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Aortic valve area: too important for splendid isolation
  1. Jan Minners
  1. Department of Cardiology, University Heart Center Freiburg, Bad Krozingen, Germany
  1. Correspondence to Dr Jan Minners, Department of Cardiology, University Heart Center Freiburg, Bad Krozingen, 79189, Germany; Jan.Minners{at}universitaets-herzzentrum.de

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Echocardiography is the key diagnostic modality for the assessment of aortic stenosis (AS) with a number of parameters available to estimate stenosis severity. Morphological criteria including calcification and reduced leaflet mobility are supplemented by flow dependent (jet velocity and mean pressure gradient) and largely flow-independent parameters (aortic valve area, aortic valve area index and velocity ratio).1 2 In the majority of patients, consistent results regarding stenosis severity will be obtained over the range of parameters. However, depending on the population under study, up to 30% of patients will demonstrate discrepant stenosis severity between flow-dependent (eg, mean pressure gradient) and flow-independent (aortic valve area) markers, with the latter commonly indicating a higher grade stenosis.3

Two developments over the last decades have augmented the problem of discrepant stenosis severity. First, there has been a trend in guidelines towards easing the partition values for the assessment of AS severity with an emphasis on aortic valve area .1 2 The threshold for severe stenosis according to mean pressure gradient moved from 50 mm Hg to 40 mm Hg and according to aortic valve area from <0.8 cm2 to <1 cm2 (with an often unrecognised twitch from <1 to ≤1 cm22  toin the latest guidelines), resulting in a substantial increase in the number of patients with discrepant grading of stenosis severity. Second, flow-dependent parameters, although equipped with robust outcome data, have come under scrutiny over the last 10 years. The concept of low flow despite apparently normal ejection fraction (paradoxical low flow low gradient severe AS, using stroke volume index as an approximation to flow with a cut-off of ≤35 mL/m2) has highlighted the need for flow independent parameters beyond the emblematic patient with a significantly reduced left ventricular ejection fraction.4 However, current guidelines emphasise that a continuity equation-derived AVA <1 cm2 in isolation only suggests severe stenosis and should elicit further evaluation. Still, especially in intervention-driven environments, AVA has gained weight and has become somewhat of an arbitrator in discussions on stenosis severity and management of patients particularly with suspected paradoxical low flow low gradient severe AS.

Whether AVA as derived from the continuity equation represents a reliable reflection of stenosis severity is therefore a timely question addressed by González-Mansilla and coworkers in this issue of Heart. 5 Focusing on non-severe AS, the authors analysed a total of 16 156 routine transthoracic echocardiographic studies performed in >13 000 patients divided into three groups according to jet velocity and the presence or absence of morphological findings of valve degeneration: normal valves (jet velocity <2.5 m/s and no signs of degeneration), aortic sclerosis (jet velocity <2.5 m/s and morphological signs of degeneration) and AS (jet velocity >2.5 m/s indicating valvular obstruction). Overall, the authors noted a substantial overlap between groups with respect to AVA. Most strikingly, 0.5% (38/8190) of studies in normal valves (in the absence of valvular degeneration) yielded an AVA in the severely stenotic range, increasing to 1.8% in sclerotic valves. Risk factors for the diagnosis of a severe stenosis on the grounds of AVA in morphologically apparently normal or near normal valves were female gender, small body size and low ejection fraction among others. Indexing AVA to body surface area (AVAindex) did not change results substantially. Subsequent analyses of pertinent subgroups with an ejection fraction >35%, mitral regurgitation ≤2 or regular cardiac rhythm confirmed the findings in the whole cohort. Taken together, the results indicate that in the framework of currently accepted cut-off values, AVA may overestimate stenosis severity.

The authors have to be commended on a well-performed, in-depth analysis including a very large number of patients. The results are in line with a recent report from an enormous database of >77 000 patients indicating that, on routine echocardiography, AVA had a low positive predictive value of 37.5% with respect to the final documented interpretation of AS severity.6 Furthermore, risk factors for overestimation of stenosis severity identified in the present study coincide with previously published causes for inconsistencies between AVA and mean pressure gradient. Conceptually, discrepancies in stenosis severity between AVA and mean pressure gradient may be attributed to small body size, low flow states, measurement error and underlying inconsistencies in cut-off values. The study confirms that small body size and low flow states contribute to the finding of a small AVA. However, measurement error as a contributing factor cannot be ruled out making it difficult to gauge the role of inconsistencies in cut-off values between AVA and mean pressure gradient in the individual patient.

Nevertheless, the data sound a word of caution regarding the indiscriminate use of AVA as an isolated parameter for the assessment of AS severity. Outcome data from prospective trials in patients with AS of all levels of haemodynamic severity are urgently needed to improve patient care. For the time being and in the context of echocardiography, additional information presented in the paper by González-Mansilla and coworkers suggest that VR may be a parameter deserving increased attention. Largely flow independent, VR obviates the need for measuring the left ventricular outflow tract (LVOT) with its notoriously problematic reproducibility and assumption of a, now refuted, circular anatomy. The surprisingly scarce evidence in the literature does support the additional consideration of VR as a flow independent parameter of stenosis severity.6 7

In summary, the present paper emphasises that, in the framework of currently accepted cut-off values, relying on AVA in isolation tends to overestimate stenosis severity. The findings support an integrated approach in the assessment of AS severity as outlined in current guidelines. An expert clinical look at our patients remains as important as any parameter obtained from echocardiography.

References

Footnotes

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Commissioned; internally peer reviewed.

  • Patient consent for publication Not required.

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