Imaging the Right Heart: Limitations and Technical Considerations

The Right Ventricle–Focused View

The standard apical four-chamber (A4C) view focuses predominantly on the left ventricle (LV), and consequently portions of the RV may not be visible. To overcome these limitations, the “RV-focused view” should be obtained in all studies interrogating the right heart ( Fig. 29.1 ). This view provides enhanced visualization of the RV free wall and reveals the maximal diameter of the ventricle without foreshortening, thus improving estimation of RV dimensions and reducing interobserver variability of structure. Therefore, the RV-focused view is essential for measuring fractional area change and is recommended for accurate assessment of longitudinal strain. Additionally, its unique angle may allow for better capture of a TR jet or establishment of ASDs or PFOs. ^,

To generate the RV-focused view, the standard A4C view should first be obtained. With the LV apex remaining at the center of the scanning sector, the transducer should be slightly rotated counterclockwise to focus on the RV until the maximal transverse plane is displayed (typically the basal RV diameter); this avoids foreshortening. ^{, , ,} Often, the transducer will require medial or lateral movements to produce this image. ^{, ,} To improve image quality, the frame rate can be increased by reducing sector size. A high-frequency transducer may be of benefit given that the RV is a near-field structure. The RV may also be preferentially viewed with small adjustments in transducer angle and position from the apical two- and three-chamber views, yielding a modified three-chamber view (RA, RV, and RVOT), and a modified two-chamber view (RA and RV), respectively.

Technical Considerations for Other Standard Transthoracic Echocardiography Views

In addition to the RV-focused A4C view, a comprehensive multiplane examination of the right heart also includes the parasternal long-axis (PLAX), RV inflow, and short-axis (PSAX) views; the standard A4C view; and subcostal views. ^, All of these views are essential given the complex geometry of the RV, its poor anatomic reference points, and the inability to image the three anatomical components (inlet, body, and outlet) simultaneously in any single 2D plane. ^, These obstacles create pitfalls in imaging of the RV in “standard views.”

The PLAX view produces views of the proximal RVOT, which may vary based on the rib interspace used for imaging as well as the angulation of the transducer. Excessively oblique positioning may lead to underestimation or overestimation of RVOT size. ^, Furthermore, careful adjustments in the gain may be necessary for ideal visualization. The PSAX view reveals the proximal and distal RVOT (RV outflow) as well as the RA and tricuspid valve (RV inflow). The aortic valve or root should be seen in short axis in the center of the picture, often necessitating movement of the transducer superiorly along the chest wall ( Fig. 29.2 ). Image quality and accuracy in this view are again dependent on transducer angle and position. RVOT dimensions may be inaccurate in patients with chest or spine deformities, and even without these confounders, 2D PSAX views do not typically achieve an accurate morphologic assessment. Moreover, measurements may vary with patient position (RV dimension will be smaller if the patient is supine compared to sitting up at a 30- or 45-degree angle). RV functional assessment is limited in this view as well given the asymmetric nature of RV contraction; contraction by the RV inflow and RV outflow are longitudinal and circumferential, respectively, and are thus perpendicular to one another. ^,

Linear and area measurements of the RV and concurrent functional assessment of the RV in the standard A4C and RV-focused apical four views depend on suitable endocardial definition of the RV free wall ( Fig. 29.3 ). The free wall, however, is usually retrosternal and is thus difficult to visualize. Other confounders of RV size and area include the presence of trabeculations and foreshortening caused by improper transducer positioning. Furthermore, the RV’s crescentic shape, combined with the LV’s twisting contractile motion, frequently results in end-diastolic images and end-systolic images of the RV residing in different planes. Finally, even when using the RV-focused A4C view, if the center of the sector is located over the RV (instead of the LV, as recommended), the RV may appear falsely dilated.

The subcostal view allows for assessment of inferior vena cava (IVC) size and collapsibility and thus right atrial pressures. While the IVC is typically viewed in long axis, changes in its diameter may simply be reflective of movement/translation of the vessel into another plane, and thus a cross-section evaluation may be more appropriate. Filling pressures may be overestimated if the patient is not in the left lateral decubitus position or if the patient is intubated, because IVC collapse in this instance is confounded by positive pressure ventilation. Last, although the subcostal view allows accurate assessment of RV wall thickness caused by perpendicular beam trajectory, caution with measurement is recommended in the presence of epicardial fat ( Fig. 29.4 ).

Overload States

The shape of the RV can vary dramatically with volume loading, with the overall shape becoming more globular and with varying degrees of diastolic flattening of the interventricular septum. Adequate semiquantitative evaluation of the dilated RV size still depends on linear measurements of basal and midcavity RV diameters, as well as RV longitudinal dimension in the RV-focused four-chamber view. However, because the volume-loaded RV becomes apex forming, careful adjustments in the RV-focused view planes are essential to avoid foreshortening. Even with such adjustments, TTE assessment of volume-loaded RV size is significantly less accurate/reproducible than that of normal RVs compared with cardiac magnetic resonance imaging (CMR).

Pressure overload of the RV may manifest with some degree of RV dilatation but predominantly with significant hypertrophy of the ventricular walls. Assessment of RV wall thickness is preferably performed in the subcostal view in the vicinity of the tip of the anterior tricuspid leaflet, with the ultrasound beam directed perpendicular to wall. Hypertrophied trabeculae in the pressure-overloaded RV introduce increased scatter, however, leading to overestimation of the thickness of the nontrabeculated free wall. Use of fundamental imaging with higher-frequency beam focused on the near field is essential in these situations to maximize detail and accuracy ( Fig. 29.5 ).