Association between QRS shortening and mortality after cardiac resynchronization therapy: Results from the DANISH study

Background: Changes in QRS duration (Delta QRS) are often used in the clinical setting to evaluate the effect of cardiac resynchronization therapy (CRT), although an association between Delta QRS and outcomes is not firmly established. We aimed to assess the association between mortality and Delta QRS after CRT in patients from the DANISH (Danish Study to Assess the Efficacy of ICDs in Patients with Non-Ischemic Systolic Heart Failure on Mortality) study. Methods: We included all patients from DANISH who received a CRT device and had available QRS duration data before and after implantation. Cox proportional hazards models were used to assess associations between Delta QRS (post-CRT QRS minus pre-CRT QRS) and mortality. Results: Complete data were available in 572 patients. Median baseline QRS duration was 160 ms (IQR [146;180]). Post-CRT QRS was recorded a median of 48 days (IQR [33;86]) after implantation, and the median Delta QRS was -14 ms (IQR [-38;-3]). During a median follow-up of 4.1 years (IQR [2.5;5.8]), 106 patients died. In crude Cox regression, all-cause mortality was reduced by 6% per 10 ms shortening of QRS (HR 0.94; CI: 0.88-1.00, p = 0.04). The effect did not remain significant after multivariable adjustment (HR 1.01, CI: 0.93-1.10, p = 0.77). Further, no association was found between Delta QRS and improvement of New York Heart Association functional class at 6 months (OR 1.03, CI: 0.96-1.10, p = 0.42). Conclusion: In a large cohort of patients with non-ischemic cardiomyopathy, reduction of QRS duration after CRT was not associated with changes in mortality during long-term follow-up.