Discussion
The current study described our initial experience of RT3D-TTE application (feasibility, data analysis, difficulties and limitations) in 320 patients with different cardiac abnormalities. In addition, our aim extended to standardize the technique in order to facilitate routine use of RT3D-TTE for cardiac assessment. Our initial experience demonstrated that with good image quality (75% of patients), RT3D-TTE is feasible and could provide comprehensive assessment of all cardiac structures that helps in understanding the mechanism of most cardiac abnormalities in adults. The main study findings include:
RT3D-TTE volume quantification of LV is feasible and accurate due to elimination of the geometric assumption
RT3D-TTE could define the surface anatomy of cardiac valves and their relation with surrounding structures. It can be used independently for estimation of stenosis severity and understanding the mechanism of regurgitation.
RT3D-TTE evaluation of prosthetic valves and rings allows a detailed assessment of prosthesis function which is crucial in decision making.
RT3D-TTE enface views provides a comprehensive visualization of ASD with better assessment of shape, size, area, rims and number of defects.
RT3D-TTE assessment of intracardiac thrombi and masses is feasible and could provide more valuable information than that obtained with 2D-TTE.
Quantification of LV Volume and Function
Multiple studies demonstrated the RT3DE accuracy for the assessment of LV volume and ejection fraction with very good correlation and close agreement with computed tomography and magnetic resonance imaging (MRI). In our study, RT3D-TTE assessment of LV functions was feasible in 86% of cases, while in 14% volume quantification could not be obtained due to inadequate visualization of endocardium. This is in agreement with Tighe et al who described the reliability of RT3D-TTE assessment of LV volume and function in 60% of patients who have good and fair image quality.
RT3D-TTE allowed fast and easier analysis of regional volume throughout the cardiac cycle. This was helpful in calculating the time required to attain minimum regional volume and thus detection of mechanical asynchrony. Many studies described the accuracy, reproducibility and feasibility of RT3DE in defining systolic asynchrony in patients with and without electrical asynchrony. In our study, RT3D-TTE was helpful in guiding the placement of the pacing wire and to judge the immediate response to CRT.
Assessment of right ventricular (RV) size, volume and function has been extremely challenging in clinical cardiology due to its complex geometrical crescent shape. RT3D-TTE for RV volumes quantification was shown to be accurate and reproducible as compared to MRI. In our study, we used disc summation method for calculation of RV volume and ejection fraction which was shown to be accurate and comparable to MRI findings. Complete analysis of RV volumes and function was obtained in 55% of our patients. RT3D-TTE measurements were well correlated but significantly underestimated as compared to CMR. In patients with markedly dilated RV, the analysis was incomplete due to inability to include all RV borders within the 3D box. There are only few data studying the accuracy of RT3D-TTE in significantly dilated or dysfunctional RV.
Evaluation of Valvular Heart Disease
Mitral Valve Several studies demonstrated the feasibility of RT3D-TTE in evaluation of mitral valve morphology independently from the window of image acquisition. It provides a unique orientation of leaflets, commissures and valve area in a considerable percentage of the population. Our study demonstrated that RT3D-TTE could provide better morphologic description of the MV and measurement of MVA in 20 patients with rheumatic mitral stenosis. It was useful for assessment of outcome post- balloon commissurotomy through clear visualization and proper assessment of commissural splitting.
In agreement with Agricola et al, our study showed that the RT3D-TTE assessment of MV apparatus and MV annulus was helpful in identifying the mechanism of mitral regurgitation. The shape and size of regurgitant jets were completely assessed only when the jet was central but eccentric and/or large jets were not depicted due to narrow color sector. In accordance with the previous studies, the anatomic localization of the prolapsed MV scallop (s) was obtained from the enface RT3D view.
Aortic Valve Imaging of AV from either the transthoracic or transesophageal approach is challenging, probably because of the oblique angle of incidence of the ultrasound beam combined with the thinner leaflets. RT3D-TTE quantification of aortic area by planimetery showed good agreement with the standard 2D-TEE, flow-derived methods, and cardiac catheterization data with the advantage of improved reproducibility. In our study, adequate visualization of AV was achieved in 88% by RT3D-TTE vs. 62% by 2D-TTE. Planimetered AV area by RT3D-TTE could be obtained in 67% and 80% of patients with rheumatic and congenital AS respectively while it was less obtained by 2D-TTE (44% and 46% respectively). Measurement of AV area with both RT3D-TTE and 2D-TTE continuity equation were well correlated in all cases (r = 0.89; p < 0.0001). RT3D-TTE and 2D-TTE measurements of AV annulus and LV outflow tract were well correlated (r = 0.85; p < 0.001 for both). However, the RT3D-TTE measurements were significantly larger than that obtained by 2D-TTE (p < 0.01).
Tricuspid Valve Assessment of TV by 2D-TTE is challenging due to the complex geometry of TV. RT3D-TTE overcomes the 2D-TTE limitations and provides a comprehensive morphological and functional assessment in various TV diseases. The utility of RT3D-TTE in the assessment of tricuspid regurgitation was described in various studies. In our study, RT3D-TTE analysis of TV annulus (size and function), and leaflets was helpful in understanding the mechanism of tricuspid regurgitation and providing the basis for surgical intervention. In agreement with the previous studies, RT3D-TTE allowed a detailed assessment of TV leaflets (thickness, mobility, and calcification) as well as measurement of TV area in our patients with TV stenosis.
Pulmonary Valve Echocardiographic evaluation of PV anatomy is more difficult than other valves due to poor acoustic access even by 2D-TEE. RT3D-TTE could describe the morphological features of the 3 cusps simultaneously through the en face view only in 60% of patients. This percentage increases in patients with pulmonary stenosis due to increased cusp thickness. In our study, only 5 patients with PV stenosis were examined by RT3D-TTE. It was possible to assess the cusp thickness, commissures and mobility in addition to measurement of PV annulus (area and diameter) and PV area.
Prosthetic Devices (Valves and Rings) Anatomical identification and hemodynamic assessment of valve prosthesis and rings is mainly dependant on 2DE (TTE and TEE). However the sensitivity of both 2D-TTE and 2D-TEE techniques for evaluation of prosthetic valves is lower than with native valves. The initial experience with the use of RT3D-TTE was encouraging but no large studies available. Our study showed that RT3D-TEE could identify the type of prosthesis (rings, bioprosthesis and metallic prosthesis) and assess its function. In mitral regurgitation post MV surgery, RT3D-TTE allowed clear definition of the origin of the regurgitant jet and description of the underlying mechanisms. RT3D-TTE could help in the diagnosis of prosthetic valve infective endocarditis through clear visualization of vegetation, root abscess and valve dehiscence.
Assessment of Adult Congenital Heart Diseases
The literature confirms the clinical utility of RT3D-TTE in evaluation of ASD, VSD, patent foramen ovale and atrioventrcular septal defects comparable and well correlated with the surgical and catheterization findings. In our study, the RT3D-TTE enface projection could accurately determine the site, size, number and shape of defects in addition to quantitative recording of septal defect dynamics. This valuable information facilitated the proper decision making either for surgical or catheter based management.
Assessment of Intracardiac Thrombi
RT3D-TTE was assumed to be the technique of choice for the assessment of intracardiac masses through the unlimited number of cutting planes in all directions from single full volume 3D data set. In our study, RT3D-TTE allowed a comprehensive description of the different shapes of the thrombi, their attachment to the cardiac wall and their mobility. Multiple 3D cut sections helped in identification of thrombus consistency, presence of degeneration and calcification in organized thrombi.
Clear visualization of LAA thrombus was achieved in (78%) of our patients by RT3D-TTE vs. (33%) by 2D-TTE. In accordance with Karakus et al, RT3D-TTE findings of LA and LAA thrombi showed good agreement with 2D-TEE. The accurate assessment of thrombus size is difficult by 2D-TTE due to wide variation of thrombus shape. In our patients, RT3D-TTE volume calculation of intracardiac thrombi was obtained regardless of their shape and orientation. In agreement with previous studies, Our results described the additional value of RT3D-TTE in the assessment of cardiac masses.
Study Limitation
The study described our initial experience with the RT3D-TTE application. However there are some limitations:
RV analysis was obtained using the software designed for LV mainly. The new 3D software dedicated for RV analysis was not available in our echo-lab.
The 3D quantification of RV and LV volume and function was compared with cardiac MRI in a small number of patients (25) aiming to verify our 3D measurements by the Q lab software. However, the validation of RT3DE was intensively validated in previous studies and this is beyond the target of current study.