Low-flow low-gradient aortic stenosis in patients with low ejection fraction: but is the flow truly low?

Low Transvalvular Flow Rate in Patients Undergoing Transcatheter Aortic Valve Implantation (TAVI) Is a Predictor of Mortality: The TFR-TAVI Study

BACKGROUND

Transvalvular flow rate (TFR) represents a better reflection of transvalvular flow than the stroke volume index (SVi), and has recently emerged as a useful prognostic tool in patients undergoing surgical aortic valve replacement. There is a paucity of data investigating the role of TFR and its relationship with other clinical or echocardiographic factors in patients undergoing transcatheter aortic valve implantation (TAVI).

METHOD

This was a retrospective single-centre study of 629 consecutive patients who underwent TAVI between March 2009 and September 2020. Pre-TAVI low TFR was defined as <200 c/s. The primary study end point was all-cause mortality.

RESULTS

Low TFR was observed in 41.8% (263/629) of included patients and was associated with increasing age, low body surface area, hypertension, diabetes, atrial fibrillation, left ventricular (LV) dysfunction, and significant mitral regurgitation. LV function status and severity of aortic valve disease were independent predictors of low TFR. Low TFR was significantly associated with long-term all-cause mortality even after adjustment for other risk factors (adjusted hazard ratio [aHR] 1.44; 95% confidence interval [CI] 1.02-2.03; p=0.038). When data were stratified according to SVi, low TFR was an independent predictor of long-term all-cause mortality in patients with normal SVi (aHR 1.98; 95% CI 1.06-3.69; p=0.032) but not in patients with low SVi (HR 1.23; 95% CI 0.71-2.11; p=0.46; p=0.016 for interaction).

CONCLUSIONS

Low TFR is common in patients undergoing TAVI and is an independent predictor of all-cause mortality, particularly in patients with normal SVi.

Multimodality Imaging for Discordant Low-Gradient Aortic Stenosis: Assessing the Valve and the Myocardium

Aortic stenosis (AS) is a disease of the valve and the myocardium. A correct assessment of the valve disease severity is key to define the need for aortic valve replacement (AVR), but a better understanding of the myocardial consequences of the increased afterload is paramount to optimize the timing of the intervention. Transthoracic echocardiography remains the cornerstone of AS assessment, as it is universally available, and it allows a comprehensive structural and hemodynamic evaluation of both the aortic valve and the rest of the heart. However, it may not be sufficient as a significant proportion of patients with severe AS presents with discordant grading (i.e., an AVA ≤ 1 cm² and a mean gradient <40 mmHg) which raises uncertainty about the true severity of AS and the need for AVR. Several imaging modalities (transesophageal or stress echocardiography, computed tomography, cardiovascular magnetic resonance, positron emission tomography) exist that allow a detailed assessment of the stenotic aortic valve and the myocardial remodeling response. This review aims to provide an updated overview of these multimodality imaging techniques and seeks to highlight a practical approach to help clinical decision making in the challenging group of patients with discordant low-gradient AS.