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The paradoxical finding of mitral valve incompetence and cor triatriatum: a mechanism revealed?
  1. W Keeble,
  2. E Lundmark,
  3. H J Dargie

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Magnetic resonance imaging demonstrated features of cor triatriatum in a 27 year old woman (upper panel). In the absence of associated congenital anomalies, obstructive cor triatriatum due to a small, flow limiting fenestration will present in a similar manner to mitral stenosis. However, this woman presented with exertional breathlessness, paroxysmal nocturnal dyspnoea, and prominent murmur of mitral incompetence.

Echo confirmed significant mitral regurgitation with an enlarged but contractile left ventricle. (End diastolic dimension 7 cm and end systolic dimension of 3.9 cm.) Panels A–C below demonstrate the mechanism of association between cor triatriatum, mitral incompetence, and left ventricular dilatation. A fenestration jet impinges on the anterior mitral leaflet, holding it open at the onset of ventricular systole while the posterior leaflet is closing. This abnormality of phase over a chronic period appears to have led to a spiral of mitral incompetence and compensatory left ventricular dilatation. This hypothesis was confirmed by the result of the surgical intervention. With the aid of intraoperative transoesophageal echocardiograpy, it was elected to excise the membrane alone. The valve leaflets were neither repaired nor a ring inserted to tighten around the mitral valve annulus. Five weeks later echocardiography demonstrated that removal of the membrane had restored normal flow mechanics allowing the leaflets to move in phase, coapt, and for the valve to regain competence. Left ventricular end diastolic size had regressed to 5.1 cm. No change in medication had occurred and the patient was symptom-free.

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Transverse magnetic resonance image showing the “heart of three atria”. Pulmonary veins enter the postero-superior chamber of the greatly enlarged left atrium. This is partitioned from the antero-inferior chamber by a fibromuscular membrane extending from below the fossa ovalis to the posterior free wall. AI, antero-inferior left atrial septum; m, membrane; PS, postero-superior left atrial chamber; pv, pulmonary veins; RA, right atrium.

Embedded Image

Transthoracic two dimensional echocardiography with colour flow mapping overlay reveals flow through the fenestration in the membrane (panel A). Flow extends along the interatrial septum to impinge upon the atrial side of the anterior mitral valve leaflet (panel B). A subsequent broad based jet of mitral regurgitation occurs (panel C). AI, antero-inferior left atrial septum; a, anterior mitral valve leaflet; f, fenestration; p, posterior mitral valve leaflet; PS, postero-superior left atrial chamber.