Identification of a time window for therapy to reduce experimental canine myocardial injury: suppression of neutrophil activation during 72 hours of reperfusion

The cardio-protective effects of neutrophil depletion or inhibition of neutrophil activation early in the course of myocardial reperfusion has been established. Whether these treatments would be effective during extended periods of reperfusion has not been ascertained. Open-chest anesthetized dogs were subjected to left circumflex artery (LCX) occlusion for 90 minutes followed by 72 hours of reperfusion. Dogs were randomized into one of four groups: 1) control; 2) Ilo-2 (iloprost 100 ng/kg/min administered via the left atrium beginning 10 minutes after LCX occlusion and continuing 2 hours into reperfusion); 3) Ilo-48 (iloprost 100 ng/kg/min administered as above until 1 hour after reperfusion then 25 ng/kg/min for 48 hours of reperfusion; or 4) antibody (neutrophil antibody administered before occlusion and 1/2 hourly for 2 hours of reperfusion and then every 24 hours). Myocardial infarct size, as a percentage of the area at risk assessed after 72 hours of reperfusion, was significantly smaller in the antibody-treated group (32.1 +/- 5.0% mean +/- SEM) or Ilo-48 (22.6 +/- 4.0%) treatment group compared with control (48.7 +/- 5.6%) or Ilo-2 (57.6 +/- 5.2%) groups. Regional myocardial blood flow studies demonstrated that all groups developed similar degrees of ischemia. The iloprost-treated groups had lower mean arterial blood pressures during occlusion and reperfusion than groups 1 and 4 (p less than 0.05). Circulating neutrophil counts were increased in groups 1 and 2 at 24 and 48 hours after reperfusion compared to groups 3 and 4 (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Inotropic stimulation of reperfused myocardium with dopamine: effects on infarct size and myocardial function

Prolonged postischemic ventricular dysfunction ("stunned myocardium") may be responsible for heart failure after myocardial reperfusion. Although inotropic stimulation can enhance the contractility of stunned myocardium, it could potentially increase infarct size and thereby impair ultimate recovery of myocardial function. In 16 anesthetized dogs, the left anterior descending coronary artery was occluded for 2 hours, and then reperfused. At 45 minutes of reperfusion, the dogs were randomized to receive a 3 hour intravenous infusion of either saline solution or dopamine (10 micrograms/kg per min), and 1 hour after the infusion was discontinued the area of necrosis and an in vivo area at risk of necrosis were determined. All dogs had serial two-dimensional echocardiograms with computer-assisted analysis and in vivo biopsies for determination of adenosine triphosphate and creatine phosphate levels. Dopamine caused an increase in the contractility of the reperfused myocardium, with systolic wall thickening increasing from -4.1 +/- 2.6 (mean +/- SEM) to +24.0 +/- 3.7% (p less than 0.002) and short-axis cross-sectional ejection fraction increasing from 27.1 +/- 4.7 to 71.6 +/- 4.4% (p less than 0.002) after 15 minutes of infusion. Regional myocardial blood flow in the previously ischemic epicardium was increased from 1.18 +/- 0.11 ml/min per g with saline to 2.95 +/- 0.36 ml/min per g with dopamine (p less than 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhancement of salvage of reperfused ischemic myocardium by diltiazem

Concomitant use of pharmacologic agents may be required for maximal salvage of ischemic myocardium by reperfusion. Accordingly, in dogs with induced thrombotic coronary occlusion, the effects of intravenous diltiazem given 30 minutes before administration of streptokinase on myocardial blood flow and myocardial salvage were evaluated. Two independent types of end points were employed. Positron emission tomography was utilized for noninvasive assessment of myocardial perfusion and infarct extent. Direct measurements included quantification of myocardial infarction by assay of creatine kinase activity in myocardial homogenates. Infarct extent averaged 27.9 +/- 11.4% of left ventricular weight in 10 control dogs in which coronary occlusion was maintained for 24 hours. In eight dogs given streptokinase alone, the infarct extent averaged 16.7 +/- 10.0% of left ventricular mass (p less than 0.05 versus control). In nine other dogs given diltiazem (15 micrograms/kg per min continuously until death was induced) beginning 30 minutes before streptokinase, infarct extent averaged 9.4 +/- 6.7% of left ventricular mass (p less than 0.05 compared with reperfusion alone). At the dose administered, diltiazem did not alter blood flow, heart rate or mean arterial pressure after coronary occlusion or thrombolysis. The region at risk, determined in 16 dogs from perfusion images obtained with positron tomography and oxygen-15-labeled water after coronary occlusion, was similar in the three groups (30.6 +/- 7.3% of the left ventricle in six control dogs, 31.8 +/- 4.5% in five dogs with reperfusion alone and 30.5 +/- 11.6% in five dogs with reperfusion plus diltiazem). Infarct size quantified in terms of the extent of myocardium exhibiting less than 50% of peak carbon-11-labeled palmitate uptake 24 hours after occlusion and expressed as the percent of the region at risk averaged 89.6 +/- 11.4% in control dogs, was significantly reduced to 45.1 +/- 29.8% in dogs with reperfusion alone and was reduced further to 22.3 +/- 16.4% in dogs given diltiazem and reperfusion. Thus, concomitant treatment with diltiazem markedly enhances salvage of reperfused myocardium after coronary thrombolysis.     

Limitation of myocardial reperfusion injury by intravenous perfluorochemicals. Role of neutrophil activation

Neutrophil activation and infiltration into the ischemic myocardium after reperfusion may limit the amount of salvageable myocardium (reperfusion injury). The effects of intravenous perfluorochemicals (Fluosol-DA) on infarct size, ventricular contractility, and neutrophil function were assessed in an occlusion-reperfusion canine model. Closed-chest dogs were subjected to 90 minutes of left anterior descending artery occlusion followed by 24 hours of reperfusion. Animals were randomized to receive either Fluosol-DA (FDA, n = 8) or Ringer's lactate (CONT, n = 10) intravenously over 30 minutes just before left anterior descending artery reperfusion. Neutrophil demargination and infiltration into the myocardium were assessed in vivo with In111. Neutrophil chemotaxis, superoxide radical production, and lysozyme degranulation were evaluated ex vivo at baseline, 1 hour after occlusion, and 1 hour after reperfusion. Perfluorochemicals significantly reduced infarct size expressed as percent of area at risk (FDA, 7 +/- 4%; CONT, 24 +/- 6%; p less than 0.01). This was associated with positive wall motion in the jeopardized zone of Fluosol-DA animals compared with dyskinesis in control animals (FDA, +4.4 +/- 2.1%; CONT, -1.1 +/- 1.5%; p less than 0.05). Electron microscopy showed reduced neutrophil and erythrocyte plugging of capillaries with relative preservation of endothelial cells in the Fluosol-DA animals. Myocardial blood flow was greater in the ischemic endocardium of Fluosol-DA animals 1 hour after reperfusion (FDA, 1.23 +/- 0.21; CONT, 0.62 +/- 0.08 ml/g/min; p less than 0.01). Neutrophil demargination and infiltration into the ischemic myocardium was reduced in the animals treated with Fluosol-DA. (FDA, 2.5 +/- 0.7 x 10(3); CONT, 14.1 +/- 2.7 x 10(3) neutrophils/g; p less than 0.01). Neutrophil chemotaxis and lysozyme release were also markedly suppressed in the Fluosol-DA groups ex vivo. These results show that intravenous Fluosol-DA significantly reduces reperfusion injury with greater salvage of myocardium and improved left ventricular function. The chief mechanism of action of Fluosol-DA appears to be the suppression of neutrophil function.     

Dissociation between two-dimensional echocardiographic left ventricular wall motion and myocardial salvage in early experimental acute myocardial infarction in dogs

This study was designed to evaluate whether the effects of coronary reperfusion with or without a pharmacologic agent could be detected in the early hours after infarction by 2-dimensional (2-D) echocardiography applied in a manner analogous to its clinical use. Proximal left anterior descending coronary occlusion was performed in 24 dogs, and the dogs were then randomized into 3 groups. In group 1 (n = 8), coronary occlusion was maintained for 6 hours; in group 2 (n = 8), coronary occlusion was maintained for 2 hours and was followed by 4 hours of reperfusion; in group 3 (n = 8), 2 hours of coronary occlusion were followed by 4 hours of reperfusion but methylprednisolone (30 mg/kg intravenously) was also administered 15 minutes after coronary occlusion. At 6 hours, 2-D images were obtained through the closed chest wall and the percentage of the left ventricular wall motion abnormalities was determined at 4 short-axis levels. The mass at risk was defined by in vivo Monastral blue injection and infarction by triphenyltetrazolium chloride staining. The mass of necrosis was 74 +/- 4% (mean +/- standard error of the mean) of the mass at risk in group 1 and was smaller in groups 2 and 3, 44 +/- 6% and 35 +/- 4%, respectively (p less than 0.01). Percent necrosis of the left ventricle was 22 +/- 3% in group 1, 15 +/- 3% in group 2 (difference not significant) and 10 +/- 2% in group 3 (p less than 0.05 vs group 1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of reperfusion after coronary artery occlusion on post-infarction scar tissue

Early reperfusion after a coronary occlusion may reduce myocardial infarct size, but late reperfusion into necrotic myocardium may alter post-infarction healing. In rabbits, we compared 1- or 3-week-old scars resulting from permanent coronary occlusion to those resulting from a 1- or 3-hour occlusion followed by reperfusion. Reperfusion at 1 hour post-occlusion did not affect scar mechanical properties assessed at 1 week post-infarction, but at 3 weeks post-infarction, these scars had a tensile strength significantly lower than those not reperfused (78 +/- 11 vs. 158 +/- 15 g/mm2, P less than 0.001). They also were composed of a mixture of fibrous tissue (58 +/- 8%) and myocytes (43 +/- 8%) with a hydroxyproline content of 23 +/- 2.5 mg/g dry weight. The nonreperfused scars had a higher proportion of fibrous tissue (73 +/- 3%) by histological evaluation and a 35% higher hydroxyproline content (31 +/- 2 mg/g dry weight, P less than 0.001) than the scars reperfused after 1 hour. In contrast, 3-week-old scars resulting from "late" reperfusion at 3 hours post-occlusion were similar to nonreperfused scars in fibrous tissue composition and hydroxyproline content. Nonetheless, the tensile strength of these scars reperfused 3 hours post-occlusion was significantly less than that of the nonreperfused scars (72 +/- 5 vs. 158 +/- 15 g/mm2, P less than 0.001). The lower tensile strength was associated with a lower collagen cross-link density in this reperfused group of scars. At physiological stress levels (approximately 3 g/mm2), all groups of reperfused and nonreperfused scars had similar mechanical properties in terms of natural strain, stiffness, creep, and stress relaxation. Thus, although the reperfused scars ruptured more easily at high stresses, when assessed at physiological stresses their mechanical properties were not significantly different from those of nonreperfused scars.     

Intracoronary adenosine administered after reperfusion limits vascular injury after prolonged ischemia in the canine model

Myocardial salvage after reperfusion may be limited by deleterious vascular changes in the previously ischemic microcirculatory bed. This could result in a progressive decrease in blood flow in the capillary bed to potentially viable myocytes (no-reflow phenomenon). The effect of intracoronary adenosine on these changes was assessed in 15 closed-chest dogs subjected to 2 hours of proximal left anterior descending artery (LAD) occlusion followed by 3 hours of reperfusion. Animals randomly received adenosine (n = 8) 3.75 mg/min into the proximal LAD or an equivalent volume of saline (control) (n = 7) for 1 hour after reperfusion. Endothelial-dependent and independent coronary vasodilator reserve was determined using a chronically implanted volume-flowmeter on the mid-LAD at baseline and 1 and 3 hours after reperfusion with acetylcholine and papaverine infusions, respectively, into the proximal vessel. Regional myocardial blood flow was measured serially with radioactive microspheres and regional contractile function with contrast ventriculography. Both agonists produced a significant increase in LAD flow before occlusion. Endothelial-dependent and independent vasodilatory reserve was significantly reduced (p less than 0.05) at 1 and 3 hours after reperfusion in control animals compared with adenosine treatment. A progressive decrease in mid-LAD flow and increase in coronary vascular resistance after reperfusion was observed in control animals (p less than 0.05). The treated group manifested improved regional myocardial blood flow in endocardial regions from the central (0.73 +/- 0.15 versus 0.24 +/- 0.11 ml/g/min; p less than 0.02) and lateral ischemic zones (0.80 +/- 0.15 versus 0.34 +/- 0.12 ml/g/min; p less than 0.05) 3 hours after reperfusion. A significant reduction (p less than 0.05) in endocardial and midmyocardial flow compared with baseline was seen in control animals at 3 hours. Intravascular and interstitial neutrophil infiltration was reduced in adenosine animals and this was associated with relative ultrastructural preservation of endothelial cells. Regional ventricular function in the ischemic zone was improved in the adenosine group 3 hours after reperfusion (13.4 +/- 3.9% versus -5.3 +/- 1.6%; p less than 0.001). This study demonstrates that selective administration of adenosine after reperfusion significantly attenuates functional and structural abnormalities in the microvasculature after prolonged (2 hours) regional ischemia in the canine model. Prevention of microvascular injury and the non-reflow phenomenon by adenosine may preserve reversibly injured myocytes following restoration of blood flow to previously ischemic myocardium.     

Immediate rebound followed by deterioration of regional left ventricular function with coronary reperfusion

The immediate and early effects of coronary artery reperfusion initiated 1 and 3 hours after coronary artery occlusion were evaluated by two-dimensional echocardiographic measurements of overall and regional left ventricular function. A total of 29 anesthetized open chest dogs underwent one of the following: 1 hour occlusion followed by reperfusion (Group I, n = 9), 3 hour occlusion followed by reperfusion (Group II, n = 12) or 5 hour occlusion without reperfusion (Group III, n = 8). Serial two-dimensional echocardiography was performed at baseline; at 1, 3 and 5 hours of coronary occlusion; within 5 minutes of reperfusion; and at 2 hours of reperfusion. After occlusion, all groups manifested significant (p less than 0.01) increases in left ventricular diastolic and systolic area and decreases in left ventricular area ejection fraction. With coronary reperfusion, there was no improvement in these global variables in Groups I and II. However, immediately after reperfusion, there was improvement in the regional extent of dysfunction (Group I, 138 +/- 35 to 66 +/- 62 degrees, p less than 0.05; Group II, 156 +/- 51 to 85 +/- 77 degrees, p less than 0.05) as well as improvement in the regional degree of dyskinesia (p less than 0.05). These regional improvements were transient and resolved by 2 hours of coronary reperfusion. This immediate rebound of function was not associated with the duration of coronary occlusion, hemodynamic variables or ultimate infarct size. Thus, in the anesthetized open chest dog model, coronary artery reperfusion at 1 or 3 hours produces an immediate but transient improvement in regional systolic myocardial function.     

Kinetics of thallium-201 in reperfused canine myocardium after coronary artery occlusion

To study the kinetics of thallium-201 in nonsalvaged acutely infarcted myocardium and salvaged myocardium, the tracer was administered after experimental left anterior descending coronary artery reperfusion 2 hours after occlusion. In 19 dogs, thallium activity was then monitored for 4 hours in the reperfused anterior wall and normal posterior wall using miniature cadmium telluride radiation detectors. After sacrifice, 13 of the dogs were found to have an infarcted anterior wall by triphenyltetrazolium-chloride staining. In these dogs, mean (+/- standard deviation) fractional 4 hour thallium clearance was 0.33 +/- 0.08 for the infarct zone and 0.15 +/- 0.06 for the normal control zone (p less than 0.001). When computer-modeled, the clearance curve from the infarct zone was biexponential. The second exponential clearance curve from the infarct zone began 19.1 +/- 3.2 minutes after tracer administration, and was indistinguishable from the monoexponential clearance curve from the normal control zone. Thallium clearance from the blood pool was triexponential, the final exponential clearance curve being indistinguishable from the normal control zone clearance curve. Six dogs were found to have a salvaged noninfarcted anterior wall by triphenyltetrazolium-chloride staining. In these dogs, mean fractional 4 hour thallium clearance was 0.20 +/- 0.07 for the reperfused zone, and 0.19 +/- 0.08 for the normal control zone (p = NS). When computer-modeled, clearance curves for the reperfused and control zones were monoexponential. The monoexponential clearance curve for the salvaged reperfused zone was indistinguishable from the monoexponential clearance curve for normal myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Temporal relation of epicardial electrographic, contractile and biochemical changes after acute coronary occlusion and reperfusion.

The increasing use of changes in the S-T segment of local epicardial electrograms to quantitate myocardial infarct size has led to the need for a better understanding of this method. Accordingly, we studied the local electrographic, tension and biochemical changes that occurred after coronary occlusion and subsequent reperfusion in 44 dogs using epicardial electrograms from 10 to 12 sites, Walton-Brodie strain gauge arches and myocardial ratios of potassium ion to sodium ion (K+/Na+). After coronary occlusion for 1 hour, total S-T segment elevation increased from 10.2 +/- 2.4 to 78.3 +/- 13.7 mv (P less than 0.001) and tension development decreased to 63.6 +/- 7.0% of control value (P less than 0.001); occlusion for 3 hours resulted in a total S-T segment elevation increase from 5.8 +/- 3.4 to 56.7 +/- 8.7 mv (P less than 0.001) and a tension decrease to 61.4 +/- 5.3% (P less than 0.001) of control value. After reperfusion two types of response were observed. In nine experiments new local pathologic Q waves appeared in an average of 5.3 of 8.2 ischemic electrode sites within 5 to 10 minutes of reperfusion concomitant with a marked further decrease in total tension from 67.3 +/- 5.5% to 42.4 +/- 6.0% of control value (P less than 0.001). Simultaneously, total S-T elevation decreased from 66.1 +/- 8.2 to 25.3 +/- 3.4 mv (P less than 0.001). In seven experiments no Q waves appeared after reperfusion and there was no significant change in tension. Total S-T elevation again decreased from 58.3 +/- 12.7 to 27.1 +/- 5.7 mv (P less than 0.025). When normal saline solution was perfused distal to the coronary arterial occlusion total S-T elevation decreased from 68.0 +/- 3.6 to 36.3 +/- 5.2 mv (P less than 0.001). After 3 hours of coronary occlusion, myocardial K+ decreased and Na+ increased in the ischemic zone, resulting in a significant decrease in the K+/Na+ ratio (P less than 0.005). Reperfusion for 2 hours resulted in a further depletion of K+ and an increase in Na+ with a resultant complete reversal of the K+/Na+ ratio (P less than 0.001). In summary, after reperfusion the S-T segment abnormalities rapidly decreased in all experiments despite the appearance of new Q waves in more than half of these studies concomitant with either a decrease or no change in contractile ability and continuing myocardial K+ loss and Na+ accumulation. S-T segment mapping therefore appears to be of limited value in assessing the effect of reperfusion on infarct size. The decrease in S-T segments that occurred with perfusion of either blood or saline solution suggests a "washout" phenomenon.     

Effects of reperfusion on the regional contraction of ischemic and nonischemic myocardium following partial coronary obstruction

In 14 dogs the effects on regional tension (Walton-Brodie gauges) and length (mercury-in-silastic) following 50% reduction (52.9 +/- 2.1) in coronary flow for two hours and reperfusion afterwards for one hour were addressed. Within five minutes of partial coronary occlusion, ejection tension in the ischemic zone decreased to 36.3 +/- 7.2% (P less than 0.001) and total tension to 64.4 +/- 5.7% of control (P less than 0.001) while phasic segment length increased to 165.2 +/- 16.3% control. No further significant changes in regional tension or length were observed throughout the two hour period of partial occlusion. Ejection tension remained positive and segment length maintained systolic shortening during the ejection phase throughout the period of occlusion. Following reperfusion, ejection tension in the ischemic zone increased from 35.1 +/- 5.9 to 87.0 +/- 22.0% (P less than 0.05) and total tension increased from 56.6 +/- 5.4 to 70.2 +/- 7.2% (P less than 0.02) while segment length decreased from 149.3 +/- 6.5 to 105.7 +/- 5.7% (P less than 0.001) within five to 15 min of reperfusion. The improvement in both regional tension development and segment length shortening was maintained throughout the one hour period of reperfusion. No significant changes were seen in the nonischemic zone. The present experimental study suggests that partial coronary occlusion producing a 50% reduction in coronary blood flow results in regional contractile changes. These changes are reversible at least twice as long as those following complete occlusion.     

Early assessment of tissue viability with radioiodinated heptadecanoic acid in reperfused canine myocardium: comparison with thallium-201.

Myocardial scintigraphy with heptadecanoic acid labeled with iodine-123 (123I-HDA) may allow early noninvasive delineation of viable myocardium after reperfusion. In this study myocardial uptake of 123I-HDA was compared with that of thallium-201 in six closed-chest dogs after 5 hours of occlusion followed by 1 hour of reperfusion of the left anterior descending coronary artery. Myocardial blood flow was measured with microspheres, and myocardial viability was assessed by means of triphenyltetrazolium chloride staining. In viable areas of the reperfused region, 123I-HDA uptake, thallium-201 uptake, and myocardial blood flow were similar to those measured in the control circumflex region. However, in infarcted areas they were reduced to 48 +/- 2% (mean +/- SEM; p less than 0.001), 59 +/- 3% (p less than 0.001), and 74 +/- 5% (p less than 0.001) of control values, respectively. Results of multiple regression analysis showed that thallium-201 uptake primarily reflected the level of flow during reperfusion, whereas 123I-HDA uptake was dependent on both myocardial blood flow and viability. At each level of flow, 123I-HDA uptake was significantly lower in infarcted than in viable myocardium. By means of discriminant analysis, 123I-HDA uptake was found to be the single most important predictor of viability, whereas thallium-201 was only of limited importance. Myocardial 123I-HDA uptake greater than or equal to 71% or myocardial thallium-201 uptake greater than or equal to 73% best differentiated viable from infarcted myocardium. According to these criteria, 123I-HDA predicted myocardial viability with a sensitivity of 77%, a specificity of 84% and a predictive accuracy of 81%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of acute coronary occlusion on hemodynamics in an adjacent coronary artery in dogs

The effects of acute occlusion of 1 coronary artery on flow responses in another were studied in 24 open-chest dogs. Left circumflex (LC) flow was measured with and without LC stenoses before and during reactive hyperemia. In 19 dogs the left anterior descending artery (LAD) was occluded and measurements were repeated after 1 hour (group 1). Four dogs had measurements before and after 1 hour without LAD occlusion (group 2). In group 2 no systemic, left ventricular (LV) or coronary hemodynamic changes were observed after 1 hour. In group 1, an hour after LAD occlusion, heart rate and aortic pressure had not changed but stroke volume decreased slightly (-8 +/- 7%, mean +/- SD, p = not significant) and LV end-diastolic pressure had increased (2 +/- 3 mm Hg, p less than 0.05). Basal LC flow was not changed by less than 90% LC stenosis. Ninety percent LC stenosis decreased LC flow both before and after LAD occlusion. During reactive hyperemia without LC stenosis, LC flow decreased after LAD occlusion in 15 of 19 dogs (from 154 +/- 80 to 141 +/- 75 ml/min, p less than 0.05). With 60 and 80% LC stenoses, LC flow during reactive hyperemia decreased before LAD occlusion (110 +/- 62 and 74 +/- 40 ml/min, respectively), but decreased further (both p less than 0.05) after LAD occlusion (98 +/- 54 and 63 +/- 43 ml/min).(ABSTRACT TRUNCATED AT 250 WORDS)     

Reduction in infarct size by the prostacyclin analogue iloprost (ZK 36374) after experimental coronary artery occlusion-reperfusion

In this study we attempted to determine whether administration of iloprost (ZK 36374), a chemically stable prostacyclin analogue, would reduce infarct size after experimental coronary artery occlusion and reperfusion. One hour of coronary artery occlusion was performed in 28 open-chest, anesthetized rabbits++, followed by 5 hours of reperfusion. Two minutes after occlusion, 99mTc-labeled albumin microspheres were injected into the left atrium for later assessment of the area at risk of infarction. Fifteen minutes after occlusion animals were randomly assigned to either the treatment group (iloprost, 1.2 micrograms/kg/min intravenously for 6 hours; n = 14) or the control group (n = 14). In vitro platelet aggregation was inhibited in rabbits receiving iloprost. In 10 rabbits (five treated and five control) regional myocardial blood flow was also measured by means of differentially labeled radioactive microspheres. Infarct size was significantly smaller in treated rabbits (53.6 +/- 4.1% of the risk zone vs 89.4 +/- 3.8% in control rabbits; p less than 0.001). Flow to the nonischemic myocardium was higher in treated animals, that is, 1.87 +/- 0.20 ml/min/gm of tissue 50 minutes after occlusion and 1.90 +/- 0.20 ml/min/gm of tissue 4 hours after reperfusion, compared with 1.54 +/- 0.20 and 1.64 +/- 0.30 ml/min/gm of tissue, respectively, in control rabbits (p less than 0.01). Collateral flow to the ischemic region was not affected by the drug. Mean arterial blood pressure, heart rate, and pressure-rate product in treated rabbits were not significantly different from values in control rabbits. In conclusion, administration of iloprost reduced myocardial infarct size in this model of myocardial ischemia and reperfusion in absence of major hemodynamic effects.     

Protection by superoxide dismutase from myocardial dysfunction and attenuation of vasodilator reserve after coronary occlusion and reperfusion in dog

Previous studies indicate impairment of coronary arterial ring relaxation and loss of coronary vasodilator reserve after coronary artery occlusion and reperfusion. These changes are mediated in part through loss of endothelium-derived relaxing factor (EDRF) and/or myocardial neutrophil accumulation. To examine if superoxide dismutase (SOD), a scavenger of superoxide radicals, would modify the diminished coronary vasodilator reserve after temporary coronary occlusion in the intact animal, open-chest mongrel dogs were subjected to 1 hour of circumflex (Cx) coronary artery occlusion followed by 1 hour of reperfusion and treated with saline or SOD. Before Cx occlusion, coronary blood flow increased, and vascular resistance decreased (both p less than 0.01) in response to EDRF-dependent vasodilator acetylcholine as well as EDRF-independent vasodilator nitroglycerin. After Cx reperfusion, resting Cx coronary blood flow and vascular resistance were similar to the preocclusion values. In the saline-treated animals, there was evidence of myocardial dysfunction, which was measured by segmental shortening (-6 +/- 2% vs. 10 +/- 2%). Furthermore, increase in Cx coronary blood flow and reduction in vascular resistance in response to both vasodilators were significantly (p less than 0.01) impaired; these occurrences suggested loss of coronary vasodilator reserve. Myocardial histology showed extensive capillary plugging by neutrophils in the Cx-supplied myocardium. Myocardial myeloperoxidase activity, an index of neutrophil infiltration, was also increased in the Cx compared with the left anterior descending coronary artery region (p less than 0.02). Treatment of dogs with SOD, started at the end of Cx occlusion and continued during reperfusion, exerted significant (p less than 0.01) protective effect against reperfusion-induced attenuation of coronary vasodilator reserve in response to both acetylcholine and nitroglycerin. Loss of myocardial function (segmental shortening 5 +/- 1% vs. 10 +/- 1%) was less than in the saline-treated animals (p less than 0.01). Cx region-myocardial neutrophil accumulation and myeloperoxidase activity were also less (p less than 0.02) in the SOD-treated than in the saline-treated dogs. These observations suggest that coronary reperfusion impairs coronary vasodilator reserve in intact dogs. This impairment can be modified by treatment of animals with SOD before reperfusion. Capillary plugging by neutrophils may contribute to the altered coronary vasodilator reserve observed in the immediate postreperfusion period, and SOD modifies this reperfusion-induced impairment.     

"Reperfusion injury" by oxygen-derived free radicals? Effect of superoxide dismutase plus catalase, given at the time of reperfusion, on myocardial infarct size, contractile function, coronary microvasculature, and regional myocardial blood flow

Do oxygen-derived free radicals, generated at the time of reperfusion, lethally injure viable, previously ischemic myocardium, damage vascular endothelium, and impair recovery of postischemic contractile function? To address these issues, 23 anesthetized open-chest dogs underwent 2 hours of left anterior descending coronary artery occlusion followed by 4 hours of reperfusion. Immediately prior to reflow, each dog was randomized to receive either the free radical scavenging agents superoxide dismutase (SOD) + catalase, or saline alone. SOD + catalase had no significant beneficial effect on infarct size measured by triphenyltetrazolium staining: area of necrosis averaged 38.5 +/- 6.1% vs. 46.3 +/- 6.2% of the area at risk in treated compared with control animals respectively (p = NS). Furthermore, infusion of SOD + catalase did not alter contractile function of the viable subepicardium: mean segment shortening (measured using sonomicrometry) at 4 hours postreperfusion was -23 +/- 5% of baseline, preocclusion values in controls dogs and -24 +/- 9% of preocclusion values in animals that received the scavenging agents. However, SOD + catalase treatment preserved the endocardial microvasculature (assessed by semiquantitative electron microscopic analysis) and enhanced regional myocardial blood flow after reperfusion. Specifically, mean score for microvascular injury was 0.41 +/- 0.14 vs. 0.10 +/- 0.08 (p less than 0.05) in control compared with SOD + catalase treated groups, and blood flow averaged 0.56 +/- 0.11 vs. 1.27 +/- 0.33 ml/min/g tissue (p less than 0.05), respectively, in the previously ischemic endocardium at 2 hours postreflow. Thus, SOD + catalase given at the time of reperfusion had no acute beneficial effect on either the extent of myocyte necrosis or postischemic contractile function in this canine model. SOD + catalase did, however, attenuate both endocardial vascular injury and the "low reflow" phenomenon. These data suggest that microvascular injury and low reflow following prolonged (2 hour) but transient coronary occlusion may be mediated by oxygen-derived free radicals generated at the time of reperfusion.     

Iloprost inhibits neutrophil function in vitro and in vivo and limits experimental infarct size in canine heart

The prostacyclin analogue iloprost (ZK 36374) inhibits neutrophil activation in vitro, reduces neutrophil accumulation in inflammatory skin lesions, and reduces ultimate infarct size in an anesthetized open-chest canine model of regional ischemia and reperfusion. Iloprost (0.1-100 microM) inhibited the in vitro production of superoxide anion by canine neutrophils in a concentration-dependent manner. Iloprost (100 ng/kg/min i.v.) inhibited C5a-induced neutrophil migration into inflammatory skin lesions as assessed by the neutrophil-specific enzyme marker, myeloperoxidase. The myeloperoxidase activity determined 2 hours after the intradermal administration of C5a in each of the groups was control 13.3 +/- 1.8 units/g tissue (n = 12) and iloprost 6.5 +/- 0.9 units/g (n = 12), p less than 0.01. Iloprost was administered to anesthetized open-chest dogs (100 ng/kg/min) 10 minutes after left circumflex coronary artery (LCCA) occlusion and continued during the 90-minute occlusion period and the first 2 hours of reperfusion. Regional myocardial blood flow was similar between treatment groups at baseline, 5 minutes and 80 minutes after LCCA occlusion, and after 1 hour of reperfusion. Infarct size, assessed 6 hours after reperfusion, was reduced by iloprost treatment: 22.4 +/- 3.1% of the area at risk (n = 15) compared with 42.4 +/- 3.3% of control (n = 13), p less than 0.01. Iloprost treatment reduced the accumulation of neutrophils (measured by myeloperoxidase activity) in the ischemic myocardium at the interface between infarcted and noninfarcted tissue: control (n = 9) 9.0 +/- 1.8 units/g tissue, iloprost (n = 6) 2.0 +/- 0.4 units/g, p less than 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)     

Limitation of myocardial infarct size by superoxide dismutase as an adjunct to reperfusion after different durations of coronary occlusion in the pig

Superoxide dismutase (SOD) has been documented to limit myocardial infarct size in the richly collateralized dog heart. This study was designed to explore this concept in a low-collateralized animal model. A blind, randomized, placebo-controlled protocol was used in 65 pentobarbital-anesthetized pigs subjected to closed-chest left anterior descending coronary artery occlusion for 30 (n = 22), 60 (n = 22), and 90 (n = 14) minutes followed by reperfusion up to 24 hours from the start of occlusion. Another seven control pigs were subjected to 24 hours of permanent occlusion. A total dose of 9 mg/kg bovine CuZn SOD was administered as a bolus injection immediately before reperfusion followed by a 1-hour infusion. Infarct size was assessed by tetrazolium staining. Myocardium at risk and collateral flow were determined by using cerium-141-labeled microspheres (15 microns) during the occlusion. After 30 minutes of occlusion, infarct sizes in placebo versus SOD-treated animals were 45.5 +/- 15.7% vs. 23.8 +/- 15.6% of myocardium at risk (p = 0.007). The corresponding values after 60 minutes of occlusion were 78.6 +/- 9.3% vs. 66.9 +/- 14.6% (p = 0.035). SOD administered after 90 minutes of occlusion did not limit infarct size (88.5 +/- 4.8% vs. 92.3 +/- 5.2%). Twenty-four hours of coronary occlusion resulted in infarction of 92.4 +/- 4.2% of myocardium at risk. (All values are mean +/- SD.) Ventricular fibrillation occurred in only nine pigs distributed equally between SOD and placebo. The results indicate that CuZn SOD has the potential to further improve the myocardial salvage established by reperfusion of an ischemic pig heart territory. However, the narrow time window for limiting infarct size in the pig by reperfusion is not much extended by SOD.     

Experimental and clinical investigations for the time interval from onset of symptoms to the coronary reperfusion

To clarify the relationship between time interval from the onset of coronary occlusion to the reperfusion and reperfusion rates or left ventricular function, an experiment with 113 mongrel dogs was carried out. Coronary thrombi experimentally induced within 4 hours in 63 dogs were rapidly lysed by intracoronary thrombolytic agent (Experiment 1). Infarct size was investigated in 17 dogs. The infarct size (% of left ventricle) in 9 dogs with 4-hour reperfusion following 2-hour coronary occlusion was significantly smaller than that in 8 dogs with 6-hour occlusion (12.0 +/- 7.9 vs 19.1 +/- 8.7% respectively p less than 0.05) (Experiment 2). The infarct size in 8 dogs with 7-day reperfusion following 2-hour occlusion was also significantly reduced compared to that in 7 dogs with 7-day occlusion (16.3 +/- 7.4 vs 28.5 +/- 8.9%, respectively p less than 0.02) (Experiment 3). The infarct size in 11 dogs with 4-hour reperfusion with verapamil administration following 2-hour occlusion was significantly reduced compared to that in 7 dogs with 6-hour occlusion without verapamil (5.5 +/- 1.9 vs 20.3 +/- 3.3%, respectively p less than 0.01) (Experiment 4). In experiment 3, anterior wall motion also was assessed by contrast ventriculography and infarct related areas in reperfused group was found to be improved compared to non-reperfused group at 7 days after infarction. In clinical studies, 121 patients who were admitted within 12 hour of onset of symptoms, were investigated to evaluate reperfusion rates and left ventricular function. The reperfusion rate of young age thrombus within 3 hours was 89% of 18 patients with completely occluded coronary artery. It was 77% of the 52 patients with 3 to 6 hour occlusion and 72% of the 18 patients with over 6 hour occlusion. There was a tendency towards high reperfusion rates in younger thrombus. In patients who were recanalized within 3 hours from the onset of symptoms ejection fraction of left ventricle at the chronic stage had a significantly higher percentage when compared to the unsuccessful group. Wall motion of infarct-related areas in patients who were thrombolysed within 6 hours was improved compared to the unsuccessful group. Administration of verapamil during reperfusion in patients with acute myocardial infarction suppressed rapid CK release and sigma CK. Thus, young age thrombus can be lysed easily, earlier recanalization after coronary occlusion can reduce infarct size and improve left ventricular function. Reinforced administration of verapamil during reperfusion can also reduce infarct size.     

Acute effects of delayed reperfusion on myocardial infarct shape and left ventricular volume: a potential mechanism of additional benefits from thrombolytic therapy

The purpose of this study was to characterize the effects of late reperfusion on myocardial infarct shape and to quantitate associated changes in left ventricular volume. Reperfusion was delayed until there was no salvage of ischemic myocardium. Dogs underwent 6.5 h of left anterior descending coronary artery occlusion (n = 5) or 5.5 h of occlusion and 1 h of reperfusion (n = 5). Infarct shape was measured with pairs of ultrasonic crystals implanted circumferentially in the mid myocardium. Infarct stiffness was determined from end-diastolic pressure-segment length curves produced by aortic clamping. Left ventricular volume was measured with three pairs of endocardial ultrasonic crystals and the effect of infarct shape change on left ventricular volume was determined. Infarct size, expressed as a percent of the area at risk, was similar in reperfused (97 +/- 1%) and nonreperfused (98 +/- 1%) hearts. After coronary artery occlusion, infarct segments became akinetic and functional dilation, measured as end-diastolic ultrasonic crystal separation, increased to a similar extent in reperfused (24 +/- 7%) and nonreperfused (19 +/- 3%) hearts. In 13 additional dogs that underwent reperfusion and instrumentation with endocardial ultrasonic crystals for volume measurement, left ventricular volume increased 42 +/- 6% over the preocclusion level (p less than 0.001). Within minutes of reperfusion, the infarct stiffened, infarct dilation decreased to 1 +/- 4% over the baseline preocclusion level (p less than 0.05 vs. prereperfusion) and left ventricular volume decreased to 16 +/- 11% over the baseline level (p less than 0.01 vs. postocclusion). Thus, coronary artery reperfusion reverses initial infarct dilation. Changes in infarct dilation occur immediately after reperfusion and are accompanied by infarct stiffening and a decrease in left ventricular volume. Reperfusion can affect infarct shape and stiffness at a point in time when myocardial salvage is no longer possible.