Echocardiography in Pediatric and Adult Congenital Heart Disease, 2nd Ed.

11. Ventricular Septal Defects

Ventricular septal defect (VSD), the most common form of congenital heart disease, is frequently seen by both the adult and pediatric echocardiographer. Fifty percent of all children with congenital heart disease have an associated VSD, with 20% of cases being isolated VSDs. VSDs are an integral part in many forms of congenital heart disease, including tetralogy of Fallot, truncus arteriosus, and double-outlet right ventricle. The incidence of an isolated VSD in live births is 1.5 to 53 per 1000, with wide variation in reported incidence rates.

As in most congenital heart lesions, echocardiography has become the mainstay for clinical diagnosis, for direction of clinical care, and for determination of the approach to therapeutic intervention. Thus, while the presence of a VSD is often easily appreciated, ideal echocardiographic study and interpretation require that the echocardiographer have a detailed understanding of septal anatomy, relationships of VSDs to other intracardiac structures, and the impact of these VSDs on intracardiac hemodynamics.

ANATOMY OF THE VENTRICULAR SEPTUM

The normal ventricular septum is a curved structure extending from the posterior interventricular groove at its inferior and rightward aspect to the pulmonary outflow tract and anterior interventricular groove superiorly and leftward. The ventricular septum can be divided into four regions: the membranous, inlet, outlet, and trabecular septa (Fig. 11.1). The borders of these regions are determined by the tricuspid, pulmonary, and aortic valves, with subdivisions of the regions determined by the muscular bands in the right ventricle: the septal, parietal, and moderator bands. Of the muscular bands, only the moderator band is easily appreciated by standard two-dimensional echocardiography. This muscular bundle originates from the right ventricular (RV) side of the mid-septum at its apical third and crosses the RV chamber to the parietal wall. Also called the trabeculum septomarginalis, the septal band is difficult to appreciate echocardiographically. It is a muscular ridge extending along the RV side of the mid-septum from the insertion of the moderator band, toward the aortic outflow where it bifurcates into an anterior and posterior limb. Within this bifurcation are the membranous septum and the subpulmonary outlet septum.

The membranous septum is a small fibrous portion of the ventricular and atrioventricular (AV) septum located at the base of the heart, adjacent to the anteroseptal tricuspid commissure, the right posterior aortic valve commissure, and the anterior mitral valve leaflet. Because of the relative apical placement of the tricuspid valve compared with the mitral valve, a portion of the membranous septum, the membranous AV septum, separates the left ventricle (LV) from the right atrium.

The three other regions of the ventricular septum are all muscular; they radiate out from the membranous septum. The inlet septum is located between the AV valves inferior to the membranous septum with its apical border being the chordal attachments of the AV valves. The outlet septum makes up the most anterior and superior part of the ventricular septum and is located above an imaginary line between the membranous septum, the papillary muscle of the conus, and the anterior infundibular wall. The remainder of the ventricular septum is the trabecular septum, which is the largest region. The trabecular septum is broken into the subregions shown in Fig. 11.2: posterior (sometimes called inlet muscular), anterior, mid-muscular, and apical. The posterior trabecular (or muscular) septum is posterior to the septal attachment of the tricuspid valve. The anterior trabecular septum is anterior to the septal band (or trabeculum septomarginalis). As the septal band is difficult to appreciate by echocardiography, the anterior trabecular septum is identified as anterior to the mid-septum and at, or superior to, the level of the moderator band. The mid-muscular septum is posterior to the septal band and superior to the moderator band. The apical septum is inferior to the moderator band and can be divided into an anterior or “infundibular” apex and posterior or “inflow” apex.

ANATOMY OF VENTRICULAR SEPTAL DEFECTS

VSDs can be divided into two fundamental types. In the first type, there may be adequate septal tissue, but there is malalignment of portions of the ventricular septum causing a “gap” or VSD. The malaligned septal components can be parallel but offset, can cross each other in oblique planes, or even can be perpendicular to each other. The second fundamental type of VSD is due to a deficiency in septal tissue. This deficiency either can be congenital or can be acquired following myocardial infarction or trauma.

Figure 11.1. Diagrammatic (A) and pathologic (B) representations of the normal interventricular septum as viewed from the right ventricular aspect. APM, anterior papillary muscle of the tricuspid valve; I, inlet; M, membranous; MB, moderator band; O, outlet; SB, septal band; T, trabecular. (B, Reprinted with permission from Becker A, Anderson R. Anomalies of the ventricles. In: Cardiac Pathology and Integrated Text and Colour Atlas. New York: Raven Press, 1983:12.2.)

Several classification schemes to describe the location of VSDs are in common use. Thus, the nomenclature can be quite confusing. Efforts to synthesize the various naming systems have been made by the Congenital Heart Surgery Nomenclature and Database Project and subsequently by the International Working Group for Mapping and Coding of Nomenclatures for Pediatric and Congenital Heart Disease. The classification systems most commonly used are shown in Table 11.1. We use the Congenital Heart Surgery Nomenclature system in this chapter and have chosen to use the following names: perimembranous (including VSDs due to malalignment of the conal septum), subarterial, inlet, and muscular. Defects can occur entirely within a portion of the septum or can extend across portions of the septum (e.g., a perimembranous-to-inlet defect). Regardless of which naming system is used, it is most important to be consistent so that accurate and clear communication can occur.

ECHOCARDIOGRAPHIC ASSESSMENT OF VENTRICULAR SEPTAL DEFECTS

A systematic echocardiographic assessment of VSDs involves a detailed anatomic and hemodynamic description. This includes description of the exact location of the defect in the ventricular septum with particular attention paid to (a) the relationship of the VSD to valves and valve attachments, (b) identification of complicating factors specific to the VSD location, (c) description of the anatomic size of the defect, (d) estimation of right ventricular systolic pressures, and (e) estimation of overall shunt size.

The general imaging strategy used to identify and describe VSDs consists of sweeping the entire septum in both two-dimensional and color Doppler imaging modalities from apex to base and from left to right. Imaging should be performed from the best acoustic window that shows the septum perpendicular to the ultrasound beam and the flow across the defect parallel to the beam. Because of the curved nature of the ventricular septum, optimal imaging of a VSD can be from a subcostal, parasternal, apical, or right parasternal window. It often requires imaging from multiple planes to fully interrogate the ventricular septum.

Figure 11.2. Location of ventricular septal defects (VSDs) within the ventricular septum as seen from the right ventricular aspect. A: Locations of perimembranous, subarterial, and inlet VSDs. B: Subtypes of muscular VSDs: anterior, mid-muscular, posterior, and apical (including VSDs of the posterior right ventricular [RV] inflow apex and the anterior infundibular apex). APM, anterior papillary muscle of the tricuspid valve; MB, moderator band; SB, septal band.

Description of Ventricular Septal Defect Location

The exact location of the VSD can be identified echocardiographically and described using the categories described earlier (perimembranous, subarterial, inlet, or muscular). Figure 11.3 is a diagrammatic representation of the various types of defects and their location in standard echocardiographic views. Identification of the location of the major portion of the defect should be accompanied by descriptions of extension of the defect into adjacent portions of the ventricular septum and the direction of malalignment of the septum. Defects in larger regions, such as the trabecular septum, often need to be more precisely located by describing the relationship to adjacent cardiac structures. The presence or absence of specific complicating factors associated with each VSD location should also be evaluated and reported.

Figure 11.3. Diagrammatic representation of ventricular septal defect (VSDs) locations as seen in standard echocardiographic views. A: Parasternal long-axis view showing muscular, perimembranous outlet, and subarterial VSDs. B: Parasternal short-axis view at the base showing perimembranous and subarterial VSDs. C: Parasternal short-axis view at the level of the left ventricular (LV) papillary muscles showing muscular VSDs. D: Apical four-chamber view showing inlet and muscular VSDs. E: Apical five-chamber view showing muscular and perimembranous VSDs. Ao, aorta; LA, left atrium; MV, mitral valve; PA, pulmonary artery; PV, pulmonary valve; RA, right atrium; RV, right ventricle; TV, tricuspid valve.

Perimembranous VSDs

Perimembranous defects are the most common type of VSD, comprising about 80% of VSDs. Perimembranous VSDs involve the membranous ventricular septum adjacent to the aortic and tricuspid valves. Perimembranous defects can be imaged from a parasternal, apical five-chamber, or subcostal window where they are seen immediately adjacent to both the tricuspid and aortic valves as demonstrated in Figure 11.4 When the VSD extends primarily toward the aortic valve, it is called a perimembranous outlet defect; when the defect is primarily adjacent to the tricuspid valve, it is called a perimembranous inlet defect.

FIGURE 11.4. Perimembranous ventricular septal defect (VSD) (arrows). A: Parasternal long-axis showing the VSD adjacent to the aortic valve. B: Parasternal short-axis image showing defect between aortic and tricuspid valves. Apical five-chamber view with two-dimensional (C) and color (D) images showing relationship of VSD to left ventricular (LV) outflow tract. Ao, aorta; LA, left atrium; LV, left ventricle; mb, moderator band; PA, pulmonary artery; RA, right atrium; RV, right ventricle. See Video 11.1.

Figure 11.5. Anterior malalignment perimembranous ventricular septal defect in a patient with tetralogy of Fallot as seen in parasternal long-axis (A) and short-axis (B) views. Anterior deviation and rotation of the outlet septum results in the ventricular septal defect, an enlarged aortic outflow overriding the main body of the ventricular septum, and narrowed subpulmonary outflow. Ao, aorta; LV, left ventricle; RV, right ventricle. See Video 11.2.

A perimembranous VSD may be related to deficiency of tissue in the region of the membranous septum or may be due to malalignment of the outlet septum with the muscular ventricular septum. The gap caused by malalignment of the outlet septum can be due to either anterior or posterior deviation of the outlet septum. Anterior deviation creates a VSD of the type seen in tetralogy of Fallot (Fig. 11.5), with override of the aorta; this type of malalignment VSD can also be seen without associated pulmonary stenosis. Posterior deviation of the outlet septum creates a VSD of the type seen in association with interrupted aortic arch with muscular narrowing of the LV outflow tract (Fig. 11.6).

Because of their location adjacent to the tricuspid valve, perimembranous defects can be associated with tricuspid septal leaflet distortion and tricuspid regurgitation. Accessory tissue from the septal leaflet of the tricuspid valve, or a part of the septal leaflet itself, can partially or completely close the defect; this tissue is sometimes referred to as a ventricular septal aneurysm (Fig. 11.7). Occasionally, blood flow traverses through the VSD from the LV, through the aneurysmal tissue, and across the tricuspid valve and enters the right atrium resulting in LV–to–right atrial shunt (Fig. 11.8AB). Misinterpretation of this high-velocity flow from this LV–to–right atrial shunt as tricuspid regurgitation can lead to an erroneous overestimation of RV pressure. A related, but distinct, type of LV–to–right atrial shunt is the Gerbode defect, which is an LV–to–right atrial connection created by a defect in the portion of the membranous ventricular septum separating the LV from the right atrium (Fig. 11.8CD).

As perimembranous VSDs are also adjacent to the aortic valve, this valve can also be affected. In about 10% of perimembranous VSDs, there is associated aortic valve prolapse, and in 6% to 8%, there is associated aortic regurgitation. Aortic valve prolapse into the VSD is identified echocardiographically by identification of the right or noncoronary aortic cusp protruding into the VSD; this is typically best seen in the parasternal long- and short-axis views. Because aortic cusp prolapse is more common with subarterial defects, it is discussed in detail below. Because of its importance in the development of aortic regurgitation, the presence or absence of aortic cusp prolapse should be reported with any defect located immediately adjacent to the aortic valve.

Figure 11.6. Posterior malalignment perimembranous ventricular septal defect in a patient with interrupted aortic arch. Posterior displacement of the outlet septum results in creation of the ventricular septal defect, narrowing of the left ventricular (LV) outflow tract, and enlargement of pulmonary outflow. Ao, aorta; LV, left ventricle; RV, right ventricle. See Video 11.3.

Figure 11.7. Ventricular septal aneurysm (arrow) made up of redundant tricuspid valve tissue that partially closes a perimembranous ventricular septal defect as seen in a parasternal short-axis view with two-dimensional and color Doppler. Ao, aorta; LA, left atrium; PA, pulmonary artery; RA, right atrium; RV, right ventricle. See Video 11.4.

A subaortic ridge, with or without significant subaortic obstruction, is seen in 3% to 6% of cases of perimembranous VSDs. In most of these cases, the subaortic ridge or ring is fibromuscular and is located immediately at the inferior aspect of the VSD (VSD is located distal to the ridge). In about half of these cases, there is an associated ventricular septal aneurysm. The subaortic ridge may develop with time; in a study by Eroglu et al., three-quarters of the patients developed a subaortic ridge after initial presentation. Blood flow disturbance beyond the subaortic ridge may also contribute to the development of aortic regurgitation.

Subarterial VSDs

Subarterial defects make up 5% to 10% of VSDs and are more common in the Asian population. These defects are located beneath both semilunar valves and result from a deficiency in the conal, or outlet, septum. Subarterial defects are seen by echocardiography to be immediately beneath the aortic valve in long-axis views and immediately adjacent to both the aortic and pulmonary valves in short-axis views (doubly-committed VSD) (Fig. 11.9). These defects are sometimes referred to as supracristal, but there is controversy regarding the definition of the crista supraventricularis, which determines the location of a supracristal defect. There is agreement that the crista supraventricularis is the muscle mass separating the tricuspid and pulmonary valves, but its exact location in relation to the parietal band, infundibulum, and septal band is inconsistently defined in the literature. As it is typically difficult to appreciate these muscle bands by echocardiography, we believe that the term subarterial is a more precise echocardiographic description. With subarterial VSDs, there is typically an absence of muscular tissue between the semilunar valves. However, occasionally the defect can be completely surrounded by muscle.

Prolapse of the right coronary cusp of the aortic valve into the defect, with distortion of the aortic valve, is present in up to 60% to 70% of subarterial VSDs. Prolapse is demonstrated as a diastolic bulging of the right aortic cusp and portion of the sinus into the RV in the long-axis and short-axis views (Fig. 11.9). It can be mild and transient during early systole, or severe, encompassing the entire cusp with tethering to the VSD throughout systole and diastole. The aortic cusp that is tethered into the defect will appear “beaked” and shortened in systole as compared to the uninvolved cusps. Because aortic prolapse can be associated with aortic regurgitation in up to one-third of patients, the presence or absence of aortic cusp prolapse should be reported with any defect located immediately adjacent to the aortic valve. Because of the risk of aortic regurgitation, some cardiologists advocate surgical repair of all subarterial defects regardless of the size of the VSD. However, development of and progression of substantial aortic regurgitation in patients with aortic cusp prolapse into a subarterial VSD is not universal. Cheung et al. reported that in patients with mild to moderate aortic cusp prolapse, 92% had no change or improvement in their degree of aortic regurgitation following VSD closure; none progressed to moderate or severe aortic regurgitation. In contrast, moderate to severe aortic cusp prolapse was associated with moderate to severe aortic regurgitation in most cases, and the degree of aortic regurgitation was unchanged or worsened following VSD closure with concomitant aortic valvuloplasty.

Occasionally, blood flow traverses through the VSD from the LV, through the aneurysmal tissue, and across the tricuspid valve and enters the right atrium resulting in LV–to–right atrial shunt (Figure 11.8. Fig. 11.8AB). Misinterpretation of this high-velocity flow from this LV–to–right atrial shunt as tricuspid regurgitation can lead to an erroneous overestimation of RV pressure. A related, but distinct, type of LV–to–right atrial shunt is the Gerbode defect, which is an LV–to–right atrial connection created by a defect in the portion of the membranous ventricular septum separating the LV from the right atrium (Fig. 11.8CD).

Figure 11.9. Parasternal long-axis (A and B) and parasternal short-axis (C) views of a subarterial ventricular septal defect (VSD) with prolapse of the right coronary cusp of the aortic valve (arrows) into the defect and mild aortic regurgitation. The subarterial defect is characterized by absence of muscular separation of the pulmonic valve from the VSD in the short-axis view. Ao, aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RV, right ventricle. See Video 11.6.

Inlet VSDs

Inlet VSDs are located posteriorly immediately adjacent to both AV valves. These defects are often best imaged from an apical four-chamber view or a parasternal short-axis view (Fig. 11.10). They most commonly occur as part of atrioventricular septal defects (AVSD) but can be isolated. Inlet VSDs should be distinguished from posterior muscular (also called inlet muscular) VSDs, which are located near the inlet septum but are separated from the AV valves by a rim of muscle. Inlet VSDs may be formed by malalignment of the atrial and ventricular septa, resulting in some degree of AV valve override and not infrequently with straddling of AV valve chordal attachments.

AV valve override occurs when an AV valve is positioned over a VSD and relates to both ventricles. AV valve straddling occurs when chordal attachments from an AV valve cross the VSD to the opposite side of the ventricular septum or contralateral ventricle. An AV valve can override, straddle, or both. Tricuspid valve straddling with chordal attachments to the left ventricular side of the septum can be seen with inlet VSDs (Fig. 11.11). The mitral valve typically does not straddle an inlet VSD but more commonly may straddle an outlet or a perimembranous defect. Because chordal apparatus crossing the defect impairs placement of the surgical patch, straddling and overriding of either AV valve must be accurately identified and interpreted by the echocardiographer.

Other types of AV valve involvement are common with inlet VSDs, most often involving the tricuspid valve. The tricuspid valve may be intrinsically abnormal with associated tricuspid regurgitation. The inlet defect may be partially or completely closed by redundant tricuspid septal leaflet tissue. When the VSD is associated with a partial AVSD, there is a cleft in the anterior leaflet of the mitral valve, which may result in regurgitation. Valve abnormalities associated with inlet VSDs should be identified as part of the complete echocardiographic evaluation.

Muscular VSDs

Muscular defects comprise 5% to 20% of VSDs. They can be described as being anterior, mid-muscular, posterior, or apical in location (Fig. 11.2). Anterior muscular defects are located anterior to the septal band (or trabeculum septomarginalis), which extends along the mid-septum from the insertion of the moderator band toward the membranous septum. The septal band bifurcates into an anterior and a posterior limb to surround the membranous septum and a portion of the outlet septum. The anterior muscular septum also includes anterior outlet defects, which are located in the smooth walled outlet septum but separated by a muscular rim from the semilunar valves. Mid-muscular defects are posterior to the septal band, anterior to the septal attachment of the tricuspid valve, and superior to the moderator band. Posterior muscular defects are located posterior to the septal attachment of the tricuspid valve; posterior-inlet muscular defects are located immediately below the AV valves but separated from the valves by muscle tissue.

Figure 11.10. Inlet ventricular septal defect (arrows) imaged from apical four-chamber (A) and parasternal short-axis views (B). LA, left atrium; LV, left ventricle; mb, moderator band; RA, right atrium; RV, right ventricle. See Video 11.7.

Figure 11.11. Apical four-chamber view (A) of the tricuspid valve overriding an inlet ventricular septal defect with tricuspid valve tissue partially closing the defect. Apical four-chamber (B) and subxiphoid oblique sagittal (C) en face views of a straddling tricuspid valve with attachments to the posteromedial papillary muscle of the left ventricle (LV) (arrow in C). ant, anterior; inf, inferior; LA, left atrium; MV, mitral valve; post, posterior; RA, right atrium; RV, right ventricle; sup, superior; TV, tricuspid valve. See Video 11.8.

Apical muscular VSDs are located inferior to the moderator band and include defects of the RV inflow apex (which is located more posteriorly) and the more anterior “infundibular” apex. The two RV apices are divided by dense trabeculations that run from the septum to the RV free wall; the LV may connect with the infundibular apex (43% of cases), the RV inflow apex (45% of cases), or both RV apices. In LV infundibular apical VSDs, there are usually multiple openings on the RV side of the septum. Hypertrophied RV apical trabeculations and the moderator band separate the infundibular apex and the VSD from the remainder of the RV. Occasionally, closure of these defects, either by surgery or transcatheter device, results in placement of the device or patch among RV trabeculae rather than across the true septum. This may result in closing off the infundibular apex of the RV, thereby making it physiologically part of the LV.

The best imaging plane for muscular VSDs is dependent on the exact location of the defect within the muscular septum; the ideal plane will demonstrate the VSD in the axial resolution and the flow across it parallel to the ultrasound beam. Determining the precise location of a muscular VSD may require combining information gained from several imaging planes as shown in the example in Figure 11.12. Defining the particular subtype of muscular VSD can be difficult because, with the exception of the moderator band, the muscular bands of the RV that are used to define the subtypes of muscular VSD can be difficult or impossible to visualize by echocardiography. To help clarify the location of a muscular VSD, we recommend describing the defect in both the anterior/posterior location as well as an apical/basal location. In the example shown in Figure 11.12, the defect is located in the RV infundibular apex anterior to the position of an imaginary apical extension of the septal band. Fig. 11.12 demonstrates a specific caveat of localization of VSDs using the apical four-chamber view. The apical four-chamber image plane demonstrates more posterior structures in the far field such as the atria and AV valves, but in the near field of the imaging plane it often displays a more anterior portion of the apical ventricular septum. The short-axis image in Figure 11.12 shows the more anterior location of this defect.

A patient may have multiple muscular VSDs, sometimes referred to as “Swiss cheese” septum, or may have a muscular VSD in addition to a VSD in another location (e.g., perimembranous or inlet). These additional defects can be easy to miss, especially when the first defect is large in size and there is equalization of pressures in both ventricles.

Special Considerations

Additional Abnormalities

As many as 60% of patients with VSDs have associated cardiac lesions. Some can be easily missed if not specifically looked for. Ventricular septal defects and aortic arch abnormalities keep close company. From 17% to 33% of patients with coarctation of the aorta have an associated VSD, as do nearly all patients with an interrupted aortic arch. The VSD is mid-muscular in almost half of these cases and perimembranous in almost a quarter of patients with coarctation and a VSD.

Figure 11.12. Localization of a muscular ventricular septal defect (VSD) near the right ventricular (RV) infundibular apex. Parasternal long-axis (A), short-axis (B), and apical four-chamber views (C) demonstrating localization of muscular VSD. D: Three-dimensional image acquired from a subxiphoid transducer position with the RV free wall cropped to show the entire septum from the RV aspect with localization of the defect in the anteroapical septum at the RV infundibular apex. Movie of this image demonstrates rotation of the septum with VSD imaged from left ventricular (LV) and RV aspects. E: Pathologic specimen showing the divisions of the ventricular septum as viewed from the RV aspect with the location of the muscular VSD circled. F: Representation of the subtypes of muscular VSDs with the location of the VSD seen in images A–D circled. MB, moderator band; RA, right atrium; RVOT, right ventricular outflow tract. See Video 11.9. (E, Reprinted and modified with permission from Becker A, Anderson R. Anomalies of the ventricles. In: Cardiac Pathology and Integrated Text and Colour Atlas. New York: Raven Press, 1983:12.2, Figure 12.1.)

A patent ductus arteriosus is commonly coincident with a VSD. With a large VSD and associated pulmonary artery systolic hypertension, near equalization of aortic and pulmonary artery pressure often results in laminar (and difficult to appreciate) ductal flow. This same ductus may be easy to appreciate after VSD closure, when pulmonary artery pressure is decreased.

The association of subaortic stenosis with VSD has been described previously in this chapter. Subaortic stenosis associated with a perimembranous VSD is usually a fibromuscular ridge or ring with the VSD located distal to the obstruction. Muscular or tunnel-like subaortic stenosis can be created by posterior malalignment of the conal septum and is characteristically associated with aortic arch anomalies. In these cases, the VSD is located below the level of the LV outflow tract obstruction.

A double-chambered right ventricle (DCRV) has an associated VSD in 63% to 90% of patients. In DCRV, anomalous muscle bundles located below the infundibulum divide the RV into a high-pressure inlet chamber and a low-pressure outlet chamber (Fig. 11.13). The anomalous muscle bundles run from the ventricular septum to the RV anterior wall and can insert anywhere from the apex to the conoventricular junction. The VSD is most often perimembranous and connects to the high-pressure portion of the RV, but the VSD can be located anywhere. The relative locations of the anomalous muscle bundle and the VSD determine the RV chamber with which the VSD connects. When the VSD connects the LV to the low-pressure portion of the RV, it acts physiologically like an isolated VSD. When the VSD connects the LV to the high-pressure portion of the RV, it is physiologically like tetralogy of Fallot. If RV pressure is high, this can result in right-to-left shunt flow through the VSD. In natural history studies of VSD patients, 3% to 7% developed RV outflow tract stenosis, which tended to progress in severity over time. The separating RV muscle bundles are typically noted in the mid-RV. Flow disturbance across this region is poorly visualized from the parasternal transducer position as flow direction is perpendicular to the ultrasound beam. Because of their more anterior location, these bundles are poorly visualized using the apical transducer position, making the DCRV an easy lesion to miss by cursory examination. Images from the subcostal transducer position clearly demonstrate these obstructive muscle bundles and allow Doppler interrogation parallel to flow.

Figure 11.13. Large perimembranous ventricular septal defect (VSD) complicated by double-chambered right ventricle. Parasternal short-axis (A) and subcostal sagittal (B) views in two-dimensional and color flow mapping show the “napkin ring” of muscle bundles and flow disturbance (arrow) superior to the VSD. This VSD is on the “high pressure” side of the obstructing muscle bundles. ant, anterior; Ao, aorta; inf, inferior; LA, left atrium; LV, left ventricle; post, posterior; RA, right atrium; RV, right ventricle; RVOT, right ventricular outflow tract; sup, superior. See Video 11.10.

Traumatic VSDs

Traumatic VSDs occur most commonly in the muscular septum near the apex, but perimembranous defects have been reported associated with tricuspid valve injury. Multiple traumatic VSDs may also occur. A direct blow to the chest is the most common mechanism for creating this VSD. The trauma may cause septal rupture at the time of injury, or the development of the defect may be delayed for 2 to 6 days postinjury. Delayed traumatic VSDs are thought to have arisen from areas of the septum where a myocardial contusion caused sufficient devascularization to lead to myocardial necrosis and perforation. Because traumatic VSDs can develop, or extend, in the days following the initial injury, serial echocardiograms are important even if a VSD is not seen on an initial study.

Assessment of Ventricular Septal Defect Size

Historically, the size of a VSD has been related to the size of the aortic annulus with a defect less than one-third the diameter of the aortic annulus considered small, a defect one-third to one-half the size of the annulus considered moderate sized, and a large VSD being greater than one-half to two-thirds the size of the annulus. Measurement of the size of the VSD by measuring the largest diameter demonstrated by color flow mapping has been shown to closely reflect the measurements made by angiography and at surgery. However, this anatomic definition of VSD size can be limited as the defect may not be round and the size often varies throughout the cardiac cycle. Muscular defects, in particular, may have an oblique course through the ventricular septum and may have multiple openings on the RV side of the septum. Therefore, imaging the VSD in multiple planes is crucial to an accurate determination of VSD size. For irregularly shaped defects, three-dimensional echocardiographic imaging may be particularly helpful.

Determining the size and significance of a VSD can be more complicated than it may seem. While small defects typically have large Doppler-measured pressure gradients between the ventricles and large defects have small pressure gradients, variations in pulmonary vascular resistance make this relationship far from universal. The infant with a delayed fall in pulmonary vascular resistance may have a minimal gradient across a small VSD or little left heart dilation with a large VSD. Similarly, the degree of left-to-right shunting in a moderate or large VSD with left heart overload often evolves over time. If pulmonary hypertension progresses, left-to-right shunt size, the degree of left heart dilation, and the VSD pressure gradient all regress. Eisenmenger syndrome results from the progression of pulmonary vascular obstruction with resultant development of right-to-left shunting at the VSD and progressive cyanosis. Thus, we recommend independent anatomic size and hemodynamic descriptions of VSDs.

HEMODYNAMIC DESCRIPTION OF VENTRICULAR SEPTAL DEFECTS

In addition to a detailed anatomic description of the VSD, echocardiography can provide a hemodynamic or “functional” description. As moderate and large VSDs are associated with dilation of the left heart chambers and/or pulmonary hypertension, the “functional” assessment would ideally include evaluation of right heart pressures and a quantification of the amount of shunt flow through the defect.

Figure 11.14. Noninvasive Doppler evaluation of right heart pressures. Spectral Doppler tracings of ventricular septal defect (VSD) are obtained from a left parasternal window, while tricuspid regurgitation and the left ventricular–to–right atrial shunt are both obtained from an apical window. BP, blood pressure; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle; TR, tricuspid regurgitation.

Evaluation of Right Heart Pressures

The velocity of blood flow across the VSD as measured by spectral Doppler can be used to estimate right ventricular systolic pressure as long as the systolic blood pressure is known (Fig. 11.14). In the absence of LV outflow obstruction, the RV systolic pressure (RVPsystolic) is equal to four times the square of the peak VSD velocity (VVSD2) subtracted from the systolic blood pressure (BPsystolic) or

RVPsystolic = BPsystolic – 4VVSD2

The echocardiographic measurement of the peak VSD gradient works well in most cases, especially if the spectral Doppler tracing is plateau-shaped. However, it will overestimate the LV-RV peak-to-peak gradient if the tracing peaks briefly in only a portion of systole. In these types of tracings, echo measurements of both the mean systolic gradient and the end-systolic gradient correlate well with invasive measures of the VSD gradient (Fig. 11.15).

The estimate of RV systolic pressure obtained using the VSD gradient can be validated by using the tricuspid regurgitation peak velocity. The RV systolic pressure is equal to four times the square of the tricuspid regurgitation velocity (4VTR2) plus the estimated or measured right atrial a-wave (RA) pressure:

Figure 11.15. Simultaneous catheter-measured intracardiac pressure tracings from the right ventricle (RV) and left ventricle (LV) with corresponding spectral Doppler tracing of velocities across ventricular septal defects (VSDs). A: VSD with a “plateau”-shaped velocity tracing indicating holosystolic interventricular pressure gradient. B: “Spiky” tracing across a VSD with only transient early systolic interventricular pressure gradient.

RVPsystolic = 4VTR2 + RA pressure

Underestimation of RV pressure can occur due to a poor angle of Doppler interrogation or an incomplete TR signal. Overestimation of tricuspid regurgitation velocities may be due to contamination of the Doppler signal by an LV–to–right atrial shunt either through the tricuspid valve or a Gerbode defect. Estimation of RV systolic pressure by VSD gradient and tricuspid regurgitation velocities should give similar, if not identical, results. In the absence of pulmonary stenosis, the RV systolic pressure is equal to the pulmonary artery systolic pressure. Figure 11.14 gives an example of how VSD and tricuspid regurgitation velocities can be used to estimate right heart pressures noninvasively.

The pulmonary regurgitation velocity measured by spectral Doppler can be used to estimate mean and diastolic pulmonary artery pressures. This should be measured to serve as an additional validation of the hemodynamic assessment of a significant-sized VSD. Elevated pulmonary regurgitation velocity should alert the echocardiographer to the presence of pulmonary artery diastolic hypertension, while normal pulmonary regurgitation velocities ensure the absence of substantial elevation of pulmonary artery diastolic pressure.

Quantification of Shunt Flow

VSD shunt volume is determined by the size of the VSD and the pulmonary vascular resistance. Quantification of the amount of shunt flow can be determined in several ways. Left heart chamber dilation is associated with pulmonary–to–systemic flow ratio (Qp/Qs) of greater than 1.5:1. Two Doppler-based methods can also be used to quantitate shunt flow and estimate Qp/Qs, although each method makes several assumptions. The first method uses pulsed-wave spectral Doppler across representative valves to quantify pulmonary and systemic flow (Fig. 11.16). Calculating systemic flow involves measuring the LV outflow tract pulsed-wave Doppler velocity-time integral (VTI) from an apical view and the LV outflow tract diameter from a two-dimensional parasternal long-axis image. These values are then used in the following formula:

Flow (L/min) = (VTI [cm/s] × cross-sectional valve area [cm2] × 60 s/min)/1000 cm3/L

Figure 11.16. Doppler assessment of ventricular septal defect (VSD) shunt flow. A–D: Images and data necessary to calculate Qp/Qs include measurements of right and left ventricular outflow tract diameters and the velocity-time integral (VTI) of the spectral Doppler tracings of the right and left ventricular outflow tracts (RVOT and LVOT). E: Measurement of the distance (marked by calipers) from the VSD to the first aliasing velocity, which is used in the proximal isovelocity surface area (PISA) calculation of VSD shunt flow; in this patient, use of the PISA method resulted in overestimation of shunt flow as the flow toward the VSD did not accelerate in a hemispherical shape.

where the cross-sectional area of the aortic valve is π (diameter/2)2. Calculating the amount of pulmonary flow is more difficult. Accurate determination of VTI assumes laminar flow across the area in question; with VSDs, there is often turbulent flow across the pulmonary valve due to high flow volume, which may make the pulmonary outflow Doppler VTI unreliable in calculating the amount of pulmonary flow. In this case, mitral inflow Doppler VTI and mitral valve area can be used to calculate pulmonary flow. In the absence of a doming mitral valve, mitral valve area is based on two-dimensional measures of the mitral annulus in the four-chamber and/or parasternal long-axis views. Measurement of mitral valve flow volume is limited by the non-circular geometry of the mitral annulus. Several additional assumptions are made using this method of calculating systemic and pulmonary flows; these include the absence of significant semilunar valve regurgitation, the absence of other shunt lesions, and optimal Doppler angle alignment for measurement of VTI. Changes in the Doppler tracing with respiration can be minimized by averaging three consecutive heartbeats. In small children, there may be significant error in the measurement of flow volumes due to a proportionally greater error in the measurement of the diameter of flow regions. This diameter measure and its associated error are squared when calculating area for flow volumes. Because of these multiple, potential sources of error, this method of estimating systemic and pulmonary flow may not provide acceptable accuracy for decision making in many patients.

Another Doppler method for estimating the amount of shunt flow involves use of color Doppler and measures the proximal isovelocity surface area (PISA). The principle behind PISA is that blood flow crossing an orifice, such as a valve or VSD, speeds up as it approaches the orifice in a uniform, hemispherical pattern. By measuring the distance from the orifice to the point at which blood flow reaches a particular speed, the flow rate can be calculated. The location of the defined velocity can be determined by the Nyquist limit and the first line of aliasing color. This allows the following formula to be used:

Flow rate (mL/s) = 2Π(r)2 × Nyquist limit (cm/s)

where r is the distance from the VSD to the first aliasing velocity. Shunt volume across the VSD can then be calculated by multiplying the flow rate by the shunt duration time as determined by spectral Doppler across the VSD. This gives a final formula of:

Shunt volume (L/min) = [2Π(r)2 × Nyquist limit (cm/s)×

shunt duration (s) × heart rate

(beats/min)] /1000 mL/s

The PISA method requires several assumptions and has several important potential sources of error. One assumption is that the flow toward the VSD accelerates in a hemispherical shape. The second is that all the flow that enters the area of aliasing velocity is assumed to cross the VSD. Precise localization of the VSD orifice can be difficult, leading to errors in measurement of the distance from the VSD orifice to the first aliasing velocity (r). Finally, surface motion of the heart relative to the direction of VSD flow can cause additional errors in the measurement of the PISA radius (r). PISA has been reported to overestimate the Qp/Qs determined at catheterization but this method still may be helpful for serial assessment of shunt size over time in a subset of patients.

Closure of Ventricular Septal Defects

Many VSDs spontaneously close, or become significantly smaller, over time. Smaller defects are more likely to close spontaneously, but some large defects do close without intervention. In a study by Hornberger et al., all the VSDs that closed completely had an initial size, as measured by color flow mapping, of 4 mm or less. Even larger defects decreased in size with a frequency of 44% in defects less than 4 mm, 30% in defects of 4 to 6 mm, and 14% in defects greater than 6 mm in diameter. The most common mechanism of closure of perimembranous VSDs is by “aneurysmal transformation,” in which redundant tricuspid valve tissue, or the tricuspid septal leaflet itself, closes the VSD (Fig. 11.7). Perimembranous or subarterial VSDs can also be closed by prolapse of aortic valve leaflet tissue. However, the subsequent distortion of the aortic valve may result in the development of aortic regurgitation. Muscular VSDs close by ingrowth and hypertrophy of muscle; in infants this is thought to be a continuation of the in utero process of coalescence of sheets of muscle to close interventricular channels. Studies of muscular VSDs in newborns report spontaneous closure rates of 76% to 89% by 12 months of age.

Surgical Repair

Because no surgical approach allows visualization of the entire ventricular septum, a clear understanding of the number of defects, relative sizes, and exact location must be provided by the echocardiographer to facilitate a satisfactory surgical result. The surgical approach is determined by the expected defect location. Defects typically closed transatrially through the tricuspid valve include perimembranous, inlet, and some muscular defects. Subarterial defects are often best closed through the pulmonary valve. Muscular VSDs located below the moderator band and anterior to the septal band may be best approached with an anterior right ventriculotomy; an apical left ventriculotomy is occasionally used to approach posterior apical muscular defects (Fig. 11.17). The location of each defect must be presented clearly to the surgeon using the ultrasound images, mutually understood descriptors, and, often, diagrammatic presentation. Especially helpful descriptors include the distance and relationship to easily identifiable cardiac structures such as the moderator band, cardiac valves, and interventricular grooves. More detailed descriptions will result in a briefer surgical exploration, decrease trauma to adjacent myocardium or valves, and limit the potential for a significant residual intracardiac shunt.

Figure 11.17. Potential surgical approaches to ventricular septal defect closure. A: Perimembranous, inlet, posterior muscular, and mid-muscular defects are typically closed by transatrial approach. B: Subarterial and some anterior muscular defects may be closed through the pulmonic valve. C: Anterior muscular defects inferior to the moderator band may require an anterior right ventriculotomy. D: Some surgeons use an apical left ventriculotomy to close posterior apical defects. (The pathologic specimen image is reprinted and modified with permission from Becker A, Anderson R. Anomalies of the ventricles. In: Cardiac Pathology and Integrated Text and Colour Atlas. New York: Raven Press, 1983:12.2, Figure 12.1.)

Transcatheter and Hybrid Perventricular Device Closure

Recently, transcatheter device closure and hybrid surgical and transcatheter approaches have developed as effective alternatives or adjuncts to surgical intracardiac patch closure of VSDs. Currently, devices are available for closure of perimembranous and muscular VSDs. Use of perimembranous VSD devices has been limited due to the complications of complete heart block or development of significant regurgitation of the tricuspid or aortic valves.

Prior to device closure, echocardiography should describe the size of the rims around the VSD in addition to information regarding the size and number of defects and their exact locations. The device is usually placed with transesophageal echocardiographic (TEE) guidance via either a percutaneous or perventricular approach. Three-dimensional imaging either by transesophageal, epicardial, or transthoracic probe positions may help define defect and rims. In a percutaneous approach, the location of the defect is identified by TEE and by angiography. The defect is sized at end diastole using a two-dimensional measurement. With a perventricular approach, TEE can guide the surgeon to indent the RV free wall progressively closer to the defect and identify a position to place the introducer sheath immediately over the defect and unobstructed by muscle bundles. In both the percutaneous and perventricular approaches, the sheath is advanced across the VSD and an appropriate sized device is delivered. An example of transesophageal images obtained during VSD device placement via a percutaneous approach is shown in Figure 11.18.

In patients with multiple VSDs, device closure can be used in conjunction with surgical repair; this can be particularly helpful in cases where some, but not all, of the VSDs are positioned in locations that are difficult to approach surgically or when the defects are crossed by trabeculations, which can obscure visualization of the full extent of the defect. Complications of device closure that can be identified echocardiographically include device embolization or migration, residual shunts, valve regurgitation (especially with perimembranous VSDs where the device is adjacent to the tricuspid and aortic valves), and pericardial effusion.

ECHOCARDIOGRAPHY OF POSTOPERATIVE VSDS

Echocardiography is commonly used in the postoperative evaluation following VSD closure. TEE or epicardial echocardiography can be used in the operating room to evaluate the surgical repair prior to chest closure. Ventricular dysfunction may occur immediately postoperatively or may develop later; possible etiologies include damage to the myocardium following ventriculotomy, acute volume unloading of the LV, and issues related to cardiopulmonary bypass. Other well-described complications include development of regurgitation of any of the valves adjacent to the VSD and residual or additional VSDs.

Surgical distortion of, or damage to, valves adjacent to the VSD most commonly effects the tricuspid and aortic valves. During repair of malalignment or perimembranous VSDs, the surgeon may sew the VSD patch to the annular edge of the tricuspid valve septal leaflet to avoid damage to the conduction system. Similarly, septal attachments of the tricuspid valve can be disrupted during patch closure. Substantial tricuspid regurgitation can develop from either prolapse or flail leaflet (Fig. 11.19AB). The aortic valve can be affected following closure of any adjacent defect, typically perimembranous or subarterial. The development of aortic insufficiency may be related to distortion of the aortic valve leaflet (most commonly the right aortic leaflet) by the VSD patch or from perforation of the valve leaflet due to inadvertent placement of a suture through the leaflet as the VSD patch is attached to the aortic valve annulus (Fig. 11.19CD).

Figure 11.18. AMPLATZER ventricular septal occluder device closure of a muscular ventricular septal defect (VSD) in a patient with two apical muscular VSDs (arrows). A: Transesophageal four-chamber image of wire position across one of apical muscular VSDs. B:Transesophageal four-chamber image of the device still attached to the delivery cable but with the left ventricular disk delivered. C: Transesophageal four-chamber image of the AMPLATZER Septal Occluder (AGA Medical, Inc., Plymouth, MN) device in its final position across the apical muscular VSD. D: Transesophageal short-axis image of the device in its final position. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. See Video 11.11.

Residual or additional VSDs can be seen postoperatively. Additional VSDs that were not detected preoperatively are most common in patients where the identified defect was large, with equalization of right and left ventricular pressures and undisturbed flow. Once the large VSD has been closed, the smaller additional defects are easier to appreciate. Residual defects tend to occur along the margins of the VSD patch. Yang and colleagues reported residual VSDs less than 3 mm in size are generally well tolerated, even in an infant. The coarse trabeculations of the RV wall make complete closure of some defects quite difficult as blood flow can continue to traverse the margins where the patch is sewn to trabeculae.

A subtype of residual defect is the “intramural” VSD, most commonly seen with the complex interventricular tunnel type of VSD patches used to repair double-outlet right ventricle, truncus arteriosus, or with a Rastelli-type repair of transposition of the great arteries. Intramural VSDs originate anteriorly, in the RV wall between the patch insertion and the aortic valve (Fig. 11.20), traversing the RV free wall trabeculae. They can be a particular challenge to image as the shunt flow percolating through RV trabeculae may appear to originate from the RV free wall, apparently away from the septum. Intramural VSDs are often not well seen from standard echocardiographic views and may require creative imaging strategies to allow careful interrogation of the RV anterior wall adjacent to the patch. Similarly, intramural defects are especially difficult to visualize by TEE. Imaging from the deep transgastric transducer position and careful short-axis sweeps may better define the defect. Initially, these defects may be small, but they may enlarge as the channels in the RV trabeculae open up, resulting in significant left-to-right shunting. Intramural defects can be extremely difficult to repair surgically; improved understanding of these defects will likely result in greater success with operative repair.

Figure 11.19. Complications of surgical closure of ventricular septal defects. A–B: Apical four-chamber view with two-dimensional and color Doppler of a flail septal leaflet of the tricuspid valve (arrow) due to disruption of septal attachments of the tricuspid valve. Parasternal long-axis (C) and three-dimensional short-axis (D) images showing perforation of the right coronary leaflet (arrow in D) of the aortic valve adjacent to the annulus with resultant aortic regurgitation (arrow in C). Ao, aorta; L, left; LA, left atrium; LV, left ventricle; R, right; RA, right atrium; RV, right ventricle. See Video 11.12.

Complications of VSD closure may also occur late after surgical repair. Endocarditis is especially common in the presence of a residual shunt where the residual defect is adjacent to the site of a prosthetic patch and endothelialization may be inhibited. Patch dehiscence can occur in association with endocarditis or without endocarditis due to suture breakage. Subaortic obstruction can develop following either surgical or spontaneous VSD closure. In a study by Cicini et al. of postoperative VSD patients, 3.2% developed subaortic stenosis in the first 6 years postoperatively; the mechanism of subaortic narrowing was most often the development of a fibromuscular ridge or related to accessory mitral valve tissue. Other potential complications include development of a double-chambered RV, development or progression of pulmonary hypertension, and progressive aortic or tricuspid valve regurgitation.

SPECIAL STUDIES

Ventricular Septal Defect in the Fetus

Isolated VSDs make up 6% of congenital heart disease diagnosed in fetuses. Moderate to large muscular VSDs are the most common type of VSD diagnosed prenatally. Small, and even moderate sized, defects are rarely seen; defects less than 2 mm are near the limits of resolution of fetal ultrasound and the equalization of the ventricular pressures in utero makes flow across the defect laminar and more difficult to detect. As with transthoracic echocardiography, the best imaging plane is one in which the ventricular septum is perpendicular to the ultrasound beam with VSD flow parallel. This involves moving the transducer on the maternal abdomen until the appropriate imaging plane can be found. On fetal echocardiography, a VSD appears as an apparent dropout in the ventricular septum with bright margins of the defect. Muscular VSDs are the most common type of isolated VSD detected in the fetus, as is shown in Fig. 11.21. Color flow across the septum is bidirectional except in cases where there is associated outflow tract obstruction; the flow is of low velocity, usually between 40 and 70 cm/s.

Figure 11.20. Intramural VSD. A: Diagrammatic representations of an intramural VSD. B–C: Transthoracic high right parasternal long-axis images with transducer over the anterior and rightward aorta. The ventricular septal defect (VSD) patch attaches to the trabeculae of the right ventricular (RV) free wall with percolation of flow through the trabeculae and along the RV free wall. D: Transesophageal anteriorly directed apical four-chamber view demonstrating transmyocardial entry of intramural VSD flow into the right ventricle. E: Transesophageal transverse plane image showing the intramural course of the VSD (arrow). Ao, aorta; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. See Video 11.13.

Spontaneous closure of VSDs in utero is common, with closure rates between 5% and 30% The location and size of the VSD affect the rate of spontaneous closure. Up to half of defects less than 3 mm in size may close in utero, and almost all close by 3 years of age. Even larger defects in the muscular septum are likely to close, with nearly three-quarters closing in the first year of life. Larger perimembranous defects and malalignment VSD almost never close in utero. Precise localization and sizing of VSDs by fetal echocardiography can allow the fetal cardiologist to provide accurate prognostic information to families.

Transesophageal Echocardiography

While occasionally used to evaluate VSDs preoperatively, transesophageal echocardiography (TEE) is more typically used intraoperatively to direct and evaluate surgical repair or to assist with device closure, either percutaneously in the catheterization lab or in the operating room using the hybrid approach. While visualization of residual defects is often quite straightforward, transducer positions limited to the esophagus and transgastric windows may result in suboptimal Doppler interrogation angles. In addition, VSD patches and devices often have shadow artifacts, which limit visualization of VSD jets. However, careful assessment using standard and deep transgastric views can provide an accurate assessment of residual defects, including identification of patients that require a return to cardiopulmonary bypass. In a series by Stevenson et al., 6.4% of patients with surgically closed VSDs underwent repeat bypass and additional closure based on TEE findings and intraoperative hemodynamics.

In a complete multiplane transesophageal examination, the ventricular septum should be swept along its entirety in short-axis, four-chamber, and long-axis planes with two-dimensional and color flow mapping. One systematic approach begins from a transgastric short-axis view at the apex, often with mild anteflexion, slight left lateral deflection, and approximately 20 degrees head rotation. The probe is gradually withdrawn until the entire septum has been traversed. When the transducer has been withdrawn superiorly to a position behind and superior to the left atrium, the scope is retroflexed to a four-chamber view. From this position, anteflexion and retroflexion will scan the septum from the posterior to the anterior interventricular groove. Then, advancing to a low esophageal position with the transducer tip apical to the mitral annulus, the head is rotated to a long-axis plane (often 110 degrees). The ventricular septum is scanned in its long axis from its rightward and inlet portions to its leftward anterior and outlet portions. Finally, reimaging the septum from the RV aspect using a deep transgastric view is helpful to overcome shadowing artifact from a patch or device and to identify easily missed intramural VSDs.

Figure 11.21. Muscular ventricular septal defect in the fetus. Cross-sectional image of the fetal thorax with the apex of the heart pointed up and the fetal spine in the left lower portion of the image, showing a muscular ventricular septal defect (arrow). LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. See Video 11.14.

The TEE examination in the patient after VSD closure should provide a detailed assessment of ventricular function; residual defects including their size, mechanism, and location; and any damage to valves adjacent to the defect. Small “patch leak” VSDs commonly observed in the operating room after VSD closure are of little significance and typically close postoperatively, or even after intraoperative administration of protamine. Multiple studies have shown that small VSD patch leaks (,2–3 mm) can be detected in about one-third of intraoperative studies, with many closing spontaneously before hospital discharge and approximately 80% closing on short-term follow-up. However, a small number of patients with no VSD or a small residual VSD on intraoperative study may have significant enlargement of the defect due to partial patch dehiscence or progressive enlargement of an intramural defect.

Three-Dimensional Echocardiography

Assessment of VSD size and shape was identified as one of the earliest uses of three-dimensional (3D) and four-dimensional (3D in time) echocardiography. Still, difficulties with tissue thresholding “creating” nonexistent defects or seemingly “enlarging” existing defects have limited the application of 3D in the assessment of VSDs. The advent of real-time transthoracic 3D echocardiography, improved mapping protocols, and higher-frequency pediatric transducers, has made assessment of VSDs using 3D echocardiography increasingly reliable; it has been demonstrated to provide additional information to that provided by two-dimensional echocardiography. Specifically, the size of defects measured by 3D echocardiography correlates better with surgical measurements. Morphologic aspects of VSD aneurysm are better defined and the relationship of defects to important intracardiac structures is better assessed using 3D echo. The irregular nature of many VSDs and their dynamic nature are understood to a much greater degree by 3D echocardiography as well.

While a standard approach to assessing VSDs using 3D echocardiography has not met with general use, and was not included in the recently published American Society of Echocardiography and European Association of Echocardiography guidelines for 3D imaging, a reasonable approach is suggested by an understanding of the physics of the image process. Ultrasound resolution is best in the axial (depth) plane and less in the two lateral planes. Image quality is progressively reduced in proportion to the number of reflectors between the transducer and the region of interest. The major limitation of 3D imaging of the interventricular septum has been false “fallout” of information, which “expands” or “creates” defects. Thus, it is especially important that the area of interest of the ventricular septum is imaged in an axial plane, while minimizing ultrasound reflectors between the transducer and this region of the septum, with a frequency and compression appropriate to create a solid-appearing myocardium and a translucent blood pool. Typically, this area of the septum is imaged obliquely with the transducer rotated to maintain the entire septum of interest within the data set. Because of the curved nature of the ventricular septum and variable quality of acoustic windows, an optimal transducer position may be subxiphoid, low parasternal, lateral to left parasternal, or periapical. Charakida and colleagues have suggested that, in children, using the subxiphoid imaging position, the transducer can be rotated to include the entire septum within the limited real-time imaging wedge, thus optimizing resolution and frame rate of images while eliminating stitch artifact. Because the septum is parallel to the beam of insonation, this approach may be especially susceptible to false fallout (Fig. 11.22). Gain is increased until the blood pool appears solid and then reduced to the point where it just becomes translucent. The compression or opacity is then optimized.

Figure 11.22. Three-dimensional echocardiogram of a perimembranous ventricular septal defect (arrow) viewed from the right ventricle (A) with additional false fallout in the subpulmonary region and left ventricular (B) perspective. The data set was acquired from a subxiphoid plane using a method similar to that described by Charakida and colleagues. RA, right atrium; PA, pulmonary artery; LA, left atrium; LV, left ventricle. See Video 11.15.

After or during acquisition, the data set is “cropped.” The American Society of Echocardiography guidelines recommend cropping and visualizing lesions from recreated surgical views when possible. Removing portions of the LV and RV free wall allows an en face surgical view of the entire defect (Fig. 11.12D). An alternate method of cropping orients the data set in a more standard echocardiographic plane such as a four-chamber or long-axis view, and sets the cropping plane to course through the very edge of the defect (Fig. 11.23). Images are often displayed in the moving heart, but they may be more effectively understood if an end-diastolic still-frame is rotated through several planes to allow perspective.

Finally, as VSD anatomy and relationships become progressively more complicated, there is room for 3D images to enhance understanding of intracardiac relationships. Relationships of AV valves to the defect, including straddling, as well as relationships of the defect to the great arteries can be optimally understood and presented using these images. Figure 11.24 clearly demonstrates the relationship of the VSD to the great arteries in this patient with double-outlet right ventricle, subaortic VSD, and no AV valve straddling. It is clear that continued improvement of 3D imaging using both transthoracic and newly available real-time transesophageal transducers will allow understanding of complicated VSDs in detail not previously possible.

Figure 11.23. Three-dimensional image of inlet (down arrow), perimembranous (up arrow), and mid-muscular (left arrow) ventricular septal defects. The image is acquired from a low left parasternal transducer position and cropped in a pseudo–long-axis plane, allowing visualization of the membranous, inlet, and muscular septa from the left ventricular (LV) side. Ao, aorta; LA, left atrium; LV, left ventricle; RV, right ventricle. See Video 11.16.

Figure 11.24. Three-dimensional echocardiogram of double-outlet right ventricle with subaortic ventricular septal defect (VSD). Visualization of the septum en face from the left ventricular (LV) aspect (A) shows the subaortic VSD (arrow) and absence of the aorta exiting the LV. Video 11.17 (see website) demonstrates rotation of this end-diastolic image with visualization of the VSD from RV to LV aspects. Cropping the dataset in a “short-axis” view (B) demonstrates the relationships of the tricuspid, mitral, and aortic valves to the defect. Video 11.17 (see website) demonstrates superior/inferior rotation of this mid-diastolic image to clarify intracardiac relationships. Ao, aorta; LA, left atrium; LV, left ventricle; MV, mitral valve; TV, tricuspid valve.

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Questions

1.What type of ventricular septal defect is shown in the images below?

A.Perimembranous

B.Subarterial

C.Inlet

D.Muscular

2.An echocardiogram done on a patient with a ventricular septal defect and a systolic blood pressure of 110mmHg provides the following spectral Doppler tracings.

Based on the information above, the best estimate of RV systolic pressure is:

A.10-15mmHg

B.25-35mmHg

C.55-65mmHg

D.100-110mmHg

3.What abnormality associated with a ventricular septal defect is shown in these images?

A.Aortic valve prolapse

B.Subaortic stenosis

C.Double chambered right ventricle

D.Tricuspid valve straddle

E.Valvar pulmonary stenosis

4.What heart chambers dilate with a large VSD?

A.Right atrium and right ventricle

B.Right ventricle and left atrium

C.Right atrium and left ventricle

D.Left atrium and left ventricle

5.The following are all names for the same VSD location EXCEPT:

A.Subpulmonary

B.Doubly committed

C.Subarterial

D.Infracristal

E.Supracristal

6.Where is a muscular ventricular septal defect located in the infundibular apex positioned?

A.Anteriorly

B.Posteriorly

C.Superior to the moderator band

D.Adjacent to AV valve

7.A posterior malalignment VSD is most often associated with:

A.aortic arch obstruction.

B.pulmonary stenosis.

C.double-chambered right ventricle.

D.aortic valve prolapse.

E.tricuspid valve straddle.

8.What post-operative complication of repair of double-outlet right ventricle is seen in these transthoracic images from a high-right parasternal window?

A.Aortic valve injury

B.Flail leaflet

C.Intramural VSD

D.LV outflow tract obstruction

9.Which of the following best characterizes the relationship of a perimembranous VSD to the limbs of the trabeculae septomarginalis (septal band)?

A.Located between the anterior and posterior limbs

B.Anterior to the anterior limb

C.Posterior to the posterior limb

D.The relationship to the limbs is variable.

10.In a patient with VSD and down-sloped signal, LV to RV peak-to-peak gradient matches closely with:

A.end systolic VSD gradient.

B.peak instantaneous VSD gradient.

C.mean VSD gradient.

D.A, B, and C all correlate well.

E.A and B correlate well.

Answers

1.Answer: B. The subarterial VSD is seen immediately beneath the aortic valve in long-axis views and immediately adjacent to both the aortic and pulmonary valve in short-axis views.

2.Answer: B. 

3.Answer: C. Images show a large perimembranous ventricular septal defect (VSD) complicated by double-chambered right ventricle. Parasternal short-axis (A) and subcostal sagittal (B) views in two-dimensional and color flow mapping show the “napkin ring” of muscle bundles and flow disturbance (arrow) superior to the VSD. This VSD is on the “high pressure” side of the obstructing muscle bundles. Ant, anterior; Ao, aorta; inf, inferior; LA, left atrium; LV, left ventricle; post, posterior; RA, right atrium; RV, right ventricle; RVOT, right ventricular outflow tract; sup, superior.

4.Answer: D. VSDs cause left-sided volume overload.

5.Answer: D. Infracristal is a synonym for perimembranous VSD.

6.Answer: A. Apical muscular VSDs are located inferior to the moderator band and include defects of the RV inflow apex (which is located more posteriorly) and the more anterior “infundibular” apex. The two RV apices are divided by dense trabeculations that run from the septum to the RV free wall.

7.Answer: A. Posterior deviation of the outlet septum creates a VSD of the type seen in association with interrupted aortic arch with muscular narrowing of the LV outflow tract.

8.Answer: C. Transthoracic high-right parasternal long-axis images of an intramural VSD with transducer over the anterior and rightward aorta. The VSD patch attaches to the trabeculae of the right ventricular (RV) free wall, with percolation of flow through the trabeculae and along the RV free wall.

9.Answer: A. A perimembranous VSD is located between the anterior and posterior limb of the trabeculae septomarginalis.

10.Answer: E. In patients with down-sloped VSD signal (typically delayed RV contraction), LV to RV peak-to-peak gradient at catheterization has been demonstrated to match quite well with the VSD mean and end systolic gradients. The peak instantaneous gradient substantially overestimates this gradient and thus underestimates RV pressure.