Pathophysiology of Congenital Heart Disease Flashcards Preview

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Flashcards in Pathophysiology of Congenital Heart Disease Deck (33):

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


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?



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


cerebral abscesses

renal dysfunction