Abstract
The echocardiographic assessment of diseases affecting the right ventricle has until recently lagged behind that of the left ventricle, despite knowledge demonstrating that diseases affecting the right heart have been shown to have the same clinical consequences as those affecting the left heart. This chapter will provide an up-to-date review of current echocardiographic methods for assessing right ventricular anatomy and function using m-mode, two-dimensional, three-dimensional, and Doppler echocardiographic techniques.
Keywords
anatomy, echocardiography, function, quantification, right ventricle
Introduction
The assessment of right ventricular (RV) structure and function is one of the most critical roles of echocardiography, often impacting the diagnosis, management, and prognosis of patients with suspected cardiovascular disease. Historically, the echocardiographic assessment of diseases affecting the RV has lagged behind that of the left ventricle, despite knowledge demonstrating that diseases affecting the right heart have been shown to have the same clinical consequences of those affecting the left heart. More recently, the assessment of RV structure and function has been an active area of investigation. The geometry of the RV is very complex, even in normal subjects, and even more complex in diseased states, which makes it especially difficult to assess with two-dimensional (2D) echocardiographic techniques. The RV myocardium is thin-walled and has a circumferential arrangement of myofibers in the subepicardium and longitudinal fibers in the endocardium ( Fig. 16.1 ). It assumes a flattened pear-shaped appearance folded over the left ventricle and consists of three components: (1) an inlet portion consisting of the tricuspid valve, chordae tendineae, and papillary muscles; (2) a trabecular apical myocardium; and (3) an infundibulum or conus, which encompasses the smooth walled RV outflow tract beneath the pulmonic valve ( Fig. 16.2 ). The need for careful and comprehensive echocardiographic evaluation of RV systolic function occurs in multiple clinical settings, including suspected RV cardiomyopathy, inferior wall myocardial infarction, atrial and ventricular septal defects, complex congenital heart disease, as well as valvular heart disease. Systolic dysfunction of the RV is also frequently observed in acute pulmonary embolism, pulmonary hypertension, and arrhythmogenic right ventricular dysplasia (ARVD), as well as in intraoperative settings. Despite the obvious need for accurate quantitative information, the assessment of RV systolic function is frequently more difficult to obtain due to the irregular crescent shape of this chamber, making quantitative assessment based on geometric remodeling especially challenging, although newer technologies have attempted to overcome these challenges.
Clinical Assessment of Right Ventricular Anatomy and Function
Today, in the majority of clinical settings, the assessment of RV anatomy and systolic function by echocardiography is still most often performed qualitatively with 2D techniques and relies on the scanning ability of the sonographer and trained interpretive eye of the echocardiographer. There is, however, increasing demand for more quantitative assessments of RV structure and function, and newer technologies, including RV strain and three-dimensional (3D) imaging of the right ventricle, have made the quantitative assessment of RV structure and systolic function more efficient, easy to obtain, and reproducible.
The ability to accurately assess global and regional RV systolic function with echocardiography requires continuous practice and attention to detail, with frequent correlation of coronary anatomy, other imaging tests, and pathologic findings. Knowledge of coronary flow to the RV and the use of multiple echocardiographic views to ensure that the entire RV is visualized are essential.
It is especially important to recognize that RV systolic dysfunction may be regional in the setting of coronary artery disease as well as other clinical scenarios, such as pulmonary embolism. Standard transthoracic apical views tend to optimize visualization of the left ventricle, and the transducer may need to be moved more laterally to optimize visualization of the RV. Since the RV myocardium is thin, measurement of wall thickening is usually not practical, and endocardial excursion alone must be evaluated. The interventricular septum is also frequently flattened in the setting of RV systolic dysfunction, and this creates challenges to the accurate assessment of systolic function. Despite these challenges, a complete evaluation of the RV should be a routine part of every comprehensive echo study, and with practice, overall accuracy will improve.
Coronary Flow to the Right Ventricle
The echocardiographer must think about RV anatomy in the context of coronary flow to the RV. Coronary flow to the RV is unique in that it occurs in both systole and diastole. The right coronary artery (RCA) provides predominant flow, supplying the lateral wall through acute marginal branches, and it also supplies the posterior wall and posterior interventricular septum through the posterior descending artery. The anterior wall of the RV is supplied by the conus artery branch of the RCA and by branches of the left anterior descending artery ( Fig. 16.3 ).
Right Ventricular Structure as Assessed by Two-Dimensional Echocardiography
The initial evaluation of global systolic performance of the RV includes measurement of the linear dimensions of the RV cavity ( Fig. 16.4 ). A quick qualitative assessment of RV size is readily accomplished from the apical four-chamber view. In this view, the mid-cavity diameter of the RV should be smaller than the left ventricle. Quantitative measurements of the RV must be assessed from multiple views according to established protocols, as outlined in the recently published American Society of Echocardiography guidelines for chamber quantification, which include the assessment of RV size and systolic function, with new reference limits for RV chamber size, taking into account both gender and body surface area.
RV anatomy must be thought of in segmental terms, just like the left ventricle. The segments of the RV are subdivided into an anterior wall, inferior wall, lateral wall, and RV outflow tract ( Fig. 16.5 ). A segmental approach to the evaluation of RV systolic function begins with each of the standard 2D transthoracic views. In the parasternal long-axis view, the RV outflow tract is visualized. In the parasternal short-axis view, the anterior free wall, lateral free wall, and inferior free wall of the RV are visualized. In the RV inflow view, the anterior free wall and inferior free wall of the RV are visualized. In the standard apical four-chamber view, the lateral free wall and RV apex are visualized. In the subcostal four-chamber view, the inferior free wall of the RV or diaphragmatic surface of the RV is visualized ( 
). It should be emphasized that the standard apical four-chamber view optimizes the visualization of the left ventricle. To optimize the visualization of the RV, the transducer needs to be moved more laterally. This avoids dropout of the lateral free wall of the RV and RV apex ( Figs. 16.6 and 16.7 ; ).
The extent of RV regional wall motion abnormalities has been shown to correlate with the site of coronary occlusion ( 
). Gemayel et al. studied 25 patients with clinical evidence of RV infarction, who underwent echocardiography and coronary angiography, and reported that RV infarction may be missed by echocardiography in approximately 20% of patients, when the RCA occlusion is distal, if the subcostal four-chamber view of the right ventricle is not adequately obtained, and, as a result, the inferior free wall of the right ventricle, supplied by the posterior descending branch, is not visualized. In such patients, in the apical four-chamber view, the lateral free wall of the right ventricle contracts normally, while the inferior free wall of the right ventricle, best seen in the subcostal view, will be akinetic ( Fig. 16.8 ; 
).
Contrast Echocardiography for Right Ventricular Opacification
Echocardiographic contrast agents capable of opacifying the left ventricle and improving endocardial border definition following intravenous injection are valuable but are historically underutilized tools in echocardiography. Recent data suggests the use of contrast echo in climbing again, and in 2015, contrast echo comprised 4.5% of the number of echo studies. Despite the improvement in ability to improve the accuracy and reproducibility of echocardiographic structure and function, they are even less likely to be utilized to facilitate RV endocardial border definition.
Intravenous saline contrast is a less expensive tool that can also be used to facilitate visualization of the RV, although its effects last only seconds, whereas the echo contrast agents last several minutes. Imaging the RV with echo contrast agents requires slower injection of the contrast media to avoid attenuation artifact and requires optimizing transducer position for visualizing the RV ( Fig. 16.9 ; 
). Otherwise, these agents are administered using the same ultrasound machine contrast presets as for the left ventricle. The recently US Food and Drug Administration (FDA)-approved contrast agent, Lumason (sulfur hexaflouride lipid A microspheres), appears to have advantages over other available contrast agents for assessing the RV due to substantially less attenuation artifact.
