Shunt Fraction in Pediatric Congenital Heart Defects

Question 1

In the context of heart lesions, physiologic shunts are the

Answer 1

return of blood from one circulatory system into the outflow of the same circulatory system
Example: Non-restricted ASD - L-R physiologic shunt

Question 2

Describe a Left to Right shunt.

Answer 2

Flow of blood from the pulmonary venous atrium or left atrium to the pulmonary artery (PA) produces recirculation of pulmonary venous blood

Question 3

Recirculation of systemic venous blood produces a

Answer 3

physiologic right to left shunt

Question 4

Total pulmonary blood flow is the sum of effective

Answer 4

pulmonary blood flow and recirculated pulmonary blood flow

Question 5

Total systemic blood flow is the sum of effective

Answer 5

systemic blood flow and recirculated systemic blood flow

Question 6

Single-ventricle physiology assumes that

Answer 6

1. ventricular output is the sum of pulmonary blood flow (Qp) and systemic blood flow (Qs)
2. Distribution of systemic and pulmonary blood flow is dependent on the relative resistances to flow (both intracardiac & extracardiac) into the two parallel circuits
3. Oxygen saturations are the same in the aorta & the pulmonary artery

Question 7

One ventricle lesions include:

Answer 7

hypoplastic left heart syndrome
tricuspid atresia
double inlet left ventricle

Question 8

Two ventricle lesions include:

Answer 8

tetralogy of Fallot (TOF) with pulmonary atresia)
truncus arteriosus
severe aortic stenosis and interrupted aortic arch

Question 9

Blood flow will follow

Answer 9

the path of least resistance

Question 10

Normally Qp/Qs is

Answer 10

equal 1:1 in a normal heart which has equal RV & LV output

-pulmonary blood flow (Qp) is equal to System blood flow (Qs)

Question 11

The Qp/Qs is a ratio of estimated

Answer 11

pulmonary to systemic blood flow that is useful in determining over circulation to the pulmonary system or ventricular workload

Question 12

Deriving Qp/Qs assumes four assumptions:

Answer 12

1. The patient is breathing room air and pulmonary venous blood is fully saturated
2. O2 consumption is normal, resulting in a SvO2 of 25-30% less than SaO2
3. The patient is not severely anemic (has a normal SVC O2 saturation)
4. Complete mixing results in aortic and pulmonary artery O2 saturations being equal

Question 13

In most cases, the derivement of Qp/Qs assumptions

Answer 13

are valid and allow a rapid determination of Qp/Qs based on the SpO2 alone.

Question 14

Describe the shunt for a Qp/Qs <1 and the clinical status.

Answer 14

right to left shunt; cyanosis

Question 15

Describe the shunt for a Qp/Qs 1-2 and the clinical status.

Answer 15

minimal left to right shunt

asymptomatic

Question 16

Describe the shunt for a Qp/Qs 2-3 and the clinical status.

Answer 16

Moderate left to right

mild symptoms of CHF

Question 17

Describe the shunt for a Qp/Qs >3 and the clinical status.

Answer 17

large left to right shunt

severe symptoms of CHF

Question 18

The Qp/Qs reflects the amount of increased

Answer 18

myocardial work required for the cardiac output to maintain systemic demand

Question 19

If the single ventricle cannot handle the increased workload,

Answer 19

systemic perfusion will become compromised with acidosis, myocardial dysfunction, and worsening CHF