124 Stroke volume determined flow reserve does not predict the true severity of low-flow low-gradient aortic stenosis and is not a robust marker of contractile reserve in patients undergoing low-dose dobutamine echocardiography

Background During low-dose dobutamine stress echocardiography (LDDSE) in low-flow low-gradient aortic stenosis (LFLGAS), both the aortic stenosis (AS) severity and the presence of contractile reserve (CR) are conventionally assessed based on stroke volume flow reserve (SVFR), which is defined as stroke volume [SV] increase 20%. However frequent exaggerated chronotropic response to dobutamine with shortening left ventricular time result in SV drop. On the contrary, transvalvular flow rate (FR) (SV/ejection time) and left ventricular ejection fraction (LVEF) may increase. We aimed to assess the value of FR 200 ml/s (normal FR) and LVEF change in the identification of true severe AS (TSAS) and the assessment of CR respectively. Methods Accordingly 74 consecutive patients (mean age 78 years) with LFLGAS referred for LDDSE for determination of AS severity and CR underwent retrospective assessment of SV, FR, LVEF and standard echocardiographic parameters of AS severity (Table 1). The outcome assessed was all-cause mortality censored for aortic valve intervention. Results SVFR was present in 30 (40.5%) of the 74 patients whereas FR 200 ml/s was achieved in 60 (81.1%) (p 2 ). TSAS was present in 47 (63.5%) patients of whom SVFR correctly identified 17 (36.2%) compared to 34 (72.3%) with FR 200 ml/s (p=0.001). In the 48 patients with LVEF 50%, amongst SV, FR and LVEF changes, only the latter was an independent predictor of death (HR=0.92, 95% CI=0.87–0.98, p=0.02) (Table 2). LVEF change of Conclusions During LDDSE in LFLGAS normalised FR, not SVFR, is a better determinant of TSAS, whereas assessment of LVEF change instead of SVFR determines CR.