M型超声心动图二尖瓣前叶曲线DE段为（）。
A.一缓慢上升平段
B.一急速上升的直线
C.二尖瓣前叶向后运动所致
D.由于心房收缩所致
E.二尖瓣关闭随左心室后壁收缩而一起向前运动所致
参考答案：B
解析：DE段为一急速上升之直线，产生机制为在等长舒张期之后，左心室扩张，压力迅速下降，当左心室压力低于左心房，左心房内血液立即推开二尖瓣向左心室灌注，故使二尖瓣前叶迅速前移，曲线由D点直线上升而达到E峰。
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