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REVIEW ARTICLE Assessment of the Right Ventricle by Echocardiography: A Primer for Cardiac Sonographers Kenneth D. Horton, RDCS, RCS, RCIS, FASE, Rick W. Meece, RDCS, RCS, RCIS, FASE, and Jeffrey C. Hill, BS, RDCS, FASE, Salt Lake City, Utah; Nashville, Tennessee; Worcester, Masschusetts The assessment of right ventricular (RV) structure and function by echocardiography has been improved by advancements that include Doppler tissue imaging, strain imaging, and three-dimensional imaging. Doppler tissue imaging and strain imaging can be useful for the assessment of regional RV systolic and diastolic function. Three-dimensional imaging has been reported to determine RV volumes and ejection fraction, which have previously been cumbersome to measure with conventional two-dimensional echocardiography. This article addresses the role of conventional and newer methods of echocardiography to assist sonographers in understanding the technical considerations, limitations, and pitfalls of image acquisition and analysis of RV structure and function. (J Am Soc Echocardiogr 2009;22:776-792.) Keywords: Right ventricle, Doppler tissue imaging, Two-dimensional imaging, Three-dimensional imaging 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 AMA PRA Category 1 CreditsÔ. 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. Objectives: Upon completing the reading of this article, the participants will better be able to: 1. Effectively apply echocardiographic techniques to provide a comprehensive assessment of right ventricular function 2. Accurately identify normal right ventricular anatomy and define basic right ventricular physiology 3. Utilize practical technical tips to enhance right ventricular image acquisition and subsequent measurements 4. Recognize the developing role of 3D imaging for the assessment of right ventricular structure and function 5. Confidently integrate tissue Doppler methods with strain imaging techniques to assess right ventricular mechanical function Author Disclosure: Mr. Hill reported that he receives grant/research support from Toshiba America Medical Systems, Inc., is on the speaker’s bureau for Philips Healthcare and is a consultant to Medtronic, Inc. Mr. Horton reported that he is a consultant to Lantheus Medical Imaging, Inc. Mr. Meece reported that he receives grant/research support from TomTec and Toshiba America Medical Systems, Inc. He also reported that he is a consultant to Philips Healthcare. Conflict of Interest: This activity has been peer-reviewed by a non-biased member of the ASE ACCME/CME committee. No indication of an actual or potential bias in relation to the author disclosures was determined. Estimated Time to Complete This Activity: 1 hour INTRODUCTION RV dysfunction has been associated with increased morbidity and mortality in patients with congenital heart disease, valvular disease, coronary artery disease, pulmonary hypertension, and heart failure.1-3 Conventional 2-dimensional (2D) determination of RV function is often qualitative. Doppler methods of tricuspid inflow and pulmonary artery flow velocities, which are influenced by changes in preload and afterload, may not provide robust prognostic information for clinical decision making. Recent advances in echocardiographic imaging of the right ventricle include Doppler tissue imaging (DTI), strain imaging (SI), and volumetric 3-dimensional (3D) imaging, which can be used for additional information beyond standard 2D measurements. In this article, we compare the role of conventional and emerging echocardiographic techniques for evaluating RV function (Table 1). Technical considerations in using a systematic approach to image acquisition and analysis are discussed. RV ANATOMY AND PHYSIOLOGY Normally, the right ventricle is located anterior in the thoracic cavity in relation to the left ventricle, with echocardiographic assessment possible in the 3 traditional acoustic windows (parasternal, apical, and subcostal). The right ventricle is anatomically subdivided into the inflow tract, the infundibulum (outflow tract), and the apex (Figure 1).4 From the Intermountain Medical Center, Salt Lake City, Utah (K.D.H.); Saint Thomas Heart & Research Institute, Nashville, Tennessee (R.W.M.); and the University of Massachusetts Memorial Medical Center, Worcester, Masschusetts (J.C.H.). Reprint requests: Kenneth D. Horton, RDCS, RCS, RCIS, FASE, Intermountain Medical Center, Sorenson Heart & Lung Tower, Echo Lab LL-1, Murray, UT 84107 (E-mail: [email protected]). 0894-7317/$36.00 Copyright 2009 by the American Society of Echocardiography. doi:10.1016/j.echo.2009.04.027 776 Horton et al 777 Journal of the American Society of Echocardiography Volume 22 Number 7 Table 1 Echocardiographic methods used for the assessment of RV size and function 2D echocardiography Linear dimensions Fractional area change M-mode echocardiography TAM Conventional Doppler echocardiography Myocardial performance index PVR DTI and SI Tissue Doppler techniques Speckle-tracking techniques 3D echocardiography Segmental/global volumes EF Within the RV cavity, there are 3 muscular bands: the parietal band, the septomarginal band, and the moderator band. In abnormal or congenital heart disease, the moderator band may serve as a landmark to differentiate the right from the left ventricle. RV hemodynamic function is physiologically different than that of the left ventricle. This is due primarily to lower afterload in the pulmonary vascular bed, which explains the lower RV pressures compared with the left ventricle. An important principle regarding RV diastolic filling is ventricular interdependence, whereby changes in pulmonary vascular resistance (PVR) and extracardiac pressures are more often affected by respiration. This interdependence may alter filling and systolic performance in both ventricles.5 During inspiration, transtricuspid inflow (RV preload) increases by approximately 20%, while transmitral inflow (LV preload) is mildly decreased by approximately 10%, with the process reversing during expiration. Pathologies that affect loading conditions, such as pericardial constriction, pulmonary embolus, and RV infarction, often affect this relationship. In some instances, clinical conditions (eg, chronic lung disease, obesity, congenital heart disease) may lead to technical limitations that preclude the adequate visualization of RV shape and structure, in addition to associated abnormal loading conditions, for accurate the assessment of RV performance. ASSESSMENT OF RV STRUCTURE AND FUNCTION BY 2D ECHOCARDIOGRAPHY Commonly used methods for calculating diameters, areas, and volumes of the LV are difficult to implement for the right ventricle and are typically not performed. Because of the complex morphology of the right ventricle, no single view or imaging plane will provide enough information to adequately evaluate RV structure and function. As such, sonographers should perform thorough assessments of the right ventricle from standard two-dimensional (2D) acoustic windows that include RV inflow tract and RV outflow tract (RVOT) views, parasternal short-axis views, and apical views. Figure 1 Diagram of the right ventricle demonstrating its 3 major chamber components; inflow tract, infundibulum (outflow tract), and apex. Image adapted and modified from Haddad F, Hunt SA, Rosenthal DN, Murphy DJ. Right ventricular function in cardiovascular disease, part I: anatomy, physiology, aging, and functional assessment of the right ventricle. Circulation 2008;117:1436-48. from the American Society of Echocardiography recommend the use of the subcostal 4-chamber view for measurements of RV free wall thickness, because it has demonstrated higher reproducibility and correlates with RV systolic pressure.6,9 Measurements of RV chamber dimensions should include the diameters above the tricuspid valve (TV) annulus and in the mid-RV cavity, as well as the distance from the TV annulus to the RV apex (Figure 2A).10,11 Technical Tips Images obtained for 2D measurements should focus on the right ventricle at the expense of visualizing other cardiac structures. Helpful tips include (1) narrowing the 2D sector width to optimize only RV structures; (2) using harmonic imaging and adjusting gain and compression for good contrast and endocardial edge detection; (3) making RV wall thickness measurements at the level of the chordae tendineae; (4) making all measurements at end-diastole, or the frame demonstrating the largest chamber dimension; and (5) for 2D measurements, obtaining all acquisitions during quiet respiration or apnea. Measurements of RV wall thickness must exclude the epicardial fat layer that can be visualized on the RV free wall. An anterior fat pad or liver usually appears echodense and brighter than the true RV wall (Figure 2B). Foreshortening of the right ventricle may be minimized by positioning the transducer down an intercostal space and laterally until the RV apex is clearly seen. Prominent trabeculations and moderator bands can make identification of the endocardial borders challenging. If clinically indicated, endocardial enhancement from the use of echocardiographic contrast agents may improve the accuracy of chamber and wall thickness measurements and the assessment of systolic function. RV WALL THICKNESS AND CHAMBER DIMENSIONS RV FRACTIONAL AREA CHANGE RV free wall assessment is best performed from the apical and subcostal 4-chamber views. Increased RV free wall thickness or hypertrophy as measured by echocardiography has been well validated and usually indicates pressure overload from pulmonary hypertension, RV outflow obstruction, or pulmonary valve (PV) stenosis.6-8 Guidelines The assessment of RV systolic function by the calculation of RV fractional area change (RVFAC) has been compared with cardiac magnetic resonance (CMR) imaging of the RV ejection fraction (EF) in patients with heart failure and previous myocardial infarctions.11-13 778 Horton et al Journal of the American Society of Echocardiography July 2009 Figure 2 (A) Three measurements of the right ventricle obtained at end-diastole in the apical 4-chamber view: D1 = basal RV measurement; D2 = mid-RV measurement; D3 = base-to-apex measurement. (B) RV free wall thickness measurement obtained at enddiastole at level of the TV chordae tendineae in the subcostal 4-chamber view. Both images are optimized by decreasing the depth or using the zoom function. Note the clear border delineation (excluding pericardial border, fat, or liver [arrows]) of the RV wall in (B). RA, Right atrium. Figure 3 RVFAC measured at end-diastole (A) and end-systole (B). Both images are optimized by decreasing the depth or using the zoom function. The RVFAC is calculated as (25 cm2 10 cm2)/25 cm2 100 = 60% (normal). RVAD, RV area at end-diastole; RVAS, RV area at end-systole. RV fractional area change represents a ‘‘surrogate’’ measurement of RV EF and is expressed as a percentage change in the RV chamber area from end-diastole to end-systole, rather than changes in volume (Figure 3). The RVFAC is calculated as follows: end-diastolic area ðcm2 Þ end systolic area ðcm2 Þ end diastolic are ðcm2 Þ Compared with other measures of RV systolic function, including M-mode-derived tricuspid annular motion (TAM) and transverse fractional shortening, RVFAC was found to correlate best with CMR-derived RV EF (CMR vs RVFAC, r = 0.80, P < .0001; CMR vs transverse fractional shortening, r = 0.12, P = .48; CMR vs TAM, r = 0.17, P = .30).13 Measurements of RVFAC are obtained in the apical 4-chamber view. Planimetry of the RV cavity area is traced across Horton et al 779 Journal of the American Society of Echocardiography Volume 22 Number 7 Figure 4 TAM obtained before optimization (A) and after optimization (B) in the same patient. By zooming in on the TV annulus, accuracy and measurements of TAM were improved. The red line follows the contour of the annulus during the cardiac cycle. TAM in (B) = 2.0 cm (normal). nosis and increased mortality. Samad et al15 assessed TAM in 194 patients with first acute myocardial infarctions and RV involvement. TAM was significantly decreased in patients with acute myocardial infarctions compared with healthy subjects (20.9 6 4 vs 21.6 6 4 mm, P < .001). TAM # 15 mm showed an increase in mortality (>40%) compared with TAM $ 20 mm (<5%). TAM > 15 mm is generally normal. However, TAM is a one-dimensional approach, reflecting regional (basal), not global, RV systolic function. TAM is also influenced by disease states such as acute cor pulmonale or RV strain, in which annular motion may be less dynamic or significant regional variation may be present. Figure 5 Diagram of the RVMPI. A, Transtricuspid A wave; a, time from cessation of transtricuspid A wave to the following E wave; E, transtricuspid E wave; ET, transpulmonary ejection time. the TV annulus along the endocardium, then around the apex at the end-diastolic and end-systolic frames. M-MODE FOR THE ASSESSMENT OF RV SYSTOLIC FUNCTION As mentioned previously, M-mode echocardiography can be used in evaluating RV systolic function by measuring TAM. With the M-mode cursor aligned through the anterior tricuspid annulus in the apical 4chamber view, longitudinal displacement of the annulus toward the apex during systole can be recorded (Figure 4).14 RV dysfunction in the presence of acute myocardial infarction is associated with poor prog- Technical Tips To obtain TAM, use the apical 4-chamber view by adjusting the 2D image to position the M-mode cursor through the tricuspid annulus as parallel as possible. Using the zoom magnification function may assist in proper alignment of the cursor through the annulus, resulting in improved visualization of the annulus (Figure 4B). Other optimization techniques include decreasing the gain to eliminate erroneous signals from the areas around the annulus and acquisition of the tracing at a sweep speed of 75 to 100 mm/s. Because the accuracy of this measurement may be influenced by exaggerated cardiac motion during normal respiration or in patients with large pericardial effusions, TAM should be obtained during apnea. RV MYOCARDIAL PERFORMANCE INDEX RV myocardial performance index (RVMPI), or the ‘‘Tei index,’’ has been reported to determine RV global systolic and diastolic function by measuring time intervals using standard pulsed or continuouswave Doppler.6 The RVMPI is the ratio of the total isovolumic time (isovolumic contraction time [ICT] and isovolumic relaxation time [IRT]) divided by the RV ejection time and is calculated as follows: ½ICT ðmsÞ þ IRT ðmsÞ=RVET ðmsÞ The RVMPI has shown significant correlation with RV EF by nuclear ventriculography and is reported to be less affected by loading conditions than RVFAC, TAM, and SI.16,17 Tei et al18 780 Horton et al Journal of the American Society of Echocardiography July 2009 Figure 6 Echocardiographic estimation of PVR in a patient with RV dysfunction and high right atrial pressure (estimated at >20 mm Hg). (A) Continuous-wave Doppler was obtained across the TV from an off-axis apical 4-chamber view and the peak TR velocity (TRV) was measured. (B) Pulsed-wave Doppler sample volume was placed at the RVOT, and the TVI was measured. The PVR in this patient was calculated as TRV/TVIRVOT = 2.78/11 = 0.25 10 + 0.16 = 2.68 (abnormal). demonstrated abnormal RVMPIs in patients with primary pulmonary hypertension compared with age-matched controls (0.93 6 0.34 vs 0.28 6 0.04, P < .001). The sum of isovolumic time in patients with primary pulmonary hypertension was significantly increased and RV ejection time significantly decreased (P < .001 vs normal controls). Technical Tips To calculate RVMPI, (1) obtain pulsed or continuous-wave Doppler recordings of the TV inflow and PVoutflow; (2) measure the time duration from the cessation of the A wave to beginning of the subsequent E wave on the basis of the tricuspid inflow Doppler spectral velocity envelope; (3) measure the RV ejection time from the pulmonary Doppler tracing; (4) subtract the RV ejection time from the time duration (TV A wave to E wave): the difference in time is the sum of isovolumic time; and (5) divide by the RV ejection time (Figure 5). In patients with holosystolic tricuspid regurgitation (TR) and clear spectral Doppler envelopes, the duration of the regurgitation can be substituted for the interval between cessation and onset of TV inflow. Because Doppler recordings of TV inflow and PV outflow are not simultaneous, the information should be acquired with the cardiac cycle R-R interval duration difference < 5%.16 Using the parasternal short-axis view permits the rapid acquisition of both tracings. Lower wall filters may improve the demarcation of valve opening and closure timing on the Doppler spectral envelopes. A 75 to 100 mm/s sweep speed may improve accuracy. PVR BY DOPPLER ECHOCARDIOGRAPHY The assessment of pulmonary vascular resistance (PVR) is important for management in patients with cardiovascular disease. To determine invasive hemodynamic measurements of PVR, a catheter is placed in the pulmonary artery; measurements include mean pulmonary artery pressure, pulmonary capillary wedge pressure, and cardiac output. To determine the noninvasive estimation of PVR by echocardiography, the peak TR velocity (TRV) and time-velocity integral (TVI) of the RVOT is measured (Figure 6). Estimation of PVR by echocardiography is calculated as follows: TRVðm=sÞ=TVIRVOT ðcmÞ 10 þ 0:16 ðWoods unitsÞ Abbas et al19 compared both invasive and noninvasive measures of PVR in 44 patients with various cardiovascular diseases. Their results showed an excellent correlation (r = 0.929) between the two methods, demonstrating that PVR by echocardiography is reliable and highly feasible. Technical Tips Assessment of the TR jet should be attempted in several views (including the subcostal views) to ensure that peak velocities are accurate. In patients with difficulty obtaining peak velocities, the use of agitated saline contrast is recommended to enhance the TR jet. Pulsed-wave rather than continuous-wave Doppler is used for the measurement of TVIRVOT. The sample volume should be placed in the RVOT just proximal to the PV. A summary of RV measurements and normal values is reported in Table 2. DTI AND SI FOR THE ASSESSMENT OF RV FUNCTION DTI and SI (ie, myocardial deformation) are newer echocardiographic methods that provide objective assessments of global and regional RV function. DTI and SI can complement 2D methods and have been shown to be applicable in patients with right coronary artery disease, congenital defects, pulmonary hypertension, and pulmonary embolism.20-27 Both methods are not significantly affected by volume loading conditions, and both have demonstrated acceptable reproducibility. DTI and SI are relatively easy to obtain from the tricuspid annulus and RV free wall. This section describes technical aspects, pitfalls, and caveats of using DTI and SI for the evaluation of RV function. PULSED-WAVE DTI Pulsed-wave DTI is used to measure low-frequency Doppler systolic and diastolic velocities that reflect longitudinal RV myocardial motion. The sample volume is usually placed at or below (ventricular Horton et al 781 Journal of the American Society of Echocardiography Volume 22 Number 7 Table 2 Normal values of the right ventricle Parameter RV 2D free wall thickness (subcostal 4-chamber view) (cm) RV 2D chamber dimensions (apical 4-chamber view) (cm) Base Mid Base to apex RV 2D area (cm2) Systolic Diastolic RVFAC (2D) (%) RV TAM (mm) RVMPI (Doppler) PVR (Doppler) RV DTI systolic (S0 ) velocity (obtained from the apical 4-chamber view) (cm/s) Annulus Base Mid Apex RV DTI strain (obtained from the apical 4-chamber view) (%) Base Mid Apex RV 2D speckle strain (obtained from the apical 4-chamber view) (%) Base Mid Apex RV 3D volumes and EF BSA indexed; DS method (mL/m2) EDV ESV SV EF Value <0.5 Reference Matsukubo et al6 Foale et al7 2.0-2.8 2.7-3.3 7.1-7.9 Weyman et al10 7.5-16 11-28 32-60 15-20 0.28 6 0.04 <0.175 Weyman et al10 Samad et al15 Tei et al18 Abbas et al19 Kukulski et al27 4.95 6 1.76† 11.03 6 2.06‡ 8.48 6 2.04 9.96 6 1.97 Figure 7 Color DTI waveforms obtained from the RV free wall describing the various phases in ventricular systole and diastole. There are 5 discrete waveforms occurring within the cardiac cycle, as seen on the Doppler display: (1) ICT velocity, (2) systolic (S0 ) velocity, (3) IRT velocity, (4) early diastolic velocity (E0 ), and (5) late diastolic velocity (A0 ). Dotted vertical lines represent PV opening (PVO) and PV closure (PVC). Teske et al39 19 6 6* 27 6 6 32 6 6 Teske et al39 22.8 6 7.4 24.4 6 7.7 27.6 6 8.9 Gopal et al45 42.2-97.8 12.8-54.0 18.0-45.9 32.8-62.5 BSA, Body surface area; DS, disc summation; EDV, end-diastolic volume; ESV, end-systolic volume. Data are expressed as mean 6 SD or as ranges. *P < .01, base versus mid versus apical (analysis of variance). †P = .04, RV annulus versus RV basal segment. ‡P < .001, basal segments versus medial versus apical segments (analysis of variance). side) the tricuspid annulus. Other sites include positioning the sample volume at the mid-RV free wall, apex, and the ventricular septum in the apical 4-chamber view to assess myocardial contraction and relaxation. In patients with normal sinus rhythm, 5 distinct waveforms can be seen on the Doppler display: (1) the ICT waveform occurs in early systole and can be displayed above or below the zero baseline; (2) the systolic (S0 ) peak waveform occurs during RV mechanical systole (PV opening to closure time), after ICT, and is always displayed above the zero baseline; (3) the IRT waveform occurs in early diastole Figure 8 Color DTI with 3 sample volumes placed over the RV free wall (top left) in a patient with RV dysfunction. Sample volumes placed at the base and mid-RV allow for measurement of systolic and diastolic function. The highest velocities occur before PV opening (PVO; ICT [arrows]), and the absolute velocities are decrease from base to mid-RV. PVC, PV closure. (end of the T wave on electrocardiography [ECG]) and can be displayed above or below the zero baseline; (4) the early diastolic (E0 ) waveform occurs during peak RV relaxation (after IRT) and is always displayed below the zero baseline; and (5) the peak late diastolic (A0 ) waveform represents atrial contraction and is always displayed below the zero baseline (just after the P wave on ECG) (Figure 7). COLOR DTI Color encoding of myocardial velocities improves spatial resolution of RV wall motion during 2D imaging in the apical 4-chamber view. It is important to recognize that non-color-encoded–derived pulsed-wave DTI represents maximum instantaneous velocities, whereas color DTI displays the average velocities within a specific region of interest and 782 Horton et al Journal of the American Society of Echocardiography July 2009 Figure 9 The role of observing aliasing in color DTI sector and its relationship to peak DTI velocities. (A) During atrial systole (circle on electrocardiogram), there is a heterogeneous (yellow) display within the color DTI sector with aliasing of the basal RV free wall (arrow). (B) During ICT (circle on electrocardiogram), after atrial systole, there is minimal color aliasing in the RV free wall (arrow). (C) After ICT (circle on electrocardiogram), during early ejection, there is a homogeneous display with no significant aliasing within the color DTI sector. This is an indication that the velocities within the color sector do not exceed the color scale. (D) Corresponding pulsed-wave DTI waveforms with the sample volume place at the area of aliasing with a color scale pulse repetition frequency (PRF) set at 13.5 cm/s. The peak A0 and ICT waveforms measure 15 and 15.5 cm/s, respectively. Aliasing within the color sector occurred because both A0 and ICT waveforms exceed the color scale PRF (13.5 cm/s). This indicates that the color scale may be too low and therefore View video clip online. needs to be increased to reduce or eliminate aliasing before measuring peak color DTI velocities. will result in lower values in systolic and diastolic velocities. Pulsedwave DTI, however, has limitations, with the placement of a single sample site along a fixed scan line, whereas color DTI allows the placement of multiple sample sites in various myocardial segments, enabling simultaneous regional evaluation within the same cardiac cycle (Figure 8). In addition, the region of interest samples may be repositioned to apply further postanalysis of the Doppler spectral signals on the same image. TECHNICAL ASPECTS OF DTI Accurate DTI measurements of RV systolic and diastolic function require clear understanding of the waveforms, as noted above, and their relationship to the timing of hemodynamic events (Figure 9, Video 1). Myocardial velocities often vary during the cardiac cycle. For example, color DTI–derived myocardial velocities may exceed the color scale threshold (Nyquist limit) and result in aliasing of the signals. Postprocessing of color DTI waveforms is highly dependent on the settings at the time of acquiring the images. Temporal and spatial resolution may be improved by narrowing the 2D color sector and adjusting the velocity scale, resulting in increased frame rate and better displaying signals without aliasing. Abnormalities in RV structure and function can reduce the peak systolic and diastolic velocities (Figure 10, Video 2). Sonographers should not mistake the peak ICT waveform for the peak S0 waveform. The peak ICT waveform occurs before PV opening during the QRS deflection. The peak S0 waveform occurs during mechanical systole following PV opening and represents active RV contraction. Likewise, it is important to distinguish the peak IRT waveform from the peak E0 waveform (Figure 11) for measurements of RV diastolic function. The peak IRT waveform will be displayed below the baseline just after the cessation of S0 waveform. It can be difficult to differentiate when IRT is shortened and merges with E0 ; conversely, prolonged IRT may result in multiple early diastolic peak velocity waveforms. Measurement from the onset of the Q wave (QRS) to PV closure may help detect the peak IRT from E0 . In acquiring and choosing the correct peak DTI waveforms, optimizing cursor alignment, overall gain, and respiration phase can affect peak DTI velocities. A summary of the technical factors influencing the DTI waveforms is provided in Table 3. Journal of the American Society of Echocardiography Volume 22 Number 7 Horton et al 783 Figure 10 Example of a 41-year-old man with severe pulmonary hypertension. (A) Three standard measurements of the RV chamber from the apical 4-chamber view showed significant dilation, especially at the mid-RV level (4.18 cm). (B) Severe TR, with pulmonary artery systolic pressures averaging 72 mm Hg (not including right atrial pressure), continues with severe pulmonary hypertension. (C) Although overall RV function was difficult to assess, pulsed-wave DTI for the assessment of systolic and diastolic from the basal RV free wall was abnormal (S0 = 7.4 cm/s, E0 = 10 cm/s, A0 = 6 cm/s). (D) Pulsed-wave DTI of the septum was within normal limits (S0 = 10.7 cm/s, E0 = 9.5 cm/s, A0 =8.1 cm/s). View video clip online. PULSED-WAVE DTI FOR THE ASSESSMENT OF RV FUNCTION Early investigation of pulsed Doppler DTI velocities of RV contraction (S0 ), relaxation (E0 ,) and atrial (A0 ) velocities was reported by Alam et al.24 Recordings obtained at both the tricuspid and mitral annuli in the apical 4-chamber view were compared. The RV systolic and diastolic DTI velocities were higher compared with those of the left ventricle, with the lowest velocities at the ventricular septum. The early diastolic (E0 ) tricuspid annular velocity was significantly lower, and the late diastolic tricuspid annular velocity was significantly higher in older subjects than in younger subjects, demonstrating an inverse correlation with age. COLOR DTI ASSESSMENT OF RV FUNCTION Kukulski et al27 demonstrated the use of color DTI in measuring regional velocities at the TV annular, basal, mid, and apical regions of the RV free wall in 32 normal subjects. Similar to Alam et al,24 color DTI measurements were obtained in all subjects. The results showed significant variability in S0 velocities in all regions (annular, 9.96 6 1.97 cm/s; basal, 11.03 6 2.06 cm/s; mid, 8.48 6 2.04 cm/s; apical, 4.95 6 1.76 cm/s; P < .001). The RV velocities were consistently higher than those recorded in corresponding LV segments. Interobserver and intraobserver variability was variable between the TV annulus (7%), mid RV (12%), and RV apical (14%) segments. Both studies demonstrated that the use of DTI for the assessment of RV function was a highly feasible and reproducible technique. Normal DTI values are reported in Table 2. DTI ASSESSMENT OF RV DIASTOLIC FUNCTION There has been little published information regarding DTI and RV diastolic function. One study evaluated pulsed-wave DTI measurements of E0 corrected for the TVearly filling velocity (E/E0 ) to estimate RV filling pressures compared with invasive hemodynamics.28 The TV E/E0 ratio was correlated with right atrial pressure (r = 0.75), but with a standard deviation of difference of 4 mm Hg. A separate study reported that increased right atrial pressure was associated with shortened IRT, independent of RV end-diastolic pressure.29 Therefore, DTI may be useful for the assessment of RV diastolic function, combined with pulsed-wave Doppler TV inflow, but further investigation is needed. 784 Horton et al Journal of the American Society of Echocardiography July 2009 Figure 11 Prominent ICT and IRT waveforms. (A) A pulsed-wave Doppler sample volume was placed at the PV level (circle) to obtain the peak velocities. Gain was adjusted and filter decreased to identify PV opening (PVO) and PV closure (PVC) demarcations. Measurement from the onset of Q (QRS) to PVO was made (Q to PVO = 95 ms). (B) Pulsed-wave DTI obtained from the RV free wall. There are 2 peaks, with one slightly higher than the other, occurring in the early part of systole as seen on the Doppler display. Measurement of time from onset of Q to the first peak was less than the time to PVO (88 ms), indicating that the highest peak is the ICT, not S0 , and the peak S0 is just afterward (180 ms). (C) Similar to (A), a sample volume was placed at the PV level (circle) in a different patient. Automated PV measurements are made by placing a caliper at the onset of valve opening and closure. (D) Color TDI sample volume was placed at the basal RV free wall (left). To the right are the corresponding waveforms with automatic transfer of the measurements made from (C). To the right of the second dotted line is a peak waveform occurring after PVC. The peak S0 waveform occurs during the ejection period (between dotted lines). Peak DTI velocities noted during the QRS or after PVC do not represent the active myocardial contraction, and relaxation and should not be measured. Table 3 Technical factors that may affect estimation of peak pulsed-wave and color DTI velocities 1. Suboptimal image quality 2. Beam alignment 3. Sample site location 4. Doppler gain 5. Respiration 6. Frame rate (color DTI) 7. Signal-to-noise ratio (color DTI) Limitations of DTI Color DTI is highly dependent on image quality and frame rate in contrast to pulsed-wave DTI. Signal noise can be a problem with either pulsed-wave or color DTI and may influence the accuracy of measurements (Figure 12). As with any Doppler technique, limitations regarding the insonation angle and translational myocardial motion will affect measurements. Technical Tips Basic technical tips that sonographers should use when acquiring Doppler tissue images include the following: (1) the timing of PVopening and closing should be defined to determine RV mechanical systole for measurements of the peak S0 velocity, because the timing of ICT is always shorter than the time from QRS onset to PV opening; (2) in the apical 4-chamber view, the transducer should be repositioned so that the RV free wall is as parallel as possible with the Doppler cursor and sampling site(s); (3) the color sector should be positioned over the right ventricle and the sector width decreased to the maximize color DTI frame rate (ie, $120 frames/s); (4) DTI velocities should be obtained during apnea to minimize translational motion; and (5) $3 beats should be measured and the velocities averaged. SI FOR THE ASSESSMENT OF RV FUNCTION Strain is a measure of deformation in myocardial thickening or shortening and provides additional measurements of myocardial Horton et al 785 Journal of the American Society of Echocardiography Volume 22 Number 7 Figure 12 Difficult-to-measure DTI waveforms. Pulsed-wave (PW) TDI (A) and color TDI (B) waveforms obtained in the same patient. (A) Increased spectral broadening and artifact creating two peaks. (B) Noisy waveforms that are difficult to measure. Figure 13 Strain calculation from the radial (short) axis. The wall thickness increased from 10 mm at end-diastole to 14 mm at end-systole. Therefore, the 4-mm increase in wall thickness accounts for the 40% strain. mechanical function independent from myocardial velocity. Strain is expressed as the percentage change in length from the original length (Figure 13). Strain is calculated as follows: Figure 14 Color DTI SI with 4 sample volumes placed over the RV free wall (top left) in a patient with normal RV function. Peak systolic RV strains occur at or near PV closure (PVC) and are displayed below the Doppler baseline (arrow). PVO, PV opening. ðL1 L2 Þ=L2 ¼ DL=L2 ; where L1 is the instantaneous myocardial length, L2 is the original myocardial length, and DL is the absolute change in myocardial length. SI is not significantly affected by translational cardiac motion and therefore offers an advantage compared with DTI velocity for evaluation of myocardial function. using color DTI SI have been limited to the apical 4-chamber view and therefore measures of longitudinal strain only. However, longitudinal strain is 1 of 3 vectors of myocardial deformation. Radial thickening or circumferential shortening measures must be determined in short-axis or transverse planes and remain a research area that requires further study. COLOR DTI SI TWO-DIMENSIONAL SPECKLE SI Color DTI is used to measure strain and strain rate in multiple RV myocardial segments (Figure 14). Color DTI SI has been compared with CMR SI, demonstrating a good correlation, and normal valuesfor the right and left ventricles have been published (see Table 2).30-33 Technical issues regarding the angle of acquisition, signal-to-noise ratio, frame rate, and image quality affect the accuracy and reproducibility of strain tracings. For the right ventricle, current applications A recent development in echocardiography based on ultrasonic backscatter for tracking the ‘‘speckle pattern’’ of myocardial deformation is now being investigated (Figure 15, Video 3). This technique is less dependent on frame rate and angle, offering potential measurement of RV strain in both long-axis and short-axis planes (all 3 vectors of myocardial deformation). Excellent correlation between 2D speckle strain and CMR SI for the left and right ventricles has been reported.34-39 786 Horton et al Journal of the American Society of Echocardiography July 2009 Figure 15 Apical 4-chamber view with 2D speckle imaging of the LV septum and RV free wall in a normal older patient. The images display longitudinal velocity (A), strain (B), strain rate (SR) (C), and displacement (D) curves. A0 , Late diastolic waveform; AR, apical right ventricle; AS, apical septum; BR, basal right ventricle; BS, basal septum; E0 , early diastolic waveform; MR, mid right ventricle; View video clip online. MS, mid septum; S0 , systolic waveform. Table 4 Comparison of DTI SI and 2D speckle SI DTI Angle dependent Dependent on 2D image quality Frame rate dependent (color flow imaging) Apical views only 2D speckle tracking Not angle dependent Less dependent on 2D image quality Less frame rate dependent Apical and cross-sectional views A recent study compared measurements of strain, strain rate, velocity, and displacement in patients with RV dysfunction, athletes, and control subjects using color DTI and 2D speckle SI.39 Both strain techniques yielded 93% technical feasibility, which was in line with previous reports from Alam et al24 and Kukulski et al27 for the assessment of DTI. Interobserver and intraobserver variability was similar between methods. Two-dimensional speckle SI for the assessment of RV function is accurate and highly feasible. A comparison of results of 2D speckle SI and color DTI SI is presented in Table 4. Although CMR SI is considered the ‘‘gold standard’’ for quantifying RV function,30 there are significant limitations that have prevented its widespread application. Limitations include portability, the availability of suitable scanners, and its inability to be performed on patients with pacemakers and prosthetic valves. Technical Tips Color DTI peak systolic longitudinal strain occurs normally at or near end-systole (end of the T wave on ECG) and is negative and displayed below the Doppler baseline. To determine peak strain, the following procedure is undertaken: (1) The onset of QRS to PV opening and closure is measured from spectral pulsed-wave Doppler. Some ultrasound systems permit automatic entry of the measurement from time to onset of QRS to PV opening and closure that can be directly transferred to the strain display (Figure 14). (2) The transducer should be positioned in the apical 4-chamber view, with the RV free wall visualized and as parallel as possible to the Doppler interrogation. (3) The color sector should be positioned over the right ventricle and the sector width decreased to maximize color frame rate (>120 Hz). (4) The color Doppler tissue image should be obtained during apnea to minimize translational motion. In severe disease states, peak strains are reduced, and the time to peak may be shortened or prolonged, occurring well after PV closure. This abnormality is consistent with ‘‘postsystolic’’ shortening, and both clinical and structural data should be considered. For 2D speckle SI, different ultrasound Horton et al 787 Journal of the American Society of Echocardiography Volume 22 Number 7 Figure 16 Biplane imaging of the right ventricle using 3D matrixarray transducer obtained from an off-axis apical window. The orthogonal (A) and transverse (B) planes intersect at 90 (top). Both the rotation and elevation of the planes can be manipulated by the sonographer to enhance the imaging from nontraditional angles. View video clip online. Figure 17 Transthoracic 3D matrix image from the apical 4 chamber view (A). Transesophageal 3D (MTEE) of the RV demonstrates excellent detail of trebeculations and tricuspid apparatus (B). The coronary sinus (CS) is easily identified in the View view clip online. right atrial septal region. full-volume data sets derived from either a single capture or successive narrow-angle volumes, which are digitally reconstructed or ‘‘stitched’’ together; and (4) multiplanar or 2D cut-plane views that are reconstructed from a full-volume data set. platforms require different settings, and no overall consensus has been established. Two-dimensional frame rates between 40 and 80 Hz appear to be adequate for accurate speckle tracking,35-37 but further investigation is needed. THREE-DIMENSIONAL BIPLANE IMAGING WITH ORTHOGONAL ANGLE STEERING THREE-DIMENSIONAL AND FOUR-DIMENSIONAL IMAGING OF THE RV FUNCTION An immediate advantage of real-time 3D biplane or triplane imaging is the ability to visualize simultaneous orthogonal 2D imaging planes from traditional transducer acoustic windows. Using steerable imaging, sonographers can immediately visualize short-axis and oblique angles of RV structure and wall motion that are technically challenging using traditional imaging techniques (Figure 16, Video 4). Echocardiographic assessment of the right ventricle has been advanced with the use of unique three-dimensional (3D) echocardiography cardiac ultrasound imaging transducers combined with enhanced 4-dimensional (4D) software applications. The use of 3D has been validated for the measurement of RV volumes, EF, and stroke volume and compares favorably with CMR imaging.4045 Recent publications report the use of 3D for pathologies including RV cardiomyopathies, dysplasia, and calculation of regurgitant volumes, and normal values for adults have been published (Table 2).45-50 This section focuses on advancements in the use of 3D echocardiography for measuring RV dimensions and function, as well as the technical considerations of image acquisition and optimization. TECHNICAL ASPECTS OF 3D IMAGING The 3D matrix-array transducer is constructed with orthogonally intersected dense array beam formers that enable the capture of small 3D volumes of data, or ‘‘voxels.’’ A voxel represents the cube of a conventional 2D pixel. Newer ultrasound systems with this capability yield dynamic (ie, real-time) 3D renditions or full-volume images with voxel rates ranging from 20 to 60 Hz that are comparable with conventional 2D frame rates. A full-volume 3D data set can be acquired in real time, reconstructed, and analyzed immediately with various on-cart or offline methods. At present, the primary applications for using 3D and 4D imaging include (1) real-time biplane or triplane imaging with a steerable orthogonal plane; (2) real-time or live narrow-angle imaging for visualizing structure and function; (3) REAL-TIME 3D NARROW-ANGLE IMAGING An optimal approach for viewing RV structural abnormalities is using the real-time or live imaging application of the 3D transducer. Because aperture depth (elevation) is significantly greater than 2D, enhanced imaging of the RV structure and RVOT can be performed. Sonographers can maximize spatial and temporal resolution using choices in penetration depth and scan line density. Postprocessing software tools enhance brightness, smoothing, compression, and tissue gain to improve the diagnostic value of the images. Further advances using matrix-array transesophageal 3D transducers have enabled higher resolution images of RV anatomy that will influence diagnostic capabilities in the future (Figure 17, Videos 5 and 6). THREE-DIMENSIONAL MULTIPLANE RECONSTRUCTION FROM FULL VOLUMES A less used but important technique is the use of 3D and 4D data sets that may be cropped or sliced into multiple 2D planes (C-mode) and analyzed using on-cart or offline software for the display of coronal (4-chamber), sagittal (2-chamber), and transverse (short-axis) planes (Figure 18, Video 7). Multiplanar reconstruction (MPR) provides a rapid method to create multiple, simultaneous 2D views of the right ventricle that can be useful for direct ‘‘en face’’ planimetry of diameters and areas as well as evaluation of RV structural and physiological 788 Horton et al Journal of the American Society of Echocardiography July 2009 Figure 18 MPR derived from a single 3D full-volume acquisition of the right ventricle. The 3 orthogonal planes are cropped and displayed simultaneously: (A) coronal plane, (B) sagittal plane, (C) transverse plane. From the 3 planes, several measurements can be View video clip online. made to evaluate RV size, which was not previously available from 2D imaging. SAX, Short axis. abnormalities. MPR from full-volume data sets is common in the use of CMR imaging and computed tomographic techniques.45 The MPR can be performed in a limitless fashion to determine the desired cut planes to view within the cardiac chambers. or biplane locking function fixes the longitudinal planes from the original placement, allowing for discrete dynamic 2D viewing while rotating on a centered basal to apical axis. Technical Tips THREE-DIMENSIONAL AND FOUR-DIMENSIONAL VOLUMETRIC ANALYSIS OF THE RIGHT VENTRICLE Measurements of the right ventricle from MPR can be performed as follows: (1) Place two longitudinal orthogonal planes from the center of the TV annulus and then tilt the planes to the true RV apex at the septal junction with the left ventricle. The corrected 90 orthogonal alignment allows for the construction of a third transverse plane across the orifice or chamber to measure accurate direct planimetry of en face anatomic dimensions such as the RVOT. (2) An orthogonal Published studies have reported excellent correlation between 3D imaging and CMR imaging for the analysis of volumes and EF in both children and adults.41,45,51 Gopal et al45 obtained RV end-systolic, end-diastolic, stroke volume, and EF by means of 2D and 3D imaging and compared them with CMR imaging in 71 healthy Journal of the American Society of Echocardiography Volume 22 Number 7 Horton et al 789 Figure 19 (A) Graphic demonstrating the 5 cut-plane images (sagittal base, mid, and apex; apical 4-chamber; coronal) used to trace 3D RV morphology. (B) After the RV end-diastolic volume (EDV) and end-systolic volume (ESV) are automatically traced in the 5 planes, software-enhanced analysis is performed, resulting in a moving 3D model that displays volumes, EF, and stroke volume (SV). View video clip online. ability of 3D to include important volumes contributed by the RV inflow tract and the RVOT, which may appear to be discontinuous (ie, missing information) even when viewed from a short-axis orientation by 2D imaging. Recent advancements in 3D echocardiography may overcome previous limitations and permit the accurate calculation of RV volume and EF with semiautomated border detection and dynamic volumetric analysis capabilities. Current RV analysis software has a step-bystep workflow that guides sonographers in identifying the center of the TV, mitral valve, and RV apex. The software then divides the RV into the traditional diastolic and systolic cut planes that include the RVOT volume. Volumetric contribution from the RVOT is a critical component in determining accurate systolic and diastolic RV volumes. The RV end-diastolic and end-systolic borders are traced in the coronal, sagittal, and transverse planes, permitting analysis of wall motion throughout the cardiac cycle. Derived data include RV end-diastolic volume, end-systolic volume, stroke volume, and EF (Figure 19, Video 8). Full-volume 3D and 4D data sets may be archived and postprocessed in a limitless fashion, offering capabilities for retrospective analysis and comparison when serial examinations of the right ventricle are performed. Figure 20 Stitching artifact in a 3D transverse (short-axis) cutplane image. A distinct horizontal line is seen dissecting the full volume (arrows), indicating a significant spatial stitching artifact caused from respiration during acquisition. Stitching artifact is best assessed from the transverse plane in volumes captured from the apex because the beam array on subvolumes (4-7 per full volume) are directed from apex to base, then stitched from an automatic horizontal sweep across the chamber. Stitching artifact renders full volumes nondiagnostic, and the acquisition View video clip online. should be repeated. individuals.45 Data measured by 3D showed better correlation than 2D with CMR imaging by the methods of apical rotation and disc summation (P < .001). This was thought to be due to the enhanced Technical Tips Certain conditions present difficulty in obtaining quality multicycle volumetric data sets, including a patient’s inability to perform sufficient apnea, abnormal cardiac rhythm, or other compliance issues. In such situations, real-time biplane or triplane imaging can be an excellent backup approach. Three-dimensional and 4D matrix-array transducers are generally 2 to 3 times larger than conventional 2D transducers. This may offer a challenge for sonographers with smaller hands. Use of the second hand to steady the probe position can be helpful, especially in conjunction with an accessory foot pedal or voice command, to acquire the images. Because the larger probe possesses an incrementally larger ‘‘footprint,’’ there may be an increased degree of artifact from costal shadowing. However, 3D transducers 790 Horton et al Journal of the American Society of Echocardiography July 2009 Table 5 Stepwise approach for 3D and 4D full-volume acquisition Step 1 2 3 4 5 6 7 8 9 10 Process Observe electrocardiogram for regular rhythm; adjust for upright R wave Position patient comfortably and instruct on breathing maneuvers Determine optimal acoustic window for full-volume image Check initial 2D reference image and use TE image balance filter application if available, or use TGC Adjust TGC/lateral gain compensation for final balance from near field to maximum depth Maintain stable transducer scanning position View reference orthogonal/transverse planes to determine left ventricle (volume) is in 3D sector Set preacquisition full-volume density to highest level and voxel rate Instruct patient to slowly inhale and exhale to determine best part of respiratory cycle for optimal image acquisition Have patient perform breath arrest (without taking a deep breath) and acquire images Pitfall Ectopy, atrial fibrillation, low voltage Solution Poor compliance, inadequate apnea Reposition electrodes; use timed based triggering based on average heart rate Decrease number of acquired cycles May require unconventional (ie, lateral/apical) acoustic windows Balance image (TE, TGC) before obtaining best 2D reference for 3D acquisition Obtain window that encompasses right ventricle with best resolution Optimize acoustic window and have patient perform apnea before balancing Apical or near field overgained Decrease TGC or move focal zone region to central region of interest Moving hand will change acoustic resolution and negate steps 3-5 Only part of ROI will be in final volume for analysis/interrogation Repeat steps 3-5 Higher density decreases volume width and elevation Go to next lowest density to ensure ROI is completely within volume Respiratory-induced cardiac motion will affect quality and spatial resolution Rehearse before acquiring full volume Patient moves or breathes; stitching artifact noted in volumes Repeat step 10 or reposition patient and retry; attempt real-time image acquisition Rotate transducer slowly or readjust scanning position ROI, Region of interest; TE, tissue equalization; TGC, time gain compensation. have more elements (>2500) that ultimately will acquire a greater depth and number of returning echoes, albeit with some loss of spatial resolution due to the nature of the transducer architecture. THREE-DIMENSIONAL ACQUISITION LIMITATIONS The number of cardiac cycles required when obtaining a full-volume dataset (1-7) with or without an electrocardiographic tracing (for R-R tracking) will vary as according to ultrasound machine configuration and desired resolution quality for a particular diagnostic application. In general, increasing the number of cycles will increase scan line density and voxel rate, improving spatial and temporal resolution. Conversely, the requirement for more cardiac cycles and longer capture time introduce the possibility of ‘‘stitching’’ artifact from the reconstructed volume (Figure 20, Video 9). Patients with atrial fibrillation, sinus arrhythmia, or frequent ventricular extra-systoles are more difficult to accurately evaluate because of variance in the R-R timing interval. Even in the use of single-cycle full-volume capture, R-R variance on ECG will affect accurate measurement of global volume displacement when comparing one beat with the next. In situations in which a quality electrocardiographic tracing is difficult to obtain, the preset ‘‘time’’ interval (2-8 seconds) for a full-volume capture may be used. However, the same challenges during acquisition are present, and other echocardiography-based methods may serve as better surrogates for measuring RV function. The scan line density architecture of current 3D matrix transducers is inherently lower compared with conventional 2D transducers and may produce some loss of spatial and temporal resolution when used in 2D or biplane mode. A key advantage of a full-volume data set of the right ventricle is the ability to acquire from one of any traditional parasternal, apical, or subcostal views. In fact, nontraditional angles between parasternal and apical views are often useful for the evaluation of RV structure and function. Most technical pitfalls can be successfully overcome with an acquisition protocol (Table 5). As 3D and 4D transducer architecture and software-driven capabilities continues to advance, 3D echocardiography will become an increasingly routine method available for the assessment of RV anatomy and function. SUMMARY The assessment of RV function by echocardiography is an area that is undergoing much research, as the development and implementation of new modalities are now readily available. Sonographers should become familiar with both traditional and newer, quantitative techniques such as 3D, DTI, and SI for more comprehensive assessments of RV function. Journal of the American Society of Echocardiography Volume 22 Number 7 Supplementary data Supplementary data associated with this article can be found in the online version, at doi:10.1016/j.echo.2009.04.027 REFERENCES 1. Matthews JC, Dardas TF, Dorsch MP, Aaronson KD. Right-sided heart failure: diagnosis and treatment strategies. 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