Background: Cardiac resynchronization therapy (CRT) improves survival in selected patients with heart failure (HF). As the potential survival benefit of CRT performed as an upgrade from a previously implanted cardioverter defibrillator (ICD) has been discussed by only a few studies, so we evaluated total mortality and predictors after CRT upgrade in this context.

Methods and results: A total of 55 patients (45 male, mean age:61.2±9.9 years) with structural heart disease underwent CRT device implantation as an upgrade of a previously implanted single or dual chamber ICD between 2004 to 2021 at our Institute. The indication for ICD implantation was prophylactic (in 17 patients) or secondary prevention after a sustained ventricular arrhythmia (in 38 patients). Mean left ventricular ejection fraction (LVEF) was 32.9±9.3% and mean NYHA status was 2.25±0.7 at the time of ICD implantation. No indication for CRT was present in any of these patients at the time of ICD implantation. CRT upgrade was performed after a mean follow-up of 3.9±3.0 years based on the following indications: widening of the QRS complex (from 108±21 to 160±24msec.) in 30, decreasing LVEF (from 41.7±2.0 to 27±2.4%) in the presence of LBBB in 7, and an increased need for right ventricular stimulation (burden >40%) in 18 patients. A significant reduction in the QRS width after CRT upgrade (from 160.1±25.5 to 133.2±19 msec., p<0.001), an improvement in NYHA class (from 3.0±0.8 to 2.3±0.8 p=0.001) and an increase in the mean LVEF (from 27.5±5.0 to 30.0±7.9%, p=0.02) at 1-year follow-up. 25/55 patients (45%) died during a mean follow-up of mean follow-up of 3.4±3.0 years after CRT upgrade. Survivors vs. the deceased population after upgrade differed in baseline variables: NYHA IV class, severe mitral regurgitation and wider QRS.

Conclusion: Despite significant reduction in QRS width and improvement in LVEF, mortality remains high after CRT upgrade in patients with previously implanted ICD. This would question the potential benefit of upgrade in this patient population and argue for an earlier administration of alternative treatment modalities (assist device, heart transplantation) in those who demonstrate QRS widening, a significant decrease in the LVEF or a need for ventricular stimulation.