Quantitative effect of early coronary artery reperfusion in baboons. Extent of salvage of the perfusion bed of an occluded artery

Reperfusion in acute myocardial infarction: effect of timing and modulating factors in experimental models

Timely reperfusion of ischemic myocardium in experimental animals halts the advancing transmural "wavefront" of ischemic cell death and thereby limits myocardial infarct size by limiting its transmural extent. The time window of opportunity for such salvage in most experimental models of regional ischemia is the first 3 hours. The number of myocytes that can be salvaged by reperfusion decreases exponentially during this period, such that at 3 hours, reperfusion limits infarct size by only about 10%. The rate of lethal ischemic cell injury and therefore the amount of myocardium that can be salvaged by reperfusion after a particular duration of ischemia is dependent both on the degree of blood flow deficit and the rate of ischemic metabolism. In experimental animal models, several interventions, including hypothermia, calcium antagonists, and "ischemic preconditioning," have been shown to reduce the rate of ischemic metabolism and to limit myocardial infarct size when assessed after a defined period of ischemia and reperfusion. Hypothetically, interventions that could prevent additional myocyte necrosis caused by some deleterious aspects of reperfusion ("lethal reperfusion injury") also could serve as valuable adjunctive therapy. However, studies of therapies designed to prevent lethal reperfusion injury have produced conflicting results. Thus, the concept that lethal reperfusion injury occurs remains controversial. Experimental evidence indicates that reperfusion accelerates both the initial inflammatory response and later process of infarct repair. Late reperfusion of infarcts in dogs, which does not limit myocardial infarct size, appears to accelerate the replacement of necrotic myocardium by scar without altering the size of the final scar.

High- and low-dose superoxide dismutase plus catalase does not reduce myocardial infarct size in a subhuman primate model

Oxygen free radical scavengers have been found to decrease infarct size in dogs subjected to myocardial ischemia-reperfusion injury. A baboon open-chest model was used to determine if superoxide dismutase (SOD), an oxygen free radical scavenger, together with catalase would be equally effective in subhuman primates (baboons). The left anterior descending coronary artery (LAD) was ligated for 2 hours. Before reperfusion, the animals received the following: Group 1 (low-dose SOD/catalase; n = 5) received 15,000 IU/kg of SOD and 55,000 IU/kg of catalase IV over 1 hour, 15 minutes before reperfusion. Group 2 (high-dose human SOD [h-SOD]/catalase; n = 5) received an intraatrial bolus of 400,000 IU of recombinant h-SOD and 27,500 IU/kg of catalase over 30 seconds, followed by 300,000 IU of h-SOD and 55,000 IU/kg of catalase over 1 hour, beginning 15 seconds before reperfusion. Group 3 (n = 8) were control animals. Baboons were put to death 22 hours after reperfusion. Their hearts were excised and sectioned after the perfusion bed distal to the site of ligation was delineated with microvascular dye. The infarct zone was determined histologically. Areas of the perfusion bed and infarct zone were measured by planimetry. Infarct size did not differ significantly between the three groups: control, 66 +/- 7%; low-dose SOD/catalase, 68 +/- 5%; and high-dose h-SOD/catalase, 74 +/- 4%. In this model, high- and low-dose SOD with catalase did not result in any significant reduction in infarct size.

Reperfusion of infarcting myocardium: benefit of surgical reperfusion in a chronic model

Surgical reperfusion of experimental infarction leads to improved recovery of regional function compared with medical reperfusion, but sustained myocardial salvage has not been demonstrated. Twenty-two dogs were subjected to two hours of anterior descending occlusion and divided into three groups: group P (n = 7), no reperfusion; group M (n = 8), medical reperfusion; and group S (n = 7), controlled surgical reperfusion. Ischemia caused systolic bulging (-36% of control systolic shortening, p less than 0.01) and decreased regional work (9% of control pressure-length loop area, p less than 0.05). Thirty minutes after reperfusion group M had persistent systolic bulging (-9% of control systolic shortening) and decreased regional work (9% of control pressure-length loop area), whereas group S had +17% of control systolic shortening and 33% of control pressure-length loop area. After 1 week, regional function improved in all three groups (percent of control systolic shortening: group P, 26%; group M, 19%; group S, 52%), but systolic shortening was significantly better in group S (p less than 0.05 versus group M). Surgical reperfusion also resulted in one half of the eventual myocardial necrosis found in the other groups (group P, 45% of area at risk; group M, 38%; group S, 19%; p less than 0.05, group S versus group P or M). In this model, medical reperfusion offered no demonstrable benefit, whereas controlled surgical reperfusion led to a sustained (1 week) improvement in regional function and significant myocardial salvage.

Intracoronary superoxide dismutase for the treatment of "reperfusion injury", A blind randomized placebo-controlled trial in ischemic, reperfused porcine hearts

The effect of recombinant human superoxide dismutase (rh-SOD) on infarct size was investigated in porcine hearts. The left anterior descending coronary artery was occluded in each of 24 anesthetized pigs for 45 min and reperfused for 24 h. The animals were randomly assigned to either rh-SOD (n = 12) or placebo treatment (n = 12). 2 min before reperfusion, an intracoronary (i.c.) infusion of rh-SOD (total dose: 2000 U/kg) or placebo was started which lasted for up to 45 min reperfusion. At the end of the experiment, the infarcted myocardium was assessed using a tetrazolium stain (NBT) and related to the risk region which was determined with a fluorescent dye. Two pigs of the SOD group and one of the control group died before the end of the experiments. Except for a lower calculated myocardial oxygen consumption and a lower dp/dtmax in the SOD group during ischemia, hemodynamic parameters of the two groups did not differ significantly. rh-SOD i.c. treatment during reperfusion did not reduce infarct size significantly. Infarct size amounted to 74 +/- 13% in the control group and to 66 +/- 19% in the treated group. The incidence of reperfusion arrhythmias was not affected by rh-SOD treatment. It is concluded that i.c. rh-SOD treatment at the beginning of reperfusion neither significantly reduces infarct size nor diminishes the incidence of reperfusion arrhythmias in this preparation.

Coronary thrombolysis with intravenous urokinase in patients with acute myocardial infarction

Regional left ventricular wall motion, about two to three weeks after acute myocardial infarction (MI), is perhaps the best clinical measure of myocardial salvage and limitation of infarct size by thrombolytic therapy. Normal or only slightly depressed wall motion at the site of infarction indicates significant limitation of infarct size, whereas markedly abnormal wall motion indicates irreversible myocardial damage. Early studies found significant improvement in regional wall motion in only 40 percent of patients undergoing successful intracoronary thrombolytic therapy after the onset of symptoms of acute MI. Why only 40 percent of these reperfused patients demonstrated salvage of ischemic myocardium could not be answered at that time. Animal experiments show that the duration of coronary occlusion is an important factor in determining myocardial salvage after reperfusion. To study whether this time dependency also exists under clinical circumstances in patients with coronary artery disease, the relationship between regional wall motion (as an index of infarct size) and the time to thrombolytic therapy after the onset of symptoms (as an index of duration of coronary occlusion) was examined. After showing that such time dependency does indeed exist in patients with acute MI, the efficacy and safety of intravenous bolus injections of urokinase were then demonstrated.

Streptokinase alters myocardial creatine kinase depletion after ischaemia and reperfusion in rabbits

The efficacy of streptokinase as an intracoronary thrombolytic agent is well-recognized. The effect of streptokinase, distinct from its thrombolytic action, on ischaemic myocardium distal to an area of coronary artery occlusion when reperfusion occurs has not been well-defined. In order to do this, myocardial creatine kinase depletion and the histopathology of infarctions produced in rabbits after 1 h of circumflex coronary artery occlusion and mechanical release of the occlusion were assessed. Streptokinase or saline was infused intravenously for 1 h beginning 0.5 h after occlusion. Rabbits were divided into two time intervals: early (less than 10 h) and late (24 h) after release of coronary artery occlusion. When streptokinase was infused in early infarctions, haemorrhage did not correlate with infarction cross-sectional area or myocardial creatine kinase depletion. However, myocardial creatine kinase depletion was 40% less when streptokinase was infused than when saline was infused, suggesting that streptokinase might limit infarct size. In late infarctions, the degree of haemorrhage, infarction cross-sectional area, and myocardial creatine kinase depletion were similar after reperfusion with streptokinase or saline. By 24 h, the beneficial effect of a single dose of streptokinase given early in the course of occlusion-reperfusion myocardial injury was no longer evident in limiting infarct size.

Time from onset of symptoms to thrombolytic therapy: a major determinant of myocardial salvage in patients with acute transmural infarction

To determine whether myocardial salvage after successful intracoronary or intravenous thrombolysis is time dependent, the relation between left ventricular wall motion and the time to treatment was studied in 69 patients admitted less than 3 hours after onset of acute transmural myocardial infarction (42 patients with reperfusion by intracoronary streptokinase, 27 by intravenous urokinase). A similar significant relation between the time to treatment and the severity of regional hypokinesia at follow-up was found in the intracoronary and intravenous groups. To better define this relation, particularly during the early phase of infarction, the groups were combined. In patients in whom thrombolytic treatment was initiated within 2 hours after symptom onset, wall motion at follow-up was within 2 standard deviations of the normal mean in 82% (14 of 17 patients). If treatment was started 2 to 5 hours after symptom onset, the probability of improved wall motion decreased to 46% (24 of 52 patients, p less than 0.025). The time/wall motion relation appeared to be independent of infarct location, angiographically visible collateral vessels and the presence of subtotal coronary artery occlusion. The severity of hypokinesia at follow-up study correlated with the magnitude of peak serum creatine kinase (r = -0.71), indicating that thrombolytic therapy initiated within 2 hours after the onset of symptoms improves regional left ventricular function and reduces infarct size more than later therapy does.

Intracoronary hyperosmotic mannitol during reperfusion does not affect infarct size in ischemic, reperfused porcine hearts

We investigated the effect of reperfusion with hyperosmotic mannitol on the infarct size in porcine hearts. The distal half of the left anterior descending coronary artery was occluded in each of 21 anesthetized pigs for 75 min and was reperfused for 2 h. During reperfusion mannitol (1075 mosmol/kg) was intracoronarily infused at a dose of 0.5 ml/min in 6 pigs ("low" mannitol group), at a dose of 1.5 ml/min in another 6 pigs ("high" mannitol group), and at a dose of 5 ml/min in 3 pigs for the first 8 min of reperfusion ("very high" mannitol group). 6 pigs served as controls. Although mannitol infusion increased plasma osmolality in the ischemic, reperfused myocardium in all experiments, the infarct size expressed as the ratio of the infarcted tissue over the area at risk of necrosis was not significantly influenced. Infarct size amounted to 72 +/- 25% in the control group, to 75 +/- 14% in the "low" mannitol group, to 78 +/- 18% in the "high" mannitol group, and to 93 +/- 8% in the "very high" mannitol group. These results clearly indicate that reperfusion with hyperosmotic mannitol after 75 min of ischemia does not exert any beneficial effect on the infarct size.

Prevention of the "no reflow" phenomenon in the canine heart by mioflazine

The effects of oral pretreatment with mioflazine (2.5 mg X kg-1) on regional myocardial reflow, infarct size reduction and hemodynamic recovery were studied in 24 anesthetized open-chest dogs undergoing 90 minutes of acute left anterior descending coronary artery (LAD) occlusion followed by 150 minutes of reperfusion. Regional myocardial blood flow was measured with tracer microspheres, and infarct size was determined by triphenyl tetrazolium chloride staining. Pretreatment with mioflazine resulted in a reduced diastolic aortic pressure (p less than 0.05) and an elevated cardiac output and LV dpdt max (p less than 0.05). These effects persisted throughout the experiment. In control animals (n = 12) a hyperemic reflow response was found in the perfusion area of the LAD during the first minutes of reperfusion. After 150 min of reperfusion, however, the viable myocardium of the LAD area became underperfused, and almost no reflow was found in the infarcted zones. In the animals pretreated with mioflazine (n = 12) the hyperemic response persisted throughout the reperfusion phase and the no-reflow phenomenon was prevented. Infarct size (expressed as percentage of perfusion area) tended to be smaller in this group: 23.7 +/- 12.4% versus 33.7 +/- 19.2% (p greater than 0.05). Left atrial pressure increased during LAD occlusion in both groups but normalized completely in the drug-pretreated animals (p less than 0.05). It is concluded that pretreatment with mioflazine prevents the no-reflow phenomenon after reperfusion of an evolving infarction, tends to reduce infarct size and improves hemodynamic recovery.

Coronary thrombolysis and infarct size reduction after intravenous infusion of recombinant tissue-type plasminogen activator in nonhuman primates

Occlusive thrombus was produced by thrombin-induced coagulation in the left anterior descending coronary artery (LAD) of 16 open-chest baboons. In six control animals, occlusive thrombosis persisting over a period of 4 h as evidenced by coronary arteriography resulted in large transmural infarction (63.1 +/- 3.5% of the perfusion area). In 10 animals, tissue-type plasminogen activator obtained by recombinant DNA technology (rt-PA) was infused systemically at a rate of 1,000 IU (10 micrograms)/kg per min for 30 min after 30-80 min of coronary thrombosis. Reperfusion occurred within 30 min in nine animals. In one animal, intravenous infusion was followed by an intracoronary infusion at the same rate, which resulted in thrombolysis within 8 min. In the rt-PA group, mean duration of occlusion before reperfusion was 77 +/- 24 min. Reocclusion occurred in one animal. Recanalization resulted in an overall reduction of infarct size (37.8 +/- 5.9%, P less than 0.05 versus controls). Residual infarction was related to the duration of occlusion (r = 0.80, P less than 0.01). Reperfusion was associated with reduced reflow. Myocardial blood flow in the perfusion area of the LAD was only 70% of normal after 4 h despite perfect angiographic refilling. The infusion of rt-PA was not associated with systemic activation of the fibrinolytic system, fibrinogen breakdown, or clinically evident bleeding. It is concluded that intravenous infusion of rt-PA may recanalize thrombosed coronary vessels without inducing systemic lysis. The extent of residual infarction is closely related to the duration of coronary artery occlusion before thrombolysis.

Temporal and spatial development of infarcts in porcine hearts

We investigated the temporal and spatial development of infarcts in porcine hearts to evaluate the time-dependent beneficial effect of reperfusion on infarct size. The left anterior descending coronary artery (LAD) was occluded in 17 pigs for different periods of time followed by 4 hours of reperfusion. Transmural needle biopsies subdivided into subendocardial and subepicardial halves were taken from the ischemic apex after 60 min of ischemia to determine the tissue concentrations of ATP and NAD. The myocardium-at-risk was assessed with a fluorescent dye injected into the right atrium at the end of the experiments, just after the LAD had been reoccluded. The excised hearts were cut into slices parallel to the heart basis. The ischemic myocardium was measured by planimetry of the non-fluorescent areas whereas the infarcted tissue was determined with the NBT stain and related to the area-at-risk. Ischemic cell death started in the jeopardized left ventricular subendocardial septum after about 30 min of ischemia. The further progress involved the right subendocardial septum and the subendocardium of the left anterior free wall. Already after 75 min of ischemia most of the myocytes-at-risk were irreversibly injured. Infarctions reached their final extent after 90-120 min of ischemia. These results indicate that in hearts without a significant collateral blood flow reperfusion can only reduce infarct size if its initiated within 60-75 min of ischemia. Like in canine hearts infarctions progress from the ischemic subendocardium towards the outer layers.

Thrombolysis in acute myocardial infarction: effect of intravenous followed by intracoronary streptokinase application on estimates of infarct size

The effect of pretreatment with intravenous infusion of streptokinase (SK) (16,700 U/min for 90 minutes), started after diagnosis and followed by intracoronary application (2000 U/min) (protocol 1), was assessed retrospectively in 55 consecutive patients with acute transmural myocardial infarction (MI). Another 46 patients with acute MI treated previously by intracoronary thrombolysis served as control subjects (protocol 2). Reperfusion at first coronary injection was observed after pretreatment in 25 patients (45%), but in no control patient (p less than 0.001). Fifteen patients with successful pretreatment (group A), 20 patients with successful treatment according to protocol 2 (group B) and 9 patients with unsuccessful thrombolysis (group C) were restudied after 4 weeks. Data from patients with reinfarction, coronary bypass surgery or percutaneous transluminal coronary angioplasty before restudy were excluded. Thallium-201 scintigraphy was performed before and 24 hours after treatment, serum creatine kinase activity was measured every 8 hours for 3 days and regional ejection fraction (EF) of acute MI was determined before and 4 weeks after treatment. The scintigraphic, enzymatic and hemodynamic data before treatment indicated severe and comparable ischemia among the 3 groups. The thallium-201 perfusion defect decreased in group A (from 41 to 21%, p less than 0.01) and in group B (from 38 to 26%, p less than 0.01), but did not change in group C (from 37 to 31%, difference not significant). Peak serum creatine kinase levels normalized by the perfusion area of acute MI was 20, 33 and 58 U/liter unit in groups A, B and C. The mean values of groups A and C were significantly different (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Intracoronary fibrinolytic therapy in acute myocardial infarction. Report of a prospective randomized trial

We performed a randomized trial comparing intracoronary administration of streptokinase versus dextrose placebo within six hours after the onset of symptoms of acute myocardial infarction in 40 patients. The base-line clinical, hemodynamic, and angiographic findings were similar in the control and streptokinase-treated groups. Reestablishment of flow occurred in 12 of 20 patients treated with streptokinase and in 2 of 20 given placebo (P less than 0.05). Left ventricular function, angiographic ejection fraction, and regional wall motion, measured before and immediately after intervention, and serial radionuclide ejection fractions, measured at treatment, at 12 days, and at 5 months, were compared according to type of treatment (streptokinase vs. placebo) and outcome of therapy (reperfusion vs. no reperfusion). No statistically significant differences between groups were found. Thus, although streptokinase was more effective than placebo in achieving reperfusion, we detected no improvement of left ventricular function as a result of reestablished coronary flow.

Quantitative assessment in infarct size reduction by coronary venous retroperfusion in baboons

Initial favorable reports in which coronary venous retroperfusion was begun after acute coronary artery occlusion have demonstrated a reversal of ischemic injury and improved left ventricular function. However, little information has been generated to document the extent to which retroperfusion may decrease ultimate histologically determined infarct size. The objective of the present study was to evaluate the effectiveness of retroperfusion in reducing infarct size by using an accurate quantitative method in which infarct size was related to the size of the anatomic perfusion bed of the occluded artery (region at risk for infarction). In an experimental group of 5 baboons, the left anterior descending coronary artery was occluded and coronary venous retroperfusion started 1 hour after occlusion. After a 4-hour period of occlusion, retroperfusion was discontinued and anterograde perfusion was simultaneously restored. A control group of 5 baboons underwent an identical procedure without retroperfusion. Twenty-four hours after occlusion, hearts were excised and the previously occluded left anterior descending coronary artery as well as the adjacent arteries were infected with microvascular dye to delineate the perfusion bed of the occluded artery. Planimetry of serial corss-sections of the left ventricle enabled the size of the perfusion bed of the occluded artery and size of the infarct to be determined. The mean percentage of the perfusion bed infarcted in the control group was 94.1 +/- 0.9 (mean +/- standard error) and in the retroperfused group was 57.4 +/- 3.5 (p less than 0.001). Hence, the results demonstrated that when retroperfusion was initiated after 1 hour of coronary occlusion, the mean percentage of the perfusion bed salvaged was increased by 36.7%.