Limitations:
Our study has the following key limitations: (1) The NIS is an
administrative claims-based database that utilized ICD codes which may
be prone to errors and could introduce information bias due to outcome
misclassification. The hard clinical end points, however, are less
subjected to error. Additionally, AHRQ quality control measures are
routinely instituted that guarantee data integrity (12). Additionally,
the ICD-9 code utilized in this study was not specific to the Watchman
device and could be referred for any LAA occlusion procedure. Due to the
limited magnitude of other research studies of endocardial devices and
any epicardial LAA occlusion procedures performed in US during the study
period (13), we believe that application of this code for the purpose of
our study was able to mostly characterize Watchman implants. (2) The NIS
only captures inpatient admissions and does not provide any information
on outpatient encounters. This limitation may result in selection bias;
however, our data is well representative of national utilization of
Watchman devices performed during in-patient settings; in fact since
inpatient hospitalization is often required for reimbursement for the
procedure, our results may be more indicative of widespread practice
(19). (3) The NIS censors data gathering at discharge so long-term
outcomes could not be ascertained from the present dataset. (4) Specific
data on potential confounders including medications, as well as operator
and intra-procedural characteristics could not be examined from the NIS.