HONG Geu-Ru

Geu-Ru HONG

Yonsei University College of Medicine, Severance Cardiovascular Hospital, Korea

キーワード :

A vortex can be described as a fluid structure that possesses circular or swirling motion. Therefore, vorticity （the curl of the velocity field） represents the skeleton of the flow field and the principal quantity to define the flow structure. Intraventricular blood flow is optimized to facilitate efficient systolic ejection of blood. Vortices that form during left ventricular （LV） filling have specific geometry and anatomical location which are critical determinants of directed blood flow during ejection. Therefore, it is clinically important to assess the vortex flow patterns for the better understanding of LV systolic and diastolic function. Vorticity imaging by contrast echocardiography（CE） using vector profiles is a novel approach to study the LV vortex. We hypothesize that changes in LV vortex flow pattern may closely correlate with LV function and that assessment of LV function using LV vortex flow analysis affords more accurate prediction of the patient’s hemodynamic status. The aims of this study were 1） to quantify LV vortex flow by CE in normals and patients with LV dysfunction, and 2） to evaluate the impact of quantitative vortex flow parameters on the hemodynamic performance of the LV
Analysis of vortex flow using contrast echocardiographypatterns
2-D CE was performed with Definity （Bristol Myers, Billerica, MA） as the echo-enhancing agent. Definity was given as a continuous infusion. Imaging of the contrast agent was performed with a mechanical index （MI） of 0.4-0.6 and the focal zone is positioned in the middle of the left ventricle. The width of the ultrasound scan, imaging depth, as well as system spatial temporal settings was optimized to achieve the highest possible frame rate. All cine data from three consecutive cycles were acquired with the acoustic capture technique. Apical 4 chamber and apical long axis views were acquired as these have proven to provide the best visualization of the left ventricular vortex formation. All studies were stored on digital media for off-line analysis.
Analysis was performed with particle image velocitimetry （PIV） prototype software by Siemens Ultrasound. This software provides a Feature Tracking Algorithm （FTA） to handle the long range correlations due to large velocity values. Image processing was performed on Dicom clips （low jpeg compression）. Three consecutive beats were averaged to improve the blood flow tracking and quality of results. The angle independent ventricular velocity field was computed. Velocity vectors were evaluated on a regular grid with a spacing of 8 pixels （approximately. 2.8 mm）. From this, the vorticity = ∂vx/∂y-∂vy/∂x, the curl of velocity, was computed.
Quantitative vortex flow parameters related to cardiac function
Recent advances in fluid dynamics and PIV provide the technical means to track and quantify the kinematic and velocity field within the left ventricle with the help of low doses of contrast agents. These techniques provide advantages over conventional Doppler technique as they are angle-independent and provide two-dimensional flow information. However, there have been no previous studies to establish quantitative vortex flow parameters responsible for LV function. In this study, we could examine several parameters related to LV vorticity. We demonstrated that average vorticity parameters such as VD, VL, VW, SI were significantly reduced in patients with LV dysfunction. And we also demonstrated that pulsatility index RS was significantly reduced in patients with LV dysfunction.
Conclusions
In conclusion, it is feasible to quantify vortex flow in human heart by CE using PIV, and 2） these measures may determine the cardiac function more precisely and may offer new technology which can detect early changes of cardiac hemodynamics in various clinical settings.