The term ‘severe aortic stenosis (AS)’ carries a hefty prognostic connotation; it should oblige diligent workup, cautious interval follow-up or intervention on the patient.1 Trained as problem solvers, we aspire to develop a ‘theory of everything’ for diagnosis and management of complex illness, and AS has not escaped our efforts. For example, until recently, a patient with normal left ventricular EF unable to generate a mean gradient (MG) >40 mm Hg (or peak velocity >4 m/s) across a calcified and restricted aortic valve was deemed not to harbour severe AS. We now know that this oversimplification may exclude from potentially life-saving intervention a number of ‘paradoxical low-flow’ patients with substantial AS who despite having a normal EF and MG <40 mm Hg, have the same or worse prognosis as patients who generate the time-honoured ‘cut-off’ gradient.2 Thus, flow-dependent echocardiographic parameters (peak velocity and MG), despite having excellent correlation between them1 and proven prognostic value,3 do not always reflect disease severity. Interestingly, the aortic valve area (AVA), a flow-independent parameter, remains abnormally decreased (<1 cm²) in most of these ‘paradoxical low-flow’ patients, serving as a clue for their diagnosis.4

Paradoxical low-flow is partly to blame for the parameter inconsistencies found in echocardiographic severe-AS grading (defined as MG <40 mm Hg and AVA <1 cm²).5 The prevalence of severe-AS grading inconsistencies has now been studied in over 11 000 patients,1 ,5 and one out of three patients exhibits inconsistent severe-AS grading. However, there are also a significant number of patients without paradoxical low-flow (normal flow) and normal EF who also have ‘discordant’ severe AS1 with MG <40 mm Hg and AVA <1 cm², and the opposite as …