Utilization of TransMedics Organ Care System for Preservation of the Donor Heart

Patient selection
Although overall outcomes of heart transplantation have improved over the last two decades, PGD remains one of the major limitations. The International Society for Heart and Lung Transplantation (ISHLT) defines PGD as affecting the left and/or right ventricle with echocardiographic and hemodynamic alterations, need for inotropic/vasopressor support, and commonly, the use of circulatory assistance devices. The PGD is the most common cause of early mortality after a heart transplant, corresponding to up to 36% of deaths in the first 30 days. The prevalence of PGD ranges from 2.3 to 28% worldwide (1, 2).

The TransMedics Organ Care System (OCS) is the first commercially available system that allows the beating donor heart to be maintained in a warm (34°C) perfused oxygenated state during the transfer from donor to recipient hospitals. This allows for an extended “out of body” time and minimizes the detrimental effects of cold ischemic storage (3). The OCS also allows ex vivo donor heart assessment. Single-center experiences and interim results from the PROCEED II multi-center trial (a prospective, randomized [1:1] non-inferiority study comparing the safety and efficacy of the OCS with the cold storage of donor hearts) suggests that a rising lactate level is an important marker of donor heart abnormality (4). However, there is little information available regarding the metabolic changes which may contribute to lactate abnormalities and cardiac dysfunction. 

The authors’ group utilized OCS to retrieve marginal donor hearts for the first time and noticed that the use of OCS was associated with markedly improved short-term outcomes and increased the donor pool by allowing the use of organs previously not considered suitable for transplantation (5). The OCS can "resuscitate" marginal organs by decreasing ischemia-reperfusion injury and may contribute to enhancing the function of "marginal" heart allografts.

Operative steps:

Functional assessment: 

• Functional assessment of the donor heart is performed with the help of transesophageal echocardiography and Swan Ganz catheter. 

Direct assessment and warm phase dissection:

• Following chest opening, direct assessment of the donor heart is performed, paying attention to the left ventricular contractility and examination of coronary arteries by palpation and visualization.
• Dissection of the ascending aorta, pulmonary artery, and superior vena cava is performed.

OCS machine preparation:

• The OCS module is unboxed and installed into the OCS machine and prepared to receive the donor heart.

Procurement:

• Cardioplegia cannula is inserted into the ascending aorta and a drainage cannula (34°F) is inserted into the right atrium.
• Once ready for cross-clamp, a minimum of 1100 ml of donor blood is collected from the right atrial cannula in a pre-heparinized bag to prime the OCS machine.
• Superior vena cava and inferior vena cava are clamped and the right atrium is vented proximal to the clamp for venting of cardioplegia. The pulmonary veins are cut to vent the return from the lungs.
• Ascending aorta is cross-clamped and 900 ml of Bretschneider (HTK) cardioplegia is given at a pressure of 180 mm Hg along with topical hypothermia maintained with ice slush.
• The donor heart is procured by cutting vena cavae, aorta, and pulmonary arteries.

Back table preparation for OCS heart:

• Aortic and pulmonary cannulae are fixed to the respective major vessels and the donor heart is mounted on the OCS tray, ensuring continuous blood flow through the aortic cannula.
• The left atrial vent is introduced and the heart is shocked if it is still fibrillating at 34°C.
• Once in sinus rhythm, ventricular wires are placed and paced at 100 bpm.
• The pulmonary artery cannula is connected to the return spout and the inferior vena cava is closed.

Maintenance of the donor heart on the OCS:

• The target coronary flow is around 700 ml/min and mean aortic pressure around 70 mm Hg by manipulating maintenance solution rate and aortic flow. 
• Periodic arterial and venous blood gas are performed to define the lactate trend along with a periodic assessment of the LV contractility.

Explantation of donor heart from the OCS:

• The aortic vent is closed and the pulmonary artery cannula is disconnected from the OCS spout.
• The OCS flow is dropped, the aortic line is clamped, and 1 L of HTK cardioplegia is delivered through the side port. 
• Once the cardioplegia is finished, the aortic cannula is disconnected from the OCS and the heart is delivered for implantation.

Preference card

• TransMedics module

Tips and pitfalls

• In presence of any leaks in the right atrium, including PFO, the coronary flow is not reliable.
• Cut the ascending aorta at or proximal to the cardioplegia needle site. It is difficult to repair it once on OCS with high-pressure flow in aorta and prone position of the heart in the machine.
• If leak is detected from the aortic cannula site, it can be fixed with a heavy tie/tape.
• In case of a sudden increase in aortic pressure along with left ventricular distention, suspect dislodged left ventricular vent. 
• In case of high output via the vent and need to increase pump flow to maintain coronary flow, suspect moderate aortic regurgitation.
• OCS needs to be connected to the main power supply during immediate reperfusion of the heart for the temperature to rise to 34°C. 
• If overall lactate is decreasing over a period of time, but venous is always higher than arterial, it is probably related to poor venous sampling rather than myocardial ischemia.

References

1. Kobashigawa J, Zuckermann A, Macdonald P, Leprince P, Esmailian F, Luu M, et al. Report from a consensus conference on primary graft dysfunction after cardiac transplantation. J Heart Lung Transplant. 2014;33(4):327-340. 
2. Russo MJ, Iribarne A, Hong KN, Ramlawi B, Chen JM, Takayama H, et al. Factors associated with primary graft failure after heart transplantation. Transplantation. 2010;90(4):444-450. 
3. Ardehali A, Esmailian F, Deng M, Soltesz E, Hsich E, Naka Y, et al. Ex-vivo perfusion of donor hearts for human heart transplantation (PROCEED II): a prospective, open-label, multicentre, randomised non-inferiority trial. Lancet. 2015;385(9987):2577-2584.
4. Ozeki T, Kwon MH, Gu J, Collins MJ, Brassil JM, Miller Jr. MB, et al. Heart preservation using continuous ex vivo perfusion improves viability and functional recovery. Circ J. 2007;71:153–159. 
5. García Sáez D, Zych B, Sabashnikov A, Bowles CT, De Robertis F, Mohite PN, et al: Evaluation of the organ care system in heart transplantation with an adverse donor/recipient profile. Ann Thorac Surg, 2014;98:2099–2105;discussion 2105–2106.

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