In a study of patients enrolled in the Adaptive CRT trial, it was found that SSI by echocardiography was independently associated with CRT outcome, adjusting for QRS morphology, QRS duration, sex, heart failure aetiology, and treatment with angiotensin-converting enzyme inhibitors/angiotensin II receptor blockers.17 Whether SSI has added prognostic value over strict LBBB morphology is still unknown. Here, ACE is linked to heart failure.