Cardiology

The PediPump

Following the development of a small implantable ventricular assist device for adult patients, a research team at Cleveland Clinic in the US is developing a similar heart pump for paediatric use. Callan Emery spoke to Dr Brian Duncan, leader of the research team, about the device.

Implantable heart pumps or ventricular assist devices (VADs), as they are known, have given many adult patients with end-stage heart failure a new lease on life, particularly as a bridge to transplant and, as recent research shows, as devices increasingly considered for long-term heart failure destination therapy.



VAD’s are implanted most commonly in the heart’s left ventricle – the chamber of the heart that pumps blood throughout the body – when the heart is too weak to pump enough blood to nourish the body's tissues.

However, although VADs have revolutionised the treatment of cardiac disease in adults, there is a gaping need for such devices for children. According to Dr Brian Duncan, of the Children’s Hospital at Cleveland Clinic, Ohio, United States: “The development of VAD technology for children is widely recognised as one of the major unaddressed needs in paediatric cardiology and cardiac surgery.”


In 2004 the Cleveland Clinic Foundation, in partnership with US-based Foster Miller Technologies, received a US$4.2 million, five-year contract from the US National Heart Lung and Blood Institute, which is part of the National Institutes of Health, to develop a paediatric VAD called the PediPump. The PediPump's enabling technology is drawn from an implantable VAD originally designed at Cleveland Clinic’s Department of Biomedical Engineering and Foster Miller Technologies for catheter-based insertion in adults. Adaptation of this adult catheter pump for paediatric indications has resulted in a new impeller VAD, or PediPump, suitable for supporting children from newborns to adolescents.



Dr Duncan, surgical director, Paediatric Heart Transplant and Cardiac Failure, Paediatric and Congenital Heart Surgery, at Cleveland Clinic is the lead investigator in the development and testing of the PediPump. He said the development of the PediPump would address a number of issues which had not been met by other paediatric centrifugal VADs, such as Medtronic’s Bio-Pump, the MEDOS HIA VAD by MEDOS Medizintechnik and the Berlin Heart VAD.


These included support for the entire range of patient sizes including infants with a single pump; the preservation of haemodynamic performance; and ensuring minimal impact on the host. Dr Duncan told Middle East Health that they had just begun the animal testing phase of the PediPump, “which should take about two or three years. There will be about another five years of clinical trials following animal testing before FDA approval. Although during this stage patients will be able to use it on a trial basis.”

In a paper “The PediPump: A New Ventricular Assist Device for Children” published in Artificial Organs last year Dr Duncan et al describes the PediPump as a “magnetic bearing-supported rotary dynamic pump”. “Unique to the design of this pump is the absence of a seal with suspension of the rotor on magnetic bearings resulting in high durability. “A second unique feature of this pump is its extremely small size measuring approximately 7mm by 60mm with a priming volume of 0.6 mL which imparts less than 10% of the physical displacement of currently available axial flow pumps while retaining good flow capacity.

“The device provides pressure and flow capable of supporting adults, far exceeding the requirements for support of children in the 2–25 kg weight range.” Dr Duncan told Middle East Health that the magnetic bearings are a key part of the device. “Because the rotating mechanism is magnetically levitated there are no contact points, which is unique to this VAD. Because of this we expect it to show very good durability.” The pump rotating assembly consists of an impeller in the front, radial magnetic bearings in the front and rear and a motor magnet in its centre.

A small alternating current is passed across the motor which causes it to spin. The current is supplied via a small wire which is attached to an external power source. “This could be anything from a sizable console for inpatients, or for outpatients a portable energy pack that could even be wearable. The ultimate goal is to develop a fully implantable system that would have the power source implanted as well,” Dr Duncan explained. Blood enters axially at the inlet, and is turned in the impeller to exit the pump at an intermediate angle through the pump outside diameter. An inflow cannula is configured as appropriate for the size of the patient. Some arterial blood flows through windows at the rear of the pump under the influence of arterial pressure, washing and cooling the motor gap, before returning to the impeller.

The rotor is supported on passive, radial magnetic bearings. The electric motor combines small diameter with good efficiency and a large, low blood shear rotor/stator gap. Titanium shells seal all potentially corrodible components from blood and tissue. Dr Duncan said the PediPump can be inserted using standard cannulation strategies and is suitable for right and left ventricular support. He added that because of its small size complete intravascular insertion may be possible for children beyond infancy. “An even smaller pump is being constructed. It is about 15% smaller in length and width to enable catheter-based, peripheral vascular insertion.”

Dr Duncan notes in his paper that “to produce a complete, ambulatory ventricular assist system, this pump technology will ultimately be combined with supporting technology based on the experience of Cleveland Clinic Foundation/Foster-Miller Technologies (CCF/FMT) for an implantable total artificial heart. Circuit changes and new software for the implantable total artificial heart controller will be made resulting in a small, wearable paediatric controller. “The artificial heart controller presently contains substantial control, diagnostic monitoring, and data transmission capability which will be easily adaptable to the new application.

“In the future, investment in custom integrated circuitry is envisioned, which will make the CCF/FMT controller much more compact and implantable for some size ranges of children.” He said there was no initial plan to coat the PediPump with an antibiotic like those used for the coatings of drug-eluting stents. “However, Cleveland Clinic does a lot of research in this field and they could potentially incorporate it at a later stage.” Dr Duncan said he envisioned the PediPump being used to as “a bridge to transplant” – to provide support for paediatric patients waiting to get a heart transplant. “This is the initial application. Of course, we will consider it for destination therapy for children with heart failure as we expect it to be very durable. This is something that could be used for a very long time.”

                                  
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