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Case Reports

The HeartMate 6

Daneshmand, Mani A.*; Bishawi, Muath*,†; Milano, Carmelo A.*; Schroder, Jacob N.*

Author Information
doi: 10.1097/MAT.0000000000001011
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Abstract

Heart transplantation remains the gold standard therapy for patients with end-stage heart failure, but it is greatly limited by the number of available donor organs.1 A ventricular assist device (VAD) can be an alternative or a bridge to transplantation in select patients.2 In a subset of patients, heart failure is biventricular and left VAD (LVAD) support alone may not provide adequate perfusion.2–4 In these situations, the right ventricle requires mechanical support. Typical right VADs (RVADs) use large, centrally placed cannulas connected to an extracorporeal pump. Newer RVADs allow for percutaneous access, but, regardless of the cannulation strategy, patients are restricted to the hospital or Intensive Care Unit (ICU) while the ventricle recovers.5 For a limited subset of patients, another option is a total artificial heart (TAH).6 The common indications for TAH usage are: severe, irreversible biventricular failure, severe restrictive myopathy prohibiting ventricular cannulation, and a failed heart transplant requiring chronic support.6,7 However, the current food and drug administration (FDA)-approved TAH device is large (restricting its use in smaller patients), has a large pneumatic drive system that limits mobility, and is not widely available. In fact, most LVAD centers lack experience with the TAH in essence restricting its use to only a few centers. One strategy, for patients who require durable biventricular support, is the use of a second VAD to support the right ventricle. This has been made possible by recent design improvements.8,9 New, centrifugal flow VADs are much smaller than axial flow or pneumatic VADs, thus allowing for two VADs to be implanted next to each other to support both the left and right circulation. This approach remains experimental with many important challenges including balancing the right and left circulation, orientation of the devices, orientation of the outflow graft, device thrombosis, lack of native cardiac backup, potential for hemolysis, and other adverse events.9,10

Case History

A 37 year old male with viral myocarditis leading to a cardiomyopathy initially had a Heartware HVAD LVAD (Medtronic USA, Inc, Minneapolis, Minnesota.) implanted in 2014. His posthospital course was complicated mycoplasma pneumonia, enterobacter infection (2016), and more recent complications of methicillin susceptible Staphylococcus aureus (MSSA) and stenotrophomonas power cord site infection with MSSA bacteremia. He underwent multiples debridements, starting in 2017. Eventually, his infection tracked back to his pump pocket requiring explant of his HeartWare LVAD and conversion to an extracorporeal LVAD via redo sternotomy. This operation was technically complicated by the presence of significant mediastinal adhesions along with destruction of the left ventricular apex requiring left atrial cannulation of his LVAD. After recovering from this procedure, while awaiting a suitable donor for transplant, the patient developed progressive right ventricular failure and significant aortic valve insufficiency. Given the likely prolonged wait for a suitable donor organ, rather than performing aortic valve repair and inserting an extracorporeal RVAD, the decision was made to proceed with two HM3 VADs configured as TAH.

Operative Steps

After redo sternotomy, aortic and bicaval cannulation, cardiopulmonary bypass was initiated. The extracorporeal LVAD was removed. Of note, there was a moderate amount of thrombus on the inflow cannula within the left atrium. The aortic cross clamp was applied and biventriculectomies were performed. A ridge of ventricular muscle 3–4 cm distal to the right and left atrioventricular (AV) groove was left underneath the mitral and tricuspid valve annuli to allow for better pump positioning and anchoring (Figure 1). The subvalvular apparatus for the mitral and tricuspid valves was excised, but the valve leaflets were preserved and tacked to the rim of ventricular tissue. The left atrial appendage was clipped. Next, the right ventricle outflow tract muscle with the right ventricular outflow tract were excised, including the excision of the pulmonary valve. Similarly, the left ventricular outflow tract was excised with excision of the dysfunctional aortic valve. The posterior aspect of the aortic valve, however, was preserved as it is part of the aortomitral curtain. The interventricular septum was then divided and the orifice of the coronary sinus was oversewn with 5-0 polypropylene suture. For the anchoring of the sewing rings, we used pledgeted, interrupted, 2-0 braided sutures to secure the sewing ring to the ventricular tissue approximately 2–3 cm from the annuli of the AV valves annuli (Figure 2). Importantly, these sutures must exit on the epicardial surface of the rim of ventricular tissue to ensure adequate separation of the sewing ring and VAD inflow cannulas from the back of the atrium. The HM3s were then attached to the sewing rings, and the outflow graft positioning adjusted (Figure 3). The pumps were both oriented in a manner to allow access to their locking mechanism and avoid kinking of the outflow grafts. Next, the outflow grafts were cut to the appropriate length. The grafts must not be too long as that will increase the risk of kinking. Running 4-0 polypropylene sutures were used to perform an end-to-end anastomosis of the outflow grafts to the aorta (for the left-sided HM3) and pulmonary artery (for the right-sided HM3). Deairing was done before completing the anastomoses by releasing the snares on the superior vena cava and inferior vena cava drainage cannulas and allowing filing of the right and left pumps. An 18 gauge needle was placed into each of the outflow grafts for further deairing, and large volume breaths were given to allow for any air trapped in the pulmonary veins to be vented. Next, the pumps were started at a low speed (3000 rpm) with the aortic cross clamp still in place. The cross clamp was slowly removed while gradually increasing the left-sided pump speed, subsequently, the cardiopulmonary support is weaned. Using echo guidance, the speed for the left and right pumps was adjusted using the atrial septum position as a gauge. To ensure appropriate unloading of each filling chamber, we titrated the right-sided pump speed until we achieved a satisfactory central venous pressure and titrated the left-sided pump speed until there was significant respiratory variation in the interatrial septum. The patient’s chest was not initially closed (to ensure ready access in the case of bleeding) and the patient was transferred to the ICU. Staged sternal closure occurred the next day. To maintain pericardial size and ensure that an appropriately sized new heart would fit in the patient’s chest, a 325 ml breast implant is placed laterally within the pericardium. The postoperative course was complicated by a left middle cerebral artery temporal/parietal CVA that was detected on postoperative day 2. The patient had a full functional recovery from his stroke, and was transferred to the stepdown floor, with stable pump position (Figure 4). His international normalized ratio goal was 2.5–3.5, and he was also maintained on full dose Aspirin therapy. He ambulated multiple times a day. He was dischargeable, but we elected to keep him admitted because of social reasons. He was listed status 2 and was transplanted 30 days post-TAH insertion. At the time of his transplant, there was no significant concern for residual infection on gross inspection in the operating room (OR). Mediastinal cultures were obtained and were sterile. There was no evidence of thrombus in the atria or the pumps. Immediately after transplant, his chest was left open due to right ventricle dysfunction. He had an Intra-aortic Balloon Pump (IABP) placed in the OR and was transferred to our ICU with an open chest. Day one posttransplant he was taken to the OR, underwent a tricuspid valve repair due to severe Tricuspid Insufficiency, and a percutaneous RVAD placement (Rotaflow Protek duo [LivaNova PLC, United Kingdom]). The next day (posttransplant day 2), the patient was extubated and the IABP was removed. One week posttransplant, the patient was taken to the OR for evacuation of a pericardial effusion with early signs of tamponade and the RVAD was removed. The patient is now 2 weeks posttransplant and is on the stepdown floor, ambulating, on a regular diet and nearing discharge.

Figure 1
Figure 1:
Intraoperative image demonstrating the level of ventriculectomies required before attachment of the sewing rings.
Figure
Figure:
s 2. Intraoperative image demonstrating final positioning of pledgets (A) and the sewing rings (B) before pump attachment.
Figure 3
Figure 3:
Intraoperative image demonstrating final positioning of the pumps.
Figure 4
Figure 4:
Postoperative x-ray of pump positioning.

Discussion

A number of investigators, including our group, have previously described the use of 2 centrifugal flow pumps as a TAH.9 This, however, is the first reported use of two HM3s using this configuration in the United States. A previous report of the use of two HM3s as BiVAD involved placing the inflow of the right pump at either the right ventricular free wall or the right atrium. This technique is limited, however, by obstruction of flow due to a number of different structures including the septum and the tricuspid valve. Additionally, addition of an RVAD does not address aortic or pulmonic valve insufficiency. Our technique involves performing partial bilateral ventriculectomies allowing for stable positioning of the pumps with strong anchoring support using both a rim of ventricular tissue and AV valvular annuli.

Our group was motivated to try the use of the HM3 as a TAH because the full magnetic levitation technology (Full MagLev) allows for proper and stable positioning of the rotor within the pump even at lower speeds required for the right circulation. Additionally, given the promising clinical data from the HM3 trials demonstrating a very low device thrombosis rate, the HM3 may potentially also significantly decrease the incidence of right-sided pump failure.11 Utilization of the HM3 VAD in a TAH configuration is technically feasible and may be a good strategy for select patients that will require TAH support where the FDA-approved TAH is not feasible or available. Additional studies will be required to better understand short- and long-term outcomes with this configuration, especially related to right-sided thrombosis.

ACKNOWLEDGMENT

The authors would like to thank Duke Perfusion Services, Duke’s LVAD office, Duke’s Cardiac Anesthesia and Critical Care physicians, Duke Nursing, and the large team of individuals that helped care for this patient.

REFERENCES

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