Aims: Ischaemic heart disease negatively impacts response to cardiac resynchronization therapy (CRT), yet the impact of infarct scar burden on clinical outcomes and its interaction with mechanical dyssynchrony have not been well described.

Methods and results: We studied 620 NYHA classes III-IV heart failure patients with ejection fraction (EF) ≤ 35% and QRS duration ≥120 ms referred for CRT. Included were 190 ischaemic cardiomyopathy (ICM) CRT recipients with scar burden quantified by rest-redistribution Tl(201) myocardial perfusion imaging using a 17-segment (0 = normal to 4 = absence of uptake) summed rest score (SRS). Non-ICM (NICM) CRT recipients (n = 380) and 50 patients referred for CRT with unsuccessful LV lead implant comprised the comparison groups. Echocardiographic dyssynchrony analysis was performed in a subgroup of 150 patients. Follow-up left ventricular EF (LVEF) and volumes were examined at 7 ± 3 months in 143 patients. The outcome of death, cardiac transplant, or mechanical circulatory support was assessed in all. Over 2.1 ± 1.6 years, ICM patients had significantly worse survival and less LVEF improvement than NICM patients (P < 0.01). Ischaemic cardiomyopathy patients with low scar burden (SRS < 27) had favourable survival and LVEF improvement, similar to NICM patients. A high scar burden (SRS ≥ 27) was associated with reduced survival and lack of LV functional improvement (P ≤ 0.01), similar to those with unsuccessful LV lead implant, whereas baseline dyssynchrony was not predictive of outcome in these patients.

Conclusion: Extensive scar burden in ICM patients unfavourably affected clinical and LV functional outcomes after CRT, regardless of baseline dyssynchrony measures. Patients with ICM and lower scar burden had significantly better outcomes, similar to NICM patients.