Perspective:

In this secondary analysis, more data are present to support CRT-ICD therapy in patients with HF and an LBBB pattern. This is now standard of care for HF patients with reduced EFs and an LBBB. However, the data supporting device therapy for those with non-LBBB patterns remain murky. Like noted in other studies, both QRS duration and morphology appear to play a role in benefit, which makes theoretical sense given the location of the resynchronization lead in the branch coronary sinus (CS). Conduction abnormalities arising from within the right ventricle or other regions of the left ventricle may gain less resynchronization benefit, or worsen, with leads placed in the CS. However, this study does not clearly negate benefit of CRT-ICD therapy in all patients with non-LBBB patterns. It just highlights the lack of answers. Power is a significant weakness of this substudy. Only 102 patients had a QRS duration ≥160 ms and a non-LBBB pattern, and only 53 of these were randomized to CRT-ICD. While non-LBBB patients overall did not have a reduction in the primary outcome with CRT-ICD, they did have trends for improved survival, which was most prominent in the RBBB subgroup (HR for death, 0.54). For patients with a QRS <160 ms and non-LBBB, events occurred early after CRT-ICD implant (within 6 months). Was this driven by HF? Should we institute early follow-up to ensure we are not provoking HF in these patients? Were these patients displaying RBBB or NIVCD, or both? At this point, we need to ‘unlump’ the non-LBBB HF patients and perform a well-designed randomized trial of CRT-ICD versus ICD therapy in non-LBBB patients examining the impact of QRS morphology on outcomes.