Effects of frame rate on three-dimensional speckle-tracking-based measurements of myocardial deformation

Myocardial strain is useful in the evaluation of left ventricular function using high-frame rate two-dimensional (2D) speckle-tracking echocardiography (STE). Three-dimensional (3D) STE allows 3D measurement of myocardial deformation, which is potentially more accurate, because it is not affected by through-plane motion. However, the low frame rates of 3D STE are a potential limitation that has not been studied to date. Whereas with 2D STE, high frame rates are necessary because speckles may move out of the imaging plane, it was hypothesized that because they always remain within the scan volume, they should be tracked with 3D STE, even if frame rates are considerably lower.

Twenty-seven subjects were studied, including 16 normal volunteers and 11 patients with nonischemic dilated cardiomyopathy, who underwent 2D (frame rate, 62 ± 9 frames/sec) and 3D echocardiographic imaging. In normal subjects, 3D imaging was performed at four different frame rates, achieved by varying the number of beats used for full-volume acquisition (six, four, two, and one). In the patients with dilated cardiomyopathy, 3D imaging was performed using a four-beat acquisition. The principal components of strain and the corresponding strain rates were calculated in 16 myocardial segments and averaged. Both 2D and 3D images were analyzed using TomTec software to avoid analysis-related differences.

In normal subjects, strain and strain rate values were the same for 3D STE with six-beat and four-beat full-volume data sets, corresponding to 25 and 18 frames/sec, respectively. In contrast, 3D STE with one-beat and two-beat data sets, corresponding to 5 and 10 frames/sec, respectively, resulted in significantly lower values. Strain and strain rate values derived from six-beat and four-beat 3D data sets were not significantly lower than 2D STE-derived values, indicating that there was no loss of information due to lower frame rates. In patients with dilated cardiomyopathy, both 2D STE-derived and 3D STE-derived strain values were significantly reduced compared with normal hearts. The differences between 2D STE-derived and 3D STE-derived strain values echoed those noted in the normal subjects.

Three-dimensional speckle-tracking echocardiographic assessment of myocardial deformation is not compromised by low frame rates when derived from 18 or 25 frames/sec data sets but is underestimated with lower frame rates.