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Cardiac Cath Measurement of Stenotic Valve Orifice Area

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Cardiac Cath Measurement of Stenotic Valve Orifice Area Powered By Docstoc
					   Cardiac Cath
  Measurement of
Stenotic Aortic Valve
        Area
     Ryan Tsuda, MD
                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.
               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.
                    Case Report:
   PE:
            97.6 115 159/109 26            100%2L
    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
                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
               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
             Aldactone……More to
             follow………………………
     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
               Gorlin Formula
   Calculates cardiac valvular orifice area
    from flow and pressure-gradient data
   Incorporates 3 preexisting formulas
                     Gorlin Formula
   1.) Torricelli’s 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)
                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
                     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.
                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)
*SEP (systolic ejection period) begins with aortic valve opening and proceeds to
the dicrotic notch or other evidence of valve closure.
                        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)
    Alternative 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)
   Critical AS:           < 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)
Relationship between CO and Aortic Pressure Gradient
 over a range of values for AV area (Based on Gorlin
                       formula)
*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.
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.
Relationship between CO and Aortic Pressure Gradient
 over a range of values for AV area (Based on Gorlin
                       formula)
Acquiring Hemodynamic Data
Acquiring Hemodynamic Data
Acquiring Hemodynamic Data
    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.
    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).
     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
*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
              (example)

Arterial saturation 95%
Pulmonary artery saturation 65%
Hg = 13
O2 consumption is 210 ml/min (3 ml/kg given a 70 kg person)
Pressure 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
                 (example)
   Mean aortic valve pressure gradient = 40
    mm Hg
   SEP = 0.33 sec
   HR = 74
   CO = 5000 mL/min
   AV constant = 44.3
        Calculating Aortic Valve Area
                  (example)
                       CO/(SEP)(HR)
   A   =     ----------------------------------------
             44.3(C)(sq rt of pressure gradient)
   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.
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
  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.
*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
   Echo Clips…
             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
Gorlin Formula
                                 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
                        Case Report
*LV to Aorta Pullback
                          Case Report
*Simultaneous pressure gradient
                            Case Report
*Planimetry of shaded area yields pressure gradient
              Case Report:
   Hospital Course and Discharge Plan:

        *Achieved adequate diuresis in the
               hospital
        *Referral to CT Surgery for
               possible AVR and 1V-CABG
                   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.
                References
   Baim, Grossman. Grossman’s 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.

				
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posted:7/21/2011
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