Role of QRS narrowing on CRT upgrade outcomes: less is more

Introduction Chronic right ventricular (RV) pacing can lead to intraventricular desynchrony, which in approximately 30% of patients results in left ventricular (LV) dysfunction and progressive heart failure (HF) over time. In patients undergoing cardiac resynchronization therapy (CRT) upgrade, a reduction in QRS duration has been linked to improved clinical and echocardiographic outcomes, including a higher rate of responders. Accordingly, systematic assessment of QRS reduction after device implantation could provide valuable prognostic insight into patient response to CRT. Purpose To evaluate the incidence and impact of QRS narrowing within a year of CRT upgrade in a district hospital. Methods Single-center, observational and retrospective study of patients with RV pacing systems and HF with reduced LV ejection fraction (LVEF) who underwent upgrade to CRT between January 2015 to December 2024. CRT response was defined as NYHA class improvement ≥1 category and LVEF improvement by ≥5%, 6-12 months post-upgrade. Results We included 55 patients, 78% male, mean age 76±7.9 years. Most had a dual-chamber pacemaker (64%) or an ICD (20%), with a mean right ventricular pacing of 78 ± 33%. The average time from initial device implantation to CRT upgrade was 8±2.6 years. The mean age at upgrade was 73±7 years. All procedures were successful (CRT-D 76%, CRT-P 24%). HF etiology was ischemic in 54% of patients. Baseline mean QRS duration was 178±16ms. All the patients were in NYHA II-III, with mean LVEF 29.1±6.7%. 35 (64%) patients met criteria for response, with a mean ΔLVEF 10.7±8.9%. An improvement in NYHA functional class was seen in all patients with LVEF recovery, with 27 (49%) patients in NYHA I and 24 (44%) in NYHA II at 6-12 months. The average QRS duration significantly decreased from 178±16ms to 157±12ms after upgrade (P<0.001). Moreover, responders had a significantly greater QRS reduction compared with non-responders (–21±9ms vs –14±10ms; P=0.02). Patients with RV pacing ≥40% had a higher likelihood of response (P = 0.022), whereas baseline QRS duration did not differ between responders and non-responders (178±13 vs 176±16ms, P=0.786). Over a median follow-up of 5 years, 8 patients died. There was no significant association between baseline QRS duration or QRS change and mortality. Conclusion CRT upgrade in patients with prior pacemakers or ICDs was safe and effective, improving clinical and echocardiographic outcomes. Reversal of electrical desynchrony, reflected by QRS shortening, was associated higher rate of CRT response. Although responders had greater QRS reduction, this change was not linked to long-term mortality in this small cohort.