A ventricular septal defect (VSD) is a hole in the ventricular septum, the wall dividing the left and right ventricles of the heart. It is a common congenital heart defect, although restrictive muscular VSDs are not true pathological defects; they are typically just a delayed closure of the ventricular septum. They have an extremely high prevalence in newborns. The extent of the opening may vary from pin size to complete absence of the ventricular septum, creating one common ventricle. The ventricular septum consists of an inferior muscular and superior membranous portion and is extensively innervated with conducting cardiomyocytes. The membranous portion, which is close to the atrioventricular node, is most commonly affected in adults and older children in the United States. It is also the type that will most commonly require surgical intervention, comprising over 80% of cases. New research has found that muscular ventricular septal defects are more common than membranous ventricular septal defects, and are the most common congenital cardiac anomaly. Around 3-5% of newborn babies have small muscular VSDs, according to the Copenhagen Baby Heart Study.
Signs and symptoms Ventricular septal defect is usually symptomless at birth. It usually manifests a few weeks after birth. VSD is an acyanotic congenital heart defect, AKA a left-to-right shunt, so there are no signs of cyanosis in the early stage. However, an uncorrected VSD can increase pulmonary resistance leading to the reversal of the shunt and to corresponding cyanosis.
Pansystolic (Holosystolic) murmur along lower left sternal border (depending upon the size of the defect) +/- palpable thrill (palpable turbulence of blood flow). Heart sounds are normal. Larger VSDs may cause a parasternal heave, a displaced apex beat (the palpable heartbeat moves laterally over time, as the heart enlarges). An infant with a large VSD will fail to thrive and become sweaty and tachypnoeic (breathe faster) with feeds. The restrictive ventricular septal defects (smaller defects) are associated with a louder murmur and more palpable thrill (grade IV murmur). Larger defects may eventually be associated with pulmonary hypertension due to the increased blood flow. Over time this may lead to an Eisenmenger's syndrome the original VSD operating with a left-to-right shunt, now becomes a right-to-left shunt because of the increased pressures in the pulmonary vascular bed.
Cause Congenital VSDs are frequently associated with other congenital conditions, such as Down syndrome. Congenital heart disease, particularly VSDs, is the number one cause of death for children with Down syndrome ages birth to two. A VSD can also form a few days after a myocardial infarction (heart attack) due to mechanical tearing of the septal wall, before scar tissue forms, when macrophages start remodeling the dead heart tissue. A congenital VSD can result from a disturbance in the morphogenesis of the heart in its embryonic stages. In the fifth week of gestation, the heart undergoes multiple processes of septation and forming a dextral loop. Interfering with the latter leads to insufficient leftward movement of the ventricular outflow tract over the atrioventricular canal, which in turn can result in a VSD or, in the most extreme cases, a double outlet right ventricle with one. A ventricular septal defect arises when the superior part of the interventricular septum, which separates the right and left ventricles of the heart, fails to fully develop. The right ventricle pumps blood to the lungs to get oxygen, while the left ventricle pumps blood to the rest of the body to provide oxygen to tissues. A ventricular septal defect results in the mixing of oxygen-rich blood with oxygen-poor blood, increasing strain on the heart and lungs.
Pathophysiology During ventricular contraction, or systole, some of the blood from the left ventricle leaks into the right ventricle, passes through the lungs and re-enters the left ventricle via the pulmonary veins and left atrium. This has two net effects. First, the circuitous refluxing of blood causes volume overload on the left ventricle. Second, because the left ventricle normally has a much higher systolic pressure (~120 mmHg) than the right ventricle (~20 mmHg), the leakage of blood into the right ventricle therefore elevates right ventricular pressure and volume, causing pulmonary hypertension with its associated symptoms. In serious cases, the pulmonary arterial pressure can reach levels that equal the systemic pressure. This reverses the left to right shunt, so that blood then flows from the right ventricle into the left ventricle, resulting in cyanosis, as blood is by-passing the lungs for oxygenation. This effect is more noticeable in patients with larger defects, who may present with breathlessness, poor feeding and failure to thrive in infancy. Patients with smaller defects may be asymptomatic. Four different septal defects exist, with perimembranous most common, outlet, atrioventricular, and muscular less commonly.
Diagnosis
A VSD can be detected by cardiac auscultation. Classically, a VSD causes a pathognomonic holo- or pansystolic murmur. Auscultation is generally considered sufficient for detecting a significant VSD. The murmur depends on the abnormal flow of blood from the left ventricle, through the VSD, to the right ventricle. If there is not much difference in pressure between the left and right ventricles, then the flow of blood through the VSD will not be very great and the VSD may be silent. This situation occurs a) in the fetus (when the right and left ventricular pressures are essentially equal), b) for a short time after birth (before the right ventricular pressure has decreased), and c) as a late complication of unrepaired VSD. Confirmation of cardiac auscultation can be obtained by non-invasive cardiac ultrasound (echocardiography). To more accurately measure ventricular pressures, cardiac catheterization, can be performed.
Classification Although there are several classifications for VSD, the most accepted and unified classification is that of Congenital Heart Surgery Nomenclature and Database Project. The classification is based on the location of the VSD on the right ventricular surface of the inter ventricular septum and is as follows:
Multiple
Type 1 Type 1 is sub aortic
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