Acceleration Time in Aortic Stenosis

According to current guidelines, aortic stenosis (AS) in patients with preserved left ventricular (LV) ejection fraction is defined as a mean pressure gradient ≥40 mm Hg, corresponding to an aortic valve peak velocity ≥4 m/s or an aortic valve area (AVA) ≤1.0 cm2.1 However, up to 40% of patients may present an AVA in the severe range but without correspondingly high gradients and velocities.2 In such cases of discordant results, once a measurements error has been ruled out, patients who have indeed moderate AS should be differentiated from those with truly severe AS who may benefit from aortic valve replacement. Thus, additional parameters are necessary to refine the diagnostic workup of such AS patients. Severe AS is associated with a delay (tardus) and reduction (parvus) in the upstroke of the aortic pressure, beginning at aortic valve opening, thus resulting in a delay to achieve the maximal instantaneous transvalvular gradient, leading to an increase in acceleration time (AT) by continuous wave Doppler (Figure 1). In addition, although the ejection time (ET) increases in AS, it pseudonormalizes in patients with severe AS when LV dysfunction or low flow occur.3 Therefore, the ratio of AT over ET (AT/ET) integrates AS severity (AT), as well as its consequences on the LV (ET), an increased AT and relatively preserved ET resulting in an increased AT/ET. Indeed, we previously reported that decreased LV function, flow, and concentric geometry of the LV contribute to increase AT/ET beyond AS severity in a large cohort of patients with mild-to-severe AS.4 Importantly, higher systolic blood pressure is associated with a lower AT/ET. Indeed, an increase in systolic blood pressure induces compensatory lengthening of the ET and results in early systolic flow deceleration in the LV outflow tract due to the reflected waves occurring earlier, thereby inducing AT shortening.5 The interest of AT and the AT/ET ratio measured by continuous-wave Doppler flow in AS was first reported by Hatle et al6 in 1980 in a landmark study comparing hemodynamic and noninvasive data from 63 patients with moderate-to-severe AS. Pressure gradients were underestimated in one-third of patients by Doppler versus invasive measurement. The authors showed that a late peak velocity after midsystole helped to refocus the diagnosis toward severe AS. Of note, associated significant aortic regurgitation was associated with earlier peak systolic velocity. Normal values of AT and AT/ET have not been thoroughly investigated. We have observed a median AT and AT/ET (25th to 75th percentile) of 66 (58–75) and 0.24 (0.20– 0.27) ms, respectively, in 169 consecutive individuals (median age [25th to 75th percentile], 66 [51–73] years; 62% women) with normal echocardiograms (personal unpublished data). Reanalysis of individual data for the value of AT/ET for the 25 patients with moderate-to-severe AS published by Agatston et al7 in 1985 showed © 2021 American Heart Association, Inc. Circulation: Cardiovascular Imaging