An Evidence-Based Echocardiographic Image Acquisition Protocol for Evaluating Right Ventricular Function

Summary

The present protocol proposes and describes an evidence-based image acquisition sequence for multi-parametric assessment of right ventricular function.

Abstract

A major risk factor for morbidity and mortality in critical illness is the presence of right ventricular dysfunction (RVD). However, characterizing and grading the severity of RVD remains highly subjective, with significant inter-operator and intra-operator variability and the potential for the inappropriate treatment of patients. To address these issues, this study aimed to synthesize multiple echocardiographic parameters, which have been demonstrated to affect clinical outcomes, into a framework for the comprehensive evaluation of RVD. During the study's first phase, a scoping review of the literature was conducted and identified four routinely obtained echocardiographic findings that had been validated as part of multi-parametric scoring methods for scoring the severity RVD: (1) RV systolic dysfunction; (2) RV dilation; (3) RV-PA uncoupling; and (4) interventricular septal flattening. In the second phase described in the present manuscript, these four echocardiographic findings were operationalized into an image acquisition protocol and integrated into a proposed RVD scoring system compatible with the constraints of either point-of-care or consultative ultrasound workflows.

Introduction

In a wide range of clinical contexts, cardiovascular mortality and morbidity are strongly associated with right ventricular dysfunction (RVD)^1,2,3,4,5. However, grading the severity of RVD remains highly subjective because the crescentic anatomic shape and thin walls of the RV make an accurate evaluation of volume and ejection fraction challenging using standard two-dimensional assessment⁴. Recognizing these difficulties, the most recent guidelines on RV assessment from the American Society of Echocardiography (ASE) suggest numerical cutoffs that can help grade the severity of dysfunction (i.e., normal, mild, moderate, or severe) of individual RV parameters⁶. However, the guidelines do not offer guidance on how to synthesize these parameters into a global assessment of RVD.

In the absence of guidance on how to synthesize various RV echocardiographic parameters into a global score, clinicians tasked with cardiac ultrasound image interpretation are forced to rely either on their subjective assessment of the RV or on single parameters to sort RVD into grades of dysfunction⁷. For example, a 2019 global survey of over a thousand echocardiographers from 109 countries found that the three most used methods for assessing RV function were: (1) visual estimation (72)%); (2) tricuspid annular plane systolic excursion (TAPSE) (69%); and (3) RV S' (31%)⁸. In contrast, more advanced tools were rarely used, even in high-income countries: RV fractional area change (RV FAC; 9%), strain (3%), and 3D (1%). Further, 23% of echocardiographers used visual estimation alone.

The use of qualitative and single-parameter methods of RV assessment naturally leads to inaccuracy. For instance, Ling et al. conducted a quality control study comparing the interpretations of fifteen expert transthoracic echocardiographers to a gold standard of cardiac MRI for grading the severity of RV systolic dysfunction⁹. The authors found that the participating echocardiographers identified over 95% of cases of severe RV dilation. However, the echocardiographers' accuracy declined for most other RV states. For example, when attempting to identify RV size, the echocardiographers identified fewer than 60% of cases of mild dilation and fewer than 40% of cases of moderate dilation. Similarly, while the echocardiographers identified approximately 80% of cases of both normal and severely depressed RV systolic function, they identified fewer than 60% of cases of mild or moderate RVD.

This inherent subjectivity of real-world echocardiographic grading of the severity of RVD is not widely appreciated by clinicians tasked with caring for patients with RV disease. Many clinicians are unaware that RVD severity grading is often determined by subjective interpretation. As a result, clinicians receiving echocardiographic data are likely to place more confidence in the precision of RVD scoring than is appropriate. Further, appropriate treatment of patients with RVD is likely to be hampered in the absence of precise and consistent ways of identifying and monitoring the severity of disease¹⁰.

Notably, outside of conventional echocardiography (echo), there are tools under development to help grade the severity of RVD. However, each of these remains partly experimental or has significant limitations. For instance, cardiac MRI can be used for grading RVD severity, but is expensive, requires a patient to be stable enough for lengthy transport and scanner time, and is not universally available^9,11. Similarly, some emerging echocardiographic adjuncts, such as speckle-tracking strain and 3-dimensional (3-D) ultrasound, have been studied for the purposes of grading RV systolic dysfunction. However, these tools require extensive training to be used properly, extensive post-processing to be performed, and the use of special hardware or software that is not universally available, especially for point-of-care use¹¹.

As a result, there remains a major unmet need to develop a simple, multi-parametric echocardiographic method to evaluate and grade global RVD. To address this problem, a two-part project was conducted to develop an evidence-based image acquisition protocol for the evaluation of RVD. In the first phase¹², a scoping review of the literature was performed^12,13 and identified three existing, prospectively-validated, multi-parametric RVD scoring tools that can be performed using routinely obtained transthoracic echocardiographic measurements (e.g., not requiring strain or 3-dimensional ultrasound or cumbersome multi-step measurements that are outside the feasibility of routine echo)^3,4,14,15. These three studies validated, in total, four RV findings as each having independent ability to predict short-term (≤30 day) mortality: (1) RV systolic dysfunction; (2) RV dilation; (3) RV-PA uncoupling; and (4) interventricular septal flattening. In the second phase of the project (presented in the current manuscript), the four RV echocardiographic parameters were (1) operationalized into an image acquisition sequence that can be performed using routine echo equipment (i.e., B-mode, M-Mode, color and spectral Doppler) and a wide range of real-world settings, where patient factors frequently permit adequate visualization in only 1-2 sonographic windows (i.e. parasternal, apical, and/or subcostal) and (2) synthesized into a proposed RV assessment framework.

Protocol

All procedures performed in studies involving human participants were in accordance with the ethical standards of the Duke University Health System institutional research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards¹⁶. All images/clips were obtained from a de-identified internal library of educational ultrasound clips, so written consent was not possible (all images/clips in this library are fully de-identified with no way of identifying or contacting individual patients). This protocol applies to adult patients in a variety of clinical settings, including, but not limited to, perioperative, intensive, and emergency care. The only strict exclusion criterion is the inability to obtain any adequate transthoracic/transabdominal cardiac sonographic window. The equipment and software used are listed in the Table of Materials.

1. Patient positioning

1. For parasternal or apical views: if possible, position the patient in left lateral decubitus with left arm abducted and left hand behind the patient's head. If the patient cannot tolerate this position, place the patient supine with their left arm abducted away from their side as much as tolerated.
2. For subcostal views, position the patient supine with knees bent and arms at their sides.

2. Probe and mode

1. Select the sector array/sector arc (phased-array) transducer^17,18,19,20. Select the cardiac preset. Activate ECG gating (if available).

3. Preview sonographic windows

1. Preview parasternal, apical, and subcostal cardiac windows²¹.
   1. If all three windows provide adequate image quality of the heart, perform only steps 4.2.1, 4.2.3, 4.4, 5.1, 6.2 and 6.3.4.
   2. If the heart is only adequately visualized in 1-2 of these windows, perform all steps listed below for the adequate sonographic window(s).
   3. If any view is not obtainable, skip all steps where that view is requested.

4. Parasternal window

1. Parasternal long-axis view
   1. Obtain parasternal long-axis (PLAX) view²¹. Measure RVOT end-diastolic dimension (PLAX RVOT EDD) (Figure 1).
   2. Click Acquire (or equivalent).
2. Right ventricular inflow view
   1. Obtain RV inflow view (RV-I view) (Figure 2A)²¹.
   2. Anterior Tricuspid Annular Plane Systolic Excursion (A-TAPSE)
      1. Activate Zoom function and position Zoom box so that it is centered on the anterior tricuspid annulus (tricuspid annulus on right side of screen in RV inflow view) (Figure 2).
      2. Perform anterior A-TAPSE measurement (Figure 2B).
   3. Tricuspid regurgitation peak gradient measurement
      1. Place the color Doppler box over the tricuspid valve and right atrium (Figure 3A).
      2. If tricuspid regurgitation is present:
         1. Move the cursor over the center of the regurgitant jet and activate continuous-wave Doppler (CWD).
         2. When the full screen of CWD tracing materializes, click on Freeze (or equivalent).
         3. Use caliper tool (or equivalent) to measure the tricuspid regurgitation peak pressure gradient (Figure 3B).
         4. Click on Acquire (or equivalent).
3. Parasternal aortic-valve short-axis (aka RV inflow-outflow) view
   1. Obtain parasternal short-axis (PSAX) view at the level of the aortic valve²¹.
      1. Measure RVEDD at the mid-section of the RV (PSAX RVEDD) (Figure 4A).
      2. Click on Acquire (or equivalent).
      3. Measure RVOT fractional shortening (RVOT FS) (Figure 4B).
      4. Click on Acquire (or equivalent).
4. Parasternal LV mid-papillary (mid-ventricular) short-axis view (PSAX Mid-LV)
   1. Obtain parasternal short-axis view at the mid-papillary (aka mid-ventricular) level of the left ventricle²¹.
   2. Qualitatively assess interventricular septum and categorize it as one of the following: (1) bowing into RV throughout cardiac cycle (normal); (2) flat or bowing into LV for any portion of cardiac cycle (paradoxical septal motion); or (3) indeterminate (Figure 5).

5. Apical window

1. Apical 4-chamber view
   1. Obtain apical 4-chamber (A4C) view²¹.
   2. Freeze image at end-diastole (when RV size appears visually largest).
      1. Qualitatively rate RV/LV end-diastolic area ratio as either ≤2/3 (normal) or >2/3 (abnormal) (Figure 6).
      2. Use caliper tool (or equivalent) to measure and Acquire RV basal diameter (A4C RVBD)⁶ (Figure 7).
      3. Use trace tool (or equivalent) to measure and Acquire RV end-diastolic area (RVEDA), including papillary muscles, trabeculations, and the moderator band⁶ (Figure 8).
      4. Scroll through frozen video clip to find end-systole (when RV size appears visually smallest), use trace tool (or equivalent) to measure RV end-systolic area (RVESA), and click on Acquire (or equivalent)⁶.
      5. Calculate RV FAC as follows⁶: ((RVEDA - RVESA)/RVEDA) * 100.
   3. Unfreeze the image.
   4. Conventional (Lateral) TAPSE (L-TAPSE)
      1. Activate Zoom function and position Zoom box so that it is centered on the lateral tricuspid annulus.
      2. Perform L-TAPSE measurement^6,7,21 (Figure 9).
         NOTE: Since anatomic M-mode is neither offered on many devices used for point-of-care ultrasound nor is it routinely incorporated into transthoracic echocardiography (TTE), it is omitted from this protocol^4,14,15. However, if anatomic M-mode is available on the operator's machine, it could be used at the provider's discretion to maximally align the movement of the tricuspid annulus with the M-mode interrogation beam.

6. Subcostal window

1. Subcostal 4-chamber view
   1. Obtain subcostal 4-chamber (SC4C) view²¹.
   2. Freeze image at end-diastole.
      1. Qualitatively rate RV/LV area rate as either ≤2/3 or >2/3 (Figure 10).
2. IVC short-axis view
   1. Obtain IVC short-axis view^17,22.
   2. Freeze image when IVC appears largest and measure its short- and long-axis diameters to generate a sphericity index (Figure 11)²³.
3. Subcostal RV inflow-outflow / IVC long-axis view
   1. Obtain subcostal RV inflow-outflow / IVC long-axis view²¹.
   2. Subcostal echocardiographic assessment of tricuspid annular kick (SEATAK) measurement
      1. Activate Zoom function and position Zoom box so that it is centered on the anterior tricuspid annulus (Figure 12).
      2. Perform anterior SEATAK measurement (Figure 12)^24,25.
   3. Unfreeze image and perform tricuspid regurgitation assessment (repeat steps 4.2.3.1-4.2.3.2 including sub-steps).
   4. Ask the patient to take a "sniff" and then measure both maximal anterior-to-posterior IVC diameter and collapsibility per ASE guidelines⁷.
4. Subcostal LV mid-papillary short-axis view (SC Mid-LV)
   1. Obtain subcostal short-axis view at the mid-papillary (mid-ventricular) level of the left ventricle²¹.
   2. Repeat step 4.4.2 (qualitative assessment of interventricular septal kinetics).

Results

The resulting protocol assigns a point for each of the following: (1) RV dilation; (2) RV systolic dysfunction; (3) RV-pulmonary artery (PA) uncoupling; and (4) the combination of RV dilation and interventricular pressure equilibration (see definitions for each point below). For ease of recall, the essence of the RVD score can be summarized using the mnemonic "CISS": Coupling, Interventricular Septal Motion, Squeeze, and Size.

Of these four parameters, at least three should be scorable as eith...

Discussion

Significance of the method with respect to alternatives
There exists a large unmet need to add objectivity to assessing and grading RVD. To address this need, a two-phase project was conducted. In the first phase, a scoping review of the literature identified only three published, prospectively-validated, multi-parametric RV severity grading systems that utilize only routinely obtained echocardiographic data. The scoping review further compared these studies to reveal that they overlap significantl...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
CX50	Philips	https://www.philips.com/healthcare/product/HC795076GI/cx50-xmatrix-general-imaging-ultrasound-system
Edge 1	Sonosite	https://www.sonosite.com/products/ultrasound-machines-and-accessories
Epic 7C	Philips	https://www.philips.com/healthcare/product/HC795200C/epiq-7-ultrasound-system-for-cardiology
HS60	Samsung	https://www.samsunghealthcare.com/products/UltrasoundSystem/HS60/General%20Imaging/benefit
Logiq E10	GE	https://www.gehealthcare.com/products/ultrasound/logiq/logiq-e10