*3.4. LV Dimension and Function in CRT Responders Versus CRT Non-Responders*

There was no difference in baseline LV dimensions, systolic function, and QRS duration between CRT responders and the CRT non-responders: WMD = −2.18% [95% CI from −24.01 to 19.6, *p* < 0.85]; baseline left ventricle end-systolic volume (LVESV): WMD = −4.22% [95% CI from −22.1 to 13.6, *p* = 0.64]; baseline left ventricular end-diastolic dimension - LVEDd: WMD = −1.74% [95% CI from −4.76 to 1.27, *p* = 0.26]; baseline left ventricle ejection fraction (LVEF): WMD = 0.76% [95% CI from −3.34 to 4.86, *p* = 0.72] (Figure S2: Supplement 4); and baseline QRS duration; WMD = −2.60% [95% CI from −10.9 to 5.79, *p* = 0.54] (Figure S3: Supplement 5). Similarly, no difference was found in the LA dimension, which had a WMD of −2.17% [95% CI from −7.1 to 2.67, *p* = 0.38], between the two groups.

#### *3.5. The Relationship between LA and LV Function in CRT Responders*

To test for potential associates with CRT response, we calculated the weighted summary correlation coefficient between the LA function and LV parameters of CRT responders. This analysis showed that the increase in LA strain was associated with a fall in left ventricular end-systolic volume - LVESV's weighted summary correlation (*r*) [*r* = <sup>−</sup>0.56 (CI from <sup>−</sup>0.68 to <sup>−</sup>0.40, *p* < 0.001) Q<sup>2</sup> = 0.06, df = 0.2, I <sup>2</sup> = 0.0%, *p* = 0.86] and an increase in the LVEF [*r* = 0.58 (CI from 0.42 to 0.69, *p* < 0.001) Q2 = 0.72, df = 2, I<sup>2</sup> = 0.0%, *p* = 0.69; Figure 5,b]. Similarly, although with a less significance, the increase in the LA EF correlated with the fall in LVESV [*<sup>r</sup>* <sup>=</sup> <sup>−</sup>0.51 (CI from <sup>−</sup>0.63 to <sup>−</sup>0.36, *<sup>p</sup>* <sup>&</sup>lt; 0.001) Q2 <sup>=</sup> 0.92, df <sup>=</sup> 0.2, I <sup>2</sup> = 0.0%, *p* = 0.86] and with the increase in the LVEF [*r* = 0.48 (CI from 0.33 to 0.61, *p* = 0.002) Q<sup>2</sup> = 0.36, df = 0.2, I2 = 0.0%, *p* = 0.83; Figure 5c,d]. The increase in LA strain correlated with the increase in the LA EF (r = 0.57 (CI from 0.43 to 0.70, *p* < 0.001) Q2 = 0.16, df = 1, I2 = 0.0%, *p* = 0.64; Figure S4: Supplement 6).

**Figure 5.** Weighted summary correlation between (**a**) LA (left atrial) ( strain vs. left ventricle end-systolic volume (LVESV); (**b**) LA strain vs. left ventricle ejection fraction (LVEF); (**c**) LA EF (ejection fraction) (vs. LVESV; and (**d**) LA EF vs. LVEF (left ventricle ejection fraction).
