Early termination of clinical trials due to low recruitment represents an understudied challenge for clinical research. We aimed to describe characteristics of cardiovascular trials terminated because of low recruitment and identify the major predictors of such early termination.

We reviewed all cardiovascular clinical trials (7,042 studies) registered in ClinicalTrials.gov from February 29, 2000, to January 17, 2013, and assessed information about trials that were completed and those that were terminated early. Logistic regression models were developed to identify independent predictors of early termination due to low recruitment.

Our search strategy identified 6,279 cardiovascular clinical trials, of which 684 (10.9%) were terminated prematurely. Of these halted trials, the main reason for termination was lower than expected recruitment (278 trials; 53.6%). When comparing trials that terminated early because of low recruitment with those that were completed, we found that studies funded by the National Institutes of Health or other US federal agencies (odds ratio [OR] 0.35, 95% confidence interval [CI] 0.14-0.89), studies of behavior/diet intervention (OR 0.35, 95% CI 0.19-0.65), and single-arm design studies (OR 0.57, 95% CI 0.42-0.78) were associated with a lower risk of early termination. University/hospital-funded (OR 1.52, 95% CI 1.10-2.10) and mixed-source–funded studies (OR 2.14, 95% CI 1.52-3.01) were associated with a higher likelihood of early termination due to lower than expected recruitment rates.

Low recruitment represents the main cause of early termination of cardiovascular clinical trials. Funding source, type of intervention, and study design are factors associated with early termination due to low recruitment and might be good targets for improving enrollment into cardiovascular clinical trials.