Incidences and clinical outcomes of patients with a single or dual chamber implantable cardioverter-defibrillator developing an indication for cardiac resynchronization therapy.

AIMS

While studies have shown worse clinical outcomes in patients with an implantable cardioverter-defibrillator (ICD) who underwent an upgrade to cardiac resynchronization therapy (CRT) when compared to de novo CRT implantations, little is known about the clinical trajectory of these patients prior to upgrading to CRT.

METHODS AND RESULTS

This single-centre retrospective study included patients with ischaemic or non-ischaemic cardiomyopathy with a QRS duration <130 ms who underwent ICD implantation between 2010 and 2022. By reviewing the evolution of QRS duration, QRS morphology, and right ventricular pacing (RVP) percentages, it was assessed whether the patients developed an indication for CRT according to contemporary European Society of Cardiology guidelines during the follow-up. A total of 517 patients were included: median age at implant 63.8 years (range 55.5-70.2 years), 17.8% female, 29.4% secondary prevention, 65.2% ischaemic cardiomyopathy, and 53.8% single-chamber or subcutaneous ICD implants. Over a median follow-up of 6.6 years, 132 (25.5%) patients developed an indication for CRT corresponding to an incidence of 4.52% per year, of which only 46 (34.8%) actually underwent an upgrade to CRT. Independent predictors of developing an indication for CRT were baseline QRS duration (hazard ratio [HR] 1.06/ms; 95% confidence interval [CI] 1.04-1.07) and age at implant (HR 1.04/year; 95% CI 1.02-1.06). An upgrade to CRT was associated with lower all-cause mortality, heart transplant, or assist device implant (log-rank p = 0.002) compared to patients who developed a CRT indication without upgrade to CRT.

CONCLUSIONS

One-quarter of patients implanted with an ICD who had a narrow QRS duration at the time of implantation developed an indication for CRT during a median follow-up of 6.6 years. Yet, the majority of these patients did not undergo an upgrade to CRT, underscoring potential gaps in CRT utilization.