NEDA 2023 UpdateRisk-Adjusted SVI Stratification
Hemodynamic Inputs
mL
Calculated via LVOT diameter & VTI
m²
Body Surface Area
%
Ejection Fraction
Risk Profile
Requires Stroke Volume, BSA, and LVEF to determine adjusted prognostic risk based on latest NEDA findings.
Guidelines & Evidence
Verified
Last Review: 2026-07-17
When to Use
What is Stroke Volume Index (SVI)?
Stroke Volume Index (SVI) is the volume of blood ejected from the left ventricle per heartbeat, divided by the patient's body surface area (BSA). It normalizes cardiac output for patient size, allowing comparison across individuals. SVI is a key hemodynamic parameter that reflects left ventricular forward flow and helps distinguish between "true-severe" and "pseudo-severe" aortic stenosis (AS) in patients with low-gradient AS (mean gradient <40 mmHg, peak velocity <4 m/s). Unlike ejection fraction (EF), which measures the percentage of blood ejected, SVI measures the absolute volume normalized to BSA, making it sensitive to both systolic dysfunction and restrictive physiology (small LV cavity, concentric remodeling).
Primary Clinical Indications
Low-gradient severe aortic stenosis (AS): Differentiates "low-flow" from "normal-flow" states in patients with AVA ≤1.0 cm² but mean gradient <40 mmHg. SVI ≤35 mL/m² defines low-flow (classical or paradoxical).
Prognostic stratification in AS: SVI <30 mL/m² (preserved EF) or <35 mL/m² (reduced EF) identifies patients with significantly worse 1- and 3-year mortality, independent of AVA, symptoms, and cardiac damage stage.
Guiding aortic valve replacement (AVR) timing: Low SVI with dobutamine stress echo helps identify true-severe AS (SVI increases with dobutamine) vs pseudo-severe AS (SVI unchanged or decreases).
Heart failure with preserved ejection fraction (HFpEF): SVI <35 mL/m² is common in HFpEF (40-50% of patients) and predicts worse outcomes independent of LVEF.
Cardiac resynchronization therapy (CRT) response: Low SVI (<35 mL/m²) predicts worse CRT response and higher mortality.
Monitoring after AVR or TAVI: Improvement in SVI post-intervention (increase ≥5-10 mL/m²) correlates with symptom improvement and better long-term survival.
SVI vs Other Hemodynamic Parameters
| Parameter | Definition | Normal Range | Key Limitation | Clinical Utility |
|---|---|---|---|---|
| Stroke Volume Index (SVI) | SV / BSA (mL/m²) | LV: 30-66 (men), 30-59 (women); RV: 28-75 (men), 29-66 (women) | BSA-dependent (obesity underestimates, small body habitus overestimates) | Low-flow AS, HFpEF, CRT response, prognosis |
| Stroke Volume (SV) | EDV – ESV (mL) | LV: 55-127 (men), 47-99 (women) | Not indexed to body size (tall/muscular patients have higher SV) | Cardiac output calculation, preload assessment |
| Ejection Fraction (EF) | SV / EDV × 100% | LV: 50-70% (men/women) | Normal in HFpEF, concentric remodeling, and paradoxical low-flow AS | Systolic function, heart failure classification |
| Cardiac Index (CI) | CO / BSA (L/min/m²) | 2.5-4.0 L/min/m² | Rate-dependent (heart rate), requires heart rate measurement | Shock classification, low-output states |
| Transvalvular Mean Gradient | 4V² (simplified Bernoulli) | <40 mmHg: low-gradient | Flow-dependent (underestimates in low-flow states) | AS severity classification |
How it Works
Echocardiographic Calculation (Doppler Method)
SV (mL) = LVOT area (cm²) × LVOT VTI (cm)
= π × (LVOT diameter / 2)² × LVOT VTI
SVI (mL/m²) = SV (mL) / BSA (m²)
Where:
• LVOT diameter = measured in parasternal long-axis (PLAX), typically 1.8-2.2 cm
• LVOT VTI (Velocity Time Integral) = pulsed-wave Doppler in apical 5-chamber view
• BSA = Mosteller formula: √[(height in cm × weight in kg) / 3600]
Alternative (when LVOT unreliable): RVOT area × RVOT VTI (requires competent pulmonic valve)
Normal Values by Imaging Modality (MRI Reference)
| Chamber | Sex | Age Range | SV Range (mL) | SVI Range (mL/m²) | Data Source |
|---|---|---|---|---|---|
| Left Ventricle | Women | 16-83 years | 47-99 | 30-59 | Kawel-Boehm et al. (MRI, papillary muscles included in volumes) |
| Left Ventricle | Men | 16-83 years | 55-127 | 30-66 | Kawel-Boehm et al. (MRI) |
| Right Ventricle | Women | 20-83 years | 39-109 | 29-66 | Kawel-Boehm et al. (MRI) |
| Right Ventricle | Men | 20-83 years | 43-146 | 28-75 | Kawel-Boehm et al. (MRI) |
Prognostic SVI Thresholds in Low-Gradient Severe AS (Snir 2023, NEDA Study)
KEY FINDING FROM 2,473 PATIENTS: The prognostic threshold for SVI differs by LVEF status in low-gradient severe AS (AVA ≤1.0 cm², mean gradient <40 mmHg).
Low-Flow Classification (Traditional vs Updated)
| Category | Traditional Threshold (All AS) | Updated Threshold (Preserved EF, NEDA 2023) | Updated Threshold (Reduced EF, NEDA 2023) | Clinical Action |
|---|---|---|---|---|
| Normal flow | SVI >35 mL/m² | SVI >35 mL/m² (class I recommendation) | SVI >35 mL/m² | Standard management per guidelines (AVR if symptomatic, class I) |
| Mild low-flow (formerly "gray zone") | SVI 30-35 mL/m² (considered low-flow) | SVI 30-35 mL/m² = NOT low-flow (prognosis same as normal) | SVI 30-35 mL/m² = low-flow (worse outcomes) | Preserved EF: observe or CT calcium scoring. Reduced EF: consider AVR if viable |
| Moderate low-flow | SVI 25-30 mL/m² | SVI <30 mL/m² (grouped together) | SVI 25-30 mL/m² (intermediate risk) | Dobutamine stress echo to assess contractile reserve; AVR if true-severe AS (class IIa) |
| Severe low-flow | SVI <25 mL/m² | SVI <25 mL/m² (marker of very high risk) | SVI <25 mL/m² (marker of very high risk) | High surgical risk; consider TAVI; evaluate for concomitant cardiac damage (staging classification) |
Clinical Pearls
Critical Pearls for Practice
"Normal-flow" preserved EF AS has excellent prognosis – SVI 30-35 mL/m² in a patient with LVEF ≥50% and low-gradient AS should NOT be labeled as "low-flow." These patients have outcomes similar to those with SVI >35 mL/m². Avoid unnecessary AVR referrals based on SVI alone.
Integration with Cardiac Damage Staging (Genereux Classification)
SVI is a key component of the Cardiac Damage Staging Classification in AS. Stage 1: no cardiac damage (normal SVI, no LV hypertrophy). Stage 2: LV damage (LV hypertrophy, diastolic dysfunction, but SVI >35). Stage 3: Pulmonary vasculature or RV damage (tricuspid regurgitation, pulmonary hypertension, often with SVI <35). Stage 4: Biventricular damage (RV dysfunction, often with SVI <30). Higher stage predicts worse post-AVR outcomes independent of SVI. Snir 2023: SVI was inversely correlated with Cardiac Damage Stage (p<0.001 for trend), and SVI added prognostic value beyond stage alone (HR 1.38-1.80 for SVI <30 vs >35, adjusted for stage).
Next Steps
Management Algorithm Based on SVI in Low-Gradient Severe AS
Clinical Decision Tools Integration
| Tool | SVI Cut-off | Action Threshold | Reference |
|---|---|---|---|
| AVR referral (preserved EF, asymptomatic) | <30 mL/m² | Consider AVR (class IIa) if on DSE shows contractile reserve | 2020 ACC/AHA guidelines (updated from 2014) |
| AVR referral (reduced EF, asymptomatic) | <35 mL/m² | Consider AVR (class IIa) | 2020 ACC/AHA guidelines |
| Low-flow classification (traditional) | ≤35 mL/m² | Low-flow AS – further testing (DSE or CT calcium) | 2014 AHA/ACC (being revised) |
| Low-flow classification (NEDA 2023, preserved EF) | <30 mL/m² | Low-flow AS – poor prognosis, consider AVR | Snir 2023 (Int J Cardiovasc Imaging) |
| Cardiac Damage Stage (Genereux) | Decreasing SVI with stage | Stage 3-4: SVI often <30-35, high post-AVR mortality | Genereux 2017 (EHJ) |
| Poor CRT response | <35 mL/m² | Higher mortality, less likely to respond to CRT | Multiple studies |
The Evidence
Primary Source: NEDA Study (National Echo Database of Australia)
The prognostic significance of stroke volume index in low gradient severe aortic stenosis: from the national echo database of Australia
Snir AD et al. • The International Journal of Cardiovascular Imaging. 2023;39(9):1719–1727. doi: 10.1007/s10554-023-02886-y. Epub 2023 Jun 10. PMID: 37300593; PMCID: PMC10520126.
View SourceHistorical/Foundational Studies
Impact of low stroke volume on mortality in patients with severe aortic stenosis and preserved left ventricular ejection fraction
Rusinaru D et al. • European Heart Journal. 2018;39(21):1992-1999. doi: 10.1093/eurheartj/ehy123
Survival by stroke volume index in patients with low-gradient normal EF severe aortic stenosis
Eleid MF et al. • Heart. 2015;101(1):23-29. doi: 10.1136/heartjnl-2014-306151
Importance of flow in risk stratification of aortic stenosis
Guzzetti E et al. • Canadian Journal of Cardiology. 2020;36(1):27-29. doi: 10.1016/j.cjca.2019.10.020
Normal values for cardiovascular magnetic resonance in adults (updated)
Kawel-Boehm N et al. • Journal of Cardiovascular Magnetic Resonance. 2020;22(1):69. doi: 10.1186/s12968-020-00663-3
Guideline Recommendations
2020 ACC/AHA guideline for the management of patients with valvular heart disease
Otto CM et al. • Circulation. 2021;143(5):e72-e227. doi: 10.1161/CIR.0000000000000923
View Source2021 ESC/EACTS guidelines for the management of valvular heart disease
Vahanian A et al. • European Heart Journal. 2022;43(7):561-632. doi: 10.1093/eurheartj/ehab395
View SourceSupplementary Studies (Sex Differences, Cardiac Damage)
Transvalvular flow, sex, and survival after valve replacement surgery in patients with severe aortic stenosis
Guzzetti E et al. • Journal of the American College of Cardiology. 2020;75(16):1897-1909. doi: 10.1016/j.jacc.2020.02.065
Cardiac damage staging classification predicts prognosis in all the major subtypes of severe aortic stenosis
Snir AD et al. • Journal of the American Society of Echocardiography. 2021;34(11):1137-1147.e13. doi: 10.1016/j.echo.2021.05.017
Poor long-term survival in patients with moderate aortic stenosis
Strange G et al. • Journal of the American College of Cardiology. 2019;74(15):1851-1863. doi: 10.1016/j.jacc.2019.08.004
Origins & History
Historical Development of SVI
Stroke volume has been measured since the early 20th century (Fick principle, 1870; dye dilution, Stewart 1897). Indexing to BSA was proposed by Starr and Rawson (1940s) to normalize cardiac output for body size. The Doppler echocardiographic method for SV calculation was developed by Ihlen and colleagues in the 1980s, using LVOT diameter and VTI. The first guidelines defining low-flow AS (SVI ≤35 mL/m²) were published in 2009 (ASE/EAE recommendations) and incorporated into the 2014 AHA/ACC guidelines. The term "paradoxical low-flow severe AS" was coined by Hachicha et al. (2007) to describe patients with preserved EF but low SVI. The controversy over SVI thresholds began in 2018 when Rusinaru et al. suggested 30-35 mL/m² might not be pathological in preserved EF. The NEDA 2023 study by Snir et al. (Australia) definitively established the differential threshold (30 vs 35) with large sample size and is expected to influence future guideline updates (2025-2026).
Key Contributors and Timeline
| Year | Contributors | Institution | Contribution |
|---|---|---|---|
| 1870 | Adolf Fick | University of Würzburg, Germany | Fick principle: CO = O₂ consumption / (arterial-venous O₂ difference). Foundation for SV measurement. |
| 1984 | Ihlen H, et al. | Rikshospitalet, Oslo, Norway | First Doppler echocardiographic validation of SV measurement against thermodilution (r=0.96). |
| 2007 | Hachicha Z, Pibarot P, et al. | Laval University, Quebec, Canada | Coined "paradoxical low-flow severe AS" (preserved EF, SVI ≤35). Described worse outcomes (Circulation). |
| 2009 | Baumgartner H, Hung J, et al. | ASE/EAE | First standardized guidelines for AS echocardiography, defined low-flow as SVI ≤35. |
| 2014 | Nishimura RA, Otto CM, et al. | AHA/ACC Task Force | First AHA/ACC valvular guidelines to include low-flow AS definition (SVI ≤35). |
| 2015 | Eleid MF, Sorajja P, et al. | Mayo Clinic | Reported SVI ≤35 associated with worse outcomes in preserved EF (n=203). |
| 2018 | Rusinaru D, Tribouilloy C, et al. | University of Picardie, France | Challenged 35 cut-off: SVI 30-35 had same prognosis as >35 in preserved EF (n=395). |
| 2021 | Snir AD, Ng MK, Celermajer DS, et al. | University of Sydney, Australia | Initial NEDA publications characterizing low-gradient AS prevalence and cardiac damage staging. |
| 2023 | Snir AD, Ng MK, Strange G, Playford D, Stewart S, Celermajer DS | National Echo Database of Australia (NEDA) | Definitive study (n=2,473) establishing differential SVI thresholds by LVEF. SVI <30 (preserved EF) vs <35 (reduced EF) predicts mortality. Currently influencing guideline updates. |
| 2025-2026 (expected) | ACC/AHA Valvular Guidelines Update | Pending | Expected to incorporate differential SVI thresholds based on NEDA 2023 and European studies. |
Limitations of Current Evidence (NEDA 2023)
Retrospective design – Associations, not causation. Cannot prove that low SVI directly causes death (confounding by comorbidity, frailty, unrecognized cardiac damage).
No clinical symptom data – Could not adjust for symptom status (dyspnea, angina, syncope), which drives AVR decisions. However, SVI predicted mortality independently of AVA and other echo parameters, suggesting clinical utility even without symptoms.
Under-ascertainment of AVR – AVR status inferred from follow-up echocardiograms (not surgical databases). Likely underestimated true AVR rate (only 7-28% recorded), and could not analyze SVI in AVR-treated subgroups separately (due to sample size limitations in AVR patients).
No central core lab – Echocardiograms from 25+ sites with local interpretation; inter-observer variability in LVOT diameter, VTI, and BSA calculation may have introduced noise (attenuating effect sizes, not creating false positives).
BSA limitations – BSA overestimates obesity (reducing SVI artificially) and underestimates small stature (elevating SVI). Not all patients had height/weight recorded (only those with complete data included, potential selection bias).
Generalizability – Australian population (multicultural but predominantly White European descent). May not apply fully to Asian, African, or Hispanic populations with different body habitus and AS etiology (rheumatic vs degenerative).
No dobutamine stress data – Could not distinguish true-severe from pseudo-severe AS in low-gradient patients. Some patients with SVI <30 may have pseudo-severe AS (normal SVI with dobutamine) and better prognosis without AVR.
Last Comprehensive Review: 2026-07-17