原口 亮

若年者の頻脈性不整脈および心臓突然死の原因の1つである Wolff-Parkinson-White (WPW) 症候群は，心臓内の正常な刺激伝導路とは別に先天的に心房と心室とをつなぐ副伝導路が存在する疾患である．これまでに我々は心房筋・心室筋・副伝導路からなる数理モデルを構築した上で，コンピュータシミュレーションにより，副伝導路の大きさ・心房・心室の導電率・副伝導路の導電率が副伝導路を介した伝導にどのような影響を与えるのかをsource-sink の概念に基づいて明らかにした．しかしながら，イオンチャネル電流と伝導の実際との関連は明らかではない．そこで我々は年齢によるイオンチャネル電流の差異を模擬できる膜電位モデルを構築した上で，心房・心室・副伝導路のイオンチャネル電流が副伝導路を介した伝導にどのような影響を与えるのかについてコンピュータシミュレーションによる検討を行なった．それにより，小児・成人・老年いずれの場合においても，イオンチャネル電流の変化は副伝導路を介した伝導に影響を及ぼさないという結果が得られた．本研究の結果は，副伝導路における伝導の成立およびWPW症候群の顕在化はsource-sink関係が支配的な要因であることを示唆している．

<sec xml:lang="en"> <title>Background</title> <p xml:lang="en">Detection of the fiber orientation pattern of the myocardium using diffusion tensor magnetic resonance imaging lags ≈12 weeks of gestational age (WGA) behind fetal myocardial remodeling with invasion by the developing coronary vasculature (8 WGA). We aimed to use diffusion tensor magnetic resonance imaging tractography to characterize the evolution of fiber architecture in the developing human heart from the later embryonic period. </sec> <sec xml:lang="en"> <title>Methods and Results</title> <p xml:lang="en">Twenty human specimens (8–24 WGA) from the Kyoto Collection of Human Embryos and Fetuses, including specimens from the embryonic period (Carnegie stages 20–23), were used. Diffusion tensor magnetic resonance imaging data were acquired with a 7T magnetic resonance system. Fractional anisotropy and helix angle were calculated using standard definitions. In all samples, the fibers ran helically in an organized pattern in both the left and right ventricles. A smooth transmural change in helix angle values (from positive to negative) was detected in all 16 directions of the ventricles. This feature was observed in almost all small (Carnegie stage 23) and large samples. A higher fractional anisotropy value was detected at the outer side of the anterior wall and septum at Carnegie stage 20 to 22, which spread around the ventricular wall at Carnegie stage 23 and in the early fetal samples (11–12 WGA). The fractional anisotropy value of the left ventricular walls decreased in samples with ≥13 WGA, which remained low (≈0.09) in larger samples. </sec> <sec xml:lang="en"> <title>Conclusions</title> <p xml:lang="en">From the human late embryonic period (from 8 WGA), the helix angle arrangement of the myocardium is comparable to that of the adult, indicating that the myocardial structure blueprint, organization, and integrity are already formed. </sec>