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.