Re-Exploration of Flow Rate in Low-Flow, Low-Gradient Aortic Stenosis

Transaortic flow rate (TFR, mL/s) is an emerging hemodynamic index in aortic stenosis (AS), offering insights beyond stroke volume index (SVi). We evaluated the hemodynamic determinants and prognostic significance of TFR at rest and peak dobutamine stress in patients with suspected low-flow, low-gradient (LF-LG) AS and reduced left ventricular ejection fraction (LVEF < 50%).

This study aimed to assess and compare the hemodynamic determinants of TFR at rest and during peak pharmacological stress, and to evaluate their association with 3-year survival.

Among 86 patients undergoing dobutamine stress echocardiography (DSE), 34 were classified as true severe, eight as pseudo-severe, and 44 as indeterminate AS. TFR and associated parameters were assessed at rest and stress, and survival was evaluated at 3 years.

At rest, no significant between-group differences in TFR were observed (p = 0.11). However, at peak stress, TFR differed significantly between groups: true severe (226 ± 62 mL/s), pseudo-severe (334 ± 55 mL/s), and indeterminate (248 ± 67 mL/s; p < 0.01). Rest TFR was independently associated with cardiac output (CO), arterial compliance, and valvulo-arterial impedance (ZVA). During stress, TFR was predominantly associated with CO, although systemic vascular properties remained significant in pseudo-severe AS. Flow reserve (ΔTFR) was influenced only by stress-derived variables. At 3-year follow-up, stress TFR was a significant predictor of survival (p = 0.03), independent of AS classification (p = 0.04) and intervention (p = 0.04). A stress TFR > 195 mL/s was the optimal survival threshold (AUC 0.64; sensitivity 85%, specificity 70%).

These findings suggest that stress TFR reflects left ventricular contractile reserve and carries prognostic value in LF-LG AS. Stress-based assessment may enhance clinical decision-making, particularly in diagnostically ambiguous AS subsets.