The Heart OCS
The heart OCS (Transmedics Inc, Boston, MA) is composed of an organ perfusion module with disposable and non disposable parts and a compact wireless monitor. The monitor displays indicated (online time) organ measurements, such as aortic pressure, coronary flow, blood temperature, and heart rate. The heart is perfused in the resting mode. Warm oxygenated blood is pumped into the aorta, thereby perfusing the coronary arteries, and deoxygenated blood enters the right atrium through the coronary sinus and passes through the tricuspid valve to the right ventricle. The blood is then ejected through the pulmonary artery to the blood oxygenator and is returned to the reservoir.
After acceptance of donor heart based on clinical information, our team performed a detailed allograft assessment at the time of donation (transesophageal echocardiography, cardiac output studies using a pulmonary artery catheter, direct evaluation of the coronary arteries, and measurement of left and right atrial pressures). Before aortic cross clamping, the right atrial appendage was cannulated using a 34F venous cannula, thereby allowing approximately 1.5 L of donor blood to be collected to prime the OCS module. After the donor was heparinized (300 IU/kg), the donor blood was collected prior to antegrade cardioplegia and prior to cross clamping of the aorta. In blood collection bag was added heparin (10,000 IU) and this was used to prime the perfusion module. Portion of the normothermic blood (500–750 mL) was collected retrogradely for initial dose of blood cardioplegia. The aorta and pulmonary artery of the donor heart were cannulated and heart connected to the OCS with the posterior aspect facing upward and the left atrium and aorta toward the heart chamber. In the OCS, oxygenated blood was pumped into the aorta, perfusing the coronary arteries. The coronary sinus flow then passes through the tricuspid valve (as both the superior and inferior vena cavae are sutured closed) and is ejected by the right ventricle into a pulmonary artery catheter and returned to the blood reservoir. Then, the heart is reanimated to normal sinus rhythm. The pump flow and solution flow rates of the OCS were adjusted to maintain the mean aortic pressure between 60 and 90 mmHg and coronary blood flow between 650 mL/min and 850 mL/min. According to standard protocol, samples were taken in the OCS before the donor heart was connected to the OCS. These included donor lactate (CG4 + , within 30 min of blood collection), baseline OCS lactate and chemistries (CG8 + , during priming). Periodic arterial chemistry samples were taken during OCS time (approximately every 20–30 min). Samples were collected from the arterial and venous sampling port of OCS. The samples were analyzed with a handheld lactate analyzer (i-STAT, Abbott Diagnostics, East Windsor, NJ, USA). Upon arrival at recipient center, the donor heart was arrested with approximately one liter of normothermic blood cardioplegia before transplanting. The graft was conditioned with Levosimendan 45 µg/kg (using body weight of donor) while in the OCS and hemofiltration with a blood flow of 200–300 ml/h was applied in the OCS in order to protect and improve donor heart function.
For the standard cold storage group, the donor heart was arrested with the standard heart preservation solution (40C Custodiol). Transplantation and preoperative care proceeded according to the standard procedures of our center in both groups.
Study Design and Participants
From 2011, when initiated the heart failure program 353 patients were implanted with ventricular assist devices to date and 35 (10%) of them transplanted . Between 2012 and 2018, we performed a retrospective single-center review of prospectively collected data. All patients who underwent heart transplantation with MCS using the OCS Heart (n = 25) versus standard cold storage were included in this study. Eligible recipients were at least 18 years of age and had to be on the heart-transplant waiting list. The study received approval through the responsible ethics committee at our institution and all patients provided written informed consent to be part of this study and to allow their data to be used for the analysis. Endpoints included 30-day survival, heart preservation time (ischemic time, OCS perfusion time, out of body time), duration and level of inotropic support, ITU stay-day, Mechanical Circulatory Support after heart transplantation, adverse cardiac events.
Results were expressed as mean and standard deviation or median and interquartile range (continuous variables), and counts with percentages (categorical variables). Where possible, a two-sample independent t-Test was used to compare the means. Outcome measures used were 30-day survival. Statistical analyses were performed using STATA version 12 (Stata Corp, Texas, US).