*3.2. Characteristics of Included Studies*

A total of 488 patients from the seven observational studies were included (Table 1). CRT responders were 181 and CRT non-responders were 118, with mean follow-up period of six months for both groups. The mean age of patients was 62.1 ± 10.2 years, and 68.3% were males. The mean QRS duration was 156 ± 38, and ischemic etiology for heart failure was found in 33.4% of patients. Between the two groups of patients, CRT responders and non-responders had no difference in age (61.9 ± 7.3 vs. 62.4 ± 10 years, *p* = 0.67, respectively), male gender (69% vs. 66%, *p* = 0.19), ischemic etiology (34% vs. 31.8%, *p* = 0.58) or QRS duration (155.2 ± 31 vs. 156.3 ± 34 ms, *p* = 0.42, Table 2).


 study.

**Table** 


CRF (chronic renal failure), MR (mitral

regurgitation),

 2DE (two dimensional

echocardiography),

 LVESV (left ventricle end-systolic volume) and mo (months).



R (respond), Non-R (non-respond), LVESV (left ventricle endsystolic volume), LVEF (left ventricle ejection fraction), NR (non-reported) and only whole group represented. change of LVESV. LVEF was represented only in CRT responders.

#### *J. Clin. Med.* **2020** , *9*, 298

## *3.3. LA Function in CRT Responders Versus CRT Non-Responders*

The pooled analysis showed that CRT responders had no baseline difference in LA strain compared to non-responders, with a WMD of 1.46% [95% CI from −1.58 to 4.50, *p* = 0.35], whereas the LA EF was higher with a WMD of 4.25% [95% CI from 0.42 to 8.08, *p* = 0.03; Figure 2a,b] in responders.

**Figure 2.** Baseline comparison of LA (left atrial), CRT (function in group of patients with cardiac resynchronization therapy), responders vs. CRT non responders. (**a**) LA strain; (**b**) LA ejection fraction (EF).

At follow-up, LA strain increased significantly in CRT responders with a WMD of −5.70% [95% CI from −8.37 to −3.04, *p* < 0.001] compared to non-responders, in whom it remained unchanged, with a WMD of 1.29% [95% CI from −2.08 to 4.67, *p* = 0.45; Figure 3a,b]. Likewise, the LA EF increased in CRT responders: WMD = −8.98% [95% CI from −15.1 to −2.84, *p* = 0.004] vs. WMD = −0.50% [95% CI from −13.3 to 12.3, *p* = 0.10] in non-responders (Figure 4). Heterogeneity across the included studies was not encountered at follow-up in either CRT responders or non-responders (Chi<sup>2</sup> = 4.05, I<sup>2</sup> = 26 df = 3, and *p* = 0.60 vs. Chi2 = 4.78, I<sup>2</sup> = 37, df = 3, *p* = 0.37, respectively) except for the moderate heterogeneity detected at the baseline LA strain between the two groups, as tested by the random-effect analysis (Chi<sup>2</sup> = 7.47, I<sup>2</sup> = 46, df = 4, *p* = 0.11).

**Figure 3.** Mean changed LA (left atrial) strain in patients with CRT (cardiac resynchronization therapy). (**a**) CRT responders; (**b**) CRT non responders.

**Figure 4.** Mean changed LA (left atrial) EF (ejection fraction) in patients with CRT (cardiac resynchronization therapy). (**a**) CRT responders; (**b**) CRT non-responders.
