Right atrium to right ventricle and pulmonary trunk
Heart & shunts · SaO2 ~50-55% SVC ~40%
Desaturated SVC blood from the head and arms (~40%), coronary sinus blood and the rest of the IVC stream cross the tricuspid valve into the dominant right ventricle, which ejects into the pulmonary trunk toward the ductus arteriosus.
Traced from the start
- Placenta
- Umbilical vein
- Ductus venosusHepatic sinusoids (portal and umbilical mixing)
- Right atrium to right ventricle and pulmonary trunk
Detail
- Saturation
- SVC ~40%; right ventricle and pulmonary trunk ~50-55% after mixing with the IVC remainder
- Dominance
- Right ventricle ejects ~55-60% of combined ventricular output (~450 mL/kg/min in total) and is thicker than the left at birth
- Pressures
- Right ventricular and pulmonary trunk pressures equal or slightly exceed aortic pressure because both ventricles pump into one systemic-placental circuit through the duct
- Streaming
- Crista dividens and eustachian valve keep most SVC blood away from the foramen ovale, so the head is spared the desaturated stream
When it goes wrong
Neonatal ECG in the first week
Right axis deviation, tall R in V1 and an upright T wave in V1 are normal for age (right ventricular dominance); an upright T in V1 persisting beyond about day 7 suggests right ventricular hypertrophy
Practise this structure
1 question in the bank tagged Cardiac Output.