Cyanotic heart disease is a category of congenital heart defect in which a structural abnormality allows oxygen-poor (deoxygenated) blood to enter the systemic circulation without first passing through the lungs. The resulting low oxygen saturation causes cyanosis: a bluish discolouration of the skin, lips, and fingertips that becomes visible when blood oxygen levels fall significantly.
In a normal heart, deoxygenated blood returning from the body passes entirely through the right heart and lungs before returning to the left heart as oxygenated blood. Cyanotic defects disrupt this separation, either by creating a direct pathway between the right and left sides (such as a ventricular septal defect combined with other abnormalities) or by causing the great arteries to be connected to the wrong ventricles.
Common cyanotic congenital heart conditions include Tetralogy of Fallot, the most common cyanotic heart defect, combining a ventricular septal defect, pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta. Transposition of the Great Arteries involves the aorta and pulmonary artery arising from the wrong ventricles, creating two parallel circulations. Hypoplastic Left Heart Syndrome involves severe underdevelopment of the left-sided structures. Truncus Arteriosus describes a single arterial trunk arising from both ventricles, and Pulmonary Atresia involves complete absence of the pulmonary valve.
All cyanotic heart conditions require specialist management and surgical intervention. Adults who have had corrective or palliative surgery for cyanotic defects are followed up in Adult Congenital Heart Disease (ACHD) services and may be at elevated risk of arrhythmia and sudden cardiac arrest.
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