Upload
gopal-ghosh
View
237
Download
1
Embed Size (px)
Citation preview
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