Comment
In this study, we demonstrate notable postoperative differences between
patients receiving LVAD implantation by BT and sternotomy techniques. We
add our institution’s experience to the growing body of evidence
supporting sternal-sparing techniques as safe and effective alternatives
to median sternotomy.6–9 Moreover, in our cohort of
patients, inflow cannula angles were smaller and more consistent when
the BT technique was used. We therefore validate the findings of Ayerset al. , who also demonstrated smaller and more consistent inflow
cannula angles after sternal-sparing implantation in patients who
received the HM3 LVAD.13
We found that BT patients required fewer days of postoperative inotrope
support compared to sternotomy patients, similar to early clinical
outcomes reported by Wood et al. 8 The
Interagency Registry for Mechanically Assisted Circulatory Support
(INTERMACS) considers duration of post-implant inotropes when defining
the severity of right ventricular failure,10 and other
work has found significantly lower incidence of severe right ventricular
failure in sternal-sparing implants.9 Thus, our
findings may be suggestive of less right heart failure in patients who
received their implant by BT, though further prospective work will be
needed to evaluate post-operative right heart function in the index
hospitalization and ultimately long-term outcomes following discharge.
Intraoperative blood loss and shorter length of index hospitalization
both favored the BT cohort but did not reach statistical significance.
This could be due to our relatively small sample size, since shorter
hospitalizations after sternal-sparing implants have been demonstrated
in prior work,6–9 and in general, minimally invasive
cardiac surgery techniques are associated with less blood
loss.14,15
Regarding inflow cannula angulation, Imamura et al. associated
smaller cannula coronal angles with left ventricle unloading (smaller
left ventricular diastolic dimension and lower pulmonary capillary wedge
pressure) and with reduced heart failure readmission
rates.11 They offer angles ≤65° as an appropriate
target for HVAD deices to allow consistent blood removal from the left
ventricle; steeper angles may introduce turbulent flow which may impede
reverse left ventricular remodeling. Sternal-sparing LVAD implantation
techniques facilitate optimal cannula angulation by allowing direct
visualization of the cardiac apex in anatomic
position.7 In this way, the other proposed benefits of
sternal-sparing techniques, such as preservation of the pericardium
surrounding the right ventricle and lack of postoperative sternal
restrictions, may be further augmented by improved cannulation. While we
do demonstrate smaller and more consistent inflow cannula angles in our
BT patients, further work is needed to clarify the impact of cannula
angle on patient outcomes, specifically related to right ventricular
dysfunction in the postoperative period.
More BT patients in our cohort were planned as destination therapy than
sternotomy patients. This is an interesting finding, however, may be a
result of timing bias. Since mid-2019, all LVADs have been implanted by
BT as our standard institutional protocol. This timing aligns with the
introduction of the new United Network for Organ Sharing (UNOS)
allocation system for heart transplantation, which since implementation,
has shifted transplant prioritization away from patients on the waiting
list living with a durable LVAD to those who are more acutely ill on
temporary circulatory support.16
Re-operative median sternotomy is a known risk factor for postoperative
morbidity and mortality in patients who are bridged to transplant;
however, patients whose sternotomy was for LVAD placement have shown
equivalent survival to primary cardiac transplant patients, suggesting
that the medical stabilization conferred by LVAD therapy may mitigate
the risks posed by re-operative sternotomy.17 While
LVAD placement by sternotomy may not adversely affect survival after
transplant, subjectively, our experience is that sternal-sparing
approaches to LVAD placement do make subsequent transplant easier, with
anecdotally less bleeding and less time on cardiopulmonary bypass due to
ease of dissection.
Our work has several limitations inherent to its design as a
retrospective, single-institution study, which may limit its
generalizability. HVAD is the most often used device at our institution;
however, HM3 is also utilized at our institution and across the country.
As we gain comfort with non-sternotomy approaches for LVAD implantation,
future investigation is warranted to confirm findings across all pump
models and non-sternotomy approaches.
In conclusion, our data suggest inflow cannula angles are smaller and
more consistent with the BT approach, which has been associated with
improved patient outcomes. Patients who underwent BT required fewer days
of postoperative inotrope support. Further research is needed to
quantify the clinical impact of the BT approach to LVAD implantation
more fully, specifically as it relates to right heart dysfunction
following LVAD implantation both in the short and long term.