Left to Right Shunts and their Calculation Ghada ... - CardioEgypt.com

3/18/2013 

Left to Right Shunts and 

their Calculation 

Ghada El Shahed, MD 

Professor of Cardiology 

Ain Shams University 

• Flow through 

systemic & 

pulmonary 

circulations is 

normally balanced 

and equal. 

• Two circulations in 

series 

1

3/18/2013 

• Flow through 

systemic & 

pulmonary 

circulations is 

normally balanced 

and equal. 

• Two circulations in 

series 

Oxygen Saturation 

Systemic vein 

Pulmonary vein 

RA 

65% 

LA 

100% 

RV 

65% 

LV 

100% 

Pulmonary artery 

Systemic artery 

2

3/18/2013 

Left to right shunts 

• “leak" of 

blood from 

the systemic 

to the 

pulmonary 

circulation 

Left to right shunts 

• pulmonary circulation 

receives : 

* blood that entered RA 

& RV from vena cavae 

plus 

* blood entering 

through ASD, VSD, or 

a PDA 

3

3/18/2013 

Causes 

Lesions resulting in left to right shunts 

include: 

• Ventricular septal defect (VSD) 

• Patent ductus arteriosus (PDA) 

• Atrial septal defect (ASD) 

• Atrioventricular defect (AVSD) 

Determinants of shunt size 

• In VSD and PDA: 

* size of defect 

And 

* relative resistance 

in the pulmonary 

and systemic 

circuits 

4

3/18/2013 

Determinants of shunt size 

• In ASD and AVSD: 

magnitude of the shunt 

depends mainly on 

relative ventricular 

compliance. 

Left to right shunts: 

DETECTION AND 

QUANTIFICATION 

5

3/18/2013 

Clinical data: VSD 

• The intensity of the murmur 

is inversely proportional to the 

magnitude of the shunt 

• An apical mid-diastolic murmur 

(increased flow across MV) indicates 

a large shunt 

Clinical data: PDA 

• Continuous or "machinery" murmur 

• An apical mid-diastolic murmur 

denotes large shunt 

• Wide pulse pressure indicates a 

large left to right shunt 

6

3/18/2013 

Clinical data: ASD 

• Flow murmur in pulmonary area : 

>> large shunt 

• Mid-diastolic murmur due to increased 

flow across the tricuspid valve 

• Wide splitting of S2 due to increased 

flow across the pulmonary valve 

7

3/18/2013 

“with a few limitations, the Doppler index RSV/LSV 

is clinically useful in the estimation of the 

magnitude of the shunt flow in patients with ASD” 

8

3/18/2013 

Shunt Detection : 

Indocyanine Green Method 

• Indocyanine green (1 cc) injected as a bolus into 

right side of circulation (pulmonary artery) 

• Concentration 

measured from 

peripheral artery 

Baim DS: Grossman’s Cardiac Catheterization, Angiography, and Intervention. 7 th Edition. Lippincot Williams 

and Wilkins, 2007. 

9

3/18/2013 

Left-to-Right Shunt 

Appearance and washout of dye produces initial 1 st 

pass curve followed by recirculation in normal adults 



Shunt Detection: 


Bashore, TM. Congenital Heart Disease in Adults. The Measurement of Intracardiac Shunts. In: CATHSAP II. 

Bethesda: American College of Cardiology, 2001. 

10

3/18/2013 

Indicator Dilution Method 

• More Sensitive for smaller 

shunts 

• Cannot localize the level of 

left to right shunt 

Oximetric Methods 

• Obtain O2 saturations 

in sequential 

chambers, 

identifying oxygen 

step-up 

• Insensitive for small 

shunts (< 1.3:1) 



11

3/18/2013 

Shunt Detection & Measurement 

Oximetry Run 

• IVC, L4-5 level 

• IVC, above diaphragm 

• SVC, innominate 

• SVC, at RA 

• RA, high 

• RA, mid 

• RA, low 

• RV, mid 

• RV, apex 

• RV, outflow tract 

• PA, main 

• PA, right or left 

• Left ventricle 

• Aorta, distal to ductus 

x 

x 

x 

x 

x 

x 

x 

x 

x 

x 

x 

x 

x 

x 

x 



Oximetry 

ASD VSD PDA 

Systemic arterial O2 Sat No change No change No change 

RA O2 Sat No change No change 

RV O2 Sat 

No change 

PA O2 Sat 

Pulmonary blood flow 

12

3/18/2013 

ASD 

Detection of Left-to-Right Shunt 

Level of shunt O 2 % Sat Differential diagnosis 

Atrial 

(SVC/IVC RA) 

Ventricular 

(RA RV) 

Great vessel 

(RV PA) 

7 

5 

5 

ASD, PAPVR, VSD with TR, 

Ruptured sinus of Valsalva, 

Coronary fistula to RA 

VSD, PDA with PR, 

Coronary fistula to RV 

Aorto-pulmonary window, 

Aberrant coronary origin, 

PDA 

13

3/18/2013 

VSD 

SHUNT QUANTIFICATION 

14

3/18/2013 

• Calculation of systemic and pulmonary 

flows (and their ratio) are used for shunt 

quantification 

• The most common methods: 

-Fick’s method 

-Indicator dilution 

(Both have their assumptions & limitations 

that are important to remember) 

The Fick Method 

• Described by Adolph Fick in 1870 

• Is probably the most common 

method used to calculate cardiac 

flows in the pediatric cath. lab 

15

3/18/2013 

Concept 

• The total uptake (or release) of a substance 

by an organ is the product of blood flow to 

that organ and the concentration difference 

of the substance in the arteries and veins 

leading into and out of that organ 

Fick Oxygen Method 

• As applied to lungs, the substance 

released to the blood is oxygen 

>> oxygen consumption is the product of 

arteriovenous difference of oxygen across 

the lungs and pulmonary blood flow 

Q p = 

Oxygen consumption 

Arteriovenous O 2 difference 



16

3/18/2013 

Concept 

• So, using arterial and venous oxygen 

content and oxygen consumption, 

one can easily calculate flow. 

• So the important equation is: 

(Multiply denominator by 10 to convert dL to L, as 

Hb is measured in g/dL) 

17

3/18/2013 

Calcluation of oxygen content 

of blood 

Oxygen Content (mL O2/dL plasma) 

= O2 bound to Hb + dissolved O2 

= [1.36 Hgb] X saturation] + [0.003 X PaO2] 

18

3/18/2013 

O2 content 

= 1.36 Hgb X saturation + 0.003 X PaO2 

• 1.36mL is the oxygen carrying capacity 

of1 gm of hemoglobin 

• If the saturation is 98%, then use 0.98 

in the formula, not 98 

• The relatively small amount of 

dissolved oxygen in plasma is 0.003mL 

O2/dL plasma/mmHg PaO2 

19

3/18/2013 

Oxygen consumption (VO2) 

• Oxygen consumption is often assumed, 

and is readily available in tables 

• There is variation based on sex, age, and 

heart rate. 

• no data published for the very small infant. 

(Despite the limitations of assumed VO2, this 

method remains widely used) 

Measurement of VO2 

Baim DS: Grossman’s Cardiac Catheterization, Angiography, and Intervention. 7 th 

Edition. Lippincot Williams and Wilkins, 2007. 

20

3/18/2013 

• Using this principle, systemic and 

pulmonary flows can be calculated 

Pulmonary blood flow 

QP= 

21

3/18/2013 

Shunt Measurement: 


• Fick Principle: The total uptake or 

release of any substance by an organ is 

the product of blood flow to the organ 

and the arteriovenous concentration 

difference of the substance. 

– Pulmonary circulation (Qp) utilizes PA 

and PV saturations 

RA (MV) 

RV 

Lungs 

LA (PV) 

LV 

PBF = 

O2 consumption 

(PvO 2 – PaO 2 ) x 10 

(O 2 content = 1.36 x Hgb x O 2 saturation) 

PA 

Ao 

(Alan Keith Berger, MD 

University of Minnesota, 

2003) 








– Systemic circulation (Qs) utilizes MV and 

Ao saturations 

O2 consumption 

SBF = (AoO 2 – MVO 2 ) x 10 

(O 2 content = 1.36 x Hgb x O 2 saturation) 

RA (MV) 

RV 

PA 

Body 

LA (PV) 

Ao 

LV 

(Alan Keith Berger, MD 

University of Minnesota, 

2003) 

22

3/18/2013 








– Pulmonary circulation (Qp) utilizes PA 

and PV saturations 

– Systemic circulation (Qs) utilizes MV and 

Ao saturations 

RA (MV) 

RV 

PA 

LA (PV) 

Ao 

LV 

PBF = 

O 2 consumption 

(PvO 2 – PaO 2 ) x 10 

SBF = 


(AoO 2 – MVO 2 ) x 10 

Mixed venous O2 saturation: 

RA receives blood from several sources 

– SVC: Saturation most closely approximates 

true systemic venous saturation 

– IVC: Highly saturated because kidneys receive 

25% of CO and extract minimal oxygen 

– Coronary sinus: Markedly desaturated because 

heart maximizes O2 extraction 



23

3/18/2013 

Mixed venous O2 saturation: 

• Phlamm Equation: Mixed venous saturation 

used to normalize for differences in blood 

saturations that enter RA 

Mixed venous saturation = 

3 (SVC) + IVC 

4 



• For pediatric catheterization, we 

most often express the indexed flow 

(to BSA), distinguishing between 

cardiac output (CO; L/min) and 

cardiac index (Qs; L/min/m2). 

Because the VO2 tables are usually 

indexed. 

24

3/18/2013 

• For pediatric catheterization, we 

most often express the indexed flow 

(to BSA), distinguishing between 

cardiac output (CO; L/min) and 

cardiac index (Qs; L/min/m2). 

Because the VO2 tables are usually 

indexed. 

25

3/18/2013 

Example 

• Mixed venous saturation - 75%, PA 

saturations = 84% 

• pulmonary vein and aortic 

saturations = 99%. 

>>>>The net Qp:Qs in this patient is 

(99 – 75)/(99 – 84)=1.6 

Estimation of shunt size 

Flow Ratio (QP/QS): 

• < 1.5 = Small shunt 

• ≥ 2.0 = Large Left to Right Shunt 

• < 1.0 = Net Right to left Shunt 

No need for Oxygen consumption 

(Since this number will cancel out of 

the equation) 

26

3/18/2013 

Shunt Measurement: 

Effective Pulmonary Blood Flow 

• Effective Pulmonary Blood 

Flow: flow that would be 

present if no shunt were 

present 

• Requires 

– MV = PA saturation 

– PV – PA = PV - MV 

PBF 

Effective Pulmonary 

Blood Flow 

= 


(Pv – MV O 2 ) x 10 

= 


(Pv – Pa O 2 ) x 10 




Left-to-Right Shunt 

• Left to right shunt: >> in step-up 

in O 2 between MV and PA 

• Shunt is the difference between 

pulmonary flow measured and 

what it would be in the absence of 

shunt (EPBF) 

• Systemic Blood Flow = EPBF 

Left-Right Shunt = Pulmonary Blood Flow – Effective Blood Flow 


= 

(PvO 2 – Pa O 2 ) x 10 

– 


(PvO 2 – MVO 2 ) x 10 



27

3/18/2013 

Shunt Measurement 

Limitations of Oximetric Method 

• Requires steady state with rapid collection of O 2 

samples 

• Insensitive to small shunts 

• Flow dependent 

– Normal variability of blood oxygen saturation in the right 

heart chambers is influenced by magnitude of SBF 

– High flow state may simulate a left-to-right shunt 

• When O 2 content is utilized (as opposed to O 2 sat), 

the step-up is dependent on hemoglobin. 



SOME TIPS FOR QP, QS 

CALCULATIONS 

28

3/18/2013 

• If you do not directly obtain a 

pulmonary vein or LA saturation, 

assume something appropriate to the 

clinical status of the patient 

( ~95–100% in the absence of lung 

disease) 

• Always double check and confirm 

your math. 

• Always document all assumptions in 

your catheterization report. 

29

3/18/2013 

• Make sure your 

numbers make sense. 

[e.g. The SVC saturation should never be 

higher than the PA saturation 

(unless there is anomalous PV return or an 

oxygen-consuming tumor in the RV!) 


• Fick oxygen method total error 10% 

– Error in O2 consumption 6% 

– Error in AV O2 difference 5%. Narrow 

AV O2 differences more subject to error, 

and therefore Fick method is most 

accurate in low cardiac output states 



30

3/18/2013 

Cardiac Output Measurement 


• Sources of Error 

– Spectophotometric determination of blood 

oxygen saturation 

– Changes in mean pulmonary volume 

• Patient may progressively increase or decrease 

pulmonary volume during sample collection. If 

patient relaxes and breathes smaller volumes, CO is 

underestimated 

– Improper collection of mixed venous blood 

sample 

• Contamination with PCW blood 

• Sampling from more proximal site 



Indicator Dilution Methods 

• Requirements 

– Bolus of indicator substance which mixes 

completely with blood and whose concentration 

can be measured 

– Indicator must go through a portion of circulation 

where all the blood of the body becomes mixed 



31

Concentration 

3/18/2013 


Indicator Dilution Methods 

Stewart-Hamilton Equation 

CO = 

0 

Indicator amount 

C (t) dt 

C = concentration 

of indicator 

CO = 

Indicator amount (mg) x 60 sec/min 

mean indicator concentration (mg/mL) x curve duration 

• Indicators 

– Indocyanine Green 

– Thermodilution (Indicator = Cold) 





• Indocyanine green (volume and concentration 

fixed) injected as a bolus into right side of 

circulation (pulmonary artery) 

• Samples taken from peripheral artery, 

withdrawing continuously at a fixed rate 

• Indocyanine green concentration measured by 

densitometry 

CO = 

I 

(C x t ) 

(C x t) 

Recirculation 

Extrapolation 

of plot 



time 

CO inversely 

proportional 

to area under 

curve 

32

3/18/2013 



• Sources of Error 

– Indocyanine green unstable over time and with 

exposure to light 

– Sample must be introduced rapidly as single bolus 

– Bolus size must be exact 

– Indicator must mix thoroughly with blood, and should 

be injected just proximal or into cardiac chamber 

– Dilution curve must have exponential downslope of 

sufficient length to extrapolate curve. Invalid in Low 

cardiac output states and shunts that lead to early 

recirculation 

– Withdrawal rate of arterial sample must be constant 



THERMODILUTION 

33

3/18/2013 

• First introduced in the 1950s, this 

technique involves determining the 

extent and rate of thermal changes in the 

blood stream after injection of a fixed 

volume of fluid at a set temperature 

upstream. 

• From this temperature– time curve, the 

volume rate of flow can be calculated in a 

manner analogous to that used for dye 

and other indicator–dilution methods. 

Common Problems 

• High cardiac output >> only a small 

temperature drop, increasing the risk for 

error. 

• If the proximal port is not in free flowing 

blood, there will be loss of temperature 

before reaching the thermistor. 

• Slow injection of cooled solution will 

produce a smaller magnitude temperature 

change, falsely elevating the calculated 

cardiac output. 

34

3/18/2013 


Thermodilution Method 

CO = 

V I (T B -T I ) (S I x C I / S B x C B ) x 60 

 

 

0 

T B dt 

V I = volume of injectate 

S I , S B = specific gravity of injectate and blood 

C I , C B = specific heat of injectate and blood 

T I = temperature of injectate 

T B = change in temperature measured downstream 




Thermodilution Method 

• Advantages 

– Withdrawal of blood not necessary 

– Arterial puncture not required 

– Indicator (saline or D5W) 

– Virtually no recirculation, simplifying computer 

analysis of primary curve sample 



35

3/18/2013 

Summary of 

Fick Oxygen Method: AV O 2 Difference 

Step 1: Theoretical oxygen carrying capacity 

O 2 carrying capacity (mL O 2 / L blood) = 

1.36 mL O 2 / gm Hgb x 10 mL/dL x Hgb (gm/dL) 

Step 2: Determine arterial oxygen content 

Arterial O 2 content = Arterial saturation x O 2 carrying capacity 

Step 3: Determine venous oxygen content 

Mixed venous O 2 content = venous saturation x O 2 carrying capacity 

Step 3: Determine A-V O 2 oxygen difference 

AV O 2 difference = Arterial O2 content - venous O 2 content 



Importance of accurate 

calculation & avoiding pitfalls 

• Shunt size >>>> surgical decision 

• Flow is used to calculate resistance 

36

3/18/2013 

Accurate measurements & 

calculations = correct decision 

• ‘‘A catheterization is 

like a puzzle: 

everything must fit 

with everything else.’’ 

(If things don’t fit, your 

case is probably not 

complete) 

37

Left to Right Shunts and their Calculation Ghada ... - CardioEgypt.com

Create successful ePaper yourself

Delete template?

Save as template?