This document discusses the techniques used to detect, localize, and quantify intracardiac shunts in patients with congenital heart disease. An oximetry run is performed during cardiac catheterization to detect left-to-right shunts by measuring oxygen saturation levels in different chambers of the heart and identifying step-ups. The ratio of pulmonary to systemic blood flow (Qp:Qs) is also calculated using the Fick principle to quantify the size of the shunt. A Qp:Qs ratio >1.5 indicates a clinically significant left-to-right shunt.

2.  shunts are abnormal communications between the systemic
circulation and pulmonary circulation.
 Detection, localisation and quantification of intracardiac
shunts form an integral part of the hemodynamic evaluation of
patients with congenital heart disease
 Cardiovascular are quantified by measuring the ratio of
pulmonary blood flow (Qp) to systemic blood flow that is,
Qp:Qs.
 The extent of a shunt is determined by the size of the defect
and the left-to-right pressure gradient.

3.  Indicator dilution techniques
◦ Invasive cardiac catheterization – oximetry and
angiocardiography
◦ Cardio green , ascorbic acid, H2 inhalation
 Radionuclide methods
 Phase contrast MRI
 Echocardiography

4. Oximetry run
 In the oximetry run the oxygen content or %
saturation is measured in PA,RV,RA,VC.
 A left-to-right shunt may be detected and localized
if a significant step-up in blood oxygen saturation or
content is found in one of the right heart chambers
 A significant step-up is defined as an increase in
blood oxygen content or saturation that exceeds the
normal variability that might be observed if multiple
samples were drawn from that cardiac chamber.

5. 1. Left-to-right Intracardiac Shunts - Oximetry run

6.  Oxygen content
The technique of the oximetry run is based on the
pioneering studies of Dexter and his associates in
1947
Oxygen content was measured by Van Slyke
technique , and other manometric studies
It was found that multiple samples drawn from the
right atrium could vary in oxygen content by as much
as 2%.
The maximal normal variation within right ventricle
was found to be 1%.
Because of more adequate mixing, a maximal
variation within the pulmonary artery was found to be
only 0.5%.

7.  Thus using Dexter Criteria a significant step
up is present
 at the atrial level when highest oxygen content
in blood samples drawn from the right atrium
exceeds the highest content in the venae cavae
by 2 vol %.
 at the ventricular level, if the highest right
ventricular sample is 1 vol % higher than the
highest right atrial sample.
 at the level of the pulmonary artery if the
pulmonary rtery oxygen content is more than
0.5% vol% higher than the highest right
ventricular sample.
1 vol% = 1ml O2/100ml blood or 10mlO2/l

8. O2 content Vs O2 saturation
 Dexter ‘s study described normal variability and
gave the criteria for a significant step-up only for
measurement of blood oxygen content.
 In recent years nearly all cardiac cath laboratories
have moved toward the measurement of percentage
oxygen saturation by spectrophotometric oximetry
as the routine method for oximetric analysis of
blood samples.
 Oxygen content may then be calculated as :
Hb × 1.36 (ml O2/g of hb)×10×% saturation

9.  But oxygen content derived in this manner is
less accurate than by Van Slyke or other
direct oximetric technique.

10.  Antman and coworkers prospectively studied the
normal variation of both oxygen content and oxygen
saturation of blood in the right heart chambers
 Pts. without intracardiac shunts who were undergoing
diagnostic cath.
 Oxygen content and Oxygen saturation was calculated
 Finally it was concluded that O2 sat. and O2 content
correlate well and also proposed that systemic blood
flow and mixing of blood both determine step up of O2
levels.
 Antman EM. Blood oxygen measurements in the assessment of intracardiac
left to right shunts: a critical appraisal of methodology. Am J Cardiol 1980

12. CHAMBER
LEVEL
STEP UP
GARSON MOSS AND
ADAMS
GROSSMAN
(MEAN OF
SINGLE MULTIPLE
SAMPPLES)
SAMPLE
SAMPLES
SVC TO RA 7 5 9 7
RA TO RV 5 3 6 5
RV TO PA 4 3 6 5

13. Procedure of oximetry run
 2-mL sample from each of the following
locations.
1. Left and/or right pulmonary artery & Main pulmonary
artery
2. Right ventricle, outflow tract, mid & tricuspid valve .
3. Right atrium, low or near tricuspid valve , mid & high
.
4. Superior vena cava, low (near junction with right
atrium).
5. Superior vena cava, high (near junction with
innominate vein).
6. Inferior vena cava, high (just at or below diaphragm).
7. Inferior vena cava, low (at L4-L5).
8. Left ventricle.
9. Aorta (distal to insertion of ductus).

14.  Taken at mid SVC level: below the innominate and
above the azygous vein
 A location that is too high may provide a sample
from the axillary (peripheral arm) vein and give an
erroneously high O2 saturation and a sample from
the internal jugular vein can give an erroneously
low saturation.
 A sample obtained too low in the SVC (at, or close
to, the superior vena cava–right atrial junction) may
actually include some blood refluxing into the SVC
from the right atrium.
 5- 10 % lower than IVC sample (higher in GA)

15.  True IVC sample is taken below the hepatics.
 Slight catheter manipulation causes significant
change in values.
 Greatest streamlining occurs close to IVC RA
junction.
 Samples close to coronary sinus are as low as 25-
40%, from close to renal veins can be as high as
90%, saturations from hepatic veins are
intermediate between CS and renal vein
saturations.

16.  Right atrial sample should be taken at lateral mid atrial wall
to avoid the low saturation stream from coronary sinus and
to facilitate mixing from IVC and SVC streams
 Moss and adams Heart disease in infants, children and adolescent 8th edition

17. Procedure of oximetry run
 In performing the oximetry run, an end-hole
catheter (e.g., Swan-Ganz balloon flotation
catheter) or one with side holes close to its tip
(e.g., a Goodale-Lubin catheter) can be used.
 The catheter tip position further confirmed by
pressure measurements at the sites noted.
 The entire procedure should take less than 7
minutes.
 If a sample cannot be obtained from a specific
site because of ventricular premature beats,
that site should be skipped until the rest of the
run has been completed.

18.  An alternative method for performing the oximetry run is to withdraw a
fiberoptic catheter from the pulmonary artery through the right heart
chambers and the inferior and superior vanae cavae.
 Uses fiberoptic catheters, which work on spectrophotometric principals
for analysis.
 The output signal from the fiberoptic catheter is displayed as a
continuous graph of the percent saturation.
 This permits a continuous read out of oxygen saturation that follows
detection of a step-up in oxygen content.
 The greatest problem with fiberoptic catheters is the catheters
themselves, as they are not suitable for easy manipulation within the
heart.

19.  O2 saturation by spectrophotometry :
◦ Based on Beers law
◦ Advantages : quick ,accurate, precise , subject to few
errors , less dependency on Hb% .
◦ Disadvantages :
Inaccurate if large amounts of carboxy
hemoglobin is present
Indocyanin green interfere with light source of
spectrphotometry
Elevated bilirubin affect absorbtion of light

20. Disadvantages of oxygen content technique
 15 – 30 min for obtaining a reading
 Technically difficult to perform
 Dependency on Hb content

21. Limitations of Oximetry
Method
1. Antman and coworkers
shows that oxygen
saturation influenced by
the magnitude of
systemic blood flow.
◦ High levels of
systemic flow tend to
equalize the arterial
and venous and low
levels increase
difference.

22.  Therefore, elevated systemic blood flow will
cause the mixed venous oxygen saturation to
be higher than normal, and interchamber
variability owing to streaming will be blunted.
 Even a small increase in right heart oxygen
saturation might indicate presence of
significant left to right shunt
 Larger increase would indicate voluminous
left to right shunting of blood.

23. Limitations of Oximetry Method
2. Antman and colleagues , the influence of blood
hemoglobin concentration may be important when
blood O2 content (rather than O2 saturation) is used
to detect a shunt

24.  A primary source of error may be the absence of
steady state during the collection of blood
samples. That is if oxymetry run is prolonged
because of technical difficulties, if the patient is
agitated, or if arrhythmias occur during the
oximetry run, the data may not be consistent.
 It lacks sensitivity. Small shunts are not
consistently detected by this technique. Most
shunts of a magnitude that would lead to
recommendation for surgical closure would be
detected.

25. Left-to-right Intracardiac Shunts - Flow ratio
 Qualitative by oximetry and next Quantitative by
flow ratio
 Quantification is done by Qp , Qs , Qp/Qs , Effevtive
blood flow, L-R shunt , R-L shunt .
 Qp and Qs are amount of blood flowing through
pulmonary and systemic vascular bed
 Qef is quantity of mixed venous blood that carries
desaturated blood from systemic capillaries to be
oxygenated by lungs
 L-R and R-L shunt are amount of blood that bypass
systemic and pulmonary vascular bed .

26.  Qp , Qs , Qeff are based on Ficks principle for
calculation of cariac output
 Cardiac output = VO2 / AVO2 difference

27.  Qs = V O2/ m²
(SA % Sat - MV % Sat) x1.36 xHb x10
 Qp = V O2/ m²
(PV % Sat - PA % Sat) x 1.36 x Hbx 10
 In normal circulatory state mixed venous saturation is
same as pul artery saturation and the saturation of pul
vein is same as that of systemic arteries.
 Hence calculated QP is equal to Qs

28.  Any shunt from saturated left side of heart to rt
side causes a increase in the pul artery saturation
and hence decrease in the denominator value of
Qp calculation, thus resulting in a higher value of
Qp, and Qp/Qs of > 1.
 When the pulmonary blood flow is markedly
increased (e.g., pulmonary artery saturation 89%),
the difference in pulmonary vein and pulmonary
artery saturation is small (e.g., 99% - 89%), so the
normal error that occurs with each measurement
(±2%-3%) becomes significant. Thus, when there is
a large left-to-right shunt, the Qp/Qs is simply
reported as greater than 3:1.

29.  Points of importance while
calculation:
1. Oxygen consumption
2. Calculation of saturations
3. Oxygen content

30.  Oxygen consumption:
◦ Oxygen consumption = oxygen inspired – oxygen
expired
◦ Methods for OC are the Douglass bag , the
polarographic method and paramagnetic method

31. 1. Hemoglobin (Hgb in g/dl)
2. Oxygen consumption (VO2 in ml/min) : Best if
measured by an oxygen sensor at the time of
catheterization. E.g.
a) Women: VO2 = BSA × [138.1–17.04 × ln(age) +
0.378 × HR]
(b) Men: VO2 = BSA × [138.1–11.49 × ln(age) +
0.378 × HR]
Craig Broberg et al. Appendix: Shunt Calculations. Adult Congenital Heart Disease: A Practical Guide.

32. LaFarge C.G.,
Miettinen O.S. The
estimation of
oxygen
consumption.
Cardiovasc Res.
1970

33.  Calculation of saturation :
◦ PAO2 and FAO2 are usually calculated by blood
samples
◦ MVO2 and PVO2 calculations are most important
◦ MVO2 – the key to proper management of systemic
flow in the presence of intracardiac shunt is that mixed
venous oxygen content must be measured in the
chamber immediately proximal to the shunt

35.  MVO2 at atrium level
1. At rest = 3SVC + IVC / 4
Flamm's formula weights blood returning from the
superior vena cava more heavily than might be
expected on the basis of relative flows in the superior
and inferior cavae.
2. During bicycle ergometry = SVC + 2IVC / 3
3. Directly taking SVC saturation as MVO2- Flamm and
associates concluded that this method was less
accurate in patients without shunt or with shunt.
Flamm MD, Cohn K E, Hancock EW. Measurement of systemic
cardiac output at rest and exercise in patients with atrial septal
defect. Am J Cardiol 1969;23:258

36.  Calculation of saturation PVO2
◦ NOT usually entered
◦ LA vs PVO2
Assumed valve if not calculated
≥ 95% FA saturation < 95%
Take FA sat. 1. d/t R – L shunt assume 98% as
PVO2
2. Not d/t R – L shunt take FA
saturation

37.  Vena Cava SPO2=
(3x67.5+1x73)/4=69%
 Right Atrium SPO2=
(74+84+79)/3=79%
 A significant step-up
79%-69%=10% >=7%
84%-68%=16%>=11%
  SPO2 from SVC to PA
is 12%-13% i.e. >8%
37

38.  PV O2 content
=1.36×10×Hb×saturation
=1.36×10×14×0.96
=183 mlO2/liter
 PA O2 content
=1.36x10×14× 0.80
=152ml O2/liter
38

39.  Qp = O2 consumption (ml/min)/ (PVO2 content – PAO2 content)
= 240ml O2/min /(183-152) mlO2/L = 7.74 L/min
 Qs = 240ml O2/min/ (Systemic arterial O2 content –Mixed venous
O2 content )
= 240/(0.96-0.69)14(1.36)10 = 4.6 L/min
 Qp/Qs = 7.74/4.6 = 1.68
 Left-to-right Shunt=7.7- 4.6 = 3.1 L/min

40.  Qp =
260/(0.97-
0.885)15(1.36)10
= 15 L/min
 Qs=
260/(0.97-
0.66)15(1.36)10
= 4.1 L/min
 Qp/Qs=15/4.1=3.7
LShunt=15-4.1=10.9
L/min
40

41.  The ratio Qp/Qs gives important physiologic information
about the magnitude of a left-to-right shunt.
 A Qp/Qs < 1.5 signifies a small left-to-right shunt and is
often felt to argue against operative correction,
particularly if the patient has an uncomplicated atrial or
ventricular septal defect.
 A Qp/Qs between 1.5 and 2.0 are obviously
intermediate in magnitude ; surgical intervention is
generally recommended if operation risk is low.
41

42.  A Qp/Qs < 1.0 indicates a net right-to-left
shunt and is often a sign of the
presence of irreversible pulmonary
vascular disease.
 A simplified formula :
Qp (SAO2-MVO2)
Qs (PVO2-PAO2)

43.  The quantification of net right to left and left to right
shunt requires the calculation of Qeff, which is the
net amount of systemic venous return going to lungs
for oxygnation.
Qeff = V O2/ m²
(PV % Sat - MV % Sat) x1.36 xHb x10
Net right to left = Qs - Qeff
Net left to right = Qp - Qeff

44. VO2=100 & Hb = 12
Qp = 12.25 lts
Qs = 2.45 lts
 Net left to right shunt = 9.8 lts
 Net Qp ( Qpa) considering shunt only
at atrial level, and thus resulting in
PA saturation of 80 = 4.08 lt
 Net shunt at atria
 Qpa – Qs = 4.08 – 2.45 = 1.63 lt
 Net shunt at ventricle
 Qp - net atrial shunt = 9.8 – 1.63 =
8.17 lts
LA
95
LV
95
RA
80
RV
90
SVC
70
PA
90
PV
95
AO
95

45.  Many other more sensitive techniques are
availaable for detecting smaller left to right
shunts:
 Contrast angiography
 Indocyanine green dye curves
 Radionuclide techniques
 Echocardiographic methods.

46.  During invasive cardiac cath anatomic delineation
of shunt defects is carried out by contrast injection
under fluoroscopy.
 When mainly used for left to right shunts like VSD
, PDA, accuracy is high.

47.  Exogenous indicator used for both qualitative and
quantitative indicator dilution studies
 Cardio green dye is non toxic and rapidly cleared
from the circulation by liver
 Accurate cardiac output determinations can be
made.
 Swan HJC, Wood EH. Localization of left to right cardiac shunt. Proc Staff
Met Mayo Clin1953;28:95

48.  If there is intracardiac or other intravascular shunting, an
accurate total cardiac output cannot be determined, however,
the degree of right to left or left to right shunting can be semi-quantitated
using the Cardio-Green dye dilution technique.
 Extremely sensitive for the detection of very minute shunts but
the quantification of shunts is less accurate and more
cumbersome than utilizing oxygen determinations.
 The studies of Castillo and cowrkers suggest that left to right
shunt as small as 25% of systemic output can be detected.
 Hyman et al. A comparative study of detection shunt by oxygen analysis and
indicator dilution methods. Ann Intern Med 1962;56:535

49.  Requires a densitometer which measures the
concentration of dye in blood.
 After calibrating the densitometer, a known
amount of dye is injected in pulmonary artery
 Through an arterial line continuous measurement
of dye concentration is carried out by the
densitometer.
 A characteristic time/concentration output curve is
inscribed on the recorder.

50.  The height of the curve
corresponds to the
concentration of the dye in
the blood at that particular
instant.
 The tailing off or flattening
of the curve appears as
recirculation of the same dye
begins to appear and
eventually creates a second,
but less significant, peak.

51. Quantification

52.  Similar to oximetry, it is invasive, and its sensitivity
is only modestly better than oximetry in detecting
small shunts.
 Only of limited utility for left to right shunts.
 Quantitative evaluation is not as accurate.
 It is an outmoded technique, only of historical
importance.

53.  Echocardiographic estimation of Qp/Qs is based on
doppler aided calculation of cardiac output as
◦ CO = Mean Velocity x Vessel flow area x 60 s/min
Cosine θ
Where θ is the cosine of the incidence angle between Doppler
beam and direction of flow

54.  The preferred sites for determining SV and
cardiac output (in descending order of
preference) are as follows:
1.The LVOT tract or aortic annulus
2.The mitral annulus
3.The pulmonic annulus

55. The LVOT is the most widely used site. SV is derived
as:
 SV = CSA ×VTI
 The CSA of the aortic annulus is circular, with little
variability during systole.
 Because the area of a circle = πr2, the area of the
aortic annulus is derived from the annulus
diameter (D) measured in the parasternal long axis
view as:
 CSA = D2 ×π/4 = D2 × 0.785
◦ Zoghbi WA, Farmer KL, Soto JG, Nelson JG, Quiñones MA. Accurate noninvasive quantification of
stenotic aortic valve area by Doppler echocardiography. Circulation 1986;73:452- 9.

56.  Qp = RVOT CSA× RVOT TVI
 Qs = LVOT CSA × LVOT TVI

58.  Measurement of the annulus diameter done during
early systole from the junction of the aortic leaflets
with the septal endocardium, to the junction of the
leaflet with the mitral valve posteriorly, using inner
edge to inner edge.
 The largest of 3 to 5 measurements should be taken
because the inherent error of the tomographic plane is
to underestimate the annulus diameter.
 The LV outflow velocity is recorded from the apical 5-
chamber or long-axis view, with the sample volume
positioned about 5 mm proximal to the aortic valve.

59.  Although the mitral annulus is not perfectly circular,
applying a circular geometry gives similar or better
results than attempting to derive an elliptical CSA
with measurements taken from multiple views.
 The diameter of the mitral annulus should be
measured from the base of the posterior and anterior
leaflets during early to mid- diastole, 1 frame after
the leaflets begin to close after its initial opening.
 The sample volume is positioned so that in diastole it
is at the level of the annulus.
 Lewis JF, Kuo LC, Nelson JG, Limacher MC, Quiñones MA. Pulsed Doppler
echocardiographic determination of stroke volume and cardiac output:
clinical validation of two new methods using the apical window. Circulation
1984;70:425- 31.

60.  The pulmonic annulus is probably the most difficult
of the 3 sites, mostly because the poor visualization
of the annulus diameter limits its accuracy and the
right ventricular (RV) outflow tract contracts during
systole.
 Measure the annulus during early ejection (2 to 3
frames after the R wave on the electrocardiogram)
from the anterior corner to the junction of the
posterior pulmonic leaflet with the aortic root.
 Sample volume placed just proximal to the
pulmonary valve.

62.  In patients with an atrial septal defect, QP is
measured in the main pulmonary artery and
 QS is quantified at the mitral valve or in the
ascending aorta.

63.  In patients with a ventricular septal defect or a left
ventricular to right atrial shunt, QP is calculated as
transmitral valve flow, QP can also be calculated in
the pulmonary artery and
 Qs is calculated as the aortic flow.

64.  In patients with patent ductus arteriosus,
pulmonary flow (QP) is calculated as pulmonary
venous return through the mitral valve orifice and
as flow in the ascending aorta, and
 QS is calculated as systemic venous return by
measuring flow within right ventricular outflow
tract in the subpulmonary region.

65.  Intravenous contrast injection of saline remains
one of the primary diagnostic tools for detecting an
atrial septal defect and, in smaller defects, may
provide crucial information as to the presence of a
potential shunt that is not directly visualized or has
not resulted in a right ventricular volume overload

66.  In atrial septal defects
with biphasic flow
agitated saline
bubbles will be seen
immediately in left
atria.
 If the bubbles are
seen after 3 cardiac
cycles, it is diagnostic
of pulmonary AV
fistula.

67.  Error in measurement of mean velocity
◦ Error in intercept angle
◦ The lack of uniform velocity profile across the
vessel lumen
◦ Respiratory variation ( 15% at mitral level)
 Error in measurement of cross sectional area
◦ Inaccurate gain settings
◦ Cross sectional area of the vessel changes
throughout the cardiac cycle

68.  Due to these limitations the calculated flow
values by doppler show a lot of variability.
 As such in day to day practice calculation of
Qp/Qs by echocardiography is rarely performed,
which is primarily used for initial evaluation of
congenital cardiac defects, and invasive cardiac
catheterization and oximetry being the gold
standard for shunt evaluation in complex cases.

69.  Pulmonary and systemic flows can be measured by
multiplying cross sectional area x flow velocity
through that area
 MRI scans, due to high resolution can measure the
cross sectional area accurately and the velocity can
be recorded by phase contrast MRI

72.  For the proximal aorta, the section is cut
approximately 2 to 4 cm above the aortic valve and
distal to the coronary arterial ostia.
 For pulmonary artery the position is distal to the
pulmonic valve but proximal to the bifurcation.
 For patients with PDA flow is calculated separately
in LPA and RPA, and hence vessel area is also
calculated separately for the LPA and RPA

73.  On the velocity map, the gray scale intensity for
each pixel encodes for velocity.
 For each frame of the cardiac cycle, velocity within
the vessel is calculated as the average velocity for
all the pixels within the lumen.

74.  Flow is calculated by multiplying the cross-sectional
area of the vessel lumen by the mean
blood flow velocity for each frame sampled in the
cardiac cycle.
 Flow for the whole cardiac cycle was calculated by
summation of flow per frame in the cardiac cycle.
 By multiplying heart rate by the sum of the flow for
all frames of the cardiac cycle, the flow per minute
through the vessel is determined.
 K Debl et al. Quantification of left-to-right shunting in adult congenital heart disease: phase-contrast cine
MRI comparedwith invasive oximetry. The British Journal of Radiology, 82 (2009), 386–391

75.  Irregular rhythms
 MRI does not allow discrimination of patients without
shunts from those with small amounts of left-to-right
shunting.
 Patients of pulmonic or aortic regurgitation.
◦ Negative flow in the proximal great vessels during
diastole would interfere with the determination of
forward flow.
 Patients with aortic or pulmonic stenosis,
◦ since they have turbulent, high-velocity flow jets in
the proximal great vessels.

77.  Quantification of left-to-right shunting can
be performed reliably and accurately by PC-MRI
and provides results that correlate closely
with those obtained by invasive oximetry,
although there is a small overestimation of
the degree of shunting.
 In the clinical management of patients with
left-to-right shunting, MRI can provide
anatomical and functional information in a
single examination and is a useful technique
for the assessment of adult congenital heart
disease.

78.  Albumin aggregates are examined microscopically to
assure that particles are in the 10- 50 micron size
range
 The amount of albumin per test dose does not exceed
0.2 mg.
 After intravenous injection, two or more scintigrams,
each of 2 min duration, are taken with a gamma camera
to produce a whole-body image.
 % Rt to Lt shunt = total body count – total lung count
total lung count
◦ Gates.G.F., Orme.H.W and Dose,E.K: Measurement of Cardiac Shunting with Technetium labeled
Albumin Aggregate, J.Nuc.Med., 12:746,1971.

79.  This method allows the detection of Qp/Qs as
small as 1.2
 Can be carried out by peripheral injection
 Has been mainly described for lt to rt shunt
 It requires the injection of a radioactive isotope