Flow across a VSD is dependent upon:
The size of the VSD determines the initial pathophysiology of the disease. Large VSDs are classified as nonrestrictive and are at least equal in diameter to the aortic annulus. These defects allow free flow of blood from the LV to the RV, elevating right ventricular pressures to the same level as systemic pressure. Consequently, the pulmonary-to-systemic flow ratio (Qp:Qs) is inversely dependent on the ratio of pulmonary vascular resistance to systemic vascular resistance. Nonrestrictive VSDs produce a large increase in pulmonary blood flow, and the afflicted infant will present with symptoms of congestive heart failure. However, if untreated, these defects will cause pulmonary hypertension with a corresponding increase in pulmonary vascular resistance. This will lead to a reversal of flow (a right-to-left shunt), which is known as Eisenmenger syndrome.
Small restrictive VSDs offer significant resistance to the passage ofblood across the defect, and therefore right ventricular pressure is either normal or only minimally elevated and Qp:Qs rarely exceeds 1.5. These defects are generally asymptomatic because there are few physiologic consequences. However, there is a long-term risk of endocarditis, because endocardial damage from the jet of blood through the defect may serve as a possible nidus for colonization.
A child with a large VSD and no other cardiac lesion can be expected to develop all of the following EXCEPT :
A VSD produces a left-to-right shunt because systemic vascular resistance is greater than pulmonary vascular resistance. The extra work required by the shunt leads to increased basal energy expenditure and a failure to thrive. The shunt into the pulmonary circulation produces congestion and an associated increased susceptibility to lower respiratory tract infection. Large ventricular defects result in dilation but minimal hypertrophy due to decreased afterload.
Beyond early childhood, high pulmonary blood flow is most apt to produce:
High pulmonary blood flow beyond infancy may produce surprisingly little disability for a period of time, and the diminished exercise tolerance may be subtle. Cyanosis, hemoptysis, and pneumonia are not anticipated. With the volume over-loading in the RV, ventricular dilatation is more common than ventricular hypertrophy.
The most important diagnostic assessment modality for evaluating infants and children with congenital heart disease is:
Although chest X-ray may define heart size and electrocardiograms indicate cardiac rhythm, transthoracic and subcostal echocardiograms provide information on cardiac structure and function. Transesophageal echocardiogram, often very important in adults, is not required in children because children have excellent acoustic windows for the conventional studies. Cardiac catheterization is currently used most frequently for therapeutic reasons such as balloon dilatation of an uncomplicated isolated valvular pulmonic stenosis or coil occlusion of a patent ductus arteriosus.
The major determinant of operability in patients who have a VSD is:
The specific anatomy of a ventricular defect, its size, and the age of the affected patient are not much hindrance to closure of the defect, and the major determinant of operability is the degree of pulmonary vascular resistance that is present. It is important to differentiate between pulmonary artery pressure and vascular resistance. The pressure may be elevated by a large increase in blood flow, and yet the resistance may be normal; conversely, the pressure may be markedly elevated in the presence of an almost normal blood flow if the resistance is increased. When pulmonary vascular resistance exceeds onehalf the systemic resistance, the defect generally is considered inoperable. Those patients who have severe pulmonary vascular resistance increase their cardiac output by right-toleft shunting across the defect because they cannot increase their pulmonary blood flow. If the defect is closed, they have no mechanism to increase cardiac output with exercise. Most cases of VSD are detected today and the affected patient successfully operated on within the first years of life before pulmonaryvascular resistance has become severely elevated.
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