Ventricular septal defect (VSD) is the most common congenital cardiac anomaly in children and is the second most common congenital abnormality in adults, second only to a bicuspid aortic valve. An abnormal communication between the right and left ventricles and shunt formation is the main mechanism of hemodynamic compromise in VSD. While many VSDs close spontaneously, if they do not, large defects can lead to detrimental complications such as pulmonary arterial hypertension (PAH), ventricular dysfunction and an increased risk of arrhythmias.
It was first identified by Dalrymple in the year 1847. 
VSD develops when there is a developmental abnormality or an interruption of the interventricular septum formation during the complex embryologic heart morphogenesis. VSDs are frequently isolated; however, they can occur in association with other congenital heart defects such as atrial septal defects, patent ductus arteriosus, right aortic arch and pulmonic stenosis. They are also found in cases of aortic coarctation and sub-aortic stenosis, and they are a frequent component of complex congenital heart disease such as Tetralogy of Fallot and transposition of great arteries. Several genetic factors have been identified to cause VSD including chromosomal, a single gene and polygenic inheritance. A TBX5 mutation was recently discovered to cause septal defects in patients with Holt-Oram Syndrome. Non-inherited risk factors have been implicated in the development of VSDs; these include maternal infection (rubella, influenza, and febrile illness), maternal diabetes mellitus and phenylketonuria. Exposure to toxins like alcohol, marijuana, cocaine and certain medications such as metronidazole and ibuprofen is also linked to VSDs.
Isolated VSD accounts for 37% of all congenital heart disease in children. The incidence of isolated VSD is about 0.3% of newborns. Because as many as 90% may eventually close spontaneously; the incidence is significantly lower in adults. VSDs have no gender predilection. The percentage of each type is presented in the pathophysiology section.
The interventricular septum is an asymmetric curved structure due to the pressure difference in ventricular chambers. It is composed of five parts: the membranous, muscular (frequently referred to as trabecular), infundibular, atrioventricular and the inlet.
Failure of development or fusion of one of the above components during morphogenesis of the embryonic heart results in a VSD in the corresponding component. Different anatomic locations and histologic variation of VSDs has led to several classifications and nomenclature systems. Complexities in describing VSDs and multiple synonyms have been improved after a new unified classification was established and categorized VSDs into four major groups:
The main pathophysiologic mechanism of VSD is shunt creation between the right and left ventricles. The amount of blood shunted and the direction of the shunted blood determine the hemodynamic significance of the VSD. These factors are governed by the size, location of the VSD and pulmonary vascular resistance.
While VSDs are classified according to location, they can also be classified into size. The size is described in comparison to the diameter of the aortic annulus. They are considered small if they measure less or equal to 25% of the aortic annulus diameter, medium if they measure more than 25% but less than 75%, and large if they are greater than 75% of the aortic annulus diameter.
In the setting of long-standing large left-to-right shunts, the pulmonary vascular endothelium undergoes irreversible changes resulting in persistent PAH. When the pressure in the pulmonary circulation exceeds the pressure in the systemic circulation, the shunt direction reverses and becomes a right-to-left shunt. This is known as Eisenmenger syndrome, and it occurs in 10% to 15% of patients with VSD.
The presentation of unrepaired VSDs is largely dependent on the presence of hemodynamically significant shunt; hence it is directly related to the size of the defect. Small VSDs only lead to the minimal left-to-right shunt without left ventricular (LV) fluid overload or PAH; they are usually asymptomatic or found incidentally on physical exam. Medium size VSDs result in a moderate LV volume overload and absent to mild PAH; they present late in childhood with mild congestive heart failure (CHF). Those with large defects develop CHF early in childhood due to the severe LV overload and severe PAH. The murmur of VSD is typically pan-systolic best heard in the left lower sternal border; it is harsh and loud in small defects but softer and less intense in large ones. Infundibular defects are best heard in the pulmonic area. A diastolic decrescendo murmur and wide pulse pressure can be detected in the setting of aortic regurgitation. Increased LV flow may result in the mid-diastolic rumble in the lower left sternal border. A systolic click of a septal aneurysm can be appreciated sometimes in membranous defects. Eisenmenger syndrome manifests in cyanosis, desaturation, dyspnea, syncope, secondary erythrocytosis, and clubbing; in such cases, the typical murmur of VSD can be absent and accentuated pulmonic component of the second heart sound may be heard.
Colored Doppler transthoracic echocardiography (TTE) is the most valuable tool for diagnosis due to its high sensitivity. Colored Doppler TTE can detect up to 95% of VSDs, especially non-apical lesions larger than 5 mm; it provides morphologic information such as size, location, and the number of the defects as well as hemodynamic information such as jet size, severity, and estimation of pulmonary artery pressure. TTE is useful in detecting any associated aortic insufficiency and other associated congenital heart defects. Lastly, TTE is also helpful in evaluating the right and left ventricular chamber size and function. Limitations include operator dependent and poor acoustic window. When conventional TTE is equivocal, a trans-esophageal echo (TEE) is recommended.
Electrocardiography (ECG) is entirely normal in half of the patients with VSD. When the ECG is abnormal, it may detect LV hypertrophy in those with large shunts. In patients with PAH, the ECG may show right bundle branch block, right axis deviation, and RV hypertrophy and strain.
Chest radiography (CXR) is often normal in those with small defects. Enlarged cardiac silhouette can be observed in those with larger defects and increased LV size. RV enlargement and increased pulmonary diameter can be observed in those with PAH.
Cardiac Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) are useful in cases where anatomy is complex such as VSD accompanied with other congenital heart anomalies and in defects in unusual locations that are hard to visualize by conventional TTE.
Cardiac catheterization gives accurate hemodynamic information regarding the pulmonary vascular resistance and response to vasodilators; this is particularly useful in those who are being evaluated for surgical closure. It provides more details on coexisting Aortic Regurgitation, in multiple VSDs and when coronary artery disease is suspected.
Approximately 85% to 90% of small isolated VSDs close spontaneously during the first year of life. Patients with small, asymptomatic VSDs with the absence of PAH have an excellent prognosis without any intervention. Otherwise, the management approach includes endocarditis prophylaxis and VSD closure. Patients with Eisenmenger syndrome are usually managed in advanced centers due to the complexity of managing of such cases. Historically, surgical repair of VSDs was the only option; however, recent advances in interventional techniques make percutaneous VSD closure possible. Endocarditis prophylaxis is mainly indicated in cyanotic congenital heart disease, prior episodes of endocarditis and in those who have prosthetic heart valves or had repair with prosthetic material. In general, VSD closure is indicated in medium to large defects with a significant hemodynamic compromise such as those who are symptomatic and have LV dysfunction. An intervention should be also considered in cases of progressive aortic insufficiency or after an episode of endocarditis. The indications of a surgical closure according to the ACC/AHA 2008 guidelines are summarized in the following:
Surgical repair reduces the risk for endocarditis, might improve PAH and overall it increase survival. Without PAH, the operative mortality rate is approximately 1%. Complications include residual or recurrent VSD, valvular incompetence such as tricuspid regurgitation and aortic insufficiency, arrhythmias, LV dysfunction and progression of PAH. The arrhythmias which accompany VSD repair include atrial fibrillation, complete heart block and uncommonly, ventricular tachycardia. The main contraindication for surgical VSD closure is the presence of irreversible PAH; this is due to the high surgical perioperative mortality and pulmonary complications.
Percutaneous device VSD closure is reserved for those whom surgery is very risky due to severe PAH, multiple comorbidities, and those who had prior cardiothoracic surgery such as residual or recurrent VSD. Muscular VSDs are the main type amenable to this procedure, the proximity of other defects to the inlet valves makes performing this technique challenging in such cases. Despite the fact that it is still unpopular in the United States, current data shows excellent outcomes with complete closure and low mortality. The most frequent complication is complete atrioventricular block mostly related to perimembranous defects.
In conclusion, VSD is the most common congenital anomaly at birth. Small defects are expected to close spontaneously in the first year of life; however, larger defects can result in severe complications. Surgical VSD closure and device closure are the main intervention for large defects.
The prognosis is good for patients who have undergone VSD repair. However, they have a higher risk of arrhythmia, endocarditis and Congestive heart failure in the long run in comparison to the general population.
The pansystolic Murmur of VSD can be confused with the pansystolic Murmur of Mitral Regurgitation. The VSD becomes louder towards the sternum, and the murmur of Mitral regurgitation gets louder away from the sternum.
The management of VSD is done by an interprofessional team that includes a pediatrician, cardiologist, cardiac surgeon, ICU nurse, physical therapist and a social worker. Parents and patients need to be educated about the need to follow up. Small VSDs that are not repaired are at risk for developing infectious endocarditis. In addition, some children with perimembranous VSD may develop aortic valve prolapse and require surgery. Finally, all unrepaired VSDs have the potential to increase pulmonary vascular resistance leading to Eisenmenger syndrome. At this stage, except for a heart and lung transplant, there is no other viable therapy. With a marked shortage in organs for transplantation, the majority of these patients succumb to progressive right heart failure and cyanosis. (Level V)
Young children who remain asymptomatic and have a small VSD have a good outcome. However, the presence of anemia, infection or endocarditis may trigger symptoms in these children. But the outcomes in people with a large VSD is poor if the defect is not repaired. The continued left to right shunt eventually leads to the development of pulmonary hypertension and Eisenmenger syndrome. Today, in North America most infants have the VSD repaired electively within the first two years of life. The mortality is less than 1%, and most patients have a normal lifespan. 
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