Assessment of Contractile Reserve of Infarcted Myocardium Using
Contrast Echocardiography: a Novel Index of Myocardial Blood Volume
Fraction Compensating for Ultrasound Attenuation
Kaoru Komuro1, Satoshi Yamada1, Taisei Mikami2, Kazutomo Goto1,
Hisao Onozuka1 Akira Kitabatake1
1Hokkaido University Graduate School of Medicine
2College of Medical Technology, Hokkaido University
Background: Inhomogeneous acoustic field caused by the attenuation of incident
ultrasound is one of major limitations of quantitative myocardial contrast
echocardiography (MCE). We have previously proposed a novel index ‘relative
signal intensity (RelSI)’ to estimate myocardial blood volume (MBV) fraction bycompensating for ultrasound attenuation, which is calculated as the relative signal
intensity of myocardium to that of the intracavity blood area adjacent to themyocardium. The purpose of this study was to elucidate whether RelSI measured
in multiple segments reflects contractile reserve of infarcted myocardium.
Methods: Using Phillips Sonos 5500, harmonic power Doppler images wereacquired at end systole of every 6 beats during continuous infusion of Levovist (2-3ml/min) in 12 normal subjects (apical 4-chamber views), and 25 patients with priormyocardial infarction (apical views). In the normals, interventricular septum wasdivided into 3 segments (control segments). In the patients, 35 segments showing
severe asynergy were defined as infract segments (15 apical, 10 mid and 10 basalsegments). In each segment, RelSI was calculated by subtracting the signal
intensity (in decibels) of the intracavity blood area adjacent to the segment from thatof myocardium. RelSI represents the ratio (myocardium/adjacent blood) of
microbubble concentration, which means MBV fraction because the bubble
concentration in blood pool is constant and blood volume fraction of blood is 100%.
Contractile reserve (CR) of the infarct segments was determined by dobutamine
echocardiography.
Results: In the normals, although the myocardial signal intensity of basal segment
was lower than those of the other segments, RelSI was not different among apical,
mid and basal segments (-14.7±1.5; -15.0±1.2; -15.7±1.1dB, p=0.25, ANOVA).
RelSI in the infarct segments was significantly lower than that in the control
segments (-18.3±2.8 vs -15.1±1.3dB, p<0.0001). RelSI in the 17 segments with
CR was significantly higher than that in the 18 segments without CR (-16.8±2.1 vs–19.8±2.7dB, p<0.01).
Conclusion: RelSI, representing MBV fraction, reflects contractile reserve of
infarcted myocardium. This novel index is useful for multi-segment analysis of
myocardial viability by compensating for ultrasound attenuation in MCE.

コントラストエコー法を用いた慢性期梗塞心筋の収縮予備能評価：心筋内血液量推定のための新しい指標
小室 薫、山田 聡、三神大世*、後藤数智、小野塚久夫、北畠北海道大学循環病態内科学
北海道大学医療技術短期大学部*

顕

背景：我々は、超音波造影剤濃度と画像輝度(AU2)との直線関係の観察に基づき、心筋コントラストエコー法における音場不均一性を補正する心筋輝度の指標‘relative signal intensity (RelSI)’を考案した。
目的：RelSIが慢性期梗塞心筋の収縮予備能を反映するか否かを検討する。
方法：健常者1１例、陳旧性梗塞患者25例において、レボビスト持続静注下に1:6心拍収縮末期の心尖部断面ハーモニックパワードプラ画像を収集し、各セグメントで心筋とそれに隣接する左室腔との輝度(dB)の差RelSIを求めた。RelSIは気泡密度比を表し、心筋内血液量分画を表すと考えられる。梗塞心筋の収縮予備能(CR)は、低用量ドブタミン負荷心エコー法での壁運動改善の有無により判定した。
結果：健常者の心筋輝度そのものはセグメント間で異なったが、RelSIには差がなかった。梗塞心筋のRelSIは健常心筋に比し低く(-18.3±2.8 vs -15.1±1.6dB, p＜0.0001)、また梗塞巣のうちCR(-)と判定された18区域のRelSIはCR(+)と判定された17区域より低かった(-19.8±2.6 vs –16.8±2.0dB, p＜0.001)。
結論：RelSIを用いることにより、音圧の異なる多セグメントで慢性期梗塞心筋の収縮予備能を推定可能である。

質疑応答
質問 1 AU2とはどういう単位か。
応答
受信信号パワーに比例する単位で、dB(X)との間にはAU2 = 10X/10が成り立つ。音圧の等しい条件下では、AU2の比、dBの差が気泡密度を表す。
質問２ 新しい方法の利点は何か。
応答 心筋輝度そのものは音場不均一の影響を受けるが、RelSI はそれを克服できる。