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Complex scenarios: Low gradient in low EF AS patients

Authors: Martin Swaans, Philippe Pibarot.


 

Complex scenarios: Low-flow Low- gradient (LFLG) aortic stenosis in patients with a depressed LV ejection fraction

Severe aortic stenosis is defined as an aortic valve effective orifice area (AVA) ≤ 1.0 cm2 or ≤ 0.6 cm2 if indexed for body surface area and a mean transvalvular gradient ≥40 mmHg. Important is to note that gradients are a squared function of flow in the continuity equation. So even a modest decrease in left ventricular ejection fraction (LVEF) may result in a significant reduction in the transvalvular gradient. Low flow state can occur with both reduced LVEF (i.e. “Classical” Low-Flow) or preserved LVEF (“Paradoxical” Low-Flow).

 

Different subtypes of low-flow, low-gradient AoS Different subtypes of low-flow, low-gradient AoS Different subtypes of low-flow, low-gradient AoS
Normal-LVEF
Normal-flow
high-gradient
Normal-LVEF
"Paradoxical" low-flow
low-gradient
Normal-LVEF
"Calssical" low-flow
low-gradient
Different subtypes of low-flow, low-gradient AoS

 

It is estimated that 5% to 10% of the patients with a severe AoS have a low-flow low-gradient (LF-LG) severe aortic stenosis due to a decreased left ventricular ejection fraction. These patients typically have a dilated left ventricle with markedly decreased LVEF, most often due to ischemic heart disease and/or to afterload mismatch.1

 

http://www.youtube.com/watch?v=lQ_nt-HGtSo
http://www.youtube.com/watch?v=bD3I9ftfGAw
Normal-LVEF
"Paradoxical" Low-flow
Low-Gradient

LVEF=60%
SV=46mL
MG=29mmHg.
Low-LVEF
"Classical" Low-Flow
Low-Gradient

LVEF=25%
SV=42mL
MG=25mmHg.

 

A LF-LG severe aortic stenosis is defined as an aortic valve AVA ≤ 1.0 cm2 or indexed ≤ 0.6 cm2/m2, a mean transvalvular gradient < 40 mmHg and a LVEF ≤ 40 %. A low flow state is defined as a cardiac index < 3.0 l/min/m2 or a stroke volume of < 35ml/m2. Because the gradient especially depends on the flow per beat the latter is the most frequent used parameter. The stroke volume can be measured by pulsed wave Doppler in the left ventricular outflow tract.

It is necessary to distinguish between true severe and pseudosevere aortic stenosis (prevalence between 20% and 30% of the patients) since patients with pseudosevere stenosis may not benefit from aortic valve replacement. In a true severe AoS, the aortic valve is the primary culprit and the decreased LVEF is a secondary or concomitant phenomenon. Pseudosevere aortic stenosis is a result of decreased contractility due to myocardial disease whereas a true aortic stenosis is a primary valve problem.

Dobutamine stress echocardiography

To distinguish between true en pseudosevere aortic stenosis dobutamine stress echocardiography (DSE) may be helpful (Figure 2). A pseudosevere aortic stenosis will show an increase in AVA (peak stress AVA> 1.0-1.2 cm2) with none or relative little increase in transvalvular gradient (peak stress mean gradient

 

Figure 2
(Figure 2) - Usefulness of dobutamine stress echocardiography and multi-slice CT to differentiate true- versus pseud- severe stenosis and guide therapy in patients with classical (low LVEF), low-flow, low-gradient AoS.

 

 

Figure 3A.

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Figure 3A.

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Resting Echo

 

Figure 3A.

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Figure 3A.

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Dobutamine stress echo in a patient with flow reserve and pseudo-severe stenosis.

 

Resting Echo

Figure 3B.

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Figure 3B.

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Figure 3B.

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Figure 3B.

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Dobutamine stress echo in a patient with flow reserve and true severe stenosis.

 

In cases where DSE is inconclusive (e.g. peak stress AVA1.0 cm2 with a peak gradient >40 mmHg): the calculation of the projected AVA at normal flow rate might be helpful.

 

Aortic Valve
Area (cm2)
  Mean Transvalvular Flow Rate (ml/s).
AVAprojected=AVA at rest+ΔAVA/ΔQx(250 ml/s–Q at rest)=0.7+0.0025x(250–185)=0.86cm2

 

In this method, the AVA is plotted against the mean transvalvular flow (Q) at each stage of the DSE, and the AVA at a standardized flow rate of 250 ml/s is projected from the slope of the regression line fitting the plot of AVA vs. Q (projected AVA = AVA at rest + [(ΔAVA/ΔQ) x (250 – Q at rest)], where ΔAVA and ΔQ are, respectively, the increase in AVA and Q during DSE (Figure 4). A projected AVA ≤ 1.0 cm2 is used to discriminate between a true severe AoS and a pseudosevere AoS.2 It has been suggested that higher values of peak stress AVA and projected AVA (i.e. 1.2 vs. 1.0 cm2) should be used to differentiate true vs. pseudo-severe AS based on the fact that moderate-to-severe AS may be equivalent to severe AS for a depressed ventricle (Figure 2).1, 2

DSE is also useful to assess flow reserve. Absence of flow reserve (


CT Valve Calcium Scoring

An accurate and complementary method to TTE and DSE for the assessment of the severity of aortic stenosis is the measurement of the degree of aortic valve calcification with multislice computed tomography. An Agatston score > 1200 AU in women and >2000 AU in men has been shown to provide a good accuracy to distinguish severe from non-severe AoS.3 This method is particularly helpful in patients with no flow reserve given that, in these patients, stenosis severity often remains indeterminate at the outset of DSE (Figures 2 and 3CD).

 

http://www.youtube.com/watch?v=afBONByQN4I
http://www.youtube.com/watch?v=ZV7VItfEGPg
LVEF=25% SV=51ml
AVA=0.8cm2
ΔP=46/27mmHg.
LVEF=30% SV=57ml
AVA=0.8cm2
ΔP=52/30mmHg.
 
 
Figure 3C

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Figure 3C

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Resting Echo. Dobutamine Stress Echo.

 

Figure 3D
Patient with no flow reserve and severe stenosis.

References

  1. Pibarot P and Dumesnil JG. Low-flow, low-gradient aortic stenosis with normal and depressed left ventricular ejection fraction. J Am Coll Cardiol 2012; 60:1845-53.
  2. Blais C et al. The projected valve area at normal flow rate improves the assessment of stenosis severity in patients with low flow aortic stenosis: the multicenter TOPAS (Truly or Pseudo Severe Aortic Stenosis) study. Circulation 2006; 113:711-21.
  3. Cueff C et al. Measurement of aortic valve calcification using multislice computed tomography : correlation with haemodynamic severity of aortic stenosis and clinical implication for patient with low ejection fraction. Heart 2011; 97:721-6.
  4. Clavel MA, Burwash IG, Mundigler G et al. Validation of conventional and simplified methods to calculate projected valve area at normal flow rate in patients with low flow, low gradient aortic stenosis: the multicenter TOPAS (True or Pseudo Severe Aortic Stenosis) study. J Am Soc Echocardiogr 2010 April;23(4):380-6.
  5. Fougères É, Tribouilloy C, Monchi M et al. Outcomes of pseudo-severe aortic stenosis under conservative treatment. Eur Heart J 2012 June 24;33(19):2426-33.
  6. Clavel MA, Messika-Zeitoun D, Pibarot P et al. The complex nature of discordant severe calcified aortic valve disease grading: New insights from combined doppler-echocardiographic and computed tomographic study. J Am Coll Cardiol. In press 2013.