Congenital cyanotic heart disease

# Overview
Congenital cyanotic heart disease is a group of heart defects that will causes neonatal cyanosis. The patient appears blue (cyanotic), due to deoxygenated blood bypassing the lungs and entering the systemic circulation. This can be caused by right-to-left or bidirectional shunting, or malposition of the great arteries. Such defects include persistent truncus arteriosus, total anomalous pulmonary venous connection, tetralogy of Fallot, transposition of the great vessels, and Ebstein's anomaly.

# Classification
Congenital cyanotic heart disease may be classified according to anatomical defect into 5 subgroups:
- Tetralogy of fallot
It is understood that tetralogy of fallot is the result of improper positioning of the outlet septum.
In the normal heart, the outlet septum is an indistinguishable component of the crista supraventricularis that communicates with the septomarginal trabeculae to divide the right and left ventricular cavities.
In Tetralogy of Fallot, proper ventricular septation is perturbed by anterocephalad displacement of the outlet septum relative to the septomarginal trabecula.
The direct consequence of this misalignment is an overriding aortic orifice and a ventricular septal defect, resulting in an intracardiac right to left shunt of blood.
In addition, anterocephalad displacement of the outlet septum indirectly predisposes the pulmonary trunk to stenosis in the setting of septoparietal trabecular hypertrophy.
Together, the displacement of the outlet septum coupled with the hypertrophic arrangement of the septoparietal trabeculae account for the three anatomical cardinal defects in Tetralogy of Fallot - aortic dextroposition, interventricular communication (VSD), and pulmonary stenosis.
The fourth defect - right ventricular hypertrophy - is a hemodynamic consequence of these three morphologic changes, as the right ventricle physiologically adapts to the increased resistance of a stenotic pulmonary trunk.
- It is understood that tetralogy of fallot is the result of improper positioning of the outlet septum.
- In the normal heart, the outlet septum is an indistinguishable component of the crista supraventricularis that communicates with the septomarginal trabeculae to divide the right and left ventricular cavities.
- In Tetralogy of Fallot, proper ventricular septation is perturbed by anterocephalad displacement of the outlet septum relative to the septomarginal trabecula.
- The direct consequence of this misalignment is an overriding aortic orifice and a ventricular septal defect, resulting in an intracardiac right to left shunt of blood.
- In addition, anterocephalad displacement of the outlet septum indirectly predisposes the pulmonary trunk to stenosis in the setting of septoparietal trabecular hypertrophy.
- Together, the displacement of the outlet septum coupled with the hypertrophic arrangement of the septoparietal trabeculae account for the three anatomical cardinal defects in Tetralogy of Fallot - aortic dextroposition, interventricular communication (VSD), and pulmonary stenosis.
- The fourth defect - right ventricular hypertrophy - is a hemodynamic consequence of these three morphologic changes, as the right ventricle physiologically adapts to the increased resistance of a stenotic pulmonary trunk.
- Total anomalous pulmonary venous connection
n this condition,the right side of heart is receiving blood both from pulmonary and systemic circulation.
There is a mixing of oxygenated pulmonary venous blood with deoxygenated blood from systemic circulation.
The mixing of blood could occur at three levels i.e. supracardiac, infracardiac and cardiac.
In the former two the mixing occurs outside the heart and in latter inside the heart (right atrium).
- n this condition,the right side of heart is receiving blood both from pulmonary and systemic circulation.
- There is a mixing of oxygenated pulmonary venous blood with deoxygenated blood from systemic circulation.
- The mixing of blood could occur at three levels i.e. supracardiac, infracardiac and cardiac.
- In the former two the mixing occurs outside the heart and in latter inside the heart (right atrium).
- Transposition of the great arteries
In the TGA the aorta arises from the morphologic right ventricle via a subaortic infundibulum and the pulmonary artery arises from the morphologic left ventricle, without a subpulmonary infundibulum.
These ventriculoarterial connection is known as ventriculoarterial discordance.
As a consequence, there is a a fibrous continuity between the mitral and pulmonary valve, but no continuity between the tricuspid and aortic valve.
The abnormal origin of the great arteries results in an altered spiral relationship.
Therefore, the aorta and pulmonary artery run parallel to each other
In normal heart thus the circulation is in series.
However, in transposition of the great vessels circulation is in parallel
- In the TGA the aorta arises from the morphologic right ventricle via a subaortic infundibulum and the pulmonary artery arises from the morphologic left ventricle, without a subpulmonary infundibulum.
- These ventriculoarterial connection is known as ventriculoarterial discordance.
- As a consequence, there is a a fibrous continuity between the mitral and pulmonary valve, but no continuity between the tricuspid and aortic valve.
- The abnormal origin of the great arteries results in an altered spiral relationship.
- Therefore, the aorta and pulmonary artery run parallel to each other
- In normal heart thus the circulation is in series.
- However, in transposition of the great vessels circulation is in parallel
- Truncus arteriosus
In truncus arteriosus, the pulmonary arteries are connected to the aorta.
A decrease in PVR at birth causes a left to right shunt with evidence of congestive heart failure.
These patients have a very high incidence of pulmonary hypertension and vascular disease.
- In truncus arteriosus, the pulmonary arteries are connected to the aorta.
- A decrease in PVR at birth causes a left to right shunt with evidence of congestive heart failure.
- These patients have a very high incidence of pulmonary hypertension and vascular disease.
- Ebstein's anomaly
Pathophysiology mainly involves the right ventricle, right atrium and tricuspid valve:
Failure of TV(tricuspid valve) leaflet delamination
Apical descent of the functional tricuspid orifice
Right ventricular dilation and atrialization
Anterior leaflet abnormal fenestrations and tethering
Right atrioventricular junction dilation
- Pathophysiology mainly involves the right ventricle, right atrium and tricuspid valve:
Failure of TV(tricuspid valve) leaflet delamination
Apical descent of the functional tricuspid orifice
Right ventricular dilation and atrialization
Anterior leaflet abnormal fenestrations and tethering
Right atrioventricular junction dilation
- Failure of TV(tricuspid valve) leaflet delamination
- Apical descent of the functional tricuspid orifice
- Right ventricular dilation and atrialization
- Anterior leaflet abnormal fenestrations and tethering
- Right atrioventricular junction dilation

# Differential diagnosis
Congenital cyanotic heart disease should be differentiated from other conditions that causes cyanosis: