4. Discussion
This study is the first to describe national trends in utilization,
mortality, LOS, and cost for patients receiving surgically implanted
internal and external BiVADs. From 2009 to 2015, the utilization of all
BiVADs nationwide decreased, driven by a decrease in utilization of
external BiVADs. Compared to the significant decline in mortality and
cost associated with LVAD implantation during this
period,1,2 our analysis demonstrated no change in
mortality and a rise in cost and LOS associated with BiVADs. The
unchanged mortality for BiVAD patients was coupled with an increase in
the burden of comorbidities. While LOS and the cost associated with
survivors stayed the same, LOS and cost related to the deceased patients
increased, even after controlling for all comorbidities and
complications. These findings may suggest that we have also evolved in
our capability of caring for higher-risk patients utilizing BiVADs
although this has required higher costs caring for the sickest patients
who eventually died during the hospitalization.
The decline in surgically implanted BiVAD utilization was driven by a
decrease in utilization of external BiVADs, which outnumbered the
increase in utilization of internal BiVADs. Our finding correlated with
one other prior study that used the UNOS database, which showed a
decrease in utilization of PF-BiVADs from 2010 to
2013.6 There are several potential reasons for the
decline in BiVAD utilization. First, the availability of percutaneous
biventricular MCS, such as ECMO, Impella RP, and ProtekDuo, may be
obviating the need for surgically placed BiVADs. Second, LVAD
utilization has significantly increased during this
period.1,2 Earlier implantation of LVADs leads to
decompression of the left ventricle and a decrease in pulmonary
pressures and subsequent afterload on the RV. The latter may therefore
reduce the incidence of RVF and decrease the need for BiVADs.
This is the first study to directly compare outcomes of surgically
implanted internal and external BiVADs. Patients with internal BiVADs
had significantly longer LOS and higher cost of hospitalizations
compared to that of external BiVADs; however, the mortality was lower in
patients with internal BiVADs. Significantly more of the internal BiVAD
implantations occurred in urban teaching hospitals. Prior analysis of
the INTERMACS database showed that patients receiving BiVADs at higher
volume centers (>10 implantations per year) had a better
chance of 1-year survival (71% vs. 53%, p =
0.003).7 As a result, the lower mortality seen in
internal BiVAD patients may be the result of higher implant volumes seen
at urban teaching hospitals compared to rural or non-teaching
facilities. More studies are needed to better understand the differences
in mortality, LOS, and cost between various BiVAD configurations –
specifically with regards to patient selection, implant center volume,
and rates of complications.
Despite the advancement of LVAD technology and patient care, RVF after
LVAD placement remains a significant source of complication – up to
3.9-14.5% according to the recent multi-national
studies.8,9 Prior studies have demonstrated that
planned, and earlier BiVAD implantation is associated with higher
survival rates.10,11 Other studies have demonstrated
that angiotensin-converting enzyme inhibitors (ACEI) can significantly
reduce the risk of GI bleeds associated with LVAD
implantation12 and improve
mortality.13 However, it is unclear whether these
findings have led to changes in practice. Future investigation should
focus on implantation of evidence-based strategies for practical
improvements in the care of patients with BiVADs.
This study used ICD-9 codes to identify the population that received
BiVADs, and thus, have limitations inherent to the coding system. For
example, the off-label use of two separate surgically implanted VADs
used for biventricular support was classified as two single ventricular
devices (ICD-9 37.65), and thus, were excluded from our study.
Consequently, our study captures only a subset of internal BiVADs, and
likely underestimates the total number of internal and all BiVADs.
Despite this limitation, our study demonstrated a significant rise in
internal BiVAD utilization during the study period. Future studies are
needed to assess and compare the outcomes of this particular
configuration of biventricular support. This study also does not include
many other types of MCS, such as paracorporeal devices and other
external systems. Outcomes of other temporary systems of circulatory
support should be considered in a different forum, and is an important
area for future investigation.
Our study was limited to ICD-9 codes, which capture only three-quarters
of the hospitalizations in 2015 (switched to ICD-10 thereafter). We
addressed this limitation by evaluating time trends based on quarterly
numbers. One of the limitations of the NIS database is that it does not
allow for stratification of the data based on a center’s volume of BiVAD
implantations. Moreover, given that most centers that perform BiVADs
were large-volume centers, this analysis was not powered to detect
differences based on implantation experience. As an exploratory
analysis, our study tested several hypotheses, which likely reduced the
power of the study. This study is retrospective and our findings should
be confirmed with prospective trials when possible.