Here, we provide a step-by-step acquisition and analysis protocol for the 3D volumetric assessment of the right ventricle, mainly focusing on the practical aspects that maximize the feasibility of this technique.
Traditionally, it was believed that the right side of the heart has a minor role in circulation; however, more and more data suggest that right ventricular (RV) function has strong diagnostic and prognostic power in various cardiovascular disorders. Due to its complex morphology and function, assessment of the RV by conventional two-dimensional echocardiography is limited: the everyday clinical practice usually relies on simple linear dimensions and functional measures. Three-dimensional (3D) echocardiography overcame these limitations by providing volumetric quantification of the RV free of geometrical assumptions. Here, we offer a step-by-step guide to obtain and analyze 3D echocardiographic data of the RV using the leading commercially available software. We will quantify 3D RV volumes and ejection fraction. Several technical aspects may help to improve the quality of RV acquisition and analysis as well, which we present in a practical manner. We review the current opportunities and the limiting factors of this method and also highlight the potential applications of 3D RV assessment in current clinical practice.
Echocardiography came a long way from its first clinical applications in the 1950s1. The first one-dimensional ultrasound probes were designed to provide simple linear diameters of the chamber walls and lumens; however, they undoubtedly represent a milestone in cardiovascular imaging. The development of two-dimensional (2D) ultrasound imaging was another major step by providing much more precise quantification of morphology and function and is still considered to be the standard method in everyday clinical practice. Nevertheless, 2D echocardiography-based assessment still carries a major limitation of the technique: imaging of a given chamber from a few tomographic planes does not adequately characterize the morphology and function of a three-dimensional (3D) structure. This problem is even more pronounced in the case of the right ventricle (RV): compared to the relatively simple bullet-shaped left ventricle (LV), the RV has a complex geometry2 that cannot be adequately quantified using linear diameters or areas3. Despite these widely known facts, RV morphology and function are usually measured by such simple parameters in the clinical practice.
For many decades, the RV was considered to have a much less important role in circulation compared to its left counterpart. Several landmark papers defeated this standpoint showing the strong prognostic role of RV geometry and function in a wide variety of diseases4,5,6,7. Numerous studies demonstrated the incremental value of RV measurement even by using relatively simple conventional parameters, which highlights the importance and need for more precise quantification of the chamber with potentially meaningful clinical value.
3D echocardiography overcomes several limitations of the 2D assessment of the cardiac chambers. While the measurement of volumes and also functional parameters free of geometrical assumptions may be of high interest in the case of the LV as well, it may gain particular importance in the assessment of the RV8. 3D-derived RV volumes and ejection fraction (EF) are shown to have significant prognostic value in various cardiovascular conditions9,10.
Nowadays, several vendors provide semi-automated solutions for 3D RV assessment with validated results against gold standard cardiac magnetic resonance (MR) measurements11,12. The technical requirements of 3D assessment are essential parts of a state-of-the-art cardiovascular imaging department nowadays, and it is expected that it will soon be part of the general equipment in every echocardiography lab. With proper expertise in 3D acquisition and post-processing, 3D RV analysis can be easily implemented into the standard examination protocol.
The protocol follows the guidelines of the institution's human research ethics committee and the patients of the clinical cases gave their written informed consent to the study.
1. Technical requirements
2. Acquisition
3. 4D RV analysis
3D analysis of the RV is feasible in a wide variety of cardiovascular diseases. Case 1 is a healthy volunteer with normal ventricular volumes and function (Figure 1). Case 2 is a post-mitral valve repair patient who is a typical example for the conflicting results of conventional 2D assessment: while TAPSE is markedly reduced, the patient does not show any signs of RV dysfunction and a maintained RV global systolic function was confirmed by normal 3D RV EF (Figure 2). Both patients had excellent echocardiography window with consequential great tracking quality. Case 3 is a semi-professional athlete with dilated cardiomyopathy (Figure 3). Only moderate image quality was achievable (the outflow tract is poorly visualized); however, 3D RV analysis was successful, showing good agreement with cardiac MR results.
Figure 1: 3D RV analysis of a healthy volunteer. On the left panels, a long axis (upper panel) and a short axis (lower panel) image of the RV can be seen. The green line represents the endocardial border. The central upper image is a 3D model of the RV based on the current analysis. Beyond RV volumes and ejection fraction, the software displays 2D parameters, such as linear (mid, basal and long-axis) diameters, as well as FAC and TAPSE values derived from the predefined apical four-chamber view (right upper panel) and a volume-time curve is also generated (right lower panel). Please click here to view a larger version of this figure.
Figure 2: 3D RV analysis of a post-mitral valve repair patient. While 3D RV volumes and EF are in the normal range, TAPSE is markedly lower. Reduced longitudinal shortening of the RV is a common phenomenon following cardiac surgery however, the majority of these patients do not show signs of RV failure. 3D EF assessment confirms maintained global systolic function despite markedly reduced TAPSE values. Please click here to view a larger version of this figure.
Figure 3: Case of an athlete with dilated cardiomyopathy. 3D RV volumes are increased, while 3D RV EF is mildly reduced. Note the suboptimal image quality with a poorly visualized RV outflow tract. Despite the poor echocardiographic window, RV analysis shows good agreement with cardiac MR-derived measurements considering the known systematic volume underestimation of 3D echocardiographic RV analysis compared to the gold-standard cardiac MR (RVEDV: 168 mL; RVESV: 99 mL; RVEF: 41%). Please click here to view a larger version of this figure.
3D analysis of the RV represents an important step in everyday cardiology practice. In parallel with the growing interest of the morphology and function of the previously neglected cardiac chamber, these novel solutions provide clinically meaningful information about the right side of the heart. While 3D acquisition has several aspects that markedly differ from 2D echocardiographic imaging, by keeping special attention to the critical points and by using a thorough protocol, 3D RV analysis may progress from a scientific tool to an essential step of echocardiographic examination. With optimal image quality and proper expertise, RV volumetric analysis using echocardiography may take only a few minutes from acquisition to results with high feasibility13. The significantly lower costs and shorter procedure time make it an appealing alternative to the gold standard cardiac MR examination in several cases.
Nevertheless, 3D analysis may not be feasible in every scenario. The most important limitation factor is echocardiographic image quality: in patients with a poor 2D echocardiographic window, acceptable 3D image quality is rarely achievable. Still, it is important to mention that various maneuvers (lateral positioning of the probe, foreshortening, proper presets) may improve 3D image quality. Suboptimal visualization of the RV outflow tract is not uncommon, however it is usually well tolerated by the RV analysis solutions providing reliable results. Using 3D loops with stitching, drop-out artifacts are strongly discouraged, therefore, recording of multiple loops and post-acquisition control are highly recommended.
3D examination of the RV opens the possibility of 3D RV deformation analysis and regional assessment of the chamber as well14. It is well known that maintained EF does not preclude significant changes in RV mechanics4. Evaluation of RV deformation reveals distinct changes of RV contraction pattern in a wide variety of populations, such as post-cardiac surgery patients15,16,17, congenital heart disease18, pulmonary arterial hypertension19,20,21, and elite athletes22. Moreover, measurement of segmental morphology and function may be of high interest in diseases where regional remodeling of the RV is expected, such as arrhythmogenic cardiomyopathy23 or congenital heart disease patients24. In conclusion, post-processing of 3D RV data may provide novel parameters of the chamber with incremental diagnostic and prognostic value.
Project no. NVKP_16-1–2016-0017 (’National Heart Program’) has been implemented with the support provided from the National Research, Development and Innovation Fund of Hungary, financed under the NVKP_16 funding scheme. The research was financed by the Thematic Excellence Programme (2020-4.1.1.-TKP2020) of the Ministry for Innovation and Technology in Hungary, within the framework of the Therapeutic Development and Bioimaging thematic programmes of the Semmelweis University.
3V-D/4V-D/4Vc-D | General Electric | n.a. | ultrasound probe |
4D Auto RVQ | General Electric | n.a. | software for analysis |
E9/E95 | General Electric | n.a. | ultrasound machine |
EchoPac v203 | General Electric | n.a. | software for analysis |