Stroke volume can also be calculated as the difference between end-diastolic and end-systolic ventricular volume. Volumes are generally calculated from two-dimensional and M-mode images which rely upon assumptions about left ventricular shape. Recently developed technology allows three-dimensional reconstruction of images of the left ventricle.
1. Cube method: this assumes that wall motion is symmetrical and V = D3, where D is the short-axis diameter of the left ventricle.
2. Teichholz method: this uses the equation V = D3[7.0/(2.4 + D)] which corrects better for ventricular shape.
3. Bullet method: this assumes that the left ventricular cavity is bullet-shaped and that V = 5AL/6 where A is the cross-sectional area of the short axis and L is the cavity length.
4. Area-length calculations: these assume the left ventricle is an elongated ellipse. Images in two planes (best measured by a biplanar transesophageal approach) are derived, and the volume is calculated as 0.524 D1D2L where L is length and D1 and D2 are the orthogonal short-axis diameters.
5. Simpson's method: the volume of each 'slice' obtained from multiple short-axis images of known spacing is either calculated from its dimensions or measured by planimetry. The volumes are summed to yield a total ventricular volume. Irregular ventricular shape entails deriving more slices, good endocardial imaging, and accurate timing of images in the cardiac cycle.
6. Automated quantitation of cavity size using sophisticated real-time edge-detection technology has recently been demonstrated. Advantages are continuous measurement with little operator dependence.
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