Introduction
Tetralogy of Fallot – R-to-L shunt – CYANOTIC
THE most common cause of cyanotic heart disease – but only accounts for <10% of all congenital cardiac abnormalities
Has four features:
THE most common cause of cyanotic heart disease – but only accounts for <10% of all congenital cardiac abnormalities
Has four features:
- Large VSD – usually so large that pressures in the left and right sides of the heart are equal
- Right ventricular outflow obstruction – often pulmonary valve stenosis – due to the overriding aorta, and sometimes, muscle overgrowth around the valve.
- Overriding of the aorta – this is where the aorta is position directly over the ASD – and not over the left ventricle. The aorta will receive blood from both the left and right ventricles, reducing the concentration of oxygenated blood that goes into system circulation.
- Right ventricular hypertrophy – resulting from the other three factors
Epidemiology
- The most common cyanotic heart condition
- The most common cause of blue baby syndrome
Clinical features
- Cyanosis – possibly at rest depending on severity
- Dyspnoea on feeding / crying / exertion
- Failure to thrive
- Murmur – usually harsh, and at the left sterna edge, grade 3-6. Due to pulmonary outflow obstruction rather than VSD
- Systolic thrill may also be present
‘Tet Spells’
- Sudden onset dyspnoea / cyanosis
- Typically triggered by an event that slightly reduces O2 concentration, e.g. crying, defecating, feeding, distress
- Can be a vicious cycle, as the tet spell can make the child more distressed
- Sometimes preceded by rapid, deep breathing
- This increases venous return to the right ventricle, whose output is mainly via the aorta – and thus this is part of the vicious cycle
- Tet spells typically occur in those aged 2-4M
- Severe spells can lead to death
- Some toddlers may adopt a squatting position – which reduces venous return to the heart, and may help increase blood O2
References
- Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
- Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
- Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy
Hi
great article… a little correction…
Overriding of the aorta – you have written ‘ the aorta is positioned directly over the ASD’ … it read VSD.