林 あかね¹, 荒川 元孝^{1, 2}, 金井 浩^{1, 2}

Akane HAYASHI¹, Mototaka ARAKAWA^{1, 2}, Hiroshi KANAI^{1, 2}

¹東北大学大学院医工学研究科, ²東北大学大学院工学研究科

¹Graduate School of Biomedical Engineering, Tohoku University, ²Graduate School of Engineering, Tohoku University

キーワード : echocardiography, myocardial contraction, propagation of contraction, phased tracking method

目的：虚血性心疾患の初期段階である心筋虚血部は，速やかに再灌流を図ることで壊死を回避できる．そのため，虚血部の範囲の迅速な同定が，虚血性心疾患の治療や診断において重要である．本研究は，心臓内の電気的興奮の伝播特性の解明を目的として，ヒト心臓の心室中隔壁と左室後壁両方の各点における壁の微小速度波形を超音波によってin vivo計測し，心筋の収縮応答伝播の描出を試みた．方法：ヒト心臓の心室中隔壁および左室後壁に対して400 Hz以上の高フレームレートで超音波計測を行い，取得したRF信号に位相差トラッキング法を適用して心筋の微小振動速度波形を得た．さらに，各計測点における微小振動速度波形に対して相互相関法を適用し，基準位置における収縮応答からの遅延時間を算出することで心筋の収縮応答伝播を描出した．結果：心室中隔壁における心筋収縮応答は，心基部側から心尖部側へ約1.9 ～ 3.8 m/sの速度で伝播することが示された．一方，左室後壁における心筋収縮応答は，心尖部側から心基部側へ約2.0 ～ 3.2 m/sの速度で伝播することが示された．これら両壁の計測を同時に行っているため，合わせることで，心筋収縮応答は，心室中隔壁を心基部側から心尖部側へ伝播した後に，左室後壁を心尖部側から心基部側へ伝播することが確認され，プルキンエ線維の走行と対応していた．結論：提案する手法を用いることで，心室中隔壁と左室後壁の両心筋の収縮応答伝播が超音波によって同時に描出できることが示された．

Purpose: For myocardial ischemic regions, when medical diagnosis and treatment are applied in the early stage of ischemic heart disease, fatal necrosis of the myocardium can be avoided by prompt reperfusion. Therefore, appropriate and rapid identification of ischemic regions is essential. In the present study, to noninvasively elucidate the propagation characteristics of the myocardial response to electrical excitation in the heart, the propagation of myocardial contraction was visualized by applying ultrasonic measurement of a minute vibration velocity waveform to each point in both the interventricular septum (IVS) and left ventricular posterior wall (LVPW) of the human heart. Methods: By simultaneously applying the phased-tracking method with a high frame rate of over 400 Hz to the IVS and the LVPW, vibration velocity waveforms in the myocardium were obtained at about 3,000 points in both walls. In addition, using a cross-correlation between the resultant vibration velocity waveform at each measurement point and that at the reference point, the delay time of the contraction response at each point from that at the reference point was determined so that the propagation of myocardial contraction could be visualized. Results: In the IVS, the myocardial contraction response propagated at 1.9-3.8 m/s from the basal to the apical side. In the LVPW, on the other hand, the response propagated at 2.0-3.2 m/s from the apical to the basal side. Since the above measurement was simultaneously applied to both walls, it was confirmed that the myocardial contraction propagated from the basal to the apical side in the IVS, and then from the apical to the basal side in the LVPW. These results correspond to the route of the Purkinje fibers. Conclusion: Using the proposed measurement and analysis method, it was shown that propagation of myocardial contraction in the IVS and the LVPW could be visualized by ultrasound.