Long-Term Conditioning of a Donor Heart by Autoperfusion

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Introduction.
Over the past 15 years, heart failure has remained the leading cause of death worldwide. This disease affects 1–2% of the entire population, and the risk of developing in people over 55 is 33 and 28%, respectively, in men and women [1, 2]. The lack of donor organs significantly limits the performance of heart transplants in patients with end-stage chronic heart failure. Due to the discrepancy between the ability and the need for waiting lists for a donor heart, almost 15% of patients die every year [3]. However, about 60% of potential allografts are considered unsuitable for transplantation for various reasons, including the impossibility of prompt delivery of the organ to the recipient [4]. In the United States, only 30–35% of donated hearts are used for transplant due to storage restrictions using standard pharmaco-cold protection. A similar situation is observed on the territory of the Russian Federation, the large distances between donor bases and transplant centers do not allow full use of the donor reserve, due to the limitation of the transportation time. Therefore, the development of a safe long-term method of preserving the viability of donor organs remains an urgent problem in modern transplantology.
Despite the fact that pharmaco-cold cardioplegia is the standard for the preservation of donor organs, within four hours the graft function can be compromised by a long ischemic period, especially in older donors [5]. This method of organ preservation is the greatest risk factor for primary allograft dysfunction and death [6, 7]. An increase in the time of cold ischemia from 3 to 6 hours doubles the risk of death 1 year after transplantation, compared with a 50% reduction in predicted mortality at 1 year if the ischemic period is less than 1 hour [8]. These data were confirmed by American scientists, proving that a reduction in ischemic time by 1 hour increases the survival rate by 2.2 years [9]. According to J. Kobashigawa et al., Ischemia exceeding 4 hours significantly increases the risk of primary graft dysfunction, which is associated with 8% mortality at 30 days and increased mortality at 5 and 15 years after transplantation [10]. To reduce non-perfusion ischemia, special devices have been developed, one of which is the TransMedics System (Massachusetts) (CTM), which was the first commercially available device for transporting a donor heart in a normothermal perfusion state. However, the widespread use of CTM is limited by the high cost of this system. In the UK, the National Institutes of Health reports that the cost of a disposable CTM perfusion kit is around £ 30,000 [11]. It should be noted that this estimate includes only the cost of a disposable set of apparatus and does not take into account the cost of additional consumables.

An alternative way to reduce the time of ischemia of the donor heart can be the maintenance of autoperfusion in the composition of the pulmonary-cardiac complex. For the first time, the method of isolating a working drug heart-lungs by means of autoperfusion for physiological experiments was developed by Ernest Henry Starling in 1920 [12]. V.P. Demikhov used this technique for transplantation in 1948 [13], Francis Robichek and his collaborators [14] applied this model to research on the preservation of the heart and lungs in 1959, proving the possibility of autonomous survival of such a complex for more than 24 hours. However, by 1976, research in this direction was suspended due to the discovery of a number of promising cardioplegic solutions that allow the safe preservation of organs with an acceptable result [15].
Over time, with the increase in experience and the quality of the procedures performed, the lack of organs also increased, which required both an expansion of the criteria for heart collection and the geography of donor bases. Therefore, the development of a simple, cost-effective method of long-term conditioning of the donor heart is an urgent problem in modern transplantology.
Materials and methods.

As an experimental model for a series of acute experiments were used mini-pigs, females, weighing 25-30 kg at the age of 3-4 months. Care, maintenance of the experiment, observation and withdrawal of animals from it were carried out in accordance with the European Convention for the Protection of Vertebrate Animals Used for Experiments or Other Scientific Purposes (Strasbourg, 03/18/1986). On the day of the experiment, the animal was premedicated on an empty stomach (zoletil-100). The dose was selected individually according to weight-height parameters. After the onset of sleep, the surgical site and the area of ​​catheterization of the vessels of the neck were prepared. After that, the animal was transported to the operating table and fixed in the supine position for subsequent catheterization of the peripheral vein, tracheal intubation, and installation of central arterial and venous catheters.
The experiment was performed under conditions of endotracheal anesthesia with sevoflurane and muscle relaxation (pipcuronium bromide). During the experiment, monitoring was carried out: invasive blood pressure (IBP) by catheterization of the femoral artery, cardiac arrhythmias (electrocardiography), body temperature, blood gas composition, activated clotting time (AST). Blood analysis was performed using an XT-4000i automatic hematological analyzer (Sysmex, Germany) according to the manufacturer's recommendations. Arterial and venous catheters for monitoring and infusion were inserted in accordance with generally accepted international guidelines for working with laboratory animals [16]. Artificial lung ventilation (ALV) was performed using the FabiusPlus anesthesia-respiratory apparatus (Draeger, Germany) with positive pressure on inspiration (16–20 cm H2O) and on expiration (3–5 cmH2O) with tidal volume 240 ml with a frequency of 12-18 breaths per minute. Vital activity parameters were recorded using an IntelliVue MP70 monitor (Philips). The dynamics of the data was recorded in the anesthetic chart of the experimental animal every 10 minutes.

After performing a median sternotomy, the main arteries were isolated from the surrounding tissues and taken on the holders. Isolation began with mobilization of the superior vena cava (SVC), then the brachiocephalic trunk (BCS), left subclavian artery (LPA), and inferior vena cava (IVC) were isolated. The trachea was carefully removed from the esophagus using an electrocoagulator. After the introduction of heparin (3 mg / kg body weight), the LPAA was ligated and a catheter was inserted through the orifice to measure iBP in the aortic root. Then, ligation and catheterization of the BCS were performed with a cannula, which was connected to an elastic reservoir suspended at a height of 30-40 cm above the level of the heart. The outflow line from the reservoir was connected to a venous cannula installed in the SVC. Also, a two-way venous catheter was installed through the SVC into the cavity of the right atrium to measure the central venous pressure (CVP) and collect blood flowing from the coronary sinus. The descending thoracic aorta was clamped and the animal's blood was exfused into the reservoir, after the pressure in the aortic root was reduced to 70-80 mm. rt. Art. The IVC was ligated and transected. The trachea was also transected and intubated with a cuffed tube. The complex was finally separated from the surrounding tissues and transferred to a container with warm saline solution (38 ° C). Immediately after the placement of the complex, stabilization of the heart was achieved by changing the level of the volemic load with the exfusate. Throughout the entire observation period, continuous monitoring was performed for IAP in the aortic root, IAP in the pulmonary trunk, CVP, heart rate, activated clotting time (AST), arterial and venous blood gases.
Results.

In a series of acute experiments, animals weighing 25, 26 and 30 kg were used, while the operating time of the "heart-lungs" ex vivo complex was 3, 3.5 and 4 hours. In all cases, the cardiopulmonary complexes were successfully isolated and stable hemodynamic parameters were achieved, the heart continued to work independently and efficiently for 3-4 hours (Fig. 1). The expiratory carbon dioxide (et CO2) level during the observation period remained at the level of 6-8 mm Hg.

Figure 1. General view of the isolated complex "heart-lungs": 1 - pulmonary artery, 2 - aortic root, 3 - catheter for measuring IAP in the pulmonary artery, 4 - brachiocephalic trunk, 5 - cannula for blood sampling, 6 - left subclavian artery , 7 - catheter for measuring the blood pressure in the aortic root, 8 - cannula for blood return from the reservoir, 9 - trachea, 10 - catheter for measuring central venous pressure, 11 - superior vena cava.

The level of systolic blood pressure in the aortic root was maintained from 70 to 130 mm Hg, the heart rate was 76-104 per minute and gradually decreased by the end of the third hour to 60-70 per minute as the volume of exfusate decreased and the level was adjusted. volemia (Table 1). None of the experiments required external pacing to maintain heart rate.

Table 1. Parameters of hemodynamics and homeostasis in experiment No. 1.
Table 1. Parameters of hemodynamics and homeostasis in experiment No. one.

Upon reaching the critical hematocrit value (<20%), monitoring of the complexes was stopped and potassium cardiac arrest was performed. When opening the chambers of the heart, the lumen of the coronary arteries and vessels of the pulmonary circulation, not a single case of thrombosis was recorded. Heart function remained stable even during the traumatic phase of explantation and ex vivo placement. The cardiopulmonary complexes isolated by the method described above had a high adaptive plasticity and did not require pharmacological assistance.

Discussion.

An important stage of transplantation is the stage of conservation of donor material. For many decades, the field of transplantation has focused on the development of an optimal and cost-effective way to prolong organ vitality ex vivo. The successful development of pharmacology, surgical technologies, as well as the legislative framework determined the strategy for choosing both the method of conditioning donor organs and the logistics of their distribution and use. Organ preservation techniques today encompass a variety of approaches; ex vivo perfusion at various temperatures [17–20], “extreme” freezing methods [21, 22], pharmacological induction of the hypometabolic state of tissues [23, 24] and related innovative techniques. These methods are actively used in various combinations, which makes it possible to reduce the negative aspects of each individual method [25–28]. However, the high level of medical technologies today should not lead to ousting from the memory of the historically established methods of prolonging the viability of organs outside the body.
The problem of the lack of donor organs is a complex issue that requires an analysis of the situation in each specific country and territory. Each of the donors can theoretically provide eight vital organs, but currently two or three of them are used [29]. In the United States, only 0.3% of deaths result in organ donation due to difficulties in the logistics of delivery to transplant centers [30–33]. The time of organ ischemia is the main limiting factor, disrupting the balance between the number of donors and recipients [34, 35].
A number of works provide data that approximately 70% of donor hearts are not currently transplanted [36, 37] due to the impossibility of delivering the organ to the recipient on time [38, 39], while successful transplantation of only 10% of these organs is able to provide organs of all recipients on the waiting list [40]. In addition, advances in organ preservation can reduce the cost of both the transplant itself and the cost of resolving post-transplant complications.
The study of the dynamics of the qualitative parameters of the isolated cardiopulmonary complex is an important stage in understanding the conditions of stable and long-term work. In the course of the study, the surgical technique of explantation was worked out and the basic principles of maintaining hemodynamic parameters were determined. In the course of this work, some complications were identified that could limit the survival time of an isolated ex-vivo complex. So, despite careful hemostasis, there was a gradual outflow of blood from the wound sites of the lung parenchyma and other areas (especially the area of ​​the roots of the lungs, the descending thoracic aorta and bronchial arteries) into the container, which required partial replenishment of the circulating blood volume. The reserved blood volume (~ 350-400 ml), as a rule, was consumed during the first 2-2.5 hours, then the blood loss was corrected by hemodilution with sterofundin solution, which was accompanied by a decrease in hematocrit, oxygen delivery to the myocardium and bradycardia. Since, even in the case of achieving a thorough surgical hemostasis, insignificant blood loss is observed (in our experiments, 3-4 ml per minute), it is necessary to reconsider the design of the container and the method of maintaining the temperature of the complex. The best option may be a double-circuit reservoir, with heated walls of the outer casing and a perforated bottom of the inner one, with the possibility of leukocyte filtration and reinfusion of the flowing blood. The development and introduction into clinical practice of a method for long-term conditioning of autoperfused donor hearts will solve the problem of the "capabilities" of transplant centers by simplifying the logistics of donor organ delivery.

Conclusion.
As a result of the study, the possibility of long-term autonomous operation of an isolated cardiopulmonary complex was proved. Further development of the protocol for autoperfusion of the heart-lung complex, the study of criteria for the stable operation of the ex vivo complex, as well as the development of devices for transportation can significantly reduce the shortage of donor hearts by facilitating logistics and expanding the geography of donor bases.

 

About the authors

Maksim Olegovych Zhulkov

FGBU "NMITs named after Academician E. N. Meshalkin" of the Ministry of Health of Russia

Email: medicus-maligna@mail.ru
ORCID iD: 0000-0001-7976-596X

Cardiovascular surgeon, MNS of the Research Department of Aortic Surgery, Coronary and Peripheral Arteries of the Institute of Circulatory Pathology

Russian Federation, 630055, Russia, Novosibirsk, st. Rechkunovskaya, 15,

Ilya Sergeevich Zykov

FGBU "NMITs named after Academician E. N. Meshalkin" of the Ministry of Health of Russia

Email: i_zykof@meshalkin.ru
ORCID iD: 0000-0001-6253-9026

doctor anesthesiologist of the Federal State Budgetary Institution “National Medical Research Center named after ac. E. N. Meshalkina "Ministry of Health of Russia

Russian Federation, 630055, Russia, Novosibirsk, st. Rechkunovskaya, 15

Dmitriy Андреевич Sirota

FSBI NMITs named after ac. E. N. Meshalkina "Ministry of Health of Russia

Email: d_sirota@meshalkin.ru
ORCID iD: 0000-0002-9940-3541

PhD, doctor of cardiovascular surgeon, head of the research department of surgery of the aorta, coronary and peripheral arteries of the Institute of Circulatory Pathology

Russian Federation, 630055, Russia, Novosibirsk, st. Rechkunovskaya, 15

Hava Abdullaevna Agaeva

FSBI NMITs named after ac. E. N. Meshalkina "Ministry of Health of Russia

Email: agaeva_h@meshalkin.ru
ORCID iD: 0000-0002-1648-1529

cardiovascular surgeon, cardiac surgery department of the aorta and coronary arteries

Russian Federation, 630055, Russia, Novosibirsk, st. Rechkunovskaya, 15

Azat Kerimbekovich Sabetov

FSBI NMITs named after ac. E. N. Meshalkina "Ministry of Health of Russia

Email: sabetov_a@meshalkon.ru
ORCID iD: 0000-0001-8956-6585

cardiovascular surgeon, cardiac surgery department of the aorta and coronary arteries

Russian Federation, 630055, Russia, Novosibirsk, st. Rechkunovskaya, 15

Olga Vladimirovna Poveschenko

Federal State Budgetary Scientific Institution "Federal Research Center Institute of Cytology and Genetics of the Siberian Branch of the Russian Academy of Sciences"

Email: poveschnko_o@meshalkon.ru
ORCID iD: 0000-0001-9956-0056

Doctor of Medical Sciences, Head of Laboratory, Federal State Budgetary Scientific Institution "Federal Research Center Institute of Cytology and Genetics of the Siberian Branch of the Russian Academy of Sciences"

Russian Federation, 630090, Russia, Novosibirsk, prosp. Academician Lavrentiev, 10

Samandar Shukrulloevich Bozorov

FSBI NMITs named after ac. E. N. Meshalkina "Ministry of Health of Russia

Email: bozorov_s@meshalkin.ru
ORCID iD: 0000-0001-7913-4594

physician resident of the Federal State Budgetary Institution "National Medical Research Center named after ac. E. N. Meshalkina "Ministry of Health of Russia

Russian Federation, 630055, Russia, Novosibirsk, st. Rechkunovskaya, 15

Alexei Vyacheslavovich Fomichev

FSBI NMITs named after ac. E. N. Meshalkina "Ministry of Health of Russia

Email: a_fomichev@meshalkin.ru
ORCID iD: 0000-0001-9113-4204

MD, PhD, Cardiovascular Surgeon, Cardiac Surgery Department of the Aorta and Coronary Arteries

Russian Federation, 630055, Russia, Novosibirsk, st. Rechkunovskaya, 15

Alexander Mikhailovich Chernyavsky

FSBI NMITs named after ac. E. N. Meshalkina "Ministry of Health of Russia

Author for correspondence.
Email: a_cherniavsky@meshalkin.ru
ORCID iD: 0000-0001-9818-8678

Doctor of Medical Sciences, Professor, Director of the Federal State Budgetary Institution “National Medical Research Center named after Ac. E. N. Meshalkina "Ministry of Health of Russia

Russian Federation, 630055, Russia, Novosibirsk, st. Rechkunovskaya, 15

References

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