Free radicals and myocardial injury: pharmacologic implications

Augmented endothelium-dependent constriction to hypoxia early and late following reperfusion of the canine coronary artery

1. Canine coronary arteries with intact endothelium respond to hypoxaemia or serotonin infusion with dilatation, but when the endothelium is injured or dysfunctional, these stimuli can cause constriction. The present studies investigated whether or not regional ischaemia and reperfusion alter endothelium-dependent responsiveness of canine coronary arteries in vivo and in vitro. 2. In organ chamber experiments, isolated control and reperfused coronary artery rings were contracted with prostaglandin F2 alpha and exposed to hypoxia (PO2 less than 5 mmHg). 3. Hypoxia augmented the response of reperfused arteries more than that of controls. The hypoxic augmentation was blocked by NG-monomethyl-L-arginine, an inhibitor of nitric oxide synthesis from L-arginine. 4. These findings demonstrate that early following coronary reperfusion the hypoxic augmentation, which is mediated by a nitric oxide-dependent pathway in the endothelium, is facilitated. 5. In vivo studies revealed hyperconstriction of reperfused arteries in response to hypoxaemia (PO2 = 30-40 mmHg) and administration of either serotonin or ergonovine. 6. Twelve weeks following reperfusion injury, coronary arteries still exhibited augmented endothelium-dependent hypoxic augmentations in vitro, which were inhibited by NG-monomethyl-L-arginine. 7. Furthermore, resting coronary segments with endothelium displayed hypoxia-induced contractions that could not be inhibited by indomethacin, the lipoxygenase inhibitor AA861, superoxide dismutase plus catalase, deferoxamine, ouabain, or NG-monomethyl-L-arginine. 8. These endothelium-dependent hypoxic response may play a role in the pathogenesis of hyperconstriction (vasospasm) following coronary reperfusion.

Diurnal systolic blood pressure variability is the strongest predictor of early carotid atherosclerosis

We studied the relationship between circadian blood pressure changes and development of early carotid atherosclerosis in 208 hypertensive and 216 normotensive patients older than age 55 years. Blood pressure patterns were evaluated noninvasively with a long-term blood pressure monitor, and extent of atherosclerosis was measured as the intima to media wall thickness (IMT) of the common carotid artery. No significant differences regarding age, sex, smoking, diabetes, cholesterol, and triglycerides were found between both patient groups. The age-adjusted IMT was significantly larger in the hypertensive patients (1.34 mm [95% confidence interval 1.24, 1.44] versus 1.18 mm [1.14, 1.22]; p < 0.05). However, after adjustment for diurnal systolic blood pressure variability, which was significantly increased in the hypertensive group, the significant IMT difference between both patient groups was no longer observed (1.32 mm [1.27, 1.37] versus 1.29 mm [1.25, 1.33]). Multivariate regression analysis revealed the diurnal systolic blood pressure variability as the strongest predictor for IMT. The IMT was most increased in hypertensive patients with increased diurnal systolic blood pressure variability and additional nocturnal blood pressure increase (1.64 mm [1.45, 1.83]. The odds ratio of having early atherosclerosis (age-adjusted IMT > 1.5 mm) increased with raised diurnal systolic blood pressure variability (> 15 mm Hg) in both groups (normotensive: 8.5 [2.30]; hypertensive: 12.6 [4, 43]). The diurnal systolic blood pressure variability is the strongest predictor of early carotid atherosclerosis measured with B-mode ultrasonography and is useful to define the risk-benefit ratio of therapeutic approaches, particularly in patients with only slightly elevated blood pressure levels.

Lipid peroxidation in cord blood at birth

OBJECTIVE

The purpose of this study was to determine oxygen free radical activity in the neonate at birth and relate it to umbilical cord blood acid-base status.

STUDY DESIGN

A series of 110 singleton deliveries had determination of two lipoperoxides in umbilical cord blood: malondialdehyde and organic hydroperoxide. Umbilical pH, PO2, PCO2, bicarbonate, and base excess were also measured.

RESULTS

There was a significant association between lipoperoxides and cord blood pH and base excess. A significant difference existed in the levels of umbilical artery lipoperoxides between nonacidemic and acidemic fetus, as defined by an umbilical arterial pH < 7.20.

CONCLUSION

There is a positive association between lipoperoxide production and acid-base balance at delivery.

Oxygen free radical-induced damage during colonic ischemia/reperfusion in rats

Reperfusion injury following ischemia is thought to be the consequence of reactive oxygen species. Role of these free radicals on the damaging effects of ischemia in colon has been investigated. A rat experimental model was used in which colon was subjected to ischemia and reperfusion and mucosal damage was assessed by biochemical and histological studies. Activity of myeloperoxidase, a neutrophil marker, was increased after ischemia (I) and ischemia/Reperfusion (I/R). Lipid peroxidation products such as malonaldehyde and conjugated diene did not show any change in the experimental colonic mucosa as compared to control. Mucosal level of low molecular weight thiols were found to be altered after I/R. A decrease in alpha-tocopherol level was noticed after ischemia and the decrease was prominent after reperfusion. Histology indicated morphological changes in colon due to ischemia and reperfusion and the damage was more severe after reperfusion. These results suggest that colonic mucosal damage occurs during I/R and free radicals generated by the infiltrated neutrophils may play a role in this damaging process.

Effect of dietary antioxidant trace element supply on cardiac tolerance to ischemia-reperfusion in the rat

Over a 10-week period, female Wistar rats received a diet containing various levels of four trace elements (Zn, Cu, Mn, Se), co-factors of antioxidant enzymes (superoxide dismutase SOD, glutathione peroxidase GPx), in order to examine the influence of supplementation or deficiency of these elements (i) on tissue antioxidant enzyme defence systems, and (ii) on the susceptibility of the myocardium to ischemia-reperfusion injury. At the end of the dietary treatment, hearts were perfused at constant flow (11 ml/min) before being subjected to 15 min of total global normothermic ischemia, followed by reperfusion. The effects of the various diets (deficient, standard or supplemented) were estimated by studying functional recovery of various cardiac parameters (left ventricular developed pressure LVDP, dP/dtmax, heart rate x LVDP) as well as ultrastructural tissue characteristics. Furthermore, SOD and GPx activities were measured before ischemia and at the end of the reperfusion period. Results suggest that: (a) the activity of antioxidant enzymes increased or decreased significantly when diet was respectively supplemented with, or deficient in, trace elements, but was not further modified by an ischemia-reperfusion episode: (b) the recovery of cardiac function during reperfusion, and ventricular myocardial ultrastructure were significantly improved under the influence of trace element supplementation when compared to both standard and deficient groups. These results illustrate the protective effect of trace elements which are co-factors of antioxidant enzymes in limiting ischemia-reperfusion induced injury, and suggest a possible use in the field of anti-ischemic therapy.

Activation of the intracellular glutathione system by oxydative stress during cardiopulmonary bypass and myocardial perfusion

The glutathione (GSH) system is the main defence of tissues against free radicals and red blood cells (RBC) are the most efficient sites for GSH redox cycle activation. Total GSH was assayed during cardiopulmonary bypass (CPB) in RBC and serum from the coronary sinus, peripheral arteries and veins in 18 children corrected of their cardiac defect. Our conclusions are: (1) RBC-GSH redox cycle is activated during heart ischaemia and reperfusion; (2) the activation of intracellular GSH system is preponderant compared with the extracellular one; (3) variations in intraerythrocytic total GSH during heart ischaemia and perfusion are detectable in peripheral veins and arteries, which can be the convenient sites for monitoring changes in the GSH cycle; and (4) increased total GSH levels are present in RBC before aortic crossclamping: at the beginning of mechanical ventilation in veins and, when CPB is started, also in arteries.

Autonomic cardiac control. II. Noninvasive indices and basal response as revealed by autonomic blockades

Heart period, systolic time intervals, low and high frequency heart period variability, blood pressure, and respiration were measured in female subjects under three drug conditions (saline, atropine sulfate, metoprolol) while sitting and standing on three consecutive days. Following preinfusion baseline recordings, saline, metoprolol (14 mg), or atropine sulfate (2 mg) was infused for 15 min (by using a double-blind procedure). Recordings were taken during a postinfusion baseline and in response to an orthostatic stressor (standing versus sitting postures). At the end of the metoprolol session, atropine sulfate was infused and responses were monitored during the postinfusion (i.e., double blockade) baseline and during orthostatic stressor. Analyses of the blockade data revealed that the preejection period (PEP) reflected sympathetic but not vagal influences on the heart, and high frequency (HF, 0.12-0.40 Hz) heart rate variability (respiratory sinus arrhythmia) reflected vagal but not sympathetic influences on the heart. No other measure provided a specific index of the tonic sympathetic or vagal activation of the heart. Postinfusion PEP under saline predicted individual differences in postinfusion cardiac sympathetic activation, whereas postinfusion heart period (but not HF variability) under saline predicted individual differences in postinfusion cardiac vagal activation.

Determination of MDL 74,405, a synthetic analogue of alpha-tocopherol, in dog plasma and heart tissue by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic (HPLC) procedure with electrochemical detection was developed to analyze MDL 74,405 (I), the (-)-(S)-enantiomer of an alpha-tocopherol analogue, in dog plasma and heart tissue after infusion (0.3 mg/kg/h). The sample preparation involved the addition of an internal standard to either the dog plasma and heart tissue prior to protein precipitation. After centrifugation, the resulting supernatant was directly analyzed by HPLC with a Zorbax Rx C8 column and a mobile phase of acetonitrile-0.04 M potassium phosphate, pH 7.0 (70:30, v/v). The concentration of I found was ca. 100 ng/ml in plasma and ca. 3 micrograms/g in heart tissue. A chiral separation with an Ultron ES-OVM column and a mobile phase of methanol-0.025 M potassium phosphate, pH 6.5 (17:83, v/v) was also used to investigate the enantiomeric conversion of I. Preliminary results of a probe study indicated that I is not inverted to the (+)-(R)-enantiomer in vivo.

Beyond thrombolysis: other effects of thrombolytic drugs

OBJECTIVE

To review the effects of plasminogen activators (tissue plasminogen activator, streptokinase, and anistreplase) on fibrinogen and thrombin, platelets, complement, blood rheology, and neutrophils.

DATA SOURCES

A MEDLINE search, as well as a review of recent scientific abstracts, was conducted to identify pertinent literature.

STUDY SELECTION

Focus was placed on studies conducted in humans. However, many in vitro studies have been performed to fully elucidate the effect of plasminogen activators on different aspects of hemostasis and on the fibrinolytic and immune systems.

DATA EXTRACTION

Data from in vitro, human, and animal studies were evaluated.

DATA SYNTHESIS

There is a discrepancy between 90-minute patency and mortality in acute myocardial infarction patients treated with thrombolytic drugs. This could be caused, in part, by other hematologic and immunologic effects of thrombolytic drugs. Though the emphasis of clinical trials has been infarct-related artery patency, left ventricular function, and mortality, some studies have evaluated the effect of thrombolytic agents on fibrinogen and thrombin, platelets, blood rheology, complement, and neutrophils. This review discusses the alteration of systemic hematologic and immunologic parameters by thrombolytic drugs and the possible clinical implications of these effects.

CONCLUSIONS

Although the interactions between thrombolytic drugs, hemostasis, and the fibrinolytic and immune systems are complex and still not fully understood, it appears that these drugs differ in their effects on these systems. A greater understanding of these properties and their clinical implications may ultimately enhance the care and outcome of acute myocardial infarction patients treated with thrombolytic therapy.

The free radical system in ischemic heart disease

The present work was conducted to evaluate the oxygen free radical system in 29 patients and comparing them with nine matched healthy controls of acute and chronic myocardial ischemic syndromes. The parameters assessed for oxidative stress were superoxide anion and malonyldialdehyde, and for the antioxidant defence system were superoxide dismutase, catalase and glutathione reductase. Both oxidative stress and the antioxidant defence system were altered in myocardial ischemia. Subset analysis revealed that in unstable angina and acute myocardial infarction, superoxide anion, malonyldialdehyde and glutathione reductase were elevated while superoxide dismutase and catalase levels were reduced. In stable angina only increased levels of superoxide anion and decreased levels of superoxide dismutase were found. However, this alteration was less marked than in unstable angina and acute myocardial infarction. In the post myocardial infarction group there was no alteration in any of these parameters.

Free radical scavenger depletion in post-ischemic reperfusion brain damage

In the present study the influence of pretreatment with various GSH depletors such as buthionine sulfoximine (BSO) and diethylmaleate (DEM) was investigated in rats following cerebral post-ischemic reperfusion. Moreover, the effect of diethyldithiocarbamic acid (DDC), inhibitor of endogenous Cu,Zn-SOD, was evaluated. A significant depletion (40% of control value) of GSH levels was observed 24 h after DEM administration; after 48 h the value reached control levels. BSO showed maximal GSH depletion (59%) 24 h after administration and it was constant for almost 48 h. DDC administration caused a marked decrease (60%) of Cu,Zn-SOD activity 4 h after the injection and induced a marked decrease in percentage of survival with respect to control (untreated, ischemic) rats, when administered 4 h before ischemia. BSO and DEM prolonged the survival time of animals when administered 24 h before ischemia. This last paradoxical effect is unclear at present, but it might be due to an influence on glutamate cascade.

Cypridina luciferin analog reduces the incidence of ischemia/reperfusion-induced ventricular fibrillation

A Cypridina luciferin analog (CLA), considered to be a sensitive and specific agent for the assay of superoxide, was assessed in isolated hearts for its effects on ischemia/reperfusion injury. Hearts of anesthetized male Wistar rats were isolated and perfused with a modified Krebs-Henseleit bicarbonate buffer to serve as non-recirculating working heart preparations. After 15 min of perfusion to achieve stability, they underwent 20 min of global ischemia and were then reperfused for 30 min with or without 250 microM of CLA, dissolved in the perfusate. The incidence of ventricular fibrillation was only 13% in the CLA group, whereas it was 88% in the controls. The CLA treatment was further associated with significantly increased left ventricular developed pressure and cardiac output; and in contrast, the left ventricular end-diastolic pressure was significantly reduced, as compared with the control group. Thiobarbiturate reacting substance content in the hearts of the CLA group was significantly decreased (27.5 +/- 2.4 versus 36.9 +/- 9.7 mumol/g dry weight). This study thus indicates that CLA may be useful for alleviating ischemia/reperfusion injury (reperfusion-induced arrhythmia and damage to heart function) involving free radicals.

The effect of supplementing hypothermic crystalloid cardioplegia with catalase plus allopurinol in the isolated rabbit heart

The effect of adding allopurinol and catalase to hypothermic cardioplegia for ischemic-reperfusion injury was investigated in the isolated rabbit heart. Hearts were divided into two groups, namely: Group C (n = 7), which received a hypothermic crystalloid cardioplegic solution alone (4 degrees C), and group T (n = 7), which received the hypothermic cardioplegic solution with allopurinol (148 mumol/L)13 and catalase (37 nmol/L).12 The cardioplegic solution was infused continuously into the isolated hearts, which had been placed in ice-cold saline, during a 12 h preservation. Subsequently, the hearts were mounted on a noncirculating, nonpulsatile perfusion circuit using Krebs-Henseleit buffer solution at 37 degrees C for 1 h at a constant perfusion pressure of 75 mm Hg. The left ventricular developed pressure (LVDP), maximum rate of pressure change (max dp/dt), and percent recovery of coronary flow were higher, while the creatine phosphokinase concentration and left ventricular end diastolic pressure (LVEDP) were lower in group T. The tissue malondialdehyde concentration and water content were similar in both groups. Thus, cardiac function after a 12 h preservation was enhanced by the added combination of allopurinol and catalase to the cardioplegic solution, supporting its role in the prevention of free radical reperfusion injury in cardiac preservation.

Intracellular catalase inhibition does not predispose rat heart to ischemia-reperfusion and hydrogen peroxide-induced injuries

The objective of this study was to determine whether inhibition of intracellular catalase would decrease the tolerance of the heart to ischemia-reperfusion and hydrogen peroxide-induced injuries. Isolated bicarbonate buffer-perfused rat hearts were used in the study. Intracellular catalase was inhibited with 3-amino-1,2,4-triazole (ATZ, 1.5 g/kg body weight, two hours prior to heart perfusion). In the ischemia-reperfusion protocol, hearts were arrested with St. Thomas'II cardioplegic solution, made ischemic for 35 min at 37 degrees C, and reperfused with Krebs-Henseleit buffer for 30 min. The extent of ischemic injury was assessed using postischemic contractile recovery and lactate dehydrogenase (LDH) leakage into reperfusate. In the hydrogen peroxide infusion protocol, hearts were perfused with increasing concentrations of hydrogen peroxide (inflow rates 0.05-1.25 mumol/min). Inhibition of catalase activity (30.4 +/- 1.8 mU/mg protein in control vs 2.4 +/- 0.3 mU/mg in ATZ-treated hearts) affected neither pre-ischemic aerobic cardiac function nor post-ischemic functional recovery and LDH release in hearts subjected to 35 min cardioplegic ischemic arrest. Myocardial contents of lipid hydroperoxides were similar in control and ATZ-treated animals after 20 min aerobic perfusion, ischemia, and ischemia-reperfusion. During hydrogen peroxide perfusion, there was an increase in coronary flow rate followed by an elevation in diastolic pressure and inhibition of contractile function in comparison with control hearts. The functional parameters between control and ATZ-treated groups remained unchanged. The concentrations of myocardial lipid hydroperoxides were the same in both groups. We conclude that inhibition of myocardial catalase activity with ATZ does not predispose the rat heart to ischemia-reperfusion and hydrogen peroxide-induced injury.

Segmental systolic responses to brief ischemia and reperfusion in the hypertrophied canine left ventricle

OBJECTIVES AND BACKGROUND

Left ventricular hypertrophy is associated with increased mortality, increased myocardial infarct size and an increased incidence of sudden death. Although reperfusion after ischemia has been shown to result in decreased infarct size and recovery of systolic thickening, it is unknown how left ventricular hypertrophy might influence recovery of regional systolic thickening after ischemia and reperfusion. We hypothesized that left ventricular hypertrophy might attenuate or abolish the functional response to reperfusion.

METHODS

Three groups of chronically instrumented, conscious dogs (dogs with left ventricular hypertrophy and hypertension; dogs with left ventricular hypertrophy and reduced blood pressure and a control group without hypertrophy and with normal blood pressure) underwent 15 min of ischemia and 24 h of reperfusion. Segmental systolic thickening was measured by sonomicrometers and myocardial segments were grouped by percent of control segmental systolic thickening retained at 15 min of ischemia (class 1 greater than or equal to 67%, class 2 from 0% to 66%, class 3 less than 0% control systolic thickening). The recovery of each class of segment was measured serially during reperfusion. Hemodynamic variables and regional myocardial blood flow were also measured.

RESULTS

There were no differences among groups in recovery of segmental systolic thickening for class 1 segments. Systolic thickening in class 2 (hypokinetic) segments was significantly depressed (p less than 0.05 compared with control value) in the group with left ventricular hypertrophy and reduced blood pressure (but not in the group with hypertrophy and hypertension) during early reperfusion; systolic thickening in class 3 (dyskinetic) segments showed a similar trend in the group with hypertrophy and reduced pressure.

CONCLUSIONS

Although left ventricular hypertrophy with hypertension did not attenuate the contractile response to reperfusion, hypertrophy with reduced blood pressure was associated with significantly greater depression of segmental systolic thickening early during reperfusion.

Role of atrial contraction and synchrony of ventricular contraction in the optimisation of ventriculoarterial coupling in humans

OBJECTIVE

To examine the effects of pacing modes on the interaction between the left ventricle and arterial system in humans.

DESIGN

The slope of the end systolic pressure-volume relation (end systolic elastance), effective arterial elastance, the ratio of effective arterial elastance to end systolic elastance, and mechanical energy efficiency were compared under different pacing modes (atrial, atrioventricular, and ventricular).

PATIENTS

Nine male patients with sick sinus syndrome who had cardiac catheterisation for diagnosis and to see whether they needed a pacemaker.

INTERVENTIONS

A conductance catheter with tip-manometer was inserted into the left ventricle to obtain pressure-volume loops, and two pacing catheters were inserted into the right atrium and into the right ventricle respectively.

RESULTS

End systolic elastance was lower in atrioventricular pacing than in atrial pacing, but effective arterial elastance was not significantly different. End systolic elastance was lower in ventricular pacing than in atrioventricular pacing, and effective arterial elastance was higher in ventricular pacing than in atrioventricular pacing. Consequently the ratio of effective arterial elastance to end systolic elastance was lowest in atrial pacing and highest in ventricular pacing, and mechanical energy efficiency was highest in atrial pacing and lowest in ventricular pacing.

CONCLUSIONS

Atrial contraction and synchronous ventricular contraction independently optimise ventriculoarterial coupling in terms of a transfer of energy. Thus atrial pacing gives the best ventriculo-arterial coupling among these pacing modes.

The effect of exercise-induced myocardial ischemia on postischemic left ventricular diastolic filling

To determine whether exercise-induced ischemia impairs left ventricular diastolic filling in the postischemic period in humans, 101 men (mean age 57 +/- 10 years) were studied before and 2 h after a symptom-limited thallium-201 tomographic treadmill with pulsed Doppler echocardiography of mitral valve inflow. In the postischemic period 2 h after exercise, diastolic filling was significantly impaired in the ischemia group (reversible thallium defect; n = 24) as reflected by a decrease in the peak early filling velocity (44.5 +/- 10.1 to 39.9 +/- 9.9 cm/s, p less than 0.01), peak early to atrial filling velocity ratio (0.91 +/- 0.27 to 0.76 +/- 0.25, p less than 0.001), and deceleration rate of early filling (281 +/- 104 to 245 +/- 86 cm/s2, p less than 0.01). Similar alterations in the postischemic period occurred in the myocardial infarction-ischemia group (partially reversible defect; n = 28) as seen by a decrease in the peak early filling velocity (47.6 +/- 11.6 to 41.8 +/- 12.0 cm/s, p less than 0.001), peak early to atrial filling velocity ratio (0.84 +/- 0.21 to 0.68 +/- 0.18, p less than 0.001), and early time-velocity integral (7.06 +/- 1.78 to 5.64 +/- 2.07 cm, p less than 0.001). In the control group (no defects; n = 33) and myocardial infarction group (fixed defect; n = 16), diastolic filling was unchanged in the postexercise period. Heart rate and blood pressure were unchanged post-exercise in all groups. Exercise-induced ischemia impairs diastolic filling in the postischemic period in humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Dimethylthiourea, an oxygen radical scavenger, protects isolated cardiac myocytes from hypoxic injury by inhibition of Na(+)-Ca2+ exchange and not by its antioxidant effects

Myocardial reoxygenation injury may be attenuated by oxygen free radical scavengers, arguing for a role of oxygen radicals in this process. To determine whether free radical scavengers affect reoxygenation injury in isolated cardiac myocytes, resting rat ventricular myocytes were exposed to hypoxic (PO2 less than 0.02 mm Hg) glucose-free buffer alone (n = 50) or with the addition of the oxygen radical scavengers 1,3-dimethyl-2-thiourea (DMTU, 25 mM, n = 46), human recombinant superoxide dismutase (SOD, 1,000 units/ml, n = 40), or the combination of these agents (n = 41). All cells responded by undergoing contracture to a rigor form. Hypoxia was then continued for a second period (T2), the duration of which correlates inversely with survival. After reoxygenation, cells either retained their rectangular shape (survival) or hypercontracted to a rounded form (death). For the group of cells with a T2 period greater than 30 minutes, no cell exposed to buffer alone (n = 20) or to SOD (n = 16) survived, in contrast to 15 of 24 (63%) cells exposed to DMTU. The addition of SOD to DMTU offered no advantage to DMTU alone. The protective effect of DMTU was not observed when it was added at reoxygenation, suggesting that this agent has an important effect during the hypoxic period when intracellular Ca2+ is known to rise, most likely because of the reversal of Na(+)-Ca2+ exchange. Therefore, the effects of DMTU on Ca2+ regulation (indexed by indo-1 fluorescence) during hypoxia were studied. DMTU significantly blunted the [Ca2+] rise during the hypoxic period.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect on Ventricular Performance of Direct Current Electrical Shock for Catheter Ablation of the Atrioventricular Junction

In ten patients undergoing catheter ablation of the atrioventricular junction (CAVJ) because of therapy refractoriness of supraventricular arrhythmias, the effect of repeated high energy direct current (DC) shock on left ventricular function has been investigated. End-systolic pressure-volume relation (ESPVR) and the positive first derivative of ventricular pressure (dP/dt) have been used as indices of left ventricular systolic function, while the time constant of isovolumic pressure decay, the diastolic stiffness, and the negative dP/dt represented the diastolic function parameters, respectively. Each patient received at least two and no more than three DC shocks for successful CAVJ, with an energy of 360 joules. Significant acute reduction of both systolic and diastolic function was noted after each DC shock, with a slow partial recovery of both phases. The recovery process involved the systolic phase earlier and more completely than the diastolic one. The alterations observed could not be predicted from preablation values, but were significantly related to cumulative energy dose index for body weight. In conclusion, repeated high energy DC shocks acutely, but reversibly, impair left ventricular function; in addition, the ventricular function reduction is primarily related to the total ablation energy indexed for body weight.

Are enzymatic tests good indicators of coronary reperfusion?

OBJECTIVE

To assess the accuracy of four enzymatic tests, including early release rates of creatine kinase and alpha-hydroxybutyrate dehydrogenase, in assessing coronary reperfusion after thrombolytic therapy.

DESIGN

A prospective clinical trial identifying patients with a successful thrombolytic treatment.

PATIENTS

Eighty nine patients with acute myocardial infarction were studied. Arteriography showed a closed infarct related artery in all of them. Reperfusion due to thrombolysis occurred in 74 patients and there was no reperfusion in 15 patients.

RESULTS

The 74 patients showing coronary reperfusion had a significantly shorter time to peak creatine kinase activity, higher early release rates for creatine kinase and alpha-hydroxybutyrate dehydrogenase, and a more rapid release of alpha-hydroxybutyrate dehydrogenase (ratio of cumulative release of alpha-hydroxybutyrate dehydrogenase during the first 24 hours to that 72 hours after infarction). All these differences were statistically significant (p less than 0.001). Optimum cut off levels were determined with decision level plots and the accuracy of the four enzymatic tests was calculated. Accuracy was low for all four tests (73%, 70%, 70%, and 82%).

CONCLUSION

None of the four enzymatic tests accurately predicted the perfusion state of the infarct related coronary artery after thrombolysis. These tests cannot be used reliably in routine clinical practice as non-angiographic markers of coronary reperfusion.

Antioxidant enzyme response to selenium deficiency in rat myocardium

Influences of dietary selenium (Se) deficiency, physical training and an acute bout of exercise on myocardial antioxidant enzyme activity, lipid peroxidation and related biochemical properties were investigated in post-weanling male Sprague-Dawley rats. An experimental group was fed a diet containing less than 0.01 mg Se/kg and had free access to distilled water (Se-D), whereas control rats were supplemented with 0.5 mg Se/l in drinking water (Se-A). Se deficiency depleted heart mitochondrial and cytosolic Se-dependent glutathione peroxidase activity to 24 and 3%, respectively, of those in Se-A rats. Heart mitochondrial superoxide dismutase (Mn SOD) activity was 24% higher (p less than 0.05) in Se-D than in Se-A rats. Cytosolic (copper-zinc) SOD and catalase activities were not altered, whereas glutathione S-transferase activity was significantly decreased in Se-D (p less than 0.01). Myocardial antioxidant enzyme activities were not affected by either training or an acute exercise bout. Heart lipid peroxidation and activities of several enzymes in substrate metabolism were also unaffected by Se or exercise. It is concluded that rat heart has sufficient reserve of antioxidant enzyme capacity in coping with oxidative stress imposed by Se deficiency or exercise. The adaptation of Mn SOD may reveal its potential role in myocardial antioxidant defense.

Reduction of infarct size by cell-permeable oxygen metabolite scavengers

The timely restoration of blood flow to severely ischemic myocardium limits myocardial infarct size. However, experimental studies demonstrate that the myocardial salvage achieved is suboptimal because of additional injury that occurs during reperfusion, due in part to the generation of reactive oxygen metabolites. Initially, superoxide (O2-) was considered to be the central mediator of reperfusion injury. While there are several potential pathways of O2- generation in reperfused myocardium, O2- is poorly reactive toward tissue biomolecules. However, O2-, in the presence of redox-active metals such as iron, generates .OH or hydroxyl-like species that are highly reactive with cell constituents. Thus, while O2- may initiate reaction sequences leading to myocardial injury, it may not be the actual injurious agent. In vitro studies suggest that oxygen metabolite injury occurs at intracellular sites and involves iron-catalyzed processes. Consistent with this mechanism, extracellular oxygen metabolite scavengers have not convincingly reduced infarct size. However, treatment around the time of reperfusion, after ischemia is well established, with cell-permeable scavengers of .OH reduce infarct size. Results with these cell-permeable agents suggest that in the intact animal during regional ischemia and reperfusion, oxygen metabolite injury also occurs at intracellular sites. Cell-permeable scavenger agents are a promising class of drugs for potential clinical use, though further experimental and toxicologic studies are required.

Interrelationships of ultrastructure and function in the microvasculature of normal and ischaemic myocardium

This paper reviews various methods involving electron microscopy that have been used to investigate the ultrastructure of the vasculature of the normal and diseased heart. Whereas scanning electron microscopy is more commonly employed to record surface topography, it can be used to examine freeze-fracture planes within the myocardium and, using heavy-metal staining and back-scattered electron imaging, to examine large 2-mu-thick resin-embedded sections through the heart. The latter technique allows the comparison of structural alterations across the wall of the heart and thus accurate definition of the transmural progression of pathological processes. Transmission electron microscopy can then be used to provide more detailed information from precisely localised regions. Human myocardium can be usefully studied up to 12 hours post-mortem provided that suitable control material is included. Intravascular tracers including low-viscosity resin and nuclear track emulsion can be used to determine whether or not particular vessels allow flow at the time of fixation, and thus changes in the pattern of flow through the microvasculature due to ischaemia and reperfusion can be quantified and defined. Particular care is required in the fixation of ischaemic tissues because oxygen dissolved in the fixative can lead to the rapid formation of oxygen-free radicals on contact with the tissue. This produces artefactual reoxygenation damage characterised by membrane disruption and cell and organelle swelling, which has previously been attributed to ischaemic injury per se. Bubbling glutaraldehyde with nitrogen substantially reduces this artefact.

Mitral valve surgery: replacement vs reconstruction

In comparative series, valve repair has been effective, with few of the problems--notably, thromboemboli--associated with replacement procedures. Although many patients are elderly and have coronary artery disease, reparative surgery not only is low-risk but also allows earlier intervention, before irreversible left ventricular damage occurs.

Role of oxygen-derived free radicals in myocardial edema and ischemia in coronary microvascular embolization

BACKGROUND

Oxygen-derived free radicals are thought to injure the ischemic heart during coronary microvascular embolization.

METHODS AND RESULTS

To test this idea, microspheres (15 microns in diameter) were repetitively administered into the left anterior descending coronary artery to cause microvascular embolization in dogs. Myocardial contractile and metabolic dysfunctions were significantly attenuated after treatments with recombinant human superoxide dismutase, an acyl derivative of ascorbic acid (CV3611, 2-O-octadecylascorbic acid), and xanthine oxidase inhibitor (allopurinol). The free radical scavengers and inhibitor enhanced the coronary hyperemic flow response during embolization, and the total number of microspheres causing maximal embolization was increased by these drugs. When 8-phenyltheophylline was additionally administered with superoxide dismutase, these beneficial effects were abolished, indicating that coronary effects of these drugs may be due to increased release of adenosine during coronary microvascular embolization.

CONCLUSIONS

We conclude that oxygen radicals worsen the ischemic injury in coronary microembolization.

Mitral valve repair: a valuable procedure with good long term results even when performed infrequently

OBJECTIVE

To assess the results of mitral valve repair in a series with a low frequency of repair despite a policy to conserve the valve whenever possible.

DESIGN

Retrospective review of case notes with clinical and echocardiographic examination of survivors.

SETTING

Cardiac surgery unit in a university teaching hospital.

PATIENTS

62 consecutive patients undergoing mitral valve repair by one surgeon between 1979 and 1989.

INTERVENTIONS

Mitral valve repair according to the criteria and techniques of Carpentier.

MAIN OUTCOME MEASURES

Frequency of repair, operative mortality, actuarial survival, freedom from reoperation and thromboembolism, clinical state, and echocardiographic state.

RESULTS

The 62 patients, median age 58 years (interquartile range 51 to 64 years), represent 14% (70% confidence interval 12% to 15%) of the 454 mitral valve operations performed in the study period. Operative mortality was 8% (70% CI 5% to 13%). Actuarial survival was 62% (70% CI 43% to 81%) at nine years. At nine years actuarial freedom from reoperation was 91% (70% CI 79% to 102%) and freedom from thromboembolism 91% (70% CI 80% to 102%). At a median follow up of 33 months (interquartile range 21 to 74 months), 38 of 46 survivors had improved functional state. Of 21 patients who underwent echocardiography one had severe mitral regurgitation and one mitral stenosis.

CONCLUSION

Although compared with other reports of mitral valve repair the prevalence of repair was low in this series the results are comparable and justify a positive approach to repair in all patients undergoing mitral valve surgery even if this can only be achieved in a small proportion of patients.

The effect of superoxide dismutase and catalase on myocardial reperfusion injury in the isolated rat heart

This study was designed to evaluate the efficacy of superoxide dismutase (SOD) and catalase on ischemic and reperfusion injury in the isolated working rat heart. The temperature and duration of ischemia varied under three conditions: 1) at 37 degrees C for 35 minutes, 2) at 28 degrees C for 120 minutes and 3) at 20 degrees C for 120 minutes. SOD (100 mg/L) and catalase 10 mg/L) were either added to St. Thomas' Hospital cardioplegic solution during ischemia (CP group) or to the reperfusion solution for 10 minutes after reflow (RS group). They were compared with a control group which received no free radical scavengers. The postischemic recovery ratio of cardiac functions were markedly superior to the values of the control group with a significant difference being noted in the CP and RS groups under ischemia at 37 degrees C and 28 degrees C. In the series done at 20 degrees C, a significant improvement was seen in the RS group, and the CP group also showed better functional recovery rates compared with the control group, although the differences were not statistically significant. Thus, SOD and catalase added to the cardioplegic solution or reperfusion fluid demonstrated an excellent protective effect on the myocardium against ischemic or reperfusion injury in both hypothermic ischemia and normothermia.

Reduction of canine myocardial infarct size by a diffusible reactive oxygen metabolite scavenger. Efficacy of dimethylthiourea given at the onset of reperfusion

A number of scavengers of reactive oxygen metabolites reduce myocardial injury when given before ischemia and reperfusion, but few, if any, have proven to be effective when given near the onset of reperfusion. This is particularly true when infarct size is measured after at least 48 hours of reperfusion, when the full extent of myocardial damage has become apparent. Dimethylthiourea (DMTU) is an extremely diffusible, potent scavenger of hydroxyl radical, hydrogen peroxide, and hypochlorous acid, with a long half-life of 43 hours. Sixteen chloralose-anesthetized dogs underwent 90 minutes of left anterior descending coronary artery (LAD) occlusion followed by 48 hours of reperfusion. Collateral flow was measured by radioactive microspheres. Infarct size and risk area were measured by a postmortem dual-perfusion technique using triphenyl tetrazolium chloride and Evan's blue dye. In eight dogs, therapy with DMTU (500 mg/kg i.v.) was given during the last 15 minutes of ischemia and the first 15 minutes of reperfusion. In eight control dogs, the same volume of 0.9% saline was given during the last 15 minutes of ischemia through the first 15 minutes of reperfusion. Infarct size as a percent of risk area was reduced in the DMTU-treated group compared with the saline-treated controls (DMTU = 42 +/- 4% versus saline = 59 +/- 4%, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen content of the fixative is important in the interpretation of the ultrastructure of ischaemic myocardium

Isolated rat hearts were subjected to 15, 45, or 60 minutes of global ischaemia and then fixed by perfusion at 37 degrees C with glutaraldehyde containing various amounts of oxygen. This either had been bubbled with 100% oxygen (PO2 620 mm Hg) or with 100% nitrogen (PO2 40 mm Hg) immediately before use, or it had been routinely prepared and stored exposed to atmospheric oxygen (PO2 245 mm Hg). The ultrastructure of myocytes and endothelial cells subjected to 15 minutes of ischaemia was not affected by the treatment of the fixative. However, when the tissue subjected to longer periods of ischaemia was fixed with routinely prepared or oxygen-bubbled glutaraldehyde, ultrastructural changes characteristic of reoxygenation damage were uniformly evident in both the microvasculature and myocytes. These qualitatively distinct changes included mitochondrial swelling, cell swelling, endothelial bleb formation, and narrowing of capillary lumina. These abnormalities were not observed in tissue fixed with nitrogen-bubbled glutaraldehyde. These findings indicate that deliberate steps should be taken to reduce or eliminate dissolved oxygen from the fixatives used to study ischaemic tissues. Otherwise artefactual reoxygenation damage in vitro may occur and make valid ultrastructural interpretation difficult or impossible.

Early experience with intra-arterial thrombolytic therapy for peripheral arterial occlusion

The authors present their early experience with local intra-arterial thrombolytic therapy for peripheral arterial occlusions causing limb threatening ischaemia, using streptokinase or urokinase. Ten patients were treated in a period of one year. Five patients had successful recanalisation, two patients had partial success and three patients required major amputation. The indications, contraindications and results of this treatment are reviewed.

Recombinant tissue-type plasminogen activator: current concepts and guidelines for clinical use in acute myocardial infarction. Part II

The extraordinarily high prevalence of coronary heart disease, coupled with the alarming incidence of MI in Western society, has encouraged the investigation and development of pharmacologic agents that can be employed widely, quickly, effectively, and safely. Recombinant t-PA has played a vital role in the treatment of MI, restoring coronary arterial patency, limiting infarct size, preserving ventricular function, and improving patient survival. It has been shown to be safe when given to carefully selected patients and, although indications for clinical use have been relatively restricted, they appear to be expanding considerably. Future investigations must continue to focus on patient selection to allow treatment for all patients who would derive benefit and to establish dosing regimens and adjuvant therapies that will maximize coronary reperfusion while concomitantly limiting reocclusion and hemorrhagic complications.

Effect of a cardioselective alpha-tocopherol analogue on reperfusion injury in rats induced by myocardial ischaemia

Free radicals may cause some of the irreversible injury which occurs during myocardial ischaemia and reperfusion. In the present study the effects of a cardioselective, free radical scavenger, MDL 74270, which is an analogue of alpha-tocopherol, on myocardial infarct size in an anaesthetised rat model of coronary artery ligation (60 min) and reperfusion (30 min) has been evaluated. Infusion of MDL 74270 (0.3-3.0 mg/kg per h) commencing 10 min before occlusion until the end of reperfusion significantly reduced infarct size. The highest dose also caused a significant reduction in serum creatine phosphokinase levels. Similar findings have been obtained with the bromide salt of MDL 74270. Tissue distribution studies with 14C-labelled MDL 74270 and its tertiary amine analogue (MDL 74366) showed heart/blood ratios of total radioactivity, 1-6 h after i.v. administration, greater than 20 after MDL 74270 and around 1 after MDL 74366. The importance of accumulation of total radioactivity in the heart after MDL 74270 is supported by the fact that MDL 74366 was 30 times less potent as a myocardial protector in the ligation/reperfusion studies. It is concluded that MDL 74270 has potential for cardioprotective use in conditions of acute reperfusion.

Alterations in endocardial vascular resistance after reperfusion in a low flow, high demand model of ischemia: effects of dipyridamole and WEB-2086, a platelet-activating factor antagonist

To determine if alterations in regional coronary vascular resistance could occur in the type of myocardial ischemia present in severe angina pectoris, regional perfusion and function were studied in 35 conscious sedated dogs. A stenosis producing severe hypokinesia of the perfused segment was created for 2 h on the left anterior descending coronary artery and 10 episodes of 1 min of high demand ischemia (atrial pacing at a rate sufficient to induce dyskinesia in the hypoperfused segment) were superimposed before reperfusion. The dogs were randomized into three treatment groups: control (n = 13), dipyridamole (n = 10) or WEB-2086 (n = 12), an antagonist of the effects of the endogenous platelet-activating factor. During stenosis, residual endocardial blood flow in the ischemic but nonnecrotic area averaged 0.72 +/- 0.14, 0.38 +/- 0.13 and 0.68 +/- 0.17 ml/min per g in the control, WEB-2086 and dipyridamole groups, respectively. Twenty-four hours after reperfusion, endocardial blood flow in the ischemic area was significantly lower in control dogs (1.04 +/- 0.15 ml/min per g) than in dogs treated with WEB-2086 (1.44 +/- 0.28 ml/min per g; p less than 0.03) or dipyridamole (3.00 +/- 0.83 ml/min per g; p less than 0.01). Accordingly, in control dogs, endocardial coronary vascular resistance in the ischemic area was increased after reperfusion from 85 +/- 11 to 124 +/- 27 mm Hg/(ml/min per g) (p less than 0.05) after 24 h. In contrast, coronary vascular resistance in the ischemic area remained unchanged in dogs receiving WEB-2086 (77 +/- 8 to 79 +/- 9 mm Hg/(ml/min per g); p = NS) and it decreased significantly in dogs receiving dipyridamole (72 +/- 8 to 44 +/- 8 mm Hg/(ml/min per g); p less than 0.01). Regional function after 24 h remained depressed in all three groups. These data indicate that low flow, high demand ischemia induces alterations in the subendocardial microvasculature. Such alterations in regional coronary vascular resistance might play a role in several forms of ischemic heart disease such as in severe angina, but they appear susceptible to improvement by therapeutic interventions that influence granulocyte and platelet activation.

Inhibitory effect of unstimulated neutrophils on platelet aggregation by release of a factor similar to endothelium-derived relaxing factor (EDRF)

Previous studies have indicated a possible role for polymorphonuclear leukocytes (PMNLs) in the maintenance of hemostasis and vascular tone. We now demonstrate that unstimulated isolated PMNLs maintained at 37 degrees inhibited human platelet aggregation in a concentration- and time-dependent fashion. In addition, PMNLs increased platelet cyclic GMP concentrations. The platelet aggregation inhibitory effect of PMNLs was potentiated by superoxide dismutase and attenuated by hemoglobin and methylene blue. This inhibitory effect of PMNLs was not observed in 48-hr-old killed cells and was not modulated by aspirin treatment or by adenosine deaminase. These observations suggest that human PMNLs maintained at 37 degrees produce a substance with biological characteristics similar to those of the endothelium-derived relaxing factor.

Effect of polyoxyethylene-modified superoxide dismutase on recovery of myocardial dysfunction after coronary stenosis in dogs

The effects of superoxide dismutase modified with polyoxyethylene (SOD-POE) on impairment of myocardial segment shortening (SS) during coronary stenosis plus pacing-induced tachycardia (CSPT) and the recovery after reperfusion was examined in anesthetized dogs. SOD-POE or saline was administered i.v. 30 min before reperfusion. Changes in hemodynamic variables and SS by CSPT were similar in both groups. However, the SOD-POE group showed improved recovery of SS compared with the control group. Results indicate that oxygen-derived free radicals may partially be involved in the genesis of myocardial dysfunction after CSPT-induced regional ischemia.