Date Published: June 29, 2017
Publisher: Public Library of Science
Author(s): Yasufumi Nagata, Victor Chien-Chia Wu, Yutaka Otsuji, Masaaki Takeuchi, Maurizio Galderisi.
Newer 2D strain software has a potential to assess layer-specific strain. However, normal reference values for layer-specific strain have not been established. We aimed to establish the normal ranges of layer-specific longitudinal and circumferential strain (endocardial global longitudinal strain (GLS), transmural GLS, epicardial GLS, endocardial global circumferential strain (GCS), transmural GCS, and epicardial GCS).
We retrospectively analyzed longitudinal and circumferential strain parameters in 235 healthy subjects, with use of layer-specific 2D speckle tracking software (GE). The endocardial strain/epicardial strain (Endo/Epi) ratio was also measured to assess the strain gradient across the myocardium. The endocardial, transmural, and epicardial GLS values and the Endo/Epi ratio in the normal subjects were -23.1±2.3, -20.0±2.0, -17.6±1.9, and 1.31±0.07, respectively. The corresponding values of GCS were -28.5±3.0, -20.8±2.3, -15.3±2.0, and 1.88±0.17, respectively. The layer-specific global strain parameters exhibited no age dependency but did exhibit gender dependency except for endocardial GCS. A subgroup analysis revealed that basal and middle levels of endocardial LS was decreased in the middle and elderly aged group. However, apical endocardial LS was preserved even in the elderly subjects.
We proposed normal reference values for layer-specific strain based on both age and gender. This detailed strain analysis provides layer-oriented information with the potential to characterize abnormal findings in various cardiovascular diseases.
Two-dimensional (2D) speckle tracking echocardiography (STE) derived strain imaging in an emerging method to characterize left ventricular (LV) function in health and disease [1, 2]. Deformation imaging by STE has been shown to have superior prognostic value to conventional measures for predicting major adverse cardiac event . Although LV ejection fraction (LVEF) is the most often used parameter to evaluate LV mechanics, and is closely coupled to adverse cardiovascular outcomes , it is not sufficiently sensitive to detect subtle myocardial dysfunction . Strain by 2DSTE has gained popularity, because it allows clinicians to perform a more sophisticated assessment of LV systolic and diastolic function [1, 2, 6]. Among the various strain parameters derived from 2DSTE, global longitudinal strain (GLS) is most frequently used because of its robustness and reliability to detect latent systolic dysfunction and distinguish between high-risk patients with poor prognoses and patients with benign prognoses [7–9]. The usefulness of global circumferential strain (GCS) also reported in several studies [10, 11]. The LV myocardium has a complex architecture and consists of circumferential fibers in the midwall layer and longitudinal fibers in the endocardial and the epicardial layers [1, 12]. As acquired myocardial disease processes often develop firstly in the endocardium and endocardial fibers , the endocardial longitudinal strain (LS) may be more sensitive than transmural LS in the detection of subtle abnormalities observed during the early stages of heart disease. Recent advancements in 2D strain software have provided the capability to measure layer-specific strain (e.g., endocardial strain or epicardial strain), the usefulness of which has been described in recent publications [14–17]. However, normal ranges for each type of layer-specific strain and the normal strain gradient from the endocardium to the epicardium have not been determined [15, 18].
To the best of our knowledge, this was the first study to describe normal ranges for layer-specific GLS and GCS in a relatively large number of healthy subjects with approximately equal proportions of gender and age distributions. The primary findings of this study are summarized as follows: (1) gender dependency was observed for majority of layer-specific GLS and GCS values, whereas age dependency was not observed in all layer-specific GLS and GCS; (2) the Endo/Epi GLS and GCS ratio remained constant across all age groups. The Endo/Epi ratio of the female was lower than that of the male; (3) regarding the LS at each LV level, endocardial LS at the basal and the middle levels was significantly decreased after the 5th decade of life, a finding reflective of aging process of endocardial function.
This study was characterized by several limitations. First, we did not validate the accuracy of the 2D layer-specific strain measurements against reference standard such as CMR in our study subjects. Second, we could not exclude the possibility that some subjects have coronary artery disease. However, it is ethically impossible to perform invasive coronary angiography or coronary computed tomography in asymptomatic healthy subjects. Third, we did not compare the value of layer-specific strain between the different ultrasound vendors. Inter-vendor variability exists even in full-thickness strain due to differences of analytical algorithm. To make layer-specific strain clinical use, inter-vendor variability of layer-specific strain analysis should be investigated. Forth, this was a retrospective analysis which may call some selection bias. Fifth, this study did not cover the whole age group of subjects, which could not support generalizability of the results. Lastly, we did not include patients with ischemic heart disease (IHD). Clinical utility of 2D layer-specific STE for detection of IHD have recently been reported in several studies [16, 18, 23]. Further studies should be required to determine the usefulness of measuring layer-specific strain in various clinical settings.
We proposed normal reference values for layer-specific strain based on both age and gender. A layer-specific strain analysis provides layer-oriented information with the potential to characterize abnormal findings in the setting of cardiovascular disease.