Definition and Morphology
Ventricular septal defects (VSDs) are openings in the ventricular septum and occur both in isolation and in conjunction with other cardiac defects. The classification of VSDs is based on the location of the defect within the ventricular septum.
The ventricular septum can anatomically be considered as having two components, the membranous and the muscular septum ( Fig. 30.1 ).
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The membranous septum is a small fibrous structure located at the base of the heart below the right and noncoronary cusps of the aortic valve. It is divided into two parts by the septal leaflet of the tricuspid valve.
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The right aspect of the muscular ventricular septum can be designated as having 3 components corresponding to the three portions of the ventricle: inlet, apical trabecular, and outlet.
Although numerous anatomic classification systems of VSDs exist, none is universally accepted and the nomenclature of VSDs is diverse. Therefore a uniform reporting system of VSDs has been proposed by the Society for Thoracic Surgery–Congenital Heart Surgery Database Committee in association with the European Association for Cardiothoracic Surgery. This classification system assigns VSDs according to their margins and localization to one of four different anatomic types (see Fig. 30.1 ).
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Type 1 defects are those located in the outlet portion of the muscular septum and have been termed conal , subpulmonary , infundibular , or supracristal defects. Also in this category are doubly committed juxta-arterial VSDs, which are located directly underneath the semilunar valves; the roof of those defects is formed by the fibrous continuity of the leaflets of the aortic and pulmonary valves.
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Type 2 defects are confluent with the membranous septum. These defects usually extend into 1 of the 3 components of the muscular septum; the term perimembranous has been used to describe these defects ( Fig. 30.2 ).
Fig. 30.2
Autopsy specimen showing a type 2 perimembranous ventricular septal defect (VSD) ( A ) and a tvpe 4 trabecular muscular VSD ( B ) as viewed from the right ventricle.
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Type 3 defects are located in the inlet portion of the muscular septum inferior to the atrioventricular valves and are also termed inlet or atrioventricular canal/septal-type defects.
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Type 4 defects are those located in the trabecular portion of the muscular septum and are completely surrounded by muscle. Defects are in the trabecular muscular septum ( muscular VSD ) and can be midmuscular, apical, posterior, anterior, or multiple (see Fig. 30.2 ). Multiple muscular VSDs (Swiss cheese VSDs) may be difficult to visualize from the right side at surgery because of overlying coarse trabeculations.
Associated Abnormalities
A ventricular septal pseudoaneurysm can be formed by abundant tissue of the tricuspid valve septal leaflet and its chordae and can lead to the partial or complete occlusion of a perimembranous VSD.
Infundibular and perimembranous defects can be associated with malalignment of the ventricular septum in relation to the aorta, which may result in an override of a semilunar valve. Malalignment exists in isolation but is most frequently associated with other defects, such as tetralogy of Fallot.
VSDs may occur in association with other cardiac lesions, including left-sided obstructive lesions (bicuspid aortic valve, subaortic stenosis, aortic coarctation), pulmonary valve stenosis, and atrioventricular valve malformations.
VSDs also constitute an essential component of more complex cardiac defects, including tetralogy of Fallot, double-inlet or double-outlet ventricle, and common arterial trunk.
Muscle bundles arising from the lower infundibular septum and traversing and obstructing the right ventricular outflow tract can result in a double-chambered right ventricle. The VSD associated with this abnormality is usually perimembranous and can become smaller or may even close spontaneously.
A VSD can also result from acute myocardial infarction (1% to 2%). This lesion obviously differs from congenital VSDs and is not discussed further here.
Prevalence and Genetic Factors
VSDs are the most common congenital heart anomalies of childhood. Recent data from Danish national cohort studies document an overall prevalence of congenital heart disease of 8 per 1000 live births, with a prevalence of isolated VSDs of 2 per 1000 live births. In the adult population the prevalence of simple VSDs is estimated to be lower (0.3 per 1000), since there is a high incidence of spontaneous closure of small defects during childhood.
In the vast majority of patients with a VSD the underlying etiology is unclear. Chromosomal disorders associated with an increased incidence of VSD are trisomy 21 (Down syndrome), 22q11 deletion (DiGeorge syndrome), and 45X deletion (Turner syndrome). Familial forms of cardiac septation defects have also been linked to TBX5, GATA4, and NKX2.5 mutations.
The risk of recurrence of the same heart defect phenotype among first-degree relatives with a VSD is 6 per 1000 live births, which represents a threefold increase in risk. Maternal pregestational diabetes mellitus increases this risk further.
Pathophysiology
The magnitude and direction of flow through a VSD depend on the size of the defect and the state of the pulmonary vascular resistance. Usually, the direction of shunting across a VSD is left to right; with significant defects, this can result in increased pulmonary blood flow and pulmonary venous return, causing left atrial and left ventricular volume overload and enlargement. A left-to-right shunt is considered significant when the ratio of pulmonary-to-systemic blood flow (Qp/Qs) is greater than 1.5/1.0 or if it causes dilation of the left heart chambers.
In general, VSDs can be categorized into small , moderately sized , and large defects.
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The size of a small defect is less than or equal to 25% of the aortic annular diameter. Such defects are usually restrictive , with normal right ventricular and pulmonary artery pressures (systolic pulmonary artery to aortic pressure ratio <0.3). The magnitude of left-to-right shunting and pulmonary overcirculation is limited (pulmonary to systemic flow ratio [Qp/Qs] <1.4/1), so that the main pulmonary artery, the left atrium, and the left ventricle are not dilated or only mildly enlarged.
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In moderately sized VSDs, the diameter of the defect is more than 25% but less than 75% of the aortic annular diameter. These defects are moderately restrictive , and the right ventricular and pulmonary artery pressures can be normal or only mildly elevated (the ratio of systolic pulmonary artery pressure to aortic pressure is <0.5). The magnitude of left-to-right shunting varies depending on the size of the defect, from mild to moderate (Qp/Qs from 1.4/1 to 2.2/1), with mild or moderate pulmonary arterial, left atrial, and left ventricular enlargement.
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If the VSD is large (greater than or equal to 75% of the aortic diameter), the defect is usually nonrestrictive, and the left ventricular pressure is transmitted directly to the right ventricle and the pulmonary artery system (systolic pulmonary artery to aortic pressure ratio 0.5 to 1.0). The magnitude of flow through the defect primarily depends on the pulmonary vascular resistance in this situation. If the pulmonary vascular resistance is still low, the flow through the defect will be high, resulting in high pulmonary blood flow with left atrial and left ventricular volume overload and enlargement (Qp/Qs >2.2/1). However, the majority of patients with a large VSD will develop irreversible obstructive pulmonary vascular disease within the first or second year of life, leading to an increase in pulmonary vascular resistance and a reduction in the degree of left-to-right shunting. Patients with trisomy 21 are prone to develop irreversible pulmonary vascular disease even earlier. When pulmonary vascular resistance exceeds that of the systemic circulation, reversal of shunting from left to right then right to left ensues, leading to Eisenmenger physiology with desaturation, cyanosis, and secondary erythrocytosis.
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Quantification of Qp/Qs can most accurately be done by oximetry in the catheterization laboratory. However, a catheter study to obtain Qp/Qs is useful only in patients in whom noninvasive data on the hemodynamic significance of a VSD are inconclusive. Echocardiographic techniques are not accurate enough to calculate Qp/Qs reliably. Cardiac magnetic resonance imaging can provide these data with sufficient accuracy but should be performed with this intention by an experienced imaging expert.
Early Clinical Presentation
Small restrictive defects rarely present in the first days of life, since it takes time for the pulmonary vascular resistance to fall. These children typically present with the incidental discovery of a systolic murmur and remain asymptomatic with normal growth and development.
In children with large nonrestrictive defects, the initial finding may as well be a systolic murmur; however, symptoms will ensue as pulmonary vascular resistance falls and pulmonary blood flow increases. Typically these children develop shortness of breath and failure to thrive.
There is also a small group of children with nonrestrictive VSDs who do not develop overt symptoms during infancy because the pulmonary vascular resistance does not drop during infancy to normal postnatal levels. These patients usually develop severe pulmonary vascular disease later in life and eventually present with exercise intolerance and cyanosis.
Some VSDs can close or decrease in size spontaneously, so that their hemodynamic significance may change. The mechanism of closure is different depending on the localization of the defect. Spontaneous closure of VSDs in the trabecular muscular septum results from muscular occlusion. Perimembranous defects can be closed by tricuspid valve tissue. Infundibular defects can be sealed by prolapse of the right coronary cusp of the aortic valve, potentially coinciding with the development of aortic regurgitation ( Fig. 30.3 ).
Management in Childhood
Medical Therapy and the Surgical Closure of Ventricular Septal Defects
The goal of managing children presenting with VSDs is to prevent the development of irreversible pulmonary vascular disease and control symptoms of heart failure.
Patients with a small restrictive VSD usually remain asymptomatic with no signs of pulmonary hypertension or significant volume load to the left heart. These patients usually require no treatment. However, regular clinical follow-up is mandatory during the first few months of life because the hemodynamic significance of the defect may increase when pulmonary vascular resistance falls.
Infants with a nonrestrictive defect usually develop congestive heart failure and need timely closure before irreversible pulmonary vascular disease develops. In some patients with a nonrestrictive VSD or a large restrictive VSD, heart failure may be controllable, and the infant may thrive with medical therapy consisting of diuretics, beta blockers, and afterload reduction. To prevent the development of irreversible pulmonary vascular disease, VSD closure is indicated in these patients if right ventricular pressure fails to fall to 50% of the left ventricular pressure by the age of 5 to 6 months. If the right ventricular pressure is lower, conservative management can be continued and spontaneous defect closure hoped for.
Banding of the pulmonary trunk is an effective procedure to control pulmonary blood flow and pulmonary artery pressure but is nowadays rarely needed and should be reserved for small infants with multiple ventricular septal defects (“Swiss cheese” defects) refractory to medical therapy, where primary closure would carry a high risk of damage to the atrioventricular valves or the conduction system or where complete surgical closure cannot be expected.
In patients with persistence of a significant left-to-right shunt across a VSD leading to left atrial and left ventricular enlargement with no evidence of pulmonary hypertension, elective VSD closure is occasionally indicated to protect left atrial and left ventricular function.
A VSD located in the subaortic region (perimembranous or doubly committed juxta-arterial) can cause aortic valve prolapse and aortic regurgitation (see Fig. 30.3 ). The risk of development of aortic regurgitation increases during childhood, peaking at 5 to 10 years of age. If more than trivial aortic regurgitation develops, these patients should undergo surgery irrespective of the hemodynamic significance of the left-to-right shunt. In the case of a doubly committed juxta-arterial VSD, a defect relatively common in Asian patients, its location per se has been used as an indication for closure because the prevalence of aortic valve prolapse with regurgitation is particularly common in these cases, and timely closure of the defect may safely preserve valve function.
Severe obstruction of the right ventricular outflow tract can also develop in 5% to 10% of patients with an unoperated VSD and may require intervention irrespective of the size of the defect.
Transcatheter Closure
Since it was introduced by Lock et al. in 1987, transcatheter closure of VSDs using the Rashkind double-umbrella device has become an alternative to surgery. Nowadays the self-expandable Nitinol occluders such as the Amplatzer VSD occluders are the most widely used devices for the closure of muscular, perimembranous, or residual defects. Complete closure rates of up to 100% after 6 to 12 months have been reported using the Amplatzer VSD occluders designed for muscular and perimembranous VSDs. Device closure of muscular VSDs has been reported to carry a complication rate of up to 10.7%, including device embolization, hypotensive episodes, blood loss, and conduction abnormalities. However, complication rates in children with muscular defects are associated with lower patient weight; hence the risk of complications of device closure of a single muscular VSD in a child weighing more than 10 kg or an adolescent or adult can be regarded as minimal.
In contrast, device closure of perimembranous defects has been documented to carry a considerable risk of injury to the aortic and tricuspid valves and especially to the conduction system, with atrioventricular block potentially progressing to complete heart block. Because, today, surgical VSD closure causes complete heart block in less than 1% of patients, transcatheter closure of perimembranous VSDs with the currently available devices has been abandoned by some groups.
In young infants with heart failure due to large or multiple muscular VSDs, periventricular device closure (the “hybrid approach”) has been proposed as an alternative to primary surgical closure or pulmonary artery banding to avoid an extensive ventriculotomy, cardiopulmonary bypass, or repeated operations.
Late Outcome and Complications
Unoperated Patients
The natural history of patients with a VSD again depends on the size of the defect and the pulmonary vascular resistance.
Patients with an isolated VSD that has closed spontaneously and with normal ventricular function have a normal long-term prognosis.
Usually the outcome of asymptomatic adult patients with an isolated small VSD that has not been closed during childhood is also excellent. Surgical closure does not appear to be required in these patients as long as the left-to-right shunt is small (estimated Qp/Qs < 1.5/1), left ventricular size is normal, and there is no pulmonary hypertension, VSD-related aortic regurgitation, or any additional heart defect. Gabriel et al. reported on a population of 222 consecutive patients transitioned into the adult cardiac services with an isolated VSD considered too small to require closure in childhood. They report a spontaneous closure rate of 6%. Infective endocarditis occurred in about 1.8% of patients, all of whom had a perimembranous defect. Aortic regurgitation had developed in 5% and was trivial or mild in all cases. On Holter monitoring, 87% of patients had no arrhythmias, with the remainder showing only benign situations, such as incomplete or complete right bundle branch block and complete left bundle branch block. No heart block was found in any of the patients. For 118 patients who were prospectively followed for 7.4 ± 1.2 years, survival free of endocarditis or surgery was 95.5 ± 1.9% at eight years. More recent follow-up data confirm that adult patients with a small and restrictive VSD can present with complications such as arrhythmia, more than mild aortic regurgitation, infective endocarditis, and a double-chambered right ventricle. These complications indicated surgery in 26 of 231 (11%) patients during a follow-up period of 4.9 (2.9 to 8.6) years. The same study also reported coexisting systolic and diastolic dysfunction in a proportion of these patients. The Second Natural History Study of congenital heart disease reported a 25-year survival rate of 95.9% among patients with a restrictive VSD. In contrast, patients with moderately sized or large defects who survived into adulthood had a worse prognosis, with a 25-year survival of 86.3% and 61.2% respectively. Patients with large defects usually developed left ventricular failure and pulmonary vascular disease often progressing to Eisenmenger syndrome.
The incidence of aortic regurgitation and atrial or ventricular arrhythmias and degree of exercise intolerance are also higher in patients with more than small defects ( Table 30.1 ).
| Unoperated Patients | Repaired Patients(Surgery or Catheter Closure) | |
|---|---|---|
|
|
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| Aortic regurgitation |
|
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| Tricuspid regurgitation |
|
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| Left-sided obstructive lesion (subaortic stenosis, bicuspid aortic valve, coarctation) |
|
|
| Subpulmonary stenosis |
|
|
| LV dysfunction |
|
|
| Atrial arrhythmias |
|
|
| Conductance disturbance / Complete heart block |
|
|
| Ventricular arrhythmia |
|
|
| Exercise intolerance |
|
|
| Sudden cardiac death |
|
|
| Pulmonary vascular disease or Eisenmenger syndrome |
|
|
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