Methodologic Standards for Follow-Up Extension in Cardiovascular Trials: A Scientific Statement From the American Heart Association

Extension follow-up trials are essential for understanding the long-term safety and efficacy of cardiovascular interventions. Whereas primary randomized trials primarily capture short-term outcomes, extended observation may reveal delayed benefits or harms that are highly relevant to clinical decision-making. However, methodologic standards for extension trials remain poorly defined, leading to inconsistent design, analysis, and reporting. This scientific statement outlines best practices for cardiovascular trial extensions, addressing outcome selection, duration and completeness of follow-up, and analytic strategies suited to evolving treatment effects. Practical considerations, including strategies for participant retention, reconsent, data continuity, and resource allocation, are also discussed.