Pulsatile ventricular assist devices (VADs) are now being used routinely in end-stage heart failure as a bridge to transplantation or to recovery of the native heart; however, generally, these devices are designed for adult body size. In Europe, there has been a growing experience in recent years with miniaturized, pulsatile pediatric pumps like the Berlin Heart and Medos VAD. 1,2 However, for lack of Food and Drug Administration (FDA) approval, these are not to date available in the United States. Extracorporeal membrane oxygenation (ECMO) and centrifugal pumps remain the standard mechanical support option for smaller children in most centers. 3,4
More recently, some adult devices have been used in the pediatric population with good results. Paracorporeal devices such as the Thoratec VAD can often be implanted in smaller patients. 5 The smallest patient supported weighed just 17 kg. 6
When compared with adults, different clinical management problems may arise, particularly in the smaller children. The application of relatively “oversized” devices in children can lead to some specific complications. Stasis in the device can lead to thromboembolism, fitting large cannulae into small patients can be technically challenging, and large stroke volumes may lead to systolic hypertension. We therefore compiled data from multiple centers, focusing only on the children with very small body size, to detect these specific problems and to develop specific recommendations for this patient group.
Between October 1988 and August 2001, 19 children with a body surface area (BSA) less than 1.3 m2 have been supported in 12 centers worldwide using the Thoratec VAD (Thoratec Corp., Pleasanton, CA), a pneumatically driven paracorporeal pump with mechanical valves with a maximum stroke volume of 65 ml. Table 1 shows the participating centers, and Table 2 shows patient demographics.
There were 11 boys and 8 girls in this population. Mean BSA was 1.09 (range 0.73–1.29) m2, mean body weight was 31 (range 17–41) kg, and mean age was 10 (7–14) years. Ten patients were supported with biventricular VADs. Only the systemic circulation was supported in nine patients (in 3 of these cases, a systemic right ventricle was supported for late failure of a Senning or Mustard procedure in transposition of the great arteries). Mean duration of support was 41 (range 0–120) days.
Indications for support were end-stage cardiomyopathies (CMP) in eight patients, acute myocarditis in three, allograft failure post cardiac transplantation in one, and various congenital lesions in seven. Table 2 gives an overview of this data and separates the patients with congenital lesions from those with other indications.
Patients with less than 1.3 m2 BSA were initially identified from the Thoratec company database. This is a voluntary registry, and this patient group may therefore not include all patients in this range of BSA. The respective centers were then contacted, and they provided detailed retrospective patient data. No formal statistical comparisons of groups were performed because of small group sizes.
Overall survival for different indications of support is shown in Figure 1. Eight of 11 (72%) patients with CMP or myocarditis survived; however, only 1 of 7 patients with congenital disease indications survived through support. One additional patient with graft failure post transplantation also died.
Characteristics and outcome for the two groups of patients with CMP or myocarditis versus congenital disease is compared in Table 3. There were no significant differences in age, weight, BSA, or male to female ratio. None of the patients with CMP or myocarditis had a cardiac operation before VAD implantation; however, as one would expect, all of the congenital disease patients had previous cardiac surgical procedures.
Anticoagulation during support consisted initially of heparin in all patients, with transition to phenprocoumon between postoperative day 2 and 38. As additional anticoagulants, aspirin was used in four patients, dextran in one, and low molecular weight heparin in another patient.
Three patients in the group of patients with CMP or myocarditis had thromboembolic neurologic events (Table 3). All three survived, and two of them made a complete neurologic recovery. In the congenital group, there were two thromboembolic events, one of which was fatal, and three hemorrhagic events, all of which were fatal. In patients with neurologic complications, no significant deviations in the anticoagulation regimen could be detected compared with those without this regimen.
In the majority of patients, the left ventricular apex was cannulated for left ventricular support. In only two patients with congenital disease was the left atrial appendage cannulated. Both patients suffered neurologic events (1 thromboembolic, 1 hemorrhagic), and neither of them survived. Of the 16 patients cannulated in the apex of the systemic ventricle, five had thromboembolic events, two of which were fatal.
Ventricular Assist Device Control Modes
For the majority of the support period, the full to empty mode was used in nine patients and the fixed rate mode in seven (in 3 patients, this information was not available). We could not detect statistically significant differences in outcome between the two control modes. However, although during the initial uses of the Thoratec VAD in children, rather low VAD rates between 50 and 70 minutes were used, more recently there appeared to be a tendency toward faster rates (80–90 min) and partial stroke volumes. Of the seven most recent patients in the current study, only one experienced a small, fully reversible thromboembolic stroke.
Device Flow Rates
There was only very limited data available with regard to flow rates of the device, particularly because the fixed rate mode was frequently used, which does not allow for calculation of flows. Therefore, we could not analyze the effect of flow rates on outcome or complications.
Despite being designed for adults, the Thoratec VAD can provide ventricular support for even quite small children with end-stage heart failure resulting from CMP or myocarditis, with acceptable survival rates. The survival of 72% in our small group is similar to that of adults supported with the Thoratec VAD. 7,8 Outcome appears to be independent of body size within the range of the current report and, when compared with the literature, also beyond this report. The Thoratec system is a valuable option for pulsatile mechanical support in children greater than approximately 17 to 20 kg of body weight. There are currently no other pulsatile devices available in the United States for this patient group. Alternatives include ECMO and centrifugal pumps. 3,9 These devices use continuous flow and allow for pulsatile perfusion only if the heart ejects over the pump pressure. They do not allow for any patient mobilization and are not suitable for longer-term support. There have only been incidental cases of pediatric use of the Abiomed system. 10,11 The Thoratec Heartmate appears to be too large for smaller children. 12
In our group of patients, congenital disease appears to be a risk factor for poor outcome. A number of factors may contribute to the fact that survival in this group was low: these patients were obviously more seriously ill when referred for support, and a number of them had had cardiac arrests before implantation or were on centrifugal pumps. Anatomic abnormalities complicated VAD implantation in some patients. All patients had previous cardiac surgeries, which might also contribute to poor outcomes, as has been reported previously for adults with the Thoratec VAD. 8
Neurologic complications are also more frequent in the congenital group. We do not have an explanation for this observation except that one could speculate that these patients were more severely ill at the time of device implantation. Ventricular apical cannulation significantly reduces the stroke risk, 5,13 presumably by unloading the systemic ventricle and not allowing clots to form in it. This appears to be even more important in these small patients. In the last few years, most centers used the fixed rate mode with partial stroke volumes and high pump rates in children, which intuitively seems the correct physiologic choice for maintaining normal systolic and pulse pressures. Keeping drive pressures high maintains high velocities and ensures complete emptying of the pump, which is thought to reduce stasis and therefore thromboembolic events. This might be reflected in the lower incidence of neurologic events in the patients later in the series.
To avoid rare, but usually fatal, hemorrhagic strokes, which also appear more frequent in small children, overanticoagulation should probably be avoided in the very sick patients. It has also been hypothesized that hemorrhagic strokes may be caused by high peak systolic blood pressure from high stroke volumes in oversized devices. In our patient group, only one of three patients with intracerebral bleeding was reported to be consistently hypertensive (systolic blood pressure >140 mm Hg). However, just short periods of hypertension may suffice to cause an event, and these periods may even go undetected. We therefore cannot definitively prove (or discard) this hypothesis given the limited data in this study.
The growing experience with the Thoratec VAD in small children shows excellent outcome in patients with CMP and myocarditis in patients of quite small sizes (17–20 kg). Children with congenital heart disease indications have a difficult prognosis. We recommend careful anticoagulation and application of higher pump rates with partial filling but complete emptying to minimize neurologic events.
1. Hetzer R, Loebe M, Potapov EV, et al: Circulatory support with pneumatic paracorporeal ventricular assist device in infants and children. Ann Thorac Surg 66: 1498–506, 1998.
2. Konertz W, Hotz H, Schneider M, et al: Clinical experience with the MEDOS HIA-VAD system in infants and children: a preliminary report. Ann Thorac Surg 63: 1138–1144, 1997.
3. Karl TR, Horton SB: Options for mechanical support in pediatric patients, in Goldstein DJ, Oz MC (eds). Cardiac Assist Devices
. Armonk, NY: Futura Publishing, 2000, pp. 37–62.
4. Meliones JN, Custer JR, Snedecor S, et al: Extracorporeal life support for cardiac assist in pediatric patients. Review of ELSO Registry data. Circulation
84(5 Suppl): III168–III172, 1991.
5. 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.
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. El-Banayosy A, Körfer R, Arusoglu L, et al: Bridging to cardiac transplantation with the Thoratec ventricular assist device. J Thorac Cardiovasc Surg 47 (Suppl. 2): 307–310, 1999.
8. Farrar DJ, Hill JD, Pennington DG, et al: Preoperative and postoperative comparison of patients with univentricular and biventricular support with the Thoratec ventricular assist device as a bridge to cardiac transplantation. J Thorac Cardiovasc Surg 113: 202–209, 1997.
9. Hopper AO, Pageau J, Job L, et al: Extracorporeal membrane oxygenation for perioperative support in neonatal and pediatric cardiac transplantation. Artif Organs 23: 1006–1009, 1999.
10. Sadeghi AM, Marelli D, Talamo M, et al: Short-term bridge to transplant using the BVS 5000 in a 22-kg child. Ann Thorac Surg 70: 2151–2153, 2000.
11. Ashton RC Jr, Oz MC, Michler RE, et al: Left ventricular assist device options in pediatric patients. ASAIO J 41: M277–M280, 1995.
12. Helman DN, Addonizio LJ, Morales DL, et al: Implantable left ventricular assist devices can successfully bridge adolescent patients to transplant. J Heart Lung Transplant 19: 121–126, 2000.
13. Farrar DJ: Atrial versus ventricular cannulation for bridge to transplantation with the Thoratec VAD system, in Proceedings of Cardiovascular Technology and Science Meeting
; Bethesda, MD, 1992.