GENERAL CONSIDERATIONS

Incidence of individual CHDs varies with sex and race. Some CHDs are commoner in males (TGA and AS) while others are more common in females (Lt gt; Rt shunts and PS). VSDs are more common in Asians while TA is common in Whites.

Etiology of CHDs is largely unidentified, considered to be multifactorial:

• Familial factors: Presence of CHD in a child or parent is associated with higher risk (3-4%) in subsequent children than in general population (lt;1%). Risk is further increased (10%) in third child, if two siblings (or one parent and one sibling) have CHDs.

• Chromosomallgenetic disorders: CHDs are common in trisomies, e.g. Down syndrome, Turner syndrome, Marfan syndrome and other genetic disorders. Nearly 85% of conotruncal defects are associated with deletion of a chromosomal segment—22q11.

• Environmental factors: CHDs are common in babies with intrauterine exposure to—(a) maternal infections, e.g. rubella, (b) maternal illnesses, e.g. diabetes or SLE, and (c) drugs, e.g. phenytoin, warfarin or alcohol. Table 17.15 lists common cardiac lesions, associated

with various genetic defects, intrauterine infections or other risk factors.

Classification: CHDs may be classified clinically as- (a) acyanotic or (b) cyanotic; or hemodynamically as—(a) left to right shunts, (b) obstructive lesions and (c) right to left shunts (Table 17.16).

• Left to right (Ltgt;Rt) shunts are commonest CHDs, characterized by an abnormal communication at atrial, ventricular or ductal level, with blood flow

*Similar lesions may develop even after postnatal exposure.

TGA: Transposition of great arteries.

from high-pressure systemic circuit to low-pressure pulmonary circuit. These CHDs are generally acya­notic (till reversal of shunt or Eisenmengerization) and age of presentation depends on the magnitude of shunt and volume overload on pulmonary circulation due to re-shunting of oxygenated blood back to the lungs.

VSD is the commonest acyanotic CHD with Ltgt;Rt shunt (~25-30%), followed by ASD (8-10%)* and PDA (6-8%). *ASD is perhaps more common as many cases remain undetected.

• Obstructive lesions (acyanotic) are characterized by ventricular (or rarely atrial) outflow obstruction. Each obstructive lesion - PS, AS and CoA, account for ~6-8% of CHDs, though many of them are mild and asymptomatic.

Unless associated with shunts, these cases usually present in later life with pressure overload and corresponding ventricular failure, i.e. RV failure in PS or LV failure in AS. Obstructive lesions with Rt gt; Lt communication, present like cyanotic CHDs.

• Right to left (Rtgt;Lt) shunts are cyanotic CHDs, characterized by abnormal communication with blood flow from pulmonary to systemic circuit, leading to mixing of unoxygenated right-sided with oxygenated left-sided blood. Age of the appearance of cyanosis depends on the magnitude of Rtgt; Lt pressure gradient, anatomical size of shunt and presence/absence of alternative communication to maintain pulmonary flow, e.g. PDA.

Tetralogy of Fallot (TOF) is the commonest cyanotic CHD (5-7%) followed by TGA (3-5%).

Clinical presentation of CHDs is highly variable, depending on the age of onset, type and severity of lesion. Some diseases may remain asymptomatic throughout life while others are lethal in utero or present soon after birth. Some important indicators of CHDs are:

TABLE 17.16: Classification of CHDs

Acyanotic CHDs

• Lt to Rt shunt

- Ventricular septal defect (VSD)

- Atrial septal defect (ASD)

- Patent ductus arteriosus (PDA)

• Obstructive lesions

- Pulmonary stenosis (PS)

- Aortic stenosis (AS)

- Coarctation of aorta (CoA)

Cyanotic CHDs

• Rt to Lt shunts with decreased PBF

- Tetralogy of Fallot (ToF)

- Tricuspid atresia (TA)

- Ebstein anomaly (EA)

- Pulmonary atresia (PA)

- Right hypoplastic heart syndrome (RHHS)

• Rt to Lt shunts with increased PBF[††††††]

- Transposition of great vessels (TGA)

- Truncus arteriosus (TrA)

- Total/partial anomalous pulmonary venous return (TAPVC)

- Single ventricle (SV)

- Double outlet right ventricle (DORV)

- Left hypoplastic heart syndrome (LHHS)

PBF: Pulmonary blood flow

**may also present with decreased PBF, if associated with PS.

• Presence of murmurs, due to abnormal blood flow through valves or shunts,

• Abnormal heart sounds or signs of the hypertrophy/ dilatation of cardiac chambers, due to altered pressure gradients between different chambers by shunts or outflow obstruction,

• Chronic pulmonary congestion, e.g. recurrent respiratory infections, chest deformities, failure to thrive, etc., indicating increased pulmonary blood flow,

• Cyanosis, cyanotic spells, clubbing, etc. Indicating mixing of unoxygenated and oxygenated blood,

• CCF, e.g. tachycardia, dependent edema, raised JVP, hepatomegaly, due to failure of compensatory mechanisms.

17.5.2