Botnar R, Nagel E, Scheidegger M B, Pedersen E M, Hess O, Boesiger P
Institute of Biomedical Engineering, University of Zurich and Swiss Federal Institute of Technology.
MAGMA. 2000 Feb;10(1):18-26. doi: 10.1007/BF02613108.
Magnetic resonance (MRI) velocity mapping was used to evaluate non-invasively the flow profiles of the ascending aorta in normal volunteers and in patients with an aortic (mechanical) valve prosthesis.
In patients with artificial aortic valves the flow profile in the ascending aorta is severely altered. These changes have been associated with an increased risk of thrombus formation and mechanical hemolysis.
Velocity profiles were determined 30 mm distal to the aortic valve in six healthy volunteers and seven patients with aortic valve replacement (replacement within the last 2 years) using ECG triggered phase contrast MRI. Peak flow, mean flow and mean reverse flow were measured in intervals of 25 ms during the entire heart cycle. Systolic reverse flow, end-systolic closing and diastolic leakage volume were calculated for all subjects.
Peak flow velocity during mid-systole was significantly higher in patients with valvular prosthesis than in normals (mean + SD, 1.9 +/- 0.4 m/s vs. 1.2 +/- 0.03 m/s, P < 0.001) with a double peak and a zone of reversed flow close to the inner (left lateral) wall of the ascending aorta of the patients. Closing volume was significantly larger in patients than in controls (-3.3 +/- 1.2 ml/beat vs. -0.9 +/- 0.5 ml/beat; P < 0.001). There was reverse flow during systole in valvular patients amounting to 15.7 +/- 6.7% of total cardiac output compared to 2.3 +/- 1.2% in controls (P < 0.001). Diastolic mean flow was negative in patients after valve replacement but not in controls (-11.0 +/- 15.2 ml/beat vs. 6.8 +/- 3.2 ml/beat; P < 0.01).
The following three major quantitative observations have been made in the present study: (1) Mechanical valve prostheses have an increased peak flow velocity with a systolic reverse flow at the inner (left lateral) wall of the ascending aorta. (2) A double peak flow velocity pattern can be observed in patients with bileaflet (mechanical) prosthesis. (3) The blood volume required for leaflet closure and the diastolic leakage blood volume are significantly higher for the examined bileaflet valve than for native heart valves.
采用磁共振（MRI）速度成像技术对正常志愿者及主动脉（机械）瓣置换术后患者升主动脉血流情况进行无创评估。
人工主动脉瓣置换术后患者升主动脉血流情况发生显著改变，这些改变与血栓形成风险增加及机械性溶血有关。
对6名健康志愿者和7名主动脉瓣置换患者（置换时间均在过去2年内）采用心电图触发相位对比MRI技术，在主动脉瓣远端30mm处测定血流速度。在整个心动周期中，以25ms为间隔测量峰值流速、平均流速和平均反流速度。计算所有受试者的收缩期反流、收缩末期关闭容积和舒张期漏血容积。
人工瓣膜置换术后患者收缩中期峰值流速显著高于正常志愿者（均数±标准差，1.9±0.4m/s对1.2±0.03m/s，P<0.001），且患者升主动脉内侧（左侧）壁附近出现双峰及反流区域。患者关闭容积显著大于对照组（-3.3±1.2ml/搏对-0.9±0.5ml/搏；P<0.001）。瓣膜置换术后患者收缩期存在反流，反流占心输出量的15.7±6.7%，而对照组为2.3±1.2%（P<0.001）。瓣膜置换术后患者舒张期平均流速为负值，而对照组为正值（-11.0±15.2ml/搏对6.8±3.2ml/搏；P<0.01）。
本研究得出以下三项主要定量观察结果：（1）机械瓣膜置换术后升主动脉内侧（左侧）壁峰值流速增加且存在收缩期反流。（2）双叶（机械）瓣膜置换术后患者可观察到双峰流速模式。（3）与天然心脏瓣膜相比，所检测的双叶瓣膜关闭所需血量及舒张期漏血容积显著更高。
