芦原 京美

Kyomi ASHIHARA

東京女子医科大学循環器内科

Department of Cardiology, Tokyo Women's Medical University

キーワード : three-dimensional echocardiography, prosthetic valve, prosthetic valve endocarditis, valve dysfunction, valvular heart disease

人工弁評価では，超音波の多重反射・音響陰影で，人工物の遠位の観察困難が問題である．通常の経胸壁心エコー図法（TTE）で評価困難なこの部分を，食道側，つまり反対側から評価するのが経食道心エコー図法（TEE）である．しかし，TTEでは，各断面から異常部位が比較的容易に判断できるのに対し，TEEでは異常部位の理解には熟達が必要となる．3次元経食道心エコー図法（3D-TEE）では，フルボリューム画像から2次元画面を切り出すことで，従来法にはない自由な断面からの画像取得が可能であり，今まででは不可能であった方向からの人工弁観察が可能である．心房・心室・大動脈から，人工弁の動く様を描出するsurgeon’s viewは，人工弁構造の理解のみならず，合併症や感染性心内膜炎の観察に大きな威力を発揮する．置換弁性感染性心内膜炎では，疣腫のみならず，人工弁周囲膿瘍や人工弁周囲逆流，人工弁の離開や脱着，人工弁stuckについても良好に描出可能である．人工弁周囲逆流に関して，3D-TEEは逆流部分の大きさ，位置の評価に重要な情報を提供し，surgeon’s viewによる僧帽弁，大動脈弁の弁離開部分の描出画像は，離開部の位置・大きさ・形・数についても情報をもたらしてくれる．特に，3次元のmulti planar image（MPR）の使用により，弁離開部分の範囲の正確な評価が可能である．画質や画角など未だ解決すべき部分はあるが，3次元による人工弁構造提示が，医療者間のみならず患者や他の科の医師達との情報共有を可能とし，治療の向上につながることからもきわめて重要な検査法と考える．

Imaging of prosthetic devices has several technical limitations, especially in cases with acoustic shadowing or reverberation when valve dysfunction is suspected. Three-dimensional (3D) transesophageal echocardiography (3D-TEE) images provide appropriate visualization of valvular anatomy and proper quantification of valvular heart disease with superior spatial and temporal resolution compared with transthoracic echocardiography (TTE). 3D-TEE has improved visualization and assessment of complications in prosthetic valves, such as endocarditis or paravalvular regurgitation. Deep anatomic structures can be well displayed by manipulation and cropping wide-angled, full-volume datasets. Moreover, 3D-TEE images provide valvular visualization from any angle, which has been limited in 2D planar views. We can see the mitral mechanical and bioprosthetic valve rings, leaflets, and struts clearly by using 3D-TEE. Paravalvular regurgitation can also be identified. Quantification of the dehisced area using multiplanar imaging can be confirmed by the use of 3D color flow. It clearly demonstrates the location and size of mitral paravalvular leaks, describing the number of sites of dehiscence and its configuration. For the imaging of prosthetic valves, ‘3D zoom’ and ‘live’ modes are the most frequently used, giving priority to frame rate and imaging resolution. Orientating a structure from the axial direction of the beam allows new perspectives of the valvular structures on its face view (surgeon's view) and on its ventricular view. These allow us to understand the morphology and spatial relation among the intracardiac structures, resulting in diagnostic confidence and better communication among the heart team, at the time of clinical decision-making for surgery, for selecting patients for percutaneous interventions, and during the effective performance of these procedures.