The Organ Care System (OCS) Heart (TransMedics Inc.) is a portable ex-vivo organ perfusion system which can preserve a donor heart in a near-normothermic beating state from retrieval until it is transplanted.
The two main elements of the OCS Heart system are the OCS Heart console and the heart perfusion set, each of which contain several sub-components.
The OCS Heart console is an electromechanical, portable console with wireless monitor. It contains an infusion pump and circulatory pump, batteries, a data card, gas delivery subsystem, and probes.
The heart is continuously monitored whilst in the OCS Heart system. Physiological measurements include coronary flow, aortic flow, mixed venous haemoglobin saturation percentage, haematocrit percentage, blood temperature and pulmonary artery pressure. A coronary angiogram and electrocardiogram are also provided. Data from a blood gas analyser can also be entered into the system. Audible and visual alarms are given if any of these values move outside of accepted levels.
The OCS Heart console also provides a docking station for the portable monitor, and storage for TransMedics maintenance solution. The OCS Heart console is reusable hardware that contains the components needed to drive and monitor the heart perfusion module, which is part of the heart perfusion set.
The heart perfusion set contains all of the components that directly contact blood or the heart during heart preservation. It is a single-use biocompatible perfusion and monitoring device, which includes the following:
heart perfusion module, which provides the sterile blood circuit and protected environment for the heart in the OCS Heart system. The module communicates wirelessly with the console monitor. The heart sits in the organ chamber of this module.
blood collection set, including a blood collection bag, line, clamp and a leukocyte filter set. The blood collection set is used to collect blood from the donor for donor heart perfusion. The blood passes through the leukocyte filter into the heart perfusion module reservoir.
heart instrumentation tool set, a set of sterilised accessories for connecting the donor heart to the OCS Heart system.
heart solution set, a 3-chamber system that delivers maintenance solution to the heart while it is in the OCS Heart system.
cardioplegic arrest set, which is used to stop the donor heart using cold cardioplegia to be able to disconnect it from the OCS Heart system prior to transplantation.
monitoring accessories package, containing valves to access the heart while it is being perfused on the OCS Heart system.
The donor heart is connected to the OCS Heart system immediately after explantation and is kept in a beating state until disconnection for transplant. The system maintains heart viability by continuously perfusing the donated heart with warmed, oxygenated blood, supplemented with TransMedics proprietary maintenance and priming solutions (which maintain the heart during transport while reducing the possibility of inflammatory reactions). The system needs at least 1,100 ml of blood from the heart donor. This blood is filtered with the TransMedics blood collection set and continuously circulated in a closed circuit with the TransMedics solutions. Implantation of the heart and subsequent patient care follow standard procedures.
The technology is the only system available for use in clinical practice for donor heart preservation which allows near-normothermic blood-based perfusion of the donor heart. This technique aims to decrease the amount of damage that occurs to the heart after removal, by reducing the rate of tissue deterioration compared with conventional cold ischaemic storage. The OCS Heart system allows for hearts to be transported for longer distances in comparison with cold storage. It is the only available technology that allows donation after circulatory death (DCD). DCD is defined as death that has been diagnosed and confirmed using cardio‑respiratory criteria, in contrast with donation after brainstem death (DBD) which uses neurological criteria to confirm death. There is a scarcity of suitable donor organs and DCD hearts are considered higher risk, so the use of OCS may increase the number of available donor hearts.
People identified as needing a heart transplant are placed on a waiting list for a donor heart and are likely to wait for several months or years. Around half the people accepted onto the heart transplant waiting list have a transplant within 3 years, but for some people, a suitable heart does not become available.
People may be fitted with a ventricular assist device (VAD) which can be used as a 'bridge to transplantation' to provide temporary circulatory support while waiting for a suitable donor heart to become available. These devices are most commonly placed in the left ventricle but can be fitted to the right or both ventricles. VADs can also be used to provide longer term circulatory support and in some cases allow the heart to recover without the need for a transplant. Another 'bridge to transplantation' method is the implantation of a total artificial heart powered by a portable 'driver' which is carried in a backpack or shoulder bag. This involves removal of some parts of the heart and aims to improve the person's condition before transplant.
Conventional heart transplantation involves removing the heart of a donor after brainstem death, from someone who has permanently lost the potential for consciousness and the capacity to breathe on their own. There is a limited number of post-brainstem death donors worldwide, but using DCD hearts could increase the number of hearts for transplantation by more than 10% (Knop et al. 2016). Heart transplantation following circulatory death is not routinely recommended clinical practice in the UK (British Transplantation Society guidelines on transplantation from deceased donors after circulatory death, 2013).
A donor heart for transplantation is usually preserved using cold ischaemic storage. A cardioplegia solution is used to stop the heart, which is then placed in a sealed bag immersed in preservation solution and packed in ice. Finally, it is transported in a non-sterile insulated box from the donor site to the recipient. The maximum recommended preservation time for donor hearts is 6 hours (Hicks et al. 2014, Hosgood et al. 2014).
NICE interventional procedure guidance on normothermic extracorporeal preservation of hearts for transplantation following donation after brainstem death states that this technology has sufficient short-term safety evidence to support its use with normal arrangements for clinical governance and audit. The guidance does not include recommendations on the procedure for preserving hearts explanted after circulatory death.
Adults or children needing heart transplants are typically those with severe heart failure for whom medical treatment with drugs, pacemakers, or revascularisation, has not worked. Heart failure can be caused by a number of factors including coronary heart disease, cardiomyopathy, valve disease or congenital heart defects.
The OCS Heart system can be used to preserve hearts for donation after either circulatory or brainstem death. The OCS Heart system would be used by qualified healthcare professionals specialising in heart transplantation and trained in the use of the OCS Heart system. The technology would be used in specialist transplant centres in the NHS.
The cost of the single-use OCS Heart Perfusion Set is about £30,000 and the approximate cost of the reusable OCS Heart console is £180,000.
The manufacturer reports that the estimated lifespan of the main components of the technology (OCS Heart console) is 3,000 hours of active use, which equates to a conservative estimate of 10 years for each NHS centre's heart transplant workload.
Around 200 heart transplants are done in the UK every year (BHF, 2016). There are 6 NHS heart transplant centres and 1 additional NHS children's hospital with a heart transplant centre (NHS, 2016). Therefore, the heart transplant caseload per centre is estimated to be around 29 per year. Taking account of the transplant consumable costs (OCS Heart Perfusion Set) and using the annuity method with a discount rate of 3.5%, the estimated (technology only) cost per transplant would be £30,758. It should be noted that this cost estimate only includes equipment costs and does not account for different rates of use or possible long-term resource consequences.
Cold ischaemic or static storage is currently used for donor heart preservation after brainstem death in the NHS. The cost of cold storing organs includes the cost of disposable consumables and the solutions in which organs are stored. A health technology assessment report comparing storage methods for kidneys states that the NHS buys generic transplant consumables together (including sterile plastic bags and a non-sterile insulated box for storage and transportation) at £45.80 per box (Bond et al. 2009). The specialist commentators for this briefing felt that this is comparable to the cost for donor heart storage. One specialist stated that their centre pays about £70 for each non-sterile insulated box to transport the heart, and about £28.80 for the saline and plastic bags. The specialists noted that St Thomas' solution for cardioplegia is used for the preservation of donor hearts for transplant and this costs about £10 per litre, with each heart using 1.0 to 1.5 litres.
According to the manufacturer the OCS Heart system is currently used in 3 NHS heart transplant centres and is being introduced in a fourth.
The OCS Heart system would not need additional facilities or technologies compared with cold ischaemic storage.
The manufacturer specifies that all relevant staff (surgeons, other clinicians and technical staff) must attend a 2-day training course before using the system. This training is included in the cost of the system. Annual maintenance of the OCS Heart system is needed and is provided free of charge by the manufacturer. No other practical issues have been identified in using the technology and no changes would be needed to the care pathway after transplantation.
No published evidence on the resource consequences of adopting the OCS Heart system was identified in the systematic review. No published papers relating to cost directly compared the OCS Heart system with standard care.