CVS - Atrial Septal Defects

Question 1

What is an ASD?

Answer 1

A defect (hole) in the septum between the two atria.

Question 2

Pathophysiology of ASD (3).

Answer 2

1. During development of the foetus, the two atria are connected.
2. Two walls (Septum Primum and Septum Secondum) grow downwards from the top of the heart and then fuse together with the endocardial cushion in the middle of the heart to separate the atria.
3. A hole in these 2 walls is a defect.

Question 3

Types of ASD (3).

Answer 3

1. Ostium Secondum (commonest - failure of Septum Secondum to fully close - a hole in the Septum Secondum).
2. Patent Foramen Ovale (the Foramen Ovale usually closes at birth).
3. Ostium Primum (failure of Septum Primum to fully close, which tends to lead to AV valve defects, making it an Atrioventricular Septal Defect).

Question 4

Presentation of Ostium Secondum (2).

Answer 4

1. Holt-Oram Syndrome (look for tri-phalangeal thumbs).

2. ECG : RBBB and RAD.

Question 5

Presentation of Ostium Primum (2).

Answer 5

1. ECG : RBBB with LAD and Prolonged PR Interval.

2. Earlier than Ostium Secondum.

Question 6

Clinical Features of ASDs (2).

Answer 6

1. Mid-Systolic Crescendo-Decrescendo Murmur.

2. Pulmonary Hypertension.

Question 7

Nature of Murmur in ASD (3).

Answer 7

1. Mid-Systolic, Crescendo-Decrescendo Murmur.
2. Heard loudest at the upper left sternal border.
3. Fixed Split S2.

Question 8

What is a normal S2 Split and an abnormal S2 Split?

Answer 8

Normal : Splitting of S2 can be normal with inspiration.

Abnormal : Fixed Split = does not change with inspiration and expiration.

Question 9

Physiology of Normal S2 Split (4).

Answer 9

1. During inspiration, the chest wall and diaphragm allow expansion of the lungs and the heart, due to negative intra-thoracic pressure.
2. This causes the right side to fill faster as it pulls in blood from the venous system.
3. Increased volume in the RV causes it to take longer to empty during systole.
4. Delay closing Pulmonary Valve (slightly later than Aortic Valve).

Question 10

Pathophysiology of Fixed S2 Split (2).

Answer 10

1. Blood is flowing from the left atrium into the right atrium across ASD.
2. This increases the volume of blood that the right ventricle has to empty before the pulmonary valve can close (so delay is elongated).

Question 11

Pathophysiology of Pulmonary Hypertension (3).

Answer 11

1. Blood moves from the left atrium to the right atrium due to the pressure gradient.
2. Blood continues to flow to the pulmonary vessels and lungs to get oxygenated.
3. Increased flow to the right side causes right-sided overload and right heart strain : RHF and Pulmonary Hypertension.

Question 12

Diagnosis of ASD (2).

Answer 12

1. Antenatal Scans.

2. Newborn checks.

Question 13

Management of ASD (3).

Answer 13

1. Small/Asymptomatic = Watch and Wait.
2. Surgical = Transvenous Catheter Closure via Femoral Vein or Open Heart Surgery.
3. Anticoagulants e.g. Aspirin, Warfarin, NOACs to reduce risk of clots.

Question 14

Prognosis of ASD.

Answer 14

50% of patients are dead at the age of 50.

Question 15

Complications of ASD (6).

Answer 15

1. Stroke (in context of VTE).
2. Atrial Fibrillation.
3. Atrial Flutter.
4. RHF.
5. Pulmonary Hypertension.
6. Eisenmenger Syndrome.

Question 16

Importance of Stroke in ASD.

Answer 16

An embolus from DVT can travel from the right atrium into the left atrium and travel up the aorta into the brain.