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What is The commonest type of congenital heart disease is – and explain in detail?
VSD is the commonest CHD.
VSD is the commonest acyanotic CHD.
Acyanotic congenital heart diseases 

Acyanotic heart disease may be of two types : -


Left to right shunts. (ASD, VSD, PDA)
Obstructive lesions (PS, AS, Coarctation of aorta).

A) Left to right shunts
Patients with a left to right shunts have following features: -

Frequent respiratory tract infection → Because pulmonary circulation is overloaded which may result in pulmonary edema, CHF and infection.
No cyanosis → Most of the blood is in pulmonary circulation. So there is no impairment in oxygenation of blood.
Pericardial bulge -4 Frequent chest infections with tachypnea causes the soft rib cage being drawn inward at the diaphragmetic attachments of the ribs. This combined with cardioamegaly gives them a precordial buldge.
Hyperkinetic precordium
Delayed diastolic murmur in tricuspid or mitral area → Due to increased flow through these areas depending on the type of CHDs.
Cardiomegaly with plethoric pulmonary vasculature on chest X-ray → Due to increased flow through pulmonary circulation (plethoric lung) there is increased volume overload to left side of heart → Cardiomegaly.

B) Obstructive Lesions

Obstructive congenital diseases have following features.


Absence offrequent chest infection → Pulmonary circulation is not overloaded.
The absence of cyanosis → No defect in pulmonary oxygenation and there is no shunt where arterial and venous blood can mix.
The absence of precordial buldge → There is no chest infection or Cardiomegaly.
Heaving (forcible) cardiac impulse → Obstructive lesions cause concentric hypertrophy of ventricles that produce forcible contraction.
Systolic thrill due to systolic ejection murmur → When hypertrophied ventricles forcibly pump the blood through stenotic pulmonary or aortic valve, systolic thrill and systolic ejection murmur are produced.
Absence of delayed diastolic murmur in mitral or tricuspid area → Blood flow through these area is not increased.
Presence of delayed corresponding second sound (A2 in AS and P2 in PS) → Because prolonged flow through these area results in delayed closure of that valve.
Normal sized heart and pulmonary vasculature in chest x-ray → There is concentric hypertrophy, i.e., hypertrophy without dilatation. So, heart size is normal on x-ray.