DISCUSSION
In some cases, AVMT is a rare anomaly in childhood and may be detected
as an incidental finding or cause LVOT obstruction. This malformation is
associated with other congenital heart malformations, such as atrial
septal defect, ventricular septal defect, transposition of the large
arteries, patent ductus arteriosus, aortic coarctation, bicuspid aortic
valve, mitral cleft, and dextrocardia.7-9 The
embryological mechanism of AMVT formation is not clear and may be
related to abnormal or incomplete separation of the mitral valve from
the endocardial cushions.9-11 In the anatomical
classification, there are three types of AVMT: type I: AMVT with
attachments at the supra leaflet level, type II: AMVT attachments on the
mitral leaflets and type III: AMVT attachments below the mitral
leaflets.
Most cases of AMVT are associated with other cardiac malformations. The
clinical signs and symptoms of this anomaly vary depending on its
location and concomitant cardiac malformations. As in this case,
congenital AMVT may remain asymptomatic for many years. In adult
patients, AMVT may be diagnosed incidentally intraoperatively. Although
AMVT can remain asymptomatic in patients, it can lead to LVOT
obstruction in some patients. As in our case, most adolescent and adult
cases are patients with vague symptoms in whom an echocardiography was
performed for another indication. The most common symptoms are chest
pain, dyspnea and palpitations. In addition, a few cases have been found
to be associated with transient ischemic attack (TIA) and
AMVT.7,10-13 The most common complaints in our patient
were shortness of breath and atypical chest pain. Her neurological
examination was normal and no TIA was detected in her medical history.
The diagnosis of AMVT should be considered especially in patients with
an unexplained cerebrovascular accident with a heart murmur and tissue
causing signs of LVOT obstruction in the subaortic area.
Accessory mitral valve tissue resection is recommended in symptomatic
isolated AMVT patients with a significant LVOT gradient (mean gradient
≥25 mmHg) or in patients who were scheduled for cardiac surgery for
additional cardiac pathology.7,10 Diagnosis of AMVT
may be difficult before or during surgery. The echogenicity of AMV
tissue is similar to that of endocardial structures. Therefore, surgeons
should know the clinical and pathological features of AMVT to avoid
overlooking it during surgery.1,7-10
Echocardiography is considered the gold standard for imaging AMVT.
Transthoracic echocardiography (TTE) is sufficient for diagnosis, but
perioperative TEE is important both for confirming the diagnosis and
completing the surgical procedure, and for assessing postoperative
mitral valve functions and possible complications that may occur after
excision of AMVT.1-6,8 In particular,
three-dimensional (3D) TEE allows assessment of the location of the AMVT
attachment and the presence of an accompanying mitral lesion. We
performed a TTE and a 3D-TEE which showed that the AMVT attached to the
anterior mitral leaflet, with a subaortic attachment, resulting in an
increase in the LVOT gradient.
Yasui et al. reported a patient who could not be separated from
cardiopulmonary bypass due to LVOT caused by an overlooked AMVT, and
pointed out that detection of this anomaly during surgery is difficult
without an accurate presurgical diagnosis.14 Surgical
excision of the AMVT should be carefully performed without affecting the
functions of the mitral valve and surrounding
structures.8,9,14