Accessory mitral valve tissue: anatomical and clinical perspectives

Echocardiographic features of accessory mitral valve tissue presenting left ventricular outflow tract obstruction in a dog

“…However, in this case, AMVT was connected with both the IVS and chordae tendineae, and the connected tendon was in turn associated with the PM and chordae tendineae of the anterior MV. Interestingly, AMVT in our case showed both mobile part connected to the chordae, and a fixed part attached to the ventricular septum, which was a unique feature compared to previously reported cases [ 2 7 ].…”

“…AMVT can induce LVOT obstruction via both the mass effect of AMVT itself and complications secondary to AMVT, such as fibrous deposition, thrombus, or remodeling of the cardiac muscle and, 86.6% of human patients with AMVT have LVOT obstruction [ 2 3 7 8 ]. The pressure gradient of LVOT in the previous cases varied from 10 to 130 mmHg; notably, a few patients had no gradient [ 2 3 4 9 10 ].…”

“…In some cases, the appearance of AMVT may change during the cardiac cycle [ 4 ]. The AMVT is usually attached to the ventricular side of anterior MV and its vicinities [ 7 ]. Some are attached to the papillary muscle, interventricular septum (IVS), or rarely to the posterior MV [ 2 ].…”

“…AMVT can induce LVOT obstruction via both the mass effect of AMVT itself and complications secondary to AMVT. It includes fibrous deposition, thrombus, or remodeling of the cardiac muscle due to turbulent flow, pressure overload, and damage to cardiac muscle [ 3 7 8 ]. Therefore, when evidence of LVOT obstruction is found, AMVT should be considered as one of the underlying lesions and differentiated from more commonly identified lesions such as aortic stenosis, abnormal papillary muscle insertion, and LV false tendon [ 1 2 ].…”

Incidental finding of accessory mitral valve tissue on routine adult echocardiography

“…6 A new anatomical classification (including three types) was recently proposed, based on the anatomical attachments of AMVT: type I is the least common type and refers to AMVT with an attachment on the supraleaflet or supravalvular level (ie, left atrial wall), type II is the most common and refers to AMVT without attachments on the supravalvular and infraleaflet level and is divided to type IIa (accessory tissue exists truly on the mitral leaflets itself) and type IIb (accessory tissue has insertion on subaortic level of interventricular septum), and finally type III, which refers to AMVT originating below the level of mitral leaflets. 7 Type I and III AMVT (with attachment on the supravalvular or subvalvular level respectively) should not be confused with congenital mitral stenosis either on the supravalvular level such as supravalvular mitral ring (a fibrous membrane located at the atrial surface of the mitral valve) or on the subvalvular level such as mitral arcade or parachute mitral valve. 8 AMVT can be diagnosed either in childhood or in adult period.…”