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Background Permanent pacemaker implantation is central to the management of bradyarrhythmias. However, chronic right ventricular (RV) pacing may promote electrical and mechanical dyssynchrony, contributing to left ventricular (LV) dysfunction. Cardiac resynchronization therapy (CRT) improves outcomes in selected patients with ventricular dyssynchrony, yet CRT upgrades are frequently performed late. Increasing recognition of pacing-induced cardiomyopathy (PICM) highlights the importance of early identification. This audit evaluates CRT upgrade practice at a UK district general hospital.Methods We performed a retrospective observational audit of patients undergoing CRT upgrade at Wrexham Maelor Hospital, Wales between 2019-2025. Patients with pre-existing pacemaker or implantable cardioverter-defibrillator systems upgraded to CRT device were included. Data collected included demographics, pacing indication, device type, RV pacing burden, lead position, LV ejection fraction before initial implantation and prior to upgrade, NYHA class, time to upgrade, and device-related costs.Results Fifty-two patients underwent CRT upgrade. Most upgrades were from bradycardia devices (80.8%; table 1).Conclusions Patients undergoing CRT upgrade represent a high-risk population characterised by pre-existing LV dysfunction. Contributing factors included apical pacing and high RV pacing. Most patients who underwent a CRT upgrade had pre-existing LV impairment suggesting delayed recognition and missed opportunities for earlier initiation of heart failure therapies. These findings highlight the need for structured surveillance, early identification of high RV pacing burden, and targeted echocardiographic screening.Abstract 486 Figure 1Left Ventricular Function Before Initial Device Implantation and CRT Upgrade (N = 52)LVEF definitions: HFrEF ≤40%, HFmrEF 41–49%, HFpEF ≥50%.RV pacing burden exceeded 40% in 65.4% with 92% of patients having apical RV lead positioning.RV pacing burden exceeded 40% in 65.4%, including 59.6% with >80% pacing, and 92% had apical RV lead positioning.Abstract 486 Figure 2Ventricular pacing burden and right ventricular lead position prior to CRT upgrade high RV pacing burden defined as >40%. CRT = cardiac resynchronization therapy. Published comparison data (NICOR) shown for contextAbstract 486 Table 1Indications for pacing and type of initial cardiac implantable electronic device in patients undergoing CRT upgrade (N = 52)VariableCategoryn (%) or n/N (%)Indication for pacingSinus node disease5 (9.6%)AV node disease28 (53.8%)Ventricular tachycardia10 (19.2%)Atrial fibrillation with slow ventricular rate9 (17.3%)Type of initial devicePermanent pacemaker (PPM)42 (80.8%)Implantable cardioverter-defibrillator (ICD)10 (19.2%)Data are presented as n (%). Pacing indications reflect the primary indication at initial device implantation. PPM = permanent pacemaker; ICD = implantable cardioverter-defibrillator.Prior to initial implantation, LV function was reduced (defined as LV EF <40%) in 19.2%. Immediately before CRT upgrade, 98% had moderate or severe LV systolic dysfunction (figure 1).