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Logo of thijTexas Heart Institute JournalSee also Cardiovascular Diseases Journal in PMCSubscribeSubmissionsTHI Journal Website
 
Tex Heart Inst J. 2010; 37(4): 442–444.
PMCID: PMC2929877

Left Ventricle on Top versus Right Ventricle on Top in Superoinferior Ventricles

What Are We Talking About?

In 2003, Porras and co-authors1 revisited one of the most complex, vexing, and unclear topics in congenital heart disease: superoinferior ventricles (SIVs). The authors' initial definition (“[SIV] means that the ventricles lie one above the other, with the ventricular septum being approximately horizontal”) did not explain the real nature of the problem, but their morphologic definition gave rise to a new embryologic theory: “The usual type of superoinferior ventricles, with RV [right ventricle] superior and LV [left ventricle] inferior, appears to represent a failure of ventricular loop formation (i.e., deficient ventricular looping).”

Actually, the purpose of Porras's article was to introduce a newly described variant of SIV—left ventricle on top—which is the opposite of the usual form (right ventricle on top). The authors reviewed all previously reported examples of SIV and interpreted them as featuring the right ventricle on top.1 The novel case described in their report involved SIV of a profoundly defective heart with situs solitus of the atria, L-loop ventricles, mitral atresia, double-outlet right ventricle, a ventricular septal defect, and pulmonary stenosis. In that case, SIV was a minor feature of a complex that functionally involved a single ventricle, in dextrocardia: the apex was tilted to the right, in situs solitus.

In the current issue of this journal, Yang and colleagues2 present a much more exceptional case of congenital heart defect, one that features isolated SIV with the left ventricle on top. Because it involves no other defect, this case may help clarify the essence of SIV. The ventricular anomaly occurred in an otherwise normal heart with {S, D, D} segmental morphology. Although the heart had no associated defects and the cardiac segments had normal connections, the cardiac apex resembled that seen in mesocardia: the left ventricular apex was located to the front and slightly to the right, while the right ventricle had a dysmorphic, “wraparound” structure that circumscribed the superiorly located left ventricular apex on the right side (Fig. 1A). The result was essentially a “normal” heart, in which the ventricles were twisted counterclockwise, along their longitudinal axes, as seen from the apex. If we assume that this is the only morphogenetic defect involved in the present case, use of the terms “SIV” and “ventricular looping defect” does not seem particularly helpful in interpreting the essence of this anomaly. More specifically, the following points should be considered.

figure 9FF1
Fig. 1 A) Schematic diagram of the cardiac anatomy in the case reported by Yang and colleagues,2 which involved an isolated counterclockwise apical malrotation defect (arrows). The ventricular apices are located opposite their normal sites, but the inflow ...
  1. Critics might claim that the case of Yang and associates did not really involve SIV. In fact, the term SIV has its basis in a superficial descriptive reading of a complex 3-dimensional deformity of the ventricular septum, and that term does not adequately describe this deformity. In this type of apical malrotation, the atrioventricular valves and ventricular inlets have a grossly normal intrinsic relationship (although one inlet is generally higher than the other), and the connections of the ventricles with the relative atria are unaffected: only the mid-distal septum and ventricles are grossly deformed, to a variable degree, consequent to clockwise twisting of the apical anatomy along the longitudinal cardiac axis. As a consequence of this malrotation, the mid-distal ventricular septum typically lies in a horizontal plane. If this is indeed the essential defect in SIV, it should be given a different, all-inclusive name to signify both the abnormal longitudinal twisting of the ventricular septum and the unusual location of the apical portions of the ventricles. An acceptable general term might be “apical malrotation defect” (AMD). Figure 1 (A and B) shows the spectrum of AMD in diagrammatic form.
    Why is the Yang case so revealing? Because, in the context of the AMD spectrum, this case beautifully illustrates the basic nature of similar developmental errors—but with a counterclockwise rotation of the distal septum. (For an example of crisscross heart [CCH] occurring as an isolated defect, but with clockwise rotation of the apical portions of both ventricles [opposite from the pattern in the Yang case], see previous reports by Angelini and colleagues4 and by Lopez and colleagues,3 as represented diagrammatically in Figure 1B.)
  2. Superoinferior ventricle is not a ventricular looping defect. To briefly summarize the essential cardiac embryogenetic steps: in a normal human heart,5,6 bulbo-ventricular loop formation occurs at an early embryonic phase and leads to an irreversible relationship between the situs of the atria (previously established) and the position of the ventricles (now forming). Normally, this process connects the right-sided morphologic right atrium to the right-sided morphologic right ventricle and connects the left-sided structures in an opposite manner. Also, the relationship between the great vessels (pulmonary and aortic) is irreversibly determined at this looping stage, even though septation of the common truncus will occur at a later stage.5,6 What is not yet determined at this stage (and is not well described by embryologists and pathologists) is the formation of the apex. At the looping stage, the heart indeed has a primitive transient apex directed to the side of the loop (in the normal heart, with a D-loop pattern, this initial apex is to the right); however, in the course of the normal selective overgrowth of the left ventricle that occurs soon afterward, the apex becomes definitely and irreversibly situated to the left. Also, formation of the apex is usually simultaneous with formation of the ventricular septum: the inlets of both ventricles lie essentially side by side in a frontal plane and posterior to the apex, while the mass of the left ventricle lies to the left and slightly posterior to the right ventricle. Because of this ventricular spatial arrangement, the ventricular septum becomes normally oriented in a grossly sagittal plane, while the conus septum is grossly vertical and oriented at a 90° angle with respect to the ventricular and atrial septa. Therefore, the left-sided apex of the normal human heart results from gradual growth of the left ventricular mass to the left, without any further morphogenetic migration or twisting of the bulboventricular loop. In my opinion, bulboventricular looping is not responsible for SIV defects; rather, these defects must be caused by an event of unknown origin that occurs after loop formation.
  3. Basically, SIV and CCH can be described anatomically as 2 separate defects. The 1st defect (SIV) involves a configuration in which the mid-distal portion of the ventricles is situated along an approximately horizontal septal plane, with either the right or left ventricle on top, as described above. The 2nd defect (CCH) involves crossing of the inflow tracts, which are typically elongated and displaced; this implies a more advanced defect of apical malrotation (Fig. 1A and B). In CCH, the ventricles can be so severely twisted that they result in a left-sided right ventricular apex and a right-sided left ventricular apex (the most frequent type), while the inflow valves of each ventricle are correctly positioned for a given situs of the atria. The heart described by Yang and associates (Fig. 1A) appears to have undergone a counterclockwise partial rotation, resulting in isolated SIV; however, the heart shown in Figure 1B seems to have undergone a clockwise rotation, leading to both CCH and SIV.
  4. Often—how often we cannot yet say, due to our limited experience with this exceptionally rare disorder—SIV is associated with supraventricular tachycardia (SVT). There was an association between SIV and SVT in the Yang case, and SVT was also the presenting symptom in the case described by Lopez and colleagues.3 It is possible that SIV involves an intrinsically defective or unstable electrical system, especially at the atrioventricular-node junction. Alternatively, in the Yang case, SVT might have been related to the abnormal draining of the left superior vena cava into the coronary sinus, which also might have resulted in a distorted atrioventricular-node region.

Is this commentary on SIV and CCH a definitive clarification? The author hopes so, despite the rarity of the defects, the acknowledged complexity and variability of similar defects, and the lack of a suitable animal model with which to study them.

Footnotes

Address for reprints: Paolo Angelini, MD, 6624 Fannin St., Suite 2780, Houston, TX 77030

E-mail: moc.ygoloidracnamhcael@inilegnAP

References

1. Porras D, Kratz C, Loukas M, van Doesburg NH, Davignon A, Van Praagh R. Superoinferior ventricles with superior left ventricle and inferior right ventricle: a newly recognized form of congenital heart disease. Pediatr Cardiol 2003;24(6):604–7. [PubMed]
2. Yang G, Wang Q, He J, Wu M. Superior left ventricle in combination with inferior right ventricle presenting with balanced hemodynamics and mild symptoms in a late adolescent. Tex Heart Inst J 2010;37(4):445–8. [PMC free article] [PubMed]
3. Lopez JA, Angelini P, Lufschanowski R. Successful ablation of atrioventricular node reentry tachycardia in a patient with crisscrossed heart and levocardia. J Interv Card Electrophysiol 2006;17(2):133–7. [PubMed]
4. Angelini P, Lopez A, Lufschanowski R, Nemeth MA, Flamm SD. Coronary arteries in crisscross heart. Tex Heart Inst J 2003;30(3):208–13. [PMC free article] [PubMed]
5. de la Cruz MV. Torsion and looping of the cardiac tube and primitive cardiac segments. Anatomical manifestations. In: de la Cruz MV, Markwald RR, editors. Living morphogenesis of the heart. Cambridge (MA): Birkhäuser Boston Inc.; 1998. p. 99–120.
6. Angelini P. Embryology and congenital heart diseases. Tex Heart Inst J 1995;22(1):1–11. [PMC free article] [PubMed]

Articles from Texas Heart Institute Journal are provided here courtesy of Texas Heart Institute