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Clinical Outcomes–Devices

Thoratec Ventricular Assist Devices in Pediatric Patients: Update on Clinical Results

Reinhartz, Olaf*; Hill, J Donald; Al-Khaldi, Abdulaziz*; Pelletier, Marc P.*; Robbins, Robert C.*; Farrar, David J.

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doi: 10.1097/01.mat.0000178214.95010.c0
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Abstract

There is a comparatively small but defined need for medium- to long-term mechanical assist systems for use in the pediatric population for bridge to transplantation or, more rarely, for bridge to recovery of the diseased heart. However, to date, all devices commercially available in the United States are designed to fit adults. For smaller patients, only extracorporeal membrane oxygenation and centrifugal pumps are available, which have known limitations in longer-term support.

Because of the lack of a pediatric device, some surgeons have implanted the Thoratec paracorporeal ventricular assist device (VAD) in children and adolescents, as we have reported in the past.1–3 In the current article, we present the updated experience of over 20 years with the Thoratec VAD in children and adolescents.

Methods

Patients

From 1982 through January 2005, 209 children and adolescents up to 18 years of age have been supported with Thoratec VADs (Thoratec Corporation, Pleasanton, CA) in 80 centers worldwide. Mean patient age was 14.5 years (5–18 years). Of the total, 136 patients were male and 73 were female. Mean body weight was 57 kg (range 17–118 kg), mean height was 163 cm (range 77–193 cm), and mean body surface area (BSA) was 1.6 m2 (range 0.7–2.3 m2).

Device Implantations

Figure 1 shows the number of implantations per year. A total of 111 patients received bi-VADs (54%), 88 left VADs (43%), and 7 right VADs (3%) (in 3 patients, the device configuration was not reported). Average duration of support was 44 days (range 0–434 days).

Figure 1.
Figure 1.:
Number of VAD implantations by year.

Indications

Indications for support are depicted in Figure 2. Congenital indications include five patients with transposition whose systemic right ventricles were supported.

Figure 2.
Figure 2.:
Indications for VAD support. CMP, various cardiomyopathies; myocard, acute myocarditis; AMI, acute myocardial infarction; fail to wean, failure to wean off bypass; tx failure, posttransplant failure; cong, congenital heart disease; misc, miscellaneous.

Data Collection

Data were retrieved from a voluntary registry maintained by Thoratec Corporation, from Stanford medical records, and from a limited survey performed for previous publications. This study was approved by the Stanford Administrative Panel for Human Subjects.

Results

Overall Survival

Data regarding hospital outcomes were available for 186 patients (89%). Nine patients (5%) were still on support. Overall survival in the remaining patients was 121 of 177 (68%). Of these, 103 were transplanted, and 18 were weaned from the device. Figure 3 shows the numbers of survivors and nonsurvivors for different indications for support. Survival was 74% for all forms of cardiomyopathies combined, 86% for acute myocarditis, 27% for congenital heart disease, and 57% for postcardiotomy patients failing to wean from bypass.

Figure 3.
Figure 3.:
Survival by indication for support. CMP, various cardiomyopathies; MYO, acute myocarditis; CONG, congenital heart disease; POSTC, postcardiotomy for failure to wean from bypass.

Experience at Stanford University

Between 1998 and 2004 at Stanford alone, 10 patients were supported with Thoratec single VADs; no bi-VADs were used. Mean age was 13.5 years, mean weight was 65 kg, and mean BSA was 1.75 m2. Nine patients were treated for cardiomyopathies, and one was treated for congenitally corrected transposition with end-stage heart failure. Mean duration of support was 31 days. All but one patient survived to transplantation.

Outcome in Patients with a BSA of Less Than 1.3 m2

We were particularly interested in the smallest patients. A subgroup of 31 children with a BSA of less than 1.3 m2 was treated with Thoratec VADs in 19 centers. Mean age was 10 years (range 5–14 years), mean weight was 30 kg (range 17–41 kg), and mean BSA was 1.07 m2 (range 0.73–1.29 m2).

Left VADs were used in only 21 of these patients (4 of these patients with transposition had a failing systemic right ventricle supported), and bi-VADs were used in 10 patients. Mean duration of support was 32 days (range 0–120 days).

Outcome data were available for 29 of these patients and were distinctly different for different indications for support, again showing the best outcomes in patients with cardiomyopathies and myocarditis (Figure 4).

Figure 4.
Figure 4.:
Outcome by indication in a subgroup of 29 patients with a BSA of less than 1.3 m2. CMP, various cardiomyopathies; post tx, graft failure after transplantation.

Discussion

The lack of availability of pediatric VADs in the United States has increasingly been recognized over the last two decades and has ultimately led to a recent effort by the National Heart, Lung and Blood Institute to foster the development of specific devices for smaller children.4 In the past and presently, however, while such devices are not yet available, surgeons have utilized adult-size devices for larger children and adolescents.5 The Thoratec VAD particularly lends itself to such use because of its paracorporeal design, making it technically implantable in patients of around 1 m2 or even less.6

Survival to transplantation or, in fewer cases, to recovery of the native heart, in patients up to 18 years of age does not seem to be different from that of adults supported with this device. Average duration of support is shorter in children. This could be because recovery from end-organ failure is usually quicker in children, and these patients tend to either stay in active status on the transplant waiting list or are placed back on active status only a few days after their VAD implantation.

We have previously reported on the use of the Thoratec in the first 58 children and adolescents,2 a subgroup of the patients described here. General outcome was not distinctly different between those studies. Because of better data quality, however, we were able to perform multivariate analyses for survival and neurologic complications in that earlier study. These analyses revealed congenital heart disease and failure to wean off bypass to be independent risk factors for death, and left atrial cannulation to be an independent risk factor for neurologic events. Given the similarity of the data of the two studies, we have reason to believe that this would still be the case today. Our recommendation, then and now, is to avoid left atrial cannulation whenever possible in favor of cannulation in the ventricular apex.

The single center experience at Stanford with 10 pediatric patients, 9 of whom could successfully be bridged to transplantation, reflects different philosophies and perhaps different patient mix or timing of implant between centers: Our patient group was exclusively treated with left VADs only, whereas in the overall group, 54% received bi-VADs. There seem to be several successful ways to manage right heart failure at left VAD implantation, because it is almost always temporary. Traditionally, the Stanford group has favored medical treatment over right VAD implantation if possible. Certainly, both concepts have advantages and disadvantages, and both can lead to good outcomes.

The subanalysis that we performed in the group of children with a BSA of less than 1.3 m2 points out some particular problems. These patients have a high incidence of congenital heart disease and overall higher complexity, leading to increased morbidity and mortality. Worse outcome seems to be unrelated to size, because small patients with cardiomyopathies and myocarditis have a similar survival than the overall group.

The increased incidence of both thromboembolic and hemorrhagic neurologic events in smaller patients illustrates that anticoagulation is a particular challenge in children. Lower blood flow in a relatively oversized device can lead to areas of stasis and thrombus formation. However, an unphysiologically large stroke volume may lead to systolic hypertension, which might increase the risk of brain hemorrhage. The solution to this problem should therefore not simply be more aggressive, but smarter, better controlled anticoagulation.7 The effects of Coumadin are harder to control in children, and delayed management with heparin may be a better option to avoid transient overanticoagulation. Further, the effects of inhibitors of platelet aggregation in children may be different from those in adults. These drugs have to be studied more extensively in children, so we can better define their role in management.

In summary, the Thoratec VAD has been used extensively in over 200 children and adolescents over the last two decades. It can be applied successfully even in small school-age children. We recommend its continued use in this patient size group until specific pediatric VADs that are currently under development become available.

References

1.Reinhartz O, Copeland JG, Farrar DJ: Thoratec ventricular assist devices in children with less than 1.3 m2 of body surface area. ASAIO J 49: 727–730, 2003.
2.Reinhartz O, Keith FM, El-Banayosy A, et al: Multicenter experience with the Thoratec ventricular assist device in children and adolescents. J Heart Lung Transplant 20: 439–448, 2001.
3.Reinhartz O, Stiller B, Eilers R, Farrar DJ: Current clinical status of pulsatile pediatric circulatory support. ASAIO J 48: 455–459, 2002.
4.Pediatric Circulatory Support Release: November 19, 2002, NOTICE: NOT-HL-03-004. National Heart, Lung, and Blood Institute (NHLBI). Available at: http://grants.nih.gov/grants/guide/notice-files/NOT-HL-03-004.html. Accessed April 2005.
5.Throckmorton AL, Allaire PE, Gutgesell HP, et al: Pediatric circulatory support systems. ASAIO J 48: 216–221, 2002.
6.Copeland JG, Arabia FA, Smith RG: Bridge to transplantation with a Thoratec left ventricular assist device in a 17-kg child. Ann Thorac Surg 71: 1003–1004, 2001.
7.Copeland JG, Smith RG, Arabia FA, et al: Total artificial heart bridge to transplantation: a 9-year experience with 62 patients. J Heart Lung Transplant 23: 823–831, 2004.
Copyright © 2005 by the American Society for Artificial Internal Organs