Abstract Body (Do not enter title and authors here): Introduction:
Cardiac pacing devices, including Permanent Pacemakers (PPM) and Implanted Cardioverter Defibrillators (ICD), are essential in managing various cardiac conditions. Exercise capacity in patients hinges on both cardiac function enhancement and an appropriate chronotropic response. This case report underscores the strategic use of Cardiopulmonary Exercise Testing (CPET) to determine the activation of the Rate Response to Exercise (RRE) function in a patient with Heart Failure with reduced ejection fraction (HFrEF).

Case Report:
Our patient is a 64-year-old male with HFrEF due to hypertensive heart disease and ICD placement. He was undergoing therapy optimization at our advanced heart diseases clinic. Initially presenting with poor functional capacity, his condition improved significantly with ongoing therapy adjustments, as reflected by his KCCQ scores. This improvement enabled a comprehensive assessment using CPET. The initial CPET trial revealed moderately reduced exercise capacity and an absent chronotropic response, with a heart rate at 65 bpm and a peak VO2 of 67% predicted, categorizing him as Weber Class B. Based on these findings, we activated the RRE function and conducted a follow-up CPET. The re-evaluation demonstrated notable improvements: extended exercise duration post-anaerobic threshold, a peak VO2 of 72% predicted, and an upgraded Weber Class A status.

Summary: This case exemplifies how tailored programming of pacing devices can significantly enhance exercise capacity in HF patients. Activating the RRE function in the patient's PPM led to marked improvements in exercise capacity and prognostic indicators derived from CPET parameters, corroborating the limited existing data on this approach. Although specific guidelines are lacking, our findings highlight the utility of CPET in customizing PPM settings, particularly for HFrEF patients. This report underscores the importance of individualized treatment and invites further research into optimizing device settings to maximize patient outcomes. Leveraging CPET in routine clinical practice could revolutionize heart failure management, offering a precise and patient-centric approach.