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Dobutamine Stress Echo Guidelines for Low-Flow, Low-Gradient Aortic Stenosis
Study Questions:
Are current American Heart Association (AHA)/American College of Cardiology (ACC) guideline criteria valid for the use of dobutamine stress echocardiography (DSE) in establishing the presence of low-flow, low-gradient (LFLG) severe aortic stenosis (AS) with reduced left ventricular ejection fraction (LVEF)?
Methods:
A cohort of 186 patients with LFLG AS and reduced LVEF was prospectively recruited and underwent DSE with measurement of the mean gradient, aortic valve area (AVA), and projected AVA (an estimate of AVA at a standardized normal flow rate). AS severity was independently assessed using one or both of two methods in 87 patients: by macroscopic evaluation of the valve at the time of valve replacement in 54 patients, by measurement of aortic valve calcium by computed tomography in 25 patients, and by both methods in eight (with concordant assessment in seven patients [88%]). According to these assessments, 50 of 87 patients (57%) had true-severe stenosis.
Results:
Peak DSE mean gradient ≥40 mm Hg, peak stress AVA ≤1.0 cm2, and the combination of peak stress mean gradient ≥40 mm Hg and peak stress AVA ≤1.0 cm2 correctly classified AS severity in 48%, 60%, and 47% of patients, respectively; whereas projected AVA ≤1.0 cm2 was better than all the previous markers (p < 0.007), with 70% correct classification. Among the subset of 88 patients managed conservatively (47% of cohort), 52 died during a follow-up of 2.8 ± 2.5 years. After adjustment for age, sex, functional capacity, chronic kidney failure, and peak stress LVEF; peak stress mean gradient and AVA were not predictors of mortality in this subset. In contrast, projected AVA ≤1.0 cm2 was a strong predictor of mortality with medical management (hazard ratio, 3.65; p = 0.0003).
Conclusions:
The authors concluded that, among patients with LFLG AS with reduced LVEF, AHA/ACC guideline criteria (cited as DSE peak stress mean gradient ≥40 mm Hg or the composite of peak stress mean gradient ≥40 mm Hg and peak stress AVA ≤1.0 cm2) have limited value to predict actual stenosis severity and outcomes. In contrast, the authors concluded that projected AVA better distinguishes true from pseudo-severe AS, and is strongly associated with mortality in patients with conservative management.
Perspective:
The 2014 AHA/ACC guidelines recommend distinguishing true-severe from pseudo-severe AS among patients with LFLG AS and reduced LVEF using DSE, with the criterion for severe AS of AVA ≤1.0 cm2 and Vmax ≥4.0 m/s at any flow rate. This study found that projected AVA (the AVA at a projected flow of 250 ml/min) using the formula:
Projected AVA = AVARest + ([AVAPeak – AVARest] / [QPeak – QRest]) x (250 – QRest)
was a better predictor of true-severe AS compared with peak stress mean gradient, peak stress AVA, or the combination. Because flows (and velocity / gradients) can rise and then fall during progressive stages of DSE, projected AVA ideally should be compared with the specific criteria used in the AHA/ACC guidelines — maximal AVA and maximal Vmax at any level of stress.
Keywords: Aortic Valve Stenosis, Cardiac Surgical Procedures, Constriction, Pathologic, Diagnostic Imaging, Echocardiography, Stress, Heart Valve Diseases, Kidney Failure, Chronic, Stroke Volume, Tomography, Ventricular Function, Left
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