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. 2023 Sep 20:16:177-188.
doi: 10.1016/j.xjon.2023.08.022. eCollection 2023 Dec.

The robustness of the flow-gradient classification of severe aortic stenosis

Bart J J Velders  1 , Michiel D Vriesendorp  1 , Federico M Asch  2 , Michael G Moront  3 , Francois Dagenais  4 , Michael J Reardon  5 , Joseph F Sabik Iii  6 , Rolf H H Groenwold  7 , Robert J M Klautz  1
Affiliations

The robustness of the flow-gradient classification of severe aortic stenosis

Bart J J Velders et al. JTCVS Open. .

Abstract

Objectives: A flow-gradient classification is used to determine the indication for intervention for patients with severe aortic stenosis (AS) with discordant echocardiographic parameters. We investigated the agreement in flow-gradient classification by stroke volume (SV) measurement at the left ventricular outflow tract (LVOT) and at the left ventricle.

Methods: Data were used from a prospective cohort study and patients with severe AS (aortic valve area index ≤0.6 cm2/m2) with preserved ejection fraction (>50%) were selected. SV was determined by an echocardiographic core laboratory at the LVOT and by subtracting the 2-dimensional left ventricle end-systolic from the end-diastolic volume (volumetric). Patients were stratified into 4 groups based on SV index (35 mL/m2) and mean gradient (40 mm Hg). The group composition was compared and the agreement between the SV measurements was investigated using regression, correlation, and limits of agreement. In addition, a systematic LVOT diameter overestimation of 1 mm was simulated to study flow-gradient reclassification.

Results: Of 1118 patients, 699 were eligible. The group composition changed considerably as agreement on flow state occurred in only 50% of the measurements. LVOT SV was on average 15.1 mL (95% limits of agreement -24.9:55.1 mL) greater than volumetric SV. When a systematic 1-mm LVOT diameter overestimation was introduced, the low-flow groups halved.

Conclusions: There was poor agreement in the flow-gradient classification of severe AS as a result of large differences between LVOT and volumetric SV. Furthermore, this classification was sensitive to small measurement errors. These results stress that parameters beyond the flow-gradient classification should be considered to ensure accurate recommendations for intervention.

Keywords: flow-gradient classification; low flow; severe aortic stenosis; stroke volume.

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Conflict of interest statement

B.V.: institutional research grant and speaker's honorarium paid to his department from Medtronic. M.V.: institutional research grant and reimbursement of travel expenses from Medtronic. F.A.: no personal conflicts of interest, but his organization receives grants or research contracts from Medtronic, Abbott, Edwards Lifesciences, Boston Scientific, Biotronik, Corcym, and HLT Medical. M.M.: trainer and consultant for Medtronic; a trainer and speaker for AtriCure; and a speaker and consultant for Haemonetics. F.D.: proctor and speaker for Medtronic and Cook Medical. M.R.: consultant to Medtronic, Abbott Medical, Boston Scientific, Gore Medical, and Transverse Medical; the fees are paid to his department. J.S.: Principal Investigator, PERIGON Pivotal Trial for Medtronic. R.K.: research support, consultation fees, and Principal Investigator, PERIGON Pivotal Trial for Medtronic. All other authors reported no conflicts of interest. The Journal policy requires editors and reviewers to disclose conflicts of interest and to decline handling or reviewing manuscripts for which they may have a conflict of interest. The editors and reviewers of this article have no conflicts of interest.

Figures

None
Graphical abstract
None
HG/LG, High/low-gradient; NF/PLF, normal/paradoxical low-flow; LVOT, left ventricular outflow tract.
Figure 1
Figure 1
Agreement between the LVOT and the volumetric method to determine indexed stroke volume in patients with severe aortic stenosis. The blue line displays the relation using linear regression, including corresponding 95% confidence intervals. The horizontal and vertical dashed red lines are placed at the threshold for low flow. LVOT, Left ventricular outflow tract.
Figure 2
Figure 2
Bland–Altman plot: agreement between LVOT and the volumetric stroke volume measurements in patients with severe aortic stenosis. The lines represent the mean difference between the 2 measurements, including the 95% limits of agreement. SV, Stroke volume; LVOT, left ventricular outflow tract.
Figure 3
Figure 3
Kaplan–Meier survival analysis according to flow-gradient patterns of patients who underwent aortic valve replacement. Censoring is indicated by the “+” sign. For the left Kaplan–Meier analysis, the survival rates were 86.5% (95% CI, 82.3%-91.0%) for NFHG, 91.4% (95% CI, 86.7%-96.2%) for NFLG, 91.5% (95% CI, 86.7%-96.6%) for LFHG, and 90.0% (95% CI, 84.4%-96.0%) for PLFLG. For the right Kaplan–Meier analysis, the survival rates were 90.7% (95% CI, 85.4%-96.4%) for NFHG, 96.3% (95% CI, 89.4%-100%) for NFLG, 88.1% (95% CI, 83.5%-92.9%) for LFHG, and 89.8% (95% CI, 85.2%-94.7%) for PLFLG. LVOT, Left ventricular outflow tract; SVi, stroke volume index; NFHG, normal-flow, high-gradient; NFLG, normal-flow, low-gradient; LFHG, low-flow, high-gradient; PLFLG, paradoxical low-flow, low-gradient; CI, confidence interval.
Figure 4
Figure 4
Clinical implication of overestimation of LVOT diameter by 1 mm for the flow-gradient classification of severe aortic stenosis. The vertical line represents the threshold for low flow and the horizontal line for severe aortic stenosis. LVOT, Left ventricular outflow tract; AVA, aortic valve area; NFHG, normal-flow, high-gradient; NFLG, normal-flow, low-gradient; LFHG, low-flow, high-gradient; PLFLG, paradoxical low-flow, low-gradient; MAS, moderate aortic stenosis.
Figure 5
Figure 5
Graphical abstract: The robustness of the flow-gradient classification of severe aortic stenosis. NFHG, Normal-flow high-gradient; NFLG, normal-flow, low-gradient; LFHG, low-flow, high-gradient; PLFLG, paradoxical low-flow, low-gradient.
Figure E1
Figure E1
CONSORT diagram for patients with severe aortic stenosis and preserved ejection fraction. ∗Data were from the PERIcardial SurGical AOrtic Valve ReplacemeNt (PERIGON) Pivotal Trial for the Avalus valve (Medtronic). SAVR, Surgical aortic valve replacement; AR, aortic regurgitation; AS, aortic stenosis; LVEF, left ventricular ejection fraction; AVAi, aortic valve area index; CONSORT, Consolidated Standards of Reporting Trials.
Figure E2
Figure E2
Concordance in flow-gradient classification of patients with severe aortic stenosis between left ventricular outflow tract (left) and volumetric stroke volume index measurements (right). NFHG, Normal-flow, high-gradient; NFLG, normal-flow, low-gradient; LFHG, low-flow, high-gradient; PLFLG, paradoxical low-flow, low-gradient.
Figure E3
Figure E3
Agreement between the LVOT and the volumetric methods to determine indexed stroke volume in patients with severe aortic stenosis and complete data. The solid blue line displays the relation using linear regression. The dashed blue lines represent the corresponding 95% confidence intervals. The horizontal and vertical dashed red lines are placed at the threshold value of 35 mL/m2 for low flow. The green filled circles represent patient values. LVOT, Left ventricular outflow tract.
Figure E4
Figure E4
Kaplan–Meier survival analysis according to flow-gradient patterns of patients who underwent aortic valve replacement and had complete data. Censoring is indicated by the “+” sign. LVOT, Left ventricular outflow tract; SVi, stroke volume index; NFHG, Normal-flow, high-gradient; NFLG, normal-flow, low-gradient; LFHG, low-flow, high-gradient; PLFLG, paradoxical low-flow, low-gradient.
Figure E5
Figure E5
Concordance in flow-gradient classification after introduction of a 1-mm overestimation of LVOT diameter (right) to the actual situation (left). NFHG, Normal-flow, high-gradient; NFLG, normal-flow, low-gradient; LFHG, low-flow, high-gradient; PLFLG, paradoxical low-flow, low-gradient; MAS, moderate aortic stenosis; LVOT, left ventricular outflow tract.
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