Open access peer-reviewed chapter
Abstract
Heart transplant is the gold-standard treatment for end-stage heart failure. However, the aging of the population, increase in the prevalence of heart failure and the shortage of available donors have led to a significant increase in the wait-list times. This increase in waiting time may cause some patients clinically deteriorate while on the list. Several bridging strategies have been developed to help patients reach heart transplant. It is mandatory to know the current results of these techniques and the specific tips and tricks these different devices may have. Survival results would also be presented to help us decide the best strategy for each of our patients.
Keywords
- heart transplant
- short-term mechanical circulatory support
- ECMO
- long-term mechanical circulatory support
- survival
1. Introduction
Heart transplant is the gold-standard treatment for end-stage heart failure since the first case, performed by Christiaan Barnard, on December 3, 1967 in Cape Town [1]. This first case was the results of previous works led mainly by Norman Shumway at Stanford. After an initial spread of the technique and the development of different transplant programs, the actual number of heart transplants declined due to impaired outcomes, mostly due to infections and rejection [2]. Only a few groups, mainly Stanford in the USA and the Pitié-Salpêtrière in Europe, continued investigating and working on trying to improve their patients’ outcomes. It was not until the introduction of cyclosporine as an immunosuppressor, that solid organ transplant outcomes significantly improved [3]. This significant change in patient management led to the final expansion of the technique and the development of multiple programs across the world.
Technical and medical developments have caused previously lethal conditions that evolve into chronic ones, increasing the prevalence of end-stage heart failure. This increase, in addition to the aging of the population, has led to a disbalance in the number of donors available, which has remained stable over the last years according to ISHLT data [4]. This disbalance has caused an increase in the waiting time period, leading to the development of different strategies to sustain patients.
This abovementioned shortage of donors, which is common to most countries, forced the transplant programs to expand their acceptance criteria with the such called “extended-criteria donors.” This means that older donors with longer ischemic times were now accepted. Despite the initial concerns, results have been acceptable, with similar survivals at 1-year, 89% vs. 86% in the published reports [5, 6]. The increase achieved in the donor pool was still insufficient, so additional donors were evaluated. The pediatric groups developed the ABO group non-compatible heart transplant [7], while adult groups developed strategies for accepting HCV+ donors [8], treating recipients with the new antiviral in the immediate postoperative period, or started programs of donation after circulatory death (DCD donors) [9, 10]. It is important to remark that these different strategies to expand the donor pool have accomplished similar survival, both short (96% vs. 89% at 1-year) and medium-term (94% vs. 82% at 5 years) results, as the conventional donors [11].
As mentioned, the shortage in the donor pool leads to prolonged times on the waiting list. Some patients, however, would deteriorate during this waiting time. Different support strategies have been developed to sustain declining patients to allow for organ recovery and patient rehabilitation before the transplant. These bridging strategies can be classified into two main groups—short-term support and long-term support. Both of them have particularities that will be further developed.
2. Short-term mechanical circulatory support (ST-MCS)
Short-term support devices are the first line of support in patients who need emergent support, such as INTERMACS 1 patients, as they provide immediate hemodynamic support with an almost immediate deployment time, in some of them, such as ECMO or Impella®. In addition to those, there are other devices, such as Levitronix-Centrimag®, that need a surgical implant. It is worth mentioning that whereas ECMO provides complete circulatory support with one device, the other ones would need two pumps to provide full biventricular support.
Recently, several allocation systems changed their distribution policies aiming at providing a fair allocation of donors. These modifications meant that patients under ST-MCS achieve the highest priority on the waiting list [12].
2.1 Indications
All ST-MCS devices share common indications, the most common ones are as follows [13]:
Postcardiotomy shock
Primary graft failure after transplant
Cardiogenic shock due to acute coronary syndrome
Myocarditis
Peripartum cardiomyopathy
Arrhythmic storm
Cardiac arrest.
The choice of the device would depend mostly on availability and patient factors. The different devices provide variable degrees of support and have inherent implantation requirements; there is general agreement that ECMO would be the device of choice in cases with cardiac arrest as it can be implanted percutaneously at the bedside. It would also be the preferred option in cases of respiratory compromise and biventricular failure.
Impella
Levitronix Centrimag
2.2 General management
During the recovery period or the waiting time, it is recommended to extubate patients if possible. If this can be accomplished, oral nutrition is the preferred option. If the patient cannot be extubated, tube feedings would be the best option, above parenteral nutrition; this should be reserved for patients with significant instability and the need for high-dose pressors.
Volume status should be maintained as neutral as possible, initially with diuretics, but it is not uncommon that patients under ST-MCS develop acute kidney injury and need renal replacement therapies (RRT). In our group, we promote early use of RRT to help to manage the volume status and avoid hypervolemia at the time of the transplant.
In addition to recovering the organ, it is important to keep the muscular tone with daily physical therapy, even with static bicycle or ambulation within the unit, whenever possible.
Simultaneously to recovering the patient, special attention should be paid to the management of the device. It should provide enough support to allow for organ recovery minimizing the potential complications. To prevent them, it is recommended to perform daily echocardiograms and keep close monitoring of central venous pressure and pulmonary pressure. Blood pressure control is mandatory to reduce the risk of neurological complications but also to reduce afterload that may interfere with the device function; the higher the afterload, the lower the left ventricular unloading. We would suggest avoiding medications with a long half-life to minimize the risk of vasoplegia during the transplant.
2.3 Specialized management
2.3.1 Anticoagulation
All devices require systemic anticoagulation; unfractionated heparin is the most common anticoagulant used. A single bolus, normally 1 mg/kg, is administered at the time of ECMO or Levitronix implant. Systemic infusion is not started until the coagulation parameters have been normalized and there are no signs of bleeding. For example, in cases of central cannulation, anticoagulation would be started once the chest tube output is less than 50–80 ml/h for 6 hours.
ECMO is a device that requires a higher dose as it has an oxygenator. The patient receives a bolus of heparin at the time of the implant and after that ACT is kept around 180–200 seconds and/or aPTT around 60–80 seconds [14].
Impella systems
Levitronix-Centrimag
During the time on support, careful attention should be paid to the platelet count; in case, a sudden drop is noticed we would recommend to test for heparin-induced thrombocytopenia. Type 2 HITT may be a terrible complication that limits a patient’s options. If suspected, heparin should be immediately replaced by bivalirudin or argatroban.
2.3.2 Infections
There is no general consensus regarding antibiotic prophylaxis while on short-term support. However, most groups administer it, especially if the implant has been performed in emergent circumstances. Regarding the duration of the therapy, the ELSO ID Taskforce [16] does not recommend using antibiotic prophylaxis for more than 48 hours. In cases of central cannulation when the chest is left open, most groups would maintain the prophylaxis while the sternum is open.
Patients on short-term support are highly instrumentalized, with increased transfusion requirements and a higher incidence of renal failure compared to the general intensive care unit population; all these factors increase the risk of systemic infections. Biffi et al. reported bacteriemia rates around 20% and lower respiratory tract infections that oscillated between 4 and 55% [17].
Due to the higher instrumentalization, the most common pathogens are coagulase-negative
Infections while on support can significantly impact the patients’ treatment options. A recent publication by the Spanish transplant group proved that infections while of support reduced the options of reaching a heart transplant [18].
2.4 Pretransplant assessment
At the time of the transplant, specific considerations should be taken into account depending on the device the patient is being bridged with:
2.4.1 ECMO or extracorporeal membrane oxygenator
ECMO has increased its use as a bridging device, as it provides immediate support for rapidly declining patients and those unstable or in cardiogenic shock. When using ECMO as a bridging strategy, several aspects should be taken into account. From the technical perspective, there are two key points. The first one is venous cannulation; careful attention must be paid to reduce the ECMO flows at the time of venous cannulation to avoid air entry. If this occurs, the device may stop or the patient may suffer systemic emboli. Secondly, ECMO support has the risk of developing left-sided intracavitary stasis with its inherent risk of systemic emboli. Unnecessary cardiac manipulation should be avoided before applying the aortic clamp.
From the medical standpoint, the team must be aware that ECMO support may cause lung congestion, which may be not evident while on support, but that may appear when trying to abandon cardiopulmonary bypass. This pulmonary impairment may cause hypoxemia or right ventricular failure.
2.4.2 IMPELLA®
This percutaneous axial pump is normally placed through the femoral artery or the axillary artery, inside the left ventricle. When used as a bridge-to-transplant, the axillary artery insertion is preferable as it allows the patient to ambulate and facilitates the patient’s rehabilitation.
At the time of the transplant, as the device crosses the aortic valve, surgeons should remove it into the aorta before applying the aortic clamp. After the implant is performed, attention should be paid to repairing the arterial entry site.
2.4.3 Levitronix-centrimag®
This magnetically levitated device provides up to 8 l/min of support and it is approved for 30 days support. It requires surgical intervention for its implant, in general, through a median sternotomy. However, some minimally invasive strategies have been proposed [19].
Its surgical implant should be performed considering the current patients’ clinical status but also the future transplant. For instance, when tunneling the cannulas, it is recommended to keep the exit site far away from the sternotomy, to avoid any potential cross-contamination. In addition, surgeons should also keep in mind the future transplant; to ease that, it is our preferred approach to place the arterial cannula low in the aortic root; so, the entry site is removed at the time of the implant and we have enough ascending aorta to cannulate and perform the aortic anastomosis. If the patient has some residual ventricular function and the surgical team decides to cannulate the left atrium as an inflow cannula, our suggestion would be to cannulate the left atrial roof. This structure would be removed while doing the cardiectomy and avoid manipulation of the pulmonary veins.
At the time of the transplant, the surgical team must take into account the time needed for surgical dissection; if the patient has been supported for more than 10 days, some extra time might be necessary to isolate the different cardiac structures. In addition, some technical details should also be considered; special attention should be placed to avoid unnecessary manipulation of the cardiac structures before applying the aortic clamp. Some small clots might have formed in the cardiac chambers and there is the risk of systemic emboli in cases of aggressive manipulation.
Cannulation is also an important step, particularly at the time of the double venous cannulation in the patient under biventricular support. In these cases, special attention must be paid to ensure the right-side device flow reduction at the time of the cannula insertion to avoid air entry. Both cannulas should be placed already clamped to prevent air entry.
As mentioned, we prefer to place the outflow cannula low in the aortic root, but if the cannula is placed in the ascending aorta, the surgical team would have to decide if the left side device is interrupted and the arterial cannula reused for the cardiopulmonary bypass (CPB) machine or if a second arterial cannula is necessary.
At the end of the procedure, it is mandatory to achieve careful hemostasis to minimize postoperative bleeding; some groups propose to leave the chest open to reduce the risk of tamponade and bleeding.
2.5 Surgical considerations
Short-term mechanical support is normally implanted in patients under cardiogenic shock. This extremely acute situation, with patients that are usually under mechanical ventilation and who can barely move due to a peripheral device, makes it difficult to complete the detailed transplant evaluation that would be performed in an ambulatory situation. Despite the urgency of the situation, we would encourage to follow a so-called “parallel pathway,” while recovering the patient like in Figure 1, an evaluation as complete as possible is performed, even more, if the patient has not been previously managed by the team. Our group has diagnosed end-stage neoplasm during these preoperative studies (Figures 2 and 3).
Figure 1.
Shows a patient, who is under biventricular temporary support, sitting on a chair during his/her intensive care unit stay. The patient was able to eat by himself/herself and do some physical therapy.
Figure 2.
Shows a lung tumor found in the pre-transplant assessment of patient support with peripheral ECMO.
Figure 3.
(a) shows the entry site of the arterial cannulas from a biventricular Levitronix-Centrimag
2.6 Results
Despite the systemic recovery achieved with these devices, several groups have shown their concerns regarding the outcomes of transplants with this ST-MCS bridging strategy. In 2018, the Spanish Transplant working group published a manuscript showing a 33% mortality when patients were bridged with ECMO and 11.9% when bridged with short-term left-sided devices [20]. Other reports have also shown reduced initial survival results when patients are bridged with ST-MCS [21, 22]. In previous publications, ECMO reveals as the bridging strategy with the shortest waiting times but also the worst post-transplant survival results. These worst results may be due to an early transplant with incomplete recovery of the organs in addition to pulmonary impairment due to insufficient left ventricular unloading.
In addition to this increased early mortality, different publications show a higher rate of postoperative transfusions and longer hospital length of stay compared to direct heart transplant or even, transplant with long-term devices [23].
3. Long-term mechanical circulatory support (LT-MCS)
As stated before, the increase in waiting list times may cause the clinical deterioration of patients awaiting a suitable organ. Long-term mechanical circulatory support offers these patients clinical stability and avoidance of multiorgan deterioration during this waiting time. Several devices have been developed, such as the Heartmate XVE
Most of them provide only univentricular support, mostly to the left ventricle. In cases where biventricular support is needed, a second device can be used “of-label’ to provide right ventricular support. Syncardia
3.1 Indications
The primary indication of LT-MCS devices is end-stage chronic heart failure. Most left ventricular assist devices require a minimal end-diastolic left ventricular diameter for their implant, which is easily accomplished in cases of ischemic or dilated cardiomyopathy. In cases of restrictive cardiomyopathy, with small left ventricular cavities or cases with biventricular failure, a total artificial heart would be indicated.
The hemodynamic indications according to ISHLT guidelines [13, 24] are as follows:
Stage D refractory heart failure
Systemic hypotension with systolic blood pressure below 90 mm Hg
Cardiac index below 1,8 l/min/m2
Pulmonary capillary wedge pressure above 15 mm Hg
Evidence of end-organ perfusion
Peak oxygen consumption <12–14 ml/kg2.
3.2 Specialized management
3.2.1 Anticoagulation
LT-MCS requires antithrombotic treatment since the early postoperative period to prevent thrombotic events [25, 26]. Each manufacturer has its own specific recommendations; however, in general, most centers follow the below strategy:
Low-dose heparin in the first 12–24 hours if there are no signs of bleeding (chest tube output below 50 ml/h during >4 hours).
Heparin infusion is gradually titrated to achieve full anticoagulation after 48 hours.
Aspirin is started on the second postoperative day.
Vitamin K antagonists are started on the third postoperative day once the patient is stable and tolerates oral intake.
The target INR is 2.0–3.0. The antithrombotic treatment should be tailored to the patient’s clinical status.
In cases of heparin-induced thrombocytopenia, intravenous direct thrombin inhibitors, such as bivalirudin or argatroban, can be used. New oral anticoagulants have not been validated for the treatment of long-term MCS devices.
3.2.2 Infection
Infections will occur in nearly 60% of the implanted patients and the rate increases with the duration of support [27, 28]. The most common pathogens are gram-positive bacteria that colonize the skin and adhere to the implanted material creating biofilms;
Before a scheduled implant, it is recommended to remove all unnecessary lines and ensure there are no active infections. In cases of active infection, in special if bacteriemia, it is recommended to delay the implant until clearance of the infection, whenever possible.
A few years ago, antibiotic prophylaxis included gram-positive cocci, gram-negative rods, and fungi and it was maintained for days. The most current recommendations moved to the general cardiac surgery prophylaxis, using a cephalosporin that is maintained for 24–48 hours. In addition, MRSA should be discarded with a preoperative nasal swab and nasal mupirocine is applied [25].
Once the device has been implanted if an infection develops, it can be classified as [26, 27]:
Device-specific infections
Device-related infections (result of the surgery, for example, bloodstream infection).
Non-device-related infections (pneumonia, urinary tract infections, etc.).
Device-specific infections are the ones that actually involve the device and they vary from driveline infection to pump infection with mediastinitis. The most important aspect is prevention. For example, during the surgical implant, it is recommended to keep all the velour parts of the driveline covered and ensure proper fixation of the driveline to avoid excessive movements.
It is of extreme importance that both the patient and the caregiver learn how to perform the sterile dressing changes of the driveline; patients also need to recognize signs of alarm, such as erythema or purulent discharge. Keeping a photographic diary might be helpful. It is also important that the wound is periodically evaluated during the clinic visits.
Driveline infections should be individually addressed; if the patient has no general symptoms, treatment can start with increased dressing changes and culture-directed antibiotics. On the other hand, in case of systemic symptoms, intravenous antibiotics should be started. In these cases, a PET-CT scan might be performed to assess the extension of the infection. If image tests reveal the presence of collections, re-routing of the driveline might be necessary. If the infection has affected the actual device, pump exchange or transplant might be the only curative option and it is recommended that blood cultures are negative at the time of the surgery.
When transplanting a patient with an infected device, the surgical must minimize deeper contaminations; for example, in cases of driveline infection, the exit site must be sealed from the rest of the surgical fields avoiding contact between infected and non-infected fields. In cases of device-specific infections involving blood contact surfaces, surgeons should minimize the embolic risk by early initiation of cardiopulmonary bypass, stoppage of the pump, and application of the aortic clamp. If active mediastinal infection is found, extensive debridement and antibiotic irrigation are recommended. After that, all surgical materials should be changed. In these circumstances, some groups would leave the chest open with antibiotic irrigation. After the surgery, antibiotic treatment should be targeted to prior cultures.
It may seem controversial to transplant patients with a current infection. However, several reports have shown no differences in survival compared with patients transplanted on LT-MCS support without infection [29].
3.2.3 Blood pressure control
Blood pressure control is mandatory while on long-term support. Hypertension leads to increase afterload, thus reducing the device flows and the left ventricular unloading. In addition, there is a significant relationship between high blood pressure and adverse events, such as stroke or aortic regurgitation [30, 31].
As the devices are continuous flow, it is possible that patients have no pulse; in an intensive care unit, it is recommended to use invasive lines to monitor the blood pressure; whereas if the patient is ambulatory, a doppler measurement of the blood pressure is the preferred system [25]. The doppler reading is equivalent to the mean blood pressure.
For blood pressure control, the current recommendations include the use of renin-angiotensin-aldosterone system antagonists as first-line; beta-blockers are recommended in cases of arrhythmias but should be carefully used if the right ventricular function is poor. Calcium channel blockers would be the third option for blood pressure control [24, 25].
3.3 Surgical implant
When a bridge-to-transplant strategy is considered in a patient who is going to receive an LT-MCS device, the surgical implant must be carefully planned to ease the future heart transplant.
The device could be divided into different components, the inlet cannula and the pump, the outflow graft, and the driveline.
The inlet cannula is placed inside the left ventricle and secured with a sewing ring. Some groups reinforce this ring with surgical glues, which may lead to increased adhesions.
Careful attention should be paid to the length and layout of the outflow graft, in special at the time of the chest closure. It should run smoothly along with the right-side cavities. A short graft would lay immediately under the sternum (Figure 4A), increasing the risk of damaging it during the reesternotomy. An excessively long graft is at risk of twisting, impairing the pump function. Its anastomotic site in the ascending aorta should be performed, taking into account that it should be removed at the time of the transplant and that enough ascending aorta should be left to perform the anastomosis.
Figure 4.
A shows an outflow tract running immediately below the sternum. In this case, the implant was performed minimally invasive, so the risk of injury at the time of the transplant was lower. B shows non-conventional outflow tract layouts; this patient had the outflow anastomosis placed at the descending aorta. This risk of injury was lower at the reesternotomy but achieving control of it might be more difficult.
The driveline should also be carefully placed. Our group does a double route; we exteriorize the driveline into the subcutaneous tissue at the left upper quadrant and then tunnel it to the right upper quadrant, leaving a short intrapericardial portion away from the sternum, to avoid damaging it during the mediastinal reentry at the transplant time.
Reinterventions in patients with long-term devices are challenging due to extensive adhesion formation [32]. Several strategies have been developed to facilitate these reinterventions. The most extended one is covering the device and the outflow tract with PTFE sheets that would reduce the adhesions and, at the same time, might protect the pump components during the dissection [33, 34]. A different approach would be pursuing a less-invasive approach, either with two thoracotomies or a left thoracotomy and a mini-sternotomy. In these less invasive approaches, the avoidance of an extended pericardial opening and limited cardiac manipulation reduces the development of adhesions [35].
3.4 Transplant surgery
Despite the careful surgical implant, we would suggest that every patient with an LT-MCS who is a transplant candidate should have a postimplant computed tomography to know the final position of the different device components (Figure 4A and B).
At the time of the implant, the surgical team must carefully plan the times as surgical dissection may be more difficult and time-consuming than conventional reinterventions. Once we accept the organ, it is our preferred approach to reverse anticoagulation with prothrombin complex to avoid volume overload and start the anesthetic process. Our advice would be to start the reintervention enough in advance to be able to perform an extremely careful dissection in order to minimize intraoperative and postoperative bleeding.
We suggest that both the abdomen and the groins should be prepped; the abdomen should be accessible to remove the driveline and femoral vessel cannulation may be necessary in some cases.
Once the reesternotomy is performed, the main goal is achieving control of the aorta and, both cava veins and the outflow graft, so, cardiopulmonary bypass (CPB) can be started. Most groups suggest completing the device dissection while on CPB support. It is important to stop the LT-MCS device and occlude its outflow graft when starting the CPB machine to avoid backward flow. In cases of different outflow graft implant sites, for example, in the descending aorta, control of it should also be achieved before starting the CPB machine. Once CPB is supported, the pump removal can be performed. The cardiectomy is completed in the usual way, making sure the outflow anastomotic site is removed.
After completion of the implant, it is mandatory to achieve proper hemostasis to minimize the need for blood products and reduce the risk of postoperative tamponade.
Following protamine administration, the driveline should be removed. In cases of driveline infection, as previously mentioned, the driveline exit site would be kept in a different surgical field to minimize the contamination of the mediastinum; thus, the internal part of the driveline would be removed from the inside and the infected part would be pulled once the chest is closed. As all foreign material should be removed, two incisions may be necessary to remove the totality of the driveline; we suggest doing extensive debridement of the exit site in cases of infection and ensure proper closing of the wounds to reduce the risk of collection development, even with the use of vacuum-assisted therapy.
3.5 Results
With the development of LT-MCS, several transplant programs report their concern regarding the impact of this bridging strategy on the transplant outcomes [36, 37]. However, long-term devices have proved themselves as successful bridge-to-transplant devices. Despite being a challenging surgery, survival results are comparable to direct transplant strategies in recent publications [23, 38, 39]and recent publications only showed a higher post-transplant transfusion need in the bridged group [23, 36].
Recent ISHLT data from its transplant registry show 90% 1-year survival in either direct transplant or bridge with left ventricular assist device; these same data showed decreased initial survival if patients were bridged with either biventricular support or total artificial heart, probably due to a worse preoperative status [40].
In addition to survival, the other main concern with this bridging strategy is post-transplant vasoplegia. Contradictory results have been published in this regard [41, 42].
3.6 Bridge-to-bridge
As previously developed, recent changes in the allocations systems give the highest priority to the sickest patients. However, this might lead to transplant patients who have had not enough time to recover organ function or who could have not been fully evaluated worsening transplant results. A way of avoiding this phenomenon would be the bridge-to-bridge strategy, which means that a patient under ST-MCS would be transitioned to a long-term device and transplanted once fully recovered and rehabilitated.
Before the surgery, a careful assessment of right ventricular function and associated valvular lesions, such as significant aortic regurgitation or tricuspid regurgitation, must be performed. The presence of intracavitary thrombi should also be evaluated. The presence of any of these lesions in addition to the initial device would impact the surgical technique and the approach. For example, if the patient is under ECMO support, the long-term device implant could be performed under the same support. In these cases, if concomitant lesions have been discarded, it is even possible to perform a minimally invasive device insertion. However, teams must keep in mind that right ventricular function is difficult to evaluate while on ECMO support. Thus, in addition to potential pulmonary congestion leads to a significantly higher incidence of postoperative right ventricular failure [43].
When the initial device is an Impella
Once the implant of the new device has been finished, it is important not to forget to repair the cannulation site, ensuring the proper distal flow of the extremity to minimize vascular complications, which may have a high impact on survival.
If the patient is bridged from a Levitronix Centrimag
Despite ST-MCS allowing for rapid recovery, these patients can still be considered the sickest ones. As mentioned, the incidence of post-device right ventricular failure may reach up to 20%, higher than in the non-bridged population [43]. In addition, 1-year survival after the implant is also worse compared to the general LVAD population (1-year survival 70% vs. 91%) [39]. Despite these initial poorer results, when these patients recover and are transplanted, results are as successful as transplant after primary LVAD insertion, with 1-year survival around 90% [39].
4. Discussion
Heart transplant remains the gold-standard treatment for end-stage heart failure since the first case was performed in 1967. Once the initial issues with rejection were solved after the introduction of cyclosporine, results significantly improved and several transplant programs developed.
Simultaneously, several therapeutic advances led to significant improvement of pathologies previously lethal. This new chronicity of several cardiomyopathies in addition to an aging population made heart failure one of the most prevalent diseases, thus increasing the number of heart transplant candidates. On the other hand, the number of potential donors for a heart transplant was actually maintained or even diminished; this situation caused a clear disbalance and the shortage of donors became a reality.
Mechanical circulatory support was initially developed for patients who could not be weaned from CPB, such as the first implant performed by Dr. DeBakey and it became a field in continuous development. However, it was not until the early 2000s when the REMATCH trial [44] showed better survival with LT-MCS than with conventional treatment for end-stage heart failure patients. These results led to a tremendous expansion of the therapy with different devices being developed. Since the first generation XVE to the current HeartMate 3, devices have become smaller and more hemocompatible, significantly improving the results, both of survival and adverse effects. With the huge advances in the field, in addition to the shortage of donors, the heart failure community realized that LT-MCS, despite requiring additional surgery and the inherent technical complexities at the time of the transplant, was the best option to allow patients to reach the transplant in the best clinical situation possible; until the last allocation system modification, nearly 50% of the recipients in the USA had a previous long-term device.
In addition to the chronic heart failure population, as physicians, we face a significant proportion of patients with acute heart failure. In these circumstances, short-term MCS would be the preferred option. Short-term devices allow for rapid patient stabilization and organ recovery. In some cases, patients’ myocardial function would recover and the device would be explanted, while in other cases, patients would need further therapies, such as heart transplants. This situation might be tricky as the transplant evaluation has to be performed under support, which might limit its depth, and the treating physicians should find the appropriate moment to list the patient finding a weak balance between patient recovery and avoidance of complications. As ST-MCS patients can be considered the sickest ones, the different allocations systems give these patients the highest priority on the transplant list, so they can have more opportunities of being transplanted. However, this strategy also increases the risk of transplanting patients not fully recovered or fully evaluated, which has proved to worsen transplant results [45], especially if ECMO is the bridging device.
The initial impairment of survival using the ST-MCS bridging strategy let to consider alternative strategies; the most used one, whenever possible, would be the bridge-to-bridge, which means transitioning a patient from short-term to a long-term device to allow for complete recovery. In these cases, patients undergo an additional surgical procedure, such as the LT-MCS implant, but they can be fully evaluated and be listed when they are completely recovered. Groups that follow this strategy have already published results comparable to the patients bridged directly with an LT-MCS device.
Aside from the device used, their common goal is to ensure the patient reaches the transplant in the best possible clinical condition. To ensure it, it is fundamental that patients’ physical status is improved with adequate nutrition and adapted physical therapy, which should be started as soon as possible, to avoid muscle mass loss. In addition to recovery, the avoidance of adverse effects is of extreme importance; accurate blood pressure control would help to reduce the incidence of neurologic events and also the development of aortic regurgitation. It would also reduce afterload, which would improve the left ventricular unloading and signs of congestion. Prevention of infections is another striking aspect; it starts in the same operating theater with the implant of the driveline and it continues during the whole time on support, with accurate dressing changes and accurate follow-up [25, 26]. In the cases of ST-MCS, the same rules apply; in these cases, removal of unnecessary lines and careful assessment of the cannulas exit site might help in the reduction of infections.
Once at the time of the transplant, the surgical team should be aware of the different particularities of each device and plan the procedure accordingly. Dissection of long-term devices might need additional time compared to other cardiac reinterventions or ST-MCS devices may need an earlier aortic clamp than other cases. As important as surgical timing is planning additional procedures that might be required, such as vascular repair, wound debridement, or removal of an infected driveline. In this last case, special care should be taken to avoid mediastinal contamination.
Post-transplant care has no differences compared to non-bridged patients; immunosuppression regimens and rejection surveillance are kept the same; the only specific situation would be the extension of antibiotic treatment in cases of device infection and it should be individually discussed with the ID team.
Despite the initial concerns regarding transplant outcomes after the use of a mechanical device, results have proved to be excellent, with survival rates similar to the non-bridged population in the case of LT-MCS. ST-MCS might not seem a good strategy due to worse initial results. However, physicians should take into consideration that we are facing the sickest patients and that these temporary devices may be the only option available for these acute patients [39].
5. Conclusions
Mechanical circulatory support as a bridge-to-transplant strategy allows for patient recovery, increased functional capacity, and a reduction in wait-list mortality.
Despite the surgical challenges the different support strategies associate, post-transplant survival results have proved them a good strategy to safely bridge patients to heart transplant.
Conflict of interest
None of the authors has any conflict of interest regarding this manuscript.
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