- This study evaluated the effect of transvalvular flow rate on the prognostic value of aortic valve area (AVA) in 1,131 patients with moderate to severe aortic stenosis
- The prognostic value of AVA for mortality was dependent on the transvalvular flow rate at the time of AVA measurement
- Current guidelines about classifying the severity of aortic stenosis based on low AVA ignore transvalvular flow rate and thus cannot be applied uniformly
- The researchers offer an algorithm for incorporating transvalvular flow rate into the assessment of aortic stenosis
Aortic valve area (AVA) is a central criterion for assessing the severity of aortic stenosis (AS). Severe AS is defined as both low AVA (≤1.0 cm2 in Europe, <1.0 cm2 in the U.S.) and high mean gradient (≥40 mm Hg).
AVA is highly dependent on the transvalvular flow rate (Q), the average volume of blood passing through the aortic valve per unit of time during ventricular ejection. Q is calculated as the ratio of stroke volume to ejection time. Therefore, at low Q, maximal ("true") AVA may not be induced due to inadequate valve opening.
In the Journal of the American College of Cardiology, Mayooran Namasivayam, MBBS, PhD, research fellow in Medicine, and Judy Hung, MD, director of the Echocardiography Lab in the Corrigan Minehan Heart Center at Massachusetts General Hospital, and colleagues confirmed that low AVA measured at low Q does not reliably detect severe AS. This novel finding has the potential to widely affect clinical care, and the researchers offer an algorithm for incorporating Q into the assessment of AS.
The researchers calculated Q for each of 1,131 patients with moderate or severe AS (AVA ≤1.5 cm2 or mean gradient ≥20 mm Hg) who underwent echocardiography between 2006 and 2016.
Most patients had normal ejection fraction, which is clinically important. Low-gradient AS with preserved EF is far more prevalent than low-gradient AS with reduced EF and is an area of diagnostic uncertainty in severe AS.
Effect of Q on Prognostic Value of AVA
Median follow-up time was 3.9 years (maximum, 7.3 years). Q determined the prognostic value of AVA:
- For patients with Q below the median (≤242 mL/s), AVA ≤1.0 cm2 was not prognostic for mortality
- For patients with Q above the median, AVA ≤1.0 cm2 was highly prognostic for mortality (HR, 1.66; 95% CI, 1.19–2.33; P = .003)
This difference was not affected by age, sex, valve replacement, comorbidity, medication or other echocardiographic data. The optimal cutoff for Q as a prognostic marker was 210 mL/s.
The results were similar in a validation cohort of 939 patients from the Quebec Heart and Lung Institute for whom follow-up was longer (median, 5.8 years; maximum, 13.5 years).
Reconsidering the Algorithm
In light of these study findings, the definition of severe aortic stenosis based on low AVA cannot be applied uniformly. Q should be incorporated into the classification algorithm for AS diagnosis and severity:
- AVA ≤1.0 cm2 and mean gradient ≥40 mm Hg: severe AS
- AVA ≤1.0 cm2 and mean gradient <40 mm Hg—consider Q as follows:
- Q ≤ 210 mL/s: AVA is not prognostic for mortality; assess the patient with an alternative modality such as computed tomography calcium score
- Q > 210 mL/s: severe AS
As this algorithm shows, Q assessment can help with the common problem of having to clarify true AS severity when measures are discordant (AVA ≤1.0 cm2 but mean gradient <40 mm Hg).
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