Limitations
This post-hoc analysis of prospectively-collected data has several limitations. First, serial measurement of EF was not dictated by the protocol. However, nearly 50% of the SCD-HeFT participants had 3 or more EF measurements. These patients were in general healthier than the rest of the cohort, who may not have exhibited as much improvement in EF. Second, the modality used for EF assessment was not standardized and the studies were interpreted locally at the enrolling institution. Thus, observed changes in EF may be partially be due to variability in modalities or reader, which has been shown to be present between different modalities even with standardized core lab measurements.21 However, these results reflect real-world practice and our observation of EF improvement in nearly 40% of patients is replicated consistently by observations from smaller, single-center studies.2–4,6 Finally, optimal medical therapy for heart failure has evolved considerably since 2005 when, SCD-HeFT trial was published. However, EF improvement in 30-40% of ICD patients was replicated in past as well as contemporary cohorts. Whether fluctuation in EF also occurs in contemporary cohorts needs to be studied.