The prognostic significance of stroke volume index in low gradient severe aortic stenosis: from the national echo database of Australia

Approximately 50% of patients with severe aortic stenosis (AS) in clinical practice present with 'low-gradient' haemodynamics. Stroke Volume Index (SVI) is a measure of left ventricular output, with 'normal-flow' considered as > 35 ml/m². The association between SVI and prognosis in severe low-gradient AS (LGAS) in currently not well-understood. We analysed the National Echo Database of Australia (NEDA) and identified 109,990 patients with sufficiently comprehensive echocardiographic data, linked to survival information. We identified 1,699 with severe LGAS and preserved ejection fraction (EF) (≥ 50%) and 774 with severe LGAS and reduced EF. One- and three-year survival in each subgroup were assessed (follow-up of 74 ± 43 months), according to SVI thresholds. In patients with preserved EF the mortality "threshold" was at SVI < 30 ml/m²; 1- and 3-year survival was worse for those with SVI < 30 ml/m² relative to those with SVI > 35 ml/m² (HR 1.80, 95% CI 1.32-2.47 and HR 1.38, 95% CI 1.12-1.70), while survival was similar between those with SVI 30-35 ml/m² and SVI > 35 ml/m². In patients with reduced EF the mortality "threshold" was 35 ml/m²; 1- and 3-year survival was worse for both those with SVI < 30 ml/m² and 30-35 ml/m² relative to those with SVI > 35 ml/m² (HR 1.98, 95% CI 1.27-3.09 and HR 1.41, 95% CI 1.05-1.93 for SVI < 30 ml/m² and HR 2.02, 95% CI 1.23-3.31 and HR 1.56, 95% CI 1.10-2.21 for SVI 30-35 ml/m²). The SVI prognostic threshold for medium-term mortality in severe LGAS patients is different for those with preserved LVEF (< 30 ml/m²) compared to those with reduced LVEF (< 35 ml/m²).