Tetralogy of fallot

Question 1

What is TOF?

Answer 1

A congenital condition of the heart which effects 1 in 3600 live births.
It is linked to various genetic disorders such as trisomy 21 (Downs syndrome).
It is multifaceted and has 4 distinct signs:
- Pulmonary stenosis
- Ventricular septal defect
- Over-riding aorta and Right ventricular hypertrophy.

Question 2

What are some common symptoms of TOF?

Answer 2

Low O2
Heart murmer
Cyanotic episodes
Clubbing
tet-spells: Increase peripheral resistance and can temp. alleviate symptoms.

Question 3

Describe the normal development of the heart into distinct regions.

Answer 3

Heart development begins with a cluster of cardiogenic mesenchyme (cardiogenic area) at roughly 18-19 days. These cells form two distinct cords: cardiogenic cords.
At 20 days 2 endocardial tubes are formed and they begin to form with venous (inferior) and arterial (superior) ends.
At day 21 the lateral folding joins the endocardial tubes forming one distinct tube: primitive heart tube.
At this stage the heart begins to beat- roughly day 22
The heart consists of the truncus arteriosus, the bulbus cordis the ventricle, the atrium and the sinus venosus in a caudal to cranial direction..

Question 4

Describe folding of the heart.

Answer 4

The bulbus cordis grows at a faster rate than the other regions of the heart.
This causes the heart to fold into an S shape with the ventricle and the sinus venosus to sit superior to the other regions.
This finishes by roughly day 35.
These structures will continue to develop into the following structures:
- Sinus venosus: part of the R atrium, the coronary sinus and the SA node.
- Atrium: Part of the R atrium, the left atrium and the L auricle.
Ventricle: The L ventricle
Bulbus cordis: R ventricle
Truncus arteriosus: ascending aorta and the pulmonary trunk.

Question 5

Describe the sectioning of the heart.

Answer 5

The sectioning of the heart begins with the formation of the endocardial cushions at day 28.
These separate the atria to the ventricles.
The septum’ form between the right and left heart chambers.
- Interatrial septum:
Constricts the foreman primum as it grows. Foreman primum closes as a new septum opens (foreman secundum which shunts blood between the atria. New septum forms over the foreman secundum which forms the septum secundum. The edges of these form the foreman ovale which acts as flutter valve.
- Interventricular septum.
Complex spiral forms from the bifurcation of the truncus arteriosus. It grows towards the interventricular septum which closes the interventricular foreman.

Question 6

What happens to pulmonary circulation at birth.

Answer 6

Ductus arteriosus constricts and pulmonary resistance drops causing blood to circulate into the lungs.

Question 7

What are the operative strategies for TOF?

Answer 7

Complete intracardiac surgery
- pulmonary artery and ventricles are enlarged using a patch
- Muscular obstruction of valve removed
- VSD removed using patch.
Temporary surgery
- Shunt used to provide more pathways for blood to reach the lungs.