Absolute risk reduction in total mortality with implantable cardioverter defibrillators: analysis of primary and secondary prevention trial data to aid risk/benefit analysis

Absolute risk reduction (ARR) and number needed to treat (NNT) are considered by many to be the most appropriate figures to use for the informed consent process, yet the results of published implantable cardioverter defibrillators (ICD) trials are frequently presented as relative risk reduction or odds ratio. The period over which risk reduction is calculated also varies between trials, making comparison difficult. Published ICD trials used to formulate national and international guidelines were examined for 1, 2, and 3 year total mortality in ICD and medically treated patients. The number of patients enrolled and at risk at these time points were also sought. Where the raw data were not included in the original text, estimates were taken from published Kaplan-Meier graphs. Eight primary prevention (PP) trials, three secondary prevention (SP) trials, and one SP meta-analyses were included. For PP, ARR at 3-year follow-up ranged from 0 (no benefit) to 24.6% (NNT = 4). For SP, ARR at 3-year follow up ranged from 3.7% (NNT = 27) to 11.3% (NNT = 9). Absolute risk reduction increased with follow-up in PP trials, whereas there was considerable variation in SP trials. Overall, very few trial patients received 3-year follow-up, giving wide confidence intervals (CIs). Absolute risk reduction from ICD trials varies significantly depending upon trial entry criteria, subgroup characteristics, and duration of follow-up. The relatively small number of patients followed for 2 or more years leads to wide CIs. Despite these limitations, the standardized ARR and NNT data presented may give a more individualized estimate of risk/benefit that could potentially aid an informed consent process.