Are low stroke volume (SV), stroke volume index (SVI), cardiac output (CO), and cardiac index (CI) indicative of a severe cardiac condition in a 73-year-old male with calculated SV using end-diastolic volume (EDV) and end-systolic volume (ESV) due to unavailable left ventricular outflow tract (LVOT) measurement?

Your Cardiac Indices Are Significantly Abnormal and Require Urgent Evaluation

Your cardiac index of 1.66-1.91 L/min/m² is severely reduced and indicates low cardiac output syndrome, which carries serious prognostic implications and demands immediate investigation to identify the underlying cause. 1, 2

Understanding Your Numbers

Normal Reference Values

• Normal stroke volume (SV): 70-100 mL at rest 1
• Your stroke volume: 40.9-47.0 mL (approximately 40-50% of normal)
• Normal cardiac index (CI): 2.5-4.0 L/min/m² 3
• Your cardiac index: 1.66-1.91 L/min/m² (approximately 50-65% of normal)
• Normal stroke volume index (SVI): >35 mL/m² 4, 5
• Your calculated SVI: approximately 23-27 mL/m² (severely reduced)

Severity Assessment

Your SVI falls well below the critical threshold of 30 mL/m², which carries significant mortality risk even in patients with preserved ejection fraction. 5 Research demonstrates that SVI <30 mL/m² is associated with a 60% increased mortality risk (adjusted HR 1.60) compared to normal values, and this prognostic impact persists regardless of symptoms or management strategy. 5

Measurement Method: EDV-ESV vs. LVOT

Your Measurement Technique

The volumetric method (SV = EDV - ESV) used in your study measures total left ventricular output, including any regurgitant flow from mitral regurgitation. 6 This is the standard approach when LVOT measurements are not performed or when image quality limits Doppler assessment.

LVOT Doppler Method

The LVOT Doppler method (SV = LVOT area × LVOT velocity-time integral) measures only forward flow through the aortic valve, excluding backward flow from mitral regurgitation but including aortic regurgitation. 6

Which Method is Superior?

Neither method is inherently "inferior"—they measure different physiologic parameters and are complementary rather than interchangeable. 6, 3 The 2019 ACC/AHA/ASE guidelines recognize both as valid approaches with distinct clinical applications. 6 Recent multicenter data confirm that cardiac output and stroke volume measurements by different echocardiographic techniques are not interchangeable and can differ by 10-20%. 3

Critical consideration: In your case with severely low stroke volume, the volumetric method may actually be more reliable because LVOT Doppler measurements become increasingly error-prone at low flow states, where small measurement inaccuracies in LVOT diameter are magnified. 6

What This Means Clinically

Low Cardiac Output Syndrome

Your cardiac index <2.0 L/min/m² meets criteria for low cardiac output syndrome, representing an imbalance between oxygen delivery and oxygen consumption at the cellular level. 2 This is not simply a number—it reflects inadequate systemic perfusion.

Potential Underlying Causes to Investigate

Severe aortic stenosis with low-flow state: Your low stroke volume could indicate severe aortic stenosis that appears "moderate" on gradients alone because low flow generates deceptively low pressure gradients even when stenosis is anatomically severe. 6, 4 The ACC/AHA guidelines emphasize that complete assessment of aortic stenosis requires measurement of transvalvular flow, pressure gradients, AND valve area—particularly in low cardiac output states where gradients are unreliable. 6

Paradoxical low-flow severe AS: If your ejection fraction is preserved (≥50%), you may have paradoxical low-flow aortic stenosis, characterized by a small, thick-walled left ventricle with restrictive physiology despite normal EF. 6, 4 This represents approximately one-third of severe AS cases and carries significant mortality risk. 4

Primary myocardial dysfunction: Reduced contractility from cardiomyopathy, ischemic heart disease, or other causes of systolic dysfunction. 1, 2

Severe mitral regurgitation: Could reduce forward stroke volume while the volumetric method captures total LV output. 6

Immediate Next Steps

Essential Diagnostic Workup

Dobutamine stress echocardiography: The ACC/AHA guidelines recommend this as a Class IIa indication to evaluate low-flow/low-gradient states and determine whether stenosis is truly severe or only moderate. 6 This test assesses:

• Whether you have flow reserve (ability to increase SV >20% with dobutamine)
• Whether valve area remains fixed (<1.0 cm²) with increased flow (true severe stenosis)
• Whether gradients rise appropriately with increased flow 6

Aortic valve calcium scoring by CT: The ACC/AHA and ESC guidelines recommend calcium scoring to confirm anatomic severity of stenosis when flow is low, as this measurement is independent of flow state. 6, 4 Thresholds indicating severe AS: ≥3000 Agatston units in men or ≥1600 in women. 4

Complete hemodynamic assessment: If echocardiographic data remain discrepant or inconclusive, cardiac catheterization with hemodynamic measurements (Class IIa recommendation) can definitively assess valve area, gradients, and cardiac output under controlled conditions. 6

Assessment for coronary artery disease: Given your age and low cardiac output, coronary angiography should be considered as ischemic cardiomyopathy is a common reversible cause. 6

Critical Pitfalls to Avoid

Do not dismiss low gradients as "moderate" stenosis: In low-flow states, pressure gradients systematically underestimate anatomic severity because gradient is flow-dependent. 6, 4 A mean gradient of 20-30 mmHg with your stroke volume could still represent severe stenosis.

Do not rely solely on AVA calculations from 2D echo: LVOT diameter measurement errors are extremely common and lead to overestimation of stenosis severity, particularly in patients with small, hypertrophied ventricles. 4 Alternative measurements using 3D TEE or cardiac CT may be needed.

Do not assume preserved EF means adequate cardiac function: Paradoxical low-flow AS demonstrates that normal ejection fraction does not guarantee adequate stroke volume or cardiac output. 6, 4

Prognostic Implications

Your severely reduced SVI <30 mL/m² carries independent prognostic significance regardless of the underlying cause. 5 This threshold is associated with significantly reduced 5-year survival and increased mortality risk even in asymptomatic patients. 5 The combination of advanced age (73 years) and severely reduced cardiac index substantially increases risk for adverse outcomes including heart failure decompensation, syncope, and sudden cardiac death. 4

This is not a "wait and see" situation—you need comprehensive evaluation now to identify treatable causes and determine appropriate management, which may include surgical or transcatheter intervention if severe valvular disease is confirmed. 6