**4.1 Heart preservation methods**

Donor heart preservation is crucial for a successful heart transplantation as measured by graft function and survival [19, 20]. Unlike other solid organs such as liver, kidney or pancreas, cold ischemic time for the heart is limited to 4–6 hours and longer ischemic times adversely affect survival outcomes [21]. Hypothermia slows metabolic rate and cell death by decreasing enzyme degradation which is necessary for cell viability [22].

### **4.2 Static cold storage**

Static cold storage is the most common method of heart preservation worldwide. After the donor heart is visualized and accepted for transplant into the known recipient, careful organ dissection is performed. The ascending aorta is partially dissected off the main pulmonary trunk to be able to apply an aortic cross clamp. The superior vena cava is freely dissected off the right pulmonary artery and the azygous vein is ligated. Intravenous heparin is given before the aortic cross clamp is applied. Cold preservation solution is rapidly delivered through the ascending aorta via a cardioplegic needle to achieve diastolic arrest. Ice slush or cold water is immediately placed for topical hypothermia [17, 20]. The heart is then stored in preservation fluid within sequential sterile bags placed and transported in an ice cooler.

For every 10-degree Celsius temperature reduction, most enzymes of hypothermic animals demonstrate 1.5–2.0 fold reduction in activity according to the Vant Hoff's rule. Still, prolonged ischemic hypothermia decreases the activity of the Na<sup>+</sup> /K+ pump and results in cell swelling. Moreover, cold ischemia stimulates anaerobic glycolysis and glycogenolysis as well as lactic acid production causing tissue acidosis. When tissue perfusion is restored, oxygen free radicals accumulated during anaerobic metabolism contribute to reperfusion cell injury [22]. Several preservation solutions have been developed to minimize these effects with differing electrolytes, supplements and antioxidant concentrations. University of Wisconsin (UW) solution, Celsior solution and Histidine-Tryptophan-Ketoglutarate (HTK) solution are the most common heart preservation solutions utilized in current practice and the posttransplant outcomes among these three solutions have not shown one to be clearly preferable [19, 20].

### **4.3 Temperature-controlled donor heart transport system**

Organ temperature between 0 and 4 degree Celsius maintains high energy phosphates efficiently but there is a significantly increased risk of frostbite or cold injury due to protein denaturation at a temperature below 2 degree Celsius [23, 24]. At higher *Heart Preservation Techniques for Transplantation DOI: http://dx.doi.org/10.5772/intechopen.113937*

**Figure 1.**

*SherpaPak™ device components. The donor heart is fully submerged in cold preservation solution. Image courtesy of Paragonix technologies, Inc.*

temperatures (> 12 degree Celsius), the study showed higher metabolic oxygen demand [24]. To avoid uneven cooling temperature and direct contact with ice, the novel Paragonix SherpaPak cardiac transport system (Paragonix Technologies Inc., MA, USA) was developed and designed to maintain organ temperature from 4 to 8 degree Celsius with special ice packs and temperature sensor. Studies demonstrated that organ storage within this temperature range prevents not only freezing injury and protein denaturization but also decreases metabolic rate and prevents tissue reperfusion injury [2, 23, 25].

The SherpaPak heart transport system (**Figure 1**) is a disposable device and has interchangeable aortic connectors fit for different sizes of hearts. Once the heart is securely attached to the connector, then it is fully submerged in a leak-proof inner canister filled with cold preservation solution. It is then placed in an outer canister surrounded by a specially designed ice pack and protective polystyrene outer shell [26, 27]. The device provides continuous real-time temperature monitoring and transmits temperature and geographic data via Bluetooth connected to a cell phone.

The Stanford team reported the first en-bloc heart-lung transplant using the Paragonix lung guard preservation system, a similar preservation device from Paragonix designed for donor lungs storage. The donor graft was stored in 4 liters of 4 degree Celsius of PhysioSol preservation solution. The average temperature was 7.42 degree Celsius during transport. The recipient was extubated the next day of surgery with good biventricular function and uneventful recovery [28].

After the first clinical study confirmed the safety of SherpaPak used for donor heart preservation with no harmful effect [26], many clinical studies have been conducted to evaluate postoperative outcomes of using SherpaPak for organ transportation [24, 29, 30].

A recent multicentre registry using propensity score matching compared the SherpaPak heart transport system versus traditional static cold storage demonstrated better 1-year survival in the SherpaPak cohort (96.4% with SherpaPak vs. 88.7% with static cold storage). Moreover, significantly fewer patients experienced severe primary graft dysfunction (PGD) requiring an extracorporeal membrane oxygenator (ECMO) in the SherpaPak group resulting in lower overall hospital costs [31].
