Controversy: in heart failure patients with a reduced ejection fraction and left bundle branch block, conduction system pacing can be a valid alternative to biventricular pacing-pro and contra.

For patients with heart failure (HF) and bundle branch block, cardiac resynchronization therapy (CRT) by biventricular pacing (BiVP) has been found effective and has been widely used for around 20 years. The effects of BiVP are well documented in a row of large randomized controlled trials (RCTs) with long-term follow-up to include prolonged survival, less HF hospitalizations, and better quality of life for the patients. More recently, conduction system pacing (CSP) as His bundle pacing or left bundle branch area pacing has been introduced for CRT and shown to in best cases establish a normal or near-to-normal electrical activation of the left ventricular myocardium. Data from large RCTs documenting the beneficial effects of CSP are awaited. Currently, the question is to what extent the contemporary literature supports a transition from BiVP to CSP for CRT in patients with HF and bundle branch block. This Europace Controversy article presents opposing viewpoints on this topic. H.B., M.J., and J.J. argue in favour of CSP being superior to BiVP. Conversely, C.L., N.B., and J.C.D. advocate for BiVP still being the first choice for CRT. This Controversy aims to present data and their interpretation from different expert perspectives on an important topic in CRT for HF.