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Background: Recently, conduction system pacing, including His bundle and left bundle branch area pacing (LBBAP), has emerged as an alternative pacing procedure for right ventricular (RV) pacing. The current study aimed to compare the clinical outcomes of LBBAP and conventional RV midseptal pacing (RVMSP) in patients with heart failure (HF) with preserved ejection fraction (HFpEF) and HF with midrange ejection (HFm-rEF) requiring frequency RV pacing due to atrioventricular block (AVB). Methods: A total of 89 patients with HFpEF and HFmrEF requiring RV pacing due to symptomatic AVB were enrolled between September 2018 and April 2021, among whom 43 and 46 underwent LBBAP and RVMSP, respectively.Results: No significant differences in baseline characteristics were observed between the two groups. The LBBAP group had a significantly shorter paced-QRS duration and paced left ventricular activation time (LVAT) compared to the RVMSP group (123.4 ± 10.4 ms vs. 152.3 ± 12.3 ms, p < .001 and 68.3 ± 10.0 ms vs. 95.2 ± 12.3 ms, p < .001, respectively). The LBBAP group had significantly lower N-terminal pro-Btype natriuretic peptide (NT-proBNP) levels at the 6-month follow-up compared to the RVMSP group [459.6 pg/ml (240.4-678.7) vs. 972.7 pg/ml (629.5-1315.9), p = .01].More patients in the LBBAP group exhibited a significant improvement in NT-proBNP, defined as a > 50% decreased from baseline levels. Conclusion: LBBAP maintains physiological ventricular activation and contributes togreater improvement in NT-proBNP value 6 months after implantation in patients with HFpEF and HFmrEF compared to RVMSP.

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Introduction: Although recent echocardiographic studies have suggested that left atrial appendage (LAA) remodeling contributes to the development of LAA thrombus (LAAT), histological evidence is absent. The objective of this study was to examine clinical parameters and histological findings to clarify the factors involved in LAAT formation. Methods: A total of 64 patients (no atrial fibrillation [AF], N = 22; paroxysmal AF, N = 16; nonparoxysmal AF, N = 26) who underwent LAA excision during surgery were enrolled. Transthoracic and transesophageal echocardiography were performed before surgery. We evaluated the fibrosis burden (%) in the excised LAA sections with Azan-Mallory staining in patients with a LAAT compared with those without.Results: Patients with paroxysmal and non-paroxysmal AF had a higher LAA fibrosis burden than those without AF (p = .005 and p < .0001, respectively). Among the patients enrolled, 16 had a LAAT and 15 of them had nonparoxysmal AF. Among the nonparoxysmal AF patients, those with a LAAT had significantly higher LAA fibrosis burden than those without (23.8% [14.8%-40.3%] vs. 12.8% [7.4%-18.2%], p = .004) and echocardiographic parameters of the left atrial volume index (R = 0.543, p = .01), LAA depth (R = 0.452, p = .02), and LAA flow velocity (R = − 0.487, p = .01) were correlated with the LAA fibrosis burden. Conclusion:This study provided histological evidence that LAA fibrosis is related to LAAT formation. Echocardiographic parameters of LAA remodeling and function were correlated with the LAA fibrosis burden.

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