Extended follow-up data: impact of selective loss to follow-up in a trial of secondary prevention of coronary artery disease

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Abstract Background We performed an extended follow-up of the RESPONSE-2 trial, which evaluated a new secondary prevention strategy for patients with coronary artery disease (CAD). Selective loss to follow-up (LTFU) however, may induce biased results. Objectives To assess LTFU and its implications on the internal validity of the trial at extended follow-up. Methods RESPONSE-2 (N=824) was a randomised trial of nurse-coordinated referral of CAD patients to ≤3 commercial lifestyle interventions, on top of usual-care, or to usual-care alone. The primary outcome was assessed at 1-year follow-up, after which the interventions were discontinued. An extended follow-up was performed two years later. We evaluated overall selective LTFU, between-group selective LTFU and within-group selective LTFU, by comparing baseline characteristics, compliance with the lifestyle interventions (intervention group only) and achievement of lifestyle-related risk factor (LRF) targets at 1-year follow-up for attendees and non-attendees of the extended follow-up. In all variables a standardized mean difference (SMD) of ≥0.2 with a p-value <0.05, based on an independent t-test for continuous data and fisher's test for discrete data, was considered evidence of selective LTFU. Results In total, 520 patients attended the extended follow-up: 266/411 in the intervention and 254/413 in the control group. Patients LTFU were generally younger (56.5 vs. 59.3 years; SMD=0.299), more often baseline smokers (37% vs. 22%; SMD=0.334) and had less often quit smoking directly after hospitalization (17% vs. 25%; SMD=0.203). We found no evidence of between-group selective LTFU and several indications of within-group selective LTFU (table). Intervention group attendees were more compliant with the lifestyle interventions compared with non-attendees (weight loss: SMD=0.450; p≤0.05 and physical activity: SMD=0.516; p≤0.01) Conclusion Baseline LRF control, compliance with the lifestyle interventions and achievement of LRF targets were less favourable for non-attendees of the extended follow-up. Effective handling of missing data is recommended to minimize loss of contrast due to within-group selective LTFU and to ensure generalizability of results. Funding Acknowledgement Type of funding source: Private company. Main funding source(s): The RESPONSE-2 trial was sponsored by Weight Watchers International, Inc. (New York, New York) and Philips Consumer Lifestyle (the Netherlands). The sponsors had no role in the design, data collection, data analysis, data interpretation, and writing of the manuscript.