Studies of controlled reperfusion after ischemia

Ex vivo perfusion of the donor heart: Preliminary experience in high-risk transplantations

BACKGROUND

The number of heart transplantations (HTs) has decreased in France since 2017 (-5%/year) despite a stable rate of patients referred on the waiting list. Ex vivo heart perfusion (EVHP) is an innovative approach for organ preservation, reducing graft ischaemic time and facilitating continuous organ monitoring before transplantation.

AIM

To report our preliminary experience of seven donor hearts preserved with EVHP, including the first heart resuscitated after circulatory-determined death in France.

METHODS

Seven hearts were procured from donation after brain death (DBD) for HT or donation after circulatory-determined death (DCD) for research purposes (Protocol PFS20-004, Agence de la Biomédecine, La Plaine Saint-Denis, France). All grafts were preserved using the Organ Care System® (TransMedics Inc., Andover, MA, USA) for normothermic EVHP. Perfusion parameters were adjusted to achieve stable or decreasing arterial lactate trend consistent with suitability for organ transplantation.

RESULTS

Indications for EVHP were assessment of a marginal graft in four cases, prolonged preservation in two cases (anticipated duration for retrieval of recipient's heart>3hours) and resuscitation after circulatory-determined death in one case. Median duration of EVHP was 270 (interquartile range 216-343) minutes. five were transplanted, with a median ex situ preservation time (ischaemic time+EVHP time) of 334 (interquartile range 326-444) minutes. The two other grafts were discarded for HT. Three recipients had extracorporeal life support after HT, and presented complete cardiac recovery within a week after HT. One patient died at day 11 because of septic shock. The 3-month survival rate was 75% among recipients. Three months after HT, the left ventricular ejection fraction was>60% in all cases.

CONCLUSIONS

EVHP enabled safe prolonged preservation and assessment of marginal grafts. This approach provides an opportunity to expand the donor pool by resuscitating grafts from donors with extended criteria, including controlled DCD.

Controlling Reperfusion Injury With Controlled Reperfusion: Historical Perspectives and New Paradigms

Cardiac reperfusion injury is a well-established outcome following treatment of acute myocardial infarction and other types of ischemic heart conditions. Numerous cardioprotection protocols and therapies have been pursued with success in pre-clinical models. Unfortunately, there has been lack of successful large-scale clinical translation, perhaps in part due to the multiple pathways that reperfusion can contribute to cell death. The search continues for new cardioprotection protocols based on what has been learned from past results. One class of cardioprotection protocols that remain under active investigation is that of controlled reperfusion. This class consists of those approaches that modify, in a controlled manner, the content of the reperfusate or the mechanical properties of the reperfusate (e.g., pressure and flow). This review article first provides a basic overview of the primary pathways to cell death that have the potential to be addressed by various forms of controlled reperfusion, including no-reflow phenomenon, ion imbalances (particularly calcium overload), and oxidative stress. Descriptions of various controlled reperfusion approaches are described, along with summaries of both mechanistic and outcome-oriented studies at the pre-clinical and clinical phases. This review will constrain itself to approaches that modify endogenously-occurring blood components. These approaches include ischemic postconditioning, gentle reperfusion, controlled hypoxic reperfusion, controlled hyperoxic reperfusion, controlled acidotic reperfusion, and controlled ionic reperfusion. This review concludes with a discussion of the limitations of past approaches and how they point to potential directions of investigation for the future.

The effects of various leukocyte filtration strategies in cardiac surgery

It is known that cardiopulmonary bypass causes an inflammatory reaction with an associated morbidity and mortality. Several anti-inflammatory strategies have been implemented to reduce this response, including leukocyte removal from the circulation using specialised filters. The aim of this study is to systematically review the available evidence on leukocyte filtration in cardiac surgery, focusing on its effect on systemic inflammation and whether this has influenced clinical outcomes. Five electronic databases were systematically searched for studies reporting the effect of leukocyte filtration at any point within the cardiopulmonary bypass circuit in humans. Reference lists of all identified studies were checked for any missing publications. Two authors independently extracted the data from the included studies. Whilst systemic leukodepleting filters do not appear to consistently lower leukocyte counts, they may preferentially remove activated leukocytes. Small improvements in early post-operative lung function in patients receiving systemic leukodepletion have been reported, but this does not lead to reduced hospital stay or decreased mortality. There is substantial evidence that cardioplegic leukocyte filtration attenuates the reperfusion injury at a cellular level, but this has not been translated into clinical improvements. Finally, whilst various strategies involving multiple leukocyte filters, or the incorporation of pharmacological agents into leukocyte-depleting protocols have been evaluated, the current available results are not conclusive. Our study suggests that there is not enough high quality or consistent evidence to draw guidelines regarding the use of leukocyte-depleting filters within routine cardiac surgical practice.

Blood cardioplegia filtration

The introduction of blood cardioplegia has been proven to limit ischaemia and reperfusion injury in cardiac surgery. But the presence of activated neutrophils in the capillary bed may cause further damage. Leukocyte filters have been shown to be very effective in reducing the leukocytes in blood cardioplegia to less than 10%. Leukocyte depletion of blood cardioplegia provides an excellent approach to minimizing myocardial injury, predominantly in high-risk cardiac surgery.

Leukocyte filtration in cardiac surgery: a review

Leukocyte filtration has evolved as an important technique in cardiac surgery with cardiopulmonary bypass to prevent pathogenic effector functions mediated by activated leukocytes. The underlying mechanisms that result in an improvement of laboratory variables as well as clinical outcome are not resolved yet. Moreover, the optimum strategy for the use of current filtration technology has not been systematically evaluated. This paper, therefore, reviews how activated leukocytes may lead to tissue damage, summarizes the known effects of leukocyte filtration on clinical outcome and laboratory parameters, and deals with current experimental and clinical efforts to further limit the pathogenic effects of leukocytes in cardiac surgery.

Timing of leukocyte filtration during cardiopulmonary bypass

The effects of leukocyte filtration on the outcome of cardiac surgery with cardiopulmonary bypass (CPB) have been shown by numerous investigators. In the majority of cases a leukocyte filter is placed in the arterial line instead of a standard arterial line filter and used throughout CPB. However, protocols to optimize onset and duration of leukocyte filtration have not been sufficiently evaluated to date. In this paper, current efforts to improve such protocols are demonstrated and discussed. These efforts are based on studies of leukocyte pathogenicity during cardiac surgery. A first study (double-blind randomized) was performed in routine coronary artery bypass graft (CABG) patients to evaluate whether short-term leukocyte filtration during reperfusion by release of the aortic crossclamp would reduce reperfusion-associated myocardial damage. Further data compare the efficacy of three different filtration concepts to reduce CPB- and/or reperfusion-associated leukocyte pathogenicity. Clinical endpoints, standard laboratory variables and functional in vitro assays are provided and discussed.

The effect of leukocyte-depleted blood cardioplegia in patients with severe left ventricular dysfunction: a randomized, double-blind study

BACKGROUND

The propensity for leukocytes to cause reperfusion injury in patients undergoing heart surgery is widely accepted. Reperfusion injury may result in myocardial damage and unfavorable operative outcome, especially in patients with severely reduced ejection fractions. This study was performed to evaluate the impact of leukocyte filtration on the postoperative course of patients undergoing coronary bypass surgery.

METHODS

Thirty-two patients with coronary artery disease and left ventricular ejection fraction less than 35% were included in this double-blind, randomized study. Two serial leukocyte removal filters (Pall BC1B filter [Pall Biomedical, Portsmouth, England], group F, 15 patients) or two dummy filters (group C, 17 patients) were connected to the blood cardioplegia line. Leukocyte count, hemodynamic measurement, and transesophageal echocardiography were performed before and after cardiopulmonary bypass. Cardiac-specific enzymes were analyzed from arterial blood during the first 72 hours and from coronary sinus blood 30 and 60 minutes after aortic unclamping.

RESULTS

Patient characteristics were similar in the two groups (ejection fraction 20.9% +/- 4.3% in group C and 21.1% +/- 4.8% in group F; P =.773). No early death or perioperative myocardial infarction occurred. Leukocyte count, hemodynamic parameters, cardiac troponin T, cardiac troponin I, and creatine kinase MB mass levels in arterial blood were similar in the two groups. Group F showed lower release of cardiac troponin T from the coronary sinus 30 minutes after unclamping of the aorta (group F, 0.263 +/- 0.12 ng/mL; group C, 0.6 +/- 0.32 ng/mL; P =.005). Lower doses of dopamine were necessary after cardiopulmonary bypass (group F, 0.36 +/- 0.11 mg x kg(-1) x min(-1); group C, 0.49 +/- 0.14 mg x kg(-1) x min(-1); P =.003). A moderate increase in ejection fraction was observed at 30 minutes in both groups (group F, 30.3% +/- 6.2%; group C, 28.0% +/- 6.3%; P =.239) and a significant increase at 60 minutes in group F (group F, 32.5% +/- 6.0%; group C, 27.4% +/- 7.5%; P =.012).

CONCLUSIONS

These results indicate that serial leukocyte filters connected to the blood cardioplegia line decrease myocardial cell injury and may therefore help to improve outcome of patients with severely depressed ejection fractions undergoing coronary artery bypass grafting.

Effects on infarct size and on arrhythmias by controlling reflow after myocardial ischaemia in pigs

Part of the myocardial damage after an ischaemic period might be related to the reperfusion conditions. Many abrupt changes occurring in the heart during reperfusion may add to the damage during the preceding ischaemic period, and increase in infarct size. In this study we tested the hypothesis that infarct size and occurrence of ventricular arrhythmias might be reduced by restricting reflow after an ischaemic period. Seventeen pigs underwent 45 min of total occlusion of the left anterior descending coronary artery with an hydraulic occluder. In the intervention group reperfusion was restricted to 50% of baseline during the first minute, to 100% during the next minute, kept constant for 1 min, and thereafter allowed to increase by 50% of baseline flow every minute until free reflow. In the control group reflow was not restricted. Arrhythmias were recorded. After 2.5 h of reperfusion the heart was excised. Infarct size was measured by using triphenyltetrazolium chloride (delineation of necrosis), fluorescent microspheres (delineation of area at risk) and planimetry. No reduction in infarct size (% of area at risk) was found between the intervention group and the control group (75.9 +/- 5.3% vs. 72.4 +/- 4.3%). The incidence of ventricular arrhythmias and ventricular fibrillation were not found to be different between the groups during reperfusion. Hemodynamic parameters were not significantly different between the two groups. Our data indicate that no substantial protection against myocardial infarct or ventricular arrhythmias could be achieved by controlling reflow using the present protocol after a period of myocardial ischaemia in pigs. Accordingly, our data do not support the notion that control of reflow may be beneficial when treating coronary artery occlusion with percutaneous coronary angioplasty (PCA).

Renal ischemia-induced increase in vascular permeability is limited by hypothermia

The purpose of the present work was to evaluate the kallikrein-kinin system and effects of hypothermia during renal ischemia and reperfusion. Male C57BL/KSJmdb mice were subjected to 20 or 60 min ischemia for different periods of reperfusion. Our results demonstrate that short periods of ischemia followed by reperfusion did not cause significant alterations in kallikrein activity, Evans Blue (EB) extravasation, prokallikreins, myeloperoxidase activity or plasma creatinine concentration. Edema was evident at 1 h reperfusion in the treated mice, but returned to basal values after 24 h reperfusion. Kallikrein activities and EB extravasation showed a significant increase in 60 min ischemic mice. Myeloperoxidase activity in the kidney of the mice confirmed net infiltration in the group with 60 min ischemia and 24 h reperfusion. The generation of kinins and activation of matrix degrading enzymes by tissue kallikrein, liberated from both renal and infiltrated leukocytes, could be responsible at least in part for the damage observed in the kidney of mice subject to 60 min ischemia and reperfusion. The hypothermia significantly reduced the inflammatory process in the 60 min ischemic mice, and did prevent an increase in vascular permeability. Nevertheless, the tissue edema was not shown to change between normothermic and hypothermic ischemic mice.

Inflammatory response to cardiopulmonary bypass: mechanisms involved and possible therapeutic strategies

BACKGROUND

Recent study of the inflammatory reactions occurring during and after cardiopulmonary bypass (CPB) has improved our understanding of the involvement of the inflammatory cascade in perioperative injury. However, the exact mechanisms of this complex response remain to be fully determined.

METHODS

Literature on the inflammatory response to CPB was reviewed to define current knowledge on the possible pathways and mediators involved, and to discuss recent developments of therapeutic interventions aimed at attenuating the inflammatory response to CPB.

RESULTS

CPB has been shown to induce complement activation, endotoxin release, leukocyte activation, the expression of adhesion molecules, and the release of many inflammatory mediators including oxygen-free radicals, arachidonic acid metabolites, cytokines, platelet-activating factor, nitric oxide, and endothelins. Therapies aimed at interfering with the inflammatory response include the administration of pharmacologic agents such as corticosteroids, aprotinin, and antioxidants, as well as modification of techniques and equipment by the use of heparin-coated CPB circuits, intraoperative leukocyte depletion, and ultrafiltration.

CONCLUSIONS

Improved understanding of the inflammatory reactions to CPB can lead to improved patient outcome by enabling the development of novel therapies aimed at limiting this response.

The effects of cardioplegic arrest and reperfusion on the microvasculature of the heart

OBJECTIVES

Despite laboratory evidence of leucocyte involvement in reperfusion injury, cardiac surgical clinical trials do not support the therapeutic effectiveness of leucocyte filtration. Furthermore, the direct effects of crystalloid cardioplegia and reperfusion on the capillaries of the heart have yet to be elucidated. We tested the effects of cardioplegic arrest and reperfusion both with and without leucocyte depletion, in a model of cardiopulmonary bypass that mimics clinical cardiac surgical conditions.

METHODS

Four groups of Landrace pigs were studied. Group A (n = 6) underwent 30 min of hypothermic (28 degrees C) cardiopulmonary bypass. Groups B (n = 6), C (n = 6) and D (n = 6) also had 90 min of cardioplegic arrest. Group C was then reperfused with whole blood, while Group D was reperfused with leucocyte-depleted blood. Microvascular methylmethacrylate corrosion casts were made at the end of the experimental period. Myocardial vascular anatomy was defined by electron microscopy and capillary abundance derived from this and from the weight of casts from representative areas. Leucocyte deposition was assessed using radioisotope-labelled leucocytes. Ischaemic damage to tissues was graded according to light and electron microscopic findings.

RESULTS

In Group A the mean (+/- S.D.) vascular cast weight/volume of myocardium (density) was 125 +/- 9 mg/mm3. After cardioplegic arrest (Group B), it fell to 74 +/- 7 mg/mm3 (P < 0.0001) due to absence of capillaries, although arterioles, venules and non-nutritive bypass vessels remained patent. Following reperfusion with whole blood (Group C), capillary numbers partially recovered but luminal diameters were reduced with a cast density of 94 +/- 5 mg/mm3 (P < 0.0001 versus Group A and B). Leucocyte-depleted (87-92%) reperfusion in Group D did not affect cast density (90 +/- 3 mg/mm3; P = 0.17). Coronary vascular resistances in Groups C and D rose slightly, but not significantly, during reperfusion.

CONCLUSIONS

Following cardioplegic arrest, microvascular changes are marked. These changes are partially reversed by 30 min reperfusion. Leucocyte depletion does not ameliorate these effects in this model.

Improvement in functional recovery of the isolated guinea pig heart after hyperkalemic reperfusion with adenosine

The aim of this study was to examine the effect of initial hyperkalemic reperfusion (HKR), with and without added adenosine, on coronary flow, myocardial function, and endothelium-dependent and endothelium-independent coronary vascular function. Cardioplegic arrest was induced in 40 isolated guinea pig hearts by infusing oxygenated cardioplegic (high in potassium ion) Krebs solution for 5 minutes. Hearts were then stored at room temperature for 3.5 hours. On reperfusion, hearts were divided into four groups of 10 hearts each: control, reperfusion with regular Krebs solution (4.6 mmol/L potassium chloride); base hyperkalemic reperfusion, initial reperfusion with 37 degrees C oxygenated, cardioplegic Krebs solution for 5 minutes; hyperkalemic reperfusion with addition of 1 mmol/L adenosine during HKR; and hyperkalemic reperfusion with addition of 5 mmol/L adenosine. Coronary reserve (adenosine bolus 2 mmol/L) and responses to acetylcholine (1 mumol/L) and nitroprusside (100 mumol/L) were examined before and after ischemia and reperfusion. Flow did not return to preischemic values in any group after reperfusion. Adenosine treatment during initial reperfusion increased coronary flow (percentage of baseline +/- standard error of the mean) from 57% +/- 4% in control and 45% +/- 3% in hearts with hyperkalemic reperfusion to 79% +/- 3% and 83% +/- 5% in hearts with hyperkalemic reperfusion also treated with, respectively, 1 mmol/L adenosine and 5 mmol/L adenosine (p < 0.05). At 30 and 60 minutes of reperfusion, however, flow remained elevated only in the group treated with 5 mmol/L adenosine. Coronary reserve and responses to acetylcholine and nitroprusside were equivalently depressed in all groups after reperfusion. Recovery of left ventricular systolic and diastolic function was improved in all groups after hyperkalemic reperfusion (54% +/- 4% of preischemic value) compared with control (39% +/- 3%), and recovery was further enhanced in the group treated with 5 mmol/L adenosine (60% +/- 4%). In this ex vivo model, hyperkalemic reperfusion improved myocardial function after cardioplegic arrest and the addition of 5 mmol/L adenosine improved coronary flow. Adenosine may counteract the potassium chloride-induced vasoconstriction that occurs during hyperkalemic reperfusion and may thus improve coronary flow and myocardial function. Postischemic depression of endothelium-dependent or endothelium-independent vascular functions, however, was not alleviated by hyperkalemic reperfusion with or without adenosine.

Role of leukocyte depletion during cardiopulmonary bypass and cardioplegic arrest

BACKGROUND

Leukocyte depletion (LD) has been shown to be beneficial during the reperfusion of acutely ischemic myocardium; however, its role during cardiopulmonary bypass (CPB) in hearts protected with blood cardioplegia (BCP) is unknown. This experimental study sought to determine whether LD filters inserted in the CPB circuit before cardioplegic arrest and in the BCP circuit during arrest would decrease ischemic myocardial damage.

METHODS

In 20 pigs, the second and third diagonal vessels were occluded for 90 minutes, followed by 45 minutes of BCP arrest and 180 minutes of reperfusion on CPB. In 5 pigs, LD filters were inserted in both the CPB and BCP circuits (LD-CPB+BCP). Five pigs had LD during BCP (LD-BCP), 5 pigs had LD during CPB (LD-CPB), and 5 pigs had no LD. Ischemic damage was assessed by wall motion scores using two-dimensional echocardiography and the area of necrosis/area of risk.

RESULTS

The LD-CPB and LD-CPB+BCP groups had the highest wall motion scores and the lowest area of necrosis/area of risk. The addition of LD to BCP alone did not significantly alter wall motion scores or the area of necrosis/area of risk.

CONCLUSION

Leukocyte depletion filters significantly reduce ischemic damage during acute surgical revascularization and appear to be most effective when placed in the CPB circuit before cardioplegic arrest.

Protection of evolving myocardial infarction and failed PTCA

Acute myocardial infarction is caused by acute coronary occlusion and is the major cause of death in Europe and the United States. In-hospital mortality is due principally to cardiogenic shock because of extensive ischemic muscle damage. Previous surgical results of coronary artery bypass grafting for left ventricular power failure have been disappointing because intraoperative ischemic injury is superimposed on severe damage already sustained by the myocardium. Surgical revascularization has, in general, been restricted to patients with acute occlusion after elective percutaneous transluminal coronary angioplasty with or without thrombolytic therapy. During the last years new knowledge has been gained in the pathophysiology of acute coronary occlusion on ischemic and nonischemic (remote) myocardium that has evolved in a new surgical strategy for revascularization of patients with evolving myocardial infarctions and failed percutaneous transluminal coronary angioplasty. Studies of the natural history of acute regional ischemia have shown that acute occlusion of a coronary artery not only affects the ischemic myocardium but causes structural, functional, and metabolic alterations in the remote and adjacent myocardium. These changes in the remote myocardium are even more severe if the remote myocardium is supplied by a stenotic coronary artery. Furthermore, many experimental and clinical studies have shown that normal blood reperfusion of myocardium injured previously by ischemia leads to additional damage (reperfusion injury).(ABSTRACT TRUNCATED AT 250 WORDS)

Role of neutrophils in myocardial ischemia and reperfusion

In the intact organism, ischemic myocardial injury initiates an acute inflammatory response in which polymorphonuclear leukocytes (PMNs) are major participants. Evidence indicates that the interplaying inflammatory reactions are augmented by reperfusion and that accumulating PMNs can contribute to myocardial damage, eg, by release of oxygen-derived free radicals, proteases, and leukotrienes. In experimental models, interventions aimed at PMN inhibition can exert cardioprotective effects, and some of these strategies raise hope for future clinical applications. A greater understanding of the mechanisms involved in PMN-mediated myocardial damage is necessary for designing a rational approach to reduce the putative detrimental effects of PMNs without antagonizing their favorable consequences in tissue healing.

Role of neutrophil-endothelial cell adhesion in inflammatory disorders

Polymorphonuclear leukocytes are armed with an impressive arsenal of bactericidal agents that allow these cells to play a vital role in host defense against invading pathogens. However, these same agents can produce extensive cellular damage in host tissues when leukocytes are activated during inflammatory conditions. Recognition of this fact, when coupled with the observation that leukocyte adhesion to post-capillary venules is a critical first step in the inflammatory process, has led to the development of the concept that inhibition of neutrophil-endothelial cell adhesion (NECA) may represent a novel therapeutic strategy for the prevention of leukocyte-dependent injury in inflammatory conditions. Indeed, pharmacological or immunologic inhibition of NECA reduces cellular injury, dysfunction, and necrosis induced by ischemia/reperfusion, circulatory shock and resuscitation, organ transplantation, cardiopulmonary bypass, frostbite, and thermal trauma. NECA also appears to play an important role in the pathobiology of airway inflammation and asthma, pulmonary oxygen toxicity, arthritis, bacterial meningitis, and cerebral malaria. The aim of this review is to summarize the evidence implicating NECA in the pathogenesis of these inflammatory conditions.

Could treatment with scavengers of oxygen free radicals minimize complications in cardiac surgery?

Cardiac surgical complications may be caused by a plethora of events. Oxygen free radicals may participate in the pathophysiology of cardiopulmonary bypass and myocardial ischaemia-reperfusion injury. The evidence of free radical production during bypass is limited, and studies of the effect of free radical scavengers even more limited. Experimental work points towards a role of oxygen free radicals in reperfusion damage of the ischaemic myocardium, but clinical data are lacking. Hitherto the clinical availability of free radical scavengers/antioxidants has been scarse. At present more such drugs are becoming clinically applicable, and trials on their effect are highly warranted, in particular as an adjuvant in myocardial protection.