From October 2016 to October 2017, a total of 67 AF patients who were about to undergo RFCA in the Second Affiliated Hospital of Harbin Medical University participated in our study, they were all with preserved left ventricular systolic function (left ventricular ejection fraction, LVEF > 50%). Exclusion criteria included intra-cardiac thrombi, structural heart disease, hyperthyroidism or other autoimmune diseases, rheumatic heart disease and LVEF < 50%. In addition, a total of 47 patients with sinus rhythm and LVEF > 50% were selected as control group, who came to hospital just because of primary hypertension, chronic coronary heart disease, or physical examination. The study complied with the Declaration of Helsinki and was approved by the Ethics Committee of Harbin Medical University. All patients signed a written informed consent form prior to participating in the study.

Baseline clinical information was collected and conventional echocardiography, M-PW mode echocardiography and dual Doppler echocardiography were performed on all subjects. Plasma NT-proBNP level was measured in the AF group. Both AF patients and the control group were subjected to transthoracic echocardiography using Aloka ProSound F75, Hitachi, Japan with a combined 1^_5-MHz Doppler transducer. All patients underwent precordial 2-dimensional, M-mode and Doppler echocardiography while in the left lateral position and all images were stored on a hard disk for subsequent playback and analysis. Left atrial diameter (LAD), LV end-diastolic and end-systolic dimensions were measured from the M-mode echocardiogram. LVEF was calculated by the Simpson method using 2-dimensional images. LA maximum volume was obtained by manually tracing the LA endocardium on the apical four-chamber and the apical two-chamber views by Simpson method before MV opening. LA maximum volume divided by body surface area, we obtained LA maximum volume index. We also recorded the early transmitral flow peak velocity (E: cm/s) and the tissue Doppler-derived mitral annular peak velocity in early diastolic (e’:cm/s), both at the lateral annulus(L) and the interventricular septal annulus(S). Transmitral velocity was tracked and peak acceleration (PkAcc) of the E velocity was measured on the machine (Fig. 1a). The flow of the right pulmonary vein was confirmed with the help of color doppler ultrasound, and the sample volume was placed 0.5 to 1 cm into the vein to record the velocity of pulmonary vein flow in the apical four-chamber view and we measured deceleration time of pulmonary venous diastolic velocity (PV-DT) (Fig. 1b).

Images from AF patients and the control group were collected with use of dual Doppler and M-PW mode echocardiography at identical cardiac cycles in the apical four-chamber view and five-chamber view. Simultaneous recordings of E and e’ were performed using the dual Doppler imaging method (Fig. 2). As shown in Fig. 2, two doppler sampling lines were placed at the tips of the mitral leaflets and mitral annulus, first at the lateral and then at the septal corners of mitral annulus, we obtained E/e’(L) and E/e’(S) in identical cardiac cycles [10]. The time interval between E and septal e’ (TE-e’) was then measured (Fig. 3). The Tei index was measured in the apical five-chamber view, with one sampling line placed between the mitral valve leaflets and the other placed at the aortic valve. The Tei index was then calculated by subtracting the LV ejection time (b) from the time interval between cessation and onset of the mitral inflow (a) divided by the LV ejection time (a-b/b) (Fig. 4a) [11]. Isovolumic relaxation time (IVRT) was measured from the end of aortic flow to the beginning of mitral flow (Fig. 4b). Placed the M-mode cursor with the pulsed sample volume in the center of the mitral valve, avoiding the surrounding area and in the same direction as the flow stream. The pulse doppler sampling volume was placed at the tips of the mitral valve to obtain E velocity. The slope of the first aliasing velocity during early filling was measured as Vp, extending 4 cm from the mitral valve into the left ventricle (Fig. 5) [12, 13]. E/e’, TE–e’, the Tei index and E/Vp were measured for 10 consecutive beats and the values were averaged.

All AF patients were required to take an anticoagulant (warfarin, dabigatran or rivaroxaban) for at least 3 weeks. A transesophageal echocardiography was performed on all patients to verify that no thrombus was present and a pulmonary vein CT to ensure that no significant variation was present among the patients. All 67 AF patients were subjected to RFCA by applying the ablation power at 35 watts with a temperature of 43 °C at the tip of the catheter. The left and right pulmonary vein ostia were ablated under the guidance of 3D electro-anatomical mapping systems (CARTO). The end point of RFCA was the elimination or isolation of pulmonary vein potential throughout the ostial circumference. If AF continued, a 120 J synchronized cardioversion was performed after a transvenous administration of 150 mg cordarone, to achieve sinus rhythm. Morphine was used to alleviate pain during the procedure. All the cases we selected were treated with the same drugs after RFCA.

Transthoracic echocardiography was performed immediately after RFCA to exclude the existence of pericardial effusion. Follow-up of patients included detailed inquiries regarding arrhythmia-related symptoms (dizziness, chest distress or cardiopalmus) and echocardiography examinations. A 24-h Holter was performed at 3, 6 and 12 months after the ablation to confirm the presence or absence of AF recurrence. Based on these follow-up results, preoperative echocardiography parameters of the patients were retrospectively analyzed.

Basic characteristics of the study sample were summarized in Table 1. No statistically significant differences in demographics or clinical risk factors were present between the AF and control group. Echocardiographic variables between the AF and control group are presented in Table 2. The LAD and LA maximum volume index of AF patients was significantly increased (p <  0.001). TE-e’、 E/e’(S)、 E/e’(L)、the Tei index and E/Vp were all increased in AF patients as compared with that of the control group (p <  0.05). PV-DT and IVRT were shorter in AF patients than the control group (p < 0.05). Of the 67 patients enrolled, 57 who had E/e’(S) ratios and 49 who had E/e’(L) ratios during 8 to 15 were analyzed, in which period E/e’ is indeterminate for the evaluation of left ventricular diastolic pressures. No significant differences between the two groups were obtained for LVEF, LV end-diastolic and end-systolic diameter.

All 67 patients with AF underwent successful pulmonary vein isolation or elimination by RFCA. In our study, 2 patients with AF recurrence underwent secondary radiofrequency ablation at their own discretion.

At the one-year follow-up examination after ablation, 21/67 (31.34%) AF patients relapsed. In the patients without AF recurrence, 7 of them had arrhythmia-related symptoms but no Holter confirmation of AF recurrence 1 year after ablation and their symptoms gradually improved. Characteristics of patients with or without AF recurrence after ablation are summarized in Table 3. Demographics, duration/type of AF, renal function and clinical risk factors were similar between the two groups. Echocardiography parameters of two groups are presented in Table 4. TE-e’ and the Tei index of patients with recurrence were significantly increased as compared with that of the group without recurrence(p <  0.001). PV-DT of the recurrence was shorter than the group without recurrence(p = 0.046). The LA maximum volume index of the recurrence was higher than the group without recurrence(p = 0.027). No significant differences were present for LV ejection fraction, LV end-diastolic diameter, LV end-systolic diameter, LAD, PkAcc of the E velocity, E, e’ (S), e’ (L), E/Vp, IVRT and NT-pro BNP between the two groups. Nor were the dual Doppler echocardiography parameters, E/e’(S) and E/e’(L) statistically significant between the groups with or without recurrence.

Univariate analysis of AF recurrence at 1 year of follow-up was shown in Table 5. LA maximum volume index and TE-e’ were associated with AF recurrence at 1 year after radiofrequency ablation. Results from multivariate analysis for AF recurrence after ablation indicated that TE-e’ was significantly associated with AF recurrence as determined at 1 year after RFCA. Accordingly, TE-e’ can serve as an independent predictor for AF recurrence after RFCA (odds ratio: 2.59; 95% confidence interval:1.45–4.64; p = 0.001) (Table 5).

Bland Altman analysis of two physicians’ measure for TE-e’ was shown in Fig. 6. The intra-class correlation coefficient of TE-e’ was 0.84, 95% confidence interval is 0.65–0.92.

Three notable limitations of our study should be acknowledged. The first being that this study involved a single-center, retrospective evaluation for AF recurrence. Second, the limited sample size of our study precluded our ability to achieve the necessary cutoff value of TE-e’ for prediction of recurrence. Third, the one-year follow-up of patients after ablation in this study may underestimate the recurrence rate of AF, because only intermittent 24-h Holter records and follow-up may lead to the omission of asymptomatic recurrence patients during clinical follow-up.