Is it appropriate for a cardiologist to disregard Stroke Volume Index (SVI) and prioritize Ejection Fraction (EF) when assessing cardiac function?

Your Patient is Correct: Both EF and SVI Are Essential and Must Be Used Together

The cardiologist's dismissal of stroke volume index (SVI) contradicts current European Society of Cardiology guidelines, which explicitly mandate that both ejection fraction (EF) and SVI be assessed together for comprehensive cardiac evaluation—they provide fundamentally different but equally critical information about cardiac function. 1

Why EF Alone is Insufficient

The 2012 ESC Heart Failure Guidelines explicitly state that EF is not an index of contractility and does not equal stroke volume—it depends on volumes, preload, afterload, heart rate, and valvular function, and therefore must be interpreted in its clinical context. 2, 1

Critical Clinical Scenarios Where EF Misleads:

• Small hypertrophied ventricles can have EF >60% while SVI <30 mL/m², resulting in inadequate tissue perfusion despite "normal" systolic function 1
• Dilated cardiomyopathy can maintain adequate stroke volume through increased end-diastolic volume despite EF <40% 1
• Preserved EF with reduced stroke volume occurs in patients with concentric LV hypertrophy and small cavity volumes—the EF appears normal but cardiac output is severely compromised 2, 1

A 2022 study in cardiogenic shock patients demonstrated only a weak correlation (r=0.44) between LVEF and stroke volume, confirming these parameters measure fundamentally different aspects of cardiac function. 3

Current Guideline Requirements

The 2017 European Heart Journal guidelines on aortic stenosis explicitly require classification using BOTH EF and SVI together—not one or the other—for comprehensive cardiac assessment. 2, 1 The recommended classification system mandates:

• Gradient assessment
• Flow status by SVI (normal flow ≥35 mL/m², low flow <35 mL/m²) 2, 1
• EF status 2, 1

The 2015 ESC/ASE chamber quantification guidelines reinforce that stroke volume and cardiac index are necessary measurements, particularly in valvular heart disease assessment. 2, 1

Prognostic Impact of SVI

SVI has independent prognostic value beyond EF across multiple cardiac conditions:

In Severe Aortic Stenosis:

• Patients with SVI <30 mL/m² have significantly worse 1-year and 3-year survival compared to those with SVI >35 mL/m² 1, 4
• In low-gradient severe AS with preserved EF, each 5 mL/m² reduction in SVI associates with a 20% increase in adjusted mortality risk 5
• The mortality threshold differs by EF status: <30 mL/m² for preserved EF versus <35 mL/m² for reduced EF 4

In Heart Failure with Preserved EF:

• Low SVI (≤35 mL/m²) predicts poor prognosis in atrial fibrillation patients with HFpEF, with only 58% event-free survival at mean follow-up 6
• The combination of SVI with diagnostic scores shows the highest accuracy for diagnosing HFpEF 1
• In the Strong Heart Study, low SVi (≤22 ml/m²⁰⁴) independently predicted incident heart failure (HR 1.38) even after adjusting for EF, LV geometry, and other confounders 7

What SVI Represents That EF Cannot

SVI represents the actual cardiac output normalized to body surface area—this is what perfuses organs and sustains life. 1 While EF tells you the percentage of blood ejected, it provides no information about the absolute volume delivered to the body. A patient with:

• Small LV cavity: EF 65%, EDV 80 mL → SV 52 mL (potentially adequate)
• Small LV cavity: EF 65%, EDV 60 mL → SV 39 mL (inadequate despite "normal" EF)

Both have identical EF but vastly different cardiac output and clinical status.

Clinical Algorithm for Integrated Assessment

When evaluating cardiac function, always calculate and report both parameters: 1

1. Measure EF (biplane Simpson's method preferred) 2
2. Calculate SVI by measuring velocity time integral at LV outflow tract 2, 1
3. Classify flow status: Normal (≥35 mL/m²) vs. Low (<35 mL/m²) 2, 1
4. Integrate findings:
   • High EF + Low SVI = restrictive physiology, small cavity, poor prognosis 1, 4
   • Low EF + Normal SVI = dilated ventricle maintaining output 1
   • Low EF + Low SVI = severely compromised cardiac function 4

Common Pitfalls the Cardiologist Should Avoid

• Never assume high EF means adequate cardiac output—small hypertrophied ventricles can have EF >60% with SVI <30 mL/m², resulting in inadequate tissue perfusion 1
• Never assume low EF means low cardiac output—dilated cardiomyopathy can maintain adequate stroke volume through increased end-diastolic volume despite EF <40% 1
• Never rely on a single metric—the 2017 guidelines emphasize that diagnosis requires clinical judgment with integration of multiple data types 1

Bottom Line

Your patient's SVI of 23.69 mL/m² is significantly below the normal threshold of 35 mL/m² and represents low-flow physiology. 2, 1 This finding has independent prognostic significance regardless of EF and should absolutely be considered in clinical decision-making. The statement that "we don't use that" or "we don't look at that" regarding SVI is inconsistent with current evidence-based guidelines from the European Society of Cardiology, which mandate assessment of both parameters together. 2, 1