Pathophysiology of Congenital Heart Disease Flashcards
Qp/Qs ratio
the ratio of flow through the pulmonary circuit compared with the flow through the systemic circuit
if greater than 2, accepted as an indication for repair
>1 means left to right
<1 means right to left
Fick principle
in the systemic circuit, O2 consumption = change in O2 sat x CO
systemic blood flow = cardiac output
O2 delivery = constant x (arterial O2 sat - venous O2 sat)
therefore CO = Qs = (O2 consumption)/(systemic arterial sat - systemic venous sat)
for the pulmonary circuit - Qp = O2 uptake/(SATpv - SATpa)
Even though the pressures in the LA are not typically that different than the pressures in the RA, why is there an R -> L shunt?
the determinant of shunting is actually the “capacitance” of the two circuits - measures of resistance
atrioventricular septal defect or complete AV canal (CAVC)
a combination of ASD and VSD
involves the malformation of the AV valves
creates a “common AV valve”
partial anomalous pulmonary venous connection (PAPVR)
some (but not all) pulmonary veins drain into the RA instead of the LA
physiology is similar to that of an ASD - increased volume load
aortopulmonary window
uncommon
incomplate separation of the pulmonary artery from the aorta
the right heart only sees a normal cardiac output
the flow crosses over outside of the heart
as a result, the chamber that has to do the extra work is the LV, because it pumps all of systemic flow, as well as the flow that will get shunted across the AP window and into the pulmonary circuit
complications of L -> R shunting
pulmonary overcirculation - initial congestion with SOB, long term pulmonary vascular disease and hypertension
ventricular volume overload - premature failure of systolic function, atrial and ventricular arrhythmias
physiologic effect of pulmonary overcirculation
lung congestion
stiff lungs increases work of breathing - tachnypnea and retractions
inftants have feeding difficulty due to heavy breathing
increased WOB (work of breathing) leads to higher calory utilization
failure to thrive because of falling off of growth curve
frequent respiratory infections
When should VSDs be closed?
if RV and PA pressure is significantly elevated, but not if PVR is too high
progression to Eisenmenger’s Syndrome
period of preserved oxygen saturation until pulmonary hypertension and gradual reversal of flow, leading to gradual desaturation
most rapid clinical progression is in patients with Down syndrome and also CAVC defects - irreversible PHT can be seen in these patients as soon as 6 months after birth
problems with closing an Eisenmenger’s Shunt
results in severe pulmonary hypertension
morphology of the RV is not suited to generating flow under high pressure
RV may not be able to maintain pulmonary flow against a high resistance
inadequate CO - syncope
RV failure, right heart congestion
How do we assess when it’s dangerous to close a shunt?
at cath, once can measure the change in pressure across the pulmonary bed (mean PA pressure - LA pressure, estimated by the PCWP)
flow is estimated by estimating the O2 consumption of thermodilution
if the resistance is < 2 Wood units, it is normal
if resistance is > 6-8 Wood units, it can cause significant problems at the time of surgery, and may contraindicate some procedures
Which L->R shunts lead to RV volume overload?
ASD/PAPVR
Which L->R shunts lead to LV volume overload?
VSD/PDA/AP window
How is the site of volume overload affected by the location of the shunt in the case of L->R shunting?
if the shunt occurs before the tricuspid/mitral valve, the RV ventricle will do the extra work and experience the volume load
if the shunt occurs after the AV valves, the LV ventricle will dilate and be affected
prostaglandin E infusion
allows a PDA to be maintained with hymodynamic stability, allowing for semi-elective repair of most lesions
basic mechanisms of cyanosis
reversed connections - transposition of the great arteries
absent connection resulting in complete mixing of systemic venous and pulmonary venous blood
shunt with an inadequate right herat pump or right heart obstruction - causes desaturated right heart blood to shunt to the left heart
transposition of the great arteries
rather than having two circuits feeding into each other, you have two circuits in parallel
key to survival - communication of the two circuits through the PDA or a sufficient hole thorugh the atrial septum
tricuspid atresia
systemic venous return into the RA crosses the PFO into the LA
complete mixing of systemic venous and pulmonary venous blood
resulting saturation is the “weighted average” of the 2 saturations
depending on the relative flow to the 2 circuits
the chamber downstream from the absent connection typically is hypoplastic, as it never received the blood flow that is a strong stimulus for development
RV communicates with LV through a VSD
2 outflows, one to pulmonary and one to systemic
ideal if some stenosis in the pulmonary outflow tract to keep the circulation balanced
left heart atresia - hypoplastic left heart syndrom
severe hypoplasia/atreasia of the mitral and aortic valves, as well as LV
pulmonary venous return crosses from LA to RA, and is ejected from the RV to the PA
systemic output to the aorta is almost completely provided through the PDA - ductual dependent lesion
ductal closure results in shock
total anomalous pulmonary venous return (TAPVR)
lack of connection of the pulmonary veins to the LA
pulmonary venous blood returns to a confluence, then drains through systemic veins to the RA
saturated pulmonary venous blood mixes completely with the desaturated systemic venous blood, causing cyanosis
What is the underlying cause of the tetralogy of Fallot?
anterior malalignment of the infundibular septum causes all of the phenotypes
Ebstein’s anomaly
severe TR
raises RA pressure
exceeds LA pressure, R->L shunt
elevated PVR neonatally can make it difficult to manage
keep PDA open as treatment - aorta will perfuse pulmonary bed
allow time to drop PVR, then try coming off prostaglandins
causes of pump failure
obstruction to flow (valvular or vascular stenosis)
severely leaky valves
myocardial failure
presentation of neonatal critical aortic stenosis or coarction
perfusion may be maintained as long as PDA is open
flow from the RV will cross the PDA and supply the descending thoracic aorta
when PDA closes - shock
neonatal shock
shock presenting in the first 2 weeks of life is frequently caused by closure of the PDA in a ductal dependent lesion
often coarctation, also critical AS and interrupted aortic arch
long-term complications of pump failure
ventricular dysfunction due to volume or pressure overload and hypertrophy
earlier diastolic dysfunction raises filling pressures, which results in congestion of the right or left heart circuits
arrhythmias may follow
dilation may pull valve leaflets apart and lead to regurgitation
a pathologic jet may distort a valve leaflet so that it loses competence over time, becoming regurgitant
long-term vascular complications of congenital heart disease
pulmonary vascular disease or hypertension
hypoplasia of a vessel due to poor flow
aneurysmal dilatation due to inherent abnormality of the vessel wall or improper repair
erythrocytosis and hyperviscosity syndromes
high RBC counts incrase the viscosity of the blood
impaired cerebral flow and CNS symptoms
treatment of erythrocytosis and hyperviscosity syndromes
prophylactic phlebotomy or red cell reduction
downside is that it results in iron deficiency, and the iron deficient, microcytic red cell is less deformable than the normal red cell, so the threshold of hyperviscosity lowers as well
complications of cyanosis
hyperviscosity
cerebral abscesses
renal dysfunction
coagulopathy
gout
