Parasternal short axis view at the height of the papillary muscle
In PHT, as a consequence of increased afterload, right ventricular hypertrophy develops in order to keep wall stress as low as possible and to increase contractility. To maintain stroke volume the right ventricle dilates, which also includes dilation of the tricuspid annulus. Eventually, with chronically increased afterload, right ventricular systolic and diastolic failure ensues leading to more dilation and tricuspid regurgitation.
To evaluate the anatomy of the right ventricle and pulmonary valve a minimal number of images should be made.
Parasternal Long Axis View of the Left Ventricle
One should keep in mind that the right ventricle consists of 3 parts, the inflow, the outflow and the trabecular part, that all parts should be visualized. The outflow part is best seen in the parasternal long axis view . In this view the abnormal position of the interventricular septum can be seen. The left ventricle, aortic valve and mitral valve can be evaluated (Fig. 12.2a).
(a) Parasternal long axis view. (b) Parasternal long axis view of the right ventricle. (c) Parasternal long axis view of pulmonary artery and right ventricle outflow tract. (d) Parasternal short axis view at the level of the aortic valve. (e) Parasternal short axis view at the level of the papillary muscles. (f) Apical 4-chamber view
Parasternal Long Axis of the Right Ventricle
This view can be obtained by tilting the probe to scan more anteriorly. The right ventricle inflow part can be visualized. This is the only view in which the right anterior (free) wall can be visualized completely, in order to assess the hypertrophic right anterior free wall and its systolic function. (Fig. 12.2b). The diaphragmatic, inferior right ventricular wall can also be seen.
Parasternal Long and Short Axis Views of the Pulmonary Valve and Main Pulmonary Artery
In order to evaluate the pulmonary valve the two most used views are the parasternal long axis view and short axis view. The long-axis view (Fig. 12.2c) is obtained by tilting the probe more cranial. In the parasternal short axis view (Fig. 12.2d), the infundibular portion or outflow portion of the right ventricle can be evaluated to assess whether a right ventricular outflow obstruction or pulmonary valve stenosis is present. Quantification of the severity of the obstruction can be done using continuous wave Doppler .
Parasternal Short Axis at the Level of the Papillary Muscles
The parasternal short axis at the level of the papillary muscles evaluates the mid segments of the left and right ventricle (Fig. 12.2e).
Progression of right ventricle pressure causes thickening of the wall and dilation of the lumen.
The pressure loaded right ventricle loses its crescent, banana-shape, configuration and becomes more spherical and dilated. The wall is thickened. The interventricular septum shows systolic flattening, which causes the left ventricle to get a typical D-shape in this view. This septal flattening can be quantified by the eccentricity index , which is the ratio of the left ventricular diameter perpendicular to the septum and the orthogonal diameter of the left ventricle at the same level. This index changes from 1 (normal) to >1 in elevated right ventricular systolic pressures. An index >1.0 is therefore one of the secondary echocardiographic signs of pulmonary hypertension. An index >1.7 denotes a poor prognosis.
Diastolic interventricular septal flatting can be seen in severe tricuspid valve regurgitation as a sign of volume overload.
Eccentricity index = D1/D2
Apical 4 Chamber View
The inflow of the right and left ventricle can be evaluated in the 4-chamber view , which further allows the comparison of the right and left ventricular dimensions. The ratio of the basal right to left ventricular diameters. >1.0 is a secondary sign of PHT (Fig. 12.2f). For a realistic measurement of these diameters one should avoid foreshortened images by placing the ultrasound probe on the apex of the heart. In some cases this can be challenging and difficult to accomplish.
Right atrial dilation is often present in the presence of PHT. In the apical 4-chamber view the maximal right atrial area (mid-systole) can be measured. A right atrial area >18 cm2 is indicative of right atrial dilatation and >27 cm2 indicates a poorer prognosis.
Beware of foreshortening with the consequence of measuring a larger right to left ventricular diameter ratio, due to oblique imaging of the right ventricle.
Tricuspid Valve Anatomy and Effect of High Pulmonary Artery Pressures and Right Ventricle Dilatation
The tricuspid valve is an anatomical structure belonging to the right ventricle. It consists of 3 valve leaflets which are kept in place by chordae, which on their part are mostly attached to the anterior papillary muscle. Chordae are also attached directly to the septum and to many smaller medial and inferior papillary muscles. The normal tricuspid valve annulus is an oval structure, with its largest diameter in the anterior to posterior direction. The tricuspid valve does not lie in one plane: the septal part is more cranially displaced in the perimembraneus region and the postero-septal region near the opening of the coronary sinus is lying more apically. During the cardiac cycle the annular area changes with a maximum area change during mid-diastole with the largest change in the septal to lateral axis. In diastole the annular plane is round and flat, while in systole the annulus becomes more oval and the curvature increases .
In the setting of right ventricular remodeling by pressure overload in PHT the morphology of the tricuspid valve changes. Dilation of the annulus is dominantly in the septal to lateral axis making the annular area larger, more round, and more planar during systole. As a consequence, a loss of leaflet coaptation area occurs. Additionally, right ventricle dilatation leads to a change in the geometry of the sub-valvular apparatus causing tenting of the valve leaflets. In Fig. 12.3a, b schematic drawing shows these changes.
(a) Change in tricuspid annulus geometry due to pressure overload of the right ventricle, the cranial view from atrium to right ventricle. (b) Change in tricuspid annulus geometry in the lateral view, due to pressure overload of the right ventricle
Pulmonary Pressure Estimation
As stated before it is important to realize that pulmonary artery pressure is dependent on left atrial pressure, pulmonary vascular resistance and pulmonary blood flow (cardiac output created by the right ventricular pump). During echocardiography , focus should lie on these parameters in order to understand and report the state of the pulmonary circulation completely.
In case of right ventricular outflow tract obstruction or pulmonary valve stenosis the estimated
A common mistake is to overlook the fact that pulmonary artery pressure is not equal to systolic right ventricular pressure in the presence of right ventricle outflow obstruction (on whatever level).
systolic right ventricular pressure is not equal to the systolic pulmonary artery pressure.
Pulmonary Artery Pressure Estimation Using Tricuspid Valve Regurgitation
Almost every tricuspid valve has some regurgitation , although sometimes hard to capture with Doppler interrogation. The regurgitation jet velocity can be used to estimate the systolic pressure differences between the right ventricle and the right atrium by using the simplified Bernoulli law equation (Fig. 12.4):
(a) Continuous wave Doppler regurgitation velocity of the tricuspid valve. (b) Continuous wave Doppler regurgitation of the tricuspid valve of another pulmonary hypertension patient
ΔP = 4 V 2
In case of tricuspid regurgitation:
ΔP = 4 TR-Vmax 2
RV systolic pressure−RA pressure = 4 TR-Vmax 2