Normal Ranges of Left Atrial Strain by Speckle-Tracking Echocardiography: A Systematic Review and Meta-Analysis

Background: Recent advances in the assessment of myocardial function have facilitated the direct measurement of atrial function using speckle-tracking echocardiography. Currently, normal reference ranges for atrial function using speckle-tracking echocardiography are based on a few initial studies, with variations among modestly sized (n = 100-350) studies. Methods: The authors searched the PubMed, Embase, and Scopus databases for the key terms left atrial/atrial/ atrium'' and strain/function/deformation/stiffness'' and speckle tracking/Velocity Vector Imaging/edge tracking.'' Studies of global left atrial function using speckle-tracking were selected if they involved > 30 normal or healthy participants without any cardiac risk factors. Normal ranges for reservoir strain, conduit strain, and contractile strain were computed using a random-effects model. Meta-regression and subgroup analysis was performed to explore between-study heterogeneity. Results: Forty studies (2,542 healthy subjects) satisfied the inclusion criteria. Meta-analysis revealed a normal reference range for reservoir strain of 39% (95% CI, 38%-41%, from 40 articles), for conduit strain of 23% (95% CI, 21%-25%, from 14 articles), and for contractile strain of 17% (95% CI, 16%-19%, from 18 articles). Meta-regression identified heart rate (P = .02) and body surface area (P = .003) as contributors to this heterogeneity. Subgroup analyses revealed heterogeneity due to sample size (n > 100 vs N < 100, P = .02). Conclusions: The normal reference ranges for the three components of left atrial function are demonstrated. The between-study heterogeneity is explained partly by heart rate, body surface area, and sample size.