Keywords
cardiac surgery - mitral valve repair - heart valve disease
Introduction
Congenital defects resulting in mitral insufficiency presenting in late adulthood
are rare.[1] They can be caused by underdevelopment of any of the four components of the mitral
valvular complex including the annulus, leaflets, chordae tendineae, and papillary
muscles.[2] We report a case of mitral regurgitation that developed as a consequence of posterior
leaflet atresia.
Case History
A 66-year-old woman, with a known heart murmur since childhood, presented with a history
of progressive shortness of breath over a 6-year period. She had been followed up
as having mitral valve prolapse and had been in atrial fibrillation for the past 6
years. At the time of referral her degree of heart failure was New York Heart Association
(NYHA) Class III. Her medical history included rheumatic joint disease and smoking.
Physical examination revealed a loud pansystolic murmur over the left sternal border
radiating to the axilla and atrial fibrillation but there were no other physical signs.
Preoperative transthoracic echocardiography revealed thickened anterior leaflet of
the mitral valve and complete prolapse of the anterior leaflet (A1, A2, and A3 scallops),
resulting in a posteriorly directed eccentric jet of severe mitral regurgitation hugging
the left atrial wall. Additional findings included a moderately dilated left atrium
and borderline dilated left ventricular cavity with preserved function. There were
no other significant valve abnormalities present. Cardiac catheterization showed no
evidence of coronary artery disease. Blood tests were unremarkable.
A decision to proceed with mitral valve repair or possible replacement was made and
the patient was listed for elective surgery. A perioperative transesophageal echocardiogram
revealed similar findings to her preoperative scan but there was a question as to
whether the posterior leaflet was absent ([Fig. 1]). During the operation, there was a congenital atresia of the posterior mitral valve
leaflet with rudimentary papillary muscle heads and exceptionally short chordae directly
implanting into the posterior annulus. The anterior leaflet was large and thickened
with prolapse at all three scallops. We did not feel that a satisfactory result would
be achieved with attempted repair, so we proceeded to replace the valve. The anterior
leaflet was excised ([Fig. 2]) and a 29-mm St Jude bileaflet mechanical valve was implanted at 90 degrees to the
anatomical position using interrupted horizontal mattress sutures. The patient was
discharged on her 5th postoperative day. Histology of the anterior valve leaflet showed
hyaline and myxoid degeneration. On follow-up at 6 weeks, she met the criteria for
NYHC 1 with a normal functioning mitral prosthesis.
Fig. 1 Long axis transesophageal echocardiogram showing absence of a posterior valve leaflet.
AMV, accessory mitral valve.
Fig. 2 Resected enlarged and thickened anterior valve leaflet.
Discussion
Classification of this type of mitral valve disease is not straightforward. Although
a congenital defect exists, this patient's regurgitation was secondary to a prolapsed
leaflet and histology showed degenerative changes. We would therefore classify this
as Carpentier Type II. The prevalence has been reported by Bär et al (2009) as 1:8,800
in a prospective analysis of 26,484 preselected asymptomatic adult population.[3]
Atresia of the posterior leaflet occurs during development of the left lateral endocardial
cushion but the underlying process is not yet understood. It is associated with a
compensatory elongation of the anterior leaflet. It has been proposed by Heper et
al (2010) that leaflet growth is disrupted by a change in the direction of blood flow
through the atrioventricular orifice during diverticulation and undermining of the
ventricular muscle from the ventricular wall.[4] However, this is only speculation and there is no evidence to support this theory.
The prognosis for this condition without treatment has not been documented. It was
initially believed that patients with this malformation did not survive beyond the
neonatal period and reports of this condition in adults are few in number.[2] Bär et al (2009) described this condition present in three adult patients. Two patients
were found to have mild mitral regurgitation and one with moderate mitral regurgitation.
In this series, mitral valve pathology was only identified as a result of selected
screening in asymptomatic patients.[3]
The surgical management of an underdeveloped mitral valve leaflet in pediatric patients
has been described. Kalangos et al reported the surgical management of a 10-year-old
girl with annuloplasty.[5] Their follow-up is limited to only 12 months. Caciolli et al similarly reported
on a 14-year-old girl with similar pathology treated by annuloplasty. No long-term
follow-up was documented.[6] The oldest patient with an underdeveloped mitral valve leaflet receiving surgical
intervention was aged 29. Stojanovic et al used pericardial patches to enlarge the
posterior leaflet area, in addition to performing an annuloplasty. Their postoperative
results were good but only a follow-up of 6 months is documented.[7]
Mitral valve repair is considered to be the optimal surgical treatment in adult patients
with mitral valve regurgitation, especially for Carpentier Type II defects. When compared
with replacement, there is a lower perioperative mortality and improved survival.
Current guidelines on the management of heart valve disease emphasize that repair
should be employed when possible; however, the durability of the repair and freedom
from reoperation are not similar for all types of pathology.[8] Thus, the optimal surgical treatment option in adults with underlying congenital
defects is not so clear. There is very little evidence supporting the use of mitral
valve repair in this situation due to the rarity of mitral valve leaflet atresia and
thus long-term outcomes are not well described. In this case, mitral valve replacement
was more appropriate to the individual needs of our patient. We decided to implant
a mechanical valve as she was older than 65 years and her likelihood for reoperation
would be minimized with replacement. In addition, we did not feel that ablation therapy
for her atrial fibrillation would be successful as she had a dilated atrium on her
preoperative echocardiogram, and so necessitating her continued need for warfarin
anyway. And finally we did not feel a repair would yield satisfactory results. A satisfactory
follow-up echocardiogram demonstrated normal functioning of her mitral prosthesis
so she was discharged back to her general practitioner.
