Author + information
- Published online September 13, 2017.
- Hugo Rodríguez-Zanella, MD,
- Kristina Haugaa, MD, PhD,
- Francesca Boccalini, MD,
- Eleonora Secco, MD,
- Thor Edvardsen, MD, PhD,
- Luigi P. Badano, MD, PhD and
- Denisa Muraru, MD, PhD∗ ()
- ↵∗Department of Cardiac, Thoracic, and Vascular Science, University of Padua, Via Giustiniani 2, 35128 Padua, Italy
Two-dimensional speckle-tracking echocardiography enables the examiner to measure the timing of segmental myocardial shortening and its synchronicity by mechanical dispersion (MD). Prolonged MD reflects increased temporal heterogeneity of myocardial contraction and has been reported to be useful to stratify arrhythmic risk among patients with different cardiac conditions (1–3). Nonetheless, the physiological determinants of MD have not been comprehensively studied, and reference values for this parameter remain to be determined. Accordingly, a cross-sectional observational study was performed at the University of Padua (Padua, Italy) and Oslo University Hospital (Oslo, Norway). We included 334 white healthy volunteers without cardiovascular risk factors to establish reference values for this parameter and to determine how demographic, physiological, and hemodynamic parameters and echocardiographic image quality may affect MD values. All patients had normal physical examinations, electrocardiograms, and echocardiographic examinations. The study was approved by the University of Padua Ethics Committee (protocol #2380 P, approved on June 10, 2011) and the Regional Committee for Medical Research Ethics in Norway (#S-05376). MD was defined as the SD of the time from the peak of the R wave on the electrocardiogram to the peak negative strain using a 16-segment left ventricular model obtained from 3 optimized apical views for speckle-tracking echocardiography analysis with a frame rate between 50 and 80 frames/s. All calculations of MD and global longitudinal strain (GLS) were done using a commercially available software package (EchoPAC version BT113, GE Vingmed Ultrasound, Horten, Norway); post-systolic peaks were included, and the system pre-set spatial and temporal smoothing was not modified.
In our cohort, the median age was 42 years (range 18 to 79 years), 54% of the patients were female, body mass index was 23 ± 3 kg/m2, left ventricular ejection fraction was 63 ± 7%, and GLS was −20.6 ± 2.2. MD was feasible in 96% of our subjects. Intraobserver and interobserver correlation coefficients were 0.95 (95% confidence interval: 0.89 to 0.98) and 0.94 (95% confidence interval: 0.88 to 0.98), respectively. MD did not differ between men and women or among the 4 image quality datasets (excellent, good, average, poor) (p = 0.39). However, MD values increased significantly with age (Table 1).
On bivariate analysis, MD showed correlation with image temporal resolution (r = 0.16; p = 0.01) and with GLS (r = −0.39; p < 0.001). Systolic blood pressure showed a tendency to correlate with MD (r = 0.11; p = 0.06). Age showed the strongest correlation with MD (r = 0.43; p < 0.001). Conversely, we did not find any correlation of MD with diastolic blood pressure (p = 0.2), sex (p = 0.79), end-diastolic volume index (p = 0.94), end-systolic volume index (p = 0.95), left ventricular ejection fraction (p = 0.57), heart rate (0.34), or image quality score (p = 0.8).
By using linear regression analysis, age, systolic blood pressure, body mass index (p = 0.004), early to late diastolic transmitral flow velocity (E/A ratio) (p < 0.001), E to early diastolic mitral annular tissue velocity (E/e′) ratio (p = 0.007), and GLS (p < 0.001) were found to be significant correlates of MD. Significant variables were entered in the multivariate regression analysis, after which only age (p < 0.001), GLS (p < 0.001), and E/e′ ratio (p = 0.007) were found to be independent correlates of MD, and together they accounted for 23% of its variability.
Given that aging leads to an increase in interstitial collagen deposition, and GLS and MD have been shown to correlate with myocardial fibrosis (1,4), it is plausible that increasing age leads to a progressive rise in MD. Accordingly, specific reference values for MD are provided, thus aiming to foster its application into clinical practice and expand its presence in the research arena. Further studies are needed to show whether age-specific reference values for MD may further improve arrhythmic risk stratification of patients and whether MD may be also a predictor of death or heart failure because it seems to reflect interstitial fibrosis.
Please note: The study was funded by Regione Veneto under the Program Ricerca Sanitaria Finalizzata RP-2014-00000409 (grant #CUP I52I15000100007). Dr. Rodríguez-Zanella received a training grant from the National Institute of Cardiology of Mexico Ignacio Chávez and the Mexican Society of Cardiology. Dr. Badano has received research equipment support from TomTec Imaging Systems and Siemens Healthineers; and has served on the Speakers Bureau for GE Healthcare. Dr. Muraru has received equipment grants from GE Healthcare and TomTec Imaging Systems; and has received a Speakers fee from GE Healthcare. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- 2017 American College of Cardiology Foundation
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