Section I: Morphologic approach to the congenitally malformed heart
Historical note
In the past, embryologic terms were commonly used in the description of congenital heart defects, even without the more complete understanding of cardiac embryology as we have today. Some of these embryology-based names still persist in the current literature, used as stand-alone terms or as synonyms to descriptive terminology.
Several acronyms were used in the 20th century, and some are still used currently in the nomenclature of the congenitally malformed hearts, for historical purposes.
But it was the introduction of the segmental approach by the Van Praaghs in the 1960s and 1970s , that allowed the description of any combination of lesions, even the ones never seen before.
The sequential segmental analysis system is based on the observation of the three cardiac segments from a malformed heart (atriums, ventricles, and great arteries), starting with the proper recognition of the anatomical features of the heart components and determination of the alignment between the segments.
A different approach to the segmental analysis was introduced by the European school in the mid-1970s, taking into consideration the way each segment effectively connects with the following and not just the alignments between them ( Fig. 26.1 ).
Schematic view of the three cardiac segments that are part of the sequential segmental analysis.
(From Bettex D, Chassot PG. Transesophageal echocardiography in congenital heart disease. In: Bissonnette B, ed. Pediatric Anesthesia: Basic Principles—State of the Art—Future . Shelton, CT: People’s Medical Publishing House-USA; 2011, with permission.)
The most constant anatomical features of each chamber or structure in the normal heart have been described in Chapter 1 . As stated initially by the Van Praaghs in the “morphologic method,” one heart chamber or structure should be recognized on its own intrinsic and characteristic morphology and not on other variable structure. A good example is why the pulmonary veins cannot be a landmark of the morphologic left atrium due the possibility of their anomalous connection outside the heart or to the morphologic right atrium.
Sequential segmental analysis: Situs determination and connections
There are different ways to describe and classify the congenital defects of the cardiovascular system, not specifically right or wrong, simply different. The diverse approaches to the nomenclature of some topics are yet not fully resolved, but consensus is closer than two or three decades ago.
Situs determination
The landmarks of cardiac anatomy are considered as a starting point to describe how each of the cardiac segments connects to the other. Situs or overall organ arrangement determination can rely on some of the cardiac anatomical features, as is the case with the morphology and position of the atrial appendages, or atrial arrangement. The most consistent anatomical feature for atrial morphology is the extent of the trabeculated internal surface, the pectinate muscles. In the morphologic right atrium, it extends from the tip of the appendage to the inferior surface of the atrial wall, next to the opening of the inferior caval vein ( vena cava ). On the other hand, the morphologic left appendage shows pectinate muscles restricted to its interior, while the rest of the atrial internal surface is smooth ( Fig. 26.2 ).
A normal heart sectioned through the short axis and above the atrioventricular junction, showing the typical appearance of the atrial appendages, the morphologic right with extensive trabeculations (pectinate muscles) extending to the inferior surface and the morphologic left with trabeculations restricted to its interior. Ao , aorta; PT , pulmonary trunk
The commonest form is the usual arrangement or situs solitus , with the morphologic right appendage to the right side and the morphologic left to the left side. There are three other possibilities: the mirror-image arrangement of the appendages, or situs inversus , and two forms of isomeric appendages, the right and the left isomerisms . In each of these isomeric arrangements, the appendages are not lateralized, which means that both appendages have the same characteristics on both sides, being of either right or left morphology.
In cases of situs solitus and situs inversus (lateralized appendages), the arrangements of the thoracic and abdominal organs inside the body are usually in harmony with the arrangement of atrial appendages; for example, in situs solitus, the morphologic right bronchus is right-sided and the morphologic left is left-sided.
In the two forms of isomerism of the atrial appendages, the thoracic organs are also isomeric, as is the case with the bronchial tree and lungs regarding anatomy and number of lobes. The arrangement of abdominal organs is usually highly abnormal, with absence of the spleen (or asplenia ) in the majority of cases of right isomerism , and multiple spleens (or polysplenia ) in left isomerism . However, the association between appendage isomerism with splenic status is far from precise, as right isomerism is found occasionally with the presence of a spleen. Also, there are rare situations with disharmony between the thoracic and abdominal situs , with the thoracic organ arrangement not in accordance with the distribution of the abdominal organs.
Bronchial anatomy is a good indicator of the situs and is almost always concordant with the atrial appendage arrangement. The main left bronchus is long and only branches after it has been crossed by the accompanying pulmonary artery, which makes it hyparterial (bronchus below the pulmonary artery). On the other hand, the main right bronchus is short, forming an angle of approximately 90 degrees with the trachea, and its superior branch passes superiorly to its accompanying pulmonary artery, which gives it an eparterial (bronchus above the pulmonary artery) pattern of branching. These bronchial patterns can be observed by x-ray or tomography and serve as a guide for the organ arrangement.
While the morphologists and surgeons are usually able to directly observe the anatomical cardiac landmarks, the images of the chambers obtained by some methods of image may not be so distinctive, and that is why the situs is determined by transsectional ultrasonography by the position of the abdominal aorta and major systemic veins relative to the spine. In the usual ( solitus ) and mirror-image ( inversus ) arrangements, the great abdominal vessels, aorta, and inferior vena cava lie on opposite sides of the spine, whereas in isomerism, they lie on the same side. In cases of right isomerism, the aorta lies anterior to the inferior vena cava, and in left isomerism, the aorta is posterior to the vein of the azygos system.
Atrioventricular connections
Description of the way the atria connect to the ventricles is the next step in the segmental analysis, provided that the atrial arrangement and ventricular anatomy have been identified.
Biventricular atrioventricular connections.
In the normal heart, there are two separate atrioventricular junctions, described as biventricular and concordant atrioventricular connections ( Fig. 26.3 ), with each atrium connected to its appropriate ventricle via an atrioventricular valve. Biventricular and concordant atrioventricular connections may also be present when there is a common atrioventricular junction and common valve. These features—one common valve or two valves—are additionally described as the mode of biventricular atrioventricular connection. An imperforate valve is also a mode of atrioventricular connection. With an imperforate valve, one atrium can still connect with a ventricular cavity. Although there is an imperforate membrane, the connection is still present; a subvalvar apparatus is also present but usually hypoplastic.
Schematic representation of the modes of biventricular atrioventricular connections: two perforate atrioventricular valves, a common atrioventricular valve, one perforate and one imperforate valve, one straddling and overriding valve.
(Anderson RH, Becker AE. Controversies in the Description of Congenitally Malformed Hearts. In Cardiopulmonary Medicine from Imperial College Press . World Scientific Publishing Co.; 1998. https://doi.org/10.1142/p056 )
Biventricular and discordant atrioventricular connections exist when the morphologic right atrium connects with the morphologic left ventricle and the morphologic left atrium to the morphologic right ventricle, usually via two atrioventricular valves or rarely via a common valve. This type of atrioventricular connection is independent of the situs .
When there is isomerism, a biventricular atrioventricular connection can also be described, but by convention, it will not be concordant or discordant but rather mixed (also called ambiguous ). In such cases, the complete description must include the ventricular topology or loop, which defines the spatial relationships between the ventricles. D-loop or right-hand topology is the anatomical situation when it would be possible to “place” the palmar surface of the right hand on the septal surface of the morphologic right ventricle with the thumb in the inlet and the other fingers toward the outlet. Contrarily, in an L-loop or left-hand topology, it is the left hand that could be “placed” on the septal surface of the morphologic right ventricle in the same way. D-loop or right-hand topology is the finding in a normal heart from an individual with situs solitus but can be also found in a person with isomeric atrial appendages.
Univentricular atrioventricular connections.
This is the situation when only one ventricle connects to the atrial cavities, and that is why the connection is called univentricular rather than biventricular. In most cases, there are two ventricles, one dominant (receiving the connections) and the other rudimentary, lacking an inlet and showing a complementary trabecular pattern to the dominant one. The dominant ventricle may be of left (more commonly) or of right morphology.
The position of the rudimentary chamber may help to determine its morphology, because the morphologic right ventricle occupies an anterior-superior position regardless of its side (right-sided, directly anterior, or left-sided), and the morphologic left ventricle lies at the diaphragmatic aspect of the ventricular mass. Very rarely is there a single ventricular chamber of indeterminate morphology when no rudimentary ventricle can be found ( Fig. 26.4 ).
Schematic representation of the possibilities of connections between the cardiac chambers and the ventricular patterns in univentricular atrioventricular connections. The upper third of the figure depicts the possible arrangements of atriums: usual arrangement (solitus), mirror image (inversus), and appendage isomerism (right or left). The middle third shows the types of atrioventricular connections: absent right, double inlet, and absent left. Absent connection means that the atrium has a muscular floor, which should not include an imperforated valve. In the inferior third of the figure, we show the patterns of the dominant and the incomplete (rudimentary) ventricles. Rarely a true single ventricle is found, with no detectable rudimentary chamber. LV , left ventricle; Ind V , indeterminate ventricle; RV , right ventricle.
(From Gatzoulis MA, Webb GD, Daubeney PEF, eds. Diagnosis and Management of Adult Congenital Heart Disease . 3rd ed. Elsevier; 2020.)
This group comprises hearts with both atriums opening into a dominant ventricle (double inlet ventricle) and those with absence of one of the atrioventricular connections (right or left-sided atrium with a complete muscular floor). As previously stated, the morphology of the dominant ventricle is variable.
In one subgroup of hearts with univentricular connections, both atrial cavities open into the dominant ventricle. This type of connection is called double inlet ventricle.
Either two atrioventricular valves or a common valve may be present in double inlet ventricles. When there are two valves, they are better referred to as “right-sided and left-sided atrioventricular valves” rather than as tricuspid and mitral, as their morphology cannot always be defined as typical. In cases showing one atrioventricular valve overriding the ventricular septum, the 50% rule should be applied, defining which ventricular cavity that valve predominantly relates to. The ventricle with both valves opening predominantly is called the dominant one, and the atrioventricular connection is diagnosed as double inlet.
Another subgroup of hearts with univentricular atrioventricular connection show only one atrium connected to one ventricle in the ventricular mass, while the other atrium has a complete muscular floor. This is called absent atrioventricular connection, as the atrium is separated from the ventricular myocardium by the fibrous fat tissue of the base of the heart. Absent connection may be right- or left-sided. Again, the dominant ventricle receiving the atrial connection may be either morphologic right or left, with the rudimentary ventricle with complimentary trabecular pattern. The so-called classical tricuspid and mitral atresia belong to this group ( Fig. 26.5 ).
Frontal view of two malformed hearts sectioned in 4-chamber fashion to show absent right (A) and left (B) atrioventricular connection. The patent valve opens in the dominant ventricle. Note the complete muscular atrial floor. RA , right atrium; LA , left atrium.
Ventriculoarterial connections
The great arteries may join the ventricular mass in several ways. Their connection to the ventricular cavities as well as their spatial relationships should be described separately and independently, irrespective of the type of atrioventricular connection and ventricular completeness, as is the case when there is a dominant and a rudimentary ventricle.
There are four types of ventriculoarterial connections: concordant, discordant, double outlet, and single outlet.
Concordant ventriculoarterial connections.
Concordant ventriculoarterial connection occurs when the aorta is connected to the morphologic left ventricle and the pulmonary trunk is connected to the morphologic right ventricle, as is the case in the normal heart. This type of connection may also be described in hearts with one dominant and one rudimentary ventricle.
Discordant ventriculoarterial connections.
In the discordant arrangement, the aorta arises from the morphologic right ventricle (it may be complete or rudimentary), and the pulmonary trunk arises from the left ventricle. It is generally accepted that the discordant ventriculoarterial connection with concordant atrioventricular connection is the essence of transposition of the great arteries ( Fig. 26.6 ), and discordant ventriculoarterial connection with discordant atrioventricular connection is the essence of congenitally corrected transposition of the great arteries.
A heart with complete transposition of the great arteries, characterized by concordant atrioventricular connections in association with discordant ventriculoarterial connections. In (A), there is a view of the right-sided chambers and in (B) of the left-sided chambers. Ao , aorta; PT , pulmonary trunk; RA , right atrium; LA , left atrium; RV , right ventricle; LV , left ventricle.
Double outlet ventricles.
Double outlet ventricles are those that support the greater part of the circumference of both great arteries, irrespective of their spatial relationship and the presence or absence of a subarterial muscular infundibulum.
When one of the great arteries overrides the ventricular septum in the presence of a ventricular septal defect (VSD), the degree of overriding will define its assignment to one ventricle or the other. This definition, however, has not always been a consensus. Controversy still exists regarding the definition of double outlet ventricles because some authors consider that the presence of bilateral infundibulums should be essential. However, the rule of commitment of the great arteries’ circumferences (the 50% rule) to the ventricles has become more accepted. For example, one case of tetralogy of Fallot with the aorta completely supported by the right ventricle can be considered as having a double outlet type of ventriculoarterial connection.
Single outlet ventriculoarterial connection.
A heart is considered to have single outlet when only one of the great arteries connects to the ventricular cavity (or cavities) because the other artery is atretic or when there is a common arterial trunk.
A common arterial trunk originates from the base of the heart and usually overrides an outlet VSD, supplying the pulmonary, coronary, and systemic circulations. This common trunk has a common valve with variable number of semilunar leaflets ( Fig. 26.7 ).
Close detail of the right ventricular outflow tract in a heart with a common arterial trunk ( truncus arteriosus communis ), which is one type of single outlet of the heart. From the same common trunk arises the aorta (Ao), both pulmonary arteries and the coronary arteries. There is a single valve (asterisk) which overrides an outlet ventricular septal defect. RPA , right pulmonary artery; LPA , left pulmonary artery; RV , right ventricle.
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