Study Of Hemodynamics Of Left Ventricle By Using Vector Flow Mapping

Background At present, echocardiographic evaluation of cardiac function is focused on the study of wall motion changes. The study on intricate intracardiac hemodynamics is limited because of a lack of an ideal tool. Just like the motion of ventricular wall, intracardiac hemodynamics also affect the cardiac function and therefore a good understanding of cardiac hemodynamics can give us a better comprehension of cardiac function. However, fundamental hemodynamic changes and features of intracavitary flow during the isovolumic contraction (IVC) period remain unknown in the clinical setting. Vector flow mapping (VFM) is a novel approach to estimate flow velocity distribution in a ventricular chamber. The purpose of this study was: 1) to investigate the hemodynamics of left ventricle (LV) in normal subjects; and 2) to characterize LV intracavitary flow during the IVC period in normal subjects and patients with heart failure by using VFM.Methods and resultsPART I Hemodynamics of Normal Left Ventricle Analyzed by Vector Flow Mapping Objective The purpose of this study was to investigate the hemodynamics of LV chamber in normal subjects by using VFM.Methods Color Doppler flow images were recorded from apical long-axis view in fifty healthy volunteers. The flow velocity vector in LV chamber during different phase of cardiac cycle was analyzed by VFM.Results During the IVC, the LV was full of a large global vortex. During the early ejection, the flow under the aortic valve was accelerated and ejected into the aorta. There were some brief local vortexes observed in the LV inflow at the early ejection and these vortexes disappeared during the mid and late ejection. At the time point of aortic valve closure, the intraventricular flow redirected rapidly from the base to the apex and persisted to the end of isovolumic relaxation. During the slow LV filling and left atrial contraction, a large global vortex occurred in the LV chamber again.PART II Left Ventricular Intracavitary Vortex during the Isovolumic Contraction Detected by Vector Flow MappingObjectives The purpose of this study was to characterize LV intracavitary flow during the IVC period in humans by using VFM.Methods Color flow Doppler imaging was performed from the apical long-axis view in 74 patients with heart failure and 68 normal subjects. Doppler flow data during the IVC period were analyzed offline with VFM.Results A single large vortex was formed from the LV inflow toward the outflow at the end of diastole. The vortex further continued into the IVC period. Both the relative area and relative flow rate of the vortex were significantly smaller in patients with heart failure than in normal subjects. In normal subjects, the size of the vortex remained sustained and the flow rate of the vortex decreased significantly during the IVC period. However, both of them decreased more severely during the IVC period in patients with heart failure.Conclusions1. The distribution of flow velocity vector in the LV chamber can be detected by using VFM during different phase of cardiac cycle. VFM would be a useful method for the investigation of hemodynamics in diseased heart.2. Isovolumic contraction phase is not the period of hemodynamic stasis but, rather, phase with dynamic changes in intracavitary flow. The vortex during the IVC makes a dynamic contribution to flow redirection and provides efficiency for momentum transfer.3. The vortex across the LV inflow-outflow region during the IVC period facilitates blood ejection during early systole. The persistence of the vortex during the IVC should be associated with cardiac function.