A Foundational Study: Quantification Of Ventricular And Myocardial Function In Acute Right Ventricular Myocardial Ischemia Using Real-Time Three-Dimensional Echocardiography And Strain Rate Imaging

ObjectiveIn autopsy studies in which a myocardial infarction was detected, isolated RVI was detected in less than 3% of the specimens examined. But right ventricular (RV) ischemia occurs in 50% of patients with acute inferior myocardial infarction and may result in a well-described clinical picture of severe hemodynamic compromise associated with a high morbidity and mortality. RV ischemia leads to acute RV dilatation and impaired RV systolic function, both of which act to reduce the preload available to the left ventricle (LV). This impairs LV systolic pressure generation, which in turn diminishes the interventricular septal contribution to RV contraction, and thus, a downward spiral of circulatory collapse is initiated .So, early recognition of RVI and accurate estimate the total cardiac function is critical for reducing mortality and complications associated with this cardiac injury.The heart is a complex geometric structure. Measuring right ventricular (RV) volume with 2-dimensional (2D) echocardiography has been difficult because of asymmetry and the ventricle's complex shape. Methods for real-time three-dimensional echocardiography (RT-3DE) have been proposed by several investigators .An important advantage of RT-3DE is the potential for improved visualization of cardiac anatomy. Dynamic RT-3DE system refers to the ability to show the heart in 3 dimensions as it beats. It is believed that RT-3DE might produce more accurate and repeatable estimations of cardiac structure size and function than conventional 2D imaging does. Most prior efforts have focused on quantitation of left ventricular size and function but for right ventricular.Strain and strain rate imaging (SRI) are measures of deformation that are basic descriptors of both the nature and the function of cardiac tissue. Echocardiographic strain and SR imaging has been applied to the assessment of resting ventricular function, the assessment of myocardial viability, and stress testing for ischemia. Resting function assessment has been applied in both the left and the right ventricles, and may prove particularly valuable for identifying myocardial diseases and following up the treatment response. The clinical availability of strain and SR measurement may offer a solution to the ongoing need for quantification of regional and global cardiac function.The first purpose of this study was to evaluate the accuracy of RV volume measurement in vitro and to test the feasibility of RV volume measurement using real-time 3D echo and to quantify noninvasively biventricular function in acute right ventricular and evaluate the extent of impairing left ventricular function. Another purpose is to quantify noninvasively regional and global myocardial function using SRI.MethodsPart one :Eleven canine models of right ventricular myocardial infarction were made by blocking right coronary artery (RCA) and part of left coronary artery. The excised right ventriculars were filled with 0.9% normal saline .The volume of normal saline was determined according to the right ventricular diastole end pressure (RVDEP) that was recorded before death, at the same time, putting 1 or 2 mass(es) in the right ventricular every time . RVV was quantified by RT-3DE Full volume and X-plane respectively online using Philips 3DQ Advanced software . Full volume images were cropped in order to get the maximum diameter and area of mass. These data of RT-3DE were compared with two dimensional echocardiography (2DE) and true volume .At the completion of the experiment ,the heart was cut into slices of 3-5 mm thickness. The slices were immersed in a solution of 2 % triphenyltetrazolium chloride (TTC) at 37℃for 30 min in order to identify infarction myocardium. Part two:Nine canines were used in this study. RCA ischemia was induced by occlusion in the proximal segment just distal to the conus and right atrial branches. Before RCA ischemia ,the canine was definited as normal control group (NC) and after RCA ischemia definited as experiment group (IRCA) . Right ventricular end diastole pressure (RVEDP), right ventricular end systole pressure(RVESP), mean arterial blood pressure (MABP), left ventricular end diastole pressure (LVEDP), left ventricular end systole pressure (LVESP) were obtained from each ventricle at baseline and after 10 minutes of RCA occlusion.RT-3DE and SRI protocol : Before ischemia and during ischemia 10 min , the right ventricular end diastole volume(RVEDV) ,left ventricular end diastole volume(LVEDV), right ventricular end systole volume (RVESV),left ventricular end systole volume(LVESV ) were measured using RT-3DE with 3DQ Advanced standard commercial software (Philips iE-33) in the apical four-chamber view (that optimally captured the entire biventricular during quiet breathing) .At the time, stroke volume (SV) , ejection fraction (EF) and regional ejection fraction (rEF) were calculated . Simultaneous SRI parameters of systole peak velocity (V_{peak sys}),systole peak strain(S_{peak sys}) , systole peak strain rate (SR _{peak sys}) and diastole peak strain rate (SR _{peak dia}) at right free wall (RFW ), left lateral wall (LLW) and post interventricular septum (PIVS)'s base segment (Bas), middle segment(Mid) were measured .ResultsPart one :RVV measured by Full volume and X-plane showed strong correlation (r = 0.90; r =0.83 , P <0.05) with the true volume and there were no significant difference between them. The method of X-plane spent shorter time than that of Full volume on measuring RVV. There were significant difference between RVV measured by RT-3DE and 2DE (P <0.05) . RVV measured by 2DE weakly correlated with true volume but underestimated volume by 22.9%. Maximum mass diameter and area measured by RT-3DE and 2DE had excellent correlation with true data . But the data measured by 2DE were underestimated respectively by 31.1% and 36.4% compared with real one.Part two:Blocking RCA did not effect post interventricular septum tissue. In IRCA group : RVEDP increased , RVESP and LVESP decreased significantly (p<0.05) compared with NC group; RVEDV and RVESV increased obviously (p<0.05) ,but LVEDV diminish obviously compared with NC group (p<0.05). RVSV , RVEF and LVSV also decreased significantly in IRCA group. Either NC group or IRCA group EDV and EDP had excellent correlation . Every SRI parameters of RFW and PIVS in IRCA group all decreased significantly compared with NC group (p<0.05) .As for LLW in IRCA group, the S_{peak sys}, SR _{Peak sys}, SR _{peak dia} decreased significantly (p<0.05) but the V_{systole peak} had no significant difference with that of NC group.ConclusionRT-3DE can exactly measure right ventricular volume and intracardiac mass size of the canine heart model with right ventricular myocardial infarction .The method of X-plane is more convenient and faster than that of Full volume on measuring RVV.Acute right Ventricular myocardial ischemia impairs left Ventricular function.RT-3DE can quantify noninvasively ventricular interaction, reflect haemodynamics variance, quantify ventricular function and region contractile function in acute right ventricular myocardial ischemia. SRI technology can assess quantitatively regional and global myocardial function sensitively.