The Investigation Of Velocity Vector Imaging To Assess Right Ventricular Function

Background and purposes: Because right heart function had not been considered as important as left heart function in total circulation system, few basic and clinical investigation were performed on right heart function. In addition, owing to its shape and volume dependency, the RV proved difficulty to accurately and reproducibly assess. Yet right ventricular dysfunction was an important independent variable to predict the mortality in patients with heart failure or pulmonary hypertension. So it was longed for to seek the simple and effective methods to evaluate RV.Acute pulmonary embolism (APE), which could cause hemodynamic change of cardiovascular system, was the main cause induced right ventricular pressure overload and an important factor to affect patients symptom,treatment and prognosis. Tranthoracic echocardiography was a noninvasive and accurate technique to detect cardiac anatomy as well as hemodynamic change. Chronic thrombeomlic pulmonary hypertension and other type PH could result in right ventricular pressure overload and gradually cause right heart failture and death. Echocardiography was a useful method to detect pulmonary hypertension and predict the prognosis of chronic PH.Velocity vector imaging (VVI) was a new technique to study myocardial strain and strain rate, and could uninvasively assess regional and global myocardial function. The investigation of VVI had focused mostly on left ventricular (LV) systolic and diastolic performance. Similar applications of VVI to the RV in clinical practice had been relatively limited. The purpose of this study was to demonstrate whether VVI could be applied to assess right ventricular function.The study included three parts. In the first part, we thought to investigate the feasibility of VVI to assess the stain and strain rate of right ventricular during varying myocardial functional state. In the second part, VVI was used to detect the change of RV strain and strain rate after acutely increasing RV pressure overload. Lastly, we tested the application of VVI to the evaluate the regional and global RV systolic function in patients with chronic pulmonary arterial hypertension compare with normal controls, and to demonstrate the improvement of RV function after inhaled iloprost.Part I: Feasibility of Velocity Vector Imaging to assess Right Ventricular Contractile Function.Methods: Velocity vector images of the longitudinal RV were recorded from the apical 4-chamber view in 7 closed-chest anesthetized mongrel dogs during 3 different inotropic states. Peak dp/dt from the RV contraction during the right cardiac catheterization was obtained simultaneously in each inotropic state, and was used as the gold standard of RV contractility. Peak systolic velocities (V) , peak systolic strain rates (SR), peak systolic strains (S) at the basal,middle and apical segments of RV free wall and septal from the longitudinal axis were quantitatively measured by using VVI software system respectively. Results: The peak systolic indices of the longitudinal RV free wall and septal were increased with the infusion of dobutamine and decreased with the infusion of metoprolol except the velocity of right ventricular wall. A significant correlation was found between peak RV dp/dt and RV mean strain and mean strain rate (r=0.79,0.75, P<0.01) . Among all RV segments, the peak systolic S,SR of RV basal free wall had the most significant correlation to peak dp/dt (with the peak systolic S at the basal segment r = 0.83, P < 0.01; SR r = 0.78, P < 0.01) .Conclusions: Strain rate imaging drived from VVI could quantitatively and sensitively detect the longitudinal RV contractile function. Peak systolic S and SR determined at the longitudinal RV basal free wall were the strong noninvasive indices of RV contractility.Part II The investigation of right ventricular function in acute embolic pulmonary hypertension by using velocity vector imaging Methods: 7 dog models of PH were established by ejecting lipiodol through right heart catheter and were divided into three states (baseline, moderate PH and severe PH) according various phase and pulmonary artery pressure. The hemodynamic indexes were measured respectively by the simultaneous echocardiography, cardiac catheterization. Myocardial velocity,strain rate,and strain were determined at RV and LV from the apical 4-chamber view during different experimental states. Results : 7 dogs had been successfully established models of PH. Comparing with baseline situation, the systolic myocardial velocity, strain and strain rate of RV in group of moderate PH raised. Diastolic function of LV was impaired from the judgement of mitral vavle flow spectrum. In group of severe PH, the systolic strain and strain rate of RV and LV decreased. Conclusions: (1) The acute moderate PH could result in the increased systolic strain and strain rate of RV reactively , as well as the decreased diastolic function of LV. (2) The severe acute PH could resulted in impaired systolic function of LV and RV by analysising strain rate imaging. Peak systolic S and SR determined at the longitudinal RV basal free wall, which exceeded -15% and -1.3 S^-1 respectively, were useful parameters to judge acute right heart failure.Part II Assessment of right ventricular function in patients with chronic pulmonarty artery hypertension by using velocity vector imagingMethods: Thirty-six patients with pulmonary atery hypertension and thirty aged-matched control were studied. Right ventricular structure and function parameters were measured and calculated. Echocardiographic imaging in apical 4-chamber views were analysised by VVI software (Axius Velocity Vector Imaging). Myocardial velocity, strain rate, and strain were determined at the basal, mid, and apical segments of the RV free wall and ventricular septum were recorded. 22 patients with PH underwent right-sided cardiac catheterization. In addition, 23 patients of PH and 12 controls underwent 6-minute walking distance tests. Right ventricular function in 7 patient of PH were observed after treatment of inhaled iloprost. Results: Patients with varying degrees of pulmonary hypertension had worse RV performance parameters than those of the controls. Peak systolic myocardial velocities, strain rate, and strain were significantly impaired in patients with PH compared with controls and were most altered in patients with the most severe PH ( P<0.05 for all). Peak systolic strain and strain rate of RV basic free wall were improved in patients of PH after inhaled iloprost ( S -9.7%vs -13.5%.; SR -0.84vs -1.07 , P<0.05 ). Systolic strain and strain rate negatively correlated with EF of RV and 6 minitue walk distance, positively correlated with pulmonary artery systolic pressure and total pulmonary resistance. Conclusions: The new Velocity Vector Imaging method provides simultaneous quantitation of global and regional RV function in patients with PH. Right ventricular function, which was represented by peak systolic strain and strain rate of RV basic free wall, was improved after Inhaled iloprost.