Extract: Extension studies are a popular approach to collecting long-term safety and efficacy data following the conclusion of a clinical trial.1 Long-term follow-up can examine whether short-term findings are sustained and provide investigators with greater statistical power to identify treatment effects as events accrue. The practice of extending follow-up is becoming increasingly commonplace, yet these analyses are seldom held to the same standards of reporting as primary investigations.2 Following the publication of the 2024 ESC Guidelines for the management of chronic coronary syndromes (CCSs),3 we explore the use of extension studies to assess the optimal mode of revascularization for left main coronary artery disease (LMCAD). Background: In low-risk surgical patients, revascularization of LMCAD is typically performed via coronary artery bypass grafting (CABG) or percutaneous coronary intervention (PCI). Percutaneous coronary intervention generally shows lower peri-procedural event rates but carries an increased risk of future revascularization compared to more invasive surgery, so sufficient follow-up must be considered to identify whether findings are sustained.3–5 An extension period is a simple approach to achieving this.