The importance of the right ventricle as a cause of perioperative morbidity is being increasingly recognized. Right ventricular (RV) failure is responsible for approximately one fifth of cases of circulatory failure after cardiac surgery and has a higher mortality rate than failure associated with left ventricular (LV) dysfunction.
Although the right-heart structures are anterior in location and therefore less well visualized by the posteriorly placed esophageal probe than the left ventricle, transesophageal echocardiography (TEE) provides valuable information regarding their function.
Anatomy
Normal values for the dimensions and flow patterns of right-heart structures are provided in Appendix 3 .
Right ventricle and atrium
The geometry of the right ventricle is complex and does not conform to any regular shape. It is separated into an inflow tract, consisting of the TV, papillary muscles, chordae tendineae, and chamber walls, and an outflow tract, consisting of the infundibulum. The inflow portion of the right ventricle forms the base of a pyramid, with the three walls formed by the ventricular septum and the anterior and posterior aspects of the RV free wall. A small muscle bundle (the crista supraventricularis) separates the inflow (with trabeculated myocardium) and outflow (with nontrabeculated myocardium) regions of the right ventricle. The moderator band is a large muscle bundle that runs from the septum to the free wall. The ventricular septum bulges into the RV cavity, imparting a crescent shape to the chamber when viewed in short axis. RV wall thickness is approximately half that of the left ventricle.
The RV free wall muscle is supplied by branches of the right coronary artery, apart from a small part of the apical anterior free wall, which is supplied by branches of the left anterior descending coronary artery. In a right-dominant system (80% of individuals), the right coronary artery also supplies the basal and mid-inferoseptal wall of the ventricular septum, with the remainder (the majority) of the septum supplied by branches of the left anterior descending coronary artery. In a left-dominant system, the entire septum (and LV) is supplied by branches of the left main coronary artery (left anterior descending and circumflex coronary arteries) (see Chapter 7 and Figure 7-15 ).
The right atrium lies superior and medial to the right ventricle. It has a triangular appendage that is broad based and trabeculated. The anatomy of the crista terminalis, eustachian valve (or Chiari network), and thebesian valve is described in Chapter 6 . The coronary sinus runs along the posterior atrioventricular groove behind the left atrium and drains into the inferior aspect of the right atrium between the septal leaflet of the TV and the eustachian valve.
Tricuspid valve
The TV consists of three leaflets (the anterior, posterior, and septal). The leaflets are thinner and less individually distinct than those of the mitral valve (MV). The largest is the anterior leaflet. The septal leaflet is usually larger than the posterior leaflet and attaches to the fibrous skeleton of the heart in a slightly more apical position than the anterior mitral leaflet. The anterior leaflet is usually larger than the posterior leaflet.
There are three papillary muscles, each associated with a tricuspid leaflet. The septal papillary muscle is usually small and may be absent. The RV papillary muscles are more variable than those of the left ventricle and therefore less useful as an echocardiographic reference point. Chordae tendineae attach the papillary muscles to the leaflets.
Pulmonary valve and artery
The pulmonary valve (PV) is a trileaflet (anterior, left, and right) semilunar valve, similar in appearance, but oriented perpendicularly to, the AV. The pulmonary leaflets are thinner and the sinuses of Valsalva less prominent than in the AV.
The PA is a short, wide vessel, approximately 5 cm in length. It follows an oblique course, arising superiorly from the PV and then curving posteriorly underneath the aortic arch as it divides into left and right branch PAs.
Physiology and pathophysiology
The function of the right ventricle is to propel deoxygenated blood through the low-impedance pulmonary circulation. The resistance of this circulation is one tenth that of the systemic circulation and requires a perfusion gradient of just 5 mm Hg.
Under normal circumstances, the ventricular septum is functionally a part of the left ventricle; consequently, the free wall contributes most to RV systolic ejection. The thin wall and crescent shape make the right ventricle highly compliant and therefore able to accommodate a large increase in volume with minimal change in end-diastolic pressure. Thus, the primary compensatory mechanism of the right ventricle is dilatation. For this reason, acute (e.g., with exercise) and chronic (e.g., with an ASD) RV volume overload is relatively well tolerated. However, with severe volume overload, functional tricuspid regurgitation develops and the right ventricle loses its crescent shape, becoming ellipsoid like the left ventricle.
The right ventricle is less tolerant of increases in afterload (pressure overload). An acute rise in pulmonary vascular resistance (PVR) (e.g., due to a pulmonary embolus), requiring a mean pulmonary artery pressure of 40 mm Hg to perfuse the pulmonary bed, is beyond the capacity of the right ventricle and results in rapid RV dilatation, failure, and circulatory collapse. Chronic pressure overload (e.g., elevated PVR due to emphysema) is somewhat better tolerated through a combination of ventricular dilatation and hypertrophy.
RV dysfunction can also occur as a consequence of direct myocardial injury, most commonly due to ischemia, infarction, stunning, or contusion.
Echocardiographic examination
The anterior location of the right-heart structures creates difficulties for imaging with TEE. The right ventricle lies in the far field, and image resolution is reduced compared with that of the left ventricle (particularly when using color flow Doppler). The presence of strong reflectors within the left heart (e.g., a calcified AV, or a prosthetic AV or MV) can lead to echo dropout of the right-heart structures. In addition, the right ventricle is commonly imaged in an oblique plane, making assessment of chamber size and wall thickness unreliable. This is a particular problem in the transgastric mid-short-axis view. Despite these limitations, careful imaging using a systematic approach and multiple views yields important information.
To examine the right heart, five standard views must be obtained ( Table 13-1 ):
- •
Midesophageal four-chamber
- •
Midesophageal RV inflow–outflow
- •
Midesophageal bicaval
- •
Transgastric mid-short axis
- •
Transgastric RV inflow
| View | Structure |
|---|---|
| Midesophageal | |
| Four chamber (15°) with image centered on right ventricle | RV free wall, ventricular septum, atrial septum, TV (anterior and septal leaflets) |
| Coronary sinus (0°) | TV (posterior and septal leaflets), coronary sinus |
| RV inflow–outflow (80°) | RV, TV (posterior and anterior leaflets), RVOT, PV |
| AV short axis (40°) | PV, TV |
| AV long axis (130°) | PV |
| Bicaval (110°) | Right atrium, RA appendage, atrial septum, vena cavae, TV |
| Ascending aortic short (0°) and long (90°) axis | Main PA, SVC |
| Upper Esophageal | |
| Aortic arch short axis (90°) | PV, RVOT, main PA |
| Transgastric | |
| Midshort axis with image centered on RV (0°) | RV free wall, ventricular septum |
| Basal short axis with image centered on TV (0°) | En face view of TV |
| RV inflow (90°) | RV free wall, TV, TV subvalvular apparatus |
| RV inflow–outflow (90°) | PV in long axis, main PA, TV, RVOT |
Additional views can also be helpful (see Table 13-1 ), in particular the transgastric RV inflow–outflow view and the upper esophageal aortic arch short-axis view (described later).
There is no standardized nomenclature for the RV free wall, but the terms basal, apical, inferior, anterior, and lateral are used in the guidelines of the American Society of Echocardiography (ASE) and Society of Cardiovascular Anesthesiologists (SCA).
Esophageal views
In the four-chamber view, with the image centered on the right ventricle ( Figure 13-1 ), the basal and apical segments of the RV free wall, the atrial and ventricular septa, and the anterior and septal leaflets of the TV can be seen. Advancing the probe slightly shows the posterior TV leaflet (identified as the coronary sinus comes into view).
The RV inflow–outflow view (see Figure 3-8 ) is used to visualize the inferior free wall, the RVOT, the posterior and anterior TV leaflets, and the PV. In this view, it is usually possible to align a CW Doppler signal through the TV to estimate pulmonary arterial systolic pressure from a jet of tricuspid regurgitation, although it may be necessary to rotate the transducer backward 10 to 20 degrees. Improved visualization of the PV leaflets may be obtained in the AV short- or long-axis views, but identification of individual leaflets may still be difficult—fortunately, this is rarely required.
The bicaval view (see Figure 3-9 ) is useful for examining the vena cavae and atrial septum. The eustachian valve (see Figure 6-2 ) or a Chiari network may be seen adjacent to the inferior vena cava (IVC), and the crista terminalis (see Figure 6-1 ) may be seen adjacent to the superior vena cava (SVC). Turning the probe to the left (anticlockwise) may bring the TV into view at the bottom of the image. This maneuver is useful if adequate alignment of a CW Doppler signal with a jet of tricuspid regurgitation cannot be obtained in other views (described later). From the standard bicaval view, advancing the probe allows inspection of more of the IVC; withdrawing the probe allows inspection of more of the SVC.
The ascending aortic short-axis view (see Figure 3-6 ) may allow visualization of the main PA. Turning the probe to the right (clockwise) may improve visualization of the distal segments of the right PA. The left PA is rarely seen due to interposition of the large airways. The ascending aortic short-axis view also visualizes the SVC in short axis. Centering on the SVC and rotating the sector scan forward to 90 degrees shows the SVC in long axis. This modified view is useful for measuring respiratory variation in SVC diameter with M-mode imaging (see Figure 18-5 ), which can be used for assessing intravascular volume status in ventilated patients (see Chapters 18 and 19 ).
In some patients, the RVOT, PV, and main PA can be visualized in the upper esophageal aortic arch short-axis view ( Figure 13-2 ). If it can be obtained, this view provides good alignment between a Doppler beam and the flow through the RVOT.
Transgastric views
In the transgastric mid-short-axis view, with the image centered on the right ventricle ( Figure 13-3 ), all segments of the free wall can be seen (anterior, lateral, and inferior). The probe may be advanced or withdrawn to inspect the apical or basal segments, respectively. Withdrawing the probe may also provide an en face view of the TV, with the anterior leaflet to the left (in the far field), the posterior leaflet to the left (in the near field), and the septal leaflet to the right of the display. Rotating the transducer forward to approximately 35 degrees may improve alignment with the tricuspid annulus.
The transgastric RV inflow view (see Figure 3-20 ) is useful for evaluating the TV subvalvular apparatus. From the transgastric RV inflow view, rotating the sector scan slightly farther forward, turning the shaft of the probe slightly leftward (clockwise), or both may bring the RVOT, pulmonary vein (PV), and main PA into view. This view may be termed the transgastric RV inflow–outflow view ( Figure 13-4 ); if it can be obtained, it provides good alignment between a Doppler beam and the flow through the RVOT.
Three-dimensional echocardiography
3-D echo allows measurement of RV volume without geometric assumptions of shape. There is good correlation to measurements obtained with magnetic resonance imaging. An adequate imaging window with TTE continues to be a limiting factor, and there is only limited experience with TEE.
Echocardiographic assessment of right ventricular function
Global and regional function
The complex nongeometric shape of the right ventricle makes echocardiographic assessment of RV volume difficult. Furthermore, RV volume changes substantially with changes in preload. A simple method to grade RV volume is to compare the relative sizes of the right ventricle and left ventricle in the midesophageal four-chamber view. The right ventricle can be classified as mildly dilated (enlarged, but RV area < LV area), moderately dilated (RV area = LV area), or severely dilated (RV area > LV area). Oblique imaging can sometimes render this comparative technique misleading. As an alternative, the apex of the heart can be inspected. Normally, the right ventricle extends two thirds of the way to the apex. If the apex includes both the right and the left ventricles, dilatation is moderate; if the right ventricle extends beyond the left ventricle at the apex, dilatation is severe.
The use of ejection fraction to quantify RV systolic function by echocardiography is limited by the problems inherent in measuring RV volume and, with TEE, by the right ventricle lying in the far field. Tracing the RV endocardial border at end systole is difficult because of extensive trabeculations. RV (FAC) using automated border detection from the midesophageal four-chamber view has been described and has shown good agreement with stroke volume. The technique is rarely used in clinical practice.
Tricuspid annular plane systolic excursion
As the right ventricle contracts during systole, it decreases in both its short- and its long-axis dimensions. The magnitude of long-axis shortening of the right ventricle provides a useful measure of global RV systolic function, termed the tricuspid annular plane systolic excursion. This measure can be quantified by calculating the end-diastolic–to–end-systolic fractional shortening of RV length ( Figure 13-5 ) and is normally about 35%. In most patients, the systolic excursion is more than 25 mm. A value below 18 mm predicts poorer survival in patients with pulmonary hypertension. While formal measurement of tricuspid annular plane systolic excursion is rarely done, subjective assessment of the descent of the tricuspid annulus is a useful qualitative guide to global RV systolic function.
Myocardial performance index (Tei index)
The myocardial performance index (MPI) is a method for assessing overall (systolic and diastolic) ventricular function developed by Tei and colleagues. The technique for calculating MPI for the left ventricle is described in Chapter 7 (see Equation 7-12 and Figure 7-9 ). MPI has also been used to assess RV function. A normal MPI for the right ventricle is 0.28 ± 0.04. Deteriorating RV function is associated with an increasing value for the MPI, for the reasons outlined in Chapter 7 . There is reasonable correlation between MPI and pulmonary arterial pressures, and the index can identify early RV dysfunction. The technique is limited by high RA pressure, which reduces the MPI (due to a shortened (IVRT)).
Myocardial velocity using tissue Doppler imaging
Tissue Doppler imaging (TDI) enables measurement of myocardial velocity. Systolic velocity correlates well with ventricular function and is less preload dependent than volume-based assessments. Measurement can be made with either pulse wave (PW) TDI ( Figure 13-6 ), which measures peak velocity, or color-coded TDI, which measures mean velocities (20% lower). An S wave value below 9.7 cm/sec measured with PW TDI by TTE in the RV free wall suggests abnormal RV contractility and may predict early RV dysfunction. TDI during systole is described in more detail in Chapter 7 .
