Valve Area calculation & Shunt Detection And Quantification
Valve Area calculation & Shunt Detection And Quantification Dr Shajudeen 2nd year DM Resident Calculation of stenotic valve area GORLIN FORMULA: 1. Torricelli's law: Flow across a round orifice F = AV CC
F = Flow rate V = Velocity of flow A =F VCC A = Orifice area CC = Coefficient of orifice contraction 2. Pressure gradient and velocity of flow Relation - Torricelli's law
V = velocity of flow Cv = coefficient of velocity - correcting for energy loss as pressure energy is converted to kinetic or velocity energy h = pressure gradient in cm H2O g = gravitational constant (980 cm/sec2) for converting cm H2O to units of pressure GORLIN FORMULA: C = empirical constant accounting for CV and CC
h = mm Hg C - empirical constant ( 0.85 for mitral valve, 1.0 for Aortic valve) Flow (F) = Total cardiac output expressed in terms of the seconds per minute during which there is actually forward flow across the valve. F= CO (ml or cm3/min) SEP/DFP (sec/min) x HR
cm3 x min Min x Sec cm3 /sec Systolic ejection period calculation AREA CALCULATION FOR MITRAL VALVE & AORTIC VALVE Transvalvular gradient some definitions
Peak-to-Peak gradient : Difference between the peak left ventricular and aortic systolic pressure. No physiologic relevance for this because these peaks occur at different times. Peak instantaneous gradient : Represents the largest gradient that exists between the left ventricle and the aorta. Mean Gradient: Average of each instantaneous gradient that exists Gradient calculation LV-AO
For accurate LV AO gradient calculation by cath 1) Preffered catheter position for LV-Ao gradient calculation is LV body & Ascending aorta Rather than LV & FA 2) Use Simultaneously taken tracing from AO and LV 3) Use Two catheter or Dual Lumen catheter (Langston Catheter) LV-Femoral Artery Pressure Tracings and its realignment
A) Time Delay Between LV and FA tracing. (LV-Gradient overestimated by 9 mm Hg) B) After realignment ( LV- Ao Gradient underestimated by 10 mm Hg) Errors in gradient measurement 1) Systolic amplification and widening of pressure waveform A) LV-AO Gradient overestimated by 9 mm Hg B) LV- AO Gradient underestimated by 10mm Hg
Errors in gradient measurement 2) LV Catheter placed in LVOT Substantial pressure gradient between the body of the LV & LVOT . This is due to acceleration of blood as it enters the relatively narrow outflow tract VALVE AREA CALCULATION CHART Alternative formula to Gorlin: Hakki formula
Assumption: Heart rate x SEP or DFP x Constant 1 When compared to the traditional Gorlin formula the above formula may lead to significant disparity if tachycardia is present (heart rate >100 beats/min). Shunt Detection and Quantification Introduction Detection of LEFT to RIGHT SHUNT
Oximetry run PBF calcualtion SBF calculation Left to right shunt Detection & Quantification Flow Ratio (QP/QS) Limitation of oximetry method Other methods of left to right shunt Detection of RIGHT to LEFT SHUNT Bidirectional Shunt
SHUNT DETECTION AND QUANTIFICATION SHUNT : Detect Localisation Quantification POINTERS TO SUSPECT INTRA CARDIAC SHUNT Unexplained Systemic arterial desaturation PA Saturation Unexpectedly High
INTRODUCTION O2 CONTENT Total amount of oxygen present in a blood (O2 bound to Hb + Plasma Dissolved O2) Calcuted directly or derived O2 SATURATION O2 bound to Hb O2 CARRYING CAPACITY OF Hb = 1.36 ML O2 PER GRAM OF HB DISSOLVED O2 = 0.03 x Partial Pressure of O2 in mm Hg
RELATION BETWEEN O2 SATURATION AND CONTENT O2 content =O2 carrying capacity of Hb x % Saturation + Dissolved O2 Left to Right shunt: Oxygenated blood that bypasses the systemic vascular bed Right to left shunt: Deoxygenated blood that bypasses the pulmonary
vascular bed Admixture lesion: Anatomical defects facilitates the mixing of oxygenated & deoxygenated blood Transposition physiology: Anatomic abnormality preventing oxygenated blood reaching the systemic vascular bed Detection Of Left To Right Shunt L RT SHUNT : Detection need Significant O2 step up in
blood oxygen saturation or content in one of the right heart chamber/PA Significant Step up : Increase in blood O2 content or saturation that exceeds the normal variability that might be observed if multiple samples were drawn from that cardiac chamber Screening for Left To Right Shunt Take blood samples from SVC and PA if O 2
saturation between these is 8% ,It means Left to right shunt is there so do complete Oximetry run to locate and to quantify the shunt Catheter for Oximetry run End hole Catheter (Swan Ganz balloon flotation catheter) or one with side hole near close to its tip Catheter tip position adjusted by pressure measurement
2 ml blood should be taken from each site OXYMETRY RUN: Sample Collection sites Low SVC (Near junction with RA Left and/or Right PA MPA High SVC (Near junction with
RVOT Mid RV innominate vein) IVC high (just at or below RV near TV or Apex diaphragm)
RA (low or near TV). IVC low (at L4- L5) Mid RA. High RA LV .
GUIDELINES FOR OPTIMUM USE OF OXIMETRIC METHOD FOR SHUNT DETECTION AND QUANTIFICATION Blood samples at multiple sites should be obtained rapidly. Blood O2 saturation data rather than O2 content data are preferable Comparison of the mean of all values obtained in the
respective chambers is preferable to comparison of highest values in each chamber. Because of the important influence of SBF on shunt detection exercise should be used in equivocal cases where a low SBF is present at rest. GUIDELINES FOR OPTIMUM USE OF OXIMETRIC METHOD FOR SHUNT DETECTION AND QUANTIFICATION conti . . The sampling to be done with the patient breathing
room air or a gas mixture containing no more than a maximum of 30% oxygen Saturation data may be inaccurate in patients breathing more than 30% oxygen, as a significant amount of oxygen may be present in dissolved form in the pulmonary venous sample. Normal values for O2 saturation Detection of Left to Right Shunt by Oximetry
Criteria for Significant Step up Difference in Mean between Distal and Proximal chamber samples Difference in Highest value between Proximal and Distal chamber
Approximate Minimal Qp/Qs required to Detection ( Assuming SBFI=3L/min/M2 O2 % sat O2 vol % O2 % sat
O2 vol% Atrial 7 1.3 11
2 1.5-1.9 Ventricular 5 1
10 1.7 1.3-1.5 Great vessel 5
1 5 1 1.3 Any level
7 1.3 8 1.5 1.5
(SVC/IVC to RA (RA to RV) (RV to PA) Causes of O2 Step up at various level Atrial :
Ventricular ASD VSD PAPVC PDA with PR
RSOV to RA Ostium Primum ASD VSD with TR Coronary fistula to RV Coronary fistula to RA
Great vessels PDA AP window
Abberant coronary artery origin What to do if significant step up detected? Calculate PBF SBF Magnitude shunt MVO2 Calculation
The mixed venous oxygen content is the average oxygen content of the blood in the chamber proximal to the left to right shunt MVO2 ( At Rest) = 3 SVC O2 + 1 IVC O2 4 MVO2 ( At Exercise) = 1 SVC O2 + 2 IVC O2 3
Calculation of Pulmonary Blood flow (QP ) PV O2 = PA O2 = Pulmonary venous O2 concentration Pulmonary artery O2 concentration VALUES PULMONARY VEIN = 95% If systemic saturation 95%
If systemic saturation <95% check whether intra cardiac shunt present or not. If not there take value as 98% if there take the arterial saturation as pulmonary vein saturation CALCULATION OF SYSTEMIC BLOOD FLOW (QS ) SA O2 = Systemic Arterial O2 content MV O2 = Mixed Venous O2 content
Magnitude of shunt Expressed in terms of either Absolute blood flow across the shunt in L/mt or as a ratio of the PBF to SBF. Left to right shunt = Q p Q S or QP/QS Flow ratio Use O2 % saturation QP/QS Ratio
< 1 means Right to Left shunt < 1.5 but >1 means Small left to right shunt 2 Large left to Right shunt Limitation of oximetry method Absence of steady state during the collection of blood sample Lacks sensitivity Elevated SBF will cause mixed venous oxygen
saturation to be higher than normal and inter chamber variability will be blunted. If oxygen content is used for calculating the shunt rather than
O2 saturation Hb concentration will effect the result Small shunts or in the presence of high cardiac output (which decreases AVO2 difference) oximetry data loses its accuracy
The magnitude of the step-up varies with the oxygencarrying capacity of blood and the cardiac output. The relationship between the magnitude of step-up and the shunt flow is nonlinear and with increasing left-to-right shunting, a given change in shunt flow produces less of a change in the saturation step-up. Other method of shunt detection Indocyanine green curve Radionuclide technique
Contrast angiography Echocardiography Indocyanine green curve It can detect shunts too small to be detected by the oxygen step-up method IF negative , no need to perform an complete oximetry run. Procedure
Dye injection: Proximal chamber and a sample is taken from a distal chamber. Using a densitometer, the density of dye is displayed over time distal chamber L- RT shunt : Injected to PA sampling done at BA Finding: Early recirculation on the downslope of the dye curve Rt - Lt shunt : Injected into the right side of the heart proximal to the location of the suspected shunt and blood samples obtained from a BA
Findings: Distinct, early peak present on the upslope of the curve Indocyanine green curve Normal LEFT TO RIGHT SHUNT Limitation of Indocyanine green curve
It cannot locate the site of shunt Right to left shunt Angiography Selective angiography done for visualizing and locating the site of left to right shunt View LAO Cranial View: IV Septum, Sinus of Valsalva , AT Aorta , DT Aorta
Detection Of Right To Left Shunt R-L shunt suspected if cyanosis or arterial desaturation is there (<93%) If hypoxemia present aim is to find out the location and magnitude of the shunt Oximetry : Take Oximetry sampling from PV, LA, LV and Aorta First chamber which shows desaturation is the site
of shunt Disadvantage: In adults PV & LA entry difficult Other Methods to detect R to L shunt Contrast echocardiography Echo doppler technique Bidirectional flow
Effective Blood Flow (EBF) is the fraction of mixed venous return received by the lungs without contamination by the shunt flow or the oxygenated blood reaching the systemic circulation without the shunt blood Left to Right shunt = QP Q eff Right to left shunt = QS Q eff THANK U
MCQ 1 1) Normal SVC TO RA & RA to PA O2 saturation difference a) 3.9% 2.4%. & 2.3% 1.7% b) 6.7% 3.3% & 5.25% 2.8% c) 6% 1.5% & 3% 2.8%
d) 2.8% 1.2% & 2% 1.8% 2) To say Significant step in O2 saturation difference between Mean of distal chamber and proximal chamber samples in SVC/IVC to RA, RA to RV, RV to PA are a) 8, 4, 3 b) 7, 5, 5. c) 9, 8, 4. d) 1.3, 1, 1.
3) Equation for calculating MVO2 at exercise a)MVO2 = 3 SVC O2 + 1 IVC O2 4 b) MVO2 = 1 SVC O2 + 2 IVC O2 3 c) MVO2 = 2 SVC O2 + 3 IVC O2 4
d) MVO2 = 1 SVC O2 + 2 IVC O2 3 4) In Gorlins equation for calculation for MVA calculation what is the value for the constant C a) 0.65 b) 0.85 c) 0.95
d) 8.5 5) Identify and quantify the lesion Small to moderate ASD 6) Identify and quantify the lesion LARGE VSD
7) Indocyanine green curve indicates what? Normal ???????????
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