In clinical practice, visual assessment is performed to gauge RV size relative to that of the LV. The advantages are its simplicity and avoidance of measurement variability. Normally the RV is only two-thirds the size of the LV in the apical four-chamber view, the LV forms the apex of the heart, and the LV is round in short axis views throughout the cardiac cycle. Deviations from this pattern may indicate RV dilatation but careful examination of multiple views is recommended for confirmation of the diagnosis because the apparent size of the RV varies with the angle of the plane (Fig. 10.10) [3]. In the presence of LV dilatation the RV should be compared to additional anatomic landmarks.

Much research has gone into attempting to find a method for quantifying RV volume. These efforts have been frustrated by the complex shape of the RV. The LV can be compared to an ellipsoid of revolution not only in normal hearts but also in patients with volume or pressure overload (Fig. 10.4). This uniformity of shape enables accurate measurement of its volume from a single view. In contrast, the RV has resisted easy comparison to a geometric reference model. The models that have been tried fall into three types. Both the multiple slice and area–length methods were originally applied to contours traced from biplane contrast ventriculograms. The third type utilizes the formula V = AL, where A is the area in one view and L spans the length of the RV in the other view; this formula computes the volumes of numerous geometric figures ranging from a prism to a crescent [11, 12]. However the subcostal views that are required may be obtainable in only 52 % of children older than 5 years [13].

Other limitations of 2D echocardiography for RV volume quantification are difficulty in locating and acquiring views that yield the maximal area and long axis length measurements, and RV remodeling in response to the hemodynamic overload. As a consequence of the shape change, a given model may better fit diseased hearts than normal subjects, resulting in variable accuracy. For example, the observation that error in RV volume determination by both ellipsoidal approximation and multiple slice methods was significantly higher in normal subjects compared to patients with congenital heart disease [13] may be attributable to RV remodeling to a more ellipsoid shape in the latter. It is therefore not surprising that RV volume measurement from 2D echocardiograms has proven inaccurate in comparison with magnetic resonance imaging (MRI) [13, 14]. In addition, the dearth of clear anatomic landmarks in the RV reduces reproducibility in volume determination because it is so difficult to locate and image the same anatomical image planes on serial studies. The problem is exacerbated when the RV dilates because this chamber may change position and rotate within the thorax [15]. For a good discussion of 2D echo methods and their limitations the reader is referred to Jiang et al. [16].

Three-dimensional (3D) echocardiography enables accurate analysis of RV volume by avoiding the need to match the RV to a geometric reference figure. Instead the RV is analyzed in its entirety, and even pathologically misshapen ventricles can be measured accurately, even those in congenital heart defects.

Volumetric 3D Echo. Most commonly 3D echocardiography refers to acquisition of a volume of image data using a matrix array transducer. The image data are viewed and the RV endocardial contour is delineated in multiple parallel, evenly spaced planes, the area of each contour is multiplied by the interplane distance, and the products are summed to provide a true multiple slice analysis of volume (Fig. 10.11). Studies have shown excellent accuracy for RV volume measurement from 3D echo image data when compared with MRI or with direct volume measurement [17–20].

The RV is usually “sliced” into short axis views, like the LV. As for MRI or computed tomography, image quality is poorer due to partial volume effects at the first and last slices where the RV wall is nearly tangential to the image plane. As a result, the apex and basal limit of the RV may be difficult to delineate. Some investigators have attempted to solve the problem by using alternate slice orientations [21, 22]. Another approach is to utilize information from orthogonal views to assist in delineating the endocardium, e.g., by tracing the short axis contours with guidance from one or two long axis views [23].

A limitation of current matrix array transducers is that the sector width does not allow imaging of the RV in its entirety in a significant proportion of adult patients within the single apical scan that is most commonly employed to acquire the image data [24]. This disadvantage is particularly present when the RV is enlarged, the very situation where quantification of RV function is important.

The biggest source of variability derives from delineating the endocardium, which is particularly difficult in heavily trabeculated RVs at end systole. One area of previous controversy has been resolved by an MRI study, which recommended tracing the contour outside rather than around the trabeculations to maximize reproducibility (Fig. 10.12) [25]. Another issue is the definition of end systole. Because of the RV’s peristaltic pattern of contraction the timing of minimum chamber area varies from region to region and from slice to slice [26]. One approach is to select the time at which minimum chamber area occurs in the greatest number of views. Another approach is to select this time point from the four-chamber view; application of its systolic interval to the entire RV has been shown to provide a highly accurate measurement of end-systolic volume [27]. Volume analysis by 3D echo is more reproducible than by 2D echo [18].

3D Analysis of Multiple 2D Views. A 3D reconstruction of the RV surface can be generated by analyzing multiple 2D views acquired while tracking the spatial location and orientation of the view planes [28, 29]. The RV endocardial surface is reconstructed after tracing the images, and volume is computed from the 3D surface. An advantage of this approach is the use of freehand scanning, so that views providing optimal image quality are acquired. As for multiple slice analysis of volumetric data sets, multiple views must be traced. Several methods have been validated for 3D reconstruction of the RV from manually traced borders. The method of Jiang et al. was based on deforming a spherical template to fit traced borders (Fig. 10.12) [30]. Buckey et al. swept the RV from a single fixed transducer location in angular increments that defined a series of wedges whose volumes were computed and summed to determine RV volume [31]. The piecewise smooth subdivision surface (PSSS) method fits a model mesh to traced borders (Fig. 10.3) [32]. The PSSS method is the only method shown to reproduce the 3D shape of the LV and RV with anatomical accuracy [33].

Despite these methods’ demonstrated accuracy for measuring RV volume, clinical application has been discouraged by the labor required to trace the RV border in multiple images. In a comparison of accuracy when volume is measured using the multiple slice method from 2 to 16 slices, Chen et al. found 8 slices to be the “optimum choice for accurate and convenient measurement” of mass as well as volume [34]. Since analysis must be performed at both end diastole and end systole, the effort is nearly prohibitive for clinical application. Indeed one author opined that an “easily applicable, real-time, three-dimensional assessment of right ventricular volume is the Holy Grail of cardiographic assessment” [35].

Current Commercial 3D Echo Products for RV Analysis. Development of methods for automatically delineating the RV endocardial contour was slowed behind that of the LV by the heavier trabeculation of the RV compared to the LV, and by the diverse shape abnormalities adopted as the RV remodels in response to hemodynamic overload. Tomtec Imaging Systems (Unterschleissheim, Germany) markets a product that employs semiautomated analysis of volumetric 3D echo data sets (Fig. 10.13); its accuracy and reproducibility have been extensively validated by comparison with MRI [17, 18, 20, 24].

An alternative approach to reducing the workload of manual tracing is to utilize knowledge of the expected shape of the RV and of the range of shapes that it can adopt in disease processes. The method marketed by VentriPoint, Inc. (Seattle, WA) generates PSSS surface reconstructions from user-entered points at anatomic landmarks (Fig. 10.14) and does not require whole borders be traced. Its accuracy has been verified by comparison with MRI [36, 37].

As the RV tolerates badly a long-standing increased afterload, assessing pulmonary pressures and their early changes is of great importance. By using continuous wave Doppler technique to measure the peak retrograde pressure drop across the tricuspid valve (tricuspid regurgitation velocity), applying the modified Bernoulli equation, and adding right atrial pressure (RAP), peak systolic pulmonary artery pressure (sPAP) can be estimated. A multiview approach should be used to secure the clearest tricuspid regurgitation velocity profile (Fig. 10.20).

Although transtricuspid regurgitation peak gradient is currently the most accurate measure of PA systolic pressure it has its limitations. It tends to underestimate the severity of PH in patients [62] with elevated RAP, e.g., due to a stiff right ventricle and raised end-diastolic pressure [63]. Also, it tends to underestimate the PA pressure in patients with significant tricuspid regurgitation, even in the absence of obvious organic tricuspid valve disease. Finally, the transtricuspid pressure drop by continuous wave Doppler can be accurately recorded in approximately 50–70 % of patients, hence the need for an alternative similarly accurate marker for PH assessment (Fig. 10.21) [64]. In the remaining cases the pulmonary regurgitant velocity curve can be useful in measuring the early and late diastolic pressure drops that reflect the mean and end-diastolic PA pressures (Fig. 10.22) [65].

Estimation of RAP is an ongoing topic of discussion and a number of measures [3] as well as a fixed value of 7 or 10 mmHg in patients without right heart failure have been proposed [66, 67]. Inferior vena cava diameter and collapsibility with inspiration have also been found to correlate with RAP and are probably the most commonly used [68], but have limited value in the presence of mechanical ventilation or hypovolemia [69]. The ratio of E from tricuspid flow to e′ from RV free wall (E/e′) using tissue Doppler imaging (TDI) can also be used to estimate the RAP.

Pulmonary artery acceleration time (PAcT) has been shown to be related to both pulmonary pressures and pulmonary vascular resistance (PVR), and a cutoff value of less than 90 ms identifies patients having a PVR more than 3 Wood units with high sensitivity and specificity (Fig. 10.23) [70]. However PAcT is less reliable at higher heart rates and not useful for detecting an optimal flow signal when the outflow tract is dilated.

Furthermore, a prolonged isovolume relaxation time (IVRT) from pulsed TDI (>75 ms corrected for heart rate) accurately identified patients with sPAP > 40 mmHg, a marker that has proved the best in predicting patients with raised pulmonary artery pressure (Fig. 10.24) [71]. However increased RV IVRT is not specific for PH as it also increases with increased wall thickness in hypertrophic cardiomyopathy and ischemic heart disease [72, 73].

The myocardial performance (or Tei) index is a non-volumetric method using the sum of isovolumic time intervals (relaxation and contraction) in relation to RV ejection time. This index has been shown to be useful in determining both RV function and pulmonary hemodynamics and can be assessed using both conventional Doppler and tissue Doppler [74].

All these methods are complementary in identifying patients with PH.

The next question that should be answered is the cause of the raised PA pressure. The guidelines for diagnosing PH classify it into four levels; with level 4 caused by pre-capillary pathologies and level 1 due to post-capillary hypertension [75]. Pre-capillary PH is defined as a mean PAP ≥ 25 mmHg and pulmonary capillary wedge pressure (PCWP) ≤ 15 mmHg. Post-capillary PAH is defined as mean PAP ≥ 25 mmHg and PCWP >15 mmHg. The pre-capillary PH can be caused by (1) idiopathic forms of pulmonary arterial hypertension, (2) lung diseases with and without hypoxia, (3) collagen vascular diseases, (4) HIV-AIDs, (5) chronic thromboembolism, or (6) unclear or multifactorial reasons, whereas the post-capillary type is caused by various forms of left heart disease and venooclusive pathology. In both types cardiac output at rest can be normal or reduced.

Post–capillary pulmonary hypertension (left heart dysfunction). In post-capillary hypertension, whether due to valve disease or LV dysfunction, RV function may be preserved in patients with mild to moderate disease. It is only when left atrial pressure or PCWP rises significantly, as a result of increased LV stiffness or significant mitral or aortic valve diseases, that RV dysfunction is seen [76, 77]. It may take time for the increased left atrial pressure to affect the pulmonary pressures and for the RV to develop a restrictive filling pattern. This process can easily be determined and followed up closely by Doppler echocardiography [78].

Patients with well-established raised left atrial pressure (restrictive LV filling pattern) usually present with raised RV systolic pressure, assessed by tricuspid regurgitation velocities, with values exceeding 35 mmHg but rarely as high as in pre-capillary PH [77, 79]. In such patients, long-standing post-capillary PH may result in irreversibly raised pulmonary pressure but also increased PVR and stiff pulmonary circulation, defined as reactive or combined pre- and post capillary PH [80, 81].

Doubling RV afterload (from 25 to 50 mmHg) has been shown to reduce its EF by approximately 10 %. The RV can tolerate even moderate degrees of PH but eventually the tricuspid annulus dilates and secondary tricuspid regurgitation develops which itself, if significant, adds to the clinical deterioration by further decreasing RV stroke volume and increasing diastolic pressures and fluid retention.

Pre–capillary pulmonary hypertension (pulmonary vascular disease). The most common cause of RV dysfunction in this scenario is chronic obstructive pulmonary disease (COPD, see Chap. 18). Long-standing COPD may result in various degrees of RV hypertrophy with systolic and diastolic dysfunction, but it rarely causes PH at rest [82]. Systemic sclerosis (scleroderma) is another parenchymal or pulmonary arterial venous disease that causes PAH and LV and RV subendocardial fibrosis and dysfunction [83]. Severe cases may present with significant PH associated with poor clinical outcome [84]. Finally, other parenchymal fibrotic diseases such as cystic fibrosis may also involve the RV myocardium and cause significant systolic and diastolic dysfunction even in the absence of PH [85]. Patients with end-stage cystic fibrosis may present with a picture resembling cardiac tamponade as a result of the increased intrathoracic pressure. Although RV function in most lung diseases may appear to be normal at rest, RV function at fast heart rates needs to be determined.

The most common pulmonary vascular disease that affects the RV is pulmonary embolism which represents an acute increase in afterload. As for the left heart, acute changes in the pulmonary circulation at any level are poorly tolerated. A small pulmonary embolism may be compensated for but a massive one can be fatal [86] (see Chap. 9). The RV systolic pressure will acutely increase, its cavity dilates, and systolic function deteriorates rapidly [87].

In addition to the investigations mentioned above, assessment of PVR is necessary when PH is suspected [88, 89]. A number of equations have been developed over the years for estimating PVR (Table 10.1) with varying sensitivities and specificities.