Cardiac Cath Measurement of Stenotic Aortic Valve Area

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Cardiac Cath Measurement of Stenotic Aortic Valve
Area

• Ryan Tsuda, MD

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Case Report

• CC Shortness of Breath
• HPI 62 y/o Caucasian male, without previous
  significant medical history, presents with 6-8
  months of progressively worsening dyspnea.
  Recalls 1 month h/o new onset leg and belly
  swelling. Describes 2 pillow orthopnea and
  occasional PND. Denies CP, syncope, or
  lightheadedness.

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Case Report

• PMHx Childhood murmur
• Meds None
• All NKDA
• SHx Denies etoh, smoking, or illicit drugs
• FMHx Did not have a relationship with his
  family, and therefore, is was not familiar with
  their medical problems.

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Case Report

• PE
• 97.6 115 159/109 26
  1002L
• Gen Middle aged male with mild
• respiratory distress
• Neck Short and thick, No obvious jvd
• CV Tachycardic w/ RR, nl S1 S2, S3, 2/6
  
• crescendo decrescendo systolic
  murmur at URSB
• Pulm Mild bilateral base crackles
• Abd Diffuse abdominal wall edema,
  shifting dullness
• GU scrotal edema
• Ext 3 Bilateral pitting edema

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Case Report

• Na 143, K 4.3, Cl 105, CO2 30, BUN 23, Cr 1.3,
  Glu 108
• WBC 10.6 w/ NL diff, Hg 15.8, Hct 50.8, Platelets
  219,000 .
• Tprot 6.7, Alb 3.5, Ast 66, Alt 57, Alkphos 127,
  Tbili 1.2
• UA protein
• BNP 3690

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Case Report

• EKG STach 115, LVH
• CXR CM, Increased PVC, Small bil pleural
• effusions
• Initial A/P New CHF..Started on Natrecor,
• Lasix, Digoxin, Captopril, and
• AldactoneMore to
• follow

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Cardiac Cath Measurement of Stenotic Aortic Valve
Area

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

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Gorlin Formula

• Calculates cardiac valvular orifice area from
  flow and pressure-gradient data
• Incorporates 3 preexisting formulas
• 
  
  
  

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Gorlin Formula

• 1.) Torricellis Law (flow across a round
  orifice)
  
  
• F AVCc
• F Flow Rate
• A Orifice Area
• V Velocity of Flow
• Cc coefficient of orifice contraction
• (compensates for the physical phenomenon,
  that except for a perfect orifice, the area of a
  stream flowing through an orifice will be less
  than the true area of the orifice)

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Gorlin Formula

• 2.) Relates pressure gradient to velocity of flow
• V2 (Cv)2 x 2gh
• Cv coefficient of velocity, corrects for
  energy
• loss as pressure energy is converted
  to
• kinetic energy
• g acceleration due to gravity (980
  cm/sec/sec)
• h pressure gradient in cm H2O

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Gorlin Formula

• Combining the two equations, yields
• F
• A ----------------------------
• (C)(44.3) (sq root of h)
• C Empirical constant incorporating Cv and
  Cc, and accounting for h adjusted to units of
  mmHg, and correcting calculated valve area to
  actual valve area as measured at surgery or
  autopsy. Using this constant, the maximum
  derivation of calculated valve area from measured
  valve area was 0.2 cm2.

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Gorlin Formula

• Since antegrade aortic flow occurs only in
  systole, F is the total CO during which there is
  forward flow across the valve
• F CO/(SEP)(HR)
• F (cm3/sec)
• CO (cm3/min)
• SEP (sec/beat) HR (beats/min)

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

• Thus, the final Gorlin equation for the
  calculation of valve orifice area (in cm2) is
• 
  CO/(SEP)(HR)
• Area --------------------------------------
  --
• 44.3(C)(sq rt of pressure
  gradient)
• Where C empirical constant
• For MV, C 0.85 (Derived from
  comparative data)
  
  
  
  
• For AV, TV, and PV, C 1.0 (Not derived,
  is assumed based
• 
  on MV data)

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Alternative to the Gorlin Formula
A simplified formula for the calculation of
stenotic cardiac valves proposed by Hakki et
alCirculation 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
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Aortic Valve Area (cm2)

• Critical AS lt 0.7
• Moderate AS 0.7 1.5
• Mild AS 1.5 - 2.5
• NL Aortic Valve 2.5 - 3.5
• Ranges have variability based on body size (i.e.
  a larger person, requiring higher CO for
  perfusion, may become symptomatic at a larger
  aortic valve area)

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Relationship between CO and Aortic Pressure
Gradient over a range of values for AV area
(Based on Gorlin formula)
A
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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.
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Relationship between CO and Aortic Pressure
Gradient over a range of values for AV area
(Based on Gorlin formula)
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.
B
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Relationship between CO and Aortic Pressure
Gradient over a range of values for AV area
(Based on Gorlin formula)
C
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Acquiring Hemodynamic Data
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Acquiring Hemodynamic Data
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Acquiring Hemodynamic Data
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Acquiring Hemodynamic Data

• Indicator Dilution Method (CO)
• Based on the principle that a single
  injection of a known amount of indicator
  (cold/room temperature saline for thermodilution
  technique or indocyanine green dye) injected into
  the central circulation mixes completely with
  blood and changes concentration as it flows
  distally.

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Acquiring Hemodynamic Data

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

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Acquiring Hemodynamic Data
Accurate method of measuring CO, especially in
patients with low cardiac output.

• O2 consumption measured from metabolic hood or
  Douglas bag it can also be estimated as 3
  ml/min/kg or 125 ml/min/m2.
• AVo2 difference calculated from arterial mixed
  venous (pulmonary artery) O2 content, where
  O2 content saturation x 1.36 x Hg

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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 patients 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.
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Cardiac Output by Fick Method (example)
Arterial saturation 95 Pulmonary artery
saturation 65 Hg 13 O2 consumption is 210
ml/min (3 ml/kg given a 70 kg person)
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Pressure Gradients
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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.
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May then obtain mean pressure gradient across
aortic valve by planimetry
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In addition to time delay, peripheral artery
waveforms are distorted by systolic
amplification and widening of the pressure
waveforms.
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Errors in pressure gradient can also occur if,
during pullback, the LV catheter is placed in
the LV outflow tract
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Alternative to measuring transaortic valve
gradient using simultaneous LV and femoral
artery pressures, as introduced by Krueger et al.
at the University of Utah.
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Calculating Aortic Valve Area
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Calculating Aortic Valve Area (example)

• Mean aortic valve pressure gradient 40 mm Hg
• SEP 0.33 sec
• HR 74
• CO 5000 mL/min
• AV constant 44.3

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Calculating Aortic Valve Area (example)

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

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Assessment of Aortic Stenosis in Patients with
low Cardiac Output

• Valve calculations using the Gorlin formula
• are flow dependent. Therefore, low CO
  states may give an errantly low
• calculation of aortic valve area.
• Decreased flow through the stenotic valve in
  conjunction with decreased LV pressure,
  physically opens the valve to a lesser orifice
  area, and thus, the valve orifice really is
  smaller during low flow states.
• Should keep this in mind when calculating
  aortic valve area using standard techniques in
  patients with low cardiac output.

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Assessment of Aortic Stenosis in Patients with
low Cardiac Output

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

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Assessment of Aortic Stenosis in Patients with
low Cardiac Output

• Valve resistance may be an adjunct to the
  Gorlin equation in differentiating truly severe
  AS in patients with low cardiac output states.
  (Cannon et al.JACC 1992)
• (mean gradient)(SEP)(HR)(1.33)
• VR ------------------------------------
  ----
• CO
• Advantage of being calculated from two directly
  measured variables, and requires no discharge
  coefficient. Resistance appears to be less flow
  dependent than valve area.

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Patients with resistance gt 250 dynes sec cm -5
are more likely to have significant AS, while
those with resistance lt 200 dynes sec cm -5 are
less so.
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Case Report

• Echo Clips

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Case Report

• 2D-Echo
• LVEF 15-20
• Severely reduced RVEF
• 4-Chamber DCM
• Abnormal LV Relaxation
• Severe Aortic Stenosis (PK AV Vel 4.3
  m/s, Mean AV
• gradient 33 mmHg, AV area 1.0
  cm2)
• Mild Aortic Insufficiency, Mild Tricuspid
  
• Regurgitation, and Mild Mitral
• Regurgitation

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Gorlin Formula
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LHC RHC

• CO 4.2 L/min
• CI 2.2 L/min/m2
• RA pressure 12
• RV pressure 65/10-13
• PA pressure 56/41
• Wedge 32-35
• LV pressure 200/35
• Aortic pressure 150/85
• Simultaneous pressure gradient 48.5 mmHg
• Valve Flow 178 cm3/sec
• Mean gradient 60 mmHg
• Aortic Valve Area 0.52 cm2
• Distal LCX 80-90 prior to large PDA filling via
  right to left collaterals

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Case Report
LV to Aorta Pullback
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Case Report
Simultaneous pressure gradient
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Case Report
Planimetry of shaded area yields pressure
gradient
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Case Report

• Hospital Course and Discharge Plan
• Achieved adequate diuresis in the
  
• hospital
• Referral to CT Surgery for
• possible AVR and 1V-CABG

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Summary

• Cath measurement of aortic valve stenosis is
  based on the Gorlin formula.
• Proper calibration and procedural techniques
  using the catheter is important in acquiring
  accurate cardiac output and pressure gradients.
• During low cardiac output states (i.e. CHF), may
  need to use adjunctive techniques to acquire
  reliable hemodynamic data to calculate accurate
  aortic valve area, and in turn, make the
  appropriate recommendation regarding valve
  replacement.

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References

• Baim, Grossman. Grossmans Cardiac
  Catheterization, Angiography, and Intervention,
  6th Edition. 2000. pp 193-207.
• Kern, Morton. The Cardiac Catheterization
  Handbook, 2nd Edition. 1995. pp 108-138.
• Braunwald. Heart Disease, 6th Edition. 2001.
  pp 371-385.