林 英宰

Young-Jae LIM

河内総合病院循環器科

Department of Cardiology, Kawachi General Hospital

キーワード : myocardial ischemia, collateral circulation, harmonic imaging, intermittent imaging, real time imaging

虚血性心疾患において, 心筋バイアビリティや心筋虚血の評価のために, 経静脈心筋コントラストエコー法が用いられる. レボビスト™を用い, ハーモニック法と間歇送信法を併用して, 経静脈心筋コントラストエコー法を行った. 冠動脈完全閉塞例では, グレースケールイメージとパワードプライメージの両方で梗塞領域を明瞭に描出できた. しかしながら, 現時点では再灌流後の症例においては梗塞領域を明瞭に描出することは困難であった. 冠動脈注入法に比し, 静注法では心筋染影性がまだ不十分で, ジピリダモール負荷や多重送信比較法(multi-frame triggering method)などの併用が必要である. 狭心症患者でジピリダモール負荷前後で時間輝度回復曲線を作成し, 心内・外膜側の灌流状況を評価した. A値は心筋血液量を表し, Beta値は心筋血流速度を表すとされる. A値は負荷後, 心内膜側と心外膜側の両方で増加した. Beta値は心外膜側で増加したが, 心内膜側では低下した. 経静脈心筋コントラストエコー法により, ヒトで非観血的に心内膜下の灌流動態を評価可能である. 冠動脈造影法は側副血行路の機能を必ずしも正しく反映しない. 冠動脈造影法と比較することにより, 側副血行路の機能評価における経静脈心筋コントラストエコー法の有用性を検討した. ジピリダモール負荷前後で正常域と側副血行灌流域の心筋染影度を比較することにより, 側副血行灌流を評価可能であった. また, 本手法はバイパスグラフトの機能評価にも有用で, 心筋梗塞症例におけるグラフト灌流域は低染影でかつ染影が遅れることが示された. 最近, 微小気泡の反射により敏感なサードハーモニックイメージングや1.5ハーモニックイメージングが臨床に導入された. このような新技術により, 近い将来リアルタイム心筋コントラストエコー法が可能になるであろう.

Intravenous myocardial contrast echocardiography (IV-MCE) was used to assess myocardial viability and myocardial ischemia in patients with coronary artery disease. IV-MCE study was performed by intravenous continuous injection of Levovist™ utilizing second harmonic imaging and intermittent imaging in end-systole. Gray scale and Power Doppler technique were both able to clearly visualize the infarct area in patients with total occlusion of the related vessel. However, at present, IV-MCE is not sufficient to assess myocardial viability after reperfusion therapy because it has less ability to facilitate myocardial opacification companed with intracoronary injection (IC-MCE) and it thus requires some additional methods such as Dipyridamole stress and multi-Frame triggering. IV-MCE was used to assess myocardial ischemia in patients with effort angina pectoris. Time-Intensity curve was plotted in the endo- and epimyocardial halves of the apical segment before and after Dipyridamole stress changing pulse interval acquisition. A and Beta values, calculated from Wei’s curve, indicate capillary blood and volume velocity. A value tended to increase in both endo- and epicardial half during stress. On the other hand, Beta value increased in only epicardial half and decreased in enocardial half during stress. It was thus possible to perform a noninvasive assessment of subendocurdid perfusion change during stress in human with IV-MCE. Coronary angiographic visualization of epicardial coronary collateral vessels does not provide significant information about the activity of the collaterals. Thus, the value of IV-MCE in assessing collateral function was studied by comparing coronary angiography and IV-MCE findings. The functional significance of collateral circulation was evaluated by comparing myocardid opacification in collateralized area to that of normal area before and after Dipyridamole stress with IV-MCE. Moreover, IV-MCE was validated as a useful tool for assessing myocardial perfusion via coronary bypass graft. Myocardial opacification appeared to be lower and slower in the graft area than in the normal area in patients with old myocardial infarction with IV-MCE. Recently, third harmonic imaging and 1.5 harmonic imaging, which are more sensitive to microbubble reflection, have been introduced into the clinical setting. New contrast techniques will more real time MCE possible in the clinical setting in the near future.