cardiac cath measurement of stenotic aortic valve area ryan tsuda, md

Cardiac Cath Cardiac Cath Measurement of Measurement of

Stenotic Aortic Valve Stenotic Aortic Valve AreaArea

Ryan Tsuda, MDRyan Tsuda, MD

Case Report:Case Report:

CC: Shortness of BreathCC: Shortness of Breath HPI: 62 y/o Caucasian male, without HPI: 62 y/o Caucasian male, without

previous significant medical history, previous significant medical history, presents with 6-8 months of progressively presents with 6-8 months of progressively worsening dyspnea. Recalls 1 month h/o worsening dyspnea. Recalls 1 month h/o new onset leg and belly swelling. new onset leg and belly swelling. Describes 2 pillow orthopnea and Describes 2 pillow orthopnea and occasional PND. Denies CP, syncope, or occasional PND. Denies CP, syncope, or lightheadedness.lightheadedness.


PMHx: Childhood murmurPMHx: Childhood murmur Meds: NoneMeds: None All: NKDAAll: NKDA SHx: Denies etoh, smoking, or illicit SHx: Denies etoh, smoking, or illicit

drugsdrugs FMHx: Did not have a relationship FMHx: Did not have a relationship

with his family, and therefore, is was with his family, and therefore, is was not familiar with their medical not familiar with their medical problems.problems.

Case Report:Case Report: PE:PE: 97.6 115 159/109 26 100%2L97.6 115 159/109 26 100%2L Gen: Middle aged male with mild Gen: Middle aged male with mild respiratory distressrespiratory distress Neck: Short and thick, No obvious jvdNeck: Short and thick, No obvious jvd CV: Tachycardic w/ RR, nl S1 S2, +S3, 2/6 CV: Tachycardic w/ RR, nl S1 S2, +S3, 2/6 crescendo decrescendo systolic murmur at crescendo decrescendo systolic murmur at

URSBURSB Pulm: Mild bilateral base cracklesPulm: Mild bilateral base crackles Abd: Diffuse abdominal wall edema, +shifting Abd: Diffuse abdominal wall edema, +shifting

dullnessdullness GU: +scrotal edemaGU: +scrotal edema Ext: 3+ Bilateral pitting edemaExt: 3+ Bilateral pitting edema


Na 143, K 4.3, Cl 105, CO2 30, BUN Na 143, K 4.3, Cl 105, CO2 30, BUN 23, Cr 1.3, Glu 108………23, Cr 1.3, Glu 108………

WBC 10.6 w/ NL diff, Hg 15.8, Hct WBC 10.6 w/ NL diff, Hg 15.8, Hct 50.8, Platelets 219,000 …….50.8, Platelets 219,000 …….

Tprot 6.7, Alb 3.5, Ast 66, Alt 57, Tprot 6.7, Alb 3.5, Ast 66, Alt 57, Alkphos 127, Tbili 1.2Alkphos 127, Tbili 1.2

UA: +proteinUA: +protein BNP 3690 BNP 3690


EKG: STach 115, LVHEKG: STach 115, LVH CXR: CM, Increased PVC, Small bil pleural CXR: CM, Increased PVC, Small bil pleural

effusionseffusions

Initial A/P: New CHF…..Started on Initial A/P: New CHF…..Started on Natrecor, Natrecor,

Lasix, Digoxin, Captopril, and Lasix, Digoxin, Captopril, and

Aldactone……More to Aldactone……More to

follow………………………follow………………………

Cardiac Cath Measurement of Cardiac Cath Measurement of Stenotic Aortic Valve AreaStenotic Aortic Valve Area

As valvular stenosis develops, the As valvular stenosis develops, the valve orifice produces more valve orifice produces more resistance to blood flow, resulting in resistance to blood flow, resulting in a pressure gradient (pressure drop) a pressure gradient (pressure drop) across the valveacross the valve

Gorlin Formula Gorlin Formula

Calculates cardiac valvular orifice Calculates cardiac valvular orifice area from flow and pressure-gradient area from flow and pressure-gradient datadata

Incorporates 3 preexisting formulas Incorporates 3 preexisting formulas

Gorlin FormulaGorlin Formula 1.) Torricelli’s Law (flow across a round orifice) 1.) Torricelli’s Law (flow across a round orifice)

F = AVCc F = AVCc

F = Flow RateF = Flow Rate A = Orifice AreaA = Orifice Area V = Velocity of FlowV = Velocity of Flow Cc = coefficient of orifice contractionCc = coefficient of orifice contraction (compensates for the physical phenomenon, that except for (compensates for the physical phenomenon, that except for

a perfect orifice, the area of a stream flowing through an a perfect orifice, the area of a stream flowing through an orifice will be less than the true area of the orifice)orifice will be less than the true area of the orifice)

Gorlin FormulaGorlin Formula 2.) Relates pressure gradient to velocity of flow2.) Relates pressure gradient to velocity of flow

V2 = (Cv)2 x 2ghV2 = (Cv)2 x 2gh Cv = coefficient of velocity, corrects for Cv = coefficient of velocity, corrects for

energy energy loss as pressure energy is converted to loss as pressure energy is converted to kinetic energy kinetic energy g = acceleration due to gravity (980 g = acceleration due to gravity (980

cm/sec/sec) cm/sec/sec) h = pressure gradient in cm H2O h = pressure gradient in cm H2O

Gorlin FormulaGorlin Formula Combining the two equations, yields:Combining the two equations, yields:

FF A = ----------------------------A = ---------------------------- (C)(44.3) (sq root of h) (C)(44.3) (sq root of h)

C = Empirical constant incorporating Cv and Cc, and C = Empirical constant incorporating Cv and Cc, and accounting for h adjusted to units of mmHg, and correcting accounting for h adjusted to units of mmHg, and correcting calculated valve area to actual valve area as measured at calculated valve area to actual valve area as measured at surgery or autopsy. Using this constant, the maximum surgery or autopsy. Using this constant, the maximum derivation of calculated valve area from measured valve derivation of calculated valve area from measured valve area was 0.2 cm2.area was 0.2 cm2.

Gorlin FormulaGorlin Formula

Since antegrade aortic flow occurs only in Since antegrade aortic flow occurs only in systole, F is the total CO during which systole, F is the total CO during which there is forward flow across the valvethere is forward flow across the valve

F = CO/(SEP)(HR)F = CO/(SEP)(HR)

F (cm3/sec) F (cm3/sec)

CO (cm3/min)CO (cm3/min)

SEP (sec/beat) HR (beats/min) SEP (sec/beat) HR (beats/min)

*SEP (systolic ejection period) begins with aortic valve opening and proceeds to the dicrotic notch or other evidence of valve closure.

Gorlin FormulaGorlin Formula Thus, the final Gorlin equation for the calculation of valve orifice Thus, the final Gorlin equation for the calculation of valve orifice

area (in cm2) is:area (in cm2) is:

CO/(SEP)(HR)CO/(SEP)(HR) Area = ----------------------------------------Area = ---------------------------------------- 44.3(C)(sq rt of pressure 44.3(C)(sq rt of pressure

gradient)gradient)

Where C = empirical constant Where C = empirical constant For MV, C = 0.85 (Derived from comparative data) For MV, C = 0.85 (Derived from comparative data)

For AV, TV, and PV, C = 1.0 (Not derived, is assumed based For AV, TV, and PV, C = 1.0 (Not derived, is assumed based on MV data)on MV data)

Alternative to the Gorlin FormulaAlternative to the Gorlin Formula

*A simplified formula for the calculation of stenotic cardiac valves proposed by Hakki et al…Circulation 1981. Tested 100 patients with either AS or MS.

*Based on the observation that the product of HR, SEP or DFP, and the Gorlin equation constant was nearly the same for all patients measured in the resting state (pt. not tachycardic). Values of this product were close to 1.0.

*Calculations somewhat comparable………

Aortic Valve Area (cm2)Aortic Valve Area (cm2) Critical AS: < 0.7 Critical AS: < 0.7 Moderate AS: 0.7 – 1.5 Moderate AS: 0.7 – 1.5 Mild AS: 1.5 - 2.5Mild AS: 1.5 - 2.5 NL Aortic Valve: 2.5 - 3.5NL Aortic Valve: 2.5 - 3.5

*Ranges have variability based on body size *Ranges have variability based on body size (i.e. a larger person, requiring higher CO (i.e. a larger person, requiring higher CO for perfusion, may become symptomatic at for perfusion, may become symptomatic at a larger aortic valve area) a larger aortic valve area)

Relationship between CO and Aortic Pressure Gradient Relationship between CO and Aortic Pressure Gradient over a range of values for AV area (Based on Gorlin over a range of values for AV area (Based on Gorlin

formula)formula)

A

*As HR increases (i.e. during exercise), the SEP shortens. However, SEP shortening is attenuated by increased venous return and peripheral arteriolar vasodilation. CO / (HR)(SEP) 2 Change in pressure = [ ------------------- ] (44.3)(AVA)

Therefore, the increase in CO will be partially offset by the increase in (HR)(SEP), so that the gradient across the valve will not quadruple with a doubling of CO during exercise.


formula)formula)

B

*As HR slows in patients with AS, the SV increases if CO remains constant. Thus, Flow across the valve increases, as does the pressure gradient.


formula) formula)

C

Acquiring Hemodynamic DataAcquiring Hemodynamic Data


Indicator Dilution Method (CO):Indicator Dilution Method (CO): *Based on the principle that a single *Based on the principle that a single

injection of a known amount of injection of a known amount of indicator (cold/room temperature indicator (cold/room temperature saline for thermodilution technique saline for thermodilution technique or indocyanine green dye) injected or indocyanine green dye) injected into the central circulation mixes into the central circulation mixes completely with blood and changes completely with blood and changes concentration as it flows distally. concentration as it flows distally.


Thermodilution Indicator Method:Thermodilution Indicator Method:

*Rapidly inject 10 cc of saline through *Rapidly inject 10 cc of saline through proximal port of PA catheter. An external proximal port of PA catheter. An external thermistor measures the temperature of thermistor measures the temperature of the injectate. Complete mixing of saline the injectate. Complete mixing of saline with blood causes a decrease in the blood with blood causes a decrease in the blood temperature, which is sensed by a distal temperature, which is sensed by a distal thermistor. Computer calculates CO based thermistor. Computer calculates CO based on the change in indicator concentration on the change in indicator concentration (using temperature over time).(using temperature over time).


O2 consumption measured from metabolic O2 consumption measured from metabolic hood or Douglas bag; it can also be estimated hood or Douglas bag; it can also be estimated

as as 3 ml/min/kg or 125 ml/min/m2.3 ml/min/kg or 125 ml/min/m2. AVo2 difference calculated from arterial – AVo2 difference calculated from arterial –

mixed venous (pulmonary artery) O2 content, mixed venous (pulmonary artery) O2 content, where O2 content = saturation x 1.36 x Hgwhere O2 content = saturation x 1.36 x Hg

*Accurate method of measuring CO, especially in patients with low cardiac output.

*Metabolic Hood (Polaragraphic method) *Utilizes a polaragraphic oxygen sensor cell to measure oxygen content of expired air. *Room air is withdrawn at a constant rate through a plastic hood over the patient’s head. *Measures the contents of the hood (room air/expired air) through a flexible tubing that feeds to the polaragraphic oxygen sensor.

*Douglas Bag *Patient is asked to breathe into a large, sealed, air-tight bag for a specific period of time. *The mouthpiece to the bag has a two-way valve. *Allows patient to inspire room air, while the expired air (pt. wears a nose clip) goes into the Douglas bag. *After the specified interval, the bag is sealed and the contents analyzed.

Cardiac Output by Fick Method Cardiac Output by Fick Method (example)(example)

Arterial saturation 95%Pulmonary artery saturation 65%Hg = 13O2 consumption is 210 ml/min (3 ml/kg given a 70 kg person)

Pressure GradientsPressure Gradients

*Multiple sites for recording transaortic valve gradients *Simultaneous tracings between site 1 and 3 would give the most accurate pressure gradient

*Usually use sequential readings (pullback) from 1 to 3, and use simultaneous tracings at 1 + 5

*Assey et al. measured the transaortic valve gradients in 15 patients from eight different combinations of catheter locations. In some patients, the differences in gradient among the different measurement sites were as much as 45 mmHg.

May then obtain mean pressure gradient across aortic valve by planimetry

*In addition to time delay, peripheral artery waveforms are distorted by systolic amplification and widening of the pressure waveforms.

*Errors in pressure gradient can also occur if, during pullback, the LV catheter is placed in the LV outflow tract

*Alternative to measuring transaortic valve gradient using simultaneous LV and femoral artery pressures, as introduced by Krueger et al. at the University of Utah.

Calculating Aortic Valve Area

Calculating Aortic Valve Area Calculating Aortic Valve Area (example)(example)

Mean aortic valve pressure gradient Mean aortic valve pressure gradient = 40 mm Hg= 40 mm Hg

SEP = 0.33 secSEP = 0.33 sec HR = 74HR = 74 CO = 5000 mL/minCO = 5000 mL/min AV constant = 44.3AV constant = 44.3

Calculating Aortic Valve Area Calculating Aortic Valve Area (example)(example)

CO/(SEP)(HR)CO/(SEP)(HR) A = ----------------------------------------A = ---------------------------------------- 44.3(C)(sq rt of pressure gradient)44.3(C)(sq rt of pressure gradient)

Assessment of Aortic Stenosis in Assessment of Aortic Stenosis in Patients with low Cardiac OutputPatients with low Cardiac Output

* Valve calculations using the Gorlin formula* Valve calculations using the Gorlin formula are flow dependent. Therefore, low CO states may give an errantly low are flow dependent. Therefore, low CO states may give an errantly low calculation of aortic valve area. calculation of aortic valve area.

* Decreased flow through the stenotic valve in conjunction with decreased LV * Decreased flow through the stenotic valve in conjunction with decreased LV pressure, physically opens the valve to a lesser orifice area, and thus, the pressure, physically opens the valve to a lesser orifice area, and thus, the valve orifice really is smaller during low flow states. valve orifice really is smaller during low flow states.

* Should keep this in mind when calculating aortic valve area * Should keep this in mind when calculating aortic valve area using standard techniques in patients with low cardiac using standard techniques in patients with low cardiac output. output.


In patients with AS, an In patients with AS, an infusion of infusion of nitroprusside or nitroprusside or dobutamine dobutamine substantially increases substantially increases forward output, and forward output, and may substantially may substantially decrease the decrease the transvalvular gradient.transvalvular gradient.

Potentially dangerousPotentially dangerous


*”Valve resistance” may be an adjunct to the Gorlin *”Valve resistance” may be an adjunct to the Gorlin equation in differentiating truly severe AS in equation in differentiating truly severe AS in patients with low cardiac output states. (Cannon patients with low cardiac output states. (Cannon et al….JACC 1992) et al….JACC 1992)

(mean gradient)(SEP)(HR)(1.33)(mean gradient)(SEP)(HR)(1.33) VR = ----------------------------------------VR = ---------------------------------------- COCO

*Advantage of being calculated from two directly *Advantage of being calculated from two directly measured variables, and requires no discharge measured variables, and requires no discharge coefficient. Resistance appears to be less flow coefficient. Resistance appears to be less flow dependent than valve area. dependent than valve area.

*Patients with resistance > 250 dynes sec cm -5 are more likely to have significant AS, while those with resistance < 200 dynes sec cm -5 are less so.

Case Report Case Report

Echo Clips…Echo Clips…


2D-Echo:2D-Echo:

LVEF 15-20%LVEF 15-20%

Severely reduced RVEFSeverely reduced RVEF

4-Chamber DCM4-Chamber DCM

Abnormal LV RelaxationAbnormal LV Relaxation

Severe Aortic Stenosis (PK AV Vel 4.3 m/s, Severe Aortic Stenosis (PK AV Vel 4.3 m/s, Mean AV Mean AV

gradient 33 mmHg, AV area 1.0 cm2) gradient 33 mmHg, AV area 1.0 cm2)

Mild Aortic Insufficiency, Mild Tricuspid Mild Aortic Insufficiency, Mild Tricuspid

Regurgitation, and Mild Mitral Regurgitation, and Mild Mitral

RegurgitationRegurgitation

Gorlin FormulaGorlin Formula

LHC + RHCLHC + RHC CO 4.2 L/minCO 4.2 L/min CI 2.2 L/min/m2CI 2.2 L/min/m2 RA pressure 12RA pressure 12 RV pressure 65/10-13RV pressure 65/10-13 PA pressure 56/41PA pressure 56/41 Wedge 32-35Wedge 32-35 LV pressure 200/35LV pressure 200/35 Aortic pressure 150/85Aortic pressure 150/85

Simultaneous pressure gradient 48.5 Simultaneous pressure gradient 48.5 mmHgmmHg

Valve Flow 178 cm3/secValve Flow 178 cm3/sec Mean gradient 60 mmHgMean gradient 60 mmHg

Aortic Valve Area 0.52 cm2 Aortic Valve Area 0.52 cm2

Distal LCX 80-90% prior to large PDA filling via right to left collateralsDistal LCX 80-90% prior to large PDA filling via right to left collaterals

Case ReportCase Report*LV to Aorta Pullback

Case ReportCase Report*Simultaneous pressure gradient

Case ReportCase Report*Planimetry of shaded area yields pressure gradient


Hospital Course and Discharge Plan: Hospital Course and Discharge Plan:

*Achieved adequate diuresis in *Achieved adequate diuresis in the the

hospital hospital

*Referral to CT Surgery for *Referral to CT Surgery for

possible AVR and 1V-CABGpossible AVR and 1V-CABG

Summary:Summary: Cath measurement of aortic valve stenosis Cath measurement of aortic valve stenosis

is based on the Gorlin formula.is based on the Gorlin formula. Proper calibration and procedural Proper calibration and procedural

techniques using the catheter is important techniques using the catheter is important in acquiring accurate cardiac output and in acquiring accurate cardiac output and pressure gradients. pressure gradients.

During low cardiac output states (i.e. CHF), During low cardiac output states (i.e. CHF), may need to use adjunctive techniques to may need to use adjunctive techniques to acquire reliable hemodynamic data to acquire reliable hemodynamic data to calculate accurate aortic valve area, and calculate accurate aortic valve area, and in turn, make the appropriate in turn, make the appropriate recommendation regarding valve recommendation regarding valve replacement.replacement.

ReferencesReferences

Baim, Grossman. Grossman’s Baim, Grossman. Grossman’s Cardiac Catheterization, Cardiac Catheterization, Angiography, and Intervention, 6Angiography, and Intervention, 6thth Edition. 2000. pp 193-207.Edition. 2000. pp 193-207.

Kern, Morton. The Cardiac Kern, Morton. The Cardiac Catheterization Handbook, 2Catheterization Handbook, 2ndnd Edition. 1995. pp 108-138.Edition. 1995. pp 108-138.

Braunwald. Heart Disease, 6Braunwald. Heart Disease, 6thth Edition. 2001. pp 371-385. Edition. 2001. pp 371-385.

cardiac cath measurement of stenotic aortic valve area ryan tsuda, md

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