Conduction System Pacing Improved Cardiac Functions, Myocardial Work and Functional Capacity in Heart Failure with Reduced Ejection Fraction and Right Bundle Branch Block

<b>Background/Objectives:</b> Conduction system pacing (CSP) is a potential alternative to biventricular pacing (BVP) in heart failure with reduced ejection fraction (HFrEF) and left bundle branch block (LBBB) or non-LBBB. Available data also suggest that unlike BVP, CSP may improve clinical outcome in patients with right bundle branch block (RBBB), although its effects on cardiac mechanics and energetics are ill-defined. Herein, we report on echocardiographic and clinical outcomes of CSP in this patient cohort. <b>Methods:</b> CSP either with His bundle pacing or LBB area pacing was attempted as a primary strategy in patients with RBBB, QRS duration ≥ 130 ms, LVEF < 35% and NYHA II-IV symptoms after optimized medical therapy for 6 months. Data on functional status, NT-proBNP and echocardiographic parameters were collected at baseline and 6 months after CSP. <b>Results:</b> CSP performed in 16 patients reduced QRS duration from 155.3 ± 12.8 ms to 130 ± 16.5 ms (<i>p</i> < 0.001), increased LVEF from 27 ± 7% to 33 ± 9% (<i>p</i> = 0.01), improved LV global longitudinal strain from -7 ± 3% to -10 ± 4% (<i>p</i> = 0.004) and improved LV peak strain dispersion from 126 ± 28 ms to 96 ± 23 ms (<i>p</i> = 0.004). Global myocardial work index increased from 582 ± 277 mmHg% to 840 ± 306 mmHg% (<i>p</i> = 0.003), as did global constructive work (900 ± 374 mmHg% to 1203 ± 393 mmHg%; <i>p</i> = 0.006) and global work efficiency (from 71 ± 7% to 77 ± 8%; <i>p</i> = 0.004). NYHA class (12.5% with NYHA II, 87.5% with NYHA III before vs. 25% with NYHA I, 50% with NYHA II and 25% with NYHA III at 6 months; <i>p</i> = 0.002) and 6 min walk distance (from 354 ± 88 m to 411 ± 95 m; <i>p</i> = 0.003) improved, while NT-proBNP decreased (from 4093 ± 7215 ng/L to 2087 ± 2872 ng/L, <i>p</i> = 0.003). <b>Conclusions:</b> CSP improved functional capacity and echocardiographic parameters related to cardiac functions and myocardial work in HFrEF patients with RBBB. Nevertheless, these results await further confirmation by large-scale, multi-center randomized trials.