Effects of angiotensin-converting enzyme inhibitor during warm blood cardioplegia

BACKGROUND: Effects of captopril, an angiotensin-converting enzyme inhibitor, during warm blood cardioplegia were assessed in the blood-perfused, isolated rat heart. METHODS: The isolated hearts were arrested for 60 minutes with warm blood cardioplegia given at 20-minute intervals and were reperfused for 60 minutes. The control group (n = 10) received standard cardioplegia and the captopril group (n = 10) received cardioplegia supplemented with captopril (2 mmol/L). Cardiac function, myocardial metabolism, and cardiac release of circulating adhesion molecules were assessed before and after cardioplegic arrest. RESULTS: Left ventricular end-diastolic pressure and -dp/dt were significantly (p<0.05) lower and coronary blood flow was significantly (p<0.05) greater in the captopril group than the control group during reperfusion. The captopril group resulted in significantly (p<0.05) less cardiac release of lactate, thiobarbituric acid reactive substances during reperfusion. Cardiac release of intercellular adhesion molecule-1 was significantly (p<0.05) less in the captopril group at 60 minutes of reperfusion. CONCLUSIONS: The results suggest that supplementation of captopril during warm blood cardioplegia provides superior myocardial protection by suppressing lipid peroxidation and leukocyte-endothelial cell interaction during reperfusion.     

Safety of prolonged aortic clamping with blood cardioplegia. III. Aspartate enrichment of glutamate-blood cardioplegia in energy-depleted hearts after ischemic and reperfusion injury

This study tests the hypothesis that aspartate enrichment of glutamate-blood cardioplegia improves metabolic and functional recovery after ischemic and reperfusion damage. Ischemic and reperfusion damage were produced in 15 dogs by 45 minutes of aortic clamping at 37 degrees C and 5 minutes of blood reperfusion, before 2 more hours of aortic clamping (simulated operation). Six received multidose blood cardioplegia at 4 degrees C. In nine others, the cardioplegic solution was infused at 37 degrees C for the first 5 minutes, followed by multidose infusions at 4 degrees C. Four received 26 mmol glutamate-enriched cardioplegic solution. In five, the glutamate (13 mmol) cardioplegic solution was enriched with aspartate (13 mmol). Oxygen uptake and ventricular function (stroke work index, left atrial pressure) were measured. These data suggest aspartate enrichment produced the highest oxygen uptake (32 +/- 4 versus 17 +/- 2 ml/100 gm for glutamate and 7 +/- 1 ml/100 gm for 4 degrees C blood cardioplegia). Complete functional recovery occurred in aspartate/glutamate-treated hearts (stroke work index 90% +/- 4%, left atrial pressure 12 +/- 2 mm Hg), whereas recovery was incomplete with both glutamate alone (stroke work index 66% +/- 14%, left atrial pressure 20 +/- 3 mm Hg) and 4 degrees C blood cardioplegia at low cardiac outputs. Eight of 10 hearts not receiving aspartate failed at high cardiac outputs. Aspartate enrichment of glutamate-blood cardioplegia improves recovery after severe ischemic/reperfusion damage by improving oxidative metabolism during cardioplegic infusion and during postischemic work.     

L-Arginine given after ischaemic preconditioning can enhance cardioprotection in isolated rat hearts.

OBJECTIVE: Ischaemic or pharmacological preconditioning with L-arginine has been reported to be insufficient for optimal cardioprotection. The ability of nitric oxide (NO) to enhance ischaemic preconditioning was assessed, and the role of L-arginine-induced ischaemic preconditioning in myocardial protection was determined. METHODS: Isolated rat hearts were prepared and divided into six groups: control hearts (control, n=6) were perfused without global ischaemia at 37 degrees C for 160 min; global ischaemia hearts (GI, n=6) were subjected to ischaemia for 20 min and reperfusion for 120 min; ischaemic preconditioned hearts (IP, n=6) received 2 min of zero-flow global ischaemia followed by 5 min reperfusion, before 20 min of global ischaemia; L-arginine hearts (ARG, n=6) received 1 mmol/l L-arginine for 5 min, before 20 min of global ischaemia; ischaemic preconditioning plus nitro-L-arginine methyl ester hearts (IP+L-NAME, n=6) received 2 min of ischaemic preconditioning and 5 min reperfusion with 3 mmol/l L-NAME in Krebs-Henseleit buffer, before 20 min of global ischaemia; and ischaemic preconditioning plus L-arginine hearts (IP+ARG, n=6) received 2 min of ischaemic preconditioning and 5 min reperfusion with 1 mmol/l L-arginine in Krebs-Henseleit buffer. Haemodynamic parameters and coronary flow were recorded continuously. Nitrites and nitrates (NOx) were measured 5 and 60 min after reperfusion, and infarct size was also determined. RESULTS: In the IP+ARG group, significant amelioration and preservation of left ventricular peak developed pressure and coronary flow was observed compared with the GI, IP, ARG and IP+L-NAME groups. Infarct size in the IP+ARG group was reduced significantly compared with that in the GI, IP, ARG and IP+L-NAME groups. Significant preservation of NOx was observed during reperfusion in the IP+ARG group compared with the GI group. CONCLUSIONS: Inhibition of NO synthase with L-NAME had little impact on ischaemic preconditioning, suggesting that endogenous NO is not a major mediator of ischaemic preconditioning. Nevertheless, enhancement of the effects of ischaemic preconditioning can be achieved with L-arginine, a precursor of NO, improving post-ischaemic functional recovery and infarct size in the isolated rat heart.     

Experimental evaluation of myocardial protective effect of prostacyclin analog (OP-41483) as an adjunct to cardioplegic solution

A stable prostacyclin analog (OP-41483) was evaluated for myocardial protective effect against global ischemia with the use of cardioplegia. Isolated canine hearts (n = 25) were exposed to 60 minutes of warm (37 degrees C) global ischemia after the arrest by crystalloid cardioplegia. Prostaglandin analog was given in three different ways: preadministration (700 ng/kg body weight per minute) before ischemia for 30 minutes (group I, n = 5), given as a component of cardioplegic solution (600 ng/ml, group II, n, = 6), and post-administration (25 ng/kg body weight per minute) during reperfusion for 30 minutes (group III, n = 7). During reperfusion, coronary sinus blood flow, 6-keto-prostaglandin F1 alpha in coronary sinus blood, and myocardial oxygen consumption were measured during reperfusion. As a result, groups II and III showed significantly better global left ventricular function (developed pressure, maximum dP/dt, and diastolic compliance) than the control group (without prostaglandin analog, n = 7) and group I. Myocardial oxygen consumption at reperfusion (1 minute) was significantly larger in group II than in the control group. 6-keto-prostaglandin F1 alpha flux was significantly larger in group II than in the other three groups during reperfusion. The results indicated that prostaglandin analog has a beneficial effect on myocardial protection under global ischemia with cardioplegia, particularly when used as a component of cardioplegic solution and also during reperfusion. The mechanism may relate to the cytoprotective effect (including protection of endothelium with enhanced endogenous prostacyclin production at reperfusion and also to the modulation of reperfusion per se.     

Protectant activity of defibrotide in cardioplegia followed by ischemia/reperfusion injury in the isolated rat heart

BACKGROUND: Previous studies have shown that defibrotide, a polydeoxyribonucleotide obtained by depolymerization of DNA from porcine tissues, has important protective effects on myocardial ischemia, which may be associated with a prostacyclin-related mechanism. The purpose of this study was to investigate the direct effects of defibrotide (given in cardioplegia or after ischemia) on a model of rat heart recovery after cardioplegia followed by ischemia/reperfusion injury. METHODS: Isolated rat hearts, undergoing 5 minutes of warm cardioplegic arrest followed by 20 minutes of global ischemia and 30 minutes of reperfusion, were studied using the modified Langendorff model. The cardioplegia consisted of St. Thomas' Hospital solution augmented with defibrotide (50, 100, and 200 microg/mL) or without defibrotide (controls). Left ventricular mechanical function and the levels of creatine kinase, lactate dehydrogenase, and 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha; the stable metabolite of prostacyclin) were measured during preischemic and reperfusion periods. RESULTS: After global ischemia, hearts receiving defibrotide in the cardioplegic solution (n = 8) manifested in a concentration-dependent fashion lower left ventricular end-diastolic pressure (p < 0.001), higher left ventricular developed pressure (p < 0.01), and lower coronary perfusion pressure (p < 0.001) compared to the control group. After reperfusion, hearts receiving defibrotide in the cardioplegic solution also had, in a dose-dependent way, lower levels of creatine-kinase (p < 0.01), lactate dehydrogenase (p < 0.001), and higher levels of 6-keto-PGF1alpha (p < 0.001) compared to the control group. Furthermore, when defibrotide was given alone to the hearts at the beginning of reperfusion (n = 7), the recovery of postischemic left ventricular function was inferior (p < 0.05) to that obtained when defibrotide was given in cardioplegia. CONCLUSIONS: Defibrotide confers to conventional crystalloid cardioplegia a potent concentration-dependent protective effect on the recovery of isolated rat heart undergoing ischemia/reperfusion injury. The low cost and the absence of contraindications (cardiac toxicity and hemodynamic effects) make defibrotide a promising augmentation to cardioplegia.     

Terminal Warm Blood Cardioplegia Improves Cardiac Function Through Microtubule Repolymerization

Background. To elucidate the mechanisms responsible for the beneficial effects of terminal warm blood cardioplegia, we studied dynamic change in microtubules induced by cold cardioplegia followed by rewarming. Further, we investigated the relationship between cardiac function and morphologic changes in microtubules caused by hyperkalemic, hypocalcemic warm cardioplegia during initial reperfusion.

Methods. In protocol 1 isolated rat hearts were perfused at 37°C with Krebs-Henseleit buffer (KHB). After 3 hours of hypothermic cardiac arrest at 10°C, hearts were reperfused at 37°C with one of two buffers: group C, 60-minute reperfusion with KHB (K⁺, 5.9 mmol/L; Ca²⁺, 2.5 mmol/L); and group TC, 10-minute initial reperfusion with modified KHB (K⁺, 15 mmol/L; Ca²⁺, 0.25 mmol/L), followed by 50 minutes of reperfusion with KHB. Cardiac function after reperfusion was determined as a percentage of the prearrest value. In protocol 2 hearts were perfused at 37°C with KHB containing colchicine (10⁻⁵ mol/L) for 60 minutes.

Results. There was spontaneous contractile recovery after 10 minutes of initial reperfusion in hearts from group TC as well as improved cardiac function after 15, 30, and 60 minutes of reperfusion compared with that in group C. Immunohistochemical staining and immunoblot analysis demonstrated microtubule depolymerization during hypothermic cardiac arrest and complete repolymerization after 10 minutes of reperfusion with warm buffers in both groups. Colchicine-induced microtubule depolymerization is associated with deterioration of cardiac function.

Conclusions. One mechanism responsible for improved cardiac function mediated by terminal warm blood cardioplegia is the restart of contraction after complete microtubule repolymerization.     

Dose dependency of L-arginine in neonatal myocardial protection: the nitric oxide paradox.

OBJECTIVES: Recent experimental studies have suggested that enriching cardioplegic solution with L-arginine improves myocardial protection by increasing nitric oxide production. Nitric oxide, however, also generates the toxic oxygen-derived free radical peroxynitrite; thus these beneficial effects may be dose dependent, especially in vulnerable (stressed) hearts. METHODS: Fifteen neonatal piglets underwent 60 minutes of ventilator hypoxia (inspired oxygen fraction 8%-10%) followed by 20 minutes of normothermic ischemia on cardiopulmonary bypass (stress). They were then protected for 70 minutes with multiple doses of blood cardioplegic solution. In 5 (group 1), the cardioplegic solution contained no L-arginine, in 5 (group 2), it was enriched with a 4 mmol/L concentration of L-arginine, and in 5 (group 3), a 10 mmol/L concentration of L-arginine. Myocardial function was assessed by means of pressure volume loops and expressed as a percentage of control, and coronary vascular resistance and conjugated diene production were measured during infusions of cardioplegic solution. RESULTS: Compared with the protection afforded by blood cardioplegic solution without L-arginine (group 1), the addition of a 4 mmol/L concentration of L-arginine (group 2) significantly improved myocardial protection, resulting in complete return of systolic function (end-systolic elastance 38% vs 100%; P <.001 vs 4 mmol/L L-arginine) and preload recruitable stroke work (40% vs 100%; P <. 001 vs 4 mmol/L L-arginine); minimal increase in diastolic stiffness (239% vs 158%; P <.001 vs 4 mmol/L L-arginine); and lower coronary vascular resistance, conjugated diene production, and myeloperoxidase activity (P <.001 vs 4 mmol/L L-arginine in each case). Conversely, supplementing the cardioplegic solution with a 10 mmol/L dose of L-arginine (group 3) negated these beneficial effects, resulting in depressed systolic function (end-systolic elastance 41% +/- 2%; P <.001 vs 4 mmol/L L-arginine) and preload recruitable stroke work (40% +/- 2%; P <.001 vs 4 mmol/L L-arginine); increased diastolic stiffness (246% +/- 7%; P <.001 vs 4 mmol/L L-arginine); and higher conjugated diene production, myeloperoxidase activity, and coronary vascular resistance (P <.001 vs 4 mmol/L L-arginine in each case). CONCLUSIONS: Enriching cardioplegic solution with a 4 mmol/L concentration of L-arginine significantly improves myocardial protection by reducing oxygen-derived free radical formation by white blood cells, thus preserving vascular and myocardial function. However, these beneficial effects are dose dependent because 10 mmol/L concentrations of L-arginine increase oxygen-derived free radical production, resulting in vascular and myocardial dysfunction.     

Nitric oxide-generating beta-adrenergic blocker nipradilol preserves postischemic cardiac function.

BACKGROUND: Preconditioning protects the heart from ischemic injury, but some of its effects are reversed by beta-adrenergic blockade. We hypothesize that because nitric oxide is known to precondition the heart, the nitric oxide-generating beta-blocker nipradilol may simultaneously precondition and provide clinically relevant beta-blockade. METHODS: Isolated, crystalloid-perfused rabbit hearts underwent 1 hour of left anterior descending coronary artery ischemia followed by 1 hour of reperfusion. Before ischemia, six hearts received nipradilol, six received the nitric oxide donor L-arginine, four hearts received the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester before L-arginine, nine underwent ischemic preconditioning, and six received beta-blockade by esmolol before ischemic preconditioning. Seven hearts received no pretreatment (control). Action potential duration and ventricular pressure were measured. Infarct size was determined at the end of reperfusion. RESULTS: Both L-arginine and ischemic preconditioning prolonged action potential duration significantly at 60 minutes of reperfusion. Compared with control, infarct size was reduced by ischemic preconditioning (26%+/-4% versus 49%+/-3%, IPC versus control; p<0.01), L-arginine (24%+/-2%; p<0.01 versus control), and nipradilol (24%+/-2%; p<0.01 versus control). Only nipradilol preserved peak developed pressure during reperfusion. CONCLUSIONS: Despite its properties as a beta-adrenergic blocking agent, nipradilol was able to precondition the heart, probably as a result of its ability to produce nitric oxide.     

L-arginine during long-term ischemia: effects on cardiac function, energetic metabolism and endothelial damage.

BACKGROUND: We have evaluated the addition of L-arginine, a precursor of nitric oxide, to a cardioplegic solution (named CRMBM) designed for long-term heart preservation. METHODS: Isolated isovolumic-perfused rat hearts (n = 22) were arrested with the CRMBM solution either with (Arg) or without L-arginine (2 mmol/L) (Arg group, n = 12, vs control group n = 10), submitted to 8 hours of cold storage (4 degrees C) in the solution, and then reperfused for 60 minutes at 37 degrees C. In 11 hearts, we evaluated the quality of cardiac preservation with P-31 magnetic resonance spectroscopy and the measure of function and cellular integrity. Endothelium-dependent and independent vasodilatations were measured in 11 other hearts, using 5-hydroxytryptamine and papaverine to assess endothelial and smooth muscle function. RESULTS: Adding L-arginine to the cardioplegic solution improved functional recovery during reflow, as shown by the rate pressure product (31% +/- 3% for control vs 47% +/- 3% for Arg, p = 0.003) together with higher coronary flow and diminished contracture. Purine release in coronary effluents during reperfusion was lower in the Arg group. During ischemia and reflow kinetics of intracellular pH and high-energy phosphates were similar in both groups. Coronary endothelium-dependent vasodilatation was similarly impaired in both groups, but smooth muscle was less altered with L-arginine. CONCLUSIONS: As an additive to the CRMBM cardioplegic solution, L-arginine provides a protective effect for long-term heart preservation. Our data do not show coronary endothelial protection as the prominent mechanism.     

Myocardial protection in the hypertrophied right ventricle.

Hypertrophied right ventricle presents a sensitive state that may not be adequately protected by modern cardioplegic methods. Cardiac metabolism, performance, and ultrastructure were measured in response to 1 hour of cardioplegic arrest in 15 pigs with right ventricular hypertrophy using intermittent hypothermic crystalloid, blood, and Flusol DA 20%-based cardioplegia. Reperfusion time was 1 hour. One hour after a 60-minute cross-clamp period, there were no differences in light microscopy. Total energy stores increased in 4 of 5 animals given blood cardioplegia compared with 1 of 5 for each of the other groups. Cardiac performance data also showed better results for animals treated with blood cardioplegia. After 30 minutes of reperfusion, animals receiving blood cardioplegia recovered 131% +/- 42% of preoperative systolic performance compared with 106% +/- 49% for Fluosol-treated animals and only 82% +/- 27% recovery for the crystalloid-treated group. After 60 minutes of reperfusion, the blood group showed 119% +/- 20% recovery compared with 89% +/- 23% and 85 +/- 50% recovery for Fluosol- and crystalloid-treated hearts, respectively. In conclusion, blood cardioplegia provided better protection than did crystalloid or Fluosol DA 20% cardioplegia when animals with right ventricular hypertrophy underwent 1 hour of cardioplegic arrest. It may have repaired damaged myocardium, leaving better hearts after cross-clamping than before.     

Overdose reperfusion of blood cardioplegic solution. A preventable cause of postischemic myocardial depression

Reperfusion of warm blood cardioplegic solution is useful in minimizing reperfusion damage after ischemia. This study tests the hypothesis that overzealous administration of blood cardioplegic solution at reperfusion counteracts these benefits and can lead to a prevalence of depressed ventricular performance and mortality similar to that seen after normal blood reperfusion. Thirty-one dogs underwent 45 minutes of 37 degrees C global ischemia on vented bypass. Six received normal blood reperfusion and 25 were reperfused with a warm aspartate/glutamate-enriched blood cardioplegic solution; of these, eight received high-dose (3600 +/- 600 ml) and 17 received limited-dose (1180 +/- 120 ml) blood cardioplegic reperfusion over 10 to 20 minutes. High-dose blood cardioplegic perfusion (5100 +/- 200 ml) without prior ischemia was tested in an additional five dogs. High-dose blood cardioplegia without preceding ischemia did not alter ventricular function (peak stroke work index 96% of control). After ischemia, normal blood reperfusion (no cardioplegia) resulted in marked left ventricular dysfunction (peak stroke work index 36% of control, p less than 0.05 versus control) and a 33% mortality rate (2/6 died). High-dose cardioplegic reperfusion yielded marginal recovery of stroke work index (40% of control, p less than 0.05 versus control) and a 25% mortality rate (2/8 died). In contrast, limited-dose reperfusion of blood cardioplegic solution allowed 100% survival (17/17) and restored stroke work index to 90% of control (1.3 versus 1.45 gm.m/kg). We conclude that reperfusion damage can be avoided by initial reoxygenation with limited doses of substrate-enriched blood cardioplegic solution. Conversely, high-dose reperfusion of blood cardioplegic solution offsets this benefit, reduces recovery substantially, and may be lethal.     

温血停搏液术终灌注对缺血再灌注心肌的保护作用

利用猫体外循环模型观察含甘露醇的温血停搏液术终灌注对缺血再灌注心肌的保护作用。心肌缺血恢复正常血液灌注前，从主动脉根部以５～６ｋＰａ的压力注入３７℃含甘露醇的低钾温血停搏液５０ｍｌ。结果显示用含甘露醇的温血停搏液术终灌注可保护缺血后再灌注心肌的功能，提高心肌能量储备，降低线粒体丙二醛含量。结论：含甘露醇的温血停搏液术终灌注，可提高心肌对氧自由基的清除能力，减轻线粒体膜脂质过氧化，提高心肌能量储备，有利于再灌注后心肌功能的恢复     

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.     

Effect of nitric oxide in ischemia/reperfusion of the pancreas

BACKGROUND: Ischemia/reperfusion injury, and thus graft pancreatitis, remains a major problem in pancreas transplantation. Contradictory results about the role of nitric oxide (NO) in pancreatic ischemia/reperfusion have been reported; however, in none of the reports has a detailed comparison between inhibition of NO synthase and NO supplementation been carried out. METHODS: Vascular isolation of the pancreatic tail was performed in landrace pigs. After splenectomy catheters placed in the distal part of the splenic vessels allowed collection of the venous effluent and perfusion of the pancreatic tail. Three hours of complete warm ischemia was followed by 6 h of reperfusion. The effect of the NO donor sodium nitroprusside (SNP) and L-arginine was compared to a control group and NO synthase inhibition with L-NAME. RESULTS: Lipase in the venous effluent of the pancreas was significantly decreased in the SNP and the L-arginine groups. Vascular resistance was markedly elevated in the L-NAME group and reduced in the NO donor groups. Tissue pO2 after reperfusion was only significantly elevated in the SNP group. Granulocyte infiltration and also overall histological tissue injury were most severe in the control group followed by the L-NAME group, the SNP group, and the L-ARG group. CONCLUSION: The data show that supplementation of nitric oxide is clearly protective in pancreatic ischemia/reperfusion. However, inhibition of NO synthesis does not lead to an equally clear aggravation of tissue injury.     

Oxygen-radical regulation of renal blood flow following suprarenal aortic clamping

OBJECTIVE: Renal insufficiency continues to be complication that can affect patients after treatment for suprarenal aneurysms and renal artery occlusive disease. One proposed mechanism of renal injury after suprarenal aortic clamping (above the superior mesenteric artery) and reperfusion (SMA-SRACR) is the loss of microvascular renal blood flow with subsequent loss of renal function. This study examines the hypothesis that the loss of medullary and cortical microvascular blood flow following SMA-SRACR is due to oxygen-derived free radical down-regulation of endogenous medullary and cortical nitric oxide synthesis. METHODS: Anesthetized male Sprague-Dawley rats (about 350 g) either had microdialysis probes or laser Doppler fibers inserted into the renal cortex (depth of 2 mm) and into the renal medulla (depth of 4 mm). Laser Doppler blood flow was continuously monitored. The microdialysis probes were connected to a syringe pump and perfused in vivo at 3 microL/min with lactated Ringer's solution. The animals were subjected to SMA-SRACR (or sham) for 30 minutes, followed by 60 minutes of reperfusion. Laser Doppler blood flow after the 30 minutes of SMA-SRACR followed by 60 minutes of reperfusion was compared with the time zero (basal) and with the corresponding sham group and reported as percent change compared with the time zero baseline. The microdialysis fluid was collected at time zero (basal) and compared with the dialysis fluid collected after 30 minutes of SMA-SRACR followed by 60 minutes of reperfusion as well as the corresponding sham group. The microdialysis dialysate was analyzed for total nitric oxide (microM) and prostaglandin E2 (PGE2), 6-keto-PGF(1alpha) (PGI2 metabolite), and thromboxane B2 synthesis. The data are reported as percent change compared with the baseline time zero. The laser Doppler blood flow and microdialysis groups were treated with either saline carrier, N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME) (30 mg/kg, nitric oxide synthesis inhibitor), L-arginine (400 mg/kg, nitric oxide precursor), superoxide dismutase (SOD, 10,000 U/kg, oxygen-derived free radical scavenger), L-NAME + SOD, or L-arginine + SOD. SOD was given 30 minutes before the reperfusion, and the other drugs were given 15 minutes before reperfusion. The renal cortex and medulla were separated and analyzed for inducible nitric oxide synthase (iNOS), cyclooxygenase-2, prostacyclin synthase, and PGE2 synthase content by Western blot. RESULTS: Superior mesenteric artery-SRACR caused a marked decrease in medullary and cortical blood flow with a concomitant decrease in endogenous medullary and cortical nitric oxide synthesis. These changes were further accentuated by L-NAME treatment but restored toward sham levels by L-arginine treatment after SMA-SRACR. The kidney appeared to compensate for these changes by increasing cortical and medullary PGE2 synthesis and release. SOD treatment restored renal cortical and medullary nitric oxide synthesis and blood flow in the ischemia-reperfusion group and in the ischemia-reperfusion group treated with L-NAME. CONCLUSIONS: These data show that nitric oxide is important in maintaining renal cortical and medullary blood flow and nitric oxide synthesis. These data also support the hypothesis that the loss of medullary and cortical microvascular blood flow following SRACR is due in part to oxygen-derived free radical downregulation of endogenous medullary and cortical nitric oxide synthesis.     

Studies of myocardial protection in the immature heart. V. Safety of prolonged aortic clamping with hypocalcemic glutamate/aspartate blood cardioplegia

This study tests the hypothesis that multidose, hypocalcemic aspartate/glutamate-enriched blood cardioplegia provides safe and effective protection during prolonged aortic clamping of immature hearts. Of 17 puppies (6 to 8 weeks of age, 3 to 5 kg) placed on vented cardiopulmonary bypass, five were subjected to 60 minutes of 37 degrees C global ischemia without cardioplegic protection and seven underwent 120 minutes of aortic clamping with 4 degrees C multidose aspartate/glutamate-enriched blood cardioplegia ([Ca++] = 0.2 mmol/L), preceded and followed by 37 degrees C blood cardioplegic induction and reperfusion. Five puppies underwent blood cardioplegic perfusion for 10 minutes without intervening ischemia to assess the effect of the cardioplegic solution and the delivery techniques. Left ventricular performance was assessed 30 minutes after bypass was discontinued (Starling function curves). Hearts were studied for high-energy phosphates and tissue amino acids. One hour of normothermic ischemia resulted in profound functional depression, with peak stroke work index only 43% of control (0.7 +/- 0.1 versus 1.7 +/- 0.2 gm x m/kg, p less than 0.05). There was 70% depletion of adenosine triphosphate (7.6 +/- 1 versus control 20.3 +/- 1 mumol/gm dry weight, p less than 0.05) and 75% glutamate loss (6.6 +/- 1 versus control 26.4 +/- 3 mumol/gm, p less than 0.05). In contrast, after 2 hours of aortic clamping with multidose blood cardioplegia preceded and followed by 37 degrees C blood cardioplegia, there was complete recovery of left ventricular function (peak stroke work index 1.6 +/- 0.2 gm x m/kg) and maintenance of adenosine triphosphates, glutamate, and aspartate levels at or above control levels adenosine triphosphate 18 +/- 2 mumol/gm, aspartate 21 +/- 1 versus control 2 mumol/gm, and glutamate 25.4 +/- 2 mumol/gm). Puppy hearts receiving blood cardioplegic perfusion without ischemia had complete recovery of control stroke work index. We conclude that methods of myocardial protection used in adults, with amino acid-enriched, reduced-calcium blood cardioplegia, can be applied safely to the neonatal heart and allow for complete functional and metabolic recovery after prolonged aortic clamping.     

Intraoperative myocardial protection: current trends and future perspectives

BACKGROUND: The results of contemporary coronary artery bypass graft surgery (CABG) are excellent. However, recently changing trends in the population at risk have necessitated new measures to minimize perioperative morbidity and mortality. METHODS: We reviewed cardioplegic innovations developed, evaluated, and currently employed at the Toronto Hospital. In addition, we conducted an evaluation of novel cardioplegic formulations, with an eye towards future clinical applications. RESULTS: At the Toronto Hospital, we demonstrated that blood provided better protection than crystalloid cardioplegia. Subsequently, we found that a terminal infusion of warm blood cardioplegia repleted myocardial adenosine triphosphate (ATP) levels and improved postoperative ventricular function. Recently, we reported that tepid (29 degrees C) cardioplegia reduced lactate and acid production during cardioplegic arrest, and improved postoperative ventricular function. Combining antegrade and retrograde cardioplegic delivery reduced lactate production, preserved ATP stores, and improved metabolic recovery after cross-clamp release. Cardioplegic flows of at least 200 mL/min were required to washout detrimental metabolic end-products and improve ventricular function. To further optimize myocardial protection, attempts have been made to harness the beneficial effects of ischemic preconditioning using adenosine. Similarly, insulin cardioplegia has been employed in order to enhance ventricular performance by stimulating early postoperative aerobic metabolism. Finally L-arginine, a nitric oxide donor has been demonstrated to be beneficial in experimental studies and may represent a further option for the enhancement of intraoperative myocardial protection. CONCLUSIONS: Despite continued improvements in cardioplegic techniques, low output syndrome following high-risk CABG remains an ongoing concern. The development of novel additives with various protective properties may provide added protection, allowing for a reduction morbidity and mortality following CABG.     

Orthotopic transplantation of pig hearts harvested after 30 min of normothermic ischemia: controlled reperfusion with blood cardioplegia containing the Na-H-exchange inhibitor HOE 642

Objectives: The aim of our study was to develop a surgical technique for a successful transplantation of hearts harvested after 30 min of normothermic ischemia without donor pretreatment. Successful transplantation of ischemic compromised hearts could help to expand the severely limited donor pool. We used the pig model because this species is very susceptible to myocardial ischemia. Na⁺-H⁺-exchange (NHE) inhibitors have shown excellent protective properties in several in vitro and in vivo models of myocardial ischemia and reperfusion. Methods: In group I (n=12) hearts were harvested after 30 min of normothermic ischemia following cardiac arrest induced by exsanguination. Hearts were perfused with warm blood cardioplegia and transplanted orthotopically. In group II (n=9) controlled reperfusion with cold leucocyte-depleted blood cardioplegia was performed after 30 min of normothermic ischemia. In group III (n=8) the same procedure was performed as in group II but blood cardioplegia contained 1 mmol/l HOE 642. Results: In group I massive myocardial oedema was observed and none of the animals could be weaned from cardiopulmonary bypass (CPB). In contrast, all animals in groups II and III could be weaned from CPB with low dose inotropic support. In groups II and III the contractility of the hearts, expressed as maximal left and right ventricular stroke work index was significantly impaired after transplantation as compared with the preoperative value. Supplementation of blood cardioplegia with HOE 642 resulted in a significantly better recovery of the LVSWImax (Group II vs. III). Conclusions: Successful transplantation of pig hearts is possible after 30 min of normothermic ischemia without donor pretreatment if a controlled reperfusion with cold leucocyte-depleted blood cardioplegia is performed. HOE 642 given during reperfusion only improves posttransplant left ventricular function.     

Controlled postcardioplegia reperfusion: mechanism for attenuation of reperfusion injury

OBJECTIVE: Controlled reperfusion and secondary cardioplegia are used to minimize reperfusion injury. The mechanisms for their benefit are incompletely defined and may include attenuation of myocyte sodium uptake. METHODS: Pigs had 1 hour of cardioplegic arrest followed by reperfusion with blood (control) or warm cardioplegic solution followed by blood (test). Reperfusion injury in the control and test groups was quantified by measuring changes of intramyocyte ion content with atomic absorption spectrometry and by analyzing electrophysiologic recovery from recordings of reperfusion arrhythmias. RESULTS: Control animals had an increase in intramyocyte sodium content at 5 minutes after initiating reperfusion (+20.2 micromol/g dry weight, P <.04), whereas the test group had an insignificant decrease (-14.0 micromol/g dry weight, P =.33). The first rhythm after initiating reperfusion was more often ventricular fibrillation in the control group (100% vs 50%, P <.02), and the control group required more defibrillations to establish a nonfibrillating rhythm (4.5 +/- 1.2 vs 1.1 +/- 0.3, P <.03). CONCLUSIONS: Controlled reperfusion eliminated the increase in intramyocyte sodium that was observed in the control group at 5 minutes after cardioplegic arrest. This improvement in myocyte ion homeostasis during postcardioplegia reperfusion was associated with fewer reperfusion arrhythmias. These data support the hypothesis that attenuation of myocyte sodium gain during postischemic reperfusion is a mechanism by which controlled reperfusion and secondary cardioplegia are beneficial.     

A comparison of blood and crystalloid cardioplegia during heart transplantation after 5 hours of cold storage

Four methods of protecting the heart during implantation were compared. All hearts were arrested in situ by perfusing 4 degrees C cardioplegic solution into the aortic root and were stored by a nonperfused cold storage technique for 5 hours at 4 degrees C. The hearts were then transplanted orthotopically with the use of topical iced slush alone or with infusions of either blood cardioplegic solution or one of two crystalloid cardioplegic solutions after each atrial anastomosis. Five dog hearts were included in each group. Biopsy samples to test for adenylates were taken before the arrest, at the end of storage, before cross-clamp removal, and 3.5 hours after cross-clamp removal. The dogs were removed from cardiopulmonary bypass, and with the chest open, left ventricular function curves were measured at 1, 2, and 3 hours after cross-clamp removal. At 3.5 hours of reperfusion time, a full-width section was obtained from the left ventricle for measurement of tissue sodium and water content. No differences in tissue water, sodium, or potassium content were found among the groups. Left ventricular function was significantly better in the blood cardioplegia group than in any other groups. Adenosine triphosphate levels were significantly reduced 3.5 hours after reperfusion in the crystalloid cardioplegia groups but were not significantly depressed at any other measurement time. Excellent early graft function was observed after crystalloid cardioplegic arrest and blood cardioplegic reperfusion during graft implantation.