Low-gradient ‘severe’ aortic stenosis with preserved ejection fraction: new entity, or discrepant definitions?
Department of Cardiology, Herz-Zentrum Bad Krozingen, Südring 15, 79188 Bad Krozingen, Germany
* Corresponding author. Tel: +49 7633 402 0; fax: +49 7633 402 4409. E-mail address: nikolaus.jander{at}herzzentrum.de
Surgery of aortic valve stenosis (AS) is often dependent on whether stenosis is considered severe, as defined by aortic valve area (AVA) and/or mean pressure gradient (dPm) criteria set forth by the American College of Cardiology/American Heart Association and the European Society of Cardiology. Problems arise in determining whether AS is severe in patients with normal left-ventricular (LV) function who meet either an AVA criterion or a dPm criterion but not the other, especially in patients with low-gradient ‘severe’ AS (dPm 
40 mmHg, AVA < 1.0 cm2). This article considers whether low-gradient ‘severe’ AS with preserved ejection fraction (EF) is a new entity or merely an example of discrepant or inconsistent criteria for defining severe AS.
Studies concerning the frequency of inconsistent grading of severe AS by AVA and dPm criteria were reviewed, with a focus on factors that may give rise to inconsistency. Inconsistent grading was found to be frequent and more frequent with AVA determined by echocardiography than by catheterisation. Inconsistent grading may be due to low flow despite normal EF (low-flow severe AS); however, many patients show inconsistent grading with normal flow (NF) (NF non-severe AS), possibly because of inconsistent AVA and dPm cut-off values. Small errors in measuring the LV outflow tract diameter via echocardiography may lead to an inaccurate diagnosis of low-gradient ‘severe’ AS.
Low-gradient ‘severe’ AS with preserved EF is not a new clinical entity; the term encompasses many patients with truly severe AS and low stroke volume and the attendant serious prognosis associated with severe AS. Low-gradient ‘severe’ AS is also found in patients with NF; the prognosis and indications for surgical therapy for these patients are not well defined, particularly, in the presence of non-specific symptoms. Differentiation by transthoracic echocardiography of low-flow severe AS from NF non-severe AS may be difficult and may be aided by transoesophageal echocardiography and functional testing with exercise.
Key Words: Aortic valve stenosis • Severity • Grading • Low-gradient • Echocardiography