Case reports

LB presented cyanosed on the first day of life, and was found to have transposed arterial trunks with an intact ventricular septum. Following an atrial balloon septostomy, he came forward to an uneventful arterial switch on the seventh day. He developed a supraventricular tachycardia with aberrancy on the 19th day, but responded well to intravenous adenosine, and remained symptom-free on twice-daily Sotalol, eventually being weaned from that medication 8 months later. His subsequent course was complicated by increasing incompetence of his neoaortic valve, associated with mild-to-moderate incompetence of the mitral valve. The latter was eventually shown to be due to an isolated cleft, positioned at about 2 o’clock when viewed from below looking at the cardiac short axis with the right ventricle to the left (Fig. 2). By the age of 4 years, he developed increasing left ventricular dilation initially helped by oral Lisinopril. His echocardiogram showed left ventricular hypertrophy. With continuing decrease in exercise tolerance and a dilated left ventricle with left ventricular function at the lower limit of normal, he now has been accepted at the age of 6 years for repair of his neoaortic valve and suture of the cleft mitral valve.

Figure 2. Parasternal short axis of the left ventricle showing a cleft in the pulmonary leaflet of the mitral valve positioned at 2 o’clock in the setting of transposition and intact ventricular septum. VS: ventricular septum; LV: left ventricle; AMVL: anterior mitral valve leaflet; MURAL: mural leaflet of mitral valve; MR: mitral regurgitation; MV: mitral valve. *Reprinted from: Tamura M, Menahem S, Brizard C. Clinical features and management of cleft mitral valve in childhood. J Am Coll Cardiol 35: 764–770. Copyright 2000 with permission from the American College of Cardiology Foundation.

DF presented on the first day of life with cyanosis, initially attributed to meconium aspiration. Cross-sectional echocardiography revealed transposed arterial trunks with an intact ventricular septum. A balloon atrial septostomy was followed 5 days later by an uneventful arterial switch. He has remained well subsequently. His neopulmonary valve, however, was noted to be bicuspid, initially producing mild-to-moderate stenosis, for which he required no treatment. Subsequent echocardiograms revealed increasing mitral incompetence. Careful review of the valve showed an isolated cleft in a similar position as the previous patient. At the age of 11 years, he came forward to balloon valvoplasty of his moderately stenosed neopulmonary valve, with a drop of his right ventricular pressure from just over two-thirds systemic pressures to just under half systemic pressures. He currently remains well at the age of 14, with evidence of mild pulmonary valvar stenosis and mild mitral incompetence. There is no immediate plan to attend to his cleft mitral valve.

Discussion

As far as we are aware, isolated clefts of the mitral valve have not been reported in transposition with intact ventricular septum. Our observations, nonetheless, are in keeping with our current knowledge of cardiac development. Thus, the Taussig-Bing lesion represents a spectrum between double outlet right ventricle with subpulmonary defect and discordant ventriculo-arterial connections with a malalign-ment ventricular septal defect. This spectrum shows us that, when the heart has discordant ventriculo-arterial connections, the pulmonary trunk enters the right ventricle through the left side of the ventricular outflow tract, with the outlet septum fusing with the muscular ventricular septum to wall the pulmonary trunk, rather than the aorta, into the left ventricle.⁸ In the process of normal development, the outlet septum fuses antero-superiorly relative to the interventricular communication, thus walling the aorta into the left ventricle. This arrangement gives us the spectrum seen with double outlet and subaortic defect, of which tetralogy of Fallot is part.

In the setting of discordant ventriculo-arterial connections with intact septum, therefore, the pulmonary outflow tract is positioned much more leftward in comparison to the subaortic outflow tract of the normal heart, and is not “wedged” between the mitral valve and the septum to the same extent as is the normal subaortic outflow tract.

Thus, when the forming mitral valve retains a cleft between its component parts, this cleft will also be positioned more leftward, as is seen with straddling of the mitral valve, also often cleft, in the Taussig-Bing malformation.^{6, 7}

The location of the cleft in our two cases, therefore, is in keeping with our current knowledge of cardiac development. It provides additional evidence that transposition with an intact ventricular septum is, indeed, the end-point of the Taussig-Bing spectrum.

In both of our cases, surprisingly, retrospect review of the earlier echocardiograms failed clearly to demonstrate the cleft. Had there been an awareness of the possible association, and a more careful study undertaken at the time, it may have led to an earlier diagnosis and possible correction at the time of the initial surgery.