The staggering prevalence of heart failure and the lack of sufficient donor hearts for transplantation have fostered increasing interest in novel treatment strategies for these challenging patients. Since the ReMATCH trial, mechanical-assist device implantation has grown exponentially for treatment of patients with refractory heart failure despite maximal medical treatment.1 Novel left ventricular-assist device (LVAD) technology, such as continuous-flow pumps, have continued to improve survival in patients with advanced heart failure when compared with older pulsatile models.2 The centrifugal, continuous-flow Heartware (HeartWare International, Inc., MA) ventricular-assist device (HVAD) has similar outcomes when compared with axial-flow device technology for bridged patients.3 Miniaturized intrapericardial device design has allowed the development of novel less invasive surgical approaches.4 Thus, as newer LVAD pump designs decrease in size and weight, and the need for less invasive implant strategies becomes relevant.
Increased literature on minimally invasive LVAD implantation techniques demonstrates the impact of advancing mechanical support device technology.5–9 Given promising results from early implantation trials with axial-flow pumps inserted via thoracotomy,5 surgical strategies have focused on lowering perioperative complications and decreasing re-entry complications at the time of transplantation. Novel approaches include tunneling of the outflow graft anastomosis to the subclavian artery and descending aorta.10 Heartware ventricular-assist device implantation has been safely conducted via left thoracotomy (LT) and hemisternotomy and by bilateral anterior thoracotomies.7
Left ventricular-assist device implantation through minithoracotomy or subcostal approaches has demonstrated safe results, with reports of in-hospital mortality less than 15%.11 Other studies of minimally invasive LVAD implantation demonstrate encouraging results, including short hospital stay, reduced postoperative inotrope requirement,12 and decreased perioperative blood transfusions.6 One long-term prospective study showed 100% survival at 18 month follow-up in four patients undergoing minimally invasive HVAD implantation.
Despite the constantly evolving pump design and growing volume of literature on less-invasive surgical strategies, no large comparative outcome studies have been conducted between minimally invasive LT and conventional sternotomy (CS) LVAD implantation. The primary objective of this study was to compare outcomes between LT and CS techniques. We report our 6 months’ outcomes comparing these two implantation strategies, and specifically evaluate whether LT ventricular-assist devices (VAD) implantation strategy is a safe alternative surgical approach.
Design and Study Population
The study was approved by the institutional review board of the Vanderbilt University Medical Center. This was a retrospective analysis of prospectively collected data from January 2013 to December 2014. Patients were consented for one surgical approach and agreed to move forward with the proposed implantation technique. All patients in the CS group underwent a conventional on-pump technique with standard mid-line sternotomy,13 whereas patients in the LT group had the implant performed through a LT approach. For homogeneity, all patients in this study had a LT for inflow cannula placement and an upper “J” hemisternotomy for outflow graft positioning, and we have not included patients with a descending anastomosis for outflow graft placement. This study was constructed to mirror a larger prospective, single arm, multicenter trial to evaluate the thoracotomy implant technique of the HeartWare HVAD System (HVAD Lateral, ClinicalTrials.gov: NCT02268942).
Patient demographics including age, gender, intra-aortic balloon pump requirement (IABP), heart failure etiology (ischemic or nonischemic), previous sternotomy, and central venous pressure/pulmonary capillary wedge pressure (CVP/PCWP) were collected. Primary outcomes were 6 months mortality and presence of adverse events including cerebrovascular accident (CVA), gastrointestinal bleeding, driveline infection, thrombus, right ventricular (RV) failure, and readmission rate. Adverse event definitions were based on the fifth INTERMACs annual report.14 Early perioperative outcomes included transfusion requirements, ICU and in-hospital length of stay, time on mechanical ventilation, need for RV-assist device, need for dialysis, inotrope requirements, and 6 months mortality.
Patients who were candidates for an alternative LT approach to HVAD insertion were identified by our multidisciplinary selection committee. Criteria used to identify candidacy included adequate pulmonary function to determine suitability for LT. All patients undergo a chest computed tomography before surgery to evaluate the position of the ascending aorta. Patients were not considered for LT if they required a concomitant surgery for left atrial clot removal, significant aortic insufficiency, mitral stenosis, severe tricuspid insufficiency, or hemodynamically significant patent foramen ovale. The LT minimally invasive technique consisted of a 6 cm left anterior thoracotomy with a 4 cm upper “J” hemi-sternotomy for outflow graft placement (Figure 1). After off-pump placement of the left ventricle (LV) apical sewing ring, cardiopulmonary bypass was established using femoral access if needed. Patients were assessed for possible off-pump implantation per surgeon and institutional preferences. Absence of left ventricular intracavitary thrombus is confirmed by intraoperative repeat transesophageal and epiaortic echocardiography. Heparin was given after sewing ring placement, and full dose heparin was used (350–400 units/kg) to reach an activated clotting time (ACT) above 400. The outflow graft was tunneled within the pericardium with end-to-side anastomosis to the proximal ascending aorta. The outflow graft was tunneled through the anterior mediastinum for patients with previous sternotomy. In these patients, careful dissection of a tunnel is carried between the posterior aspect of the sternum and the anterior border of heart in the anterior mediastinum. The outflow graft is slowly advanced toward the ascending aorta using a curved tip multipurpose clamp. A 14 mm ringed-Goretex graft is placed over the outflow graft to prevent injury from reentry at the time of heart transplantation. In the off-pump LT approach, a modified nonfibrillatory technique was used for inflow cannula placement using intermittent adenosine boluses.6 This bradycardic episode allows quick LV access to be obtained to secure the LV coring tool.
Demographic and other patient-related data were obtained from Vanderbilt Heart and Vascular Institute medical record and a prospectively collected database. Data were expressed either as mean ± standard error of the mean for normally distributed data or median with range for non-normally distributed data. Data between two groups were compared using chi-square for continuous and dichotomous variables, respectively. Kaplan-Meier survival analysis was used to estimate survival outcomes, which were compared by the log-rank test. Statistical significance was considered at p < 0.05.
Eighty-one patients (76.5% male) underwent HVAD implantation via either LT (N = 27) or CS (N = 54). Patients were between the age of 31 and 69 years old (median 57 years) and were all undergoing HVAD implantation for bridge to transplant (BTT) indication. Clinical characteristics between both LT and CS groups were not statistically different, with the exception of redo-sternotomy and preoperative intraaortic balloon pump (IABP) usage being higher in CS compared with the LT cohort (p = 0.04 and 0.05, respectively; Table 1). Heart failure etiology (ischemic vs. nonischemic) was comparable between groups (p = 0.87). Twenty-two patients in the LT group underwent implantation via an off-pump technique. Surgery time for all patients was 283 ± 104 minutes, for CS was 297 ± 119 minutes, and LT was 256 ± 56 minutes (p = 0.04).
Perioperative transfusion was lower in the LT group (p = 0.05); and LT patients spent less total days on mechanical ventilation (p = 0.04; Table 2). Only one patient in the LT group was converted to an on-pump strategy. Conversion was related to significant bleeding at the inflow ring after pump insertion. Although preoperative CVP/PCWP ratio score was similar between the two surgical groups (p = 0.43), no patients in the LT group required a perioperative RV support device compared with six in the CS cohort (p = 0.22). Although there was a higher rate of early dialysis rate in LT group when compared with CS group (19% vs. 9%, p = 0.23), it is important to note that the LT group started with slightly higher creatinine (Table 1). Mortality at 30 days was 2% of the CS group, whereas no deaths occurred in LT patients (p = 0.98).
Survival and Adverse Event Outcomes
The primary outcome of this study was the comparison of adverse events between the two surgical implantation strategy groups. The cumulative incidence of adverse events was comparable between CS and LT patients with average follow-up time of 6 months (Table 3). Kaplan–Meier survival analysis at 30, 60, 120, and 180 days showed no difference between implantation strategy groups (p = 0.52; Figure 2). During the follow-up period, 13 patients were transplanted within 180 days. Of these, 12 of the 13 were in the CS group and one was in the LT group. Of these 13 who were transplanted, the average days from implant to transplant were 90 ± 36 days (range of 20–128 days).
Main Findings of the Study
Our retrospective 6 months follow-up comparative analysis between LT and CS HVAD implantation strategies showed there was no significant mortality difference between the two groups. In addition, the groups were similar in the observed incidence of complications, including CVA, infection, thrombosis, and RV failure. Analysis of in-hospital outcomes showed reduced perioperative transfusion and mechanical ventilation in the LT group when compared with CS.
Krabatsch et al. collected adverse event data from 1,035 patients implanted with the HVAD in a large multi-center European study over 8 years. Results showed HVAD implantation continued to demonstrate a comparable safety profile to previous assist devices with 30 day and 1 year survival rates of 86% and 66%, respectively. Additional reviews, such as the ReVOLVE study, included more than 250 HVAD implants and summarized adverse event data from 2009 to 2012 with an 87% success rate in patients with HeartWare systems at 6 months. Although this was a multi-center, prospective study, no control arm existed to compare outcomes to conventional techniques, and all utilized a CS.15 In addition, neither of these landmark studies compared implantation strategies effects on outcomes. In our analysis of LT compared with CS HVAD implantation, similar clinical outcomes were identified including CVA, infection, GI bleeding, and readmission rates between both groups. Survival analysis shows no increased mortality risk in LT after 6 months when compared with CS. These results should represent a benchmark by which studies such as the HVAD Lateral Trial should be measured (ClinicalTrials.gov: NCT02268942).
Could a LT Thoracotomy Reduce Blood Product Utilization?
We observed a decrease in perioperative blood product transfusion in the LT patient cohort. Decreased perioperative blood product administration in LVAD patients can potentially translate to reduced patient allosensitization and increased chance of matching for a subsequent heart transplant.16–19 A significant proportion of patients in the LT group was performed off-pump, and we postulate that these results could be related to this important difference. Although numerous randomized trails demonstrate decreased morbidity from reduced perioperative transfusions in off- versus on-pump coronary bypass surgeries, long-term outcome results remain inconsistent. Limited data exists on the effect of transfusions on the morbidity and mortality in LVAD surgeries utilizing cardiopulmonary bypass or off-pump techniques.20–23 Advantages of off-pump LVAD placement include potentially avoiding the activation of the systemic inflammatory response caused by cardiopulmonary bypass and associated deleterious effects on the coagulation system.
Theoretical Benefits of a LT Approach
Advantages of a less invasive surgical approach include avoiding the potential for complicated dissections because of adhesion formation and intrapericardial placement of the outflow graft. In patients with a history of prior sternotomy, the use of a LT approach can potentially minimize trauma associated with obtaining access to the LV. Furthermore, opening the pericardium through conventional pump placement can alter RV geometry and the delicate RV pressure–volume relationship. RV failure is a serious complication after LVAD placement and preserving RV-pericardium geometry could help limit septal shifts or RV distention leading to profound hemodynamic consequences.24,25 It is important to note that certain patients are not amenable to off- pump LVAD implantation, such as patients who require concomitant surgery for left ventricular or atrial appendage clot, significant aortic insufficiency, and those with severe mitral stenosis or tricuspid regurgitation. Lastly, off-pump approaches limit the hemodynamic resuscitation capabilities of CPB and the ability to inspect the LV for thrombus.26
Several limitations exist in the presented study. This is a retrospective analysis of prospectively collected data and is therefore subject to the limitations associated with retrospective studies. This is also a single center, single surgeon experience (S.M.), therefore outcome interpretation is limited by institutional and provider bias. LT implants were conducted on- or off-pump, but despite variability in technique, we feel that the postdischarge comparison of a surgical strategy is still valid when evaluating survival and adverse event rates between groups. Only one patient in the LT group had reoperation for bleeding and was re-explored. As the number of reoperation for bleeding in the thoracotomy group is small, meaningful statistical comparisons are difficult. As there is a necessary learning curve for the LT technique, time in the operating room is distributed variably in the LT group. As this variable is changing in time for this group, valid comparison to the CS population is difficult. Although the LT minimally invasive technique was considered on all patients in this analysis, a selection bias still exists.
This study has revealed comparable 6 months survival and adverse event profile for patients implanted with a LT approach when compared with CS. We further observed a potential reduction in blood product utilization and mechanical ventilation in the LT group. These results support the utilization of this approach for selected patients.
Less invasive ventricular support implantation strategies will continue to evolve as technology expands to smaller devices. The miniature VAD (MVAD, HeartWare, Inc.; Miramar, Fla), has showed enhanced durability and performance in animals, is one such example of reduced implant size, which will be amenable to these less invasive approaches.27 Promising evidence supports also partial mechanical support devices such as the Synergy left ventricular-assist device (CircuLite, Saddle Brook, NJ). With increasing patient demand and case complexity, progressive implant technology will continue to dictate the inevitable future of minimally invasive surgical techniques.28
The authors thank the statistical support from Frank Harrell, PhD (Department of Biostatistics, Vanderbilt University).
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Keywords:Copyright © 2016 by the American Society for Artificial Internal Organs
left thoracotomy; heart failure; minimally invasive; centrifugal pump; left ventricular assist device