Response to Letter Regarding Article, “Subclinical Left Ventricular Dysfunction and Silent Cerebrovascular Disease: The Cardiovascular Abnormalities and Brain Lesions (CABL) Study”
Authors: Cesare Russo, Zhezhen Jin, Shunichi Homma, Mitchell S.V. Elkind, Tatjana Rundek, Mitsuhiro Yoshita, Charles DeCarli, Clinton B. Wright, Ralph L. Sacco, Marco R. Di Tullio
Journal: Circulation (2014)

In their Letter to the Editor about our recent publication, 1 Drs Rai and Bughio correctly point out that we previously demonstrated that left atrial (LA) phasic volumes were independent predictors of subclinical brain disease. 2 We agree that LA strain (LAε) can detect early LA dysfunction and may be also associated with subclinical brain disease.In fact, we recently described the independent association between LAε and silent brain infarcts. 3In that study, peak positive longitudinal LAε and strain rate were associated with silent brain infarcts, with adjusted odds ratios of 2.46 and 2.39 per 1-SD decrease, respectively (both P<0.001).However, measuring highly complex speckle-tracking parameters such as LAε in large community-based studies not specifically designed for that purpose can be difficult.In our study, optimal LAε measurement was possible only in a subgroup of participants; therefore, LAε was excluded from the main analysis.We concur with Drs Rai and Bughio that other speckle-tracking parameters may help understand complex changes in myocardial mechanics associated with left ventricular dysfunction.In our experience, however, these measures require optimal image quality and suffer from lower feasibility and reproducibility compared with global longitudinal strain (GLS), besides resulting in a significant increase in analysis time.Moreover, it is not clear whether these parameters offer any substantial benefit over GLS.GLS is an established measure of left ventricular subclinical dysfunction in research and clinical settings.Its advantages over other parameters include the following: (1) high feasibility in that it can be derived from standard, routinely obtained echocardiographic views; (2) better reproducibility and less influence by frame rate compared with other parameters 4 ; (3) better comparability across different echocardiographic platforms than circumferential and radial strain; and (4) evaluation of the longitudinal component of myocardial deformation, which is affected early in the course of a variety of clinical conditions. 5rs Rai and Bughio state that the frame rate we used of 45 frames per second is too low for optimal speckle density and distribution.Actually, because of the inverse relationship between temporal resolution (frame rate) and lateral resolution (scan lines), speckle density will be lower at higher frame rates for any given width and depth of imaging.Low frame rate is instead responsible for lower temporal resolution, which may lead to inaccurate tracking and underestimation of peak strain values.In large epidemiological studies performing speckle-tracking measurements on existing echocardiograms, frame rates may be lower than those obtained in smaller dedicated studies.In the Framingham study, the mean frame rate for speckle-tracking analysis was 41±6 frames per second. 6However, frame rates as low as 30 frames per second have been demonstrated to have limited impact on GLS measurements while more strongly affecting circumferential and radial strain. 4Low frame rates, however, were not an issue in our study.As described in our article, speckle-tracking measurements were performed on cine loops recorded at ≥45 frames per second.In fact, in most studies, frame rate ranges between 50 and 90 frames per second.Therefore, the temporal resolution was adequate, and there is no reason to believe that it had a significant impact on the results of our study.