3 Two-Dimensional and Three-Dimensional Echocardiographic Evaluation of the Right Ventricle
Background
• The right ventricle (RV) originates embryologically from different progenitor cells and different sites than the left ventricle (LV).
Anatomy of the Right Ventricle
• The RV has a circumferential arrangement of myofibers in the subendocardium and longitudinal myofibers in the subendocardium (Fig. 3-1).
• As shown by three-dimensional (3D) study, the infundibular part consists of 25% to 30% of the total right ventricular (RV) volume. The shape of the RV is complex (see Fig. 3-2). In the apical view the RV looks triangular, while in the cross-sectional view it appears crescentic in the normal condition.
• The three parts of the RV are not in the same plane as seen in a 3D echocardiogram from a normal subject (Fig. 3-3). A curved septum is seen in Figure 3-3 because the RV inflow contracts earlier than the infundibulum.
Figure 3-2 Anatomy of the RV, having three separate parts.
(Image on the left from Netter FH, Atlas of Human Anatomy, second edition. Philadelphia, Novartis, 1997; Plate 208.)
Coronary Artery
The coronary artery supply to the RV myocardium is shown in Figure 3-4, and the RV segments are shown in Figure 3-5.
Figure 3-4 Coronary arteries to the RV.
(From Mangion JR. Right ventricular imaging by two-dimensional and three-dimensional echocardiography. Curr Opin Cardiol. 2010;22:423-429.)
Figure 3-5 Segmentation of the RV wall.
(From Mangion JR. Right ventricular imaging by two-dimensional and three-dimensional echocardiography. Curr Opin Cardiol. 2010;22:423-429.)
Coronary flow to the RV is primarily from the right coronary artery (RCA) (dominant in 80% of the population) (Fig. 3-5):
• Posterior descending coronary artery (PDA) to the posterior wall of the RV and posterior interventricular septum (the posterior interventricular septum will be supplied by the left circumflex when the left coronary artery is dominant).
Determinants of Right Heart Function
The function of the right heart is governed by the following four factors:
1 Preload (RV volume overload)
• RV preload is the load present before RV contraction and is determined by venous return, shunt, tricuspid and pulmonic valve regurgitation and the distensibility of the RV’s thin myocardial wall.
• Tricuspid regurgitation (TR) can be categorized as:
a Primary TR due to organic TV disease such as prolapse, carcinoid, or trauma (i.e., a car accident).
• Shunt. Atrial septal defect is the most common cause of RV volume overload in adult congenital heart disease. Other congenital diseases that cause RV volume overload are partial anomalous pulmonary venous return and Ebstein’s anomaly.
• Pulmonic regurgitation (PR) is also seen in patients who have had repair of tetralogy of Fallot or who have carcinoid heart disease. In a patient with severe PR following repair of tetralogy of Fallot, 3D reconstruction with magnetic resonance imaging (MRI) showed a uniquely enlarged RV (Fig. 3-6). Septal flattening during diastole and right ventricular enlargement are markers of RV volume overload.
2 Afterload (RV pressure overload)
• RV afterload represents the load that the RV has to overcome during ejection. Clinically speaking, RV afterload is considered to be pulmonary vascular resistance, which is affected by pulmonary flow and vasculature.
• RV pressure overload can be determined with 2D echocardiography. RV and pulmonary systolic pressure are commonly estimated using continuous wave (CW) Doppler and the simplified Bernoulli equation as follows:
where RA pressure is estimated using the American Society of Echocardiography (ASE) standard (Table 3-1).
• The normal RV wall is thin and very compliant. Therefore, when pulmonary vascular resistance is increased acutely, such as in acute pulmonary embolism, the RV cavity will dilate before pulmonary pressure increases.
• A distinct echocardiographic pattern of regional RV dysfunction in which the apex is spared may occur in acute pulmonary embolism.
• Primary and secondary pulmonary hypertension, chronic obstructive pulmonary disease, Eisenmenger’s syndrome, and pulmonary stenosis are causes of chronic RV pressure overload.
3 RV myocardial function
• The RV inflow tract contracts earlier than the infundibulum, based on the study by Geva et al.1 (Fig. 3-7).
• The response of the three RV segments to medications, sympathetic stimulation, and volume and pressure overload may be different. For example, animal and human studies have suggested that the inotropic response of the infundibulum may be greater than that of the inflow tract.
• Compliance is abnormal in RV hypertrophy and cardiomyopathy. RV diastolic abnormalities can be evaluated with echocardiography (Table 3-2).
• RV ejection may depend on the degree to which the RV walls are stretched during diastole (preload).
• RVAC is a cardiomyopathy characterized pathologically by fibrofatty replacement primarily of the RV and clinically by life-threatening ventricular arrhythmias in young people. Echocardiographic findings include dilation of the RV and localized aneurysms of the free wall during diastole. 3D echocardiographic findings are compared with pathology in Figure 3-8.
4 Pericardium or extracardiac force (constriction and pericardial effusion).
• Pericardial abnormalities typically directly impact ventricular filling though indirectly affect ejection due to altered preload. There is enhanced ventricular interdependence and respiratory changes in chamber sizes and Doppler indices of filling and ejection (RV parameters increase with inspiration while LV parameters decrease with inspiration).
Importance of Assessing RV Function
RV size and function are important prognostic factors in many cardiopulmonary conditions as follows:
• RV dysfunction noted at the time of diagnosis of pulmonary embolism is associated with a high mortality rate.
• RV dysfunction defined as a tricuspid annular plane systolic excursion (TAPSE) of less than 14 mm is an independent predictor for long-term mortality in patients with ST elevation myocardial infarction.
• In patients with idiopathic dilated cardiomyopathy, a dilated hypocontractile RV is a poor prognostic sign.
• In patients with inferior myocardial infarction, RV infarction is an independent predictor of major complications and in-hospital mortality.
• In patients undergoing mitral valve surgery, preoperative right ventricular ejection fraction (RVEF) of less than 20% predicts late postoperative death.
Echocardiographic Assessment of RV Size and Function
• For the assessment of RV size and function, 2D echocardiography uses multiple views, including parasternal long axis and short axis views, TV inflow view, and apical four-chamber view (Fig. 3-9).
• The size of the RV is evaluated in multiple 2D views, including parasternal long and short axis, and apical four-chamber views.
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