Double Mitral Valve Imaging

Double-orifice mitral valve is an uncommon anomaly of the mitral valve with a single fibrous annulus with 2 orifices opening into the left ventricle. Three major types of this anomaly are recognized: (1) the eccentric or hole type (accounting for about 85%), (2) the central or bridge type (about 15%), and (3) duplicate mitral valve, which involves 2 mitral valve annuli and valves, each with its own set of leaflets, commissures, chordae, and papillary muscles. However, some echocardiographic artifacts also may lead to interesting appearances. The duplicating of cardiac valves by refraction of the ultrasound beam or mirror images has rarely been reported. The authors present the duplication of a moving mitral valve associated with an echocardiographic refraction artifact.

Double-orifice mitral valve is an uncommon anomaly of the mitral valve with a single fibrous annulus with 2 orifices opening into the left ventricle. Three major types of this anomaly are recognized: (a) the eccentric or hole type (accounting for about 85%), (b) the central or bridge type (about 15%), and (c) duplicate mitral valve, which involves 2 mitral valve annuli and valves, each with its own set of leaflets, commissures, chordae, and papillary muscles. The differentiation of the various types in the parasternal and subxiphoid short-axis views can be done using accurate sweeping from the apex to the base of the ventricle. However, some echocardiographic artifacts also may lead to interesting appearances.

Case Report

A 60-year-old man who had been followed elsewhere with the diagnosis of dilated cardiomyopathy was referred to our echocardiography laboratory for the evaluation of mechanical asynchrony. In addition to the typical transthoracic echocardiographic findings of dilated cardiomyopathy, the parasternal long-axis view showed the interesting appearance of a double mitral valve ( Figure 1 A , Video 1 ). The color Doppler image also showed 2 regurgitation jets through the double mitral orifice ( Figure 1 B, Video 2 ). However, the off-axis apical 4-chamber view confirmed only 1 mitral valve apparatus and 1 mitral regurgitation flow jet ( Videos 3 and 4 ).

Discussion

In radiologic imaging, the term artifact is used to describe any part of an image that does not accurately represent the anatomic structures present within the subject being evaluated. Clinical significance emerges from possibly confusing and misleading findings, such as malpositioning or duplication of target objects. Important sources of these artifacts include the generation of side lobes, reverberations, lateral resolution, beam width, near-field clutter, and acoustic shadowing.

Duplication artifacts of cardiac valves by refraction of the ultrasound beam (side-by-side appearance) or mirror images (top-to-bottom appearance) have rarely been reported. Refraction results from deflection of the ultrasound beam by a medium with a speed of sound different from that of the surrounding tissue. Anatomic structures between the transducer and the heart, such as the pleura, pericardium, costal cartilage, or fascial structures and fat, may act as the media inducing refraction of the ultrasound beam and resulting in the doubling of cardiac structures. Doubling by refraction is different from other artifacts generating double images, such as mirroring of the ultrasound beam (eg, by prosthetic valves) ; in general, mirroring appears as a duplication of structures, with the mirror image always appearing deeper than the real structure.

These artifacts can be eliminated by changing the transducer’s angle and position. It is well known that an artifact that originates from a fixed reflector will not move with the motion of the heart and is not likely to be reproduced in multiple echocardiographic planes on real-time echocardiography. In current case, we present the duplication of a moving mitral valve associated with an echocardiographic imaging artifact generated by ultrasound refraction.