Role of echocardiography in the assessment of right ventricular function in the pediatric population

This review article summarizes the use of echocardiography in the evaluation of the right ventricle with special emphasis on pediatric patients. After reading this article, anesthesiologists will develop a better understanding of the anatomy and echocardiographic parameters for hemodynamic and functional assessment of the right ventricle. This knowledge will assist with the perioperative management of patients with cardiopulmonary disorder.


| INTRODUC TI ON
The right ventricle (RV), which has been abandoned in the past as merely a conduit chamber, is now recognized to perform a conspicuous role in the clinical outcome and functional status of a patient with a cardiopulmonary disease. For an anesthesiologist providing care to pediatric patients with cardiopulmonary disease, it is important to understand key echocardiographic parameters utilized to assess the hemodynamics, size, dimensions, and function of the RV. In conjunction with clinical information, echocardiographic data render pathophysiological information about the RV and facilitate optimal perioperative management of such patients.

| ANATOMY
As the anterior most chamber of the heart, the RV is located underneath the sternum. The thin-walled RV extends from the tri- Tricuspid valve is composed of three leaflets: septal, anterosuperior, and inferior/posterior leaflet. Inferior papillary muscle provides support to the septal and inferior/posterior TV leaflets. Medial papillary muscle reinforces inferior/posterior and anterosuperior leaflets. The anterosuperior leaflet is anchored by anterior papillary muscle. The hinge point of the septal leaflet of the TV is closer to the ventricular apex in comparison to the anterior leaflet of the mitral valve. Also, the chordae supporting the septal leaflet extend to the right ventricular surface of the ventricular septum. A band of muscle between the RV body and the infundibulum called the septomarginal band or moderator band is unique to the RV. These features assist in distinguishing the morphologic RV from the morphologic LV. Finally, PV has three leaflets: anterior, right and left cusps.

| B LOOD SUPPLY OF THE RV
Right ventricle receives its blood supply principally from the right coronary artery in both systole and diastole, distinguishing it from LV which is perfused predominantly by the left coronary system during diastole. Also, the blood supply to the diaphragmatic surface of the RV and posterior interventricular septum from the posterior descending/inferior interventricular artery is dependent on the dominance of coronary circulation. In the right dominant coronary system (incidence 85%), the posterior descending/inferior interventricular artery arises from the right coronary artery. In left dominant coronary system (incidence 7%), the posterior descending artery either receives branches just from the left circumflex or left anterior descending/anterior interventricular artery. In codominant coronary circulation (incidence 4%), the posterior descending artery receives branches from both right coronary and anterior interventricular or circumflex arteries. Other branches of the right coronary artery are infundibular or canal artery, atrial branches, artery to sinus node, right marginal artery, and atrioventricular nodal arteries.

| Interventricular septal morphology
Visual inspection of the interventricular septum can ascertain the RV volume as well as the pressure load in parasternal basal or mid SAX view, apical view, and subcostal 4-Ch view. Under normal conditions, the LV cavity appears circular in the parasternal SAX view as the LV pressure is higher than the RV pressure throughout the cardiac cycle.
The implication of significant RV pressure overload, as seen with pulmonary hypertension results in the RV pressure potentially being greater than the LV pressure during late systole and early diastole.
This increased RV pressure causes a shift of interventricular septum in the direction of the LV culminating into a flat septum and a D-shaped LV during end-systole (at the end of T-wave) ( Figure 1).
Further increase in RV pressure will cause the septum to curve toward the LV.
Right ventricle volume overload, as seen with tricuspid and pulmonary regurgitation (PR), leads to increased RV pressure during mid-diastole, consequently shifting the septum toward the LV and to a D-shaped septum in diastole. The systolic conformation of the interventricular septum remains normal. LAX, and DTG Sagittal views can be used to ascertain the same measurements. The measurements are gathered using the inner edge to inner edge method at end-diastole. In parasternal LAX view, the proximal RV outflow diameter is the distance between the anterior RV wall and the interventricular septum at the level of the aortic junction. In the parasternal SAX view, the distal RV outflow diameter is the distance measured from the anterior RV wall to the aortic valve just proximal to the PV.

| Area and fractional area change of RV
Right ventricle endocardial border is traced manually at end-diastole (first frame when mitral valve closes or peak R-wave on electrocardiogram mid esophageal (ECGME) or maximum ventricular volume) and end-systole (first frame when the aortic valve closes or end of T-wave on ECGME or minimum ventricular volume). This In comparison to magnetic resonance imaging (MRI), 2D echocardiography can be limited in calculating the FAC in patients with congenital heart disease (eg repaired tetralogy of Fallot). The limitations exist due to complicated three-dimensional geometrical features of RV, the proximity of RV to the anterior wall and resultant artifact, and longitudinal rather than concentric motion of the fibers in RV.

| RV wall thickness
Both 2D and M-mode can be utilized to measure the wall thickness of the RV at the level of the tip of the anterior leaflet of TV.
Obtain the end-diastolic measurement in a region which is devoid of the trabeculations, papillary muscles, and moderator band. order to ensure that the TR velocity is not underestimated. (Figure 3) During TEE it can be measured in the ME 4-Ch view.

| Right atrial pressure
The three parameters described below provide an estimate of the

| Hepatic vein velocity
In TTE, the hepatic vein flow velocity profile is acquired in the subcostal view using pulsed wave Doppler. It has a retrograde Awave above the baseline that occurs during the atrial systole due to movement of blood toward the liver. It commences with the P-wave and peaks with the QRS complex on ECGME. The A-wave is followed by an anterograde S-wave below the baseline during ventricular systole. The S-wave occurs due to the movement of blood from the liver to the right atrium created by tricuspid annulus motion toward the cardiac apex in systole. During spontaneous respiration, the passive flow of blood from the liver into the heart during diastole translates into anterograde D-wave below the baseline. The D-wave occurs after the T-wave during diastole on ECGME. With normal RAP, systolic wave velocity (V s ) is greater than diastolic flow velocity (V d ). With increased RA pressure, the difference between the two decreases and eventually reverses.
Hepatic vein systolic filling fraction is defined as V s /(V s + V d ).
Elevated RA pressure is associated with a hepatic vein systolic filling fraction less than 55%.

| Atrial septal position
The position of the right atrial septum can provide an estimate of RAP in comparison to left atrial pressure (LAP). If the atrial septum is bulging toward the left atrium, then RAP is greater than LAP. 6,7

| Pulmonary artery diastolic pressure
In TTE, the pulmonary artery diastolic pressure (PADP) is derived from the PR jet velocity that is acquired in parasternal and subcostal SAX views. Color Doppler at the level of the PV in these views shows systolic blue (away) flow going from RVOT into the pulmonary artery through the PV. PR blood flow in this view appears red. In spectral Doppler, this PR flow occurs during diastole and is above the baseline.

| Mean pulmonary artery pressure
Mean pulmonary artery pressure (mPAP) can also be derived from

| E VALUATI ON OF FUN C TI ON OF RV
The following parameters are used in the assessment of RV function

| Myocardial performance index of the RV
Tei index or RV index of myocardial performance or MPI of the RV is the index that assesses the global systolic and diastolic RV function. Pulsed, continuous, and tissue Doppler can be used to capture this index.
In  In a pediatric study, right ventricular MPI in patients with idiopathic pulmonary hypertension was found to be around 0.64 ± 0.30. 9 An apical 4-Ch view is used to measure TDI with a focus on the RV. Then, the depth is adjusted to display the entire RV, tricuspid annulus, and part of the right atrium. Subsequently, the pulsed-wave

| dp/dT of the RV
The dp/dT of RV, an index of ventricular systolic function, is defined as the rate of rising of RV pressure during the isovolumetric contrac-

| Strain and strain rate
Tissue Doppler and speckle tracking is used to capture the deformation parameters such as strain (degree of myocardial deformation) and strain rate (rate of deformation of myocardium over time) to evaluate RV function. (Figure 6) Since they are altered to a less extent by the volume loading conditions, strain and strain rate are used to evaluate the regional RV dysfunction. Normal ranges of RV strain are available in children. 13

| ROLE OF ECHOC ARDIOG R APHY IN D IAG NOS ING AND MANAG ING INTR AOPER ATIVE RV FAILURE
Echocardiography, in collaboration with other clinical and invasive hemodynamic parameters, can assist the anesthesiologists in differential diagnosis and management of the etiology of RV failure.
Intraoperative acute RV dysfunction can be a consequence of the acute increase in preload or decreased diastolic filling of RV, decreased RV contractility, and increased afterload.

| Assessment of preload
Intraoperative volume overload can be a result left to right shunts, valvular regurgitation, and iatrogenic administration of excessive fluids.

| Assessment of contractility
Ischemia resulting from coronary hypoperfusion impairs RV function. Decline in perfusion pressure secondary to arrhythmias, hypotension, and decreased LV function, and metabolic abnormalities also negatively impact RV contractility.
Subjective evaluation of RV function as normal, mild, moderate, or severely depressed can be performed in tandem with quantitative parameters elucidated previously. Dobutamine, milrinone or low dose epinephrine can assist with primary RV dysfunction.
Vasopressin and norepinephrine may play a role in managing low perfusion pressure culminating from systemic hypotension.

| Assessment of afterload
Right ventricle failure may also be a corollary to increased afterload precipitated by increased PVR, pulmonary embolism, and outflow tract obstruction.
Pulmonary artery systolic pressure is estimated from TR jet velocity. Early-diastolic and end-diastolic velocities from the PR jet provides an approximation of mean and diastolic pulmonary artery pressure, respectively. Besides the parameters highlighted above, the other clues for assessment of increased afterload are:

RV:LV diameter ratio
End-systolic RV:LV diameter ratio greater than 1 in parasternal SAX view (TTE) or TG SAX (TEE) view at the level of papillary muscle signifies compression of LV by hypertensive RV in pulmonary hypertension patients. This ratio has minimal value in patients with volume-loaded ventricle secondary to the left to right shunt and severe PR.

LV eccentricity index
Left ventricle eccentricity index is the ratio of the anteroposterior and septolateral diameters of LV cavity measured in parasternal SAX view (TTE) or TG SAX (TEE) view at the level of papillary muscle. The normal end-systolic and end-diastolic LV eccentric index is 1. This value increases to more than 1 in patients with pressure or volume overload on the RV. Along with diastolic septal F I G U R E 6 This graphical display demonstrates the strain values for the six segments listed above; the color-coded graph corresponds to each segment. The dotted yellow curve shows the average strain. The greater the strain the larger the downward deflection of the curve.
The global strain which is the average of all strain curves measures to be −19.5% in this example. The peak global strain is listed below the global strain for each segment (blue and white graphical display). Finally, strain can be used to derive dyssynchrony of cardiac motion and the yellow to green display shows when the peak strain is achieved. The more synchronous the heart is then the less the difference in time to peak strain flattening, increased LV eccentricity index is used for risk stratification in pulmonary hypertension.
Elevated PVR resulting in increased afterload can be treated by improving ventilation strategies and inhaled and intravenous pulmonary vasodilators. Other contributing factors to increased afterload may require interventional or surgical procedures.

| SUMMARY
This review highlights the use of transthoracic and transesophageal echocardiography for the evaluation of the RV. The anesthesiologists taking care of pediatric patients with cardiac disease can improve clinical care by familiarizing themselves with the views, methodology, and pitfalls of various echocardiographic parameters utilized for the assessment of the RV.

D I SCLOS U R E S
None.