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|Year : 2009
: 12 | Issue : 2 | Page
|Trans-esophageal echocardiography for tricuspid and pulmonary valves
Mahesh R Prabhu
Department of Cardiothoracic Anaesthesia and Intensive care, Freeman Hospital, Newcastle Upon Tyne Hospitals, NHS Trust, United Kingdom
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|Date of Web Publication||21-Jul-2009|
| Abstract|| |
Transesophageal echocardiography has been shown to provide unique information about cardiac anatomy, function, hemodynamics and blood flow and is relatively easy to perform with a low risk of complications. Echocardiographic evaluation of the tricuspid and pulmonary valves can be achieved with two-dimensional and Doppler imaging. Transesophageal echocardiography of these valves is more challenging because of their complex structure and their relative distance from the esophagus. Two-dimensional echocardiography allows an accurate visualization of the cardiac chambers and valves and their motion during the cardiac cycle. Doppler echocardiography is the most commonly used diagnostic technique for detecting and evaluating valvular regurgitation. The lack of good quality evidence makes it difficult to recommend a validated quantitative approach but expert consensus recommends a clinically useful qualitative approach. This review ennumerates probe placement, recommended cross-sectional views, flow patterns, quantitative equations including the clinical approach to the noninvasive quantification of both stenotic and regurgitant lesions.
Keywords: Tricuspid valve, transesophageal echocardiography, pulmonary valve
|How to cite this article:|
Prabhu MR. Trans-esophageal echocardiography for tricuspid and pulmonary valves. Ann Card Anaesth 2009;12:174
| Introduction|| |
The use of transesophageal echocardiography (TEE) as a clinical monitor of hemodynamic changes and a reliable tool for intraoperative diagnosis is well established and it has been suggested that intraoperative TEE should routinely be used in patients undergoing cardiac surgery.  The right heart valves, tricuspid and pulmonary are complex anatomical structures.  In addition, they prove elusive to view with transesophageal echocardiography owing to their distance from the transducer probe. This has been offset by the lower prevalence of significant right heart valve lesions. Nevertheless, the importance of right ventricular and valvular function should not be underestimated especially its role as a determinant of cardiac symptoms, exercise tolerance and survival in pa tients.
Anatomy of tricuspid valve
The tricuspid valve (TV) consists of three, triangular shaped cusps. Their bases are attached to a fibrous annulus surrounding the atrioventricular orifice. The normal tricuspid orifice area is large, measuring as much as 6-7cm 2 . The medial/septal cusp is in relation to the ventricular septum and the posterior cusp is posteriorly situated in relation to the right margin of the ventricle. The anterior cusp is the largest of all cusps. Their ventricular surfaces are attached to the three papillary muscles (anterior, posterior and septal) by chordae tendineae. The trabeculae carneae are rounded or irregular muscular ridges which project from the whole of the inner surface of the ventricle. The moderator band is a muscular band, which extends from the base of the anterior papillary muscle to the ventricular septum. 
The TEE guidelines, published by the American Society of Anesthesiologists (ASA) and the Society of Cardiovascular Anesthesiologists (SCA), for performing a comprehensive intraoperative multiplane TEE examination have provided an objective format for performing, acquiring and archiving images during a TEE examination. 
Two dimensional (2D) echocardiography
2D Echocardiography is used to assess tricuspid valve structure and motion, measure annular and chamber size and identify other cardiac abnormalities that might influence tricuspid valve function.  The examination of the tricuspid valve begins with the mid-esophageal four-chamber view [Figure 1]. The probe is then turned to the right until the TV is in the center of the display. The tricuspid valve is generally placed more apically than the mitral valve. This normal apical displacement is not seen in endocardial cushion defects and exaggerated in Ebstein's anomaly. The TV is seen with the septal leaflet to the right of the display and the posterior leaflet to the left.  The TV annulus should not exceed 28 mm when measured at end-systole. The probe is advanced with some retroflexion to move the imaging plane across the tricuspid annulus in a superior to inferior plane and the coronary sinus view can be viewed [Figure 2]. The size and function of the right ventricle (RV) and right atrium (RA) also should be evaluated. The multiplane angle is then rotated forward to 60˚ to develop the mid-esophageal RV inflow-outflow view that shows the posterior leaflet of the TV to the left side of the display and the anterior leaflet to the right [Figure 3]. The modified mid-esophageal bicaval view [Figure 4] is next developed by turning the probe to the right and rotating the multiplane angle forward to between 110 and 140 degrees until the SVC appears in the right side of the display and the IVC in the left. The far field will show the tricuspid valve anterior leaflet to the left and the posterior leaflet to the right of the display. 
In the transgastric (TG) short axis view [Figure 5], the RV is seen to the left side of the display. A short axis view (SAX) of the TV is developed by withdrawing the probe slightly toward the base of the heart until the tricuspid annulus is in the center and rotating the multiplane angle to approximately 30 degrees. In this cross-section, the septal leaflet is to the right side of the display near the interventricular septum, the anterior leaflet of the TV is to the left in the far field and the posterior leaflet is to the left in the near field. The TG RV inflow view is developed from this view by turning the probe to the right until the RV cavity is located in the center and rotating the multiplane angle to 100˚ until the apex of the RV appears in the left side of the display. This cross-section shows the posterior leaflet on the upper part and the anterior leaflet to the lower part of the display. This view provides the best images of the subvalvular apparatus.
Color flow Doppler
Basic recommendations for use of CFD include minimum gain just below the noise threshold, a small area of interest, minimum depth settings and maximal color scales (Nyquist limit of 50-60 cm/sec). CFD imaging in the mid-esophageal four-chamber, mid-esophageal RV inflow-outflow and the mid-esophageal aortic valve SAX views is a quick and useful method to determine severity, direction and other characteristics of the regurgitant jet. The diameter of the vena contracta (VC), defined as the narrowest part of the regurgitant jet distal to the regurgitant orifice, is a simple, quantitative method which correlates well with the effective regurgitant orifice area (EROA) and the regurgitant volume. 
Pulse wave Doppler
PW Doppler is used in combination with the 2D imaging to record the flow velocity by placing the sample volume (SV) at the level of the tips of the open TV leaflets in the 4-chamber view or RV inflow-outflow view. The SV axial length is adjusted to 5-7 mm with low-level wall filters and the velocity is recorded over two or three respiratory cycles at a sweep speed of 50 or 100 mm/s.  Peak E and A velocities and E/A ratios, velocity-time integrals and deceleration times of E wave can be determined. The TV flow velocity is about 0.3- 0.7m/sec. The pressure half-time method has not been as extensively validated for the calculation of tricuspid valve area as in case of the mitral valve.
PW Doppler examination of the hepatic veins can be done by advancing the probe from the bicaval view to track the inferior vena cava into the liver. The sample volume is placed 1-2 cm into the orifice of a central hepatic vein. The normal pattern of flow velocity consists of antegrade systolic (S wave), transient flow reversal as the TV annulus recoils at the end of systole (v wave), antegrade diastolic (D wave) and a retrograde A wave caused by atrial contraction. Both the tricuspid and hepatic flow patterns are affected by respiration.
Continuous wave Doppler
In contrast to PW Doppler, CWD records the velocities of all the red blood cells moving along the path of the sound beam. The Doppler beam should be oriented as parallel as possible to the flow, guided by the 2D image, color flow imaging and the presence of a well defined envelope. CWD is used to estimate the severity of tricuspid stenosis and the pulmonary artery systolic pressures (PASP). The maximal velocity of the tricuspid regurgitation (TR) jet is measured and PASP is calculated using the simplified Bernoulli equation:
PASP = 4(TR jet velocity) 2 + central venous pressure [Figure 6]
Abnormalities of the tricuspid valve
Tricuspid stenosis (TS) is a relatively uncommon lesion. Functional TS may occur with increased flow through the right heart, caused by a left to right shunt such as an atrial septal defect. Organic TS is nearly always caused by rheumatic heart disease, congenital abnormalities, carcinoid disease and infrequently by pacemaker catheters and metabolic or enzymatic abnormalities such as Fabry's or Whipple's disease. ,
Two dimensional (2D) echocardiography shows thickening of leaflets with restricted motion, commissural fusion and doming of leaflets in diastole. There may be concomitant right atrial enlargement.  The transvalvular gradients (peak and mean) are very dependent on flow-thus significant TR may be associated with a high gradient even in the absence of any stenosis. CWD of the tricuspid inflow shows an increased peak E wave velocity (>1.5 m/sec). In the absence of significant TR, a mean pressure gradient of >7 mmHg and a pressure half-time >190 msec are signs of severe TS [Table 1].
Functional tricuspid regurgitation (TR) may be seen in the elderly, athletes and in patients with a pulmonary artery catheter or pacemaker wires. Pathological TR is caused by annular or RV dilation secondary to pressure or volume overload. Organic TR is caused by rheumatic valvulitis, carcinoid disease, endocarditis, rheumatoid arthritis, endomyocardial fibrosis and radiation therapy. Congenital heart disease such as Ebstein's anomaly, atrioventricular defect, cleft tricuspid valve and Marfan's syndrome may cause TR as well.  Evaluation of TR severity has been hampered by the lack of a quantitative standard and the echocardiographic examination should seek to determine the etiology of regurgitation and provides a semi-quantitative estimate. 
Significant TR may be associated with right atrial and annular dilatation, RV dysfunction/enlargement, paradoxical ventricular septal motion, ruptured chordae or vegetations on the valve caused by endocarditis. In functional TR, secondary to pulmonary artery hypertension, annular dilatation >3.2 cm in systole or >3.4 cm in diastole is associated with severe TR. 
In rheumatic disease, the tricuspid valve leaflets and the subvalvular structures are often thickened, shortened and retracted, leading to incomplete coaptation. In carcinoid disease, right atrial and ventricular enlargement is present in up to 90% of cases.  In myxomatous tricuspid valve disease, billowing and prolapse of leaflets is seen. In endocarditis, friable, mobile and destructive lesions can be observed. Ebstein's anomaly is characterized by apical displacement of TV into the RV causing "arterialization" of the right ventricle. It is diagnosed when the distance from the mitral annulus to the septal leaflet exceeds at least 8 mm/m 2 body surface area. 
Color flow Doppler
Overall, CFD mapping in various views using jet area correlates well with clinical measures of regurgitant severity.  Mild TR shows a small central color jet with minimal flow convergence in contrast to severe TR, which has very large flow convergence and jet area in the right atrium [Figure 7]. Color flow imaging may also be used to determine TR severity by the proximal isovelocity surface area (PISA) method or visualization of the vena contracta (VC) width but there may be an underestimation of severe TR in 20-30% of patients.  PISA method is based on the continuity equation. PISA is the surface area of a hemisphere at the aliasing region formed by layers of equal velocity caused by flow acceleration and convergence through a small circular orifice in a flat plate. The PISA method has been validated in small studies.  The vena contracta width>0.65 cm identified severe TR with a sensitivity of 89% and a specificity of 93%.  Eccentric, wall-impinging jets may be underestimated.
Severe TR will increase the early diastolic tricuspid E wave velocity (>1.0 m/s). Difficulties in measuring the TV annulus preclude the measurement of tricuspid regurgitant volume.
PW Doppler examination of the hepatic veins will show a blunting of the dominant systolic wave with increasing severity of TR and finally culminate in flow reversal with severe TR (sensitivity 80%).  However, the absence of systolic flow reversal does not rule out severe TR. The hepatic vein flow patterns are also affected by abnormalities in right atrial (RA) and RV relaxation and compliance. 
Continuous wave Doppler
Signal intensity and contour of the velocity curve help to evaluate severity of TR. A smooth, soft, parabolic curve is seen in mild TR whereas a dense spectral trace with a triangular, early peaking of the velocity can be seen in severe TR. The simplified Bernoulli equation is used to estimate the peak RA-RV gradient from the TR jet velocity and the pulmonary artery systolic pressure (PASP) can be derived by adding the gradient to the RA pressure. It is important to remember that TR jet velocity is not related to the volume of regurgitant flow [Table 2].
Anatomy of pulmonary valve
The pulmonary semilunar valves are three in number, anterior, right and left posterior. They are attached to the wall of the artery by their convex margins and their free borders being directed upward into the lumen of the vessel. Between the semilunar valves and the wall of the pulmonary artery are the sinuses of Valsalva and the sino-tubular junction. The normal size is 3.5-4.5 cm 2 .
The leaflets of the pulmonary valve (PV) are thinner compared to aortic leaflets, farther from the probe and therefore are more difficult to image with TEE. The flow through the PV is perpendicular to flow through the aortic valve (AV) and directed from anterior to posteriorly and slightly from the patient's right to left. The mid-esophageal RV inflow-outflow view [Figure 8] from 60º to 90º displays the right ventricular outflow tract (RVOT) and the PV with anterior and right/ left cusps in long-axis [Figure 2]. The mid-esophageal AV SAX view also provides a view of the PV and main pulmonary artery (PA) to the right side of the display. The multiplane angle is rotated back toward 0 degrees and the probe anteflexed or withdrawn slightly to display the bifurcation of the main pulmonary artery with the right PA in the near field coursing off to the left of display. The aortic arch is imaged by withdrawing the probe and turning to the right while maintaining an image of the descending thoracic aorta until the upper esophageal aortic arch long axis view (LAX) is developed. The multiplane angle is then rotated forward to 90 degrees to develop the upper esophageal aortic arch short axis view [Figure 9]. The pulmonary valve is seen in the distance to the left of the display and the Doppler beam can be aligned parallel to flow through the PV and main PA. The modified deep transgastric view [Figure 10] is obtained by advancing the probe deep into the stomach to the right and anteflexing such that the imaging plane is directed superiorly toward the base of the heart until the probe is adjacent to the RV apex. Some trial and error flexing, turning, advancing, withdrawing, and rotating of the probe develops this view in most patients. The view includes the tricuspid valve, the right ventricle, RVOT and the pulmonary valve.
Color flow Doppler
The mid esophageal RV inflow-outflow view displays the PV in long-axis and is useful for detecting pulmonary regurgitation by CFD. The upper esophageal aortic arch SAX view can be useful to detect pulmonary stenosis or regurgitation.
Continuous wave Doppler
CWD is used to measure high velocities across the stenotic pulmonary valve or measure diastolic pulmonary pressure. The pulmonary artery diastolic pressure (PADP) can be calculated as follows:
PADP = 4(end-diastolic PR jet velocity) 2 + central venous pressure
Pulse wave Doppler
PWD can be used to record PA flow in upper esophageal aortic arch SAX view or deep TG views by placing the sample volume near the PV. Normal peak flow ranges between 0.5-1.0 m/s. RV stroke volume and cardiac output can be determined from the velocity-time integral of the spectral flow pattern and the diameter of the PA/ RVOT.  Measurement of the annulus diameter may be inaccurate as the pulmonary annulus is difficult to visualize. In significant pulmonary hypertension, the pulmonary flow velocity acceleration time is shortened and a mid-systolic notch in the flow velocity envelope is often present.
Pulmonary valve abnormality
The common cause of pulmonary stenosis is congential heart disease, carcinoid disease or homograft dysfunction. There may be associated subvalvular and supravalvular stenosis.
The valve leaflets may be thickened, dysplastic and fused forming a conical or domed pulmonary valve.  2-D imaging may shows restricted motion of thickened leaflets, flattening of the interventricular septum, RV hypertrophy/ enlargement and post-stenotic dilatation of the pulmonary artery.
CFD will demonstrate aliasing and turbulent flow across the valve. Pulmonary stenosis is accurately quantified by calculating peak instantaneous and mean pressure gradients from Doppler signals obtained from the pulmonary valve orifice  [Table 3]. Quantifying of the pulmonary valve area by continuity equation has not been well standardized. 
Functional pulmonary regurgitation (PR) has been reported in 40-78% of patients with normal pulmonary valves. Acquired mild to moderate PR is most often seen in patients with pulmonary hypertension with dilatation of the pulmonary artery. Severe PR is uncommon and usually observed in patients with anatomic abnormalities of the valve or after valvotomy. There are very few validated studies owing to the low prevalence rates and difficulties in imaging.
Pulmonary regurgitation may be caused by congenital anomalies (quadricuspid or bicuspid valves), hypoplasia, post-repair of Tetralogy of Fallot or prolapse of the pulmonary valve. Difficulty in visualization of the pulmonary valve may limit the quantitation of PR. Dilatation of the pulmonary artery, size and function of the RV provide an indirect indicator to the significance of PR.
Color flow Doppler
CFD mapping is the most useful method to identify PR. A diastolic jet in the RV outflow tract directed toward the right ventricle is diagnostic of PR. Functional PR jets are usually very small, central and spindle-shaped.  In severe PR, where equalization of diastolic pulmonary artery and RV pressures occurs early in diastole, the color jet area can be brief and inaccurate. The vena contracta width is probably a more accurate method than jet length and planimetry to evaluate the severity of PR by color Doppler but lacks validation studies. M-mode may be used in tachycardic patients.
Continuous wave Doppler
There is no clinically accepted method of quantifying pulmonary regurgitation using CW Doppler. The density of the CW signal provides a qualitative measure of regurgitation.  In mild PR, there is a slow deceleration of the jet velocity. A rapid deceleration rate with termination of flow in mid to late diastole is not specific but compatible with severe regurgitation [Table 4].
Pulsed Doppler assessment of the forward and reverse flows at the pulmonary annulus and in the pulmonary artery can been used to calculate regurgitant volume and regurgitant fraction.  The pulmonary annulus should be measured with diligence during early ejection (2-3 frames after the R wave on the ECG), just below the valve. This technique is subject to errors in measurement and is not well validated.
| Conclusion|| |
TEE provides a practical and accurate method of assessing right-sided structures. In the absence of validated studies on quantitative measurements, an integrative approach which includes evaluation of chamber size, septal motion, color Doppler flow mapping including measurement of vena contracta, PISA and CW Doppler recording of signal contour and intensity is recommended. A qualitative evaluation is based on acquiring concurrent data to make a confident diagnosis keeping in mind the physiological conditions that can alter the accuracy of these parameters. Hopefully, the future will provide refinements in instrumentation and techniques leading to increased accuracy in reporting and cost-effectiveness in making clinical decisions.
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Mahesh R Prabhu
11 Haversham Close, Benton, Newcastle Upon Tyne, NE7 7LR
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
[Table 1], [Table 2], [Table 3], [Table 4]
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