How to determine stroke volume

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Determining Stroke Volume: Methods and Accuracy

Angiocardiographic Method for Stroke Volume Determination

Biplane Angiocardiography: One of the direct methods to determine left ventricular stroke volume is through biplane angiocardiography. This technique involves imaging the heart from two different planes to measure the volume of blood ejected from the left ventricle during each heartbeat. Studies have shown that stroke volumes determined by this method closely align with those obtained using the Fick and indicator-dilution methods, indicating its reliability in patients without arrhythmias or valvular insufficiency.

Pulse-Contour Method for Continuous Monitoring

Pulse-Contour Analysis: The pulse-contour method is a rapid and continuous technique for monitoring stroke volume, particularly useful in critically ill patients. This method involves analyzing the arterial pressure waveform to estimate stroke volume. Despite its simplicity and speed, the pulse-contour method has a coefficient of variation around 20%, making it less accurate for detecting small changes in stroke volume. However, it remains a valuable tool for continuous monitoring, especially in patients with atrial fibrillation or those undergoing various hemodynamic interventions.

Echocardiographic Methods for Stroke Volume Estimation

M-Mode and Two-Dimensional Echocardiography: Stroke volume can also be estimated using M-mode echocardiography by measuring the left ventricular dimensions. This method has been validated against two-dimensional and Doppler echocardiography, showing a mean relative error of less than 1.4%. The Z-derived method, which uses regression equations based on left ventricular dimensions, has proven to be more accurate than the traditional Teichholz formula, making it suitable for both clinical and epidemiological studies.

Doppler Echocardiography: Doppler echocardiography is another non-invasive method that measures stroke volume by calculating the time-velocity integral of blood flow at specific cardiac sites. The aortic annular leading edge technique, which combines the aortic annular cross-sectional area with the leading edge measurement of blood flow, has shown the highest accuracy among various Doppler methods, closely correlating with thermodilution measurements.

Advanced Imaging Techniques

Three-Dimensional Transesophageal Echocardiography: This advanced imaging technique involves using a transesophageal ultrasonic probe to create three-dimensional reconstructions of the left ventricular cavity. Studies in animal models have demonstrated high accuracy, with a correlation coefficient of 0.92 when compared to thermodilution measurements. This method, although currently tedious, offers a promising approach for accurate stroke volume determination.

Radionuclide Techniques: Radionuclide imaging, corrected for attenuation, provides another reliable non-invasive method for determining stroke volume. This technique has shown a high correlation with thermodilution measurements, making it a viable option for patients without intracardiac shunts or valvular disease.

Conclusion

Determining stroke volume accurately is crucial for assessing cardiac function and guiding treatment in various clinical settings. While direct methods like biplane angiocardiography and advanced imaging techniques offer high accuracy, simpler methods like pulse-contour analysis and echocardiography provide valuable tools for continuous monitoring and non-invasive assessment. Each method has its strengths and limitations, and the choice of technique may depend on the clinical context and the need for precision versus convenience.