Intraventricular Conduction Delay

The goal of this observational study is to evaluate the long-term clinical outcomes of physiologic cardiac resynchronization therapy (CRT) using conduction system pacing strategies compared with conventional biventricular CRT in patients with heart failure with reduced ejection fraction (HFrEF) and electrical dyssynchrony. The main questions it aims to answer are: * Does physiologic CRT (including left bundle branch area pacing \[LBBAP\] and LBBAP-optimized CRT) reduce the combined risk of all-cause mortality and heart failure hospitalization compared with conventional biventricular CRT? * Does physiologic CRT improve cardiac function and reverse ventricular remodeling more effectively than conventional CRT? Participants receiving physiologic CRT as part of routine clinical care will undergo standard follow-up evaluations, including electrocardiography, echocardiography, laboratory testing, and device interrogation. Clinical outcomes will be collected prospectively for 24 months and compared with a historical cohort of patients treated with conventional biventricular CRT. The study will assess clinical outcomes, echocardiographic response, electrical resynchronization parameters, and device-related safety in a real-world heart failure population.

The investigators aim to prospectively test the comparative effectiveness of His or Left bundle branch pacing in relation to patient centered outcomes (quality of life, physical activity, heart failure hospitalization, mortality) and comparative safety in relation to device-related complications and re-interventions (e.g., lead dislodgement, infection) relative to standard of care biventricular pacing in patients with heart failure due to left ventricular systolic dysfunction (LVEF≤50%) and with either a wide QRS (≥130 ms) or with/anticipated \>40% pacing who are already receiving current standard heart failure pharmacological therapy.

The main objective of the project is to demonstrate that in patients with heart failure and QRS complex of nonRBBB morphology lasting over 130 ms, UHF-ECG can differentiate patients with trueLBBB from IVCD better than existing approaches based on the assessment of QRS complex morphology and duration from 12-lead ECG. Another goal of the proposed study is to demonstrate that trueLBBB patients will benefit more from CRT using left bundle branch pacing than from CRT using biventricular pacing. The final aim of the project is to demonstrate that the echocardiographic and clinical response in patients with intraventricular conduction disturbance will be dependent on the degree of reduction in ventricular dyssynchrony after CRT.