Response to Letter Regarding Article, “Reduced Ventricular Volumes and Improved Systolic Function With Cardiac Resynchronization Therapy: A Randomized Trial Comparing Simultaneous Biventricular Pacing, Sequential Biventricular Pacing, and Left Ventricular Pacing”
We thank Drs Hamilton and Filardo for their interest in our work.1 In a prospective randomized trial in which the same patient is subjected to repeated measurements over time, missing data and repeated measures are known statistical problems for which it is difficult to account. As suggested by Drs Hamilton and Filardo, a longitudinal analysis is the most appropriate model for accounting for missing data.2 A longitudinal model was used initially to analyze the data, essentially yielded similar clinical results, and did not result in any substantive change to our published conclusions. However, at the suggestion of our reviewers and other readers, we presented the data in a way that is more conventional and easily understood and that facilitates comparison with other trials. To account for repeated measures in the same patient, paired data were used in the published analysis. This should have been more clearly stated in our Methods. We would be happy to provide the data as analyzed by the longitudinal model. With regard to multiplicity, it is correct that additional tests increase the likelihood of type I error. Although it is common practice to provide a comprehensive analysis using the available data, our analysis should be considered exploratory in nature. The limitations of multiple retrospective analyses should have been clearly emphasized; however, the results are valid and are derived from a relatively large trial that directly compared all 3 pacing modalities in a prospective randomized fashion.
Dr Foster and Dr Lurgio were principal investigators on the Device Evaluation of CONTAK RENEWAL 2 and EASYTRAK 2: Assessment of Safety and Effectiveness in Heart Failure (DECREASE-HF) trial. J. Schafer was an employee of Guidant Corp. The other authors report no conflicts.
Rao RK, Kumar UN, Schafer J, Viloria E, De Lurgio D, Foster E. Reduced ventricular volumes and improved systolic function with cardiac resynchronization therapy: a randomized trial comparing simultaneous biventricular pacing, sequential biventricular pacing, and left ventricular pacing. Circulation. 2007; 115: 2136–2144.