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.