SHUNT QUANTIFICATION

AND REVERSIBILITY

Dr. Gopal Ch. Ghosh

Cardiology unit-II

Definition

• Shunts are abnormal communications between

the systemic circulation and pulmonary

circulation.

1. Physiological

2. Pathological

3. Iatrogenic

Intracardiac shunt

• Diagnosis:

• Clinical evaluation of patient before

catheterisation

When to suspect a shunt?

(In CATH LAB )

• Unexplained arterial desaturation(Sao2<95%)

1. Excessive sedation

2. COPD

3. Pulmonary congestion/edema

• Unexpectedly high Oxygen content in pulmonary

artery (>80%)

• When data obtained in catheterisation laboratory

do not confirm the presence of suspected lesion

Oximetry run

• Pioneering studies of Dexter and his associates

in 1947(Technique)

• Oxygen content: measured by Van Slyke

technique (manometric technique)

• Volume% of oxygen: 1ml O2/100ml blood

• Present era: Oxygen saturation by

spectrophotometry

• Obtain a 2-ml sample from each of the following locations:1. Left and or right pulmonary artery2. Main pulmonary artery3. Right Ventricle, outflow tract4. Right ventricle, mid5. Right ventricle, tricuspid valve or apex6. Right atrium, low or near tricuspid valve7. Right atrium, mid8. Right atrium, high9. Superior vena cava, low (near junction with

right atrium)10. Superior vena cava, high (near junction with

innominate vein)11. Inferior vena cava, high (just at or below diaphragm)12. Inferior vena cava, low L4-L5)13. Left Ventricle

14. Aorta (distal to insertion of ductus)

Methods

• End hole catheters or side holes close to its tip

[Swan Ganz balloon flotation catheter, Goodale-

Lubin catheter]

• <7 minutes

• Withdraw fiberoptic catheter

Significant step up

• 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

Guidelines for optimal utilisation

• Rapid collection of blood samples

• O2 saturation data preferable

• Comparison of mean values

• Exercise should be used in borderline cases

Antman EM et al. Am J Cardiol 1980

Advantages

1. Easy to perform

2. Results are available immediately

3. Site of the shunt detection

4. Magnitude of the shunt determination

James D. Boehrer et al. American Heart Journal

Volume 124, Issue 2, August 1992, Pages 448–455

Limitations

• Small left to-right shunts: Not detectable

James D. Boehrer et al. American Heart Journal

Volume 124, Issue 2, August 1992, Pages 448–455

• Influence of blood hemoglobin concentration

may be important when blood O2 content

(rather than O2 saturation) is used to detect a

shunt

• A primary source of error may be the absence

of a steady state during the collection of blood

samples

Error source Problem solving

Prolonged because of

technical difficulties

Start from PCW-PA-RV-RA-VC

If the patient is agitated

(children)

Sedation

If arrhythmias occur during

the oximetry run

Leave the site and go to next site

• Presence of physiological shunt

– Thebesian veins and coronary veins entering LV

(R- L)

– Bronchial veins draining in to LA / PV (R- L)

– Bronchial artery to pulmonary artery (L – R )

• In a patient with a large L-R shunt caused by arterial

collaterals entering the distal pulmonary vascular bed,

it is impossible to obtain a blood sample distal to the

shunt

Calculation of pulmonary blood

flow(Qp) & systemic blood flow(Qs)

• If Sao2>95% then use Sao2 as Pvo2

• If Sao2<95% then use Pvo2 as 98% (look for

right to left shunt)

Mixed venous oxygen saturation

• Patients in resting state:

Mvo2 = 3 x SVC O2 + 1 x IVC O2 / 4

• Supine bicycle exercise:

Mvo2 = 1 x SVC O2 + 2 x IVC O2 / 3

Oxygen content

O2 Consumption

• Prediction from tables, nomograms, or

regression models is notoriously unreliable

• VO2 = 5.0×kg+19.8

• Direct measurement is preferable

LaFarge CG et al. Cardiovasc Res 1970

Effective blood flow

• Approximate left to right flow: Qp – Qeffective

• Approximate Right to left shunt: Qs - Qeffective

Other methods for shunt detection

• Indocyanine green dye curve

• Radionuclide technique

• Contrast angiography

• Echocardiographic methods

Indocyanine green dye curve

• Rarely used today

• Laboratories are not equipped

• Qualitative only

• Does not localise the shunt

• Can detect shunt < 25% of systemic flowCastillo et al. Am J Cardio 1966

Contrast angiography

• Visualisation & localisation of left to right

shunt

• Left ventriculogram

- Interventricular septum

- Sinuses of valsalva

- Ascending & descending aorta

• Left to right shunt except atrial septal defects

& anomalous pulmonary venous connection

Pulmonary hypertension

• Mean pulmonary artery pressure > 25mm hg

(at rest) or 30mm hg after exercise

• In infants & neonates: may not be applicable

WHO 2003

Types

• Hyperkinetic pulmonary hypertension:

minimal pathological changes

• Pulmonary vascular occlusive disease:

irreversible changes

Lesion specific pulmonary

hypertension

• Large VSD or PDA: 1-2 years of age

• Cyanotic congenital heart disease with

increased blood flow: 6 months

A saxena et al. PVRI review. 2009

ASD with pulmonary hypertension

• Behaves differently from post tricuspid shunt

• Persistence of the fetal pulmonary vascular

pattern

• Thromboembolism in small pulmonary arteries

• “Musculoelastosis"

Cherian G et al. Am heart journal. 1983

Yamaki S et al. Chest. 1987

Determination of shunt

Electrocardiogram

• Post tricuspid shunts: Biventricular

hypertrophy with left ventricular volume

overload

• Significant left ventricular voltage with “q”

wave in lateral leads suggests operability

• Eisenmenger syndrome: right axis deviation

& right ventricular hypertrophy

Significant infant VSD with moderate sized defect and a large left to right shunt.

X-RAY CHEST

• Cardiomegaly, prominent pulmonary artery

segments (except in malposed vessels) &

increased pulmonary vasculature: Large left to

right shunt

Patient with large VSD

22 year old lady with large PDA

• A large heart in X-ray chest may indicate

operabilitry

• Pruning of pulmonary artery branches are

common to both hyperkinetic pulmonary

hypertension & pulmonary vascular occlusive

disease

Echocardiography

• Most important test & most often performed

Clinical assessment for operability

• In infants & young children: Operable

• Presence of flow murmur

• Cardiomegaly & increased pulmonary blood

flow in X-ray

• Biventricular hypertrophy & left ventricular

volume overload in ECG

Clinical assessment for operability

• Older child: Unoperable

• Cyanosis

• No shunt or flow murmur

• ECG showing RVH

• Heart size normal or minimaly enlarged in X-

ray chest

Clinical assessment for operability

• Cyanotic congenital heart disease:

• Arterial saturation >85% indicates operability

in infants < 1 year of age

Role of cardiac catheterisation

• Must be performed in all borderline cases for

decision making

• Simple shunt, age < 1 year: Non invasive

monitoring

• Infants with common arterial trunk, atrio-

ventricular septal defect, transposition with

VSD presenting after 1 year: Needs

catheterisation

Antonio Augusto Lopes et al. Cardiol Young

2009; 19: 431–435

Role of cardiac catheterisation

• Patients living at high altitude: necessary even

below the age of 3 to 6 months

• Functionally univentricular physiology who

are candidates for creation of the Fontan

circulation

Anaesthetic protocols

• Adequately ventilated during the entireprocedure: Paco2 normal or slightly decreased

• Sao2 should be at precatheterisation level

• Low volume Ketamine + Midazolam

• Ketamine + Propofol

• Midazolam + Ramifentanyl

Jobeir A et al. Pediatr Cardiol 2003

Kogan A et al. J Cardiothorac Vasc Anaesth 2003

Laird TH et al. Anaesth Analg 2002

Signs of operability

• Pulmonary vascular resistance index <6 Wood

units times metre squared

• Resistance ratio of less than 0.3

• PVRI: 6-9, needs reversibility testing

• Fontan circulation: PVRI<3 woods units times

metre squared Khambdkone S et al. Circulation 2003

Reversibility testing

• Oxygen(100%)

• Inhaled nitric oxide

• Intravenous prostacyclin

• Intravenous isoprenaline

• Intravenous adenosine

Protocol

• Initial sample: breathing room air or 21-30%

oxygen inhalation for 10 minutes

• Repeat them after pure oxygen inhalation for

15 min

Signs of reversibility

• A decrease of around one-fifth in the index of

pulmonary vascular resistance

• A decrease of around one-fifth the ratio of

pulmonary to systemic vascular resistance

• A final pulmonary vascular resistance index of

less than 6 Wood units times metre squared

• A final ratio of resistance of less than 0.3

Antonio Augusto Lopes et al. Cardiol Young 2009

Cautions

• Elimination of the dissolved oxygen can

falsely increase pulmonary flow