Accreditation Statement:
The American Society of Echocardiography is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.
The American Society of Echocardiography designates this educational activity for a maximum of 1.0 AMA PRA Category 1 Credits™ . Physicians should only claim credit commensurate with the extent of their participation in the activity.
ARDMS and CCI recognize ASE’s certificates and have agreed to honor the credit hours toward their registry requirements for sonographers.
The American Society of Echocardiography is committed to ensuring that its educational mission and all sponsored educational programs are not influenced by the special interests of any corporation or individual, and its mandate is to retain only those authors whose financial interests can be effectively resolved to maintain the goals and educational integrity of the activity. While a monetary or professional affiliation with a corporation does not necessarily influence an author’s presentation, the Essential Areas and policies of the ACCME require that any relationships that could possibly conflict with the educational value of the activity be resolved prior to publication and disclosed to the audience. Disclosures of faculty and commercial support relationships, if any, have been indicated.
Target Audience:
This activity is designed for all cardiovascular physicians and cardiac sonographers with a primary interest and knowledge base in the field of echocardiography; in addition, residents, researchers, clinicians, intensivists, and other medical professionals with a specific interest in cardiac ultrasound will find this activity beneficial.
Target Audience:
This activity is designed for all cardiovascular physicians and cardiac sonographers with a primary interest and knowledge base in the field of echocardiography; in addition, residents, researchers, clinicians, intensivists, and other medical professionals with a specific interest in cardiac ultrasound will find this activity beneficial.
Objectives:
Upon completing the reading of this article, the participants will better be able to:
- 1.
Describe the conventional two-dimensional acoustic windows required for optimal evaluation of the right heart.
- 2.
Describe the echocardiographic parameters required in routine and directed echocardiographic studies, and the views to obtain these parameters for assessing right ventricle (RV) size and function.
- 3.
Identify the advantages and disadvantages of each measure or technique as supported by the available literature.
- 4.
Recognize which right-sided measures should be included in the standard echocardiographic report.
- 5.
Explain the clinical and prognostic significance of right ventricular assessment.
Author Disclosure:
The authors of this article reported no actual or potential conflicts of interest in relation to this activity.
The ASE staff and ASE ACCME/CME reviewers who were involved in the planning and development of this activity reported no actual or potential conflicts of interest: Chelsea Flowers; Rebecca T. Hahn, MD, FASE; Cathy Kerr; Priscilla P. Peters, BA, RDCS, FASE; Rhonda Price; and Cheryl Williams.
The following members of the ASE Guidelines and Standards Committee, JASE Editorial staff and ASE Board of Directors reported no actual or potential conflicts of interest in relation to this activity: Deborah A. Agler, RCT, RDCS, FASE; J. Todd Belcik, BS, RDCS, FASE; Renee L. Bess, BS, RDCS, RVT, FASE; Farooq A. Chaudhry, MD, FASE; Robert T. Eberhardt, MD; Benjamin W. Eidem, MD, FASE; Gregory J. Ensing, MD, FASE; Tal Geva, MD, FASE; Kathryn E. Glas, MD, FASE; Sandra Hagen-Ansert, RDCS, RDMS, MS, FASE; Rebecca T. Hahn, MD, FASE; Jeannie Heirs, RDCS; Shunichi Homma, MD; Sanjiv Kaul, MD, FASE; Smadar Kort, MD, FASE; Peg Knoll, RDCS, FASE; Wyman Lai, MD, MPH, FASE; Roberto M. Lang, MD, FASE; Steven Lavine, MD; Steven J. Lester, MD, FASE; Renee Margossian, MD; Victor Mor-Avi, PhD, FASE; Sherif Nagueh, MD, FASE; Alan S. Pearlman, MD, FASE; Patricia A. Pellikka, MD, FASE; Miguel Quiñones, MD, FASE; Brad Roberts, RCS, RDCS; Beverly Smulevitz, BS, RDCS, RVS; Kirk T. Spencer, MD, FASE; J. Geoffrey Stevenson, MD, FASE; Wadea Tarhuni, MD, FASE; James D. Thomas, MD; Neil J. Weissman, MD, FASE; Timothy Woods, MD; and William A. Zoghbi, MD, FASE.
The following members of the ASE Guidelines and Standards Committee, JASE Editorial staff and ASE Board of Directors reported a relationship with one or more commercial interests. According to ACCME policy, the ASE implemented mechanisms to resolve all conflicts of interest prior to the planning and implementation of this activity. Theodore Abraham, MD, FASE receives honoraria and research grant support from GE Healthcare. Patrick D. Coon, RDCS, FASE is on the speaker’s bureau for Philips. Victor G. Davila-Roman, MD, FASE is a consultant for St. Jude Medical, AGA Medical, Medtronic, Boston Scientific Corporation, and Sadra Medical. Elyse Foster, MD receives grant support from Abbott Vascular Structural Heart, EBR Systems, Inc., and Boston Scientific Corporation. Julius M. Gardin, MD, FASE is a consultant/advisor to Arena Pharmaceuticals. Jeffrey C. Hill, BS, RDCS, FASE receives grant/research support from Toshiba America Medical Systems and Philips; is a consultant to Medtronic; and is on the speaker’s bureau for Philips. Martin G. Keane, MD, FASE is a consultant/advisor to Pfizer, Inc. and Otsuka Pharmaceuticals. Gilead I. Lancaster, MD, FASE owns stock in, and is a consultant/advisor to, Cardiogal. Jonathan R. Linder, MD, FASE is a consultant/advisor to VisualSonics. Carol C. Mitchell, PhD, RDMS, RDCS, RVT, RT(R), FASE is a speaker and consultant for GE Healthcare. Marti McCulloch, MBA, BS, RDCS, FASE is a speaker for Lantheus and advisor/consultant for Siemens. Tasneem Z. Naqvi, MD, FASE is a consultant/advisor to Edwards Lifesciences and St. Jude Medical, and receives grant support from Medtronic and Actor Medical. Kofo O. Ogunyankin, MD, FASE is on the speaker’s bureau for Lantheus. Vera Rigolin, MD, FASE is on the speaker’s bureau for Edwards Lifesciences and St. Jude Medical and owns stock in Abbott Labs; Hospira; Johnson and Johnson; and Medtronic. Lawrence G. Rudski, MD receives grant support from Genzyme. Stephen G. Sawada, MD owns stock in GE Healthcare. Alan D. Waggoner, MHS, RDCS is a consultant/advisor for Boston Scientific Corporation and St. Jude Medical, Inc.
Estimated Time to Complete This Activity: 1.0 hour
Table of Contents
Executive Summary 686
Overview 688
Methodology in the Establishment of Reference Value and Ranges 688
Acoustic Windows and Echocardiographic Views of the Right Heart 690
Nomenclature of Right Heart Segments and Coronary Supply 690
Conventional Two-Dimensional Assessment of the Right Heart 690
- A.
Right Atrium 690
RA Pressure 691
- B.
Right Ventricle 692
RV Wall Thickness 692
RV Linear Dimensions 693
- C.
RVOT 694
- A.
Fractional Area Change and Volumetric Assessment of the Right Ventricle 696
- A.
RV Area and FAC 696
- B.
Two-Dimensional Volume and EF Estimation 696
- C.
Three-Dimensional Volume Estimation 697
- A.
The Right Ventricle and Interventricular Septal Morphology 697
- A.
Differential Timing of Geometric Distortion in RV Pressure and Volume Overload States 698
- A.
Hemodynamic Assessment of the Right Ventricle and Pulmonary Circulation 698
- A.
Systolic Pulmonary Artery Pressure 698
- B.
PA Diastolic Pressure 699
- C.
Mean PA Pressure 699
- D.
Pulmonary Vascular Resistance 699
- E.
Measurement of PA Pressure During Exercise 699
- A.
Nonvolumetric Assessment of Right Ventricular Function 700
- A.
Global Assessment of RV Systolic Function 700
RV dP/dt 700
RIMP 700
- B.
Regional Assessment of RV Systolic Function 701
TAPSE or Tricuspid Annular Motion (TAM) 701
Doppler Tissue Imaging 702
Myocardial Acceleration During Isovolumic Contraction 703
Regional RV Strain and Strain Rate 704
Two-Dimensional Strain 705
- A.
Summary of Recommendations for the Assessment of Right Ventricular Systolic Function 705
Right Ventricular Diastolic Function 705
- A.
RV Diastolic Dysfunction 705
- B.
Measurement of RV Diastolic Function 705
- C.
Effects of Age, Respiration, Heart Rate, and Loading Conditions 706
- D.
Clinical Relevance 706
- A.
Clinical and Prognostic Significance of Right Ventricular Assessment 706
References 708
Executive Summary
The right ventricle plays an important role in the morbidity and mortality of patients presenting with signs and symptoms of cardiopulmonary disease. However, the systematic assessment of right heart function is not uniformly carried out. This is due partly to the enormous attention given to the evaluation of the left heart, a lack of familiarity with ultrasound techniques that can be used in imaging the right heart, and a paucity of ultrasound studies providing normal reference values of right heart size and function.
In all studies, the sonographer and physician should examine the right heart using multiple acoustic windows, and the report should represent an assessment based on qualitative and quantitative parameters. The parameters to be performed and reported should include a measure of right ventricular (RV) size, right atrial (RA) size, RV systolic function (at least one of the following: fractional area change [FAC], S′, and tricuspid annular plane systolic excursion [TAPSE]; with or without RV index of myocardial performance [RIMP]), and systolic pulmonary artery (PA) pressure (SPAP) with estimate of RA pressure on the basis of inferior vena cava (IVC) size and collapse. In many conditions, additional measures such as PA diastolic pressure (PADP) and an assessment of RV diastolic function are indicated. The reference values for these recommended measurements are displayed in Table 1 . These reference values are based on values obtained from normal individuals without any histories of heart disease and exclude those with histories of congenital heart disease. Many of the recommended values differ from those published in the previous recommendations for chamber quantification of the American Society of Echocardiography (ASE). The current values are based on larger populations or pooled values from several studies, while several previous normal values were based on a single study. It is important for the interpreting physician to recognize that the values proposed are not indexed to body surface area or height. As a result, it is possible that patients at either extreme may be misclassified as having values outside the reference ranges. The available data are insufficient for the classification of the abnormal categories into mild, moderate, and severe. Interpreters should therefore use their judgment in determining the extent of abnormality observed for any given parameter. As in all studies, it is therefore critical that all information obtained from the echocardiographic examination be considered in the final interpretation.
| Variable | Unit | Abnormal | Illustration |
|---|---|---|---|
| Chamber dimensions | |||
| RV basal diameter | cm | >4.2 | Figure 7 |
| RV subcostal wall thickness | cm | >0.5 | Figure 5 |
| RVOT PSAX distal diameter | cm | >2.7 | Figure 8 |
| RVOT PLAX proximal diameter | cm | >3.3 | Figure 8 |
| RA major dimension | cm | >5.3 | Figure 3 |
| RA minor dimension | cm | >4.4 | Figure 3 |
| RA end-systolic area | cm 2 | >18 | Figure 3 |
| Systolic function | |||
| TAPSE | cm | <1.6 | Figure 17 |
| Pulsed Doppler peak velocity at the annulus | cm/s | <10 | Figure 16 |
| Pulsed Doppler MPI | — | >0.40 | Figure 16 |
| Tissue Doppler MPI | — | >0.55 | Figures 16 and 18 |
| FAC (%) | % | <35 | Figure 9 |
| Diastolic function | |||
| E/A ratio | — | <0.8 or >2.1 | |
| E/E′ ratio | — | >6 | |
| Deceleration time (ms) | ms | <120 |
Essential Imaging Windows and Views
Apical 4-chamber, modified apical 4-chamber, left parasternal long-axis (PLAX) and parasternal short-axis (PSAX), left parasternal RV inflow, and subcostal views provide images for the comprehensive assessment of RV systolic and diastolic function and RV systolic pressure (RVSP).
Right Heart Dimensions
rv dimension . RV dimension is best estimated at end-diastole from a right ventricle–focused apical 4-chamber view. Care should be taken to obtain the image demonstrating the maximum diameter of the right ventricle without foreshortening ( Figure 6 ). This can be accomplished by making sure that the crux and apex of the heart are in view ( Figure 7 ). Diameter > 42 mm at the base and > 35 mm at the mid level indicates RV dilatation. Similarly, longitudinal dimension > 86 mm indicates RV enlargement.
rv outflow tract (rvot) dimension . The left PSAX view demonstrating RVOT at the level of the pulmonic valve yields the “distal diameter” ( Figure 8 C), while the left PLAX view allows for the measurement of the proximal portion of the RVOT, also referred to as “proximal diameter” ( Figure 8 A). Diameter > 27 mm at end-diastole at the level of pulmonary valve insertion (“distal diameter”) indicates RVOT dilatation.
rv wall thickness . RV wall thickness is measured in diastole, preferably from the subcostal view, using either M-mode or two-dimensional (2D) imaging ( Figure 5 ). Alternatively, the left parasternal view is also used for measuring RV wall thickness. Thickness > 5 mm indicates RV hypertrophy (RVH) and may suggest RV pressure overload in the absence of other pathologies.
ivc dimension . The subcostal view permits imaging and measurement of the IVC and also assesses inspiratory collapsibility. IVC diameter should be measured just proximal to the entrance of hepatic veins ( Figure 4 ). For simplicity and uniformity of reporting, specific values of RA pressure, rather than ranges, should be used in the determination of SPAP. IVC diameter ≤ 2.1 cm that collapses >50% with a sniff suggests normal RA pressure of 3 mm Hg (range, 0-5 mm Hg), whereas IVC diameter > 2.1 cm that collapses < 50% with a sniff suggests high RA pressure of 15 mm Hg (range, 10-20 mm Hg). In scenarios in which IVC diameter and collapse do not fit this paradigm, an intermediate value of 8 mm Hg (range, 5-10 mm Hg) may be used or, preferably, other indices of RA pressure should be integrated to downgrade or upgrade to the normal or high values of RA pressure. It should be noted that in normal young athletes, the IVC may be dilated in the presence of normal pressure. In addition, the IVC is commonly dilated and may not collapse in patients on ventilators, so it should not be used in such cases to estimate RA pressure.
RV Systolic Function
RV systolic function has been evaluated using several parameters, namely, RIMP, TAPSE, 2D RV FAC, 2D RV ejection fraction (EF), three-dimensional (3D) RV EF, tissue Doppler–derived tricuspid lateral annular systolic velocity (S′), and longitudinal strain and strain rate. Among them, more studies have demonstrated the clinical utility and value of RIMP, TAPSE, 2D FAC, and S′ of the tricuspid annulus. Although 3D RV EF seems to be more reliable with fewer reproducibility errors, there are insufficient data demonstrating its clinical value at present.
RIMP provides an index of global RV function. RIMP > 0.40 by pulsed Doppler and > 0.55 by tissue Doppler indicates RV dysfunction. By measuring the isovolumic contraction time (IVCT), isovolumic relaxation time (IVRT), and ejection time (ET) indices from the pulsed tissue Doppler velocity of the lateral tricuspid annulus, one avoids errors related to variability in the heart rate. RIMP can be falsely low in conditions associated with elevated RA pressures, which will decrease the IVRT.
TAPSE is easily obtainable and is a measure of RV longitudinal function. TAPSE < 16 mm indicates RV systolic dysfunction. It is measured from the tricuspid lateral annulus. Although it measures longitudinal function, it has shown good correlation with techniques estimating RV global systolic function, such as radionuclide-derived RV EF, 2D RV FAC, and 2D RV EF.
Two-dimensional FAC (as a percentage) provides an estimate of RV systolic function. Two-dimensional FAC < 35% indicates RV systolic dysfunction. It is important to make sure that the entire right ventricle is in the view, including the apex and the lateral wall in both systole and diastole. Care must be taken to exclude trabeculations while tracing the RV area.
S′ is easy to measure, reliable and reproducible. S′ velocity < 10 cm/s indicates RV systolic dysfunction. S′ velocity has been shown to correlate well with other measures of global RV systolic function. It is important to keep the basal segment and the annulus aligned with the Doppler cursor to avoid errors.
RV Diastolic Dysfunction
Assessment of RV diastolic function is carried out by pulsed Doppler of the tricuspid inflow, tissue Doppler of the lateral tricuspid annulus, pulsed Doppler of the hepatic vein, and measurements of IVC size and collapsibility. Various parameters with their upper and lower reference ranges are shown in Table 1 . Among them, the E/A ratio, deceleration time, the E/e′ ratio, and RA size are recommended. Note that these parameters should be obtained at end-expiration during quiet breathing or as an average of ≥5 consecutive beats and that they may not be valid in the presence of significant tricuspid regurgitation (TR).
grading of rv diastolic dysfunction . A tricuspid E/A ratio < 0.8 suggests impaired relaxation, a tricuspid E/A ratio of 0.8 to 2.1 with an E/e′ ratio > 6 or diastolic flow predominance in the hepatic veins suggests pseudonormal filling, and a tricuspid E/A ratio > 2.1 with deceleration time < 120 ms suggests restrictive filling.
Pulmonary Systolic Pressure/RVSP
TR velocity reliably permits estimation of RVSP with the addition of RA pressure, assuming no significant RVOT obstruction. It is recommended to use the RA pressure estimated from IVC and its collapsibility, rather than arbitrarily assigning a fixed RA pressure. In general, TR velocity > 2.8 to 2.9 m/s, corresponding to SPAP of approximately 36 mm Hg, assuming an RA pressure of 3 to 5 mm Hg , indicates elevated RV systolic and PA pressure. SPAP may increase, however, with age and in obesity. In addition, SPAP is also related to stroke volume and systemic blood pressure. Elevated SPAP may not always indicate increased pulmonary vascular resistance (PVR). In general, those who have elevated SPAP should be carefully evaluated. It is important to take into consideration that the RV diastolic function parameters and SPAP are influenced by the systolic and diastolic function of the left heart. PA pressure should be reported along with systemic blood pressure or mean arterial pressure.
Because echocardiography is the first test used in the evaluation of patients presenting with cardiovascular symptoms, it is important to provide basic assessment of right heart structure and function, in addition to left heart parameters. In those with established right heart failure or pulmonary hypertension (PH), further detailed assessment using other parameters such as PVR, can be carried out.
Overview
The right ventricle has long been neglected, yet it is RV function that is strongly associated with clinical outcomes in many conditions. Although the left ventricle has been studied extensively, with established normal values for dimensions, volumes, mass, and function, measures of RV size and function are lacking. The relatively predictable left ventricular (LV) shape and standardized imaging planes have helped establish norms in LV assessment. There are, however, limited data regarding the normal dimensions of the right ventricle, in part because of its complex shape. The right ventricle is composed of 3 distinct portions: the smooth muscular inflow (body), the outflow region, and the trabecular apical region. Volumetric quantification of RV function is challenging because of the many assumptions required. As a result, many physicians rely on visual estimation to assess RV size and function.
The basics of RV dimensions and function were included as part of the ASE and European Association of Echocardiography recommendations for chamber quantification published in 2005. This document, however, focused on the left heart, with only a small section covering the right-sided chambers. Since this publication, there have been significant advances in the echocardiographic assessment of the right heart. In addition, there is a need for greater dissemination of details regarding the standardization of the RV echocardiographic examination.
These guidelines are to be viewed as a starting point to establish a standard uniform method for obtaining right heart images for assessing RV size and function and as an impetus for the development of databases to refine the normal values. This guidelines document is not intended to serve as a detailed description of pathology affecting the right heart, although the document contains many references that describe RV pathologic conditions and how they affect the measurements described.
The purposes of this guidelines document are as follows:
- 1.
Describe the acoustic windows and echocardiographic views required for optimal evaluation of the right heart.
- 2.
Describe the echocardiographic parameters required in routine and directed echocardiographic studies and the views to obtain these parameters for assessing RV size and function.
- 3.
Critically assess the available data from the literature and present the advantages and disadvantages of each measure or technique.
- 4.
Recommend which right-sided measures should be included in the standard echocardiographic report.
- 5.
Provide revised reference values for right-sided measures with cutoff limits representing 95% confidence intervals based on the current available literature.
Methodology in the Establishment of Reference Value and Ranges
An extensive systematic literature search was performed to identify all studies reporting echocardiographic right heart measurements in normal subjects. These encompassed studies reporting normal reference values and, more commonly, studies reporting right heart size and function in patients with specific disease states (eg, chronic obstructive pulmonary disease) versus normal healthy controls. In the latter, only the control group was used in the determination of normal values. It is important to note that these reference values are based on values obtained from normal individuals without any history of heart disease and exclude those with history of congenital heart disease. For each measurement, the mean value and standard deviation (SD) were extracted, ensuring that the technique used to obtain the measurement was comparable between studies. Individual patient data were not available and therefore not extracted. The mean values and SDs were pooled and weighted to take into account study size and interstudy variability, as is typical for random-effects meta-analyses. The meta-analysis yielded a pooled estimate for the mean value, a pooled estimate for the lower reference value (ie, mean value − 2 SDs), and a pooled estimate for the upper reference value (ie, mean value + 2 SDs). In addition, 95% confidence intervals surrounding the mean and upper and lower reference values were calculated to add further insight into the robustness of the reference values. Reference values were reviewed by the writing group members to ensure that they were in accordance with clinical experience, and select measures were further discussed with outside experts. Our document therefore reports the mean values along with the upper and lower reference values in a normal population, each with 95% confidence intervals. Because patient-level data were not available, it is not possible to define cutoffs for body surface area, gender, or ethnicity. As a result, a value may fall within the 95% confidence interval for a given patient, but this value may still be abnormal for that patient, or vice versa. Similarly, patient-level data were not available to divide the abnormal categories into mild, moderate, and severe degrees of abnormality. Interpreters should therefore use their judgment in determining the extent of abnormality observed for any given parameter. In the rare situation in which insufficient data were available to perform the analysis described above, but the committee believed that guidelines were required (eg, estimation of RA pressure), current data were reviewed and a consensus put forth on the basis of the best available data. Many of the values provided in this document are significantly different from those provided in the ASE’s guidelines on chamber quantification published in 2005. The prior document’s normal values were often based on limited data, at times from a single small study. Readers are therefore encouraged to use the normal values provided in the current document in the assessment and reporting on right heart size and function.
Acoustic Windows and Echocardiographic Views of the Right Heart
To differentiate normal RV structure and function from abnormal and to assess RV size, volume, and contractility, a complete set of standardized views must be obtained ( Figure 1 ). These include PLAX, parasternal RV inflow, PSAX, apical 4-chamber, right ventricle–focused apical 4-chamber ( Figure 6 ), and subcostal views. It is important to use all available views , because each view adds complementary information, permitting a more complete assessment of the different segments of the right heart chambers. This pertains to the evaluation of both structure and function. For the estimation of RVSP, it is particularly important to interrogate TR by continuous-wave Doppler from all views, because the maximal velocity depends on optimal alignment with the jet. When there are discrepancies in structure and function between different views, the interpreting physician must integrate all information contained within the echocardiographic study to synthesize a global assessment of the right heart. Figure 1 details the standardized right heart views, along with the structures identified in each view.
Nomenclature of Right Heart Segments and Coronary Supply
The right coronary artery is the primary coronary supply to the right ventricle via acute marginal branches. In the setting of acute myocardial infarction, in general, the more proximal the occlusion, the more RV myocardium will be affected. In cases of the posterior descending artery occlusion, if there is RV involvement, it may be limited to a portion of the RV inferior wall only, best seen in the RV inflow view. The posterior descending artery gives off perpendicular branches. These posterior septal perforators typically supply the posterior one third of the ventricular septal wall. The blood supply to the moderator band arises from the first septal perforating branch of the left anterior descending coronary artery. This distribution of blood supply may become relevant in cases of alcohol septal ablation. In 30% of hearts, the conus artery arises from a separate coronary ostium and supplies the infundibulum. It may serve as a collateral to the anterior descending artery. In <10% of hearts, posterolateral branches of the left circumflex artery supply a portion of the posterior RV free wall. The left anterior descending artery may supply a portion of the RV apex, and this segment may be compromised in some cases of left anterior descending artery infarction. In addition, there are certain nonischemic diseases that may be associated with regional wall motion abnormalities of the right ventricle.
Conventional Two-Dimensional Assessment of the Right Heart
A
Right Atrium
The right atrium assists in filling the right ventricle by (1) acting as a reservoir for systemic venous return when the tricuspid valve is closed, (2) acting as a passive conduit in early diastole when the tricuspid valve is open, and (3) acting as an active conduit in late diastole during atrial contraction. To date, only a few studies have focused on the role of the right atrium in disease states.
RA area was a predictor of mortality or transplantation in a study of 25 patients with primary PH. RA dilatation was documented in patients with atrial arrhythmias by both 2D and 3D echocardiography, and reverse remodeling occurred following radiofrequency ablation treatment of atrial fibrillation.
The primary transthoracic window for imaging the right atrium is the apical 4-chamber view. From this window, RA area is estimated by planimetry. The maximal long-axis distance of the right atrium is from the center of the tricuspid annulus to the center of the superior RA wall, parallel to the interatrial septum. A mid-RA minor distance is defined from the mid level of the RA free wall to the interatrial septum, perpendicular to the long axis. RA area is traced at the end of ventricular systole (largest volume) from the lateral aspect of the tricuspid annulus to the septal aspect, excluding the area between the leaflets and annulus, following the RA endocardium, excluding the IVC and superior vena cava and RA appendage ( Figure 3 ). Note that RA dimensions can be distorted and falsely enlarged in patients with chest and thoracic spine deformities.
Normal values for major and minor dimensions and end-systolic area on transthoracic echocardiography are shown in Table 2 .
| Dimension | Studies | n | LRV (95% CI) | Mean (95% CI) | URV (95% CI) |
|---|---|---|---|---|---|
| RV mid cavity diameter (mm) ( Figure 7 , RVD2) | 12 | 400 | 20 (15-25) | 28 (23-33) | 35 (30-41) |
| RV basal diameter (mm) ( Figure 7 , RVD1) | 10 | 376 | 24 (21-27) | 33 (31-35) | 42 (39-45) |
| RV longitudinal diameter (mm) ( Figure 7 , RVD3) | 12 | 359 | 56 (50-61) | 71 (67-75) | 86 (80-91) |
| RV end-diastolic area (cm 2 ) ( Figure 9 ) | 20 | 623 | 10 (8-12) | 18 (16-19) | 25 (24-27) |
| RV end-systolic area (cm 2 ) ( Figure 9 ) | 16 | 508 | 4 (2-5) | 9 (8-10) | 14 (13-15) |
| RV end-diastolic volume indexed (mL/m 2 ) | 3 | 152 | 44 (32-55) | 62 (50-73) | 80 (68-91) |
| RV end-systolic volume indexed (mL/m 2 ) | 1 | 91 | 19 (17-21) | 33 (31-34) | 46 (44-49) |
| 3D RV end-diastolic volume indexed (mL/m 2 ) | 5 | 426 | 40 (28-52) | 65 (54-76) | 89 (77-101) |
| 3D RV end-systolic volume indexed (mL/m 2 ) | 4 | 394 | 12 (1-23) | 28 (18-38) | 45 (34-56) |
| RV subcostal wall thickness (mm) ( Figure 5 ) | 4 | 180 | 4 (3-4) | 5 (4-5) | 5 (5-6) |
| RVOT PLAX wall thickness (mm) (not shown) | 9 | 302 | 2 (1-2) | 3 (3-4) | 5 (4-6) |
| RVOT PLAX diameter (mm) ( Figure 8 ) | 12 | 405 | 18 (15-20) | 25 (23-27) | 33 (30-35) |
| RVOT proximal diameter (mm) ( Figure 8 , RVOT-Prox) | 5 | 193 | 21 (18-25) | 28 (27-30) | 35 (31-39) |
| RVOT distal diameter (mm) ( Figure 8 , RVOT-Distal) | 4 | 159 | 17 (12-22) | 22 (17-26) | 27 (22-32) |
| RA major dimension (mm) ( Figure 3 ) | 8 | 267 | 34 (32-36) | 44 (43-45) | 53 (51-55) |
| RA minor dimension (mm) ( Figure 3 ) | 16 | 715 | 26 (24-29) | 35 (33-37) | 44 (41-46) |
| RA end-systolic area (cm 2 ) ( Figure 3 ) | 8 | 293 | 10 (8-12) | 14 (14-15) | 18 (17-20) |
| Variable | Normal (0-5 [3] mm Hg) | Intermediate (5-10 [8] mm Hg) | High (15 mm Hg) | |
|---|---|---|---|---|
| IVC diameter | ≤2.1 cm | ≤2.1 cm | >2.1 cm | >2.1 cm |
| Collapse with sniff | >50% | <50% | >50% | <50% |
| Secondary indices of elevated RA pressure |
| |||
Disadvantages: RA area is a more time-consuming measurement than linear dimensions alone but is a better indicator for RV diastolic dysfunction.
Recommendations: Images adequate for RA area estimation should be obtained in patients undergoing evaluation for RV or LV dysfunction, using an upper reference limit of 18 cm 2 . RA dimensions should be considered in all patients with significant RV dysfunction in whom image quality does not permit for the measurement of RA area. Upper reference limits are 4.4 and 5.3 cm for minor-axis and major-axis dimensions, respectively ( Table 2 ). Because of the paucity of standardized RA volume data by 2D echocardiography, routine RA volume measurements are not currently recommended.
RA Pressure
RA pressure is most commonly estimated by IVC diameter and the presence of inspiratory collapse. As RA pressure increases, this is transmitted to the IVC, resulting in reduced collapse with inspiration and IVC dilatation. Combining these two parameters results in a good estimation of RA pressure within a limited number of ranges in a majority of patients. Traditional cutoff values for IVC diameter and collapse have recently been revisited, acknowledging that these parameters perform well when estimating low or high RA pressures and less well in intermediate values. Secondary indices of RA pressure may be useful in such scenarios to further refine estimates. In patients being ventilated using positive pressure, the degree of IVC collapse cannot be used to reliably estimate RA pressure, and RA pressure measured by transduction of a central line should be used if available. An IVC diameter ≤ 12 mm in these patients, however, appears accurate in identifying patients with RA pressures < 10 mm Hg. In this same patient group, if the IVC is small and collapsed, this suggests hypovolemia.
The subcostal view is most useful for imaging the IVC, with the IVC viewed in its long axis. The measurement of the IVC diameter should be made at end-expiration and just proximal to the junction of the hepatic veins that lie approximately 0.5 to 3.0 cm proximal to the ostium of the right atrium ( Figure 4 ). To accurately assess IVC collapse, the change in diameter of the IVC with a sniff and also with quiet respiration should be measured, ensuring that the change in diameter does not reflect a translation of the IVC into another plane. It may be better to view the IVC in the cross-sectional view to make sure that the long-axis view is perpendicular to it. Although a distended IVC usually denotes elevated RA pressures, in patients with otherwise normal exam results, reassessing the IVC size and collapsibility in the left lateral position may be useful to avoid the potentially erroneous inference of increased RA filling pressure. The IVC may also be dilated in normal young athletes, and in this population, it may not reflect elevated RA pressure.
Hepatic vein flow patterns provide complementary insights into RA pressure. At low or normal RA pressures, there is systolic predominance in hepatic vein flow, such that the velocity of the systolic wave (Vs) is greater than the velocity of the diastolic wave (Vd). At elevated RA pressures, this systolic predominance is lost, such that Vs is substantially decreased and Vs/Vd is <1. The hepatic vein systolic filling fraction is the ratio Vs/(Vs + Vd), and a value < 55% was found to be the most sensitive and specific sign of elevated RA pressure. Importantly, hepatic vein flow velocities have been validated in mechanically ventilated patients, provided that the velocities are averaged over ≥5 consecutive beats and comprising ≥1 respiratory cycle.
Other 2D signs of increased RA pressure include a dilated right atrium and an interatrial septum that bulges into the left atrium throughout the cardiac cycle. These are qualitative and comparative, and do not allow the interpreter to assign an RA pressure but if present should prompt a more complete evaluation of RA pressure as well as a search for possible etiologies.
Advantages: IVC dimensions are usually obtainable from the subcostal window.
Disadvantages: IVC collapse does not accurately reflect RA pressure in ventilator-dependent patients. It is less reliable for intermediate values of RA pressure.
Recommendations: For simplicity and uniformity of reporting, specific values of RA pressure, rather than ranges, should be used in the determination of SPAP. IVC diameter ≤ 2.1 cm that collapses >50% with a sniff suggests a normal RA pressure of 3 mm Hg (range, 0-5 mm Hg), whereas an IVC diameter > 2.1 cm that collapses <50% with a sniff suggests a high RA pressure of 15 mm Hg (range, 10-20 mm Hg). In indeterminate cases in which the IVC diameter and collapse do not fit this paradigm, an intermediate value of 8 mm Hg (range, 5-10 mm Hg) may be used, or, preferably, secondary indices of elevated RA pressure should be integrated. These include restrictive right-sided diastolic filling pattern, tricuspid E/E′ ratio > 6, and diastolic flow predominance in the hepatic veins (which can be quantified as a systolic filling fraction < 55%). In indeterminate cases, if none of these secondary indices of elevated RA pressure are present, RA pressure may be downgraded to 3 mm Hg. If there is minimal IVC collapse with a sniff (<35%) and secondary indices of elevated RA pressure are present, RA pressure may be upgraded to 15 mm Hg. If uncertainty remains, RA pressure may be left at the intermediate value of 8 mm Hg. In patients who are unable to adequately perform a sniff, an IVC that collapses < 20% with quiet inspiration suggests elevated RA pressure. This method of assigning an RA pressure is preferable to assuming a fixed RA pressure value for all patients.
B
Right Ventricle
RV Wall Thickness
RV wall thickness is a useful measurement for RVH, usually the result of RVSP overload. Increased RV thickness can be seen in infiltrative and hypertrophic cardiomyopathies, as well as in patients with significant LV hypertrophy, even in the absence of PH. RV free wall thickness can be measured at end-diastole by M-mode or 2D echocardiography from the subcostal window, preferably at the level of the tip of the anterior tricuspid leaflet or left parasternal windows. From the subcostal view, one can align the ultrasound beam perpendicular to the RV free wall. Excluding RV trabeculations and papillary muscle from RV endocardial border is critical for accurately measuring the RV wall thickness. Moving the focus to the RV wall region and decreasing the depth will improve the endocardial border definition. Every effort must be made to exclude epicardial fat to avoid erroneously increased measurements. When image quality permits, fundamental imaging should be used to avoid the increased structure thickness seen with harmonic imaging. When there is significant thickening of the visceral pericardium, the measurement of the RV wall may be challenging.
Certain conditions are associated with RV wall thinning, such as Uhl anomaly or arrhythmogenic RV cardiomyopathy. There are no accepted echocardiographic criteria to define an abnormally thin RV wall.
Advantages: RV wall thickness can be measured by M-mode or 2D echocardiography from either the subcostal or left parasternal window.
Disadvantages: There is a lack of established prognostic information.
Recommendations: Abnormal RV wall thickness should be reported, if present, in patients suspected of having RV and/or LV dysfunction, using the normal cutoff of 0.5 cm from either PLAX or subcostal windows ( Table 2 ).
RV Linear Dimensions
The right ventricle dilates in response to chronic volume and/or pressure overload and with RV failure. Indexed RV end-diastolic diameter has been identified as a predictor of survival in patients with chronic pulmonary disease, and the RV/LV end-diastolic diameter ratio was shown to be a predictor of adverse clinical events and/or hospital survival in patients with acute pulmonary embolism. Correlation of RV linear dimensions with RV end-diastolic volumes appears to worsen with increased preload or afterload.
Using 2D echocardiography, RV size can be measured from a 4-chamber view obtained from the apical window at end-diastole. Although quantitative validation is lacking, qualitatively, the right ventricle should appear smaller than the left ventricle and usually no more than two thirds the size of the left ventricle in the standard apical 4-chamber view. If the right ventricle is larger than the left ventricle in this view, it is likely significantly enlarged. This may be applied to certain conditions such as severe RV pressure or volume overload, in which the right ventricle may measure within the normal reference limits but appears larger than the small, underfilled left ventricle. In the standard transthoracic apical 4-chamber window, the left ventricle is considered the “apex-forming” ventricle. As the right ventricle enlarges, it may displace the left ventricle and occupy the apex. This usually signifies that the right ventricle is at least moderately dilated, though this finding has not been validated quantitatively.
One major limitation of RV imaging by transthoracic echocardiography is the result of a lack of fixed reference points to ensure optimization of the right ventricle. As a result, the imager can image the RV through various cut planes, resulting in a normal, medium, or smaller dimension ( Figure 6 ). As a result, it is critical to attempt to adjust the apical 4-chamber to acquire the “ right ventricle–focused view ,” as detailed below. To optimize imaging of the RV lateral wall, the 4-chamber image may require adjustment from its usual attention on the left ventricle to a focus on the right ventricle. To avoid underestimating the minor distance, the transducer is rotated until the maximal plane is obtained. To avoid overestimation, the transducer must be properly positioned over the cardiac apex with the plane through the left ventricle in the center of the cavity. One must ensure that the RV is not foreshortened and that the LV outflow tract is not opened up (avoid the apical 5-chamber view).
The basal and mid cavity RV diameters, as well as the RV longitudinal dimension, may be obtained ( Figure 7 ). The basal diameter is generally defined as the maximal short-axis dimension in the basal one third of the right ventricle seen on the 4-chamber view. In the normal right ventricle, the maximal short-axis dimension is usually located in the basal one third of the ventricular cavity. The mid cavity diameter is measured in the middle third of the right ventricle at the level of the LV papillary muscles. The longitudinal dimension is drawn from the plane of the tricuspid annulus to the RV apex. Note that RV dimensions can be distorted and falsely enlarged in patients with chest and thoracic spine deformities.
Advantages: RV linear dimensions are easily obtained on an apical 4-chamber view and are markers of RV dilatation.
Disadvantages: RV dimensions are highly dependent on probe rotation by the user, which can result in an underestimation of RV width.
Recommendations: Patients with echocardiographic evidence of right-sided heart disease or PH should ideally have measurements of RV basal, mid cavity, and longitudinal dimensions on a 4-chamber view. In all complete echocardiographic studies, the RV basal measurement should be reported, and the report should state the window from which the measurement was performed (ideally the right ventricle–focused view), to permit interstudy comparisons. The relative size of the right ventricle should be compared with that of the LV to help the study interpreter determine if there is RV dilatation, and the interpreter may report the right ventricle as dilated despite measuring within the normal range, on the basis of a right ventricle appearing significantly larger than the left ventricle. The upper reference limit for the RV basal dimension is 4.2 cm ( Table 2 ).
C
RVOT
The RVOT is generally considered to include the subpulmonary infundibulum, or conus, and the pulmonary valve. The subpulmonary infundibulum is a cone-shaped muscular structure that extends from the crista supraventricularis to the pulmonary valve. It is distinct from the rest of the right ventricle in origin and anatomy. The delay in regional activation of the RVOT contributes to the peristalsis-like contraction pattern of the normal right ventricle. The role of the RVOT is particularly important in some patients with congenital heart disease or arrhythmia, and the RVOT is often the first segment of the right ventricle to show diastolic inversion in the setting of tamponade.
The RVOT is best viewed from the left parasternal and subcostal windows, but it also may be evaluated from the apical window in thin individuals or adults with large rib spaces. The size of the RVOT should be measured at end-diastole on the QRS deflection. In the PLAX view, a portion of the proximal RVOT can be measured (RVOT-Prox in Figure 8 A). In the short-axis view, the RVOT linear dimension can be measured from (1) the anterior aortic wall to the RV free wall above the aortic valve (RVOT-Prox in Figure 8 B) and (2) just proximal to the pulmonary valve (RVOT-Distal in Figure 8 C). This latter site, at the connection of the RV infundibulum with the pulmonary valve is preferred, especially when measuring right-sided stroke volume for the calculation of Qp/Qs or regurgitant fraction. The PLAX view of the RVOT is used in particular in the evaluation for arrhythmogenic RV dysplasia. With transesophageal echocardiography, the RVOT is well visualized in the midesophageal RV inflow-outflow view. The use of 3D echocardiography has been shown to be helpful in the assessment of the RVOT. Note that RVOT dimensions can be distorted and falsely enlarged in patients with chest and thoracic spine deformities.
Advantages: RVOT dimensions are easily obtained from the left PSAX window. Certain lesions may primarily affect the RVOT.
Disadvantages: Limited normative data are available. The window for measurement of RVOT size has not been standardized, and oblique imaging of the RVOT may underestimate or overestimate its size. The endocardial definition of the anterior wall is often suboptimal.
Recommendations: In studies on select patients with congenital heart disease or arrhythmia potentially involving the RVOT, proximal and distal diameters of the RVOT should be measured from the PSAX or PLAX views. The PSAX distal RVOT diameter, just proximal to the pulmonary annulus, is the most reproducible and should be generally used. For select cases such as suspected arrhythmogenic RV cardiomyopathy, the PLAX measure may be added. The upper reference limit for the PSAX distal RVOT diameter is 27 mm and for PLAX is 33 mm ( Table 2 ).
Fractional Area Change and Volumetric Assessment of the Right Ventricle
A
RV Area and FAC
The percentage RV FAC, defined as (end-diastolic area − end-systolic area)/end-diastolic area × 100, is a measure of RV systolic function that has been shown to correlate with RV EF by magnetic resonance imaging (MRI). RV FAC was found to be an independent predictor of heart failure, sudden death, stroke, and/or mortality in studies of patients after pulmonary embolism and myocardial infarction. FAC is obtained by tracing the RV endocardium both in systole and diastole from the annulus, along the free wall to the apex, and then back to the annulus, along the interventricular septum. Care must be taken to trace the free wall beneath the trabeculations ( Figure 9 ).
Recommendations: Two-dimensional Fractional Area Change is one of the recommended methods of quantitatively estimating RV function, with a lower reference value for normal RV systolic function of 35%.
B
Two-Dimensional Volume and EF Estimation
The complexity of estimating RV volume and function with 2D echocardiography has been well documented, and interested readers are referred to reviews for a more complete discussion. In brief, the 2D echocardiographic methods of calculating RV volume can be divided into area-length methods, disk summation methods, and other methods.
The area-length methods, initially adopted for biplane angiography, require an approximation of RV geometry, most commonly based on modified pyramidal or ellipsoidal models. It underestimates MRI-derived RV volume and is inferior in comparison with 3D echocardiographic methods of RV volume estimation.
The disk summation method has also been applied to determine a RV “body” volume, using predominantly the apical 4-chamber view. RV volumes are therefore underestimated because of the exclusion of the RVOT and technical limitations of the echocardiographic images.
RV EF from 2D methods is calculated as (end-diastolic volume − end-systolic volume)/end-diastolic volume. The lower reference limit of pooled studies using these methods for the measurement of RV EF is 44%, with a 95% confidence interval of 38% to 50% ( Table 4 ).
