Europace Advance Access originally published online on September 16, 2008
Europace 2008 10(10):1243-1244; doi:10.1093/europace/eun262
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LETTERS TO THE EDITOR
Data analysis and interpretation of results in DATAS trial: reply
Estadistica e Investigacion Operativa
Universitat Politecnica de Catalunya
Barcelona
Spain
Cardiology Department
Hospital General Universitario de Valencia
Valencia
Spain
Cardiology Department
Hospital Universitario 12 de Octubre
Madrid
Spain
Cardiology Department
Hospital General Universitario Gregorio Marañon
5a Planta, 5100
Dr Esquerdo 46
Madrid
Spain
Tel: +34 91 586 8276 Fax: +34 91 586 8018 Email address: almendral{at}secardiologia.es
We appreciate the letter from Vardanyan and Kanna, which provides us with the opportunity to clarify some issues about the DATAS trial.
Studies comparing dual-chamber (DC) and single-chamber (SC) implantable cardioverter defibrillator (ICD) have so far focused on a single aspect of ICD therapy. Our aim was a global evaluation of their ability to reduce the clinically significant adverse events (CSAE) frequently suffered by ICD patients. Thus, we faced the challenge of evaluating patient outcome by a single variable. This would allow to (i) concentrate on alpha risk and (ii) have only one interpretation of the results as an answer to the objective question ‘do DC-ICDs improve patient outcome by reducing CSAE?’
As patient evolution has to consider different undesired events, we decided to define a composite end-point, and that was mentioned in the DATAS design manuscript.1
This strategy has two advantages: first, the possibility to concentrate patient evolution in a single measure. This requires the assumption of clinical homogeneity,2 i.e. that only aspects of similar medical relevance are pooled together and second, the chance to increase the study power allowing for smaller sample sizes. The required assumption is that of statistical homogeneity.3
The two ‘softer’ CSAE, i.e. inappropriate shocks and atrial tachyarrhythmias (AT), were ‘hardened’ in number and duration, respectively, to reinforce their clinical relevance. However, we believed that the assumption of clinical homogeneity was not met if death was pooled together with the other CSAE. We wanted to avoid, for example, that a patient with three hospitalizations had a worse score than a patient who died. The developed scoring system ensured that death, the worst expected outcome, had the highest score. Unplanned crossovers, a failure of the allocated treatment, received a relatively high score.
Although it has been demonstrated a higher rate of AT during follow-up in patients having them previously, this is presently neither a contraindication for ICD therapy nor an indication for DC-ICD. Thus, it was appropriate and justified to measure the potentially more active role of DC-ICD against AT. As described in the manuscript, inappropriate discharges were never a reason for premature crossover.
DATAS ICD indications, in accordance to contemporary guidelines, included secondary prevention in more than 85% of patients. Thus, the extent to which DATAS results could also apply to primary prevention patients is unclear.
We agree with Vardanyan and Kanna in the interest of the quality of life results, presently undergoing analysis.
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[1] Quesada A, Almendral J, Arribas F, Ricci R, Wolpert C, Adragao P, et al. The DATAS rationale and design: a controlled, randomized trial to assess the clinical benefit of dual chamber (DDED) defibrillator. Europace (2004) 6:142–50.
[2] Freemantle N, Calvert M. Weighing the pros and cons for composite outcomes in clinical trials. J Clin Epidemiol (2007) 60:658–9.[CrossRef][Web of Science]
[3] Ferreira-González I, Permanyer-Miralda G, Busse J, Bryant D, Montori V, Alonso-Coello P, et al. Methodologic discussions for using and interpreting composite endpoints are limited, but still identify major concerns. J Clin Epidemiol (2007) 60:651–7.[CrossRef][Medline]
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