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.