Invasive Hemodynamic Characteristics of Low Gradient Severe Aortic Stenosis Despite Preserved Ejection Fraction
How do invasive hemodynamics compare with echocardiography/Doppler data among patients with echo/Doppler-defined low-flow low-gradient severe aortic stenosis (AS) with “paradoxical” normal left ventricular ejection fraction (LVEF)?
Echocardiographic and invasive hemodynamic data were compared from 58 patients (43% male, mean age 77 ± 5 years) with “paradoxical” low-flow low-gradient severe AS (aortic valve area <1 cm2, mean gradient <40 mm Hg, EF >50%). Data from 22 patients (45% male, mean age 73 ± 7 years) with conventionally defined severe AS (aortic valve area ≤1 cm2, mean gradient >40 mm Hg, EF ≥50%) also were analyzed.
In patients with “paradoxical” AS, orifice area by echo/Doppler (0.80 ± 0.15 cm2) and by catheterization showed modest agreement, whether stroke volume was measured by oxymetry (0.69 ± 0.16 cm2, bias +0.14 ± 0.17 cm2), or by thermodilution (0.85 ± 0.19 cm2, bias –0.03 ± 0.19 cm2). Mean systolic gradients were very similar (32 ± 7 mm Hg vs. 31 ± 6 mm Hg; bias –0.08 ± 7.8 mm Hg). In comparison, in patients with conventionally defined severe AS, orifice area by echo/Doppler was 0.72 ± 0.17 cm2 and by catheterization 0.51 ± 0.15 cm2 (oxymetry) and 0.68 ± 0.21 cm2 (thermodilution), respectively, and mean systolic gradient 51 ± 10 mm Hg and 55 ± 8 mm Hg, respectively. EF did not differ significantly between groups. Ascending aortic diameter was significantly smaller in the “paradoxical” AS group than in patients with conventionally defined severe AS (28 ± 5 mm vs. 31 ± 5 mm), and energy loss index was significantly larger (0.51 ± 0.12 cm2/m2 vs. 0.42 ± 0.09 cm2/m2, respectively). Heart rate and mean blood pressure during echo/Doppler and during catheterization were not significantly different.
The authors concluded that low-gradient severe AS despite preserved EF was confirmed by invasive hemodynamics, and was not the result of a systematic bias in the echo/Doppler calculation of aortic orifice area.
Aortic valve gradients are inversely related to the square of aortic valve area and directly related to the square of flow. Because of this, gradients can underestimate the severity of AS in any low-flow condition. Low-flow low-gradient severe AS typically has been associated with severe LV systolic dysfunction, in which a low-flow state is readily apparent. In 2007, Pibarot and colleagues first described patients (and associated adverse outcomes) with low-flow low-gradient severe AS with paradoxical normal LVEF (Hachicha Z, et al. Circulation 2007;115:2856-64). Among these patients, stroke volume is low despite normal LVEF presumably due to a small LV cavity and/or LV contractile dysfunction despite preserved LVEF. However, because echo/Doppler effective orifice area (EOA) is subject to error in calculation, controversy has existed as to whether low-flow low-gradient severe AS and paradoxical normal LVEF is mostly due to error in echo/Doppler calculation of EOA rather than genuine pathophysiology. It is certainly true that errors in echo/Doppler analysis can result in an incorrect EOA that underestimates true aortic valve area (and would incorrectly suggest the presence of low-flow low-gradient severe AS). However, data from this study suggest that, when calculated carefully and correctly, echo/Doppler EOA suggest that low-flow low-gradient severe AS with paradoxical normal LVEF is a real pathophysiological condition that can be confirmed on measurement of invasive hemodynamics. The echocardiographer has the responsibility to correctly diagnose severe AS using an integrated approach that does not rest solely on gradients or solely on EOA.
Keywords: Echocardiography, Doppler, Ventricular Function, Left, Oximetry, Catheterization, Stroke Volume, Blood Pressure, Heart Rate, Angioplasty, Balloon, Coronary, Hemodynamics
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