Angle Independency of Fetal Speckle-Tracking Echocardiography: Response

Abstract

Response of the Authors: We thank Dr. Nichting and colleagues for their interest in our paper. With respect to possible explanations of the results we reported, as we stated in our paper, the anisotropic nature of B-mode ultrasound “could be a possible explanation for the degree of angle dependence of the GLS [global longitudinal strain] values in our data.”1Semmler J. Day T.G. Georgiopoulos G. Sharland G. Charakida M. Simpson J.M. et al.Fetal speckle-tracking: impact of angle of insonation and frame rate on global longitudinal strain.J Am Soc Echocardiogr. 2020; 33: 1141-1146.e2Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar Given the semiautomated nature of the speckle-tracking software, the user has little insight into the processes in the background, so assertions about the reasons during fetal life remain somewhat speculative. The angle independency referred to by Nichting and colleagues is from animal and human studies2Amundsen B.H. Helle-Valle T. Edvardsen T. Torp H. Crosby J. Lyseggen E. et al.Noninvasive myocardial strain measurement by speckle tracking echocardiography: validation against sonomicrometry and tagged magnetic resonance imaging.J Am Coll Cardiol. 2006; 47: 789-793Crossref PubMed Scopus (1029) Google Scholar and confirmed angle independency to the extent that both apical four-chamber and short-axis views correlated with sonomicrometry. In postnatal life, the four-chamber view is limited by the sonographic window, so different projections of the four-chamber view are technically very difficult or impossible. We agree entirely that probe selection, sector width optimization, and the other measures described are important to optimize. In the up/down projection, the visualization of the full myocardial thickness will depend on lateral resolution. This projection is the one that is used during postnatal life for technical reasons as outlined above and for which the most validation data exist. We are not certain what is meant by not examining oblique and perpendicular angles as a reference. For the assessment of the effect of the insonation angle on GLS, apex up/down was selected as the reference group to compare its GLS values with those of apex oblique and apex perpendicular. In our paper, the measured GLS in each of the projections for the same fetus during the same study is presented and clear trends emerge, irrespective of whether a high frame rate or low frame rate setting was used. The method of analysis employed in our paper compared the results of GLS within the same fetus and accounted for the gestational age of the measurement, and we do not accept that the differences observed are due to normal variation between different gestational ages. Essentially, the comparisons within each fetus are being analyzed. With respect to clinical relevance, our study only included fetuses with normal cardiac structure and function. We did not set out to assess disease states or to look at predictive value of any measures. In clinical practice, no fetal cardiology guideline to date has included routine use of speckle-tracking, and we agree with the comments about vendor dependency of normal ranges. Many studies, however, are using speckle-tracking as a research tool to examine subclinical changes in myocardial function in different cohorts. One of the key points of our publication is that the design of prospective studies should take account of potential angle dependency of speckle-tracking measurements in their design, particularly with respect to the image acquisition protocol. Angle Independency of Fetal Speckle-Tracking Echocardiography: A Commentary LetterJournal of the American Society of EchocardiographyVol. 35Issue 7PreviewSpeckle-tracking echocardiography (STE) was introduced in 2004 to assess cardiac strain in adults. The assumed angle independency of STE can be a major advantage in the assessment of the fetal heart function in a highly motile fetus. Angle independency has been verified in in vitro studies,1 but validation has never been performed during fetal life. Semmler et al.2 were the first to investigate this objectively in a clinical setting. They found a significant difference between insonation angles and fetal left ventricular global longitudinal strain (GLS). Full-Text PDF