Shunt quantification by means of non - invasive and invasive methods. Echo and doppler

1. By: Dr. Ankur Gupta
Resident, DM Cardiolgy

2. Introduction
Majority of the congenital lesions are asso. with
intracardiac shunts.
Detection, localisation and quantification of shunts –
integral part of hemodynamic evaluation of these
patients.
Quantification of shunts by:
Invasive
Noninvasive methods.

3. Non invasive methods
Clinical evaluation
CXR and ECG
Echo and Doppler
MRI
CT
Nuclear scanning

4. Invasive
Oximetry
Indicator dilution

6. 2 –D Echocardiography:
direct visualization of any communication and their
shunting
excellent for localization of shunt
limited in the ability to quantify shunt
Indirect estimations
ASD with large shunting
 RA, RV dilated
 diastolic septal flattening
VSD with large shunting
 LA, LV dilatation
 Systolic and diastolic septal flattening

7. Contrast Echo
Agitated saline
 Detection of small R  L shunts
Large left to right shunts may cause a negative
contrast jet in the Rt. atrium

8. Doppler echocardiography
Most of the studies were done in ASD & VSD.
Based on the measurement of flow across the valves
or the defect itself.
Based on the formula that flow can be calculated
from CSA & VTI.

9. Volumetric flow measurement requires
- calculation of temporal mean flow velocity and
cross sectional area
- velocity profile is uniform across the vessel
- single sampling of the flow velocity in the center
of the vessel is recorded
To calculate 
computerised calculation of the area under the
doppler curve/ flow period

10. For systemic flow
Aortic velocity is recorded from the apical view.
Vessel diameter is measured from the parasternal long
axis view.

11. Pulmonary blood flow:
Pulm. mean velocity is recorded from the
parasternal short axis view
In case of large shunt and a shunt located close
to PA, the doppler tracing shows spectral
broadening or signs of disturbed flow, in such
cases uniform velocity cannot be assumed
Doppler tracing cannot be used if any PS is
present.

12. Measurement of the cross sectional area
- at the valve annulus (as it is the flow limiting
point of the vessel)
- measurement is made from the inner edge to
the inner edge.
- diameter is measured at the early systole –
time when vessel is at peak systolic dimension.
- flow velocity should be measured at same
location

13. Methods:
1.Qp/Qs calculation from flow velocity (velocity
time integral) and cross sectional area
Qp/Qs = Area of Pa x VTI
Area of Aorta x VTI
Sanders et al used pulmonary flow with good
correlation , r=0.85.
Barron et al used Mitral flow with better
correlation , r= 0.9 vs 0.69.

14. 2. Simplified method - the square of the pulmonary
to aortic diameter ratio was substituted for the
area ratio and the flow peak velocity ratio for the
velocity time integral.
 Qp/Qs = Vel. Pk PA x r2
Vel. Pk Ao x r2
r= radius / diameter
square of the ratio of the pulmonary to aortic
luminal diameter (or radius)is used instead of
vessel areas.

15. 3. Qp/Qs = (pulm + mitral flow)/2
(tricuspid + aortic flow)/2
 Assumption that tricuspid and aortic flow
represent systemic flow and pulmonary &
mitral flows represent pulmonary flow.
 Maximal diameter of mitral and tricuspid
valve annulus is measured during diastole in
an apical 4 –chamber view & area calculated
assuming the annulus to be circular.
 Laborious & time taking.
 Combines measurements from all the 4 valves
but was not shown to be better than the
previous 2.

16. 4. Qp/Qs = Shunt flow + aortic flow
aortic flow
 Shunt (VSD) flow  as the product of the VTI
and color-derived cross-sectional area of VSD jet
measured at its narrowest point.
 This method does not use the pulmonary flow &
outflow diameter which are more variable.

17. Difficulties : It is assumed that
1. The defect is circular.
2. The size does not vary during systole.
3. No angle correction is needed.
4 . Flow velocity is uniform across the orifice.

18. Most studies show moderate correlation of
doppler techniques with oximetry data.
Sabry et al, studied above 4 methods with
cardiac cath calculated shunts.
First 2 methods showed moderate correlation
( r=0.54 & 0.56 ). Correlation improved
when large VSDs were excluded (r=0.62 &
0.66 ).
3rd
method showed no better correlation & it
was more time taking (r =0.57).
4th
method showed best correlation (r =0.82).
When large VSDs were excluded it was r = 0.9.

19. Sources of error
Mainly from the assumptions made
1) assumption that velocity profile is uniform
through out the cross sectional area
2) alignment of the doppler beam with the
direction of the flow ( angle < 200
)
3) turbulent flow in the vessels mainly in the
PA.
4) inaccuracy in measurement of cross
sectional area of vessels
- PA dimensions vary significantly during
cardiac cycle

20. 5) errors in calculation because of presence of
additional defects
e.g PDA present downstream from the PA
6) semilunar valve regurgitation results in
overestimation of flow because of failure to measure
the regurgitant volume
7) All these methods overestimate the shunt in large
VSDs.
8) Quantification of PDA is not accurate due to the
turbulent flow across the defect & difficulty in
measuring the flow distal to the shunt.

21. Quantification of ASD
TTE estimation of ASD diameters & shunt
quantification by cath showed only fair correlation
(r=0.56).
• The size of the defect by transesophageal Doppler
color flow mapping correlated fairly well with the
size estimated at surgery (r = 0.73 ).
Other measurements by TTE for ASD are –
- RV/LV diameter (r=0.64)
- Area of PA (r=0.62)
- RV volume (r=o.71)
- PA/Ao (r=0.89)

22. Doppler colour flow mapping by
TEE
• Area of the ASD- calculated by assuming it to be
circular and taking the maximal Doppler color flow jet
width at the defect site as its diameter.
• The pulsed Doppler sample volume is to be placed
parallel to the shunt flow direction at the defect site to
obtain the mean velocity and flow duration.

23. • From these values, the shunt volume can
calculated as a product of the defect area, mean
velocity, flow duration and heart rate.
• The calculated shunt flow volume obtained by
transesophageal study showed a good correlation
with shunt flow volume (r = 0.91) and pulmonary to
systemic blood flow ratio (r = 0.84) obtained at
cardiac catheterization.

24. R  L shunt quantification
Aortic flow + VSD flow = Input to RV
Pulmonary flow + R  L shunt = output from RV.
Hence R  L shunt = Aortic flow + VSD flow –
Pulmonary flow.
Only fair correlation found with Cath data (r = 0.61 –
0.77 )

25. Automated cardiac flow
measurement method
ACM method – using spatial and temporal
integration of colour Doppler profiles .
Method  velocity profile in a region of interest
set on the flow tract is detected in each frame ,
imaged & recorded on the image memory
Flow volume rate is calculated by integration of
the velocity profile
Stroke volume is measured by temporal
integration, throughout the systolic period.

26. ACM method:
Advantages:
Quick and requires only two manual procedures.-
selection of systolic period in the stored image
memory, positioning at the area of interest
Calculations are done without tracing the
Doppler wave form to measure VTI
No need to measure area of outflow tract, because
the edge of the color profile is detected as the width
of the flow tract.

27. ACM method
ACM uses velocity profile across the flow tract
diameter, while in conventional pulsed Doppler
method the spectral velocity from a centrally
placed sample point is measured
Flow rate at each frame is temporally integrated
for the stroke volume calculation
Thus this method requires fewer assumptions
than pulsed Doppler method.

28. Martin et al found strong correlations between
ACM and invasive QP/QS ratio and the agreement
with invasive data was better using ACM than
using conventional echocardiographic method ( r
= 0.91 )
The only restriction remains to select manually
the systolic period and to carefully choose the
region of interest.
Gain must be optimised, allowing to see only one
colour throughout the outflow tract

29. Avoids the potential error of conventional PWD
method for the calculation of pulmonary output,
linked to the difficulty of measuring the exact
pulmonary diameter.
This method was applied to ASD & VSD with better
correlation .

31. Principle: oxygenated blood shunted from left
side of the heart to the rt cause an abnormal
increase (step – up) in the oxygen content or
saturation of blood in the chamber into which
shunting occurs
Dexter et al, max. increase in oxygen content
from,
RV to PA - 0.5 ml/dl
RA to RV - 1.0 ml/dl
SVC to RA - 2.0 ml/dl

32. Barratt -Boyes and Wood suggested that multiple
blood samples to be obtained from each Rt. heart
chamber.
Data to be averaged before applying Dexter
Criteria
Advantages
- easy to perform, results available immediately
- can ascertain the site of shunt
- magnitude of the shunt can be calculated

33. Detection of left to right shunt
Level of
shunt
Mean O2 sat % in
distal chambers
(Highest value in
proximal
chambers)
Mean O2
vol. % in
proximal
chambers
(Highest
value in
distal
chambers)
Min Qp/Qs
reqd. for
detection at
3L/min/m2
Possible causes
of step up
Atrial
(SVC/IVC
to RA)
≥7 (≥11) ≥1.3 (≥2.0) 1.5 – 1.9 ASD, RSOV,
VSD with TR,
coronary fistula
to RA,
anomalous PV
drainage
Ventricular
(RA to RV)
≥5 (≥10) ≥1.0 (≥1.7) 1.3 – 1.5 VSD, PDA with
PR, Primum
ASD, coronary
fistula to RV

34. Detection of left to right shunt
Level of
shunt
Mean O2 sat % in
distal chambers
(Highest value in
proximal
chambers)
Mean O2
vol. % in
proximal
chambers
(Highest
value in
distal
chambers)
Min Qp/Qs
reqd. for
detection at
3L/min/m2
Possible causes
of step up
Great
vessel
(RV to PA)
≥5 (≥5) ≥1.0 (≥1.0) ≥1.3 PDA, Aorta-
pulmonic
window,
Aberrant
coronary artery
origin
Any level
(SVC to
PA)
≥7 (≥8) ≥1.3 (≥1.5) ≥1.5 All of the above

35. Detection of left to right shunt
Chambers
sampled
Single
Sample
Multiple
samples
SVC – RA 7% 5%
RA – RV 5% 3%
RV – PA 4% 3%
PV/LA –
LV/SA
-3% -2%

36. Oximetry – limitations:
It lacks sensitivity – i.e. does not allow detection of
small left to right shunts
Requirement of steady state during collection of blood
samples
Calculation of Mixed venous saturation: Normal
variability of blood oxygen saturation in the Rt heart
chambers is strongly influenced by the magnitude of
systemic blood flow.
Higher levels of systemic blood flow  higher mixed
venous saturation  blunting of inter-chamber
variability.

37. Step up in oxygen content of the receiving chamber
depends also on the oxygen carrying capacity of blood
i.e. Hb conc.
Depends on the associated lesions also – like TR, PR.

38. Precautions
Samples at multiple sites to be obtained rapidly ,
should take < 7 min.
O2 saturation data rather than O2 content are
preferable,
Comparision of mean values is preferable to
highest values.
When the systemic blood flow at rest is low,
exercise shoud be used.
At higher FiO2 the dissolved O2 should also be
considered.

39. Shunt calculation
Qp = VO2 / (PVO2- PAO2) (Hb) (1.36) (10)
Qs = VO2 / (AoO2 – SVCO2) (Hb) (1.36) (10)
Qp eff. = VO2 / (PVO2 – SVC O2) (Hb) (1.36) (10)
Qp / Qs = (AoO2 – SVC O2) / (PVO2 – PAO2)
Q L  R shunt = (Qp – Qp eff)
 Q R  L = (Qs – Qs eff)

40. Carter formula
Determines the left to right shunting.
Best used when there is a smooth downstroke
They can detect a minimum shunt of 25 – 30%.
Simplified formula of Victoria & Gessner is used when
there is no smooth transition.

41. Calculation of Rt to Lt shunt
BT1
T2

42. %Qs = BT1 x P1x 100
BT1xP1 + 0.44xT2xP2
%Qs = percentage of systemic blood flow due to Rt to
Lt shunt.
PC1 = height of first peak.
BT1 = bulid up time from appearance to first peak.
T2 = time from injection to P2.