Left to Right Shunts and their Calculation. Ghada El Shahed, MD

Transcription

1 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

2 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 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

4 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

5 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

6 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

7 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

8 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

9 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,

10 Left-to-Right Shunt Appearance and washout of dye produces initial 1 st pass curve followed by recirculation in normal adults Baim DS: Grossman s Cardiac Catheterization, Angiography, and Intervention. 7 th Edition. Lippincot Williams and Wilkins, Shunt Detection: Indocyanine Green Method Bashore, TM. Congenital Heart Disease in Adults. The Measurement of Intracardiac Shunts. In: CATHSAP II. Bethesda: American College of Cardiology,

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

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

13 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) 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

14 VSD SHUNT QUANTIFICATION 14

15 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

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

17 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

18 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

19 O2 content = 1.36 Hgb X saturation 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

20 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,

21 Using this principle, systemic and pulmonary flows can be calculated Pulmonary blood flow QP= 21

22 Shunt Measurement: Oximetric Methods 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) Shunt Detection & Measurement Oximetric Methods 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. 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

23 Shunt Detection & Measurement Oximetric Methods 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 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 = O 2 consumption (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 Baim DS: Grossman s Cardiac Catheterization, Angiography, and Intervention. 7 th Edition. Lippincot Williams and Wilkins,

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

25 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

26 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

27 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 = O 2 consumption (Pv MV O 2 ) x 10 = O 2 consumption (Pv Pa O 2 ) x 10 Bashore, TM. Congenital Heart Disease in Adults. The Measurement of Intracardiac Shunts. In: CATHSAP II. Bethesda: American College of Cardiology, Shunt Detection & Measurement 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 O 2 consumption = (PvO 2 Pa O 2 ) x 10 O 2 consumption (PvO 2 MVO 2 ) x 10 Bashore, TM. Congenital Heart Disease in Adults. The Measurement of Intracardiac Shunts. In: CATHSAP II. Bethesda: American College of Cardiology,

28 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. Baim DS: Grossman s Cardiac Catheterization, Angiography, and Intervention. 7 th Edition. Lippincot Williams and Wilkins, SOME TIPS FOR QP, QS CALCULATIONS 28

29 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

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

31 Cardiac Output Measurement Fick Oxygen Method 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 Baim DS: Grossman s Cardiac Catheterization, Angiography, and Intervention. 7 th Edition. Lippincot Williams and Wilkins, 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 Baim DS: Grossman s Cardiac Catheterization, Angiography, and Intervention. 7 th Edition. Lippincot Williams and Wilkins,

32 Concentration 3/18/2013 Cardiac Output Measurement Indicator Dilution Methods Stewart-Hamilton Equation CO = Indicator amount 0 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) Baim DS: Grossman s Cardiac Catheterization, Angiography, and Intervention. 7 th Edition. Lippincot Williams and Wilkins, Cardiac Output Measurement Indocyanine Green Method 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 Baim DS: Grossman s Cardiac Catheterization, Angiography, and Intervention. 7 th Edition. Lippincot Williams and Wilkins, time CO inversely proportional to area under curve 32

33 Cardiac Output Measurement Indocyanine Green Method 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 Baim DS: Grossman s Cardiac Catheterization, Angiography, and Intervention. 7 th Edition. Lippincot Williams and Wilkins, THERMODILUTION 33

34 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

35 Cardiac Output Measurement Thermodilution Method CO = V I (T B -T I ) (S I x C I / S B x C B ) x 60 T B dt 0 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 Baim DS: Grossman s Cardiac Catheterization, Angiography, and Intervention. 7 th Edition. Lippincot Williams and Wilkins, Cardiac Output Measurement 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 Baim DS: Grossman s Cardiac Catheterization, Angiography, and Intervention. 7 th Edition. Lippincot Williams and Wilkins,

36 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 Baim DS: Grossman s Cardiac Catheterization, Angiography, and Intervention. 7 th Edition. Lippincot Williams and Wilkins, Importance of accurate calculation & avoiding pitfalls Shunt size >>>> surgical decision Flow is used to calculate resistance 36

37 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