Overview of sub-study Design Patients participating in the RAFT trial, at participating sites, will be randomized to have DFT testing or no testing at the time of device implant. Up to 450 patients will be eligible for enrollment at Canadian and European centres. The study will have two primary outcomes: a short-term safety outcome and a long-term efficacy outcome. The safety outcome will be a composite of all adverse events potentially related to DFT that occur within 30 days following ICD implant. The long-term efficacy outcome will be a composite of failed first appropriate clinical ICD shock and sudden death. This pilot study is intended primarily to confirm the anticipated rates of events and to demonstrate feasibility of enrollment, but will not have statistical power to determine if intra-operative DFT testing is associated with significant short-term risk. If complication rates are as high as predicted and enrollment is feasible, then a larger study would be justified to determine the impact of intra-operative DFT testing on long-term rates of failed appropriated ICD shocks and sudden death. Events rates determined in this pilot study would then be used to estimate the sample size of this larger study.