Double-Outlet Left Ventricle

Why is Double-Oulet Left Ventricle so Rare?

At least part of the answer is that because DOLV is not part of the normal development of the cardiovascular system. Many forms of congenital heart disease appear to be arrests of normal cardiovascular development, such as double-outlet RV (DORV). But DOLV is not part of normal development. Something abnormal has to happen for DOLV to occur, as will be seen.

Definition

DOLV is present ^, when both great arteries arise entirely or predominantly above the morphologically left ventricle (LV). In this definition, “arise entirely or predominantly above the morphologically left ventricle” means “are aligned entirely or predominantly with the morphologically left ventricle,” no matter what the spatial orientation of the great arteries and the ventricles relative to fixed external spatial coordinates (superior-inferior, right-left, and anterior-posterior) may be ( Fig. 24.1 ).

The great arteries do not arise from the ventricles. The great arteries arise from the infundibulum, be it well developed or resorbed to an intervalvar fibrosa. This is why we say that the great arteries typically arise above the ventricles, not from the ventricles.

The clinical relevance of the rarity of DOLV is that when this anomaly occurs, pediatric cardiologists and cardiac surgeons may well be confronted by a malformation that they have never seen or heard of before. The task of this chapter is to prepare physicians as well as possible for this challenge.

What DOLV is not

DOLV has been reported when both great arteries arise from the left-sided ventricle, but the left-sided ventricle was the morphologically right ventricle (RV) because ventricular inversion (L-loop formation) was present. Diagnostically, it is important to distinguish between a positionally left-sided ventricle and a morphologically LV. One of Dr. Maurice Lev’s most important papers, published in 1954, presented the distinction between the morphologic anatomic diagnosis of the various cardiac chambers, which is a constant, and the spatial locations of the various cardiac chambers, which is a variable in congenital heart disease. This distinction—morphologic anatomic diagnosis versus spatial location—is the basis of accurate diagnosis in complex congenital heart disease. That is why this is one of the all-time greatest papers ever written about congenital heart disease.

The diagnosis of DOLV also has been made in a patient with normally related great arteries and a large infundibular septal defect. How could expert cardiovascular surgeons make the diagnosis of DOLV during surgery on such a patient?

They were right, of course. When a large infundibular septal defect is present, it is possible—particularly if you are a cardiac surgeon or a pathologist—to look downward through an open and normally located pulmonary valve into the LV. Most people do not know that their pulmonary valve is located above their LV. This anatomic fact is normally concealed by a normally developed infundibular septum. But when the infundibular septum is absent, what may be called a form of DOLV is surprisingly present. Would we call it that? No. Why not? How can you call normally related great arteries DOLV? The primary abnormal diagnosis in cases such as this is infundibular (conal) septal defect. The great arteries are normally related. Nonetheless, the observations of the surgeons and their cardiologists were correct, and illuminating.

Anatomic Types of Double-Outlet Left Ventricle

The first well-documented case of DOLV, to my knowledge, was that of Paul, Muster, Sinha, Cole, and Van Praagh, reported in 1970. The patient was a 2 7/12-year-old white boy. His clinical and autopsy-proved diagnosis was DOLV {S,D,D} with bilateral absence of the infundibulum, that is, no subaortic and no subpulmonary muscular infundibulum, aortic-mitral and pulmonary-mitral direct fibrous continuity, intact ventricular septum, thick-walled and small-chambered RV with infundibular atresia, severe endocardial fibroelastosis of the apical half of the RV. No great artery arose from the RV. There was a fistula between the right ventricular apex and the anterior descending coronary artery. Both atria and the LV were hypertrophied and enlarged. The left coronary ostium was absent, resulting in so-called single right coronary artery.

Salient clinical features included cardiomegaly on the posteroanterior chest radiograph at 6 months of age ( Fig. 24.2 ), with a cardiothoracic ratio of 61% and increased pulmonary vascularity. Electrocardiography ( Fig. 24.3 ) revealed biatrial enlargement, mainly right, and increasing biventricular hypertrophy with strain.

He was in chronic congestive heart failure. Cardiac catheterization at 6 months of age revealed increased pulmonary blood flow (Qp/Q _s = 3.5/1), following which the main pulmonary artery was banded. Repeat cardiac catheterization at 25 months of age revealed that the pressure in the small-chambered and thick-walled RV with an atretic outflow tract and no VSD was 220/20 mm Hg. The right atrial a wave was 17 mm Hg, the v wave was 11 mm Hg, the left ventricular pressure was 95/9 mm Hg, and the aortic saturation was 90%.

Selective left ventricular angiocardiography showed a large LV; the pulmonary artery was banded, but filled before the aorta. Both great arteries arose above the left-sided and posterior LV. The aortic valve was to the right of the pulmonary valve, and both valves were at approximately the same horizontal level. There was no ventricular septal defect (VSD).

Selective right ventricular angiocardiography showed that the RV was small-chambered. There was no tricuspid regurgitation, despite the fact that the cardiac catheter passed through the tricuspid valve. A fistula from the right ventricular apex connected with the anterior descending coronary artery. Contrast flowed from the RV cavity through the fistula into the anterior “ascending” coronary artery, all the way up to the origin of the single right coronary artery. Contrast also flowed into the right coronary artery and into the circumflex coronary (Circ) artery. This was an example of marked perfusion of ventricular myocardium by unoxygenated blood from the RV. There was infundibular outflow tract atresia. The only outflow tract from this very hypertensive RV (220/20 mm Hg) was by the apical fistula.

This heart displayed complete infundibuloarterial dissociation. The infundibulum was associated with the RV; infundibular atresia is why there was no patent RV outflow tract.

Both great arteries were located above the LV. As will be seen, there was no muscular infundibulum beneath either great artery.

This is total infundibuloarterial dissociation: the infundibulum is right ventricular, and both great arteries are left ventricular. This is the first time I have ever seen complete dissociation or separation of the muscular infundibulum (or conus arteriosus) from both great arteries.

The pathologic anatomy of the Paul type of DOLV is presented photographically in Fig. 24.4 . Viewed externally from the front (see Fig. 24.4A ), it is obvious that the LV is very large and that the RV is small. The LV does not just form the ventricular apex. The junction between the LV and the RV, marked by the anterior descending coronary artery (not labeled), bisects the anterior ventricular surface; that is, much more LV is seen from the front than ever occurs normally. Both the aorta (Ao) and the pulmonary artery (PA) are large, indicating that there is no aortic or pulmonary outflow tract stenosis.

The opened right atrium (RA) (see Fig. 24.4B ) shows that the patent foramen ovale (PFO) was small and potentially obstructive; but the surgically created atrial septal defect (Surg ASD) was of good size. The exterior surface of the RV confirms that the RV is small-chambered.

Viewed from above (see Fig. 24.4C ), the tricuspid valve (TV) is seen to be small, again confirming that the RV, into which the TV opens, is small-chambered.

The opened right atrium (RA), tricuspid valve (TV), and right ventricle (RV) (see Fig. 24.4D ) show hypertrophy and enlargement of the RA, hypoplasia and stenosis of the TV, and a thick-walled and small-chambered RV with endocardial fibroelastosis (EFE) of the apical portion of the RV. The septal band (SB) is also seen.

The opened right ventricular infundibulum (see Fig. 24.4E ) shows that there is infundibular atresia (Blind RV Out). The parietal band (PB), the septal band (SB), and the moderator band (MB) are identified.

The opened coronary arteries are shown in Fig. 24.4F . The single right coronary artery gives origin to the right coronary artery, the anterior descending coronary artery, and the left circumflex coronary artery. The left coronary ostium was absent. A fistula connects the apex of the RV with the anterior descending coronary artery, as is seen in Fig. 24.5 .

The opened left atrium (LA), mitral valve (not labeled), and left ventricular inflow tract (LV) are shown in Fig, 24.4G ).

A view of the opened LV from the apex shows (see Fig. 24.4H ) the intact ventricular septum, the unopened aortic valve (AoV), the unopened pulmonary valve (PV), the truncal septum (TS), or aortopulmonary septum that extended 3 mm below the semilunar valves and demarcated the separation between the aortic and the pulmonary outflow tracts. There was aortic-mitral direct fibrous continuity and pulmonary-mitral fibrous continuity between both semilunar valves above (AoV and PV) and the anterior leaflet of the mitral valve (MV) below. There was no infundibular musculature beneath either semilunar valve, or in the fibroelastic truncal septum (TS), either grossly or histologically.

More than 1000 serial sections were done of the tissue between both semilunar valves and the anterior mitral leaflet and of the 3 mm septum (TS) extending down between and beneath the semilunar valves, searching microscopically for infundibular musculature. None was found grossly or histologically. Consequently, there was direct fibrous continuity between the aortic and mitral valves and between the pulmonary and mitral valves. The 3 mm septum (TS) was identified as the aortopulmonary (or truncal) septum, not as a remnant of the infundibular (or conal) septum.

A geometric horizontal plane diagram of this heart specimen is presented in Fig. 24.4I . Cardiac geometry (measured in degrees relative to the Z axis or anteroposterior plane): The atrial septum (AS) measured 0 degrees; hence, the atrial septum lay in the anteroposterior plane. The ventricular septum (VS) was 45 degrees to the left of the sagittal plane. The semilunar valves were rotated 90 degrees to the right relative to the anteroposterior plane. Consequently, the semilunar valves were side-by-side, with the aortic valve to the right of the pulmonary valve.

Valve circumferences, in centimeters, are given in the middle of the left panel: tricuspid valve, 0.8 cm; mitral valve, 8.3 cm; aortic valve, 3.0 cm; and pulmonary valve, 3.2 cm. The circumference of the hypoplastic tricuspid valve was only 9.6% of that of the mitral valve. The pulmonary valve’s circumference was 6.7% greater than that of the aortic valve.

Thicknesses of the atrial and ventricular free walls are given, in centimeters, in the bottom third of the left panel of Fig. 24.4I : The right atrium (RA) varied from 0.4 to 0.7 cm in thickness. The left atrial (LA) free wall thickness varied from 0.2 to 0.5 cm. The right ventricular (RV) free wall thickness varied from 0.7 to 1.5 cm. The left ventricular (LV) free wall thickness varied from 0.7 to 1.1 cm.