The prognostic value of low-flow in severe aortic stenosis patients undergoing TAVI - should we follow the flow?
Authors: Santos Ferreira D A , Diaz S , Fernandes I , Guerreiro C , Brandao M , Teixeira R , Nunes F , Pereira E , Sampaio F , Pires-Morais G , Melica B , Santos L , Rodrigues A , Braga P , Fontes-Carvalho R 
Published: June 2023

Abstract

Funding Acknowledgements
Type of funding sources: None.

Background
Low-flow conditions are associated with higher mortality after transcatheter aortic valve implantation (TAVI) for severe aortic stenosis (SAS). Two parameters have been described to determine low-flow status – although the most currently used is stroke volume index, transaortic flow rate (FR – stroke volume divided by left ventricle ejection time) was recently suggested as being superior, as it more closely reflects valvular resistance.

Purpose
Determine the prognostic impact of low-flow conditions in survival of patients undergoing TAVI for SAS, using low-FR and low-SVi definitions.

Methods
A database comprising all patients treated with TAVI between 2011 and 2019 in a single-centre was retrospectively analyzed, and cases with echocardiograms performed before intervention in our centre were included. Low-flow patients were defined according to a basal FR&lt;200mL/s or SVi&lt;35mL/m2, and compared with normal counterparts. The prognostic impact of flow was tested using Kaplan-Meier curves, log-rank test and Cox proportional hazard model adjusted for EuroSCORE II, using FR or SVi both as categorical and continuous variables. A subsequent analysis compared patients with preserved and reduced ejection fraction (EF, &lt;52%). Primary endpoint was defined as time to all-cause mortality or last follow-up over the five years after TAVI.

Results
Of 657 TAVI performed, 490 (74.6%) patients were included in the present analysis, over a median follow-up of 56 months. Of these, 59.6% presented low-FR, and 43.3% had low-SVI. Low-flow patients, using each definition, were of higher estimated surgical risk (EuroSCORE and STS), presented a more advanced NYHA class, had a worse estimated creatinine clearance, and more frequently had coronary disease. Additionally, low-FR patients were older and more frequently female. Atrial fibrillation was more common in low-SVi cases. Echocardiographic studies revealed a lower functional aortic valve area in low-flow cases, and low-SVi was associated with lower transaortic gradients, and lower EF before and after TAVI. Low-FR before TAVI was associated with higher mortality over follow-up [Hazard Ratio (HR) 1.43 (1.06–1.92), p = 0.019)], even after adjusting for EuroSCORE II [HR 1.39 (1.03–1.90), p = 0.034], which was not observed for low-SVi (p = 0.06 and p = 0.2 for uni- and multivariable analysis, respectively). When analyzing FR and SVi as continuous variables, a higher SVi, but not FR, was associated with improved survival [HR 0.98 (0.97–1.00), p = 0.018; HR 0.99 (0.97–1.00), p = 0.044 for uni- and multivariable analysis, respectively). When stratifying by preserved or reduced EF, both FR and SVi did not predict mortality.

Conclusions
About half of SAS patients undergoing TAVI present with a low-flow condition, which is frequently associated with more advanced heart failure symptoms and higher estimated surgical risk. Low-FR negatively impacts survival after intervention. SVi is also prognostic, but not at a &lt;35ml/s cut-off.