Flow-status and survival in severe aortic stenosis treated with TAVI – is flow rate superior to stroke volume index?
Authors: Santos Ferreira D A , Fernandes I , Diaz S , Saraiva F , Guerreiro C , Brandao M , Silva G , Silva M , Sampaio F , Pires-Morais G , Melica B , Santos L , Rodrigues A , Braga P , Fontes-Carvalho R 
Published: October 2022

Abstract

Background
Low-flow status, currently defined as a stroke volume index (SVi) &lt;35 mL/m2, is an important prognostic predictor for mortality after Transcatheter Aortic Valve Implantation (TAVI) for severe aortic stenosis (SAS). However, transaortic flow rate (FR) – defined as stroke volume divided by left ventricle ejection time - has recently been suggested to be superior to SVi in defining low-flow states, as it reflects more closely valvular resistance, while being independent of body surface area. Low FR is most consistently defined as FR&lt;200 mL/s.

Purpose
Determine the prognostic impact of FR and SVi before TAVI in survival after intervention for SAS.

Methods
A single-centre retrospective database of all TAVI performed between 2011 and 2019 was analyzed, and cases with pre-intervention echocardiograms available were included. Low-flow patients were identified according to basal FR (&lt;200 mL/s) or SVi (&lt;35 mL/m2), and compared with normal-flow cases. The primary endpoint was defined as time to all-cause death or last follow-up. The impact of flow-status (using FR or SVi) in survival was assessed using Kaplan-Meier curves and log-rank test, as well as Cox proportional hazard model adjusted for EuroSCORE II, using FR or SVi either as categorical or continuous variables. A subanalysis further compared patients with preserved and reduced ejection fraction (EF, &lt;52%). p&lt;0.05 was considered statistically significant.

Results
From 657 TAVI performed, 490 (74.6%) cases were included, with a median follow-up of 43 months. From those, 59.6% were defined as low-flow according to FR, and 43.3% using SVi. Low-flow patients, using each parameter, were of higher surgical risk (EuroSCORE II and STS scores), had more advanced NYHA classes, worse estimated creatinine clearance, and suffered more frequently from coronary artery disease. Low-FR patients were also older, and more predominantly female. Atrial fibrillation was more prevalent among low SVi cases. Functional aortic valve area was lower in low-flow patients using both assessments, but low-SVi was also associated with lower transaortic gradients, as well as lower EF before and after TAVI. Regarding all-cause mortality, low-SVi was associated with worse survival [p=0.02, hazard ratio (HR) 1.43 (1.05–1.94)], but not low-FR (p=0.4). However, low-SVi, when adjusted for EuroScore II, was no longer a predictor of all-cause mortality (p=0.08). When considering FR and SVi as continuous variables, a higher SVi (but not FR) was associated with better survival (HR 0.98, p=0.047) in multivariable analysis adjusted for EuroSCORE II. When stratifying according to preserved and reduced EF, both FR and SVi did not predict all-cause mortality.

Conclusions
Low-flow states are common in SAS population treated with TAVI, being frequently associated with worse symptoms and higher procedural risk. Low-SVi, but not low-FR, negatively impacts survival after intervention, representing a marker for prognosis after TAVI.

Funding Acknowledgement
Type of funding sources: None.