The Right Ventricle



The Right Ventricle





SECTION 1 ANATOMY OF THE RIGHT VENTRICLE

The right ventricle is located anterior to and wraps around the left ventricle. The entrance to the right ventricle is defined by the tricuspid annulus and the tricuspid valve leaflets. The exit is the right ventricular outflow tract and the pulmonary valve. In cross-sectional views, it has a crescent shape. In the apical four-chamber view of the echocardiogram, the right ventricle has a triangular shape. Anatomically from the anterior view with the free wall is removed, it resembles a check mark with the tricuspid valve at the entrance and the pulmonary valve at the exit. When the heart is viewed on chest x-ray, the right margin of the heart forms an acute angle with the diaphragm resulting in this region being called the acute margin of the heart. The acute marginal branches of the right coronary artery lie in this anatomic area. In contrast to the prolate ellipse shape of the left ventricle, the overall shape of the right ventricle defies traditional geometry.


In general, the right ventricle can be divided into three anatomic regions: the inlet, apical, and outlet regions. The inlet region consists of the tricuspid valve and its apparatus. The apical region of the right ventricle has several heavy trabeculations including the apically located moderator band and the septomarginal band. These prominent trabeculations are thick and distinguish the right ventricle from the less trabeculated left ventricle. The third region or outflow region is less trabeculated and leads to the pulmonary valve. From the frontal view, the outflow region of the right ventricle crosses the midline and situates itself to the left of the left ventricular outflow tract. This results in the left and right circulations crossing each other in the frontal plane—a feature that is not present in some congenital abnormalities such as transposition of the great arteries.

The interventricular septum is a part of all three regions of the right ventricle. It supports the apical region, the tricuspid valve apparatus, and the outlet region. It gives rise to papillary muscles and trabeculations and supports the outlet region. The interventricular septum is muscular except for the membranous portion of the septum. The membranous septum usually gives rise to the septal leaflet of the tricuspid valve. The upper regions of the interventricular septum support the pulmonary valve. The left side of the septum relates to the right cusp area of the aortic valve.

The right ventricle has two layers of myocardium in contrast to the left, which has three. The thin-walled right ventricle has an outer, subepicardial circumferential layer and an inner subendocardial longitudinal layer. The shape of the right ventricle and the muscle fiber arrangement make remodeling a challenge. These factors are especially important in clinical situations such as pulmonary hypertension and transposition of the great vessels in which the right ventricle faces pressures that can be in the systemic range.

The blood supply of the right ventricle consists of a conus branch, acute marginal branches, and, to a small degree, the posterior descending. The conus branch supplies the right ventricular outflow tract area and may continue and supply some of the interventricular septum. The acute marginal branches supply the free wall of the right ventricle. The posterior descending coronary artery supplies the surface of the right ventricle close to the interventricular groove. A proximal occlusion of the right coronary artery before the conus branch and the acute marginal branches can result in the serious right ventricular infarction syndrome in which there are high central venous pressures and low cardiac output.1



LINEAR MEASUREMENTS OF THE NORMAL RIGHT VENTRICLE






FIGURE 7.1 In general, the measurements for the right ventricular size are taken from the A4C view with the left ventricle at the center and the right ventricle imaged such that the transverse dimensions appear the largest. Diameters of >41 mm at the base and >35 mm at the midlevel suggest that the right ventricle is dilated.






FIGURE 7.2 The parasternal long-axis view offers an opportunity to view the right ventricular outflow tract for the first time and gives clues to the size of the right-sided chambers. This is measured from the base at the junction of the interventricular septum and the free wall of the right ventricle and normally varies from 7 to 27 mm.



NORMAL VALVES FOR RV CHAMBER SIZE






FIGURE 7.3 The following recommendations for chamber quantification have been established by the ASE/EACI. From Lang RM, Badano LP, Mor-Avi V, et al. Recommendations for chamber quantification by echocardiography in adults: an update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging. J Am Soc Echocardiogr. 2015;28:1-39.


STANDARD VIEWS OF THE RIGHT VENTRICLE, INFLOW, AND OUTFLOW






FIGURE 7.4 The RV inflow tract view is easily obtained by tilting the transducer under the sternum from the parasternal long-axis view. The inflow portion of the RV is visualized along with the anterior and septal leaflets of the tricuspid valve. S, septal; A, anterior.







FIGURE 7.5 The RV outflow tract to include the pulmonary valve and proximal pulmonary arteries. RVOT, right ventricular outflow tract; PA, pulmonary artery.


SECTION 2 RIGHT VENTRICULAR SYSTOLIC FUNCTION

Parameters used for measurement:



  • Visual examination of the size and contraction pattern of the right ventricle


  • Fractional area change (FAC)


  • Tricuspid annular plane excursion (TAPSE)


  • Tricuspid annular systolic velocity (TASV)


  • dP/dT of the tricuspid regurgitation velocity profile


  • Longitudinal strain imaging using speckle tracking


  • Velocity profiles of the free wall of the right ventricle using tissue Doppler


  • Three-dimensional echo volume and ejection fraction


  • Index of myocardial performance (RIMP)—global right ventricular function



SYSTOLIC FUNCTION OF THE RIGHT VENTRICLE2,3






FIGURE 7.6 End-diastolic frame has been traced here to include the trabeculations of the right ventricle and the moderator band if visible. A focus view of the right ventricle is used from the apex. The tracing begins at the tricuspid annulus and extends around to the apex and back to the opposite annulus and a line is drawn across the tricuspid valve annulus.






FIGURE 7.7 A similar line is drawn from a focused view in systole to include trabeculations and moderator band. The fractional area change is obtained by taking the systolic area divided by the diastolic area, which in this case is EDA – ESA/EDA = 6.2/12.2 = 51%. Normal is >35%. (The 2015 ASE guidelines suggest that 3D volumes be used when possible. The above program uses the method of disks and calculates a volume using the same software as for the left ventricle.)



FOUR ADDITIONAL METHODS FOR ASSESSMENT OF RIGHT VENTRICULAR SYSTOLIC FUNCTION






FIGURE 7.8 Each of the above displays illustrates techniques for evaluation of systolic function of the right ventricle (RV). The overall assessment of the right ventricle requires a coalition of multiple modalities. A: Tricuspid annular plane systolic excursion (TAPSE) is most commonly used to assess systolic function of the RV and has been studied extensively in the setting of pulmonary hypertension. B: Tricuspid annular systolic velocity (TASV) is a measure of the downward velocity of the lateral tricuspid annulus and offers another modality that gives information on systolic function of the RV. C: RV strain by speckle tracking is a third method for evaluation of systolic function of the RV. D: Tissue Doppler assessment of RV systolic function by analysis of velocities at selected points along the free wall of the RV. Each has something to offer, and overall assessment is enhanced by analysis of several modalities.


SECTION 3 RIGHT VENTRICULAR DIASTOLIC FUNCTION

Evaluation of diastolic function of the right ventricle is similar to that of the left ventricle. Pulse wave analysis of the tricuspid inflow velocity profile sampled at the tips of the tricuspid leaflets produces E and A waves. Tissue Doppler analysis of the lateral tricuspid annular velocities also offers analysis of e′ and a′ values. Similar patterns to those on the left allow for identification of abnormal relaxation, pseudonormal filling, and restrictive filling. Usually, abnormal findings of these patterns are associated with significant findings in functional class and other findings such as a dilated right atrium, dilated inferior vena cava, hepatic vein flow abnormalities, and elevated pressures on the right.

Parameters that indicate abnormal relaxation include E/A ratio of <0.8 or e′/a′ <0.5. E/A ratio of 0.8 to 2.1 or e′/a′ of 0.5 to 1.9 suggests high filling pressures. E/e′ < 6 or diastolic flow predominance in the hepatic veins suggests pseudonormal filling, and E/A > 2.1 and e′/a′ > 1.9 and an abbreviated deceleration time <120 ms along with diastolic integrate flow in the pulmonary artery suggests restrictive filling.4



SECTION 4 RIGHT VENTRICLE AND PULMONARY HYPERTENSION

The right ventricle is designed to function by generating volume and not pressure. Abnormalities that result in pressure overload result in remodeling of the right ventricle in response to the imposed load. As the right ventricle changes shape, distorts the interventricular septum, and dilates the tricuspid annulus, coaptation of the tricuspid valve is compromised and tricuspid regurgitation results.

Elevations of right ventricular systolic pressure can occur in several clinical settings. Individuals with chronic obstructive lung disease, idiopathic pulmonary hypertension, pulmonary embolism, and systemic diseases such as systemic sclerosis and many others can result in elevations in pressures in the right ventricle and the pulmonary artery. Much interest has been present in recent years in measuring and estimating these pressures associated especially since a host of novel drugs are available to alter pulmonary vascular resistance.

The importance of carefully separating out primary elevations of pulmonary artery pressure from secondary elevations has become important. Elevations in left ventricular filling pressure or pulmonary artery wedge pressure >15 mm Hg changes the target of treatment from the pulmonary circulation to the left ventricle and the systemic circulation. Once this issue has been eliminated, focus can be directed to the pulmonary vasculature at rest and sometimes with exercise.

Echocardiography and right heart catheterization have played a major role in the diagnosis of pulmonary hypertension and in the treatment and follow-up of interventions. Measurements of the tricuspid regurgitation jet velocity along with estimation of right atrial pressure offer a noninvasive approach for estimation of right ventricular systolic pressure. Direct measurement of these pressures with Swan-Ganz catheters offers objective information for diagnosis and treatment of these conditions. Many standards have been set, but currently mean pulmonary artery pressures at rest of >25 mm Hg and mean pulmonary artery pressures with exercise >30 mm Hg define pulmonary hypertension. This assumes pulmonary capillary wedge pressure is <15 mm Hg. Pulmonary arterial resistance as measured in Wood units normally should be <2 units. Generally when pulmonary hypertension is present, the pulmonary vascular resistance is >3 Wood units. These standards have been outlined in recent publications.5,6

Examples of alterations of the right ventricle and estimations of right ventricular systolic pressure as estimated by echocardiography and Doppler techniques are illustrated in the following pages. It should be noted that in the absence of right ventricular outflow obstruction, pulmonary valve stenosis or stenosis within the pulmonary arteries right ventricular systolic pressure is the same as pulmonary artery systolic pressure.7




May 5, 2019 | Posted by in CARDIOLOGY | Comments Off on The Right Ventricle
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