In this prospective, randomized, multicenter, open-label interventional clinical trial, the investigators' aim to test the effect of Cardiac Resynchronization Therapy (CRT) in cases of new-onset and persistent Left Bundle Branch Block (LBBB) occurring in the context of Transcatheter Aortic Valve Implantation (TAVI), in patients with moderately reduced left ventricular systolic function (35% < EF < 55%). The investigators hypothesize that in patients with persistent LBBB developing after TAVI and mildly reduced left ventricular systolic function (35% < EF < 55%), early postoperative CRT implantation favorably influences the process of myocardial reverse remodeling by reducing electromechanical dyssynchrony, thereby decreasing the combined endpoint of heart failure-related hospitalizations and mortality at one year.

Inclusion Criteria:

• Age over 18 years
• Successful and complication-free TAVI implantation for significant aortic stenosis
• Signed informed consent after detailed patient information
• New-onset LBBB wider than 130 ms after TAVI, persisting at the time of planned discharge (assessed postoperatively on or after day 5)(21)
• Mildly reduced left ventricular systolic function on echocardiography at the planned time of discharge (at the earliest on postoperative day 5), with EF between 35% and 55%

Exclusion Criteria:

• Pre-existing right bundle branch block, or prior pacemaker/ICD implantation associated with significant (>20%) ventricular pacing

  • Progression of LBBB during hospitalization to a degree indicating pacemaker implantation (e.g., Mobitz II or third-degree AV block, alternating bundle branch block) before the planned discharge date
  • Concomitant severe valvular disease of other valves (mitral, pulmonary, or tricuspid)
  • Severe infection and/or septic state
  • TAVI-associated stroke
  • More than moderate paravalvular leak of the TAVI valve on postoperative echocardiography
  • EF < 35% or > 55% on echocardiography performed at the planned time of discharge
  • GOLD stage IV COPD
  • Chronic renal failure requiring regular dialysis
  • Concurrent participation in another clinical trial