Single ventricle means that one ventricular sinus, body, or inflow tract is present; in other words, one ventricular sinus, body, or inflow tract is absent.

In single LV (morphologically left ventricle), the right ventricular sinus is absent (component 2, Fig. 17.1A ).

(A) The normal right ventricular (RV) septal surface. (B) The normal left ventricle (LV) of septal surface. The ventricular septum and the free walls of both ventricles are composed of four anatomic and developmental components. Component 1 is the atrioventricular (AV) canal and the AV valves. Component 2 is the sinus, body, or inflow tract and the main pumping portion of the RV and LV. Component 3 is the proximal or apical portion of the infundibulum or conus arteriosus. In the RV, component 3 is called the septal band, and its apical extension to the anterior papillary muscle of the RV is known as the moderator band. In the LV, component 3 is the smooth, nontrabeculated superior portion of the left ventricular septal surface. The inferior part of the left ventricular septal surface is finely trabeculated and is part of component 2. Component 4 is the distal or subarterial part of the infundibulum or conus arteriosus. From the RV aspect, component 4 is known as the infundibular or conal septum. Its right ventricular free wall extension is called the parietal band. The septal band is so designated because it forms the upper part of the RV septal surface. The parietal band is also known as the crista supraventricularis, or supraventricular crest, because it normally forms a crest above the RV sinus. Normally, component 4 makes a small contribution to the top of the left ventricular septal surface. Single LV results from absence of the right ventricular sinus (component 2). But components 3 and 4 are present. That is why single LV (absence of component 2) has an infundibular outlet chamber—because components 3 and 4 are present. Also, the muscular ventricular septum is displaced toward the location of the absent right ventricular sinus: in a rightward and anterior direction with a ventricular D-loop, or in a leftward and anterior (ventral) direction with a ventricular L-loop. This displacement of the ventricular septum places the crest of the muscular ventricular septum beneath the opening leading into the infundibular outlet chamber. In turn, the crest of the displaced muscular ventricular septum narrows the opening leading into the infundibulum, making the infundibulum look like an outlet chamber . This somewhat narrowed opening leading from the single LV into the infundibulum is called the bulboventricular foramen, or the infundibuloventricular foramen. Single RV is absence of the LV sinus (component 2). The ventricular septum is displaced toward the location of the absent LV sinus, posteriorly and to the left with a ventricular D-loop or posteriorly and to the right with a ventricular L-loop. Because the ventricular septal remnant is displaced posteriorly, not anteriorly , there is no narrowing of the outflow tract leading from the single RV into the infundibulum. Consequently, the infundibulum in single RV does not look like an outlet chamber because there is no inlet narrowing by the displaced ventricular septal remnant.

Reproduced with permission from Van Praagh R, Geva T, Kreutzer J. Ventricular septal defects: how shall we describe, name, and classify them? J Am Coll Cardiol. 1989;14:1298.

In single RV (morphologically right ventricle), the left ventricular sinus is absent (component 2, see Fig. 17.1B ).

In single LV, the most common form of single ventricle occurring in about 74% of cases, ^, there is an infundibular outlet chamber (component 3, see Fig. 17.1A ).

The infundibular outlet chamber which is characteristic of single LV is shown in Figs. 17.2 , 17.3 , and 17.4 .

Holmes Heart With Single Left Ventricle (LV), Infundibular Outlet Chamber, and Normally Related Great Arteries (i.e., a Normal Anatomic Type of Infundibulum and Great Arteries).

The segmental anatomy is normal: {S,D,S}; that is, each segment is in situs solitus. (A) The opened right atrium, tricuspid valve (TV), and single LV. A probe is seen passing from the single LV through the infundibuloventricular foramen into the infundibular outlet chamber. (B) The opened subpulmonary infundibular outlet chamber. A probe passes through a normally located pulmonary valve (PV). A probe passes through a widely patent infundibuloventricular foramen (F) . Note that what normally should be the right ventricular sinus septal surface (below F) is extremely shallow, that is, extremely undeveloped or absent. (C) The geometric diagram shows a single LV; no right ventricular sinus, a subpulmonary infundibular outlet chamber (Inf); rightward and anterior displacement of the ventricular septum (VS); a normally located atrial septum (AS) angulated 35 degrees to the left of the sagittal plane; a normally angulated VS, 40 degrees to the left of the sagittal plane; double-inlet left ventricle (DILV), the TV with bicameral insertions, barely into the outlet chamber, with thickened tricuspid leaflet margins indicating tricuspid regurgitation; and mitral valve (MV) unremarkable; semilunar valves normally related, displaying 150 degrees of dextrorotation relative to the sagittal plane; and no evidence of outflow tract obstruction or regurgitation. A and M, Anterior and medial leaflets of the TV; AL, anterior leaflet; AO, aorta; CS, conal septum or crista supraventricularis; PA, pulmonary artery; PB, parietal band; SB, septal band; FW, free wall of the infundibular outlet chamber.

Reproduced with permission from Van Praagh R, Plett JA, Van Praagh S. Single ventricle: pathology, embryology, terminology, and classification. Herz. 1979;4:113; and Van Praagh R, Ongley PA, Swan HJC. Anatomic types of single or common ventricle in man: morphologic and geometric aspects of 60 necropsied cases. Am J Cardiol. 1964;13:367. ^,

Holmes Heart With Pulmonary Outflow Tract Stenosis, That Is, Single Left Ventricle (LV) Because of Absence of the Right Ventricular Sinus, With an Infundibular Outlet Chamber and Normally Related Great Arteries.

The great arteries are normally related to each other and to the LV, but not to the right ventricular sinus that is absent. The segmental anatomy is normal, that is, {S,D,S}. (A) Note that the left ventricular septal surface is well developed, but what normally should be the right ventricular septal surface is absent. The ventricular septum (VS) is displaced to the right and anteriorly. Consequently the infundibulum looks like an outlet chamber. There is double-inlet left ventricle, with the tricuspid valve (TV) straddling the VS to insert a small amount into the outlet chamber. The bicameral insertions of the TV were associated with tricuspid regurgitation, indicated by thickening and rolling of the free margins of the tricuspid leaflets. Note that the medial leaflets of the regurgitant TV and of the normal mitral valve are indirect fibrous continuity. The atrioventricular (AV) valves are not separated by the ventricular septum because the VS is displaced abnormally to the right and anteriorly. Note the direct fibrous continuity between the aortic valve and both AV valves, which is normal with normally related great arteries. (B) Note that the valve of the pulmonary artery (PA) is hypoplastic and bicuspid. Relative to the sagittal plane, the atrial septal angle is 30 degrees to the left (normal) and the ventricular septal angle is 60 degrees to the left (a bit greater than normal). AO and Ao, Aorta; AS, atrial septum; Inf, infundibular; MV, mitral valve.

Reproduced with permission from Van Praagh R, Plett JA, Van Praagh S. Single ventricle: pathology, embryology, terminology, and classification. Herz. 1979;4:113. Van Praagh R, Ongley PA, Swan HJC. Anatomic types of single or common ventricle in man: morphologic and geometric aspects of 60 necropsied cases. Am J Cardiol. 1964;13:367. ^,

Single Left Ventricle (LV) With an Infundibular Outlet Chamber and Transposition of the Great Arteries {S,D,D}.

(A) Opened infundibular outlet chamber (Inf) and the D-transposed ascending aorta (Ao). The infundibuloventricular foramen (F) is obstructively small, resulting in subaortic stenosis, hypoplasia of the aortic valve, and ascending Ao, and atresia of the aortic isthmus. The infundibuloventricular foramen lies between the infundibular septum above and the displaced ventricular septum below. This foramen is not called a ventricular septal defect (VSD) because VSD is short for interventricular septal defect (IVSD). To have an IVSD, two ventricles must be present. But in single ventricle, only one ventricle is present. So accurately speaking, these communications are called infundibuloventricular foramina, not VSDs. (B) The opened single LV is seen, with double-inlet LV by both the tricuspid valve (TV) and the mitral valve (MV). The restrictive infundibuloventricular foramen, the hypoplastic ascending D-transposed Ao, and the dilated transposed pulmonary artery (PA) are seen. (C) The diagram shows absence of the right ventricular sinus beneath the infundibular outlet chamber, the rightward and anterior displacement of the ventricular septal (VS) remnant, and double-inlet single LV. In this case, the TV inserted only into the LV, without straddling of the TV into the Inf. The cardiac geometry was as follows: relative to the sagittal plane, the atrial septal angle was 30 degrees left, the ventricular septal angle was 60 degrees left, and the dextrorotation at the semilunar valves was only 30 degrees right (normal is 150 degrees right). The RV is the anterior ventricle. The LV is the posterior ventricle. Absence of the RV sinus results in anterior displacement of muscular VS, bringing the muscular VS close to and beneath the infundibular septum that lies between the semilunar valves. This resulted in a restrictively small infundibuloventricular defect (IVD) in this case. Absence of the LV sinus results in posterior displacement of the muscular VS, away from the infundibular septum that is anterior. This results in no narrowing of the inlet into the subarterial infundibulum produced by approximation of the muscular VS crest and the infundibular septal crest. Hence, in this patient, absence of the anterior right ventricular sinus is associated with an infundibular outlet chamber appearance, whereas absence of the left ventricular sinus typically has no such association. AoV, Aortic valve; PV, pulmonary valve.

Reproduced with permission from Van Praagh R, Plett JA, Van Praagh S. Single ventricle: pathology, embryology, terminology, and classification. Herz. 1979; 4:113; and Van Praagh R, Ongley PA, Swan HJC. Anatomic types of single or common ventricle in man: morphologic and geometric aspects of 60 necropsied cases. Am J Cardiol. 1964;13:367. ^,

In single RV with absence of the left ventricular sinus (about 26% of cases) even though the infundibulum is present, it does not look like an infundibular outlet chamber . Why not? With single LV, the infundibulum looks like an outlet chamber because the infundibulum has an inlet constriction or narrowing that is produced by displacement of the ventricular septum. When the right ventricular sinus is absent, the ventricular septum is displaced in that direction—toward the location of the absent right ventricular sinus. This is similar to the shift of the mediastinum in the direction of a small or absent lung.

This “right ventriculad” shift of the ventricular septum brings the crest of the muscular ventricular septum abnormally close beneath the inferior rim of the infundibular septum, creating the appearance of an inlet narrowing leading into the infundibulum. The inlet narrowing makes the subarterial infundibulum look like a chamber—a diagnostically helpful appearance. An outlet chamber appearance strongly suggests a single LV with an infundibular outlet chamber. By contrast, with single RV, because of an absent left ventricular sinus, the ventricular septum moves away from beneath the infundibular septum. The ventricular septal remnant moves “left ventriculad,” posteriorly and to the left with a ventricular D-loop, or posteriorly and to the right with a ventricular L-loop. Consequently, there is no inlet constriction leading into the infundibular or outlet part of the heart: no inlet constriction and no outlet chamber appearance.

The premorphologic definition of single or common ventricle used to be as follows. Single or common ventricle is present if both atrioventricular (AV) valves or a common AV valve open into the same ventricular chamber. ^,

Lambert reported a case of single ventricle with a rudimentary outlet chamber in 1951 in which the tricuspid valve opened predominantly into the outlet chamber. In other words, we knew in the early 1960s that single ventricle with an infundibular outlet chamber did not necessarily have double-inlet single ventricle. In other words, we knew that the premorphologic definition of single ventricle was not always accurate.

When I speak of the premorphologic definition of single or common ventricle I mean that before 1964 the morphologic anatomy of single or common ventricle was not understood. That is why Dr. Jeremy Swan, my boss in the Cardiac Catheterization Laboratory at the Mayo Clinic in Rochester, Minnesota, gave me this as a research project in 1960 to 1961. I was his fellow in the Catheterization Laboratory for 1 year, a high privilege. Before this time, I had been an Assistant Resident in Pathology in 1956 to 1957 at Boston Children’s Hospital, between my junior and senior years as a Resident in Pediatrics. During my year of training in Pathology, I had fortunately learned of the work of Dr. Maurice Lev in Chicago in which he introduced the morphologic anatomic approach to the diagnosis of the cardiac chambers by means of the morphologic anatomy of their septal surfaces, not in terms of their relative positions, such as right-sided or left-sided.

I expanded Lev’s approach by including the morphologic anatomy of the septal surfaces and of the free wall surfaces. Both were specific, different, and diagnostically very helpful. Then it became obvious that using the AV valves to diagnose the presence or absence of single ventricle was a violation of logic, in the following sense. Using one variable (the AV valves) to diagnose the status of another, different variable (the presence or absence of single ventricle) was a violation of logic in the sense that each variable should be diagnosed primarily in terms of itself, not in terms of some other, different variable. The principle that each variable should be diagnosed primarily in terms of itself, if possible, not in terms of some other different variable, is important and has widespread applicability. In addition to cases like Dr. Edward Lambert’s, ^, later we would also learn that the type of ventricular loop (D- or L-) should be diagnosed specifically in terms of itself, not in terms of whether the AV alignments and connections are concordant or discordant :

• 1.
  

  When the atria are in situs solitus and the AV alignments (“connections”) are concordant, L-loop ventricles can be present, not the expected D-loop ventricles.

  
  
• 2.
  

  When the atria are in situs solitus and the AV alignments are discordant, D-loop ventricles can be present, not the expected L-loop ventricles.

In other words, to avoid diagnostic errors, the ventricular situs must be diagnosed specifically per se, not in terms of a different variable.

Before morphologic anatomic understanding, single ventricle used to be called common ventricle, based on the impression that single ventricle is a huge ventricular septal defect (VSD), that is, absence of the ventricular septum. Does common ventricle occur? The answer is yes, but it is rare ( Fig. 17.5A–B ). In our last large study of single ventricle, we found no cases of common ventricle.

Does common ventricle exist? Is it possible for the free walls of the right ventricular sinus and the left ventricular sinus to be present, but with absence of the muscular ventricular septum, and consequently the right ventricular sinus and the left ventricular sinus are in common (not separated)? We think the answer is probably yes, but, if so, common ventricle must be very rare. In this patient, dextrocardia was present because the ventricular apex pointed rightward and posteriorly. (A) View of the interior of the ventricular part of the heart as seen from the ventricular apex. The right-sided free wall myocardium is finely trabeculated, consistent with left ventricular myocardium (LVM). The left-sided ventricular free wall is more coarsely trabeculated, consistent with right ventricular myocardium (RVM). (B) Right lateral view of the exterior of this extremely malformed tubular heart, with the ventricular apex pointing posteriorly and rightward. (C) Geometric diagram. The atria were in situs solitus, that is, {S,-,-}. The ventricular segment may well have had an L-loop, as is suggested by inversion of the tricuspid valve (TV) and the mitral valve (MV); and the RVM (stippled) is left-sided and the LVM is right-sided. Hence, the segmental anatomy appears, so far, to be {S,L,-}. The great arteries are in D-malposition, with 30-degree dextrorotation of the semilunar valves. Hence the segmental anatomy appears to be {S,L,D}. A coronary artery arises anomalously from the anterior nonseptal sinus of Valsalva of the aortic valve (Ao). The pulmonary valve is tricuspid, but hypoplastic, indicating pulmonary outflow tract stenosis. Double-inlet RV and double-outlet RV appear to be present in C, but absence of the ventricular septum makes these diagnoses less certain and less meaningful than usual. The diagnosis appears to be common ventricle (absence of the interventricular septum) with dextrocardia (ventricular apex pointing rightward and posteriorly), with double-outlet RV {S,L,D}, with pulmonary outflow tract stenosis, and with an anomalous coronary arterial origin from the anterior nonseptal aortic sinus of Valsalva. AO, Aorta; AS, atrial septum; LV, left ventricle; PB, parietal band; RtLat, right lateral; RV, right ventricle; SB, septal band; SVC, superior vena cava. Note that this case is not included in the database of this chapter (see Table 17.1 ) for several reasons: (1) I am not certain that the previously mentioned diagnosis is entirely correct. (2) This chapter is about single ventricle, not about common ventricle. These are two very different anomalies. (3) Previously, it was widely assumed that single ventricle is common ventricle, that is, that single ventricle is “a huge VSD.” This premorphologic assumption is not supported by morphologic anatomic data. I have not seen a case of common ventricle in the Cardiac Registry, the Cardiac Pathology Laboratory, of Boston Children’s Hospital (1965 to 2002).

Reproduced with permission from Van Praagh R, Ongley PA, Swan HJC. Anatomic types of single or common ventricle in man: morphologic and geometric aspects of 60 necropsied cases. Am J Cardiol. 1964;13:367.

Single Left Ventricle With Infundibular Outlet Chamber

Six different anatomic types of single LV with infundibular outlet chamber were found ( Table 17.1 ). Single LV with an infundibular outlet chamber and a segmental situs set of solitus atria, ventricular D-loop, and solitus normally related great arteries were found in only 1 case (3% of this series as a whole).

TABLE 17.1

Our Findings in 31 Postmortem Cases of Single Ventricle ( Table 17.1 )

Anatomic Types of Single Ventricle	No. of Cases (n = 31)	% of Series
Single Left Ventricle
1. Single LV {S,D,S}	1	3
2. Single LV TGA {S,D,D}	6	19
3. Single LV TGA {S,D,L}	2	7
4. Single LV TGA {S,L,L}	12	39
5. Single LV TGA {S,L,D}	1	3
6. Single LV {S,L,S}	1	3
Subtotal	23	74
Single Right Ventricle
1. Single RV DORV {S,D,D}	2	7
2. Single RV DORV {I,L,I}	1	3
3. Single RV TGA {A,D,D} and asplenia	1	3
4. Single RV DORV {A,D,D} and asplenia	3	10
5. Single RV TGA {A,L,L} and asplenia	1	3
Subtotal	8	26

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