1. 1. Cardiovascular system begins forming at 3 weeks
Pediatric Fundamentals – Heart and Circulation
Embryology
1. Cardiovascular system begins forming at 3 weeks
(diffusion no longer adequate)
2. Angiogenetic cell cluster and blood islands ->
intraamniotic blood vessels
3. Heart tube
4. Heart begins to beat 22 – 23 days
5. Heart looping -> 4 chambers, 27 – 37 days
6. Valves 6 – 9 weeks

2. umbilical vein (UV)-> ductus venosus (50%) -> IVC -> RA ->
Pediatric Fundamentals - Growth and Development
Cardiovascular system
In utero circulation
placenta ->
umbilical vein (UV)->
ductus venosus (50%) ->
IVC ->
RA ->
foramen ovale (FO) ->
LA ->
Ascending Ao ->
SVC ->
tricuspid valve ->
RV (2/3rds of CO) ->
main pulmonary artery (MPA) ->
ductus arteriosus (DA) (90%) ->
descending Ao ->
umbilical arteries (UAs)->

3. Transitional circulation Placenta Out and Lungs In
Pediatric Fundamentals – Heart and Circulation
Transitional circulation
Placenta Out and Lungs In
PVR drops dramatically
(endothelial-derived NO and prostacyclin)
FO closes
DA closes
hours to 3 days to few weeks
prematures: closes in 4-12 months
PFO potential route for systemic emboli
DA and PFO routes for R -> L shunt in PPHN

4. Persistent pulmonary hypertension of the newborn (PPHN)
Pediatric Fundamentals – Heart and Circulation
Persistent pulmonary hypertension of the newborn (PPHN)
Old PFC misnomer
Primary
Secondary
meconium aspiration
sepsis
birth asphyxia
Treatment
cardiopulmonary support
inhaled NO
ECMO

5. ↓ ↓ ↓ ↓ ↓ Pediatric Fundamentals – Heart and Circulation
Nitric oxide (NO) – cGMP transduction pathway
l-arginine ↓
eNOS (endothelial NO synthetase)
oxidation of quanidine N moiety NO
activates ↓
GTP ↓
sGC (soluble guanylate cyclase)
cGMP (cyclic-3’,5’-guanosine monophosphate)
activates ↓ ↓
PDE (phosphodiesterase)
protein kinase
GMP

6. Increased sensitivity to calcium channel blockers (e.g. verapamil)
Pediatric Fundamentals – Heart and Circulation
Neonatal myocardial function
Contractile elements comprise 30% (vs 60% adult) of newborn myocardium
Alpha isoform of tropomyosin predominates
more efficient binding for faster relaxation at faster heart rates
Relatively disorganized myocytes and myofibrils
Most of postnatal increase in myocardial mass due to
hypertrophy of existing myocytes
Diminished role of relatively disorganized sarcomplasmic reticulum (SR)
and greater role of Na-Ca channels in Ca flux so
greater dependence on extracellular Ca
may explain:
Increased sensitivity to
calcium channel blockers (e.g. verapamil)
hypocalcemia
digitalis

7. lactate: primary metabolite
Pediatric Fundamentals – Heart and Circulation
Myocardial energy metabolism
Young infant heart
lactate: primary metabolite
later: glucose oxidation and amino acids (aa’s)
metabolize glucose and aa’s under hypoxic conditions
(may lead to greater tolerance of ischemic insults)
Gradual transition to adult:
fatty acid primary metabolite by 1-2 years

8. Age (months) Sys/Dias mean 1 85/65 50 3 90/65 50 6 90/65 50 9 90/65 55
Pediatric Fundamentals – Heart and Circulation
Normal aortic pressures
Wt (Gm) Sys/Dias mean / /
/35 50
/40 50
Age (months) Sys/Dias mean / / / / /

9. Babies are vagotonic Adrenergic receptors Sympathetic receptor system
Pediatric Fundamentals – Heart and Circulation
Adrenergic receptors
Sympathetic receptor system
Tachycardic response to isoproterenol and epinephrine
by 6 weeks gestation
Myocyte β-adrenergic receptor density
peaks at birth then
decreases postnatally
but coupling mechanism is immature
Parasympathetic, vagally-mediated responses are mature at birth
(e.g. to hypoxia)
Babies are vagotonic

10. Age (days) Rate 1-3 100-140 4-7 80-145 8-15 110-165 Age (months) Rate
Pediatric Fundamentals – Heart and Circulation
Normal heart rate
Age (days) Rate
Age (months) Rate
Age (years) Rate

11. Avoid (excessive) vasoconstriction Maintain heart rate
Pediatric Fundamentals – Heart and Circulation
Newborn myocardial physiology
Type I collagen (relatively rigid) predominates (vs type III in adult)
Neonate Adult
Cardiac output HR dependent SV & HR dependent
Starling response limited normal
Compliance less normal
Afterload compensation limited effective
Ventricular high relatively low
interdependence
So:
Avoid (excessive) vasoconstriction
Maintain heart rate
Avoid rapid (excessive) fluid administration