Comparative Evaluation of Three Transthoracic Echocardiographic Techniques for Cardiac Output and Stroke Volume Assessment Across Hemodynamic States

Abstract

Objective

This study compared the accuracy of three transthoracic echocardiographic (TTE) techniques—fractional shortening (FS), left ventricular outflow tract velocity-time integral (LVOT/VTI), and Simpson's method—for measuring cardiac output (CO) and stroke volume (SV) in hemodynamically unstable patients (systolic pressure < 90 mmHg), using pulse index continuous cardiac output (PiCCO) as the reference.

Methods

A retrospective analysis was conducted involving 12 patients admitted to an Emergency Intensive Care Unit between October 2023 and October 2024, who underwent a total of 54 echocardiographic examinations. The median length of hospital stay is 14 days. CO and SV values obtained using the three TTE methods as part of routine assessment were compared with simultaneous PiCCO measurements. The median number of examinations for patients is 4. Statistical analysis was performed using correlation methods.

Results

All three TTE methods demonstrated the capability to estimate CO and SV. The VTI method showed the highest overall accuracy (CO-VTI vs. CO-PiCCO: r = 0.950, p< 0.001). Under reduced CO conditions, correlations between echocardiographic and PiCCO-derived measurements decreased for all methods; however, the VTI method maintained superior reliability (r = 0.606, p = 0.006). In contrast, the Simpson's method did not accurately reflect CO in this setting (SV-Simpson vs. SV-PiCCO: r = 0.408, p = 0.083). Notably, the performance of the VTI method remained consistent regardless of SV or heart rate variations (SV-VTI vs. SV-PiCCO: overall r = 0.970; with heart rate > 100 bpm, r = 0.946; with heart rate ≤ 100 bpm, r = 0.988).

Conclusion

The LVOT/VTI method exhibits the highest accuracy and consistency for measuring SV and CO, making it the preferred non-invasive technique for hemodynamic evaluation in critically ill patients.