True about ASD –
- Foramen ovale is patent
- Left parasternal peeve is due to increased pulmonary artery flow
- S2 is wide and variable
- Systolic murmur is due to rapid flow of blood across the shunt.
Hemodynamics of ASD
There is abnormal connection between left and right atrium, which is due to defect in atrial septum (not a patent foramen ovale).
Blood flows from left atrium to right atrium because left atrium has slightly higher pressure than right atrium → Left to right shunt.
Because the pressure difference between two atria is small, blood passes at a narrow pressure difference No shunt murmur.
There is volume overload to right atrium because of left to right shunt →.Right atrial dilatation and hypertrophy.
During diastole large amount of blood passes from right atrium to right ventricle through tricuspid valve → delayed diastolic murmur and accentuation of first heart sound.
Volume overload to right ventricle → Right ventricular hypertrophy that produces parasternal heeve.
Large blood volume passes through pulmonary valve → Pulmonary ejection murmur.
Prolonged blood passage along pulmonary valve causes delayed closure of pulmonary valve → P2 is delayed and accentuated, wide split and fixed S2.
Increased blood flow through pulmonary circulation → Pulmonary plethora that may cause pulmonary hypertension