Some major limitations to this surveillance study are to be
noted. (1) Existence of bias may be the fate of observational
studies. Dosages and duration of tolvaptan treatment were dependent
on physicians’ therapeutic strategies and patients’ conditions.
(2) Approximately 30% of patients were treated for more
than 2 weeks in this study, but the usefulness of long-term treatment
should be explored in the future study. (3) Urine osmolality
was reported to predict responses to tolvaptan,27 but those
data were not available in this study. (4) B-type natriuretic
peptide is an excellent marker of HF in terms of diagnosis,
severity/staging, and prognosis, but those data were available
for only 15% of this cohort.