The risk of stroke in patients with atrial fibrillation (AF) is five times that of the general population [1,2], more than 75 % of stroke in patients with AF was due to left atrium or left atrial appendage (LAA) thrombi [2], over 90 % of which in non- valvular AF were found in LAA [3,4].

The congestive heart failure, hypertension, age ≥ 75, diabetes, stroke, vascular disease, age 65–74, and female sex (CHA2DS2-VASc) score is widely used to predict the risk of thromboembolic events in patients with AF [5]. However, the CHA2DS2-VASc score with a C-statistic of only 0.6, had modest accuracy to predict the risk of LAA thrombosis [6,7]. Besides, several studies found that CHA2DS2-VASc score of 0–2 could not completely exclude the risk of LAA thrombosis in patients with AF [8,9]. How to further stratify LAA thrombus risk and the indication for transesophageal echocardiography (TEE) before cardioversion or catheter ablation in patients with AF, especially those with lower CHA2DS2-VASc scores, is an important but unresolved issue.

As we know, the impaired LAA emptying velocity and spontaneous echo contrast (SEC) in LAA indicates blood stasis [10], especially severe SEC or sludge considered to be prethrombotic, is significantly associated with thrombosis in LAA, transient ischemic attack, and stroke [10,11]. The acquisition of these parameters depends on TEE [10]. However, TEE, as a semi-invasive examination, commonly leads to complications of throat and esophagus injury, furthermore, some patients are refused TEE due to fasting, nausea, vomiting and fear, resulting in difficulties in obtaining LAA function parameters. Thus, it is urgent necessary to explore a transthoracic echocardiography (TTE) parameter to evaluate LAA mechanical function and thrombosis risk in patients with non-valvular AF.

The LA is directly connected to the LAA, of which the mechanical function is affected by the spatial displacement and pressure of the LA [12,13]. Recently, several studies found that LA strain was significantly associated with LAA emptying velocity, SEC in LAA, or stroke [11,14,15].

Therefore, we hypothesized that LA strain parameters might be useful to assess LAA mechanical function and blood stasis in LAA. To the best of our knowledge, no data regarding the evaluation of the role of the LA strain parameters, which are LA filling index, LA filling rate, LA stiffness index, and LA stiffness rate, in assessing LAA mechanical function and thrombosis risk was reported, besides, there was limited data that LA strain parameters combined with conventional TTE parameters to evaluating the thrombosis risk in patients with non-valvular AF. Thus, we conducted this study to explore the relationship between the novel LA strain parameters and LAA mechanical function, furthermore, and to find a nice way in which the novel LA strain parameters combine with conventional TTE parameters to evaluating the thrombosis risk in patients with non-valvular AF, especially in those with lower CHA2DS2-VASc score (0–2).