Effects of Atrial Natriuretic Peptide After Prolonged Hypothermic Storage of the Isolated Rat Heart

Primary graft failure (PGF) caused by ischemia‐reperfusion injury (IRI) is the strongest determinant of perioperative mortality after heart transplantation. Atrial natriuretic peptide (ANP) has been found to reduce the IRI of cardiomyocytes and may be beneficial in alleviating PGF after heart transplantation, although there is a lack of evidence to support this issue. The purpose of this study was to investigate the cardioprotective effects of ANP after prolonged hypothermic storage. For this purpose, an isolated working‐heart rat model was used. After the preparation, the hearts were arrested with and stored in an extracellular‐based cardioplegic solution at 3–4°C for 6 h and followed by 25 min of reperfusion. The hearts were divided into four groups (n = 7 in each group) according to the timing of ANP administration: Group 1 (in perfusate before storage), Group 2 (in cardioplegia), Group 3 (in reperfusate), and control (no administration of ANP). Left ventricular functional recovery and the incidence of ventricular fibrillation (VF) were compared. ANP administration at the time of reperfusion improved the percent recovery of left ventricular developed pressure (control, 45.5 ± 10.2; Group 1, 47.4 ± 8.8; Group 2, 45.3 ± 12 vs. Group 3, 76.3 ± 7; P < 0.05) and maximum first derivative of the left ventricular pressure (control, 47.9 ± 8.7; Group 1, 46.7 ± 8.8; Group 2, 49.6 ± 10.8 vs. Group 3, 76.6 ± 7.5; P < 0.05). The incidence of VF after reperfusion did not differ significantly among these four groups (71.4, 85.7, 57.1, and 85.7% in Groups 1, 2, 3, and control, respectively). This result suggests that the administration of ANP at the time of reperfusion may have the potential to decrease the incidence of PGF after heart transplantation.     

Performance of pig heart after 30 or 120 minutes hypothermic arrest

The effect of the duration of hypothermic (T = 15°C) potassium cardioplegic arrest and ischemia on the heart was determined by measuring the response of the isolated in situ pig heart to 180 min of perfusion (n = 12) to provide appropriate control values for the study of 30 (n = 25) or 120 (n = 27) min of ischemia, followed by 60 min of reperfusion. In some of these animals, myocardial tissue samples were obtained for measurement of adenosine triphosphate (ATP) and creatine phosphate (CP), (6 in the perfusion group, 7 in the 30 min of ischemia and 60 min of reperfusion group and 15 in the 120 min of ischemia and 60 min of reperfusion group). In the remaining animals, measurements of either left ventricular performance (LVP), myocardial oxygen metabolism (MV?O₂) or plasma creatine kinase (CK) were obtained (6 in the prolonged perfusion group, 12 in the 120 min of ischemia and 60 min of reperfusion group, [6 LVP and MV?O₂ and 6 CK] and 18 in the 30 min of ischemia and 60 min of reperfusion group [13 LVP, 17 MV?O₂ and 6 CK]). During prolonged perfusion, left ventricular performance, expressed as developed pressure, ΔP, fell from an initial value of 175 ± 36 to 128 ± 19 mm Hg at 30 min of perfusion, followed by a more gradual decline to a final value of 113 ± 8 mm Hg at 180 min of perfusion. These decreases were not significantly lower than the initial value. The percentage of myocardial extraction declined in a similar manner, but coronary blood flow was constant over this interval. The primary effect of 30 or 120 min of ischemia was to reduce left ventricular developed pressure, ΔP, during reperfusion to more than 70% of the corresponding value in the control group (these differences were statistically significant) which suggests that prolonging the period of ischemia did not cause further deterioration of cardiac performance. The plasma concentration of CK rose in the control group of hearts subjected to prolonged perfusion from an initial value of 35 ± 6 to a final value of 59 ± 8 IU/liter (P < 0.05). While plasma CK increased during reperfusion in both ischemia/ reperfusion groups, these values were not significantly higher from prearrest values. Thus hypothermic cardioplegic ischemia of this duration did not appear to result in tissue necrosis, but there was a significant reduction in left ventricular performance which was independent of the duration of ischemia between the limits of 30 and 120 min.     

Intra‐Aortic Balloon Pump Support in the Isolated Beating Porcine Heart in Nonischemic and Ischemic Pump Failure

The blood pressure changes induced by the intra‐aortic balloon pump (IABP) are expected to create clinical improvement in terms of coronary perfusion and myocardial oxygen consumption. However, the measured effects reported in literature are inconsistent. The aim of this study was to investigate the influence of ischemia on IABP efficacy in healthy hearts and in shock. Twelve slaughterhouse porcine hearts (hearts 1–12) were connected to an external circulatory system, while physiologic cardiac performance was restored. Different clinical scenarios, ranging from healthy to cardiogenic shock, were simulated by step‐wise administration of negative inotropic drugs. In hearts 7–12, severe global myocardial ischemia superimposed upon the decreased contractile states was created. IABP support was applied in all hearts under all conditions. Without ischemia, the IABP induced a mild increase in coronary blood flow and cardiac output. These effects were strongly augmented in the presence of persisting ischemia, where coronary blood flow increased by 49 ± 24% (P < 0.01) and cardiac output by 17 ± 6% (P < 0.01) in case of severe pump failure. As expected, myocardial oxygen consumption increased in case of ischemia (21 ± 17%; P < 0.01), while it slightly decreased without (?3 ± 6%; P < 0.01). In case of progressive pump failure due to persistent myocardial ischemia, the IABP increased hyperemic coronary blood flow and cardiac output significantly, and reversed the progressive hemodynamic deterioration within minutes. This suggests that IABP therapy in acute myocardial infarction is most effective in patients with viable myocardium, suffering from persistent myocardial ischemia, despite adequate epicardial reperfusion.     

The Protective Effect of St. Thomas Cardioplegia Enriched With Zacopride on the Isolated Rat Heart

The activation of the heart inward rectifier potassium channel (I_K1) can reduce the injury of myocardial cells by shortening the action potential duration and reducing intracellular calcium overload. Zacopride is a selective I_K1 agonist and suppresses triggered arrhythmias in rat hearts. This investigation studied the effects of St. Thomas (ST) cardioplegia enriched with Zacopride on the isolated rat heart model. Sprague‐Dawley rat hearts were harvested and perfused for 20 minutes with 37°C Krebs‐Henseleit (KH) buffer followed by 15 minute perfusion with 4°C calcium‐free KH buffer in the Control group (Con, n = 8), ST cardioplegia in the ST group (ST, n = 8) and ST cardioplegia with Zacopride in the STZ group (STZ, n = 8). After 45 minutes of arresting, all hearts were reperfused with 37°C KH buffer for 60 minutes. Hearts in the STZ group arrested faster than the Con and ST groups (9.25 ± 2.38 s vs. 72.25 ± 8.1 s, 12.75 ± 2.87 s). The recovery of the left ventricular developed pressure, ± dP/dtmax, heart rate, and coronary flow in the STZ group is significantly better than the other two groups during reperfusion. Compared with the Con and ST groups, the STZ group showed significant decreases in the maximum carciac troponin I level (P < 0.05) and the infarct size (P < 0.05). The superoxide dismutase level in the STZ group increased during the first 20 minutes of reperfusion (P < 0.05). ST cardioplegia enriched with Zacopride has beneficial effects against ischemia‐reperfusion injury in this isolated rat heart model.     

The Harmful Effects of Ventricular Distention during Postischemic Reperfusion

To assess the effects of left ventricular distention during the early reperfusion period following ischemic arrest, 16 canine heart preparations were subjected to 45 minutes of hypothermic (27°C) cardioplegic arrest and normothermic reperfusion. Isovolumic left ventricular developed pressure and rate of rise of left ventricular pressure (dP/dt) were measured with an intraventricular balloon; endocardial/epicardial flow ratios were determined with microspheres; and myocardial gas tensions were monitored with mass spectrometry.During early reperfusion, Group 1 hearts (n = 8) were not distended (end-diastolic pressure = 0). Group 2 hearts (n = 8) were subjected to an end-diastolic pressure of 20 mm Hg for the initial 15 minutes of reperfusion. Group 2 hearts demonstrated impaired subendocardial blood flow after 5 minutes of reflow (0.75 ± 0.06 vs 0.96 ± 0.04, endocardial/epicardial flow rates, Group 2 vs Group 1) and persistent elevation of intramyocardial carbon dioxide (CO₂) tension (68 ± 4 vs 51 ± 4 mm Hg, Group 2 vs Group 1). In addition, postischemic ventricular function was significantly worse in Group 2 hearts (60 ± 7 vs 79 ± 3% of control dP/dt, Group 2 vs Group 1, and 53 ± 6 vs 81 ± 5% of control left ventricular developed pressure, Group 2 vs Group 1).These data demonstrate that even mild distention during early reperfusion can result in reduced subendocardial perfusion and delayed washout of tissue CO₂. Although myocardial blood flow and CO₂ tension subsequently returned to normal in the distended hearts, left ventricular performance remained significantly depressed. This injury can occur clinically in nonvented hearts prior to the resumption of effective ventricular contraction.     

Does adenosine administration during the early reperfusion period affect ischemic preconditioning?

We hypothesized that the adenosine administration during the early reperfusion period might affect ischemic preconditioning (IPC) and might reduce infarct size and enhance post-ischemic functional recovery. Twenty-four anesthetized rabbits underwent 30 min. normothermic global ischemia with 120 min. reperfusion in a buffer-perfused isolated, paced heart model and divided into four groups. Global ischemic hearts (GI, n = 6) were subjected to 30 min. global ischemia without intervention. Control hearts (n=6) were subjected to perfusion without ischemia. Ischemic preconditioned hearts (IPC, n=6) were subjected to one cycle of 5 min. global ischemia and 5 min. reperfusion prior to global ischemia. IPC + Ado hearts (n=6) received IPC and adenosine administration (100 m mol/L) during 3 min. early reperfusion period. Post-ischemic functional recovery was better in IPC + Ado hearts as compared to GI and IPC hearts, but the effect of post-ischemic functional recovery in IPC + Ado hearts became weaker during 120 min. reperfusion after prolong ischemic insult. Infarct size wre 1.0 ± 0.3% in Control hearts, 32.9 ± 5.1% in GI hearts, 13.8 ± 1.3% in IPC hearts and 8.1 ± 0.9% in IPC + Ado hearts. Infarct size in IPC hearts was significantly decreased (p<0.01) as compared to GI hearts. The reduction rate against myocardial necrosis in IPC + Ado hearts versus GI hearts was higher as compared to IPC hearts versus GI hearts (p<0.001, IPC+Ado hearts vs GI hearts; p<0.01, IPC hearts vs GI hearts; p = ns, IPC + Ado hearts vs Control hearts). These data suggest that adenosine administration during the early reperfusion period reinforce IPC effect and reduce myocardial reperfusion injury. Cardiomyoprotective effects of IPC and exogenous adenosine are exerted during early reperfusion after coronary occlusion in the isolated perfused rabbit hearts.     

Establishment of a porcine right ventricular infarction model for cardioprotective actions of xenon and isoflurane

Background: Right ventricular (RV) function is an important determinant of post‐operative outcome. Consequences of RV infarction might be limited by pre‐conditioning with volatile anesthetic drugs. Therefore, we used a porcine model of RV ischemia and reperfusion (IR) injury to study the influence of isoflurane and xenon on the extent and degree of myocardial injury. Methods: IR injury was induced by a 90‐min ligation of the distal right coronary artery and 120‐min reperfusion in thiopental anesthetized pigs. A control group (n=12) was compared with two groups, which received either 0.55 minimum alveolar concentration (MAC) isoflurane (n=10) or xenon (n=12) starting 60 min before ischemia. Myocardial injury was described by three criteria: the infarct size related to area at risk (IS/AAR), the infiltration of neutrophils as determined by myeloperoxidase (MPO) activity, and the plasma levels of tumor necrosis factor α (TNFα), interlukin 6 (IL‐6), myoglobin and troponin‐T (TnT). Results: IS/AAR was reduced from 58.3±6.2% in the control group to 41.8±7.8% after isoflurane and 42.7±8.5% after xenon pre‐treatment, which equals an absolute reduction of 16.5% [95% confidence interval (CI): 10.9–22.1] and 15.5% (95% CI: 10.1–20.9). The maximum increase of TnT could be observed within the xenon group. Both treatment groups were characterized by lower MPO activity, in the infarct and periinfarct region and lower plasma concentrations of TNFα and IL‐6. Conclusions: It could be demonstrated for the first time in a model of RV infarction that the continuous application of isoflurane or xenon before, during and after ischemia reduced the extent (size) and severity (inflammation) of myocardial injury.     

Sevoflurane reduces dysrhythmias during reperfusion in the working rat heart

Purpose. The effects of sevoflurane on myocardial reperfusion injury have not been well studied. The purpose of this study was to determine the effects of sevoflurane on myocardial function, arrhythmia, and metabolism during reperfusion in an isolated working rat heart model. Methods. Thirty-two hearts were divided into four groups according to the timing of 2.5% sevoflurane administration: group I, control, no sevoflurane; group II, sevoflurane administered only before ischemia; group III, sevoflurane only during reperfusion; group IV, sevoflurane during the whole study period. Myocardial contractility, myocardial ATP, lactate, and glycogen levels were assessed in the reperfusion period following global heart ischemia of 15 min duration. The incidence and duration of ventricular fibrillation were also observed in the reperfusion period. Results. There was no difference in cardiac output and left ventricular dP/dt max among the four groups at 10, 15, and 20 min after reperfusion. There was no difference in myocardial ATP, lactate and glycogen contents between the groups. The incidences of ventricular fibrillation during reperfusion were 100%, 63%, 100%, and 25% (P < 0.05 vs control), and the durations of ventricular fibrillation during reperfusion were 375 ± 269, 104 ± 98 (P < 0.05 vs control), 303 ± 189, and 93 ± 245 (P < 0.05 vs control) in groups I, II, III, and IV, respectively (mean ± SD). Conclusion. The administration of sevoflurane prior to reperfusion appears to provide myocardial protection, as assessed by reduced dysrhythmias during reperfusion. Received: December 14, 1999 / Accepted: July 25, 2000     

Ischemic preconditioning in the aged heart —Myocardial protective effect as compared with the mature heart—

It is now well established that pre-treatment with sublethal ischemia, followed by reperfusion, will delay myocardial necrosis during a later sustained ischemic episode, termed ischemic preconditioning (IPC); this has been confirmed experimentally and clinically. However, the effects for the senescent heart differ from those of the mature heart at both functional and cellular levels which have not yet been determined. Comparisons were made between aged (>135 weeks, n=18) and mature (15～20 weeks, n=8) rabbit hearts which underwent 30 min. normothermic global ischemia with 120 min reperfusion in a buffer-perfused isolated, paced heart model, and the effects of IPC on post-ischemic functional recovery and infarct size were investigated. Ischemic preconditioned hearts (n=6) were subjected to one cycle of 5 min. global ischemia and 5 min. reperfusion prior to global ischemia. Global ischemic hearts (n = 6) were subjected to 30 min. global ischemia without intervention. Control hearts (n = 6) were subjected to perfusion without ischemia. Post-ischemic functional recovery was better in the ischemic preconditioned hearts than in the global ischemic hearts in both aged and mature hearts. However, in the aged hearts, post-ischemic functional recovery was slightly reduced compared to that of the mature hearts, and only the coronary flow was well-preserved. In the mature hearts, myocardial infarction in the ischemic preconditioned hearts (14.9 ± 1.3%) and in the control hearts (1.0 ± 0.3%) was significantly decreased (p<0.01) compared to that of the global ischemic hearts (32.9 ± 5.1%). In the aged hearts, myocardial infarction in the ischemic preconditioned hearts (18.9 ± 2.7%) and in the control hearts (1.1 ± 0.6%) was significantly decreased (p<0.001) compared to that of the global ischemic hearts (37.6 ± 3.7%). The relationship between infarct size and post-ischemic functional recovery of left ventricularpeak developed pressure (LVDP) was linear and the correlation negative, with r=?0.934 (p<0.001) and ?0.875 (p<0.001) for mature and aged hearts respectively. The data suggest that, in the senescent myocardium, the cellular pathways involved ischemic preconditioning responses that were post-ischemic, and that functional recovery was worse as compared to that of the mature myocardium. Furthermore, the effects of post-ischemic functional recovery became consistently weaker during the control period of 120 min. reperfusion after a prolonged ischemic insult in a buffer perfused isolated rabbit model. However, the effects of infarct size limitation were well-preserved in both senescent and mature myocardia.     

Mechanisms Underlying Myocardial Stunning

Abstract The effect of myocardial stunning on mitochondrial function was examined in rabbit hearts. After global normothermic ischemia followed by reperfusion, we previously found that mitochondrial high energy phosphate content was not significantly diminished. To determine whether myocardial stunning results from altered excitation-contraction coupling, we examined function and calcium uptake by sarcoplasmic reticulum (SR). Hearts were subjected to global ischemia under normothermic conditions. Ischemic hearts had significantly lower velocity of Ca² + uptake by the SR (V_max36.3 ± 1.94 nmol/min per mg vs 49.3 ± 2.54 nmol/min per mg control) but velocity was restored by reperfusion. Similarly, myocardial ATP content was decreased during ischemia (4.5 ± 1.23 μmol/g dry weight vs 13.6 ± 0.98 μmol/g control) but returned to normal during reperfusion. Incubation of homogenates with 610 μM ryanodine did not alter the difference in V_maxbetween control, ischemic, or reperfused hearts, suggesting that ischemia affects SR Ca² + pumping without affecting Ca² + release. Recovery of calcium uptake during reperfusion also indicates that SR Ca² + ATPase function is not the major cause of myocardial stunning. Potentiated contractions were studied in a Langendorff heart model, revealing that postrest potentiation (PRP) and peak paired-pulse potentiation (PPP) increase as a result of ischemia. On reperfusion, PPP also increased, but there was a decrease in PRP of left ventricular pressure (LVP) and LV dP/dt (PRP LV dP/dt = 127% preischemia vs 112% at 2 min postischemia), indicating than an impairment of an SR function other than Ca² + ATPase occurs during myocardial stunning.     

Anti-CD18 Attenuates Myocardial Stunning in the Isolated Neonatal Lamb Heart

Abstract Cardiac surgery for congenital heart disease often results in postoperative depression of myocardial function due to myocardial ischemia and stunning. The Boston Circulatory Arrest study indicated that myocardial stunning is also observed postoperatively in the immature heart. Neonates less than 3 months of age (N = 162) experienced cardiac outputs that averaged 20% of baseline values in spite of myocardium protection with Plegisol cardioplegia. In order to minimize the effects of myocardial stunning on the immature heart, we examined the effects of preischemic administration of monoclonal antibodies to leukocyte adhesion molecule CD18 (monoclonal R15.7 [Boehringer-lngelheim]) on the function of blood perfused neonatal lamb hearts. Hearts were arrested for 2 hours with a 15°C K⁺ cardioplegia solution. Antibody treated hearts (N = 9) had significantly better (p < 0.05) recovery of left ventricular (LV) developed pressure (83.9% ± 2.2% vs 73.6% ± 3.0% for controls), LV dP/dt (78.4% ± 3.3% vs 67.4% ± 3.4% for controls), coronary blood flow (159.5% ± 12.2% vs 84.4% ± 3.5% for controls), and myocardial oxygen consumption (129.8% ± 16.5% vs 71.2% ± 6.2% for controls) than controls. In addition, recovery of coronary vascular resistance in response to 10^?6 M acetylcholine was significantly better (p = 0.08) in antibody treated hearts (38.4% ± 4.3%) than in control hearts (13.4% ± 12.8%). These results support the notions that leukocyte adherence to the endothelium contributes to reperfusion injury after ischemia and that monoclonal antibodies to CD18 may reduce the effects of myocardial stunning after cardiac surgery.     

Assessment of Intra‐Aortic Counterpulsation in an Animal Model of Heart Failure and Myocardial Ischemia

The effectiveness of intra‐aortic balloon pumping (IABP) is currently evaluated using indirect indexes. The diastolic pressure augmentation is quantified using the subendocardial viability ratio (SEVR) and the DABAC/SABAC index (areas beneath the aortic pressure–time signals during the diastolic and systolic periods, respectively). The SEVR requires invasive recordings of left ventricular pressure; the DABAC/SABAC index may represent an alternative, since it only requires an aortic pressure signal. Nonetheless, it has never been used in an animal model of counterpulsated heart failure and ischemia‐reperfusion episode. The aims of this work were: (i) to develop an animal model of heart failure, with a myocardial ischemia‐reperfusion episode, treated with IABP during the reperfusion period; (ii) to evaluate the effects of the IABP using the SEVR and DABAC/SABAC indices; and (iii) to assess the relationship between both ratios. Cardiovascular parameters were obtained in anesthetized sheep, in which induced heart failure and ischemia‐reperfusion episodes were monitored with and without IABP 1:2. Systolic and diastolic blood pressure signals were assessed in the aorta and in the left ventricle. Values of cardiac output and left ventricular wall thickness signals were obtained. Induction of ischemia and heart failure determined decreases in SEVR and DABAC/SABAC indices with respect to their basal stage (0.807 ± 0.118 vs. 0.601 ± 0.107, P < 0.05 and 1.062 ± 0.136 vs. 0.902 ± 0.161, P < 0.05, respectively). Counterpulsated animals whose myocardial reperfusion was accompanied by heart failure showed a significant improvement of wall thickening fraction along time (R² = 0.7627, P < 0.001). During counterpulsated heart failure accompanied by myocardial reperfusion, the SEVR was positively correlated with DABAC/SABAC index.     

Blood cardioplegic protection in profoundly damaged hearts: role of Na+-H+ exchange inhibition during pretreatment or during controlled reperfusion supplementation

BACKGROUND: Inhibition of the Na+/H+ exchanger before ischemia protects against ischemia-reperfusion injury, but use as pretreatment before blood cardioplegic protection or as a supplement to controlled blood cardioplegic reperfusion was not previously tested in jeopardized hearts. METHODS: Control studies tested the safety of glutamate-aspartate-enriched blood cardioplegic solution in 4 Yorkshire-Duroc pigs undergoing 30 minutes of aortic clamping without prior unprotected ischemia. Twenty-four pigs underwent 30 minutes of unprotected normothermic global ischemia to create a jeopardized heart. Six of these hearts received normal blood reperfusion, and the other 18 jeopardized hearts underwent 30 more minutes of aortic clamping with cardioplegic protection. In 12 of these, the Na+/H+ exchanger inhibitor cariporide was used as intravenous pretreatment (n = 6) or added to the cardioplegic reperfusate (n = 6). RESULTS: Complete functional, biochemical, and endothelial recovery occurred after 30 minutes of blood cardioplegic arrest without preceding unprotected ischemia. Thirty minutes of normothermic ischemia and normal blood reperfusion produced 33% mortality and severe left ventricular dysfunction in survivors (preload recruitable stroke work, 23% +/- 6% of baseline levels), with raised creatine kinase MB, conjugated dienes, endothelin-1, myeloperoxidase activity, and extensive myocardial edema. Blood cardioplegia was functionally protective, despite adding 30 more minutes of ischemia; there was no mortality, and left ventricular function improved (preload recruitable stroke work, 58% +/- 21%, p < 0.05 versus normal blood reperfusion), but adverse biochemical and endothelial variables did not change. In contrast, Na+/H+ exchanger inhibition as either pretreatment or added during cardioplegic reperfusion improved myocardial recovery (preload recruitable stroke work, 88% +/- 9% and 80% +/- 7%, respectively, p < 0.05 versus without cariporide) and comparably restored injury variables. CONCLUSIONS: Na+/H+ exchanger blockage as either pretreatment or during blood cardioplegic reperfusion comparably delays functional, biochemical, and endothelial injury in jeopardized hearts.     

Bilirubin rinse of the graft ameliorates ischemia reperfusion injury in heart transplantation

Ischemia and reperfusion contribute to substantial organ damage in transplantation. Clinically feasible measures for the prevention thereof are scarce. We tested whether rinsing rodent hearts with the antioxidant bilirubin ameliorates ischemia reperfusion injury (IRI). Left ventricular end‐diastolic pressure (LVEDP), left ventricular developed pressure (LVDevP), rate per pressure product (RPP), coronary flow, maximum (+dP/dt) and minimum (?dP/dt) rate of contraction were analyzed in Lewis rat hearts rinsed with bilirubin prior to reperfusion on a Langendorff apparatus after 12 h of cold ischemia. In vivo, isogenic C57Bl/6 mouse hearts rinsed with bilirubin were transplanted after 12 h of cold ischemia. Cardiac function and apoptosis were assessed 24 h after reperfusion. Heart lysates recovered 15 min after reperfusion were probed for the total and the phosphorylated forms of extracellular signal‐related protein kinases (ERK), JNK, p38‐MAPK, and Akt. In isolated perfused hearts, bilirubin rinse resulted in significantly lower LVEDP and improved LVDevP, RPP, coronary flow, +dP/dt and ?dP/dt. In vivo, after reperfusion, all mitogen‐activated protein kinases (MAPKs) were suppressed significantly by bilirubin pretreatment. Bilirubin rinse improved cardiac scores (3.4 ± 0.5 vs. 2.0 ± 1.0 in controls, P < 0.05) and significantly suppressed apoptosis. Ex vivo administration of bilirubin to heart grafts prior reperfusion ameliorates IRI and provides a simple and effective tool to ameliorate outcome in heart transplantation.     

The effect of controlled reperfusion in porcine hearts submitted to three hours of cold global ischemia

At present, many investigations of myocardial function following ischemic insults concentrate on the modalities of reperfusion rather than on the mode of preservation. In this study, we tried to define the effect of reperfusion using warm blood cardioplegia (WBC) after medium-term (3 h) cold global ischemia, as required in cardiac transplantation. Twenty-one porcine hearts were harvested after preservation with cold cardioplegia (St. Thomas Hospital solution) and topical cooling. Normothermic reperfusion with blood was initiated after 3 h of ischemia utilizing a special extracorporeal pump circuit. Twelve hearts served as controls (group A), while substrate-enriched WBC was applied during the initial 20 min of reperfusion in nine hearts (group B). Hearts in both groups were then studied for myocardial function and metabolism under both working and nonworking conditions for a maximum of 180 min. In the nonworking mode, left ventricular dp/dt was significantly higher in group B than in group A at 15 min (2201±785 mm Hg/sec vs 1515±732 mm Hg/sec) and at 180 min (1730±471 mm Hg/sec vs 836±147 mm Hg/sec;P<0.05). After 3 h, lactate production was significantly higher in group A (371±45 mg/dl) than in group B (108±44 mg/dl;P<0.05). Creatine kinase release into the coronary sinus was also significantly elevated in group A at 15 min (2807±1478 IU/l vs 1148±1272 IU/l;P<0.05). Similarly, the hemodynamic data obtained under working conditions in group B were superior to those in group A. We conclude that following 3 h of cold global ischemia, reperfusion with WBC improves myocardial function and metabolism. Cautious application in clinical heart transplantation is recommended.     

Xenon and isoflurane improved biventricular function during right ventricular ischemia and reperfusion

Background: Although anesthetics have some cardioprotective properties, these benefits are often counterbalanced by their negative inotropic effects. Xenon, on the other hand, does not influence myocardial contractility. Thus, xenon may be a superior treatment for the maintenance of global hemodynamics, especially during right ventricular ischemia, which is generally characterized by a high acute complication rate. Methods: The effects of 70 vol% xenon and 0.9 vol% isoflurane on biventricular function were assessed in a porcine model (n=36) using the conductance catheter technique, and the expression of the type B natriuretic peptide (BNP) gene was measured. The animals underwent 90 min of right ventricular ischemia followed by 120 min of reperfusion. A barbiturate‐anesthetized group was included as a control. Results: Cardiac output was compromised in unprotected animals during ischemia by 33±18% and during reperfusion by 53±17%. This was mainly due to impaired contractility in the left ventricle (LV) and increased stiffness. Isoflurane attenuated the increase in stiffness and resulted in a higher preload. In contrast, xenon increased the right ventricular afterload, which was compensated by an increase in contractility. Its effects on diastolic function were less pronounced. Upregulation of BNP mRNA expression was impeded in the remote area of the LV by both isoflurane and xenon. Conclusions: Xenon and isoflurane demonstrated equipotent effects in preventing the hemodynamic compromise that is induced by right ventricular ischemia and reperfusion, although they acted through somewhat differential inotropic and vasodilatory effects.     

Atrial natriuretic peptide protects against ischemia-reperfusion injury in the isolated rat heart

BACKGROUND: Atrial natriuretic peptide (ANP), a stimulator of particulate guanylate cyclase, has been found to protect against reoxygenation-induced hypercontracture in isolated cardiomyocytes by increasing cyclic guanosine monophosphate synthesis. The purpose of this study was to investigate the cardioprotective effects of ANP against ischemia-reperfusion injury in isolated rat hearts. METHODS: Twenty-four hearts were perfused with ANP at 0.01, 0.1, and 1 micromol/L or without ANP (n = 6 each) in normoxic conditions. Because 0.1 micromol/L ANP induced a threefold increase in cyclic guanosine monophosphate release into the coronary effluent without any effect on cardiac function, we used the 0.1 micromol/L ANP dose for ischemia-reperfusion studies. Eighteen hearts were subjected to 15 minutes of normothermic global ischemia followed by 15 minutes of reperfusion. The hearts were divided into three groups (n = 6 each). RESULTS: In group 1, ANP was added before ischemia. In group 2, ANP was added to the reperfusate. Hearts were untreated in the control group.In group 1, the postischemic recovery of cardiac output, coronary flow, and cyclic guanosine monophosphate release was similar to the control group. In group 2, the recovery of cardiac output was significantly better than the control group (82.1% +/- 9.8% vs 61.8% +/- 6.8%, respectively, p < 0.01) with a similar trend to recovery of coronary flow (90.7% +/- 8.5% vs 79.3% +/- 11.8%, respectively). The improved cardiac function was closely related to a significant increase in postischemic cyclic guanosine monophosphate release. CONCLUSIONS: Administration of ANP at the time of reperfusion protects the myocardium from ischemia-reperfusion injury. The concentrations of administration must not only increase the release of cyclic guanosine monophosphate release, but also lack negative inotropic effects.     

The effect and pharmacokinetics of nafamostat mesilate adjunct to cold nondepolarizing cardioplegia in a canine model of cardiac preservation

We examined the effects of nafamostat mesilate (NM) on myocardial, biochemical, and functional changes in canine hearts. An isolated heart was preserved for 6 h at 5°C and then reperfused for 2 h at 37°C. NM was added to the cardioplegic solution. At concentrations of both 10^-7 M (n=8) and 10^-6 M (n=6), NM was able to maintain myocardial cyclic adenosine monophosphate (cAMP) at a normal level and to reduce guanosine monophosphate (cGMP) concentrations at the end of both preservation and reperfusion. The serum N-acetyl-b-D-glucosaminidase (NAG) concentration during reperfusion was lower in hearts treated with NM 10^-6 or 10^-7 M than in those without NM (P<0.05). Although NM failed to preserve myocardial concentrations of adenine nucleotide compounds, NM 10^-7 M maintained the ± dp/dt of the left ventricle after reperfusion at the same level as in the nonischemic control group and better than NM 10^-6 M or no NM (P<0.05). Myocardial uptake of NM 10^-5 M (higher concentration) was 55%±8% (6-h preservation) and 29%±15% (2-h reperfusion). We conclude that NM 10^-7 M adjunct to nondepolarizng solution does not preserve myocardial adenine nucleotide concentrations but does facilitate the recovery of left ventricular function. NM 10^-5 M (higher concentration) seems to have a high affinity for the myocardium and may depress the recovery of left ventricular function.     

Sevoflurane improves myocardial ischaemic tolerance in a closed‐chest porcine model

Aims: Volatile anaesthetics prevent experimental myocardial ischaemia–reperfusion injury (I/R) in several species, but this finding is partially inconsistent with clinical evidence. Some experimental models may not accurately represent the complex signal transduction pathways triggered by volatile anaesthetics. We therefore investigated sevoflurane I/R prevention in vivo in a porcine model with greater likeness to human physiology than models previously used and compared it with neutral anaesthetic. Methods and results: Myocardial infarct size [IS/AAR] was compared in three groups of pigs (N=35) randomised to Control anaesthesia (pentobarbital infusion, n=12), sevoflurane inhalation alone (end‐tidal concentration 3.2%) (Sevo, n=9), or both Combined (n=14), throughout ischaemia and reperfusion. Anterior/septal myocardial infarcts resulted from distal LAD coronary artery occlusion by balloon catheter for 45 min followed by 120 min of reperfusion. [IS/AAR] was measured in tetrazolium‐stained heart slices after standardised image processing with computer‐assisted planimetry. Measurements included full invasive monitoring. Control animals developed infarction in 55.0±3.9% (SEM) of the area at risk, Sevo in 17.5±4.4% (P=0.0002), and Combined with pentobarbital in 24.3±3.8% (P=0.0001) of the AAR, sevoflurane reducing infarct size significantly (68% and 60%, respectively). Conclusions: Sevoflurane markedly decreased myocardial infarct size after prolonged coronary occlusion in a porcine model. In addition to novel sevoflurane cardioprotection in the closed‐chest model, which is more comparable to normal human hearts than models previously used, sevoflurane cardioprotection is substantiated in the juvenile intact organism. The perspectives underline recommending volatile anaesthetics in risk patients and in cardiac surgery.     

Post‐conditioning with cyclosporine A fails to reduce the infarct size in an in vivo porcine model

Background: Cyclosporine A has generated intense interest in the field of cardioprotection due to its ability to protect the mitochondria at reperfusion by blocking the opening of the mitochondrial permeability transition pore. The aim of our study was to examine the cardioprotective effect of Sandimmun^®, a clinically available formulation of cyclosporine A, in an in vivo large mammal model. Methods: Forty‐eight pigs were randomly allocated to one of three groups: (i) Control group (Con, n=19), (ii) Cyclosporine group, (Cyclo, n=19) Sandimmun^® 10 mg/kg i.v. bolus 5 min before reperfusion and (iii) Pre‐conditioning group (Precon, n=10) two cycles of 10 min ischemia interspersed with 30‐min reperfusion. The study was further sub‐divided into a metabolic protocol, evaluating myocardial metabolism by measuring changes in the interstitial lactate concentration, and a coronary flow protocol. All animals were subjected to 40 min of left anterior descending coronary artery occlusion, followed by 180 min of reperfusion before histochemical staining and assessment of infarct size by planimetry. Results: Infarct sizes were measured as: Con 51.4 ± 16.5%, Cyclo 47.3 ± 15.7% and Precon 2.4 ± 3.6%, with no significant difference between the Con and Cyclo groups but a highly significant difference between the Precon and Cyclo and Con groups (P<0.0001 for both comparisons). In the Cyclo group, the interstitial lactate concentration was significantly increased compared with the Con group at 6‐min reperfusion, although significantly lower at 14 min presumably due to accelerated washout. Conclusion: In this large animal model, a 10 mg/kg bolus administration of Sandimmun^® 5 min before reperfusion did not reduce the infarct size.