Cellular response of the evolving myocardial infarction after therapeutic coronary artery reperfusion

Eosinophil-to-Monocyte Ratio is a Potential Predictor of Prognosis in Acute Ischemic Stroke Patients After Intravenous Thrombolysis

Background

Eosinophil and monocyte have been demonstrated separately to be independent predictors of acute ischemic stroke (AIS). This study aimed to evaluate the association between eosinophil-to-monocyte ratio (EMR) and 3-month clinical outcome after treatment with recombinant tissue plasminogen activator (rt-PA) for AIS patients. Simultaneously, we made a simple comparison with other prognostic indicators, such as 24h neutrophil-to-lymphocyte ratio (NLR) and 24h platelet-to-lymphocyte ratio (PLR) to investigate the prognostic value of EMR.

Methods and Results

A total of 280 AIS patients receiving intravenous thrombolysis were retrospectively recruited for this study. Complete blood count evaluations for EMR were conducted on 24 hours admission. The poor outcome at 3-month was defined as the modified Rankin Scale (mRS) of 3–6 and the mRS score for death was 6. The EMR levels in patients with AIS were lower than those in the healthy controls and showed a negative correlation with the NIHSS score. At the 3-month follow-up, multivariate logistic regression analysis indicated an association among EMR, poor outcome and mortality. In addition, EMR had a higher predictive ability than popular biomarkers like NLR and PLR for 3-month mortality.

Conclusion

The lower levels of EMR were independently associated with poor outcome and dead status in AIS patients.

Association of eosinophil-to-monocyte ratio with 1-month and long-term all-cause mortality in patients with ST-elevation myocardial infarction undergoing primary percutaneous coronary intervention

Background

To determine the relationship between eosinophil-to-monocyte ratio (EMR) on admission and one-month and long-term all-cause mortality in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (P-PCI).

Methods

A total of 426 consecutive STEMI patients treated with P-PCI were enrolled and categorized in terms of tertiles of EMR on admission between September 2015 and October 2017. Final follow-up for long-term outcomes was January 2017.

Results

As EMR decreased, all-cause mortality at 1 month (mean, 29.5±3.5 days) and at mean 14.1±7.8 months follow-up increased (P=0.012, P=0.003, respectively). Kaplan-Meier survival curve analysis showed EMR was associated with 1-month and long-term all-cause mortality (P=0.048, P=0.015, respectively). In multivariate Cox proportional hazards analysis, EMR was independently associated with one-month and long-term mortality (hazard ratio =0.097; 95% CI, 0.010-0.899; P=0.04; hazard ration =0.176; 95% CI, 0.045-0.694; P=0.013). The area under the curve of EMR for the prediction of 1-month and long-term total mortality in receiver operating characteristic analysis was 0.789 (95% CI, 0.658-0.921; P=0.003) and 0.752 (95% CI, 0.619-0.884; P=0.001), respectively.

Conclusions

EMR on admission was independently correlated with 1-month and long-term all-cause mortality in STEMI patients undergoing P-PCI, suggesting EMR as a potential simple, useful, and inexpensive index for risk stratification of STEMI patients.

Prognostic Value of Eosinophil to Leukocyte Ratio in Patients with ST-Elevation Myocardial Infarction Undergoing Primary Percutaneous Coronary Intervention

Aim: Leukocyte profile has been related to clinical outcome in patients with ST-segment elevation (STE) myocardial infarction (MI). However, whether eosinophil to leukocyte ratio (ELR) predicts clinical outcome in patients who have undergone primary percutaneous coronary intervention (PCI) remains unclear. Therefore, we examined the prognostic value of ELR in this patient population.

Methods: We retrospectively analyzed the data of 331 consecutive patients who underwent primary PCI for STEMI between January 2009 and March 2015. All leukocyte types were counted and ELR was calculated for all patients 24 h after hospital admission. The primary study endpoint was major adverse cardiac events (MACEs) within up to one year of follow-up duration.

Results: MACEs including cardiac deaths in 9.4% of the patients, MI in 1.5%, and target lesion or vessel revascularization in 10.3%, occurred within one year in 68 patients (20.5%). The mean ELR was significantly lower in patients with MACEs than in patients without MACEs (0.20 ± 0.51 vs. 0.49 ± 0.66, respectively; p < 0.001). An ELR < 0.1 at 24 h was identified as the best cut-off value for mortality prediction. Multivariate analysis identified that an ELR < 0.1 (odds ratio [OR] = 0.38; 95% confidence interval [CI] = 0.22–0.67; p < 0.001) and chronic kidney disease (OR = 2.38; CI = 1.33–4.24; p = 0.003) are independent predictors of MACEs.

Conclusion: In primary PCI patients with STEMI, ELR at 24 h was an independent predictor of MACEs in addition to the usual coronary risk factors and commonly used biomarkers.

Early markers for myocardial ischemia and sudden cardiac death

The post-mortem diagnosis of acute myocardial ischemia remains a challenge for both clinical and forensic pathologists. We performed an experimental study (ligation of left anterior descending coronary artery in rats) in order to identify early markers of myocardial ischemia, to further apply to forensic and clinical pathology in cases of sudden cardiac death. Using immunohistochemistry, Western blots, and gene expression analyses, we investigated a number of markers, selected among those which are currently used in emergency departments to diagnose myocardial infarction and those which are under investigation in basic research and autopsy pathology studies on cardiovascular diseases. The study was performed on 44 adult male Lewis rats, assigned to three experimental groups: control, sham-operated, and operated. The durations of ischemia ranged between 5 min and 24 h. The investigated markers were troponins I and T, myoglobin, fibronectin, C5b-9, connexin 43 (dephosphorylated), JunB, cytochrome c, and TUNEL staining. The earliest expressions (≤30 min) were observed for connexin 43, JunB, and cytochrome c, followed by fibronectin (≤1 h), myoglobin (≤1 h), troponins I and T (≤1 h), TUNEL (≤1 h), and C5b-9 (≤2 h). By this investigation, we identified a panel of true early markers of myocardial ischemia and delineated their temporal evolution in expression by employing new technologies for gene expression analysis, in addition to traditional and routine methods (such as histology and immunohistochemistry). Moreover, for the first time in the autopsy pathology field, we identified, by immunohistochemistry, two very early markers of myocardial ischemia: dephosphorylated connexin 43 and JunB.

Epicardial ablation for ventricular tachycardia

Epicardial ablation has lately become a necessary tool to approach some ventricular tachycardias in different types of cardiomyopathy. Its diffusion is now limited to a few high volume centers not because of the difficulty of the pericardial puncture but since it requires high competence not only in the VT ablation field but also in knowing and recognizing the possible complications each of which require a careful treatment.

This article will review the state of the art of epicardial ablation with special attention to the procedural aspects and to the possible selection criteria of the patients

Stress echocardiography as a gatekeeper to donation in aged marginal donor hearts: anatomic and pathologic correlations of abnormal stress echocardiography results

BACKGROUND

Owing to the shortage of donor hearts, the criteria for acceptance have been considerably expanded. Pharmacologic stress echocardiography is highly accurate in identifying prognostically significant coronary artery disease, but brain death and catecholamine storm in potential heart donors may substantially alter the cardiovascular response to stress. This study assessed correlates of an abnormal resting/stress echocardiography results in potential donors.

METHODS

From April 2005 to December 2007, 18 marginal candidate donors (9 men) aged 58 +/- 5 years were initially enrolled. After legal declaration of brain death, all marginal donors underwent bedside echocardiography, with baseline and (when resting echocardiography was normal) dipyridamole (0.84 mg/kg in 6 min) or dobutamine (up to 40 microg/kg/min) stress echo. Non-eligible hearts (with abnormal rest or stress echo findings) were excluded and underwent cardioautoptic verification.

RESULTS

Resting echocardiography showed wall motion abnormalities in 5 patients (excluded from donation). Stress echocardiography was performed in the remaining 13 (dipyridamole in 11; dobutamine in 2). Results were normal in 7, of which 6 were uneventfully transplanted in marginal recipients. Results were abnormal in 6, and autoptic verification performed showed coronary artery disease in 5, and initial cardiomyopathy in 1.

CONCLUSIONS

Bedside pharmacologic stress echocardiography can safely be performed in candidate heart donors, is able to unmask occult coronary artery disease or cardiomyopathy, and shows potential to extend donor criteria in heart transplantation. Further experience with using marginal donors is needed before exact guidelines can be established.

Pathophysiology of acute myocardial infarction

More than 80% of acute myocardial infarcts are the result of coronary atherosclerosis with superimposed luminal thrombus. Uncommon causes of myocardial infarction include coronary spasm, coronary embolism, and thrombosis in nonatherosclerotic normal vessels. Additionally, concentric subendocardial necrosis may result from global ischemia and reperfusion in cases of prolonged cardiac arrest with resuscitation. Myocardial ischemia shares features with other types of myocyte necrosis, such as that caused by inflammation, but specific changes result from myocyte hypoxia that vary based on length of occlusion of the vessel, duration between occlusion and reperfusion, and presence of collateral circulation.

Immunohistochemical expression of activated caspase-3 in human myocardial infarction

There is mounting evidence that apoptosis is important in the pathogenesis of myocardial infarction (MI). One of the key events in the process of apoptosis is activation of caspase-3. Much attention has been recently paid to caspase inhibition as a potential treatment for ischemic cardiac disease. To predict the long-term effect of such treatment, it is essential to understand the significance of caspase-3 in the evolution of MI. Our aim was therefore to analyze immunohistochemical expression of activated caspase-3 in MI. Our study included autopsy samples of infarcted heart tissue from 50 patients with MI. Immunohistochemistry was performed by a sensitive peroxidase-streptavidin method on formalin-fixed, paraffin-embedded tissue, using monoclonal antibodies against activated (cleaved) caspase-3. We found caspase-3-positive myocytes in 18 MI less than 24 h old and in 3 MI that were presumably 48 h old. Their density (number of labeled myocytes/mm(2)) was greater in patients who received reperfusion treatment (mean 0.160+/-0.373 vs 0.025+/-0.037, p=0.06). In MI older than 48 h, positive reaction was observed in neutrophil granulocytes in the interstitium and, in subacute MI, it was observed in mononuclear inflammatory cells, myofibroblasts, and vascular endothelial cells. Our results suggest that apoptosis of myocytes is an important mode of cell death in the early MI, being enhanced in patients who received reperfusion treatment. After 48 h, apoptosis is an important mechanism of the clearance of neutrophil granulocytes and other inflammatory cells and of scar formation. Treatment with caspase inhibitors therefore will not only affect myocyte loss but will also interfere with the clearance of neutrophils and with the transformation of granulation tissue into a scar.

Effects of an Augmented Postoperative Fluid Protocol on Wound Healing in Cardiac Surgery Patients

• Background Cardiac surgery patients are vulnerable to hypoperfusion postoperatively and often have subcutaneous tissue oxygen tension less than 50 mm Hg. Hypovolemia most likely contributes to this hypoperfusion and may lead to impaired wound healing.

• Objective To determine if a modified postoperative fluid replacement protocol would result in improved tissue oxygen tension, blood flow, and healing in cardiothoracic surgery patients.

• Methods A total of 166 cardiac surgery patients, 18 to 90 years old, participated in a randomized, 2-group, repeated-measures study. The experimental group received fluid augmentation during the first 36 hours after surgery; the control group received standard postoperative replacement fluids. Subcutaneous tissue oxygen tension and temperature were measured 8, 18, and 36 hours after surgery. Tissue cellularity and accumulation of hydroxyproline were evaluated in tissue obtained from subcutaneous expanded polytetrafluoroethylene tubes. Wound complications were evaluated by using the ASEPSIS Wound Scoring System.

• Results Tissue oxygen levels, tissue cellularity, and accumulation of hydroxyproline were similar in the 2 groups. A negative correlation (P = .01) existed between higher tissue oxygen values and lower (better) ASEPSIS leg wound scores. More than 80% of the patients had tissue oxygen levels of 50 mm Hg or less at each time of measure. Many values were 30 to 40 mm Hg less than the ideal for control of bacteria and healing.

• Conclusions The frequency of low oxygen levels is consistent with data from earlier studies. Determination of other interventions to improve subcutaneous tissue perfusion in cardiac surgery patients is needed.

Pathophysiologic role of myocardial apoptosis in post-infarction left ventricular remodeling

Left ventricular (LV) remodeling and heart failure (HF) complicate acute myocardial infarction (AMI) even weeks to months after the initial insult. Apoptosis may represent an important pathophysiologic mechanism causing progressive myocardiocyte loss and LV dilatation even late after AMI. This review will discuss the role of apoptosis according to findings in animal experimental data and observational studies in humans in order to assess clinical relevance, determinants, and mechanisms of myocardial apoptosis and potential therapeutic implications. More complete definition of the impact of myocardiocyte loss on prognosis and of the mechanisms involved may lead to improved understanding of cardiac remodeling and possibly improved patients' care. Mitochondrial damage and bcl-2 to bax balance play a central role in ischemia-dependent apoptosis while angiotensin II and beta(1)-adrenergic-stimulation may be major causes of receptor-mediated apoptosis. Benefits due to treatment with ACE-inhibitors and beta-blockers appear to be in part due to reduced myocardial apoptosis. Moreover, infarct-related artery patency late after AMI may be a major determinant of myocardial apoptosis and clinical benefits deriving from an open artery late post AMI (the "open artery hypothesis") may be, at least in part, due to reduced myocardiocyte loss.

Tissue and wound healing effects of short duration postoperative oxygen therapy

The purpose of this study was to determine the effects of 28% oxygen given in the first 36 hours after surgery on tissue oxygen, collagen deposition, and clinical healing outcomes. Twenty-four subjects having cervical spine surgical procedures participated in a randomized, repeated-measures pilot study of tissue and healing effects of postoperative supplemental oxygen. The treatment group (n = 13) received 28% oxygen for the first 36 postoperative hours, whereas the control group (n = 11) was maintained on room air. Subcutaneous tissue oxygen and temperature were measured at intervals up to 36 hours postsurgery. Wound healing was evaluated by hydroxyproline content in a subcutaneous polytetrafluoroethylene tube removed on the 7th postoperative day. Clinical outcomes were evaluated for the 30 days post-hospital discharge. Subjects in the treatment group had significantly higher tissue oxygen tension overall, and at postoperative hours 1, 2, 18, and 36, with mean values 10 to 20 mm Hg higher than control subjects. Significant differences were not found in hydroxyproline levels or clinical wound outcome measures. Low level, short duration, supplemental oxygen increased and sustained wound tissue oxygen and was well tolerated by subjects. Larger studies of populations at risk for wound complications are needed to investigate variables of dose and duration of oxygen therapy in relation to clinical and cellular wound healing outcomes.

Fibronectin fragments modulate monocyte VLA-5 expression and monocyte migration

To identify the mechanisms that cause monocyte localization in infarcted myocardium, we studied the impact of ischemia-reperfusion injury on the surface expression and function of the monocyte fibronectin (FN) receptor VLA-5 (alpha(5)beta(1) integrin, CD49e/CD29). Myocardial infarction was associated with the release of FN fragments into cardiac extracellular fluids. Incubating monocytes with postreperfusion cardiac lymph that contained these FN fragments selectively reduced expression of VLA-5, an effect suppressed by specific immunoadsorption of the fragments. Treating monocytes with purified, 120-kDa cell-binding FN fragments (FN120) likewise decreased VLA-5 expression, and did so by inducing a serine proteinase-dependent proteolysis of this beta(1) integrin. We postulated that changes in VLA-5 expression, which were induced by interactions with cell-binding FN fragments, may alter monocyte migration into tissue FN, a prominent component of the cardiac extracellular matrix. Support for this hypothesis came from experiments showing that FN120 treatment significantly reduced both spontaneous and MCP-1-induced monocyte migration on an FN-impregnated collagen matrix. In vivo, it is likely that contact with cell-binding FN fragments also modulates VLA-5/FN adhesive interactions, and this causes monocytes to accumulate at sites where the fragment concentration is sufficient to ensure proteolytic degradation of VLA-5.

Infarct size, myocardial hemorrhage, and recovery of function after mechanical versus pharmacological reperfusion: effects of lytic state and occlusion time

BACKGROUND

Whether myocardial reperfusion obtained with thrombolysis or primary angioplasty is associated with a similar recovery of function and with the same risk of hemorrhagic infarction is unknown. We evaluated the effects of mechanical and pharmacological reperfusion (with or without a plasma lytic state) on infarct size, myocardial hemorrhage, and left ventricular (LV) function in a canine model.

METHODS AND RESULTS

Six groups of six dogs were subjected to balloon occlusion of the left anterior descending coronary artery (LAD) followed by 2 hours of reperfusion. The study had a two-by-three factorial design with two occlusion periods (90 and 240 minutes) and three different reperfusion strategies (placebo, 0.4 mg/kg recombinant tissue plasminogen activator, and 40 microg/kg recombinant staphylokinase). In a seventh control group, LAD occlusion was maintained without reperfusion. All dogs received aspirin and heparin. A systemic lytic state was present in staphylokinase-treated dogs. Planimetry of LV slices showed larger infarcts (percent of area at risk) and more hemorrhage (percent of IA) after 240 minutes of occlusion than after 90 minutes of occlusion (54+/-17% versus 37+/-18% and 52+/-27% versus 29+/-27%, respectively; P<.01 for both comparisons), with no significant difference among treatments. Hemorrhage was not observed in the control group without reperfusion. LV angiography showed no differences in global and regional LV function between mechanical and pharmacological reperfusion.

CONCLUSIONS

In this experimental model, hemorrhagic infarctions of similar extent were observed after both pharmacological and mechanical reperfusion. The extent of hemorrhage was increased by the delay in reperfusion but not by the presence of a lytic state.

Early apoptosis in human myocardial infarcts

Myocardial apoptosis has previously been observed in human acute myocardial infarcts. We examined the time of appearance and extent of apoptosis in human acute myocardial infarcts, and compared these with necrotic cell death. Because nuclear internucleosomal DNA fragmentation is a hallmark of apoptosis, autopsied tissue from cases of acute myocardial infarct of varying histological ages was subjected to two tests that identify such fragmentation: in situ end-labeling (ISEL) and DNA electrophoresis on agarose gels. Both tests showed widespread apoptosis in infarcts only a few hours in age before the appearance of coagulative necrosis. No apoptosis was detected in normal myocardium. ISEL in recent infarcts was visible primarily in myocytes containing contraction bands, which occur predominantly in regions of reperfused myocardium. During the next 1 to 2 days, ISEL remained extensive but increasingly appeared in cells with morphological features of coagulative necrosis, representative of nonreperfused myocardium. In older infarcts, the incidence of apoptosis declined in myocytes, but increased in invading inflammatory cells. These data suggest that apoptosis is the early and predominant form of cell death in infarcted human myocardium, and that its appearance is accelerated in reperfused myocardium. Therapies directed at early rescue of apoptotic myocytes may, therefore, prove valuable.

Complement C5a, TGF-beta 1, and MCP-1, in sequence, induce migration of monocytes into ischemic canine myocardium within the first one to five hours after reperfusion

BACKGROUND

Recent studies suggest that reperfusion promotes healing of formerly ischemic heart tissue even when myocardial salvage is no longer possible. Since monocyte-macrophage infiltration is the hallmark of the healing infarct, we have attempted to identify mechanisms that attract monocytes into the heart after reperfusion of ischemic canine myocardium.

METHODS AND RESULTS

Isolated autologous 99mTc-labeled mononuclear leukocytes injected into the left atrium localized preferentially in previously ischemic myocardium within the first hour after reperfusion. Histological studies revealed CD64+ monocytes in small venules and the perivascular connective tissue within the first hour after reperfusion. Flow cytometric analysis of cells in cardiac lymph showed systematically increasing numbers of neutrophils and monocytes between 1 and 4 hours after reperfusion; monocyte enrichment was eventually greater than neutrophil enrichment. Monocyte chemotactic activity in cardiac lymph collected in the first hour after reperfusion was wholly attributable to C5a. Transforming growth factor (TGF)-beta 1 contributed significantly to this chemotactic activity after 60 to 180 minutes, and after 180 minutes, monocyte chemotactic activity in lymph was largely dependent on monocyte chemoattractant protein (MCP)-1 acting in concert with TGF-beta 1.

CONCLUSIONS

Beginning in the first 60 minutes after reperfusion, C5a, TGF-beta 1, and MCP-1, acting sequentially, promote infiltration of monocytes into formerly ischemic myocardium. These events may promote the healing of myocardial injury facilitated by reperfusion.

Myocardial kinetics of technetium-99m teboroxime in the presence of postischemic injury, necrosis and low flow reperfusion

OBJECTIVES

This study evaluated technetium-99m (Tc-99m) teboroxime kinetics in postischemic and partially necrotic myocardium with complete and low flow reperfusion using an isolated perfused rat heart model.

BACKGROUND

Technetium-99m teboroxime has been proposed for use in the early diagnosis of reperfusion after thrombolysis on the basis of models of myocardial necrosis with complete reperfusion. Clinically, however, reperfusion is frequently incomplete, resulting in a mixture of necrotic, ischemic and postischemic tissue.

METHODS

Hearts were classified into five groups: group 1 (n = 8, control); group 2 (n = 7, 30 min of no flow with complete reperfusion); group 3 (n = 12, 60 min of no flow to induce partial necrosis, followed by complete reperfusion); group 4 (n = 8, continuous low flow without flow interruption); and group 5 (n = 9, 60 min of no flow with low flow reperfusion). Buffer containing Tc-99m teboroxime was perfused for 15 min, followed by tracerfree buffer for 35 min, to evaluate uptake and clearance, respectively.

RESULTS

Uptake slopes for groups 1 to 5 were (mean +/- SD) 3.0 +/- 0.7, 2.6 +/- 0.8, 2.1 +/- 0.5, 0.8 +/- 0.2 and 0.8 +/- 0.3, respectively (p < or = 0.0005 for groups 1, 2 and 3 vs. groups 4 and 5, and p = 0.003 for group 3 vs. groups 1 and 2). Clearance curves from groups 1 to 3 were best fit by a biexponential function (p < 0.001); those from groups 4 and 5 were monoexponential. In groups 1, 2 and 3, the initial clearance rate constants (ki) (0.9 +/- 0.5 x 10(-3); 1.0 +/- 0.2 x 10(-3); 1.1 +/- 0.5 x 10(-3) s-1, respectively) and the monoexponential rate constants (Kmono) (2.0 +/- 0.3 x 10(-4); 2.2 +/- 0.4 x 10(-4); 2.1 +/- 0.2 x 10(-4) s-1, respectively) were significantly greater than those in groups 4 and 5 (0.9 +/- 0.5 x 10(-4); 1.2 +/- 0.3 x 10(-4) s-1, respectively, p < or = 0.005).

CONCLUSIONS

The uptake and initial clearance kinetics of Tc-99m teboroxime depend mainly on myocardial flow in this model. The presence of partial necrosis and postischemic injury has little effect on the initial clearance but leads to some reduction in uptake at normal flow rates. Evaluation of Tc-99m teboroxime kinetics may permit early noninvasive detection of inadequate reperfusion in acute myocardial infarction.

Enzyme and immunohistochemical assessment of myocardial damage after ischaemia and reperfusion in a closed-chest pig model

The usefulness of different enzyme and immunohistochemical stains to distinguish reversible and irreversible myocardial cell injury after experimental coronary artery occlusion of varying duration and reperfusion with or without superoxide dismutase as adjunct was investigated. Biopsies or parts of the infarcted and non-infarcted area were rapidly frozen and sectioned in series for enzyme and immunohistochemical evaluation. Sections were stained for the demonstration of phosphorylase, myofibrillar ATPase and mitochondrial oxidative enzymes and also with periodic acid-Schiff, alizarin red S and routine histological stains. Other sections in series were stained with antibodies against fibronectin and the intermediate filament proteins desmin and vimentin. In 49 biopsies a blind quantitative estimation of the area stained for fibronectin, phosphorylase and alizarin red S was performed and evaluated statistically. Phosphorylase, periodic acid-Schiff, fibronectin and alizarin red S allowed delineation of affected myocardium after 30 min of ischaemia followed by reperfusion whereas with the other stains, affected myocardium was readily detectable only after 60 or 90 min of ischaemia followed by reperfusion as well as after 24 h of ischaemia without reperfusion. The immunostaining for fibronectin was very distinct and inversely related to the phosphorylase activity. We show that fibronectin is an excellent marker for damaged cells and that these positively stained myocytes are necrotic as confirmed ultrastructurally. Using alizarin red S as a marker of calcium accumulation in myocytes, a marked discrepancy was observed between the area of fibronectin-containing myocytes and that of myocytes stained by alizarin red S. Calcium accumulation in mitochondria is thus not a prerequisite for myocyte necrosis but does occur only in some of the irreversibly damaged cells. Of special interest is the finding that there was a significant reduction of intracellular calcium in pigs where superoxide dismutase had been used as an adjunct at reperfusion, thus supporting the theory that free radicals do play a role during reperfusion of ischaemic myocardium.