Pulmonic Valvular Disease

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Pulmonic Valvular Disease SHUBHIKA SRIVASTAVA  |  PUNEET BHATLA

Diseases of the pulmonary valve (PV) are most often congenital

and only rarely acquired in origin. Disorders of the right ventricular outflow tract (RVOT) encompass conditions that cause obstruction to flow and/or regurgitation across the PV. Pulmonary valve stenosis can be isolated or associated with more complex malformations, such as tetralogy of Fallot (TOF) or transposition of the great arteries. This chapter focuses on preoperative echocardiography of isolated abnormalities of the RVOT. The abnormalities can be divided into PV stenosis, subpulmonary stenosis, main pulmonary artery (MPA) stenosis, and dysplastic PV. When imaging the PV, the subpulmonary ­infundibulum and MPA must also be imaged.

Pulmonary Valve Stenosis Pulmonary valve stenosis is defined as obstruction at the level of the PV and is found in 80% to 90% of all patients with RVOT obstruction. It is the fourth most common congenital heart lesion, occurring in approximately 53 (35-83) per 100,000 live births.1 The recurrence risk of cardiac disease (pulmonary stenosis [PS] or TOF) in siblings of patients with PS has been reported as 2.1%.2 The second natural history study of congenital heart defects reported an incidence of definite and possible congenital cardiac defects as 1.1% and 2.1%, respectively.3 The associated genetic abnormalities include Noonan, Williams, and Alagille syndromes. The MPA and left pulmonary artery are often dilated with isolated PV stenosis. Absence of MPA dilation is seen in conjunction with a dysplastic PV or isolated supravalvar stenosis.

Subvalvar Pulmonary Stenosis Primary fibromuscular narrowing limited to the RVOT is an extremely rare phenomenon that is probably part of the spectrum of illness associated with a double-chambered RV.4 In comparison, varying degrees of secondary outflow tract narrowing are commonly seen as part of the overall muscular hypertrophy of the RV induced by PS. This secondary obstruction often regresses following valvotomy or valvuloplasty.5 Supravalvular pulmonic stenosis—isolated or multiple areas of narrowing of the MPA or branches—has been described but is a rare de novo finding in the adult.6

Morphology The most common morphology seen in isolated PS is that of a normal PV that is trileaflet, with a normal annulus dimension and three commissures with varying degrees of fusion.7 Rarely, bicuspid and unicuspid valves are seen in isolated PS, though these are a more common finding in association with TOF. A small proportion of patients (particularly those with Noonan syndrome) have a markedly dysplastic valve with myxomatous and thickened leaflets, little commissural fusion, and often a hypoplastic annulus and proximal pulmonary artery.8 These valves are often severely stenotic and usually require repair during childhood. Secondary changes typical of patients with long-standing valvar stenosis include poststenotic dilation of the pulmonary artery, varying degrees of right ventricular hypertrophy, and ultimately, right ventricular dysfunction and dilation.

Transesophageal Echocardiography for Pulmonary Valve Assessment The PV is the farthest valve from the esophagus; it is anterior and superior in location, and the leaflets are thin. Hence, both its position and morphology make it more difficult to image with transesophageal echocardiography (TEE). The direction of flow across the PV is somewhat anterior to posterior, right to left, and hence, it is difficult to align parallel to the flow using standard midesophageal (ME) views. Thus, reliable spectral Doppler interrogation of the PV may be limited.

Imaging Planes Used to Evaluate Right Ventricular Outflow Tract and Pulmonary Valve 1. ME RV inflow-outflow view. In the RV inflow-outflow (RVOT) view (60-75 degrees), the imaging plane is directed through the left atrium to image the RV inflow from the tricuspid valve (displayed on the left) and RV outflow through the PV (displayed on the right) in a single view (Fig. 17-1). Two-dimensional (2D) long-axis imaging of the PV, MPA, and RVOT in a single view is best imaged using this plane. This plane is excellent for assessing additional levels of obstruction involving both the supravalvar and infundibular regions, and in assessment of pulmonary regurgitation (PR).9 2. ME ascending aorta short axis (SAX). From ME RV inflow-outflow (60 degrees), withdraw probe from the ascending aorta (AAo) SAX, and rotate the omniplane angle back to 0 degrees. 2D imaging of the right pulmonary artery (RPA) and MPA in long axis is performed using this plane (Fig. 17-2). The left pulmonary artery (LPA) arches over the left mainstem bronchus after originating from the MPA and is often difficult to visualize because of the interference of the airway (Videos 17-1 and 17-2). 3. Upper esophageal (UE) aortic arch SAX. From the ME AAo SAX (0 degrees), withdraw probe to obtain the UE aortic arch LAX (0 degrees) view, rotate the omniplane angle to 60 to 90 degrees, and turn the probe to the left to bring the PV and MPA into view (Fig. 17-3). Retroflexion of the probe at this level will improve the view of the PV. This is also a good imaging plane to align the continuous wave Doppler parallel to flow through the PV and MPA and is useful in assessment of severity of obstruction at these levels. 4. Transgastric (TG) LAX. From the deep TG view, with hard antiflexion, rotate the omniplane angle between 70 and 110 degrees (usually at 90 degrees) with rightward flexion to profile the RVOT (Fig. 17-4). This will provide a good imaging plane and an insonation angle parallel to flow that will allow for accurate and a more reliable spectral Doppler interrogation across the RVOT (Videos 17-3 and 17-4; also see Fig. 17-3).

Usual Indications for Assessment Indications for perioperative assessment of the pulmonic valve include: 1. Preoperative assessment of congenital heart disease (TOF, doublechambered RV, valvar and supravalvar PS, transposition and PS, anomalous origin of coronary artery from the pulmonary artery, coronary artery fistulae). Prior to the Ross procedure, it is very

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SECTION II  Understanding How Transesophageal Echocardiography Demonstrates Cardiovascular Pathology

PV

A

B

Figure 17-1  A, Midesophageal (ME) right ventricular (RV) inflow-outflow view simulation on three-dimensional heart model. B, ME RV inflowoutflow view. PV, Pulmonary vein.

MPA

A

B

Figure 17-2  A, Midesophageal (ME) ascending aorta short-axis (SAX) three-dimensional simulation on heart model. B, ME ascending aorta SAX. MPA, Main pulmonary artery.

important to define normal PV morphology and function, since a bicuspid PV is a contraindication for a successful Ross procedure. It is also imperative to image the atrial septum and confirm that it is intact prior to PV or conduit replacement surgery in order to avoid air embolism. 2. Intraoperative assessment for these conditions. Following an initial attempt at repairing a lesion of the RVOT, PV, or PA, the indications for returning to cardiopulmonary bypass (CPB) to revise the repair would be significant residual obstruction at any level of the RVOT, including the MPA. It is recommended that Doppler gradients be confirmed by direct intraoperative measurement prior to going back on CPB. Some ventricular septal defects (VSDs), such as doubly committed subarterial or subpulmonary VSDs, are closed

surgically via the PV approach. Hence, imaging for residual PV regurgitation and MPA stenosis should also be part of the routine exam. Supra-annular stenosis should also be examined following PV replacements and conduit revisions. 3.  Post–catheter-based interventions to assess for residual lesions and the degree of PR. Residual PV gradients greater than 20 to 30 mm Hg or anything greater than mild regurgitation would be considered suboptimal results. 4. PV tumors (fibroelastoma, fibroma, and Lambl excrescence) and for endocarditis. 5. Carcinoid syndrome. 6. TEE guidance is not currently used for assisting placement of percutaneous transcatheter PVs (e.g., the “Melody” valve).

17  Pulmonic Valvular Disease

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MPA PV

A

B

Figure 17-3  A, Upper esophageal (UE) aortic arch short-axis (SAX) simulation on three-dimensional heart. B, UE aortic arch SAX. MPA, Main pulmonary artery; PV, pulmonary vein.

PV

A

B

Goals for TEE Evaluation of the Pulmonary Valve The following represent the elements of a comprehensive evaluation of the PV using TEE: 1. Imaging PV leaflet excursion and thickness 2. Measurement of PV annular and supra-annular dimensions 3. Imaging the branch pulmonary arteries in 2D, and using color flow and spectral Doppler 4. Imaging the RVOT to assess whether obstruction is present at the subvalvar level 5. Color flow and spectral Doppler assessment for PS and regurgitation 6. Determining the degree of RV dilation and hypertrophy 7. Assessing RV function 8. Assessing the magnitude of the tricuspid valve regurgitation gradient so as to estimate the systolic RV pressure 9. Evaluating for associated congenital defects, such as tricuspid valve abnormalities, atrial septal defects, patent ductus arteriosus, VSDs, and coronary fistulae 10. Determining whether anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA) or an abnormal coronary

Figure 17-4  A, Transgastric (TG) right ventricular outflow tract (RVOT) long-axis (LAX) simulation on threedimensional heart model. B, TG RVOT LAX. PV, Pulmonary vein.

artery course is present. Anomalous origin of a coronary artery from the wrong sinus can course between the aorta and pulmonary artery. Dual left anterior descending or left main origin from the right coronary cusp can course anteriorly across the RV infundibulum or have an intramyocardial course just below or at the level of the PV annulus.

Assessing Severity of Pulmonary Stenosis The following are criteria for assessing the severity of PS:10 1. Mild PS: RV pressures less than half systemic pressures and a peak instantaneous gradient by continuous wave Doppler of less than 35 to 40 mm Hg 2. Moderate PS: RV pressures 50% to 75% of systemic pressures and a peak instantaneous gradient by continuous wave Doppler of 40 to 70 mm Hg 3. Severe PS: RV pressures greater than 75% of systemic pressures and a peak instantaneous gradient by continuous wave Doppler of greater than 70 mm Hg

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Pulsed wave Doppler interrogation below, at, and above the PV would differentiate among different levels of stenosis if present. In the absence of accurate or suboptimal angles for interrogation of the RVOT, the tricuspid valve regurgitation (TR) gradient can be used to estimate RV pressures. Natural History of Pulmonary Stenosis Patients with mild PS have a benign prognosis, excellent survival, and a normal response to exercise. This mild degree of stenosis does not progress, as observed in the natural history study,3 so in this subset of patients, recommendations are to follow patients without intervention. One exception noted is in neonates and infants; of the 56 patients younger than 1 month of age with mild obstruction, 16 progressed to moderate stenosis, and 50% of these patients did so in the first 6 months of life.3 In patients with moderate obstruction, more controversy surrounds follow-up and treatment. This degree of obstruction is more likely to progress and carries a higher likelihood that intervention will be required. It has also been shown that asymptomatic adults with moderate obstruction have a suboptimal cardiac output response and higher RV end-diastolic pressure when exposed to formal exercise testing. This suggests that these patients have evidence of both systolic and diastolic dysfunction of the RV. Patients with severe PV obstruction have evidence of low stroke index and higher RV end-diastolic pressure at rest, and this worsens with exercise. The effects have shown to be irreversible when left untreated beyond childhood. The treatment option for isolated PS is transcatheter balloon dilation in most patients. Surgical treatment is infrequently required. Surgical treatment is required when there are other levels of obstruction, such as in the supra- or subvalvar regions. The 2006 American College of Cardiology/ American Heart Association guidelines for management of PS recommend balloon valvotomy in asymptomatic patients with peak-to-peak catheterization gradients greater than 40 mm Hg (Class 1c indication).11 In symptomatic patients, treatment is recommended for peak-to-peak catheterization gradients greater than 30 mm Hg (Class 1c). Measuring the PV annulus is required to plan for the intervention. Typically a balloon size of 1.1 to 1.3 times the size of the PV annulus is used for dilation. Surgery is still usually required for the dysplastic valves that are often seen in Noonan’s syndrome, supravalvar PS, and double-chambered RVs.

Pulmonary Regurgitation PR is usually an acquired lesion that follows pulmonary valvotomy, transannular patch repairs for TOF, and is often seen with carcinoid syndrome or endocarditis. The echocardiographic criteria that define moderate severity or greater are: 1. The width of the vena contracta is greater than 50% of the width of the PV annulus. 2. There is diastolic flow reversal in the branch pulmonary arteries. 3. The duration of PR exceeds two thirds of the duration of diastole. 4. The pressure half-time is less than 100 milliseconds.12 TEE that is performed preoperatively can confirm the degree of PV regurgitation. Imaging and measurement of the PV annulus is important to guide the sizing of prosthetic PV replacements. A poor result is present when greater than mild pulmonary insufficiency is noted by TEE following surgical valve replacement, catheter interventions, or valved conduit placement or revision.

Assessment of Prosthetic and Conduit Pulmonary Valves There is a paucity of data that address assessment of the prosthetic PV in isolation or as part of a valved conduit. This is largely related to the technical limitations that affect imaging of the PV using either transthoracic echo or TEE. The usual measures of prosthetic valve function, such as effective orifice area, cannot be used because of the invalidity of the continuity equation related to the presence of a “funnelshaped” infundibulum. The characterization of pulmonary prostheses

is limited to pulmonary homograft valved conduits or xenografts in patients needing PV replacements due to congenital heart disease, or to the cryopreserved homografts that are used in the Ross procedure.13 Current guidelines recommend that a complete evaluation of prosthetic PV function include: 1. Noting cusp or leaflet thickening or immobility 2. Determining whether there is narrowing of forward flowing color map 3. Assessing whether peak velocity is greater than 2 to 3 m/s through a homograft 4. Monitoring for an increase in the peak velocity on serial studies 5. Assessing RV function and RV systolic pressure For prosthetic PV regurgitation, there are no definite TEE criteria. The criteria discussed for estimation of PR can be applied for estimation of the degree of prosthetic PV regurgitation.

Three-Dimensional TEE The utility of three-dimensional (3D) TEE has not yet been defined for imaging of the PV. In present applications of 3D TEE, PV imaging is limited by the thinness of the leaflets and its distance from the esophagus. Its potential utility has yet to be established.

Summary TEE guidance for PV interventions is challenging, and one needs to use adjunct information from imaging and spectral Doppler interrogation of adjacent structures, including the RV, tricuspid valve, and pulmonary arteries. Since the perioperative use of TEE for PV surgery in congenital heart disease often involves reoperations for PV replacements and conduit revisions, imaging using standard views alone may not suffice. Assistance from echocardiographers experienced in congenital heart disease is recommended.

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