SynCardia Temporary Total Artificial Heart: Single-Center Experience at a Children’s Hospital : ASAIO Journal

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Pediatric Circulatory Support

SynCardia Temporary Total Artificial Heart: Single-Center Experience at a Children’s Hospital

Perry, Tanya; Morales, David L. S.; Villa, Chet R.; Benscoter, Alexis; Fields, Katrina; Lorts, Angela

Author Information
doi: 10.1097/MAT.0000000000001659
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Abstract

The SynCardia temporary total artificial heart (TAH-t) is a pneumatic, pulsatile, complete biventricular replacement system that is surgically implanted.1 Techniques for implantation are adaptable to almost all patients with heart failure, including various forms of cardiomyopathy, complex congenital heart disease, failed ventricular assist device (VAD) support, and graft failure in cardiac transplant recipients.1,2 The use of mechanical circulatory support (MCS) in children and adults continues to evolve, and the total artificial heart is a definitive option for those requiring biventricular support.3,4

The TAH-t is now available in two sizes, 50 cc and 70 cc (SynCardia Systems, LLC, Tucson, AZ).1 Given the advent of the 50 cc device size, the TAH-t has increasingly been used in smaller and younger patients, as size of the patient is the main limitation of its use.5 Herein, we describe a single children’s hospital experience with implantation of the TAH-t.

Methods

Patients implanted with a TAH-t at Cincinnati Children’s Hospital Medical Center from November 2012 to March 2021 were included. The decision to implant a TAH-t was determined based on patient-specific clinical factors precluding placement of a left ventricular assist device (LVAD), such as severe right ventricular failure, transplant graft failure, intracardiac thrombus, or uncontrolled malignant arrhythmia. Patient chest and device size was evaluated with computed tomography (CT) reconstruction or “fit studies” and reviewed with the cardiothoracic surgeon before implant.

Implantation consists of excision of both ventricles and four valves.2 The two artificial ventricles are directly sutured to the patient’s native (or previously transplanted) atrioventricular annuli and connected to the external console via two drivelines. Implantation technique with this device has been further described in detail previously.6,7

Patient Management

Patient anticoagulation was managed postoperatively by the VAD team. If chest tube output was deemed acceptable (<2 ml/kg/hour and serosanguinous), heparin was initiated and titrated to a goal partial thromboplastin time (PTT) of 40–50 seconds for the first 24–48 hours postimplant and increased to 50–60 seconds after bleeding had subsided, usually >72 hours. Aspirin was initiated by 2–5 days postoperatively, and when tolerating enteral feeds, the heparin was transitioned to warfarin for a goal international normalized ratio (INR) of 2–3. Postoperative hypotension was managed with vasopressin if indicated, and hypertension was managed with nitroprusside or nicardipine for goal normotensive for age. Intravenous antihypertensives were transitioned to oral hydralazine as needed with or without enalapril when the patients were tolerating oral medication. All four patients that were implanted for transplant graft rejection were taken off of all immunosuppressive medications. Patients were transferred out of the intensive care unit (ICU) when they were extubated, off of continuous infusion medications, and demonstrated stable end-organ perfusion. They were activated on the transplant waitlist when they were extubated and demonstrated end-organ recovery.

Data Collection and Statistical Analysis

Demographics, clinical, and laboratory data were collected retrospectively. All patients were followed prospectively at the heart failure and VAD clinic at our institution, and outcomes were recorded. There was no missing data. Statistical comparative tests were not performed.

Results

Baseline Characteristics

From November 2012 to March 2021, seven patients underwent TAH-t implant at our institution. Patient demographics and etiology of heart failure is presented in Table 1. Patient age ranged from 14 to 34 years with a median of 19 years. The smallest implanted patient had a body surface area of 1.37 m2 (37 kg).

Table 1. - Demographics and Preimplant Variables
Patient Age (Years) Sex Weight (kg) BSA (m2) Number of Prior Sternotomies Preimplant Variables
MCS Mech Vent CRRT Creatinine (mg/dl) Bilirubin (mg/dl) Albumin (gm/dl)
1 19 F 63 1.75 1 No No Yes NA due to dialysis 0.9 3.1
2 34 F 88.6 1.93 4 HMII Trach Yes NA due to dialysis 2.7 2.8
3 16 M 135 2.6 0 ECMO Yes No 0.73 3.2 2.3
4 25 M 97.5 2.2 1 ECMO/ECPR Yes No 1.54 1.4 2.9
5* 17 M 42.5 1.5 1 No No No 1.65 0.4 1.9
6* 22 F 50 1.5 1 No No No 1.9 0.6 3.1
7* 14 F 37 1.37 2 ECMO Yes No 0.52 1.8 3.4
*50 cc SynCardia.
BSA, body surface area; CRRT, continuous renal replacement therapy; ECMO, extracorporeal membrane oxygenation; ECPR, extracorporeal cardiopulmonary resuscitation; F, female; HMII, HeartMate II; M, male; MCS, mechanical circulatory support before total artificial heart implant; Mech Vent, invasive mechanical ventilation before transplant; NA, not applicable; Trach, tracheostomy.

Patient Status Before Implant

All patients were Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) profile 1 or 2.8 Three patients were on extracorporeal membrane oxygenation (ECMO) before implant, and one was on a HeartMate II (Abbott Inc) LVAD implanted at an outside institution who presented to us with failing physiology from chronic right heart failure. Two of the seven patients were on continuous renal replacement therapy. Laboratory values before implant and other preoperative variables are displayed in Table 1.

Outcomes and Complications While on TAH-t Support

Pump settings were adjusted for target blood pressure and cardiac output. Patient central venous pressure and cardiac index in the first postoperative day is displayed in Table 2. Other patient outcomes are displayed in Table 3. Duration of support ranged from 10 to 414 days with a median of 27 days. Time to extubation after implant ranged from 1 to 5 days, with the three most recent patients being extubated on postoperative day 1. There was a trend toward decreased ICU length of stay over time. Two patients died while on support, and the other five were successfully transplanted following their TAH-t placement, all without any adverse neurologic events, and were discharged home.

Table 2. - Hemodynamics on Postoperative Day 1
Patient CVP POD 1 (mm Hg) CI (L/min/m2)
1 12–18 2.8–4
2 17–21 3.1
3 12–18 2.5
4 10–12 2.7
5 10–14 3.6–4.6
6 10–12 2
7 16–19 3.6
CI, cardiac index in liters per minute per meter squared; CVP, central venous pressure; POD, postoperative day.

Table 3. - Indication for VAD Placement and Outcomes
Patient Cardiac Diagnosis Indication for Device Duration of Support (Days) ICU LOS LOMV Days to Transplant Listing Outcome Adverse Events
1 OHT CAV/graft failure 414 78 4 196 Transplant Bleeding POD 1, dialysis
2 CHD* RV failure on LVAD 53 57 NA trach NA Died on support DSC, bleeding POD 14, infection, dialysis
3 DCM Refractory ventricular arrhythmias 96 16 5 17 Transplant DSC
4 OHT CAV/graft failure 27 11 3 13 Transplant DSC, bleeding POD 1
5 OHT CAV/graft failure 17 28 1 NA Died on support Infection, dialysis
6 OHT CAV/graft failure 11 6 1 6 Transplant None
7 CHD Refractory ventricular arrhythmias 10 7 1 3 Transplant None
Days to transplant listing indicates number of days postimplant the patient was activated on the transplant waitlist. Bleeding indicates bleeding requiring re-exploration. Dialysis indicates acute renal failure requiring continuous renal replacement therapy.
*Shone complex s/p arch repair and ventricular septal defect closure, subsequently s/p Ross procedure followed by left ventricular assist device placement with tricuspid and pulmonary valve replacements.
Atrial and ventricular septal defect s/p repair with mitral valve cleft s/p mechanical mitral valve with subsequent development of ventricular dysfunction.
CAV, coronary artery vasculopathy; CHD, congenital heart disease; DCM, dilated cardiomyopathy; DSC, delayed sternal closure; ICU, intensive care unit; LOMV, length of invasive mechanical ventilation, in days, after implant; LOS, length of stay; LVAD, left ventricular assist device; NA, not applicable; OHT, orthotopic heart transplant; POD, postoperative day; RV, right ventricular; s/p, status post; trach, tracheostomy; VAD, ventricular assist device.

The two patients who died while on support from multiorgan failure were chronically ill before implant. One had congenital heart disease and had developed endocarditis that led to progressive heart failure necessitating placement of a HeartMate II (Abbott Inc) LVAD at an outside institution. She had been discharged home but developed progressive right ventricular systolic dysfunction requiring chronic dobutamine for several months, tracheostomy and was deemed not to be a candidate for heart transplant due to poor immune, physical, and nutritional condition. Due to worsening biventricular failure, clot in the HeartMate II (Abbott Inc) circuit and overall worsening clinical condition, this patient was transferred to our institution for SynCardia TAH-t as a bridge to transplant candidacy. The second patient who did not survive had multiple prior episodes of transplant rejection and had been inpatient at another hospital for several months. His comorbidities included fluid overload with recurrent pleural effusions and ascites secondary to right heart failure, severe malnutrition, and continuous milrinone and dopamine infusions. Despite attempts at desensitization, he remained highly sensitized and thus a poor retransplant candidate, so he was referred to our institution for SynCardia TAH-t.

Both patients were well-supported hemodynamically with one being extubated but subsequently died of infectious complications. One had positive cultures of stenotrophomonas and candida but ultimately died of invasive norovirus enteritis and varicella encephalopathy. The other developed candida fungemia but ultimately died of multiorgan failure including renal failure, fluid overload, gastrointestinal bleeding, liver dysfunction, systemic inflammatory response syndrome, and respiratory failure. None of the patients who were successfully bridged to transplant had any postimplant infectious complications.

Three patients required continuous renal replacement therapy following device placement. Two of those patients had multiorgan failure before implant and did not survive to discharge. The third patient who required renal replacement therapy after implant had a history of clear cell carcinoma and had previously undergone a nephrectomy with chemotherapy, leading to anthracycline toxicity and subsequent dilated cardiomyopathy and heart transplant. She recovered kidney function 6 weeks after SynCardia TAH-t implant. No patients had postoperative compression of the vena cava or pulmonary veins.

At long-term follow-up and when this article was prepared, of the five successfully transplanted patients, three patients remain alive and well at 6 years, 2.3 years, and 71 days after transplant. The cause of death of the two patients who died after transplant were unrelated to their TAH-t support. One patient died due to acute rejection 6.8 years following orthotopic heart transplant (OHT). The other died 3.1 years following successful OHT from support secondary to trauma.

Discussion

As the number of implants in pediatric hospitals are increasing, specifically with the development of the smaller 50 cc device, TAH-t provides an effective hemodynamic support option in candidates where VAD support is challenging.4 Our overall outcome to successful transplant was 71%. This is compared to other studies, with an overall 37–58% survival from TAH-t to transplant rate.3,9 Additionally, patients who underwent TAH-t placement for transplant rejection were previously demonstrated to have the lowest survival to retransplant rate (25%), although, in our cohort, 75% of the patients with transplant rejection survived to retransplant.3

In a recent study by Morales et al.,3 only 19% of children in a total cohort had the TAH-t implanted for transplant rejection, compared to our cohort, of which 57% were implanted for transplant rejection. Mechanical circulatory support (MCS) in transplant patients with graft failure (both acute and chronic) is challenging, and these patients are often poor candidates for traditional VAD support. Durable continuous flow LVADs are often unsuccessful in this population because of biventricular failure, small ventricular volumes, and infectious complications of VAD support while on immunosuppression.10 In cases of restrictive physiology, as seen in transplant graft failure, the TAH-t seems to be a favorable option for MCS. The TAH-t supports both ventricles eliminating the concern of right ventricular failure, and immunosuppression can be discontinued, decreasing infection risk. The International Society for Heart and Lung Transplantation registry has shown that half as many transplant graft rejection patients, when compared to primary transplant patients, were bridged to transplant on LVAD support.10 In addition, retransplant patients may be able to be discharged home on the Freedom Driver (SynCardia Systems, Inc. Tucson, AZ), improving quality of life. Our discharged case required prolonged desensitization and rehabilitation and underwent successful repeat OHT after 414 days of support.

Patient selection should be taken with caution. Frailty is described as the aggregation of subclinical physiologic insults across many organ systems, which result in increased vulnerability when faced with stress.11 In other words, poor reserve and decreased resiliency. It has been previously demonstrated that frailty has a significant impact on post-VAD outcomes, and this is supported by our patient cohort.12 The two patients who did not survive to discharge had considerable frailty evidenced by one requiring a tracheostomy and long-term home inotropic support, in addition to their previous placed LVAD, and the other with poor nutritional status with an albumin of 1.9 gm/dl and poor renal function before implant. Given the poorer outcomes in those with chronicity of disease, timing of advanced therapies for heart failure is imperative before end-organ damage and frailty is irreversible. We have created and begun to use a frailty tool that measures physical and psychologic components of reserve and resiliency to bring objectivity to this important assessment so that we can track it over time. In addition, although frailty assessment is important to decide the candidacy for surgery, it is also true that the only alternative to not offering TAH-t in these patients would be redirection of care. This is an ethical dilemma that must be considered when reviewing candidacy with a multidisciplinary approach including the patient (when able) and family.

Future directions may include alternative anticoagulation strategies and closer monitoring of pulmonary arterial (PA) pressure in these patients. The field of mechanical circulatory support in pediatrics has become skilled in the use of bivalirudin, and so it could be a potential primary anticoagulant in select circumstances. For example, in those with significant protein loss that would change the heparin effect, and thus may be challenging to anticoagulate. Regarding PA pressure monitoring, a pressure-sensing device to help estimate PA pressure such as a cardioMEMS (Abbott Laboratories, Atlanta, GA) could be an addition to the current rehabilitation of the pulmonary vasculature in select cases. We do, however, use the right-sided device to help us estimate PA pressure in interpretation of waveforms and overall device performance.

Practice change and experience at our institution has driven better outcomes and faster rehabilitation of this unique patient population throughout our experience. We demonstrate a trend toward decreased length of mechanical ventilation and ICU length of stay. Potential benefits of this practice include reducing the risk of ventilator-associated adverse events, as well as earlier rehabilitation/nutrition.13 These practices involve close collaboration between the VAD, ICU, and surgical teams and must include patient, family, and provider education. We develop preoperative goals in order to set expectations as outlined by the Advanced Cardiac Therapies Improving Outcomes Network (ACTION), flight plan. With collaboratives like ACTION, we will continue to improve the outcomes in this patient population by sharing information and standardizing care.14

Conclusions

The SynCardia TAH-t can be used to successfully bridge patients to heart transplant at a children’s hospital. Patients with transplant graft rejection requiring biventricular support with a TAH-t may have superior outcomes than previously reported. Early extubation and shorter ICU length of stay in patients who underwent TAH-t implant are possible.

References

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Keywords:

heart failure; mechanical circulatory support; pediatrics; SynCardia total artificial heart; ventricular assist device

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