Cardiology Flashcards
In antenatal circulation, what are the pressure differences between the atria? And how does the resistance differ?
The pressure in the RA is higher because it receives all systemic blood (including from the placenta).
The pressure in the LA is lower because there is little return from the lungs.
Pulmonary vascular resistance is very high because the alveoli are all closed.
Systemic vascular resistance is lower.
Flow will prefer path of least resistance so aids the required reduced flow to the lungs.
Why does the pulmonary circulation need to be bypassed?
The foetal lungs are not fully developed or functional so doesn’t make sense for foetal blood to pass through the pulmonary circulation.
What blood passes via the placenta?
Blood travels from the foetus to the placenta to collect oxygen and nutrients from the mother. It also disposes of waste products (CO2 and lactate) here via the mother.
What is present in order to bypass the lungs?
3 shunts
1) Ductus venosus - shunt connects the umbilical vein (carries 20-30% oxygenated blood from the placenta) directly to the IVC allowing blood to bypass the liver.
2) Foramen ovale - shunt connects the RA to the LA allowing blood to bypass the RV and pulmonary circulation.
3) Ductus arteriosus - shunt connects the pulmonary artery (& trunk) to the aorta allowing blood to bypass the pulmonary circulation.
What keeps the foramen ovale open?
The higher pressures in the RA compared to the LA.
What are the two different routes of blood from the umbilical vein? (inc %)
Oxygenated blood is carried from the placenta via the umbilical vein.
20-30% is carried via ductus venosus and passes directly into the IVC.
70-80% is carried to the portal vein, to the liver, to the hepatic vein and into the IVC.
What happens to the foramen ovale at birth?
Baby takes its first breath which causes alveoli in the lungs to expand causing decreased pulmonary vascular resistance. This increases the blood flow into the LA to LA pressure increases. Loss of placental circulation causes decreased RA pressure. Foramen ovale therefore CLOSES.
What happens to the ductus arteriosus at birth?
Normally prostaglandins are required to keep ductus arteriosus open. With oxygenation of the blood (following breath after birth), there is a drop in circulating prostaglandins causing ductus arteriosus to close within few hours/days. It becomes ligamentum arteriosum.
What happens to the ductus venosus at birth?
Immediately after birth, ductus venosus stops functioning as the umbilical cord is clamped and there is no flow into the umbilical veins. It structurally closes a few days later and becomes the ligamentum venosum.
What are innocent/flow murmurs caused by?
Fast blood flow through various areas of the heart during systole.
Very common in children.
What are the features of innocent murmurs?
- Soft blowing murmur
- Short
- Systolic murmur only
- Symptomless (asymptomatic)
- Left Sternal edge
- Situation dependent/may vary with posture (may get quieter with standing or may only appear when child is unwell/feverish)
- No added sounds
What are the different grades of murmurs?
Grade 1 - barely audible
Grade 2 - soft but easily heard
Grade 3 - loud but not accompanied by a thrill
Grade 4 - associated with a thrill
Grade 5&6 - very loud murmurs; may be audible with stethoscope partly or completely off the chest
What features of a murmur should prompt further investigation and referral to a paediatric cardiologist?
- murmur louder than 2/6
- diastolic murmur
- murmur is louder on standing
- other symptoms e.g. failure to thrive, feeding difficulty, cyanosis, SOB
What key investigations must be done to establish cause of murmur?
ECG
CXR
ECHO
Give differentials of a pan-systolic murmur and where they are heard loudest.
1) Mitral regurgitation (mitral area; mid-clavicular line, 5th ICS)
2) Tricuspid regurgitation (left sternal edge; 5th ICS)
3) Ventricular septal defect (left lower sternal border)
