VENTRICULAR SEPTAL DEFECTS (VSD)

The ventricular septal defect (VSD) is a congenital heart disease characterized by the persistence of an abnormal communication between the two ventricles due to an incomplete closure of the septum during embryonic development. This condition results in an abnormal passage of blood between the ventricles, leading to potential hemodynamic alterations and consequences on both pulmonary and systemic circulation.

The severity of clinical manifestations depends on the size of the defect and pulmonary resistance. In cases of small VSDs, the shunt is minimal and often closes spontaneously, whereas in larger defects, excessive pulmonary flow can cause ventricular hypertrophy, pulmonary hypertension, and heart failure. In more advanced cases, the chronic increase in pulmonary pressure can lead to Eisenmenger syndrome, an irreversible condition in which the shunt reverses to right-to-left, leading to cyanosis.

Epidemiology and Genetic Associations

VSD is the most common congenital heart disease, with an incidence of approximately 3 cases per 1,000 live births. It can occur as an isolated defect or be associated with genetic syndromes such as trisomy 21 (Down syndrome), where it is often part of an atrioventricular canal defect, or DiGeorge syndrome, which is characterized by conotruncal defects. It has also been observed in other genetic conditions, including Turner syndrome and Holt-Oram syndrome. In sporadic cases, the etiology is generally multifactorial, with a possible role of environmental and teratogenic factors.

Classification of VSD

Ventricular septal defects are classified based on their location and anatomical characteristics:

• Perimembranous VSD: The most common type, located in the upper part of the septum, just below the atrioventricular valves.
• Muscular VSD: Can be found in the posterior portion of the septum (inlet), the anterosuperior part (outlet), or the apical region. In newborns, these defects often close spontaneously.
• Subpulmonary VSD: More common in the Asian population, located near the pulmonary valve and may be associated with aortic valve prolapse.
• Atrioventricular Canal VSD: Typically seen in Down syndrome, associated with more complex defects involving the atrial septum and atrioventricular valves.

From a hemodynamic perspective, VSDs are classified as restrictive, where the defect is small and right ventricular pressure remains low, non-restrictive, characterized by a large communication with equalized ventricular pressures, and with pulmonary hypertension, where pulmonary resistance is increased.

Pathophysiology

In small VSDs, the left-to-right (L-R) shunt is minimal and does not cause significant pressure alterations. In moderate and large defects, oxygenated blood flows from the left to the right ventricle, leading to right ventricular overload and pulmonary overcirculation. Increased pulmonary flow results in ventricular hypertrophy and progressive pulmonary vascular damage. If left untreated, chronic pulmonary hypertension can lead to shunt reversal (right-to-left), with the onset of cyanosis and hypoxemia, characteristic signs of Eisenmenger syndrome.

Clinical Manifestations and Diagnosis

The clinical presentation varies depending on the size of the defect. In small VSDs, the patient is generally asymptomatic, and the diagnosis is incidental, often made due to the presence of a heart murmur. In moderate defects, symptoms such as fatigue, exertional dyspnea, and tachycardia may occur, sometimes accompanied by growth retardation in children. In large VSDs, hemodynamic overload leads to early signs of heart failure, including tachypnea, profuse sweating, and difficulty feeding.

Cardiac auscultation may reveal a holosystolic murmur at the mesocardium, often associated with a split second heart sound. The ECG may show signs of ventricular hypertrophy, while chest X-ray findings include cardiomegaly and increased pulmonary vascularization in cases with significant shunting. Echocardiography with Doppler is the gold standard for diagnosis, allowing precise evaluation of the defect's location, size, and shunt severity. In more complex cases, cardiac catheterization may be performed to measure intracardiac pressures, and cardiac MRI may be used for a detailed structural assessment.

Treatment

No treatment is required for small VSDs, except for bacterial endocarditis prophylaxis in high-risk cases. In moderate defects, surgical closure is recommended if the left-to-right shunt is significant and causes right ventricular overload. Surgery is typically performed between ages 3 and 4, before irreversible right ventricular alterations develop.
For large VSDs, early surgical correction is essential, ideally within the first six months of life, to prevent the development of pulmonary hypertension. If Eisenmenger syndrome occurs, surgery is contraindicated.
In inoperable cases with advanced pulmonary hypertension, palliative treatment is based on pulmonary vasodilators such as sildenafil or bosentan to reduce pulmonary pressure.

Follow-up and Complications

Operated patients require periodic echocardiographic monitoring to assess for residual shunting, valvular insufficiency, or ventricular dysfunction. In unoperated patients, regular cardiologic follow-up is crucial to detect early signs of progressive pulmonary hypertension. Late complications may include atrial or ventricular arrhythmias, heart failure, infectious endocarditis, and in right-to-left shunt patients, an increased risk of paradoxical stroke due to systemic embolization.

Conclusion

VSD is one of the most common congenital heart defects, with a wide clinical variability. Early management is essential to prevent long-term complications, particularly irreversible pulmonary hypertension. When surgery is indicated, prognosis is excellent if performed before the onset of advanced pulmonary damage.

References
1. Hoffman JI, Kaplan S. - The incidence of congenital heart disease. *J Am Coll Cardiol*. 2002;39(12):1890-1900. doi:10.1016/S0735-1097(02)01886-7.
2. Reller MD, Strickland MJ, Riehle-Colarusso T, Mahle WT, Correa A.** Prevalence of congenital heart defects in metropolitan Atlanta, 1998-2005. *J Pediatr*. 2008;153(6):807-813. doi:10.1016/j.jpeds.2008.05.059.
3. Baumgartner H, De Backer J, Babu-Narayan SV, et al. - 2020 ESC Guidelines for the management of adult congenital heart disease. *Eur Heart J*. 2021;42(6):563-645. doi:10.1093/eurheartj/ehaa554
4. Geva T, Martins JD, Wald RM. - Ventricular septal defects. *Lancet*. 2014;383(9932):1921-1932. doi:10.1016/S0140-6736(13)61027-6.
5. Perri G, Santoro G, Lamberti A, et al. - Long-term outcomes after ventricular septal defect repair: a systematic review. *Eur J Cardiothorac Surg*. 2021;59(4):786-794. doi:10.1093/ejcts/ezaa404.
6. Tchervenkov CI, Jacobs ML, Weinberg PM, et al.- Congenital heart surgery nomenclature and database project: ventricular septal defect. *Ann Thorac Surg*. 2000;69(4 Suppl):S25-35. doi:10.1016/S0003-4975(99)01289-8.
7. Digilio MC, Marino B.- Genetic syndromes associated with ventricular septal defects: a review. *Expert Rev Cardiovasc Ther*. 2016;14(4):397-403. doi:10.1586/14779072.2016.1146593.
8. Rudolph AM. - Congenital Diseases of the Heart: Clinical-Physiological Considerations. *Wiley-Blackwell*; 2009.