Ravi Ranjan Tripathi
Department of Pediatric Cardiology, CHL Hospital, Indore, Madhya Pradesh, India
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Correspondence Address: Dr. Ravi Ranjan Tripathi CHL Hospital, LIG Square, AB Road, Indore - 452 001, Madhya Pradesh India
Source of Support: None, Conflict of Interest: None
Ventricular septal defects (VSDs) are among the most common congenital heart defects. These defects may be isolated, associated with other defects, or occur as an intrinsic component of some complex heart defects. There is wide variation in size and location of VSD. Echocardiography plays an important role in evaluation of anatomy, hemodynamic significance, and planning of management of VSDs. With the emerging trends in transcatheter closure of VSD, echocardiography plays a crucial role in decision-making and intra- and postprocedure evaluation. A stepwise approach of echocardiography is necessary for accurate evaluation and management of VSDs.
Interventricular septum has a complex anatomy and multiple embryologic origins. Abnormal completion of this structure during embryonic and fetal life results in a ventricular septal defect (VSD). Distinction between different types of VSD is essential for a correct diagnosis as well as medical and surgical management. Echocardiography has evolved immensely over the past few decades and has revolutionised the practice of pediatric cardiology. It gives detailed anatomical and physiological information about flow and pressures without cardiac catheterization, especially in neonate and infants. Echocardiographic evaluation of VSD remains the mainstay in diagnosis and decision making for management in these patients.
The overall prevalence of congenital heart defects (CHDs) in India is almost similar to worldwide birth prevalence rate of about 8 per 1000 live births. Ventricular septal defects (VSDs) are one of the most common significant CHDs and account for up to 40% of all cardiac abnormalities. However, recent studies have shown wide variation in the incidence of CHD, especially VSD due to more frequent use of echocardiography and early diagnosis of small VSDs. A higher prevalence of VSD in newborns of up to 5% has been reported in some studies using highly sensitive color Doppler echocardiography. Most of these defects are tiny and disappear during the 1st year of life. VSD is a commonly isolated defect as well as intrinsic component of several complex cardiac malformations including tetralogy of Fallot, double-outlet right ventricle (RV), transposition of great vessels, aortic coarctation or interruption, and truncus arteriosus.
Definition and Types
VSD is defined as a perforation in the ventricular septum leading to altered cardiac flow dynamics. Different types of VSD are classified according to their location [Figure 1]. The ventricular septum is mainly divided into two morphologic components, the membranous septum and the muscular septum. The membranous septum is a small portion located at the base of the heart between inlet and outlet portions of the muscular septum, below the right and noncoronary cusps of aortic valve (AV) adjacent to septal leaflet of tricuspid valve. Defects that involve the membranous septum and extend into adjacent muscular components are called “perimembranous” defects. Perimembranous defects represent the largest subgroup of VSDs. Small perimembranous VSD may reduce in size or close spontaneously by growth of fibrous tissue at the margins of the defect and progressive adhesions of tricuspid leaflet tissue around the defect. This tissue often forms the pouch and is referred to as “aneurysm of membranous septum.”
Figure 1: Types of ventricular septal defect (VSD) according to their location in the ventricular septum as viewed from the right ventricle
The muscular septum is a three-dimensional structure. It is divided into inlet, trabecular, and infundibular components. The inlet part begins at the level of atrioventricular valve and ends at their chordal attachment, thus an “inlet” VSD has no muscular rim between defect and atrioventricular valve annulus. The trabecular septum is largest. A defect in the trabecular septum completely rimmed by muscle is called “muscular” VSD. It can further be subdivided by location into anterior, mid-muscular, apical, or posterior defect. The infundibular septum is the portion that separates right and left ventricular outflow tracts. Defects in this portion are called infundibular, outlet, conal, supracristal, subpulmonary, or doubly committed subarterial defects.
Primary factors that determine the pathophysiological response to VSD are the size of the defect and the relationship between pulmonary and systemic vascular resistance. If the defect is small or restrictive, the left-to-right shunt will be relatively small, and right ventricular and pulmonary pressure will be normal. However, if the VSD is large or nonrestrictive, the shunt will be large with corresponding overloading of pulmonary arteries, left atria, and left ventricle (LV). Pulmonary artery pressure will be elevated (hyperkinetic hyperkinetic pulmonary arterial hypertension [PAH]) with low pulmonary vascular resistance (PVR). A long-standing large left-to-right shunt across large VSD can lead to elevated PVR, elevated pulmonary artery pressure (obstructive PAH), and reversal of shunt. This is known as Eisenmenger syndrome.
Secondary structural cardiac anomalies can contribute to clinical course of patients with VSD. Malformation located near AV can be complicated by AV prolapse and regurgitation that may result from the absence of structural support for leaflets and venturi force of high-velocity jet across these defects.
Clinical features of VSD are pansystolic or holosystolic murmur, features of volume loading of LV, and chronic congestive heart failure in large defects. Intensity of the murmur depends on the size of defect. Small defects have the loudest murmur and may have a thrill. Defects with aortic insufficiency may have diastolic decrescendo murmur along the left sternal border with wide pulse pressure.
Spontaneous closure of VSD is well known, and a wide range of figures has been reported., Up to 70% of tiny defects can close spontaneously, especially in the muscular septum. Among clinically significant VSDs, closure rate during childhood is about 25%, mostly in small perimembranous or muscular defects. Most closures occur within the first 2 years of life but rarely may occur later in childhood and even in adults. More often, defects diminish in size but may not completely close.
A systematic echocardiographic assessment of VSD includes a detailed anatomic and hemodynamic description. Anatomic description must include the exact location of the defect, number of defects, relationship to valve and valve attachments, description of anatomic size of the defect, and associated lesions (if any). Hemodynamic description includes chamber size, estimation of right ventricular pressure and pulmonary artery pressure, and estimation of overall shunt size.
A patient is referred for echocardiographic evaluation on the basis of clinical suspicion. There are few common features in a case of VSD. Volume overloading of the left atrium and LV as VSD is a posttricuspid shunt lesion. The magnitude of shunt is determined by enlargement of the left atrium and ventricle. The secondary manifestations of VSD and enlargement of LV can cause mitral annular dilatation resulting in mitral regurgitation.
In a patient with a small VSD, clinical feature of loud pansystolic murmur is the only reason for echocardiographic evaluation. These patients will have normal-sized left atrium and ventricle. Careful screening of ventricular septum using two-dimensional (2D) and color imaging is crucial for detection of the defect.
Detailed assessment of ventricular septum requires sweeping the entire ventricular septum in both 2D and color Doppler imaging from apex to base and from left to right. Because of the curved nature of the ventricular septum, optimal imaging of a VSD needs to be done from subcostal, parasternal, apical, and right parasternal windows. The best acoustic window is determined by the fact that shows the septum perpendicular to the ultrasound beam and the flow across the defect parallel to the beam.
Various anatomical classifications of VSDs have been used to describe the location of the defect. In this chapter, we are using “congenital heart surgery nomenclature system” and divided VSD into perimembranous, inlet, subarterial, and muscular defects.
Perimembranous Ventricular Septal Defect
Perimembranous defects are the most common type of VSDs and involve the membranous ventricular septum adjacent to aortic and tricuspid valves [Figure 2] and [Figure 3]. These defects can be imaged from parasternal, apical, or subcostal views [Videos 1-5]. Malalignment of the outlet septum with muscular septum may be associated with perimembranous defect [Figure 4]. Anterior deviation of the outlet septum causes a VSD usually seen in tetralogy of Fallot with override of the aorta. VSD with posterior deviation of the outlet septum [Figure 5] is usually associated with interrupted aortic arch, coarctation of the aorta [Figure 6], and left ventricular outflow tract obstruction.
Figure 2: Apical four-chamber view with color image showing large perimembranous ventricular septal defect (ventricular septal defect) with enlargement of the left atrium and left ventricle. VSD: Ventricular septal defect, LA: Left atrium, LV: Left ventricular
Figure 3: Parasternal short-axis view with two-dimensional and color images showing large perimembranous ventricular septal defect (*). RV: Right ventricle, RVOT: Right ventricular outflow tract, Ao: Aorta, LA:Left atrium
Figure 4: Parasternal long-axis view showing malalignment of the outlet septum with muscular septum (arrow) associated with large perimembranous ventricular septal defect (*). RV: Right ventricle, Ao: Aorta, LA: Left atrium, LV:Left ventricle
Figure 5: Parasternal long-axis view with color showing large ventricular septal defect with posterior deviation of the outlet septum (*) causing narrowing of the left ventricular outflow tract. RV: Right ventricle, Ao: Aorta, LA: Left atrium, LV: Left ventricle, VSD: Ventricular septal defect
Located adjacent to tricuspid valve, perimembranous VSD can be associated with tricuspid septal leaflet distortion with tricuspid regurgitation. Accessory tissue or part of septal leaflet of tricuspid valve can partially or completely close the defect, referred to as “ventricular septal aneurysm” [Figure 7]. Occasionally blood from VSD can traverse through aneurysmal tissue across tricuspid valve into the right atrium leading to LV to right atrial shunt [Figure 8]. Misinterpretation of this high-velocity flow as tricuspid regurgitation can lead to false overestimation of RV pressure. About 10% of perimembranous defects are associated with AV prolapse due to close proximity with AV. It can be identified by right or noncoronary cusp protruding into the VSD best seen in parasternal long- and short-axis views [Video 6],[Video 7],[Video 8]. Due to importance in the development of aortic regurgitation, the presence of aortic cusp prolapse should be carefully reported. About 5% of perimembranous defects are associated with a subaortic ridge with or without subaortic obstruction. These are fibromuscular in origin and located at the inferior aspect of VSD commonly associated with septal aneurysm.
Figure 7: Apical four-chamber view with color showing large perimembranous ventricular septal defect (*) partially closed by tricuspid valve septal aneurysm (arrow). RV: Right ventricle, RA: Right atrium LA: Left atrium, LV: Left ventricle
Figure 8: Parasternal short-axis view with two-dimensional and color imaging shows perimembranous ventricular septal defect (arrow) with left ventricle to right atrium jet (*). RV: Right ventricle, Ao: Aorta, RA: Right atrium, VSD: Ventricular septal defect
Inlet VSDs are located posteriorly adjacent to both atrioventricular valves. These defects are commonly associated with atrioventricular septal defects (AVSDs) but can be isolated [Figure 9]. These are best imaged from apical four-chamber [Video 9] or parasternal short-axis views. AV valve involvement is common with inlet VSDs. Tricuspid valve may be intrinsically abnormal with associated tricuspid regurgitation. VSD associated with partial AVSD may have cleft in the anterior leaflet of mitral valve resulting in mitral regurgitation. Inlet VSD may rarely be associated with malalignment of atrial and ventricular septa, resulting in some degree of AV valve override, and rarely with straddling of AV valve chordal attachments [Figure 10]. Therefore, careful assessment of AV valves is required in a case of inlet VSD.
Figure 9: Apical four-chamber view showing large inlet ventricular septal defect (*). RV: Right ventricle, RA: Right atrium, LA: Left atrium, LV: Left ventricle
Figure 10: Apical four-chamber view showing large inlet ventricular septal defect (*) with straddling (arrow) of few tricuspid valve chordal attachments to the left ventricular side of the septum. RA: Right atrium, LA: Left atrium, LV: Left ventricle
Subarterial or infundibular VSDs result from deficiency in conal or outlet septum beneath both semilunar valves [Figure 11]. These defects are best assessed from parasternal long- and short-axis views. About 60% of subarterial defects are associated with prolapse and distortion of the right coronary cusp of AV with half of these patients developing aortic regurgitation. Prolapse can be demonstrated as diastolic bulging of the right coronary cusp into RV [Figure 12]. It can be mild to severe [Video 10]. AV prolapse can lead to a reduction in size of VSD with associated risk of aortic regurgitation. Hence, careful assessment of real size of the defect and degree of aortic regurgitation is required during echocardiographic assessment.
Figure 11: Parasternal long-axis view with anterior tilt showing subarterial ventricular septal defect (*) with the absence of conal septum and continuity of aortic and pulmonary valve. RV: Right ventricle, Ao: Aorta, PA: Pulmonary artery, LV: Left ventricle
Figure 12: Parasternal long-axis view showing large subarterial ventricular septal defect (*) with prolapse of the right coronary cusp of aortic valve (arrow) into the right ventricle. LA: Left atrium, LV: Left ventricle
Muscular VSDs are defects appearing in trabecular or muscular septum entirely surrounded by muscular rim [Figure 13] and [Figure 14]. They can be further subdivided into anterior, mid-muscular, posterior, or apical defects according to their location [Video 11]. The presence of multiple muscular defects especially in the mid-muscular or apical segment is referred to as “swiss-cheese” septum. Muscular VSD can occur in addition to a VSD in another location like perimembranous or inlet. These additional small defects can be missed easily, especially when the first defect is large with equalization of pressures in both ventricles.
Figure 13: Apical four-chamber view with color showing mid-muscular ventricular septal defect (*). RV: Right ventricle, Ao: Aorta, LA: Left atrium, LV: Left ventricle
Assessment of the Size of the Ventricular Septal Defect
Determination of the size of VSD is made on hemodynamic basis like degree of left-to-right shunt, presence of volume overload, and pulmonary artery pressure. Historically, the size of VSD has been related to the size of aortic root. VSD measuring <1/3 of aortic root diameter is classified as small, 1/3–2/3 of aortic root diameter as moderate, and lesion close to aortic root size is considered large. Hemodynamic classification uses pressure difference across LV to RV as a guide to size the defects. When there is equalization of pressures in two ventricles in the presence of isolated VSD in the absence of pulmonary stenosis, it is called as a large or nonrestrictive defect. A restrictive defect has a pressure gradient across LV and RV as determined by Doppler technique [Figure 15], with pressure gradient of more than 60 mmHg as restrictive defect and pressure difference of 25–60 mmHg as moderately restrictive.
Figure 15: Spectral Doppler tracing of ventricular septal defect obtained from parasternal long-axis view showing peak velocity of 3.3 m/s
Determination of size of VSD by measuring the largest diameter on color flow mapping has been shown to closely reflect the measurements made by angiography and at surgery. However, in VSD that is muscular with oblique course through ventricular septum or oval in shape, sizing may be difficult and imaging in multiple planes is crucial for accurate size determination. Three-dimensional echocardiography has shown better and accurate measurements in noncircular and multiple VSDs.
Integration of spectral and color Doppler with 2D echocardiography greatly assists with identification and characterization of VSDs. Reliable estimates of right ventricular and pulmonary artery pressures, and of pressure differences between LV and RV, can usually be obtained with 2D-directed continuous-wave Doppler. The need for cardiac catheterization to obtain pressure data is thereby eliminated in most cases.
Hemodynamic assessment of VSD using echocardiography usually includes evaluation of right heart pressure and quantification of amount of shunt flow. Velocity of blood flow across VSD as measured by Doppler is used to measure right ventricular systolic pressure using modified Bernoulli equation.
Proper alignment of Doppler beam with VSD jet is necessary for accurate determination of right ventricular pressure that is equal to systolic PA pressure in the absence of right ventricular outflow tract obstruction. In addition, tricuspid regurgitation peak velocity can be obtained to estimate RV pressure as follows:
While determining TR jet velocity, proper alignment of Doppler beam to TR jet and complete TR signal must be obtained. Any LV to RA shunt must be ruled out in the presence of perimembranous VSD to avoid false interpretation.
Pulmonary regurgitation velocity measured by Doppler can be used to estimate mean and diastolic pulmonary artery pressure and for additional validation of hemodynamic assessment.
VSD shunt volume is determined by size of VSD and PVR. Left heart chamber dilatation is associated with pulmonary-to-systemic flow ratio (Qp/Qs) of > 1.5:1. Doppler-based methods for shunt quantification are not widely accepted due to variable results.
The echocardiographer should also assess extracardiac vascular structures, since clinically important anomalies of the aorta (coarctation), pulmonary arteries, pulmonary veins, and systemic veins can be seen. About half of the patients with VSDs may have associated lesions that may be missed if not looked for carefully. Nearly one-third of the patients with coarctation of the aorta and nearly all with interrupted aortic arch have an associated VSD. A patent ductus arteriosus is commonly found with VSD. With a large VSD and associated pulmonary arterial hypertension, near equalization of pressures in the aorta and pulmonary artery results in laminar flow in ductus, making it difficult to diagnose.
Mid-cavity obstruction of the RV due to hypertrophy of muscle bands creates the entity known as double-chambered RV [Figure 16]. This process results in formation of a proximal high-pressure chamber and a distal low-pressure chamber within the cavity of the RV. It is frequently associated with VSD usually of perimembranous variety and connects to high-pressure portion of RV.
Figure 16: Parasternal short-axis views with two-dimensional and color imaging showing large perimembranous outlet ventricular septal defect (arrow) with right ventricular outflow tract muscle bundle (*) causing right ventricular outflow tract obstruction (flow disturbance). RV: Right ventricle, Ao: Aorta, LA: Left atrium, LV: Left ventricle, PA: Pulmonary artery
Three-dimensional echocardiography is becoming widely available and could provide important diagnostic assistance for assessment of unusually positioned VSDs and those associated with complex congenital heart malformations.
Planning for Surgery or Transcatheter Closure of Ventricular Septal Defect
Surgical closure of VSD remains the treatment of choice for large defects with good long-term results and quality of life. An echocardiographer must provide a clear understanding of VSD to a surgeon for planning of surgery including size, location, number of defects, and relationship with surrounding cardiac structures. This will result in a briefer surgical exploration, decreasing trauma to adjacent myocardium, and limit the potential for significant residual shunt.
More recently, transcatheter device closure [Figure 17] and hybrid approach has developed as an alternate to surgical closure in carefully selected cases. Initial echocardiography is an important tool to select these patients. A careful assessment of size of the defect, location, and distance from adjacent valvular structure is required to decide about the size and type of device required. Echocardiography plays a crucial role during the procedure for evaluating the success of procedure and avoidance of any complication [Video 12]. Transesophageal echocardiography also plays an important role in the process.
Figure 17: Apical four-chamber view showing muscular ventricular septal defect device (*) in situ. RV: Right ventricle, RA: Right atrium, LA: Left atrium, LV: Left ventricle
Echocardiography plays an important role in evaluation of patients during and after surgery for CHDs. Transesophageal or epicardial echocardiography is commonly used during surgery to evaluate the surgical repair while transthoracic echocardiography gives important information in immediate postoperative period and helps in postoperative care of such patients in intensive care units. After VSD closure, echocardiographic assessment is needed to assess myocardial dysfunction, regurgitation of valves, effusions, residual VSDs, or additional VSDs. Surgical distortion or damage to valves adjacent to VSD most commonly affects tricuspid and AVs. Development of tricuspid or aortic regurgitation needs careful assessment. Residual or additional VSDs can be seen postoperatively. Additional VSDs are detected commonly in patients where the primary defect was large with equalization of pressures in right and LV. Once large VSD is closed, smaller additional VSDs are easier to demonstrate. Residual defects can be seen along the margins of VSD patch.
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