superior caval vein; ICV: Inferior caval vein; AV: Atrioventricular


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Atrioventricular septal defects

This is a spectrum of defects ranging from those termed “ostium primum ASD” to “atrioventricular canal.” They are unified in having a common valve across the atrioventricular junction.[10] The common valve does not resemble a tricuspid or a mitral valve. Instead, the valve in AVSD is characterized by having five leaflets, two of which are bridging leaflets that cross the ventricular septum. The normal offset arrangement between right and left atrioventricular valves at the septum is lost. The common valvar orifice becomes divided into left and right orifices when the bridging leaflets join. In most of these cases, the bridging leaflets are adherent to the crest of the ventricular septum, confining shunting to atrial level (as in “ostium primum” defect). The variations in arrangement and insertions of the bridging leaflets determine the level of shunting at atrial, ventricular, or both atrial and ventricular levels.

Patent arterial duct

In the fetus, the duct joining the pulmonary trunk to the aorta allows most of the blood flow to reach the aorta instead of going to the lungs. After birth, the flow is reversed as the duct begins to close spontaneously in a process that is completed by the age of 3 months in most infants. Failure of closure is persistent PDA.

In some congenital heart malformations, for example, when the pulmonary valve is atretic and the septum is intact, the circulation is duct dependent because a PDA is the only channel for pulmonary supply.

Tetralogy of Fallot

The classic four features of this malformation are subpulmonary stenosis, VSD, overriding aorta, and right ventricular hypertrophy [Figure 8]A. The main anatomical substrate of subpulmonary stenosis is the outlet septum which is deviated anteriorly and cephalad [Figure 8]B. Usually, the VSD is large. Pressure overload in the right ventricle results in muscular hypertrophy of its wall. Variations of this malformation are associated defects such as multiple VSDs, pulmonary valve and arterial stenosis or atresia, AVSD, and aortic arch anomaly.
Figure 8: The four features of tetralogy of Fallot.
A and B, The heart specimen displays the right ventricle with the outlet septum cut through to show the overriding aortic valve seen through the ventricular septal defect and the narrow subpulmonary outflow tract (red arrows).VSD: Ventricular septal defect


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Complete transposition of the great arteries

The segmental arrangement is concordant atrioventricular connections together with discordant ventriculo-arterial connections. Thus, the aorta and the pulmonary trunk arise from the wrong ventricles. Most often, the great arteries are not normally related. They frequently arise in parallel fashion with the aorta anterior and to the right of the pulmonary trunk, but there are variations. Postnatal survival requires mixing of blood between systemic and pulmonary circulations through any septal defects or persistence of an arterial duct. The most common associated lesions are VSD, pulmonary outflow or valvar stenosis, and variations in coronary artery patterns.

Coarctation

This is a restriction in the lumen of the aortic arch. When the narrowing is a long segment of the arch, for example, at the isthmus, it is termed tubular hypoplasia. The term coarctation refers to a lesion that causes restriction at a discrete site. In the neonate and infant, this is usually at the insertion of the arterial duct and formed by a circumferential ridge of ductal tissue.[11] Normal anatomical closure of the duct postnatally exacerbates the narrowing of the aortic arch.

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  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]



 

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