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Cardiac Cath Measurement of Stenotic Aortic Valve Area. Ryan Tsuda, MD. Case Report:. CC: Shortness of Breath
Ryan Tsuda, MD
97.6 115 159/109 26 100%2L
Gen: Middle aged male with mild
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
Initial A/P: New CHF…..Started on Natrecor,
Lasix, Digoxin, Captopril, and
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)
V2 = (Cv)2 x 2gh
Cv = coefficient of velocity, corrects for energy
loss as pressure energy is converted to
g = acceleration due to gravity (980 cm/sec/sec)
h = pressure gradient in cm H2O
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.
F = CO/(SEP)(HR)
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.
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)
*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………
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)
*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 = [ ------------------- ]
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.
*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.
*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.
*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).
*Accurate method of measuring CO, especially in patients with low cardiac output.
*Utilizes a polaragraphic oxygen sensor cell to measure oxygen content of
*Room air is withdrawn at a constant rate through a plastic hood over the
*Measures the contents of the hood (room air/expired air) through a flexible
tubing that feeds to the polaragraphic oxygen sensor.
*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.
Arterial saturation 95%
Pulmonary artery saturation 65%
Hg = 13
O2 consumption is 210 ml/min (3 ml/kg given a 70 kg person)
*Simultaneous tracings between site 1
and 3 would give the most accurate
*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.
*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
44.3(C)(sq rt of pressure gradient)
* 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.
*”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)
VR = ----------------------------------------
*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.
Severely reduced RVEF
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
*LV to Aorta Pullback
*Simultaneous pressure gradient
*Planimetry of shaded area yields pressure gradient
*Achieved adequate diuresis in the
*Referral to CT Surgery for
possible AVR and 1V-CABG