This randomized controlled trial aims to investigate the impact of conduction system pacing in comparison to right ventricular apical pacing on exercise capacity, as measured by peak oxygen uptake (VO2peak), in heart failure patients with indication for pacing but no compelling indication for cardiac resynchronization therapy (CRT). The mechanisms of exercise intolerance in heart failure patients influenced by conduction system pacing will be assessed.

Heart failure (HF) is a serious condition that affects a lot of people and places a significant burden on the healthcare system. Some HF patients also have issues with the natural electrical system of their heart, causing uneven heart contractions and worsening heart function. A treatment known as CRT has been helping such patients, but it does not work for everyone. A new technique called conduction system pacing (CSP) has emerged that might offer a more natural way of maintaining heart contractions.

This study aims to determine if CSP can enhance the ability of HF patients to exercise, by looking at their maximum oxygen consumption (a measure of exercise capacity). It will also explore why some HF patients struggle with exercise more than others. Eligible patients will be randomly assigned to either the new CSP treatment or a standard pacing method (right ventricular apical pacing). Patients will be checked regularly over a follow-up period of 24 weeks.

The main goal is to see if patients can exercise better with CSP after 24 weeks. The study will also look at other heart measures and safety concerns related to the devices. This study might show that CSP can help improve exercise capacity and heart function in certain HF patients. The results could guide health care professionals in offering better, tailored treatments for their patients.

Inclusion Criteria:

Patients with heart failure as defined by European Society of Cardiology guidelines

• Signs and/or symptoms of heart failure
• AND LVEF <50% OR LVEF ≥50% and objective evidence of cardiac structural and/or functional abnormalities consistent with the presence of LV diastolic dysfunction/raised filling pressures
• AND indication for cardiac pacing as defined by European Society of Cardiology guidelines

Exclusion Criteria:

• Age under 18 years old
• Pregnancy
• Inability to provide consent or to undergo follow-up
• Class 1A indication for classical CRT as defined by European Society of Cardiology guidelines. Patients with a class 2A or higher indication for CRT can be included. However, patients with Class 1A indication for classical CRT but failure or suboptimal result of CS lead placement can be included.
• Significant cardiac or extracardiac comorbidity precluding maximal exercise testing, examples: Recent (<4 weeks) decompensation of heart failure, angina pectoris class ≥2 , uncontrolled hypertension or arrhythmia , severe valvular heart disease, significant peripheral vascular disease, orthopaedic limitation ...
• Comorbidity that may influence 6-month prognosis, examples:

Severe chronic kidney disease (eGFR ≤20 mL/kg/min or dialysis) , severe chronic obstructive pulmonary disease (≥GOLD 3) , active malignancy ...