EXPLANATION


The growth in knowledge surrounding the embryologic basis of cardiac development necessitates a consistent classification system to accurately describe and classify the many variations in cardiovascular defects. Standardization of the cardiac nomenclature and a universally accepted classification system is critical for appropriately diagnosing and disseminating accurate information across professional specialties caring for congenital heart disease (CHD) patients. Unfortunately, at present time, there is not one universally accepted classification system.


The sequential segmental approach is a widely accepted diagnostic evaluation of CHD. There are many publications describing this approach to the evaluation and diagnosis of CHD and the steps involved in a structural assessment. The segmental approach was initially described by Van Praagh and colleagues and rests upon an examination of cardiac anatomy in segments. The anatomy of each segment and the relationship of each segment to the others represents the underpinning of segmental analysis. A second system described by Robert Anderson and colleagues added to this concept but minimized the focus on the relationships between segments by using a model based on blood flow through the heart, which focused on characterizing the connections between the segments, termed a sequential segmental approach. In each segment, right and left-sided structures are evaluated based on the morphology, relative orientations, proximal and distal connections, and presence of abnormalities such as shunts and stenosis. Generally, clinicians have been segregated into followers of the Van Praagh or Anderson approach though many medical professionals have opted for a position in the middle. The chosen classification system for use at a particular institution is often based on preference.


Defining the thoraco-abdominal organ position and cardiac position/apex orientation are important components of the cardiac evaluation and should precede the sequential segmental analysis. Embryologically, all major organ systems are initially positioned in the midline and have mirror image symmetry. During normal development, the cardiovascular, respiratory and gastrointestinal systems become asymmetric, referred to as visceral situs solitus. Abnormal situs development can result in mirror-image visceral situs (visceral situs inversus) or an ambiguous visceral situs (visceral situs ambiguous). Mirror image arrangement describes reversed left-right position and orientation of the organs. Situs ambiguous refers to elements of situs solitus and situs inversus in the same patient.


Cardiac position is often described as the thoracic position where the majority of the cardiac mass is located: levocardia (left-hemithorax), dextrocardia (right-hemithorax) and mesocardia (mid-thorax). Although these prior terms have also been used to describe the base-to-apex orientation, the apex orientation is often, although not always, in agreement to the cardiac position within the chest. Dextrocardia describes the cardiac apex pointing towards the right side of the chest, mesocardia indicates apex pointing inferiorly, and levocardia pointing to the left side of the chest. Displacement of the heart into the right or left thorax should be indicated by the terms dextropositioning or levopositioning, respectively.


The Van Praagh style uses a unique three-letter notation, or code, inside curly brackets such as {X,X,X}. The letters are abbreviations that represent the sidedness or anatomic arrangement (situs) of the three main cardiac segments of the heart in venoarterial sequence (atria, ventricles, and great arteries). A normal heart is coded {S,D,S}. Atrial situs describes the arrangement of the atria as ascertained by the position of the morphologic right and left atria. When the atria are identified, their situs can then be defined. Similarly the same approach is followed for the ventricles. In the Van Praagh shorthand notation, the types of atrial situs are "S" for situs solitus (normal arrangement), "I" for situs inversus and "A" for situs ambiguous (indeterminate arrangement).


The ventricular segment is described by the type of ventricular loop (handedness of the ventricular mass) and the relationship between the atria and ventricles in three-dimensional space. In the normal D-loop (“D”) heart, the ventricles are normally related and the morphologic right ventricle is right-handed relative to morphologic left ventricle which is left-handed. L-looping of the ventricles is also known as inverted ventricles (morphologic right ventricle is left-handed and morphologic left ventricle is right-handed). The types of ventricular situs (loop or topology) per the Van Praagh system include: solitus or D-loop ventricles (D), inverted or L-loop ventricles (L); and ambiguous or X-loop ventricles (X).


The great arterial situs is described by the spatial relations between great arteries and the semilunar valves (anterior-posterior and right-left position). In patients with normally related great arteries, the main pulmonary artery is anterior to the aorta and then courses leftward. The aorta is posterior to the main pulmonary artery and courses to the right. The pulmonary valve is anterior to and to the left of the aortic valve. The Van Praagh system describes the types of great arterial situs as follows: 1) solitus (aortic valve posterior and to the right of the pulmonary valve)- normally related great arteries (S) or D-transposition (aorta is anterior and to the right of the pulmonary trunk); 2) inversus (aortic valve to left of the pulmonary valve)- inverted, normally related great arteries (I), or L-transposition/malposition (L); 3) ambiguous (right-left location of the aortic valve directly anterior to pulmonary valve is neither a right nor left location- A-transposition/malposition (A).


In this case scenario, this patient is reported to have situs solitus, levocardia, and {S,D,D} segmental anatomy. The Van Praagh segmental system denotes {S,D,D} as "S" for situs solitus or normal atrial arrangement, "D" for D-looped or normally related ventricles (morphologic right ventricle is right-handed and the morphologic left ventricle is left-handed), and "D" for D-malposed or transposed great arteries, with the aorta to the right of the pulmonary trunk rather than posterior to the main pulmonary artery.


REFERENCES


Van Praagh R. Terminology of congenital heart disease. Glossary and commentary. Circulation. 1977;56(2):139-143.


Anderson RH, Shirali G. Sequential segmental analysis. Ann Pediatr Cardiol. 2009; 2: 24-35.


Jacobs JP, Anderson RH, Weinberg PM, et al. The nomenclature, definition and classification of cardiac structures in the setting of heterotaxy. Cardiol Young. 2007;17 Suppl 2:1-28. 07001138


Kussman BD, Miller-Hance WC. Development of the cardiovascular system and nomenclature for congenital heart disease. In: Andropoulos DB, ed. Anesthesia for Congenital Heart Disease. 3rd ed. Hoboken, NJ; Wiley-Blackwell. 2015: 42-82.


Edwards WD, Maleszewski JJ. Classification and terminology of cardiovascular anomalies. In: Allen HD, Driscoll DJ, Shaddy RE and Feltes, TF, eds. Moss and Adams' heart disease in infants, children and adolescents, including the fetus and young adult. 8th ed. Philadelphia, PA; Lippincott Williams & Wilkins. 2013: 32-51.