Coronary venous lipid peroxide concentrations after coronary angioplasty: correlation with biochemical and electrocardiographic evidence of myocardial ischaemia

Myocardial ischemia-reperfusion injury; Molecular mechanisms and prevention

Cardiovascular diseases are one of the leading causes of mortality in developed countries. Among cardiovascular disorders, myocardial infarction remains a life-threatening problem predisposing to the development and progression of ischemic heart failure. Ischemia/reperfusion (I/R) injury is a critical cause of myocardial injury. In recent decades, many efforts have been made to find the molecular and cellular mechanisms underlying the development of myocardial I/R injury and post-ischemic remodeling. Some of these mechanisms are mitochondrial dysfunction, metabolic alterations, inflammation, high production of ROS, and autophagy deregulation. Despite continuous efforts, myocardial I/R injury remains a major challenge in medical treatments of thrombolytic therapy, heart disease, primary percutaneous coronary intervention, and coronary arterial bypass grafting. The development of effective therapeutic strategies to reduce or prevent myocardial I/R injury is of great clinical significance.

Oxidative Stress and Myocardial Damage during Elective Percutaneous Coronary Interventions and Coronary AngiographyA Comparison of Blood-borne Isoprostane and Troponin Release

The role of oxidative stress in clinical cardiology is still controversial. The aims of the present study were to examine if minor ischaemic episodes as may occur during elective percutaneous coronary intervention (PCI) induce oxidative stress and, eventually, if oxygen stress correlates with myocardial injury. Thirty eight and nine patients underwent PCI and diagnostic coronary angiography, respectively. Peripheral blood was sampled at different time points for plasma analyses of: 8-iso-PGF2alpha (free radical-mediated oxidative stress); 15-keto-dihydro-PGF2alpha (cyclooxygenase-mediated inflammation); troponin-T (myocardial injury); hsCRP, vitamin A and vitamin E; and, total antioxidants status (TAS). In both groups 8-iso-PGF2alpha increased transiently by approximately 80% (p < 0.001) during the procedure. There was a minor troponin-T release (p < 0.001) after PCI, but no correlation with 8-iso-PGF2alpha. Troponin-T did not increase after angiography. 15-keto-dihydro-PGF2alpha decreased by 50% after ended procedure, but increased by 100% after 24 h compared to baseline. hsCRP increased significantly (p < 0.001) from baseline to the next day in the PCI-group, but not in the angiography group. Vitamins and TAS decreased slightly after the procedures. It is concluded that a moderate oxidative stress was induced by both elective PCI and coronary angiography but that no correlation was found between oxidative stress and myocardial injury in this setting. This indicates that other mechanisms than ischaemia-reperfusion episodes caused an elevation in plasma isoprostane such like the injury at a vascular site mutual for both procedures. A secondary finding from the study was elevated markers of early inflammatory response, not only after PCI, but also after angiography.

Repeated Balloon Inflations Do Not Diminish ST Segment Elevation even though Coronary Collateral Recruitment Is Promoted in Pigs

OBJECTIVE

Attempts to demonstrate preconditioning during repeated angioplasty balloon inflations (BIs) have not been universally successful. The main obstacle is that the first BI is unreliable, due to the variable degrees of occlusion by the deflated balloon. In the present study, we examined whether ST segment elevation decreases and evaluated its relation to collateral recruitment during repeated angioplasty BIs in the pig.

METHODS AND RESULTS

Twenty male pigs, 7 months old, under general anesthesia, underwent 3 repeated BIs of 120 s, with a 5-min interval between them, in the left anterior descending artery or the right coronary artery. A pressure wave wire was used for the measurement of coronary wedge pressure and to obtain the intracoronary ST segment elevation. Intracoronary ST segment elevation was 1.97 +/- 0.76 mV during the 1st BI, 2.09 +/- 0.82 mV during the 2nd BI and 1.84 +/- 0.82 mV during the 3rd BI (p = n.s.). Coronary wedge pressure was 12 +/- 6, 18 +/- 18 and 20 +/- 20 mm Hg (p < 0.05 vs. 1st BI) during the 3 BIs, respectively.

CONCLUSION

Repeated BIs do not diminish ST segment elevation in the pig model, even though coronary collateral recruitment is promoted.

Effect of estrogen on coronary vasoconstriction in patients undergoing coronary angioplasty

BACKGROUND

Estrogen has an antioxidant potential which may contribute to its cardioprotective effect. We sought to determine whether estrogen administration can affect coronary vasomotor tone in patients after angioplasty by reducing 8-iso-prostaglandin (PG) F(2alpha) concentrations, a bioactive product of lipid peroxidation.

METHODS

The study was designed to prospectively investigate 30 consecutive patients scheduled for elective coronary angioplasty. Patients were randomized into two groups according to whether they did not (group 1, n = 15) or did have (group 2, n = 15) intracoronary (i.c.) treatment with estrogen prior to coronary angioplasty.

RESULTS

There were no significant differences of collateral circulation assessed by intracoronary Doppler flow velocity during balloon inflations between the study groups. The diameters of the coronary artery at the dilated and distal segments were significantly reduced 15 min after dilation compared with those immediately after dilation in group 1 (both P < 0.0001). The vasoconstriction was significantly blunted in group 2. The 8-iso-PGF(2alpha) levels in plasma from the coronary sinus rose significantly from 194 +/- 45 to 390 +/- 97 pg/ml (P < 0.0001, 95% confidence intervals = 142-249 pg/ml) 15 min after angioplasty in group 1, which was attenuated after administering estrogen. Significant correlation was found between the changes of coronary vasomotion of the dilated segment and 8-iso-PGF(2alpha) levels in group 1 (r = 0.73, P = 0.002).

CONCLUSIONS

8-iso-PGF(2alpha) is released into the coronary circulation during angioplasty, and this vasoactive substance may contribute to the occurrence of vasoconstriction. Estrogen administration attenuated vasoconstriction by reducing the 8-iso-PGF(2alpha) levels. This finding may provide a new strategy to treat coronary vasoconstriction after angioplasty.

Mitochondrial ATP-sensitive potassium channels in surgical cardioprotection

ATP-sensitive potassium channels allow for the coupling of membrane potential to cellular metabolic status. Two K(ATP) channel subtypes coexist in the myocardium with one subtype located in the sarcolemma membrane and the other in the inner membrane of the mitochondria. The ATP-sensitive potassium channels can be pharmacologically modulated by a family of structurally diverse agents of varied potency and selectivity, collectively known as potassium channel openers and blockers. Sufficient evidence exists to indicate that the ATP-sensitive potassium channels and in particular the mitochondrial ATP-sensitive potassium channels play an important role both as a trigger and an effector in surgical cardioprotection. In this review, the biochemistry and specificity of the ATP-sensitive potassium channels is examined in relation to surgical cardioprotection.

Elective coronary angioplasty with 60 s balloon inflation does not cause peroxidative injury

BACKGROUND

The aim of this study was to evaluate the ongoing controversial issue of whether ischemia/reperfusion during elective coronary angioplasty evokes myocardial peroxidative injury.

DESIGN

We measured indicators of free radical damage to lipids (free malondialdehyde) and proteins (sulphydryl groups) in coronary sinus blood in 19 patients with stable angina who were undergoing elective angioplasty for isolated stenosis of the proximal left anterior descending coronary artery. Ischemia induced by 60 s balloon inflations was confirmed by lactate washout into coronary sinus after deflation, with immediate and 1 min samples. Peroxidative injury was assessed from washout of (a) malondialdehyde measured directly by high performance liquid chromatography and (b) reduced sulphydryl groups, inverse marker of protein oxidative stress.

RESULTS

Mean lactate concentration immediately after each deflation increased by 120-150% of the initial value, confirming ischemia and showing that blood originated largely from the ischemic region. Lack of myocardial production of malondialdehyde was confirmed by (a) no arteriovenous differences in individual basal concentrations (aortic, range 0.33-12.03 nmol mL-1, mean 7.82; coronary sinus blood, range 0.52-15.82 nmol mL-1, mean 8.18), and (b) after deflations, mean concentrations were not significantly different from preocclusion value. There was no decrease in concentration of sulphydryl groups throughout angioplasty.

CONCLUSION

Elective coronary angioplasty with 60 s balloon inflations is a safe procedure that does not induce peroxidative myocardial injury as assessed by methods used in the present study.

Large, sustained cardiac lipid peroxidation and reduced antioxidant capacity in the coronary circulation after brief episodes of myocardial ischemia

OBJECTIVES

We sought to investigate whether a brief episode of myocardial ischemia produces a detectable cardiac oxidative stress in patients undergoing elective coronary angioplasty (PTCA).

BACKGROUND

Although cardiac oxidative stress has been clearly demonstrated in experimental models of ischemia-reperfusion, its presence in patients after transient myocardial ischemia is still unclear.

METHODS

In order to evaluate oxidative stress in ischemic cardiac regions, plasma conjugated dienes (CD), lipid hydroperoxides (ROOHs) and total antioxidant capacity (TRAP), independent indexes of oxidative stress, were measured in the aorta and great cardiac vein (GCV) before (t0), 1, (t1), 5 (t5) and 15 min (t15) after first balloon inflation in 15 patients undergoing PTCA on left anterior descending coronary artery (Group 1); six patients with right coronary artery stenosis (Group 2), which is not drained by the GCV, were studied as controls.

RESULTS

In Group 1 at baseline, CD and ROOHs levels were higher in GCV than in aorta (p < 0.01 for both), and TRAP levels were lower (p < 0.01). Aortic levels of CD, ROOHs and TRAP did not change at any time after to; venous levels of CD and ROOHs levels markedly increased at t1, at t5 and remained elevated at t15 (p < 0.01 for all comparisons vs. to); venous levels of TRAP decreased at t1 and t5 (p < 0.01 vs. t0) and returned to normal at t15. In Group 2, CD, ROOHs and TRAP levels were similar in the aorta and GCV and did not change throughout the study.

CONCLUSIONS

Short episodes of myocardial ischemia during PTCA induce a sustained oxidative stress, which is detectable in the venous effluent of reperfused myocardium.

Alternatives for myocardial protection: adenosine-enhanced ischemic preconditioning

Intrinsic to the development of new myoprotective protocols for use in cardiac surgery are the requirements of new protocols to be equal to or better than conventional cardioplegia in providing for enhanced post-ischemic functional recovery and decreased myocardial infarct size. Our data suggest that adenosine-enhanced ischemic preconditioning, in which a bolus injection of adenosine to the myocardium is used coincident with ischemic preconditioning, meets these requirements, providing equal cardioprotection as that of cold blood cardioplegia, significantly decreasing myocardial infarct size and significantly enhancing post-ischemic myocardial functional recovery in both the isolated perfused rabbit heart and in the in situ blood-perfused sheep heart. These results further suggest that adenosine-enhanced ischemic preconditioning may provide an effective, alternative myocardial protective protocol to reduce the morbidity and mortality in cardiac surgery.

Attenuation of severity of myocardial ischemia during repeated daily ischemic episodes

OBJECTIVES

The purpose of this study was to assess whether the severity of myocardial ischemia would be attenuated by repeated daily ischemic episodes, recorded by ambulatory electrocardiographic monitoring (AEM).

BACKGROUND

Repetitive ischemic episodes induced by brief coronary occlusions in animal experiments and in humans during balloon coronary angioplasty produce preconditioning. We wanted to assess whether this phenomenon also exists during daily ischemic episodes.

METHODS

Twenty-one patients with known coronary artery disease and ischemia on exercise testing and AEM were requested to walk a distance known to have previously caused myocardial ischemia on three consecutive occasions. Walking time was approximately 15 min and was followed by 5 min of rest.

RESULTS

Mean maximal heart rate during the three walks was similar; however, the mean maximal ST segment depression decreased significantly from 2.21 mm during the first walk to 1.61 mm and 1.43 mm, respectively, on the second and third walks (p = 0.001). Ischemia duration was also significantly reduced on the second and third walks by 56% from 514 to 228 and 254 s, respectively (p = 0.012). The heart rate at onset of ischemia (ischemic threshold) increased from 99 beats/min on the first walk to 101 beats/min on the second walk and to 106 beats/min on the third walk (p = 0.058).

CONCLUSIONS

This study demonstrated attenuation of myocardial ischemia with an associated increase in ischemic threshold in patients with repeated and adjacent ischemic episodes. This form of myocardial protection is likely to be encountered in patients during ordinary activity and may represent the clinical counterpart of myocardial preconditioning.

Release of glutathione from erythrocytes and other markers of oxidative stress in carbon monoxide poisoning

Rats exposed to CO in a manner known to cause oxidative stress in brain exhibited a twofold increase in plasma levels of oxidized proteins, thiobarbituric acid-reactive substances (TBARS), oxidized glutathione (GSSG), and reduced glutathione (GSH). Changes were neither directly related to hypoxic stress from carboxyhemoglobin nor significantly influenced by circulating platelets or neutrophils. Treatment with the nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester inhibited elevations in GSH and GSSG but not changes in oxidized proteins or TBARS, suggesting that two oxidative mechanisms may be operating in this model and that GSH and GSSG elevations involved nitric oxide-derived oxidants. Elevations of blood GSH and GSSG occurred at different anatomic sites, indicating that no single organ was the source of the increased peptides. Animals that underwent exchange transfusion with a hemoglobin-containing saline solution did not exhibit elevations in GSH and GSSG, suggesting that blood-borne cells released these peptides in response to oxidative stress. In in vitro studies, erythrocytes, but not platelets and leukocytes, responded to oxidative stress from peroxynitrite by releasing GSH, whereas no release was observed in response to nitric oxide or superoxide. Glucose, maltose, and cytochalasin B, agents that protect extracellular components of the hexose transport protein complex from oxidative stress, prevented GSH release. The data indicate that nitric oxide-derived oxidants are involved in CO-mediated oxidative stress within the vascular compartment and that elevations of several compounds may be useful for identifying exposures to CO likely to precipitate brain injury.

Effects of acute coronary occlusion and previous ischaemic injury on left ventricular wall motion in humans

OBJECTIVE

To assess the acute effects of single and repeated coronary artery occlusions, during percutaneous transluminal coronary angioplasty (PTCA), on left ventricular long axis function in patients with stable and unstable angina.

DESIGN

Prospective examination of ventricular systolic and diastolic long axis function using M mode echocardiography and transmitral Doppler in patients with significant coronary artery stenosis and either stable or unstable angina, during routine PTCA.

SETTING

A tertiary referral centre for heart disease with cardiac catheterisation and echocardiographic facilities.

SUBJECTS

36 patients, age (SD) 60 (8) years, with significant coronary artery disease undergoing PTCA (mean duration 100-130 seconds) to the left anterior descending coronary artery (LAD) in 18 patients, native LAD or its vein graft in eight, and right coronary artery in 10. Controls were 21 normal subjects, age 58 (11) years. RESULTS-AT BASELINE: in systole, total long axis excursion was reduced at septal, posterior, and right sites in patients with LAD disease, at right site in those with vein grafts, and at septal and right sites in patients with right coronary artery disease. Peak shortening rate was often reduced in all patients and onset of shortening delayed with respect to the Q wave in patients with LAD disease. In diastole, onset of lengthening was always delayed, peak lengthening rate reduced, and relative A wave amplitude increased in all patients. There was a consistent abnormal shortening of the long axis during the isovolumic relaxation period in the 14 patients with unstable angina, not seen in the others. Transmitral A wave velocity was also increased and the onset of E wave delayed with respect to A2. At first balloon inflation: the extent of pre-existing systolic and particularly diastolic abnormalities consistently increased in patients with LAD or right coronary artery occlusion. This was associated with further delay in the onset of the transmitral Doppler E wave as its peak velocity fell and E/A ratio increased. In unstable angina, balloon inflation caused minor changes only in systolic function and no change in diastolic function. At second balloon inflation: systolic changes were the same as with the first inflation, while diastolic changes were attenuated by 10-15%.

CONCLUSIONS

In stable angina intracoronary balloon inflation aggravated pre-existing systolic and diastolic abnormalities in the territory of the occluded vessel, indicating the dependence of both on coronary flow. In unstable angina balloon inflation caused only minor deterioration in systolic function, and diastolic changes-including the characteristic abnormal shortening during isovolumic relaxation-were unaffected. Thus resting abnormalities of left ventricular function in unstable angina are effectively dissociated from acute changes in coronary flow. Overall, the severity of systolic disturbances was unaltered by a second balloon inflation, but diastolic disturbances were attenuated by 10-15%, compatible with ischaemic preconditioning or recruitment of collaterals.

Reperfusion injury: a review of the pathophysiology, clinical manifestations and therapeutic options

Lack of blood supply or ischaemia underlies many of the most important cardiovascular and cerebrovascular diseases faced by clinicians in their daily practice. Many of these ischaemic episodes can be reversed at an early stage by surgical or pharmacological means with the ultimate aim of preventing infarction and cell necrosis in the ischaemic tissues. However, reperfusion of ischaemic areas, in particular the readmission of oxygen, may contribute to further tissue damage (reperfusion injury). For example, the use of thrombolytic therapy in acute myocardial infarction and other revascularisation procedures, such as percutaneous transluminal angioplasty and coronary artery bypass surgery, may be associated with reperfusion of ischaemic myocardium. Such ischaemia and reperfusion may result in injury to one of more of the biochemical, cellular and microvascular components of the heart. Our understanding of the significance of reperfusion injury is however restricted by the profuse literature in animal models and limited literature in the clinical situation. This article reviews the pathophysiology, clinical manifestations of reperfusion injury to the heart and discusses the possible therapeutic approaches to avoiding any adverse effects.

Lipid peroxidation-associated oxidative stress during percutaneous transluminal coronary angioplasty in humans

Animal studies suggest that myocardial ischemia/reperfusion causes oxidative stress. We, therefore, examined whether routinely performed percutaneous transluminal coronary angioplasty (PTCA) might be a human ischemia/reperfusion model for oxidative stress-induced lipid peroxidation. Fasting antecubital venous blood was sampled from 13 patients on the morning of PTCA, and 2 d after PTCA. Venous and coronary arterial blood were sampled just before and 10 min after the first balloon inflation. Samples were analyzed for plasma and LDL lipid hydroperoxide levels, in vitro oxidation of LDL, and LDL antioxidant levels. Lipid hydroperoxide levels in plasma and LDL remained unchanged throughout the study. During the first 10 min of PTCA, the lag time during oxidation of LDL in vitro did not change, but the maximum rate of oxidation decreased in venous and arterial samples (Wilcoxon signed rank test: p < .002). At the same time, total tocopherol levels in LDL significantly increased by 6.3% (p = .048) in arterial, but not in venous samples. Total carotenoid levels increased by 3.8% (p = .127) in arterial samples and decreased by 2.9% (p = .040) in venous samples. Forty hours after PTCA, LDL oxidation parameters and LDL antioxidant levels were similar to baseline, except for about 17% lower levels of delta-tocopherol (p = .037) and gamma-tocopherol (p = .014). Our results, therefore, do not support that PTCA in humans is associated with oxidative stress-induced lipid peroxidation.

Serum total antioxidant activity after myocardial infarction

Serum total antioxidant activity (TAA), albumin and uric acid were measured on admission, and for the next 2 days in 56 patients suffering myocardial infarction, 20 of whom received streptokinase. The 'antioxidant gap', the difference between the serum TAA and the sum of the serum albumin and uric acid activity, was calculated. No significant changes in serum total antioxidant activity were observed in either group of patients between admission, day 1 and day 2. However, a decline in the 'antioxidant gap' after myocardial infarction was associated with a significantly higher mortality.

No evidence for ischemic preconditioning during repeated vessel occlusion in coronary angioplasty

Coronary angioplasty has been the favoured model in studying ischemic preconditioning in humans, but results have remained controversial, possibly due to some artefacts related to coronary balloon angioplasty as an ischemia model. We examined this issue by monitoring the sequential metabolic, functional and neurohumoral changes during repeated vessel occlusion in coronary angioplasty performed in patients with chronic angina pectoris. Two groups of patients undergoing two successive balloon inflations of approximately 2 min duration were studied. These balloon inflations were preceded by a short inflation performed immediately after introduction of the balloon into the stenosis. The aim of this primary inflation was to establish adequate coronary blood flow with the deflated balloon in the stenosis and to guarantee that the subsequent two balloon inflations were truly comparable in time. Group I consisted of 23 patients, in whom the changes in the degree of angina, pulmonary capillary wedge pressure (PCWP), atrial natriuretic peptide (ANP) and circulating catecholamines during the procedure were studied. The sequential changes in myocardial metabolism were monitored in group II of nine patients by determining the lactate extraction ratios and femoroarterial coronary sinus (Fa-CS) differences in pH and pCO2 before and after each balloon inflation. In group I, PCWP and total catecholamines increased similarly during both balloon inflations, but ANP remained unchanged. In group II patients the lactate extraction ratios turned negative, the Fa-CS pH-differences increased and the pCO2-differences decreased during vessel occlusions, the changes being somewhat more prominent during the second balloon inflation. To study adaptation to ischemia, the group I patients were divided into two subgroups with and without signs of ischemic dysfunction during balloon inflations (PCWP increase > 5 mmHg and < 5 mmHg, respectively), and the group II patients were divided into two subgroups with and without metabolic ischemia (lactate-producers and non-producers). The ANP levels were constantly higher in the patients demonstrating ischemic dysfunction during balloon inflations, but catecholamine levels increased only after the second balloon inflation. The anginal pain experienced by the patients and the signs of metabolic ischemia were identical during both balloon inflations. We conclude that acute ischemic preconditioning does not occur in patients with repeated vessel occlusions of approximately 2 min duration. The patients without ischemia during the procedure had more critical stenoses and pre-existing collaterals. However, other protective mechanisms, such as chronic adaptation at the cellular level or recruitment of new collaterals, cannot be excluded.

Breath pentane and plasma lipid peroxides in ischemic heart disease

This study examined the relationship between breath pentane and plasma lipid peroxide levels sampled simultaneously in patients with stable angina (n = 17), unstable angina (n = 23), and controls (n = 10). Plasma lipid peroxides were measured in venous blood as the adduct formed between thiobarbituric acid and malondialdehyde (MDA) using high performance liquid chromatography. Pentane was measured in end-expiratory air using gas chromatography. MDA concentrations in stable (1.81 +/- 0.84 mumol/l) and unstable (1.5 +/- 1.23 mumol/l) angina were not different. However, both groups had significantly (p < 0.005) elevated MDA levels compared to controls (0.41 +/- 0.26 mumol/l). Breath pentane was 0.20 +/- 0.12 nmol/l in controls and not different from stable angina (0.26 +/- 0.20 nmol/l) or unstable angina (0.15 +/- 0.07 nmol/l). When the data from all three groups were combined, there was no correlation between pentane and MDA (rho = -0.09, p = 0.54). In five of the unstable angina patients treated with balloon angioplasty, MDA in pulmonary arterial blood rose by 69 +/- 15% (p < 0.01), and breath pentane rose by 73 +/- 20% (p < 0.01) immediately after balloon deflation. One minute after balloon deflation MDA and pentane had returned to preinflation levels. The results suggest that basal levels of pentane are less useful than MDA as an index of lipid peroxidation in patients with coronary artery disease. However, breath pentane appears to be a sensitive index of reperfusion-induced lipid peroxidation.

Myocardial release of malondialdehyde and purine compounds during coronary bypass surgery

BACKGROUND

Free radicals and lipid peroxidation have been suggested to play an important role in the pathophysiology of myocardial reperfusion injury. The purpose of the present study was to monitor myocardial malondialdehyde (MDA) production as an index of lipid peroxidation during ischemia-reperfusion sequences in patients undergoing elective coronary bypass grafting. There has been a lot of debate on the role of xanthine oxidase as a potential superoxide anion generator and thus lipid peroxidation in human myocardium. To evaluate the activity of xanthine oxidase pathway, we measured the changes in the transcardiac concentration differences in adenosine, inosine, hypoxanthine, xanthine, and uric acid.

METHODS AND RESULTS

The coronary sinus-aortic root differences (CS-Ao) of MDA, oxypurines, and nucleosides were measured by a recently developed ion-pairing high-performance liquid chromatographic (HPLC) method. Fifteen patients were included in the study, and 13 of them demonstrated a more than 10-fold increase in net myocardial production of MDA on intermittent reperfusion during the aortic cross-clamp period. In 2 patients, MDA was not detectable in any of the CS or Ao samples. Before aortic cross-clamping, the CS-Ao concentration differences in adenosine, inosine, hypoxanthine, xanthine, and uric acid were 0.59 +/- 0.19, 0.23 +/- 0.05, 0.89 +/- 0.36, 0.58 +/- 0.32, and 11.4 +/- 4.9 mumol/L, respectively. After aortic cross-clamping, the sum of the transcardiac differences of these compounds increased up to 2.8-fold and then gradually decreased after declamping of the aorta. There was a weak positive correlation between transcardiac concentration differences of MDA and xanthine plus uric acid (r = .48, P < .01). The postoperative functional recovery or leakage of cardiac enzymes was not affected by the level of MDA net release during the aortic cross-clamp period, however.

CONCLUSIONS

We conclude that myocardial lipid peroxidation, estimated as MDA formation, is common during intermittent ischemia-reperfusion sequences in coronary bypass surgery, although some patients may be better protected. Xanthine oxidase appears to be operative in human myocardium, and free radicals generated in this reaction might also be involved in the observed lipid peroxidation process. Increased degradation of myocardial adenine nucleotides and concomitant lipid peroxidation may play a specific role in the development of reperfusion injury. In this study, however, more extensive lipid peroxidation was not associated with impaired functional recovery.

Ischemic preconditioning: cardioprotection for cardiac surgery

Traditionally, surgeons have attempted to minimize myocardial ischemic and reperfusion injury during cardiac procedures by optimizing cardioplegic solutions and modifying the conditions of reperfusion. New evidence suggests that in addition to these two strategies, surgeons may be able to induce myocardial resistance to ischemic injury, which permits immediate functional and metabolic recovery after cardiac operations. Although brief episodes of cardiac ischemia may be associated with mechanical and metabolic dysfunction ("stunning"), they have also been shown to protect against damage resulting from a subsequent prolonged ischemic episode. This phenomenon, known as ischemic preconditioning, has been extensively characterized since its original description in 1986. Recent studies in surgical models of cardioplegic arrest and reperfusion have suggested that the preconditioned, arrested heart may have an increased tolerance to prolonged ischemia and improved functional recovery after reperfusion. The development of a pharmacological agent that induces the preconditioning effect may revolutionize cardioprotection for cardiac surgery. We will review the characteristics of preconditioning and data supporting the application of this natural protective capacity to reduce ischemic damage during cardiac procedures.