**4. Ayanotic heart defects: Obstructive lesions**

When there is a significant narrowing of a valve or a blood vessel, there is a higher pressure proximal to the obstruction compared to the distal pressure; this pressure gradient is necessary to maintain flow across the stenotic site. Hypertrophy of the cardiac chamber proximal to the obstruction and flow disturbance across the site of obstruction and their effects will determine the clinical features.

during pregnancy in mothers of infants with congenital heart defects than in matchedcontrol women suggested causative relationship between Coxsackie B infection and congenital heart defects, but this evidence is neither conclusive nor confirmed. Among drugs, maternal ingestion of thalidomide during pregnancy is associated with high incidence heart defects in the offspring. Similar association has been reported for some anticonvulsant drugs (particularly dilantin and trimethadione), alcohol (excessive), Lithium, sex hormones, diazepam, carticosteroids, phenolhiazine, folic acid antagonists, cocaine and dextromethamphetamines. A higher incidence of cardiac abnormalities with maternal diabetes is well known. Gross chromosomal anomalies such as trisomy 21 (Down syndrome), trisomy D and E syndromes, Turner's syndrome (XO), partial deletion of chromosome 22 and cri-du-chat (partial dilation of the short arm of chromosome 5) are associated with a higher incidence of heart defects than normal population and are likely be responsible for the congenital heart defects. Some generalized syndromes, secondary to a single mutant gene (for example, Marfan) involving multiple organ systems are associated with cardiovascular defects peculiar to that particular syndrome (Rao 1977a). Both autosomal (dominant and recessive) and sex-linked (dominant and recessive) single mutant gene syndromes have been reported with CHD. Finally, less than 1% of congenital heart defects can be explained by simple Mendelian inheritance. Autosomal dominant transmission other than single mutant gene syndrome has been reported with atrial septal defect, patent ductus arteriosus, aortic stenosis, pulmonary stenosis, tetralogy of Fallot and hypertrophic cardiomyopathy. Autosomal recessive inheritance may be present in some forms of endocardial fibroelastosis. To the best of my knowledge, sex-linked transmission has not been reported with CHD. However, recently questions have been raised as to the mitochondrial inheritance in which maternal transmission to almost all offspring occurs. In the presence of family history of congenital heart defect (parent or sibling) the probability of

CHD in the offspring is higher than that seen in general population.

some of the heart defects cannot be classified into the categories listed.

**4. Ayanotic heart defects: Obstructive lesions** 

effects will determine the clinical features.

**3. Classification** 

In summary, the cause of congenital heart defects is largely unknown and the majority of them may be explained by multifactorial inheritance hypothesis. Extensive research on gene mapping that is currently in progress may unravel previously unknown genetic mechanisms for CHD. Also, several chapters to follow address the issues related to causation of CHD.

Congenital heart defects may be classified into acyanotic and cyanotic depending upon whether the patients clinically exhibit cyanosis. The acyanotic defects may further be subdivided into obstructive lesions and left-to-right shunt lesions. The cyanotic defects, by definition, have right-to-left shunt. The relative incidence of these groups of defects and most common defects in each group are listed in table I. The total percent is not 100 because

When there is a significant narrowing of a valve or a blood vessel, there is a higher pressure proximal to the obstruction compared to the distal pressure; this pressure gradient is necessary to maintain flow across the stenotic site. Hypertrophy of the cardiac chamber proximal to the obstruction and flow disturbance across the site of obstruction and their


Table 1. Classification of Congenital Heart Defects

#### **4.1 Pulmonary stenosis**

The obstruction can be at valvar, subvalvar or supravalvar sites or in the branch pulmonary arteries (Rao 2000a). Valvar stenosis is the most common type and will be discussed in this section. Valvar pulmonary stenosis (PS) constitutes 7.5% to 9.0% of all CHDs. The pathologic features of valvar stenosis vary, but the most commonly found pathology is what is described as "dome shaped" pulmonary valve with fusion of the thickened pulmonary valve leaflets. Hypertrophy of the right ventricle (proportional to the degree of obstruction) and dilatation of main pulmonary artery (not related to the severity of obstruction) are also seen.

#### **4.1.1 Symptoms**

Children with PS usually present with asymptomatic murmurs, although they can present with signs of systemic venous congestion (usually interpreted as congestive heart failure) due to severe right ventricular dysfunction or cyanosis because of right-to-left shunt across the atrial septum.

#### **4.1.2 Physical findings**

The right ventricular and the right ventricular outflow tract impulses are increased and a heave may be felt at the left lower and upper sternal borders. A thrill may be felt at the left upper sternal border and/or in the suprasternal notch. The first heart sound may be normal or loud. The second heart sound is variable, depending upon the degree of obstruction and will be detailed later in this section. An ejection systolic click is heard in most cases of valvar stenosis. The click is heard best at the left lower, mid and upper sternal borders and varies with respiration (decreases or disappears with inspiration). An ejection systolic murmur (Figure 1, top) is heard best at the left upper sternal border and it radiates into infraclavicular regions, axillae and back. The intensity of the murmur may vary between grades II-V/VI; the intensity is not necessarily related to the severity of the stenosis.

Congenital Heart Defects – A Review 7

pulmonary valve stenosis. The peak instantaneous pressure gradient can be calculated by

Δ P = 4 V2 Where, Δ P is peak instantaneous pressure gradient in mmHg and V is the peak velocity

Fig. 2. In valvar pulmonary stenosis, severity of obstruction may be judged by auscultatory findings. In mild cases of pulmonary valve stenosis, the click (EC) is clearly separated from the first heart sound, almost normal splitting of the second heart sound with normal or slightly increased pulmonary component (P2) of the second sound is heard, and an ejection systolic, diamond-shaped murmur that peaks early in systole and ends way before the aortic closure of the second heart sound is appreciated. The findings in moderate PS include an ejection systolic click that is much closer to the first heart sound than in milder forms, widely split second sound with diminished pulmonary component of the second sound and an ejection systolic murmur that peaks in mid to late systole and ends just below the aortic component (A2) of the second sound. The features of severe valvar PS are an ejection systolic click which is either not present or falls so close to the first heart sound that it becomes inseparable from it, markedly increased splitting with a soft or inaudible pulmonary component of the second heart sound, and a long ejection systolic murmur that peaks late in systole and extends beyond the aortic

Though this procedure is not required for diagnosing valvar PS, it is usually required prior to therapeutic intervention, to be discussed below. The oxygen saturation data usually do not show evidence for left-to-right shunts. A right-to-left shunt across the patent foramen ovale (or an atrial defect) may be present in moderate to severe pulmonary valve obstruction. Right atrial pressure (particularly 'a' wave) may be increased. The right ventricular peak systolic pressure is increased. Trans-pulmonary valve peak-to-peak gradient is indicative of severity of obstruction. A peak-to-peak gradient in excess of 50 mmHg is usually considered an indication for therapeutic intervention. Angiocardiography

component of the second sound so that the latter cannot be heard.

**4.1.5 Cardiac catheterization and selective cineangiography** 

the use of a modified Bernoulli equation:

across the valve in meters/sec.

Fig. 1. Auscultatory diagrams of systolic murmurs. Ejection systolic murmur (top) begins shortly after the first heart sound (S1) and ends shortly before the second heart sound (A2, aortic component and P2, pulmonary component) whereas a holosystolic murmur (bottom) begins with and obscures the S1 and may last throughout the systole (as in the diagram) or may stop short of A2.
