Echocardiographic Assessment and Successful Valvular Repair of Congenital Mitral Arcade.

Anomalous mitral arcade is a rare congenital anomaly affecting the mitral tensor apparatus. This condition causes a restrictive movement of the leaflets and interferes with the normal closure of the valve during ventricular systole. We report a case of a 15-year-old female with this condition and initial left ventricular dysfunction, who successfully underwent mitral valve repair. This reparative technique is more technically challenging then valve replacement and only few cases are described in literature.

INTRODUCTION

Anomalous mitral arcade or hammock valve is a rare congenital anomaly of the mitral tensor apparatus, which consists in a fibrous continuity between mitral leaflets and enlarged papillary muscles, without interposition of chordae tendineae or with an underdeveloped chordal apparatus. This condition causes a restrictive movement of the leaflets that interferes with the achievement of an optimal position for valvular closure during ventricular systole.[1]

This malformation is characterized by progressive worsening of valvular defect, which could be regurgitation, stenosis or both. Usually, patients undergo surgery before reaching adulthood.[2]

CASE REPORT

We report the case of a 15-year-old female with mitral regurgitation diagnosed in infancy, in therapy with diuretics, vasodilators, and digoxin and in regular clinical and echocardiographic follow-up. The patient reported, in the last year, progressive exertional dyspnea, fatigue, and palpitations (New York Heart Association class III) with echocardiographic evidence of initial left ventricular dysfunction and severe mitral insufficiency (vena contracta 0.6 cm, effective regurgitant orifice 0.37 cm2, rigurgitant volume 57 mL). The color doppler flow of the mitral valve revealed an eccentric jet (headed to the posterolateral wall of the left atrium) due to a dysplastic valve with thickened leaflets, especially the anterior one [Figure 1 and Video 1–2], hypertrophy and partial fusion of the papillary muscles and the chordae, which appeared shortened. The mitral annulus was dilated (37 mm × 39 mm) and so was the left ventricle, without regional dysfunction but with a global systolic function mildly reduced (left ventricular ejection fraction 50-52%) and a severe left atrial enlargement (volume index 50 mL/m2). These findings, confirmed with the transesophageal approach, were consistent with the ones described in anomalous mitral arcade. The three-dimensional acquisition in this patient had not added information due to the extremely thickened tissue and the disruption of the entity “papillary muscles-chordae-leaflets.”

Figure 1

Hammock valve with hypertrophic and fibrotic papillary muscles and hypoplastic chordae in diastolic and systolic phase

The patient was referred to cardiac surgery for mitral valve repair. During surgery, the valve appeared severely dysplastic with deposition of fibrotic tissue on both leaflets. The anterior papillary muscle was hypertrophic, fibrotic, cranially deployed and directly connected to the anterior leaflet segment A1 (place of incomplete cleft) and posterior leaflet segment P1, with total aplasia of chordae tendineae. The posterior papillary muscle appeared moderately hypertrophic with hypoplastic chordae. The repair consisted of anterior and posterior papillary muscle splitting with two longitudinal lesions, removal of two secondary hypoplastic posterior paracommissural chordae and cleft closure of A1-A2 segments. A satisfactory mobility of the leaflets was obtained. Later anulovalvuloplasty was performed using a complete ring (Carpentier Physio number 30).

The procedure was successful and the postoperative course was unremarkable.

An echocardiographic study was performed on postoperative day 3 and showed good surgical result, with normal mitral leaflets coaptation, a mild residual mitral regurgitation, and a mean transvalvular gradient of 4 mmHg. Left ventricle appeared of normal dimensions with preserved systolic global function. Left atrium was only mildly enlarged. The patient was discharged on postoperative day 6 with warfarin and bisoprolol therapy. At the follow-up evaluation 3 months later the patient reported improvement of the exercise capacity without complaining fatigue or dyspnea in everyday activity; warfarin was withdrawn.

DISCUSSION

In 1967, Layman and Edwards described for the 1st time anomalous mitral arcade as a mechanism of congenital mitral insufficiency. The English word “hammock” was used firstly by Carpentier in 1976 to describe the typical aspect of the anomalous valve seen from the atrial side during cardiac surgery. Peculiar aspects of this valve are: the presence of a dimensionally adequate orifice, thickened and shortened chordae, direct link between papillary muscles and anterior leaflet and a reduced space between the anomalous chordae. This malformation may be the result of an arrest in the development of the mitral valve before attenuation and lengthening of the collagenized chordae tendineae.[1]

Clinical course could be variable and it is related to the severity of mitral stenosis/insufficiency.

Most cases described are about pediatric patients, there are only few cases described in adult; usually these patients underwent mitral valve replacement with a mechanical prosthesis,[34] only in one case the patient became asymptomatic with angiotensin-converting enzyme inhibitor and diuretics and was scheduled for follow-up.[5]

An accurate evaluation of mitral valve apparatus with transthoracic echocardiography is of paramount importance to suspect anomalous mitral arcade and it is also useful to determine the best timing for intervention and the more appropriate reparative technique.[6] The repair surgery is rare.

Sometimes this anomaly could be confused with rheumatic mitral disease on transthoracic echocardiography and the high spatial resolution of computed tomography combined with multiplanar four-dimensional images can reveal anatomic and functional details of the mitral apparatus suggesting the correct diagnoses.[7]

CONCLUSION

In our case, a careful echocardiographic evaluation of the mitral valvular and subvalvular apparatus was fundamental to diagnose anomalous mitral arcade; the patient underwent successful valve repair, which is more technically challenging than valve replacement.