Echocardiographic evaluation of ventricular septal defects

INTRODUCTION — A ventricular septal defect (VSD) is one of the most common congenital cardiac abnormalities in the newborn, but it is less common in the adult due to spontaneous closure of most muscular VSDs during childhood. It can occur as an isolated finding or in combination with other congenital defects. VSD can also be an acquired disorder, occurring after acute myocardial infarction or chest wall trauma. (See "Acute myocardial infarction: Mechanical complications".)

The echocardiographic evaluation of VSD will be reviewed here. Alternative imaging modalities for assessing VSDs, as well as the pathophysiology and clinical features of this defect, are discussed separately. (See "Clinical utility of cardiovascular magnetic resonance imaging", section on 'Congenital heart disease' and "Isolated ventricular septal defects (VSDs) in infants and children: Anatomy, clinical features, and diagnosis".)

ECHOCARDIOGRAPHIC EVALUATION — Echocardiography is valuable not only in diagnosing VSDs but also in the percutaneous and surgical treatment of these defects [1]. Echocardiographic evaluation of VSDs includes:

●Identification of the location of defects on the septum

●Establishing the number of defects

●Delineation of associated anatomic features

●Assessment of the size and hemodynamic significance of the defects

●Guidance of interventional and surgical treatment

The septum is a complex curved surface; traditionally, careful assessment using multiple two-dimensional (2D) echocardiographic planes has been used to define the location and extension of defects. Although defects are generally described as membranous, muscular, supracristal, and inlet, a single VSD may not be confined to any one region of the septum but may extend into multiple adjacent regions (figure 1). Additionally, multiple defects in one or more regions of the septum may also be present. (See "Isolated ventricular septal defects (VSDs) in infants and children: Anatomy, clinical features, and diagnosis".)

Color flow Doppler is a very useful adjunctive method to search and screen for VSDs. This modality can be used to help localize and confirm the presence of VSDs by their characteristic flow patterns.

Three-dimensional (3D) echocardiography can also be used to define the anatomy of VSDs [2,3]. 3D echocardiography allows localization of the defect and defining its relationship to other cardiac structures, and is superior to 2D imaging in delineating the shape and size of the VSD(s) (movie 1A-B). This information is particularly important in choosing candidates and selecting devices for catheter-based closure of defects, and in the management of muscular VSDs in particular [3-5]. (See "Three-dimensional echocardiography".)

Given the increasing availability of real-time 3D echocardiography and the expanding field of interventional and hybrid procedures for treatment of VSDs, echocardiography has an essential role in both the catheterization and surgical suites. Both 2D and 3D echocardiography can be performed either from a transthoracic or transesophageal approach, though transesophageal imaging is often preferred in procedural management of VSDs.

In the catheterization laboratory, transesophageal echocardiography (TEE) is used to guide the positioning of sheaths, wires, and devices, and for confirmation of appropriate position and adequacy of closure post-device deployment. In the operating room, positioning may be guided by TEE, transthoracic echocardiography (TTE), or direct visualization; echocardiography is also used for the assessment of device position and defect closure post-deployment (image 1 and movie 2 and movie 3) [6-8]. Though 3D echocardiography is uniquely suited for device closure, the majority of children undergoing percutaneous or hybrid closure procedures are below 20 to 30 kg, and 2D multiplane TEE is most commonly employed in these procedures.(see "Management of isolated ventricular septal defects (VSDs) in infants and children", section on 'Transcatheter closure')

Membranous VSD — Defects in the membranous septum are located at the intersection of the trabecular, inlet, and outlet regions of the septum, situated just apical to the aortic valve and beneath the septal leaflet of the tricuspid valve. In the parasternal long axis echocardiographic view, these defects are seen just below the aortic valve (image 2 and movie 4 and movie 5). In the orthogonal short axis views of the left ventricular outflow tract, perimembranous defects can be seen beneath the septal leaflet of the tricuspid valve (image 3 and movie 6 and movie 5).

Membranous defects can also be seen beneath the aortic valve in apical imaging planes by angling the transthoracic transducer anteriorly toward the aortic outflow tract. In smaller patients with good subcostal imaging windows, the boundaries of these defects are imaged well in the coronal (image 4 and movie 7) and sagittal (image 5 and movie 8) views of the membranous septum.

Membranous defects may close spontaneously, either partially or completely, due to apposition of the septal leaflet of the tricuspid valve. In some cases, septal leaflet apposition results in an "aneurysm of the ventricular septum," which is best seen in the parasternal long and short axis views but can be appreciated from multiple windows (image 6 and movie 9). Color flow Doppler mapping is useful for establishing the presence of residual shunt flow through the "aneurysm." Aneurysm formation most frequently begins in early infancy and may be associated with a decrease in size or spontaneous closure of even relatively large defects [9].

A number of associated findings may be seen with membranous VSDs, including:

●Double chambered right ventricle, which refers to hypertrophy of the muscle bundles between the inlet and outlet portions of the right ventricle, resulting in mid chamber obstruction (image 7 and movie 10). These muscle bundles are particularly well seen in subcostal coronal and sagittal images, but may also be seen in parasternal short axis imaging in larger patients. (See "Isolated ventricular septal defects (VSDs) in infants and children: Anatomy, clinical features, and diagnosis", section on 'Right ventricular outflow obstruction'.)

●Left ventricular to right atrial shunt (Gerbode defect), which may be demonstrated by two dimensional imaging, but is usually first suggested by color flow mapping demonstrating a high velocity jet originating in the crux of the heart in parasternal short axis, apical four chamber, or subcostal coronal images (image 8 and movie 11).

●A subaortic ridge and associated subaortic stenosis, which is an uncommon finding [10]. Nevertheless, the left ventricular outflow tract should be carefully evaluated in parasternal long axis and apical images to rule out this abnormality.

Muscular defects — Defects in the muscular septum are often multiple, especially if they are a complication of a myocardial infarction, and may be associated with defects in other regions of the septum. Doppler color flow mapping is invaluable for detecting smaller defects that may be difficult to identify within the trabeculations of the right ventricle when only 2D transthoracic imaging is used; defects in the apical septum are the most likely to be missed (image 9 and movie 12). The septum should be interrogated carefully by sweeping the transducer from the right ventricular inflow to the left ventricular outflow tract in long axis and subcostal coronal images, sweeping through serial sections of the ventricle from apex to base in parasternal and parasagittal short axis imaging planes, and by sweeping from caudal to cephalad in apical views.

Doppler color flow mapping is very helpful for identifying muscular defects, even at suboptimal angles of interrogation. However, in patients with increased right ventricular pressure, the color flow patterns for the flow velocity across these and all other types of VSDs become less apparent, decreasing the sensitivity of Doppler for their detection [11,12].

Supracristal defects — Supracristal defects, sometimes referred to as subpulmonic or subpulmonary defects, are located caudal to the pulmonary valve and cephalad to the crista supraventricularis. Although they may be difficult to distinguish from membranous defects in the parasternal long axis view by 2D TTE, they are usually easily identified beneath the pulmonary valve in the parasternal short axis images obtained at the level of the arterial roots (image 10 and movie 13). In younger patients, the relationship between the defect and the pulmonic valve can also be seen in the subcostal sagittal view (image 11 and movie 14).

Prolapse of the unsupported right coronary cusp of the aortic valve into the defect may occur with supracristal VSDs and occasionally with perimembranous defects [13,14]. Associated prolapse of the noncoronary cusp occurs less commonly, may be associated with more significant aortic insufficiency and may be associated with a higher risk of failure of surgical repair [15]. Prolapse of the leaflet into the defect is best observed in parasternal and subcostal long axis, and apical views (image 12 and movie 15). When transthoracic findings are equivocal, TEE can be particularly helpful in diagnosing prolapse. Aortic valve regurgitation may occur with leaflet prolapse due to the progressive distortion of the leaflet; this distortion may be seen in parasternal short axis views of the aortic valve leaflets. The right coronary cusp deformation index and right coronary cusp imbalance indices may be used to quantify the degree of deformation. These indices correlate with the severity of aortic valve regurgitation and may be used in decisions regarding surgical intervention [15,16].

Inlet defects — Inlet defects occur at the crux of the heart, posterior and inferior to membranous and outlet defects, and at the junction of the atrioventricular valves. Similar to other VSDs, inlet defects may be seen in many transthoracic echocardiographic imaging planes; however, these defects and their characteristic relationship to the atrioventricular valves are best demonstrated in apical and subcostal coronal views (image 13 and movie 16). The location of these defects in the posterior septum can be well seen in the parasternal short axis view.

The relationship of the atrioventricular valves to the VSD must be carefully assessed. Tricuspid valve chordal attachments commonly insert on the crest or right ventricular surface of the septum. Anomalous chordal attachments of the mitral valve may also insert on the septum. In addition, either atrioventricular valve may straddle the defect, with chordal attachments crossing the defect and attaching anomalously on the septum or free wall of the opposite ventricle, complicating approaches to repair of the defect. It is important to assure that two atrioventricular valves are present, since inlet VSDs may be part of a larger endocardial cushion defect.

Malalignment defects — Assessment of the relationship between the components of the ventricular septum and the atrial and ventricular septa must be included in the evaluation of a VSD. Malalignment defects occur when there is an abnormal relationship between the atrial and ventricular septa or between the individual components of the ventricular septa [12]. Overriding and straddling atrioventricular valves are seen when there is malalignment of the atrial and ventricular septa. Malalignment of the conal septum, which partitions the great arteries and the trabecular septum dividing the ventricular chambers, may result in subaortic obstruction when there is posterior deviation of the conal septum. Aortic override with or without subpulmonary stenosis occurs when there is anterior deviation of the conal septum (image 14 and movie 17). (See "Tetralogy of Fallot (TOF): Pathophysiology, clinical features, and diagnosis".)

HEMODYNAMIC ASSESSMENT — In addition to evaluating the anatomy of the VSD and its relationship to other cardiac structures, echocardiography also provides information about the hemodynamic abnormalities associated with the VSD, primarily the right and left ventricular pressures and the degree of shunting across the defect. The degree of shunting through a defect is influenced by the size of the defect and by the balance of resistances in the pulmonary and systemic circulations. The pressure and volume loads imposed by large VSDs result in elevations in pulmonary arterial pressure and resistance. Calculations of the ratio of pulmonary to systemic blood flow (Qp/Qs) have less clinical utility than measurements of right ventricular and pulmonary arterial pressures, which reflect the effect of the VSD on the pulmonary vascular bed.

Shunt determination — Two- and three-dimensional (3D) imaging can give important qualitative information about the degree of shunting associated with the VSD. Both left atrial and left ventricular cavity dilation are present in VSDs that produce significant left-to-right shunting. Flow-related increases in transpulmonary and transmitral velocities, assessed by Doppler, may be documented in such lesions, while pulsed Doppler and Doppler color flow mapping can delineate the timing and direction of shunting during the cardiac cycle [17]. Phase velocity mapping cardiac MRI is another quantitative approach for determining the pulmonic to systemic flows. (See "Clinical utility of cardiovascular magnetic resonance imaging", section on 'Congenital heart disease'.)

In most individuals, left-to-right shunting predominates in mid and late diastole and throughout systole, while right-to-left shunting, which may not be clinically significant, is commonly seen in early diastole. However, with evolving pulmonary hypertension and pulmonary vascular disease, right-to-left shunting may occur in early and mid-diastole, and even in late systole [18]. (See "Isolated ventricular septal defects (VSDs) in infants and children: Anatomy, clinical features, and diagnosis".)

The magnitude of left-to-right shunting at a VSD can be estimated using any of several methods.

●Traditionally, the ratio of pulmonary to systemic blood flow (Qp/Qs) has been estimated using volumetric flow data, relying on measurements of aortic and pulmonary or mitral velocity or velocity time integrals, and corresponding luminal diameters or cross-sectional areas [19-23]. Potential sources of error in this measurement include the limitations of lateral resolution in measurement of vessels and valve orifices, changes in the size of these structures during the cardiac cycle, suboptimal angle of Doppler interrogation, and the presence of turbulence in the pulmonary artery obscuring the Doppler outflow signal [24]. (See "Hemodynamics derived from transesophageal echocardiography", section on 'Cardiac output'.)

●Estimates of Qp/Qs using color Doppler and flow convergence [24-27] and of volumetric flow at the VSD have been shown to correlate with the measured Qp/Qs in the cardiac catheterization laboratory. 3D echocardiographic measurements of the color Doppler imaged vena contracta and estimates of shunt flow ratio have also been shown to correlate with cardiac catheterization data [28].

Estimation of left ventricular end diastolic pressures — Tissue Doppler indices, known to correlate with left ventricular end-diastolic pressure (LVEDP) in adults, have also been shown to reflect LVEDP in the setting of VSDs in children. In a study of children undergoing concurrent cardiac catheterization, an E/Ea ratio greater than 9.8 was consistent with an LVEDP greater than 10 mmHg [29]. (See "Tissue Doppler echocardiography", section on 'Estimation of LV filling pressures'.)

Assessment of right ventricular and pulmonary artery pressures — A number of methods can be used to estimate right ventricular and pulmonary artery pressures [30-33]. (See "Principles of Doppler echocardiography", section on 'Relationship between Doppler velocity and pressure gradient'.)

●Using the modified Bernoulli equation (gradient [mmHg] = 4 x [peak velocity]²), the maximum velocity of flow across the VSD, measured by Doppler at an optimal angle of interrogation, can be translated into the pressure gradient between the left and right ventricles (image 15). This value can then be subtracted from the patient's cuff pressure to estimate the systolic right ventricular and pulmonary arterial pressures [30]. In the absence of coexistent right ventricular outflow tract obstruction, large gradients are seen in patients with smaller VSDs and low right ventricular pressure, and small gradients are seen in patients with elevated right ventricular and pulmonary arterial pressures. However, because of differences in the timing of activation of the left and right ventricles, this method may underestimate right ventricular pressure in some patients, most notably in those with an asymmetric or sloped Doppler waveform, where end systolic or mean gradient Doppler determinations may better reflect the pressure gradient across the VSD [34,35]. Pressure recovery phenomena may also be responsible for overestimation of pressure gradients in tunnel type VSDs [36].

●The common findings of tricuspid and pulmonary regurgitation often allow estimation of right ventricular and pulmonary arterial pressures. Right ventricular systolic pressure can be estimated using the sum of the estimated right atrial pressure and the gradient between the right atrium and right ventricle as derived from the modified Bernoulli equation applied to the peak velocity of tricuspid regurgitation (image 16) [31].

●Mean and end diastolic pulmonary arterial pressures can be derived from analysis of the peak and end diastolic velocities of the pulmonary regurgitation jet, respectively (image 17) [32,33,37].

In the assessment of VSDs, these measurements of right ventricular and pulmonary artery pressures give crucial information regarding patient hemodynamics.

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Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Ventricular septal defects in children (The Basics)" and "Patient education: Ventricular septal defects in adults (The Basics)")

SUMMARY

●Ventricular septal defects (VSD) are among the most common congenital cardiac abnormalities in the newborn, but are less commonly present in adults due to spontaneous closure of many muscular VSDs during childhood. VSD can also be an acquired disorder, such as those occurring after acute myocardial infarction. (See 'Introduction' above.)

●Echocardiography is valuable not only in diagnosing VSDs, but also in the percutaneous and surgical treatment of these defects. Echocardiographic evaluation of VSDs includes identification of the number and location of defects, delineation of associated anatomic features, assessment of the size and hemodynamic significance of the defects, and guidance of interventional and surgical treatments. (See 'Echocardiographic evaluation' above.)

●VSDs may occur in a variety of locations, including the membranous septum, muscular septum, supracristal area, and AV valve inlet area. Optimal echocardiographic imaging of defects in these different areas requires imaging from multiple sites as well as the use of color Doppler imaging. (See 'Membranous VSD' above and 'Muscular defects' above and 'Supracristal defects' above and 'Inlet defects' above.)

●In addition to evaluating the anatomy of the VSD and its relationship to other cardiac structures, echocardiography also provides information about the hemodynamic abnormalities associated with the VSD, including the right and left ventricular pressures and the degree of shunting across the defect. (See 'Hemodynamic assessment' above.)