Life-years gained from defibrillator implantation - Markedly nonlinear increase during 3 years of follow-up and its implications

Background - Although treatment benefit in randomized controlled trials of defibrillators is often summarized by the numbers of lives saved ( absolute risk difference), this may not be a good representation of what matters most to patients, namely, the amount of life they should expect to gain from implantation. The estimate of gain in life-years may depend on duration of follow-up. In this study, we examine this dependency. Methods and Results - We estimated, from published data of 8 landmark defibrillator trials, the cumulative benefit in life-years gained at time points from 3 months to 3 years. Because the trial populations, clinical status, and prognosis varied widely between studies, we expressed for each study the benefit at each time point as the proportion of benefit at 3 years. The average dependency of the benefit on duration of follow-up was then calculated. We found that the number of life-years gained from 1 device implantation increases with length of follow-up considered. Importantly, this increase is markedly nonlinear. Within the 3-year span addressable, the benefit rises with the square of time (gain proportional to t(1.94), R-2 = 0.998, P < 0.001). Conclusions - Measurable benefit from a defibrillator to patients' life spans (life-years gained) is dramatically dependent on the time window over which the benefit is assessed. Because the effort of implantation is front loaded, yet benefit grows with time, the choice of an early time point artificially reduces apparent benefit and artificially increases the apparent number needed to treat to prevent an event. These are useful considerations for the formulation of treatment policy ( and even for planning of the follow-up phase of clinical trials).