Unit 11 - Congenital Heart Defects Flashcards
where does fetal gas exchange occur
placenta
Carries oxygenated blood from the mother to the fetus
umbilical vein
Carry deoxygenated blood from the fetus to the mother
umbilical artery (1)
Shunts blood from the umbilical vein to the IVC (bypasses liver)
ductus venousus
Shunts blood from the RA to the LA (bypasses lungs)
foramen ovale
Shunts blood from the pulmonary artery to the aorta (bypasses lungs)
ductus arteriosus
6 ways fetal circulation differs from adult circulation
- placenta is organ of respiration
- circulation arranged in parallel
- R-L shunting across foramen ovale and ductus arteriosus
- SVR is low
- PVR is high
- minimal pulmonary blood flow
fetal organ of respiration
placenta
purpose of foramen ovale
shunt blood from RA to LA
Oxygen-rich blood bypasses the lungs and is preferentially delivered to the heart and developing brain
purpose of foramen ovale
shunt blood from RA to LA
Oxygen-rich blood bypasses the lungs and is preferentially delivered to the heart and developing brain
purpose of ductus arteriosus
shunt blood from pulmonary trunk to aorta
Lower oxygen blood bypasses the lungs and is delivered to the lower body
purpose of ductus venosus
allows oxygen-rich blood from placenta to bypass liver
when does the foramen ovale close
functional closure: when LAP > RAP (cord clamping increases SVR)
anatomic closure: 3 days
when does the ductus arteriosus close
functonal closure: SVR > PVR (increased PaO2 & decreased prostaglandins from placenta)
Anatomic closure: several weeks
adult remnant of foramen ovale
fossa ovalis
adult remnant of ductus arteriosus
ligamentum arteriosum
when does the ductus venosus close
anatomic closure when umbilical cord is clamped
adult remnant of ductus venosus
Ligamentum venosum
% of adult population with PFO
30%
complication of PFO
Increases risk of paradoxical air embolism (embolus travels to brain instead of lungs)
meds that can open or close PDA
opens: prostaglandin E1 (PGE1)
closes: indomethacin (prostaglandin synthesis inhibitor)
plays a key role in trauma, where a rapid deceleration tears the ligament & results in partial or complete aortic dissection
Ligamentum arteriosum
adult remnant of ductus arteriosus
plays a key role in trauma, where a rapid deceleration tears the ligament & results in partial or complete aortic dissection
Ligamentum arteriosum
adult remnant of ductus arteriosus
size and direction of shunt depends on what 3 factors
- Ratio of PVR to SVR
- Pressure gradients between cardiac chambers or arteries involved
- Compliances of cardac chambers
how does ratio of PVR to SVR affect direction of shunt
R - L shunt occurs when PVR is > SVR
L - R shunt occurs when SVR is > PVR
causes of increased PVR
- hypercarbia
- hypoxemia
- acidosis
- collapsed alveoli
- Trendelenburg
- hypothermia
- vasoconstrictors
- increased SNS tone
- light anesthesia
- pain
causes of decreased PVR
- hypocarbia
- adequate oxygenation
- alkalosis
- hemodilution
- vasodilators
- nitric oxide
causes of increased SVR
- vasoconstrictors
- fluid bolus
- increased SNS tone
- pain
- anxiety
causes of decreased SVR
- volatiles
- propofol
- decreased SNS tone
- hemodilution
- sepsis
- anaphylaxis (histamine release, vasodilation, capillary leak)
patho of cyanotic shunts
↓ pulmonary blood flow = hypoxemia, LV volume overload, LV dysfunction
5 examples of R-L cardiac shunts (5 T’s)
- Tetralogy of Fallot (most common)
- Transposition of the great arteries
- Tricuspid valve abnormality (Ebstein’s anomaly)
- Truncus arteriosus
- Total anomalous pulmonary venous connection
how do cyanotic shunts affect inhalation induction
- shunted blood doesn’t pass through lungs to pick up volatile
- shunted blood dilutes volatile in L heart
- decreased FA/FI rise
- slower inhalation induction
how does volatile solubility affect inhalation induction in cyanotic shunts
slower inhalation induction
* most profound with less soluble agents (N2O and Desflurane)
* less of an issue with more soluble agents (isoflurane)
how is IV induction affected by cyanotic shunts
R - L shunt allows IV medication to bypass lungs and directly enter systemic circulation.
The drug reaches the vessel-rich organs faster, resulting in a faster onset
HD goals with cyanotic shunts
maintain SVR
decrease PVR
patho of acyanotic shunt
L-R shunt
* oxygenated pulmonary venous blood recirculates through R heart and lungs
* decreased systemic flow
* increased pulmonary flow
examples of acyanotic CHD
- VSD (most common)
- ASD
- PDA
- Coarctation of aorta
how do cyanotic shunts affect anesthesia induction
R L shunt allows IV medication to bypass lungs and directly enter systemic circulation. The drug reaches the vessel-rich organs faster, resulting in a faster onset
HD goals with acyanotic shunt
- avoid increased SVR
- avoid decreased PVR by avoiding alkalosis, hypocapnia, high FiO2, and vasodilation
complications of increased pulm blood that occurs in acyanotic shunts
- Volume overload of both ventricles -› biventricular failure
- Ventricular hypertrophy
- Decreased lung compliance + increased airway resistance
- Pulmonary hypertension
what is Eisenmenger’s syndrome
a patient with a left-to-right shunt develops pulmonary hypertension
Increased right heart pressures cause a flow reversal through the cardiac defect, ultimately leading to a right-to-left shunt, hypoxemia, and cyanosis
most common cyanotic CHD
tetralogy of fallot
4 assoc defects in ToF
- Right ventricular outflow tract obstruction
- Right ventricular hypertrophy
- Ventricular septal defect
- Overriding aorta
strongly correlates with amount of shunt in ToF
degree of RVOT obstruction
which is assoc with pHTN - cyanotic or acyanotic shunts
acyanotic (L-R shunt)
effect of increased RVOT obstruction in ToF
more deoxygenated blood is shunted through the VSD and out into the aorta
how does the body compensate for RVOTO in ToF
erythropoiesis
leads to polycythemia and increases the risk of thromboembolism and stroke
what precipitates a Tet spell
increased sympathetic activity (crying, agitation, pain, defecation, fright, or trauma)
how does a Tet spell cause hypoxemia
- ↑ SNS activity = ↑ contractility and ↑ RVOTO
- ↑ resistance at level of RVOT favors flow through VSD
- net effect: ↑ R-L shunting, hypoxemia
treatment of peri-op Tet spell
- FiO2 100%
- IVF
- Increase SVR with phenylephrine
- Reduce SNS stimulation (deepen anesthesia, beta-blockade with a short-acting agent - esmolol)
- Avoid inotropes
- Avoid excessive airway pressure
- knee-chest position to
how does a child experiencing a Tet spell respond
- hyperventilation with onset of hypoxemia
- assumes squatting position
why does a child experiencing a Tet spell squat
increased IAP compresses abdominal arteries
* increased RV preload
* increased SVR
* increased blood flow through RVOT
restores pulmonary blood flow, reduces the magnitude of the right-to-left shunt, and improves oxygenation.
medications to avoid in patients with unrepaired ToF
ephedrine
dobutamine
epinephrine
morphine
meperidine
atracurium
avoid inotropes and histamine-releasing drugs
HD goals in pts with ToF
increase SVR
decrease PVR
maintain contractility & HR
increase preload
best induction agent for pt with unrepaired ToF
Ketamine (1 - 2 mg/kg IV or 3 - 4 mg/kg IM)
increases SVR and reduces shunting
increased contractility is minor compared to benefit of increasing SVR
best induction agent for pt with unrepaired ToF
Ketamine (1 - 2 mg/kg IV or 3 - 4 mg/kg IM)
increases SVR and reduces shunting
increased contractility is minor compared to benefit of increasing SVR
CXR findings in pt with ToF
The heart may take on a “boot-shaped” appearance
EKG changes in ToF
RVH can cause RAD
best induction agent for a pt with ToF
ketamine
why are some pts with ToF polycythemic
chronic hypoxemia stimulates RBC production
failure of the fossa ovalis to close results in what type of atrial septal defect
secundum
most common congenital cardiac anomaly in children
VSD
the most common congenital cardiac defect in adults
bicuspid aortic valve.
most common site of ASD
fossa ovalis
also called an ostium secundum ASD
a significant number of VSDs close by what age
2 yrs old
early s/s of ASD
poor exercise tolerance
later s/s of ASD
include atrial flutter, atrial fibrillation, and CHF
antibiotic prophylaxis for acyanotic CHD
only indicated within 6 months of valve repair
common closure of ASD
percutaneous transcatheter device
how are VSDs usually closed
open approach
most common site of VSD
middle of the ventricular septum, just below the septal leaflet of the tricuspid valve
This is also called a perimembranous VSD
most common site of VSD
middle of the ventricular septum, just below the septal leaflet of the tricuspid valve
This is also called a perimembranous VSD
conditions assoc with VSD
- trisomy 13, 18, 21
- VACTERL
- CHARGE
The physiologic consequence of the VSD is a function of ?
the pressure gradients between the RV and LV, and in turn, these are dependent on PVR and SVR
pulmonary blood flow in large vs. small VSD
- small: marginal increase (tolerate GA well)
- large: RV/LV pressures equalize, PVR and SVR determine direction of blood flow
syndrome strongly assoc with CoA
turner syndrome
where does CoA typically occur
just before or after the ductus arteriosus
in rare instances, it occurs proximal to the left subclavian artery
where does CoA typically occur
just before or after the ductus arteriosus
in rare instances, it occurs proximal to the left subclavian artery
what is CoA
narrowing of the thoracic aortic lumen
presentation of preductal vs. postductal CoA
- Preductal coarctation is less common and usually presents in the neonate
- Postductal coarctation is more common and usually presents in the adult
SBP in upper vs lower extremities in CoA
SBP is elevated in the upper extremities
SBP is reduced in the lower extremities
CXR changes in CoA
Rib notching may be visible (due to increased vessel diameter)
required for lower body perfusion in severe CoA
PDA
what is differential cyanosis
pink, well-perfused upper body + blue, poorly-perfused lower body
may be seen in severe CoA
what is differential cyanosis
pink, well-perfused upper body + blue, poorly-perfused lower body
may be seen in severe CoA
administered to maintain ductus arteriosus patency in severe CoA
PGE1
temporary until surgery
administered to maintain ductus arteriosus patency in severe CoA
PGE1
temporary until surgery
surgical repair of CoA
- often through left thoracotomy + end-to-end anastomosis
- aortic cross clamp used - can cause paraplegia
why do some surgeons cool the child 34-35 deg C during CoA repair
aortic-cross clamp used during an open procedure can cause paraplegia
indications for CoA surgical repair
- exercise intolerance
- chest pain
- headaches
- lower extremity claudication
presentation of CoA in adulthood
secondary HTN
characterized by a downward (apical) displacement of the tricuspid valve
Ebstein’s anomaly
what causes RA enlargement in Ebstein’s anomaly
part of the right ventricle becomes part of the right atrium (atrialization), and this causes right atrial enlargement
septal defects often assoc with ebstein’s anomaly
ASD or PFO
Most common congenital defect of the tricuspid valve
ebstein’s anomaly
how does ebstein’s anomaly affect onset of IV drugs
onset of IV drugs may be prolonged due to the pooling of drugs in the enlarged RA
arrythmia commonly assoc with ebstein’s anomaly
SVT
common postop complication assoc with ebstein’s anomaly
RV failure
critical to management of a pt with ebstein’s anomaly
Maintenance of RV function is critical (risk of congestive heart failure)
what is transposition of the great arteries
each great vessel arises from the wrong ventricle
* RV gives rise to the aorta
* LV gives rise to the pulmonary artery
RV circuit in TGA
- Systemic venous (desaturated) blood → RV → aorta → repeat
- This blood circulates through the systemic circulation but not the pulmonary circulation
LV circuit in TGA
- Pulmonary venous blood (well oxygenated) → LV → lungs → repeat
- This blood circulates through the pulmonary circulation but not the systemic circulation
required for extrauterine survival with TGA
depends on the mixing of blood through an ASD (best case scenario), VSD, or PFO
management of TGA after birth
The PDA can be kept open with a prostaglandin infusion (this is a temporary fix)
management of TGA after birth
The PDA can be kept open with a prostaglandin infusion (this is a temporary fix)
TGA repair options
- Rashkind procedure creates an interarterial pathway to allow some oxygenated blood to reach the systemic circulation
- Definitive surgical correction includes intraatrial baffle and arterial switch procedures
goal of surgical HLHS correction
separating the pulmonary and systemic circulations
goal of surgical HLHS correction
separating the pulmonary and systemic circulations
4 anatomic features of HLHS
- Hypoplastic LV
- Hypoplastic aortic arch
- Mitral and aortic stenosis or atresia
- Ductal-dependent circulation
why should the RUE be used to monitor BP in CoA
rarely, obstruction can be proximal to L subclavian a. and reduce perfusion to LUE
2 cardiac signs of CoA
- upper extremity SBP > lower
- differential cyanosis
surgical goal of Norwood stage 1
Aortic reconstruction - aortic arch now arises from the pulmonary trunk
pulmonary arteries are disconnected from the pulmonary trunk and are used to create a shunt from the subclavian artery or the right ventricle
surgical goal of Norwood stage 1
Aortic reconstruction - aortic arch now arises from the pulmonary trunk
pulmonary arteries are disconnected from the pulmonary trunk and are used to create a shunt from the subclavian artery or the right ventricle
when is Norwood stage 1 completed in HLHS
neonatal period
when is Norwood stage 2 completed
3-6 months old
surgical goals of Norwood stage 2
The shunt from the first procedure is taken down and a new connection is made between the SVC and the pulmonary arteries.
surgical goals of Fontan procedure
Conversion to Fontan circulation - The IVC is connected to the PA with a conduit
when is Fontan surgery completed
2-4 yrs old
circulation after Fontan completion
- single ventricle pumps blood systemically
- pulmonary blood flow is passive from SVC/IVC to PA
what does pulmonary blood flow depen on after Fontan completion
completely dependent on negative intrathoracic pressure during spontaneous breathing
Increased PVR is detrimental to pulmonary blood flow
what does pulmonary blood flow depend on after Fontan completion
completely dependent on negative intrathoracic pressure during spontaneous breathing
Increased PVR is detrimental to pulmonary blood flow
ventilation after Fontan completion
Positive-pressure ventilation reduces pulmonary blood flow and should be avoided/ minimized. Spontaneous ventilation is preferred
what is truncus arteriosus
single artery that gives rise to the pulmonary, systemic, and coronary circulations
no specific pathway for blood to enter the pulmonary circulation before being pumped into the systemic circulation
CHD commonly seen with truncus arteriosus
VSD
consequence of decreased PVR in truncus arteriosus
steals blood from the systemic and coronary circulations
result of surgical correction of truncus arteriosus
can restore a two ventricle arrangement by separating the pulmonary from the systemic circulation with closure of the VSD
CHDs assoc with prolonged inhalation induction
R-L shunts
* ToF
* ebstein’s anomaly
hydration in HLHS patients
do not let them get dry - preload dependent
shunt lesions with outflow tract obstruction
- Tetralogy of Fallot
- Ebstein’s anomaly
- Pulmonary stenosis with atrial or ventricular septal defect
- Eisenmenger’s syndrome
fetal shunt unable to reopen after birth
ductus venosus
inhaled anesthetic to avoid with ASD
N2O
