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Eur J Cardiothorac Surg 1998;13:130-134
© 1998 Elsevier Science NL

Centrifugal ventricular assist in children under 6 kg¹

Victorian Paediatric Cardiac Surgical Unit, Royal Children's Hospital, Flemington Rd, Melbourne, 3052, Australia

Received 28 September 1997; received in revised form 20 November 1997; accepted 2 December 1997.

Corresponding author. Tel.: +61 3 93455200; fax: +61 3 93456386; e-mail: thuysc@cryptic.rch.unimelb.edu.au

	Abstract

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Objective: The clinical application of centrifugal ventricular assist devices (VAD) has generally been limited to adults and large paediatric patients. In our experience neonates and small paediatric patients requiring ventricular support post-cardiopulmonary bypass are well supported by VAD. In this study we analyse our experience. Methods: We have examined the records of our VAD patients who weighed less than 6 kg. Thirty-four patients, ranging in age from 2 to 258 days (median 60 days) and weight from 1.9 to 5.98 kg (median 3.7 kg), underwent 35 VAD procedures. One patient was supported on VAD twice. Results: All patients had congenital heart lesions and were placed on VAD either because they could not be weaned from cardiopulmonary bypass after repair or palliation of the lesion (71.5%), or for support in the post-operative period due to refractory low cardiac output (28.5%). Twenty-two of the 35 VAD procedures (0.63, 95% CI: 0.45–0.78) resulted in successful weaning and decannulation, this was similar to the weaning probability for patients greater than 6 kg (P=0.07). There were 10 late deaths in this group, with a 1-year KM survival of 0.31 (95% CI: 0.17–0.47). Most late deaths were related to irreversible cardiac disease processes as were the elective discontinuance of VAD outcomes. Neither weight, age, VAD duration, CPB duration, X clamp duration, univentricular anatomy or TGA anatomy predicted successful discharge from hospital (P>0.05)—Weight P=0.576; Age P=0.532; VAD duration P=0.181; CBP duration P=0.549; X clamp duration P=0.984; Univentricular anatomy P=0.481; TGA anatomy P=0.099. Conclusion: We believe centrifugal ventricular assist is a realistic option in very small patients who require post-cardiopulmonary bypass support. It is relatively easy to establish and manage, the results, although showing no factors predictive of successful discharge, are encouraging.

Key Words: Paediatric • Ventricular assist • Centrifugal

	Introduction

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Ventricular assist devices (VAD) utilizing centrifugal pumps have in the past been used infrequently for neonatal and very small paediatric patients. Within the paediatric age group, most of the world's experience has been in patients between over 6 and 10 kg, with smaller patients generally supported with ECMO. VAD has been used in our hospital for children of any size who cannot be weaned from cardiopulmonary bypass (CPB), for post-operative low cardiac output that fails to respond to pharmacological intervention and unoperated patients with irreversible cardiac dysfunction (planned bridge to transplant). All children must meet a number of criteria before VAD is initiated. The ventricular dysfunction should be potentially reversible. The repair or palliative procedure should have been adequate. Contra-indications include irreversible dysfunction associated with other major organs, intracranial haemorrhage, neurologic impairment or sepsis [1]. In this study we analyse the results of this VAD strategy in patients under 6 kg, including indications, techniques, long and short term outcome, and incremental risk factors.

During the period 1989–1996, 1180 open heart operations were performed on patients under 6 kg in this institution. Thirty-five VAD procedures were carried out on 34 patients. VAD was thus required in 3% of cases in this patient group. The 34 patients ranged in age from 2 to 258 days (median 37 days) and weight from 1.9 to 5.98 kg (median 3.47 kg). All patients had been operated on for repair or palliation of congenital heart defects. Among the 34 patients, the most common defect was hypoplastic left heart syndrome (12 patients) followed by transposition of the great arteries (eight patients) and complete atrioventricular septal defect (three patients; Table 1). Twenty-five procedures were performed for children who could not be weaned from CPB, and 10 for low cardiac output in the post-operative period following initially successful separation from CPB. The time from the end of CPB to the initiation of VAD in these latter 10 procedures ranged from 3 to 96 h (median 23.5 h). The duration of support for all procedures ranged from 1 to 131 h (median 68 h, mean 58.3 h). The patient who underwent two VAD procedures could not be weaned from CPB, was placed on VAD, weaned and decannulated, and then required another course of VAD due to low cardiac output.

	Materials and methods

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View larger version (18K): [in this window] [in a new window]   Fig. 1. VAD circuit.

Left heart bypass was commenced at minimal flow and quickly increased to 150 ml/min/kg. Immediately after the patients were satisfactorily on VAD, heparin was reversed with protamine to an activated clotting time (ACT) of 110 s, in an effort to attain surgical haemostasis. The sternum was generally left open and either a PFTE membrane was sutured to the skin edges or the skin alone was closed, with the cannulas exiting from either pole. When the patients were stable in ICU with minimal bleeding a heparin infusion was titrated to maintain an ACT of 160–180 s. Patients were kept sedated and paralysed in ICU with full mechanical ventilation maintained. Inotropic support was reduced to the minimum level required to support the right heart. All patients received vasodilators, antibiotics, parenteral nutrition, and periodic fresh frozen plasma and platelet infusions as required.

Patients who suffered from low cardiac output post-operatively were cannulated and placed on VAD in the intensive care unit. They were heparinised for cannulation, and then the same reversal protocol was followed.

The patients were maintained on VAD for a minimum of 24 h, unless complications arose, before any assessment of ability to be weaned from VAD was made. After a minimum of 24 h the flow was reduced to allow some LV ejection at left atrial pressures of 8–10 mmHg. Using echocardiographic guidance increased fractional shortening and a positive Starling response on a reduced degree of VAD support were considered to be indications of myocardial recovery [3]. If the haemodynamics remained stable on the reduced VAD flow, the flow was reduced again. This procedure was continued until the patients were haemodynamically stable on minimal safe flow (approximately 200 ml/min). At this point the patients were considered to be weanable. Precordial or transoesophageal echocardiography was used for this assessment.

	Results

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Twenty-two of the 35 procedures (0.63, 95% CI: 0.45–0.78) resulted in successful weaning and decannulation. Five patients could not be adequately supported by VAD for reasons of increased right atrial pressures, decreased oxygenation and poor CO₂ removal, and were converted to ECMO. Patients who could not be weaned had VAD support withdrawn. Bridging to transplant, although technically possible, was not usually undertaken due to the length of time typically required for procuring donor organs in Australia. Fourteen patients were discharged from hospital and 11 were alive 1 year post-discharge (Table 1).

When all patients were considered, analysis of various patient parameters using Student's t-test and Fishers Exact test failed to identify factors predictive of successful or unsuccessful outcome (separation from VAD and/or hospital discharge; Table 2). However, if patients who were converted from VAD to ECMO were excluded, a statistically valid predictor of successful outcome could be identified (Table 2).

In interpreting these data, one must consider several factors in the difference in duration of support (weaned and non-weaned patients). Three patients with no sign of improvement in ventricular function in the first 48 h had support withdrawn within the next 48 h. Six patients became unsupportable, and two patients had support withdrawn following VAD complications within 8 h of initiation of VAD.

There were complications noted in 27 VAD patients. The most common complication was thrombus formation in the VAD circuit. This occurred in 13 patients, necessitating pump head changes in four and a circuit change in one. The remainder required no intervention. There were six patients that required surgical intervention to control bleeding, all among the first 10 procedures done. Five patients required conversion to ECMO, two patients had complications related to cannulae, and one needed the chest opened to facilitate cardiac massage. There were no permanent renal, neurologic or vascular sequelae in any of the survivors.

	Discussion

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Since described by DeBakey [4] in 1971, VAD has been used mainly in adult patients. Its use in neonates and small paediatric patients for support of post-operative ventricular failure after surgery for correction or palliation of congenital heart defects has largely not been well accepted for a number of cited reasons. These include technical difficulties related to size of patient [5] [6] [7], unsuitable anatomy [5] [8] and lack of experience [6]. In some institutions it has been overshadowed by the use of ECMO [6] [9] [10]. In comparison to centrifugal VAD, ECMO support requires a far more complicated circuit using an oxygenator and heat exchanger. Being more thrombogenic, ECMO use requires greater heparinisation of the patient [3]. Many patients with a univentricular circulation, as shown by Perko et al. [11] and this study, can be adequately supported by centrifugal VAD. In this series the survival to discharge probability is equivalent to that of patients supported by ECMO (40%) [12], although, as we have experienced, some patients supported by ECMO have not been supportable by VAD. This study shows that in our institution patients under 6 kg have the same probability of survival to successful weaning from VAD as larger patients (P=0.07). Recent literature has shown rates of survival to discharge that are similar to our own [13] [14] (Table 3).

Ratcliffe et al. [15] has shown that VAD can sharply improve myocardial function in dilated, poorly contracting hearts by reducing end-systolic and end-diastolic pressures and ventricular wall stress. Decreased left atrial pressure reduces pulmonary capillary hydrostatic pressure which can circumvent the need to increase ventilatory support and reduce the risk of right ventricular failure.

A VAD, by providing circulatory support to augment or replace low cardiac output, may prevent the development of ischaemic injury to other organs.

In this series of patients we have shown that centrifugal VAD can provide effective haemodynamic support in many patients under 6 kg who could not be weaned from CPB, or who suffered from low cardiac output post-operatively. This study has shown that centrifugal VAD in small post-cardiotomy patients with univentricular hearts or shunt dependent circulation can be successful. Thrombus formation is an ongoing problem and may be associated with the ACTs required for haemostasis by these patients and relatively low flow rates. Successful weaning from VAD does not ensure discharge from hospital. Patients who have undergone an arterial switch for correction of TGA have the best survival potential within the under 6 kg group.

	Footnotes

 
Presented at the 11th Annual Meeting of the European Association for Cardio-thoracic Surgery, Copenhagen, Denmark, September 28–October 1, 1997.

	Appendix A. Conference discussion

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Dr von Segesser (Lausanne, Switzerland): Looking at your results compared to that published by Bartlett for the ELSO registry that you had mentioned before, one can see that following the surgery, bleeding is the most frequent clinical complication, there comes the problem with cerebral damage, either hemorrhage, CT scan-proven or stroke. What is the proportion of these problems in your series?

Mr Thuys: I could not give you exact numbers, but the incidence of these problems has been minimal. However, if I may, I would like to pass the question on to my surgical colleague. I am a perfusionist, so I do not quite have the background to answer this question.

Dr Brizard: The question was answered in the talk. In the patients that were discharged, in the survival at 1 year, we have no patient with permanent neurologic sequelae.

Dr Galletti (Paris, France): How do you manage your source of pulmonary blood flow during perfusion after a Stage 1 Norwood. In a previous experience that I had with Dr Norwood we experienced a lot of difficulties with this subject, and our conclusions were catastrophic in univentricular repair. Univentricular repair was significantly different in the outcome compared, for example, to transposition. We were only able to wean one patient.

Mr Thuys: Once again, I would like to pass this question on to my surgical colleague.

Dr Brizard: Again, the question was partially answered in the talk. We do have a very significant difference with these two groups of patients, and only three patients could be weaned from VAD in our Norwood group. But the limitation of the pulmonary flow is mainly due to the shunt, and the shunt, whether the patient is with a beating heart or VAD supported, is the same. Also, we maintain a high level of sedation and ventilation control in post Norwood patients with or without VAD, and the pulmonary resistance should be equivalent.

	References

Top Abstract Introduction Materials and methods Results Discussion Appendix A. Conference... References

 

1. Karl TR. Mechanical circulatory support at the Royal Children's Hospital. In: Hetzer R, Hennig E, Loebe M, editors. Mechanical Circulatory Support. Berlin: Springer, 1997:7–20.
2. Horton S.B., Horton A.M., Mullaly R.J., Butt W.W., Mee R.B.B. Extracorporeal membrane oxygenation life support: a new approach. Perfusion 1993;8:239-247.[Abstract/Free Full Text]
3. Karl T.R. Extracorporeal circulatory support in infants and children. Semin Thorac Cardiovasc Surg 1994;6:154-160.[Medline]
4. DeBakey M.E. Left ventricular bypass pump for cardiac assistance: clinical experience. Am J Cardiol 1971;27:3-11.[Medline]
5. Black M.D., Coles J.G., Williams W.G., Rebeyka I.M., Trusler G.A., Bohn B., Gruenwald C., Freedom R.M. Determinants of success in pediatric cardiac patients undergoing extracorporeal membrane oxygenation. Ann Thorac Surg 1995;60:133-138.[Abstract/Free Full Text]
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8. Matsuda H., Taenaka Y., Ohkubo N., Ohtani M., Nishigaki K., Ohtake S., Miura T., Taenaka N., Takano H., Hirose H., Kawashima Y. Use of a paracorporeal ventricular assist device for postoperative cardiogenic shock in two children with complex heart lesions. Artif Organs 1988;12:423-430.[Medline]
9. Del Nido P.J. Extracorporeal membrane oxygenation for cardiac support in children. Ann Thorac Surg 1996;61:336-339.[Abstract/Free Full Text]
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11. Perko M.J., Sander-Jensen K., Dehnke C., Pettersson G. BioMedicus ventricular assist for postcardiotomy heart failure: evaluation of univentricular assistance. Artif Organs 1995;19:777-781.[Medline]
12. ECMO Registry of the Extracorporeal Life Support Organisation (ELSO), Ann Arbor, MI, July 1997.
13. Scheinin S.A., Radovancevic B., Parnis S.M., Ott D.A., Bricker J.T., Towbin J.A., Abou-Awdi N.L., Frazier O.H. Mechanical circulatory support in children. J Card Thor Surg 1994;8:537-540.
14. Costa R.J., Chard R.B., Nunn G.R., Cartmill T.B. Ventricular assist devices in pediatric cardiac surgery. Ann Thorac Surg 1995;60:S536-S538.
15. Ratcliffe M.B., Bavaria J.E., Wenger R.K., Bogen D.K., Edmunds L.H., Jr. Left ventricular mechanics of ejecting postischemic hearts during left ventricular circulatory assistance. J Thorac Cardiovasc Surg 1991;101:245-255.[Abstract]
16. Del Nido PJ, Mayer JE, Jonas RA. Mechanical ventricular assist in children: Experience at the Children's Hospital, Boston (1990–1995). In: Hetzer R, Hennig E, Loebe M, editors. Mechanical Circulatory Support. Berlin: Springer, 1997:1–5.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Stephen B. Horton Andrew D. Cochrane Christian P.R. Brizard Tom R. Karl Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Thuys, C. A. Articles by Karl, T. R. Search for Related Content PubMed PubMed Citation Articles by Thuys, C. A. Articles by Karl, T. R.