Case report

A 32 year-old woman (G3P2) with unremarkable family history was referred to our office at 35 weeks gestation for fetal cardiac assessment. Our ultrasonographic examination revealed following findings:

- Situs solitus with concordant atrio-ventricular and ventriculo-arterial connections.
- Small left ventricle compared to the dilated right one. Yet, the cardiac apex is still formed by the left ventricular cavity.
- Anomalous muscle bundles are seen inside the right ventricle aligned in different planes (two are obliquely aligned and apically inserted and two are transversely aligned in a higher anatomical level) within its cavity. The anatomically higher one divides the right ventricle into proximal low chamber and distal high chamber (RVOT) without hemodynamic evidence of obstruction.
- Small mitral valve annulus is seen. Unifocal attachment of short, thick tendineous cords is seen connecting both mitral valve leaflets to a dominant elongated papillary muscle causing posteromedial displacement of mitral valve orifice suggesting that the dominant papillary muscle is posteromedial in location while there is a small anterior and lateral rudimentary muscle connected to free wall of lateral ventricle not properly seen reaching mitral annulus. This strongly suggests parachute like asymmetric mitral valve.
- A small ventricular septal defect is seen in the muscular septum showing late diastolic left to right flow shunting.
- Foramen ovale is seen aneurysmally enlarged with its flap bowing into the left atrium which appeared small in size compared to the right atrium. Foramen ovale flap shows bidirectional movement predominantly vigorous systolic left to right movement and minimal diastolic right to left movement. Bidirectional flow is seen across foramen ovale predominantly left to right during atrial systole and right to left during atrial diastole denoting very high left atrial pressure.
- The ascending aorta is seen arising from the left ventricle through a fibro muscular tunnel (the posterior wall of the aorta not connected to anterior leaflet of mitral valve but rather to the free wall of the left ventricle) with a discrete membrane seen in subvalvular area. Both of which causes aortic stenosis clearly demonstrated on 2D, color and pulsed Doppler study (tunnel like and discrete form of subvalvular aortic stenosis).
- The main pulmonary artery is seen dilated compared to ascending aorta with no evidence of pulmonary valve stenosis. Both central pulmonary arteries are seen of average diameter and normal forward flow. The aortic and ductal arches are seen approximately of equal size on 2D assessment.
- Normal inflow of pulmonary and systemic veins into their respective atria. No evidence of persistent left superior vena cava or coronary sinus dilatation.

Hemodynamic consideration

Congenital parachute like asymmetric mitral valve stenosis with discrete and tunnel like  subaortic stenosis caused severe pressure overload on the left atrium forcing it to redirect blood flow mainly during systole to the right atrium through enlarged foramen ovale (vigorous systolic left to right FOV flap movement with left to right flow shunt reflect this sequence). Volume overload on the right side attributed to the FOV and VSD flow shunt led to dilatation of the right heart and mild aneurismal dilatation of the main pulmonary artery. Bicuspid aortic valve and aortic coarctation could not be ruled out due to these hemodynamic changes despite the approximation of diameters of both ductal and aortic arches on 2D assessment in axial and sagittal planes.

Conclusion

Combined Double chambered right ventricle (DCRV) and discrete subaortic stenosis (DSAS). Tunnel like subaortic stenosis with parachute like asymmetric mitral valve causing mitral stenosis is also present with suspicion of bicuspid aortic valve and aortic coarctation. This picture of multiple left sided obstructive lesions represents an incomplete form of Shone syndrome.

In postnatal echocardiographic assessment, parachute like asymmetric mitral valve with rudimentary anterolateral papillary muscle, discrete subaortic membrane with fibromuscular tunnel, bicuspid aortic valve and non-restrictive DCRV with 4 anomalous muscle bundles were confirmed. The third anomalous bundle represented the papillary muscle of the septal leaflet of tricuspid valve. Aortic coarctation and valvular pulmonary stenosis were ruled out. Early postnatal, there was no pressure gradient attainable through aortic and subaortic regions mostly due to coexistence of a VSD and the widely opened foramen ovale that showed complete reversal of flow (entirely left to right shunt).The neonate then was referred to a cardiothoracic surgeon who recommended preparation for early surgical intervention for correction of mitral valve and aortic valvular and subvalvular areas before onset of severe pressure gradient on the left ventricle with repair of DCRV to avoid its further progression into obstruction.

Image 1,2,3,4,5,6,7,8,9,10,11 video 1, 2, 3: show situs solitus, FOV aneurysm, small left atrium, small left ventricle, color Doppler bidirectional flow across FOV, small muscular VSD.

Image 12, video 4: show vigorous systolic left to right FOV flap movement due to elevated left atrial pressure.

Image 13, 14, video 5: single dominant papillary muscle is seen with unifocal attachment through short, thick and echogenic cordae tendinae to both anterior and posterior leaflets of mitral valve. Small posteromedially displaced mitral valve orifice is also noted.

Image 15, 16, 17, 18, 19, 20, videos 6, 7: anomalous muscle bundles are seen in the cavity of the right ventricle. Two are caudad and obliquely aligned from interventricular septum to the free wall of RV (we suppose the most apical one to carry the electrical signals as the usual moderator band).  Two are cephalad and transversely oriented with no RVOT obstruction.

Image 21, 22, 23, 24, video 8, 9, and 10: Discrete fibrous membrane with tunnel like subaortic stenosis on 2D, color and pulsed Doppler study. No evidence of valvular pulmonary stenosis with slightly dilated MPA and normal major central branches.

Image 25, 26, video 11, 12: axial and sagittal 2D assessment of isthmic portion of aortic arch and distal ductal arch, dilated proximal MPA.

Image 27: Schematic drawing of the double-chambered right ventricle depicted approximately at the level of the four chamber view of the heart. The abnormally located or hypertrophied muscle bundles divide the cavity of the right ventricle into a high-pressure proximal and a lower-pressure distal chamber. In the case described above the communication between proximal and distal chamber of the right ventricle (simplistically depicted as a yellow dashed line) did not cause obstruction between the two compartments as it is usually described in postnatal period or later during life.

Discussion

To the best of our knowledge, this is the first case to be reported in prenatal literature about combined double chambered right ventricle (DCRV) and discrete subaortic stenosis (DSAS). This combination was first reported since 1978 based upon cardiac catheterization study by Baumstark et al.  Freedom and his colleagues suggested that the muscle bundles are congenital and the subaortic abnormality acquired (Freedom et al, 1985) however, an echocardiographic study was performed on 1988 by Vogel et al reported that one patient who was premature at the time of the study (35 weeks gestation) underwent echocardiographic assessment one week after delivery and showed this rare association leading to some support to the argument that this is possibly a congenital lesion. Our case gave us certainty to support that this association is of congenital origin.

References

1. Baumstark A, Fellows KE, Rosenthal A. Combined double chambered right ventricle and discrete subaortic stenosis. Circulation 1978; 57:299-303.
2. Freedom RM, Pelech A, Brand A, Vogel M, Williams WG, Trusler GA,Rowe RD. The progressive nature of subaortic stenosis in congenital heart disease. Int J CardioJ 1985; 8:137-143
3. M Vogel, JF Smallhorn, RM Freedom, J Coles. An Echocardiographic Study of the Association of Ventricular Septal Defect and Right Ventricular Muscle Bundles with a Fixed Subaortic Abnormality. (Am J Cardiol 1988; 81:857-860).