抄録
我々は通常の超音波エコー装置を用いて,反射超音波の位相を巧みに用い,心臓の各部分の微小振動を速度波形として計測できる手法を開発した.本手法では,時間分解能を2ms,空間分解能を1m以下まで向上させ,従来の診断装置にはない高精度な計測を可能にした.この計測方法を心筋に適用したところ,心電図R波前後において,心筋で発生した微小振動が伝搬する現象を見出した.また,駆出期には,心筋の収縮は,短軸面の円周方向で1方向に伝搬していく様子が描出できる.これらは,心臓収縮を引き起こす興奮に対する心筋の応答が,心臓壁を順に伝搬する様子を可視化できる可能性を示している.今後,心筋の臨床診断等に広く利用されることが期待されている.
Electrocardiography is an invaluable clinical tool for diagnosis of a broad range of cardiac conditions, and clinical imaging tools. The aim of the present study is to visualize subtle features of the initial myocardial response to the propagation of the electrochemical depolarization waves, which corresponds to the beginning of the heart contraction. The three-dimensional propagation of the proximate response to the electrical excitation caused by cell polarization in the human heart wall was visualized by a novel ultrasonic-based measurement method noninvasively for the first time. Visualization demonstrated that at the time of the Q-wave of the electrocardiogram, pulsive vibration is generated at the center of the interventricular septum, and progresses to the entire left ventricle at a propagation speed of about 0.8 m/s. The subtle dynamic response of the myocardium to the arrival of electrical excitation visualized by this approach with a high temporal resolution of 2 ms shows great potential for noninvasive assessment of heart wall damage due to heart failure and desynchronization due to fibrillation.
