Flow Characteristics of the Medtronic CoreValve: Difficulties Estimating Aortic Valve Cross-Sectional Area Following Transcatheter Aortic Valve Implantation

Alison Duncan, Eric Lim, Sarah Barker, Carlo Di Mario, Neil Moat

Abstract


Background: Echocardiographic evaluation after transcatheter aortic valve implantation (TAVI) includes estimation of effective
orifice area (EOA). EOA calculation depends on sub-valvular stroke volume (SV), which depends on sub-valvular diameter and
velocity time integral (VTI). The Medtronic CoreValve area changes throughout its length. We aimed to (i) compare SV at two
sites of flow acceleration: ‘pre-stent’ and ‘in-stent, pre-valve’, (ii) assess effects of possible differences in sub-valvular SV on
EOA, and (iii) assess agreement of measurement of EOA calculation after CoreValve TAVI.
Methods: We studied 43 patients after CoreValve implantation. All had transthoracic echocardiography 5-7 days after TAVI.
Sub-valvular SV was measured ‘pre-stent’ and ‘in-stent, pre-valve’. Measurement agreement was assessed by root mean
square (RMS) differences and Bland-Altman analyses.
Results: SV was consistently higher ‘in-stent, pre-valve’ compared with ‘pre-stent’ (62±20ml vs. 53±19ml, p<0.001), so that
EOA was correspondingly larger using ‘in-stent, pre-valve’ measurements (1.7±0.5cm2 vs. 1.4±0.5cm2, p<0.001). Betweenobserver
RMS difference for calculation of EOA was higher ‘in-stent, pre-valve’ compared to ‘pre-stent’ (0.53 cm2 vs.
0.23cm2, difference from zero 0.17, p=0.002). Though sub-valvular diameter measurements were variable, VTI variability was
additionally higher ‘in-stent, pre-valve’ compared to ‘pre-stent’ (0.42cm vs. 0.6cm, difference from zero -1.74, p=0.11).
Conclusion: Calculation of EOA after CoreValve TAVI is highly dependent on sub-valvular sample position. EOA may be
underestimated using ‘pre-stent’ SV, and overestimated using ‘in-stent, pre-valve’ SV. Limitations in SV reproducibility
suggests EOA should be used in conjunction with other indices of valve function in serial assessment of CoreValve function
following TAVI.

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DOI: https://doi.org/10.17987/icfj.v1i3.38


Copyright (c) 2015 The Authors

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