Intracoronary prostaglandin E1 plus streptokinase in acute myocardial infarction

An hypothesis on the consolidation and PGE1-induced deconsolidation of a platelet plug

Consolidation is the final stage in haemostasis in which a platelet plug blocking a bleeding area of a vessel: (a) becomes impermeable to circulating plasma proteins and (b) contracts to resist blood pressure.

HYPOTHESIS

The impermeabilization step of consolidation is accomplished through fluid uptake by the platelets from a hydrated intercellular glue formed during thrombin activation. Dehydration occurs through inhibition of the Na+,K+-ATPase of platelets with sodium and water uptake. However, and uniquely, due to the high cellular density of the platelet plug, access of peripheral plasma fluids to the plug is limited forcing the platelets to take up preferentially the fluid of interplatelet space. The increased adhesion properties of the dehydrated glue simultaneously furthers a decreased hydraulic permeability and an improved coupling of the contractile forces among platelets. In 'Deconsolidation', the fluid uptake process can be reversed and amplified by agents that increase cAMP, reactivating the Na+,K+-ATPase and expressing CFTR or equivalent Cl- secretory channels that force the extrusion of fluid from the platelets, with rehydration of the intercellular polymer and a large increase in the interplatelet space.

Selective thrombolysis in acute deep vein thrombosis: evaluation of adjuvant therapy in vivo

PURPOSE

To evaluate in a porcine model of acute deep vein thrombosis (DVT) the efficacy of dalteparin and antithrombin with respect to heparin for local adjuvant therapy during selective thrombolysis, and the utility of nitroglycerin and iloprost as heparin supplements.

METHODS

DVT was induced in both hind limbs using a previously described technique (n = 20). Thirty minutes later, the animal was heparinized (2500 IU IV), and bilateral sequestrated thrombolysis was performed using 8 mg alteplase: both external iliac veins were endoluminally occluded with Swan-Ganz catheters, and a multi-sideport infusion wire coaxially introduced through each catheter and advanced into the ipsilateral popliteal vein. In the control limbs, tissue plasminogen activator (tPA) 8 mg was injected as 0.8-ml boluses at 3-min intervals for 2 hr as a 0. 25-mg/ml solution containing heparin 50 IU/ml (n = 20). On the contralateral side, heparin was substituted with either dalteparin 50 IU/ml (n = 5) or antithrombin 12.5 IU/ml (n = 5), or supplemented with either nitroglycerin 0.075 mg/ml (n = 5) or iloprost (150 ng/ml) (n = 5). Blood samples were taken at predetermined intervals to measure the activated partial thromboplastin time (aPTT), prothrombin time (PT), and fibrinogen concentration. At autopsy, the thrombus mass in the iliofemoral veins was measured, and the extent of residual thrombosis in the venous tributaries graded at four sites.

RESULTS

Bilateral thrombolysis was successfully completed in all animals. The median thrombus mass in the iliofemoral veins after thrombolysis was 0.48 g (range 0.06-1.58 g), 0.95 g (0.59-1.29 g), 0. 74 g (0.52-0.96 g), and 0.29 g (0.0-0.77 g) for dalteparin, antithrombin, iloprost, and nitroglycerin respectively, as compared with 0.53 g (0.18-0.88 g) (p = 0.69), 0.97 g (0.46-1.15 g) (p = 0. 69), 0.53 g (0.48-1.10 g) (p = 0.69), and 0.18 g (0.13-1.04 g) (p = 0.5) for the respective controls. Likewise, the severity of residual thrombosis in the venous tributaries was not affected by the constituents of adjuvant therapy. Nitroglycerin induced a small drop in blood pressure, which was transient. The temporal change in aPTT was similar in all four groups. Invariably PT progressively shortened during thrombolysis (p = 0.0001); this effect was somewhat blunted with antithrombin. Fibrinogen levels demonstrated a time-dependent increase (p = 0.004) that was not influenced by the adjuvant therapy used.

CONCLUSIONS

Dalteparin or antithrombin demonstrated no appreciable advantage over heparin as local adjuvant therapy for selective venous thrombolysis. Supplementation of heparin with iloprost or nitroglycerin also had virtually no effect on thrombolytic efficacy.

Advances in antithrombotic therapy of acute myocardial infarction

The aim of the acute treatment of myocardial infarction is to restore, as promptly as possible, blood flow in the culprit vessel. Thrombolysis is a cornerstone of treatment, and direct coronary angioplasty (PTCA) is emerging as a valuable or even better alternative reperfusion strategy. The activation of hemostasis after plaque disruption, thrombolysis, or PTCA represents a strong rationale for the use of antithrombotic drugs. The results of the ISIS-2 trial and the data from the Antiplatelet Trialists' Collaboration indicated that aspirin is mandatory in patients with acute myocardial infarction and for secondary prevention. Recently, the efficacy of abciximab and other glycoprotein IIb/IIIa inhibitors was proven in the treatment of acute coronary syndromes and after PTCA, and their early use in patients with acute myocardial infarction is presently under evaluation. Anticoagulation with heparin appears to be only slightly effective in acute myocardial infarction not treated with thrombolysis; however, a rationale exists for its use in patients undergoing percutaneous and/or surgical revascularization and in conjunction with fibrin-specific thrombolytic agents. Further studies are under way on the possible usefulness of low-molecular-weight heparin. Direct antithrombin agents (hirudin, hirulog, and others) have been recently studied as an adjunct to thrombolysis. The data from these studies indicate the presence of a narrow therapeutic window, with only marginal advantage over heparin; studies with newer compounds are ongoing. Aspirin is still a mandatory drug in patients with acute myocardial infarction; the most promising agents in this setting seem to be glycoprotein IIb/IIIa inhibitors. Heparin and low-molecular-weight heparins are indicated in selected cases, and further studies are needed to assess the value of newer direct thrombin inhibitors.

[Optimization of thrombolytic treatment in acute myocardial infarct: the role of new fibrinoselective drugs and their combination with new antithrombotics]

Although reperfusion therapy is well recognized as the mainstay of treatment of acute myocardial infarction, mortality of myocardial infarction is still high, thrombolytic treatment remains underutilized and, usually, applied too late. Additionally, most of the patients do not experience optimal reperfusion because of the suboptimal flow rate in the infarct-related artery, abnormal microvascular flow, and reocclusion of the infarct-related artery. Strategies to enhance the results of reperfusion therapy include, expanding the population of potential candidates, earlier treatment, and newer methods to improve infarct-related artery flow rates. In this sense, new thrombolytic agents, and combination therapies with or without addition of more potent and specific new antithrombotic agents are being extensively investigated. Also, it is important to promote studies of ancillary treatments to reduce reperfusion injury, which may be one cause of decreased microvascular flow. Although aspirin and heparin have been the conventionally used agents for inhibiting thrombin and platelet function, newer agents such as hirudin or hirulog and inhibitors of the platelet glycoprotein IIb-IIIa receptors are becoming available, and their clinical application will increase in the future.

Combined accelerated tissue-plasminogen activator and platelet glycoprotein IIb/IIIa integrin receptor blockade with Integrilin in acute myocardial infarction. Results of a randomized, placebo-controlled, dose-ranging trial. IMPACT-AMI Investigators

BACKGROUND

Platelet activation and aggregation may be key components of thrombolytic failure to restore and maintain perfusion in acute myocardial infarction. We performed a placebo-controlled, dose-ranging trial of Integrilin, a potent inhibitor of platelet aggregation, with heparin, aspirin, and accelerated alteplase.

METHODS AND RESULTS

We assigned 132 patients in a 2:1 ratio to receive a bolus and continuous infusion of one of six Integrilin doses or placebo. Another 48 patients were randomized in a 3:1, double-blind fashion to receive the highest Integrilin dose from the first phase or placebo. All patients received accelerated alteplase, aspirin, and intravenous heparin infusion; all but two groups also received an intravenous heparin bolus. The highest Integrilin dose group from the nonrandomized phase and the randomized patients were pooled for analysis and compared with placebo-treated patients. The primary end point was Thrombolysis in Myocardial Infarction (TIMI) grade 3 flow at 90-minute angiography. Secondary end points were time to ST-segment recovery, an in-hospital composite (death, reinfarction, stroke, revascularization procedures, new heart failure, or pulmonary edema), and bleeding variables. The highest Integrilin dose groups had more complete reperfusion (TIMI grade 3 flow, 66% versus 39% for placebo-treated patients; P = .006) and a shorter median time to ST-segment recovery (65 versus 116 minutes for placebo; P = .05). The groups had similar rates of the composite end point (43% versus 42% for placebo-treated patients) and severe bleeding (4% versus 5%, respectively).

CONCLUSIONS

The incidence and speed of reperfusion can be enhanced when a potent inhibitor of the glycoprotein IIb/IIIa integrin receptor, such as Integrilin, is combined with accelerated alteplase, aspirin, and intravenous heparin.

Prostaglandin E1 (PGE1) reduces cardiac-derived TXA2 release in ischaemic arrest in isolated working rat heart

To determine whether PGE1 plays a beneficial role in crystalloid cardioplegia in the isolated working rat heart, twenty isolated rat hearts were studied. The hearts were subjected to 90 min cardioplegic arrest under hypothermia (25 degrees C) and 30 min reperfusion. Prior to ischaemic arrest, the amount of TXA2 in coronary effluent, left ventricular developed pressure (LVDP), left ventricular end diastolic pressure (LVEDP), coronary flow (CF), aortic flow (AF) and cardiac output (CO) did not differ between the control and PGE1 treated rats (28 nmol/l). However, at 30 min reperfusion, the recovery of LVDP, LVEDP, CF, AF, CO and SV in hearts from PGE1 treated rats was more than in control hearts. TXA2 levels from coronary effluent were increased during reperfusion in control rats. On the other hand, PGE1 (28 nmol/l) inhibited the release of TXA2 at reperfusion. The present studies confirm that the cardiac-derived TXA2 are increased after ischaemia/reperfusion. Infusion of cardioplegia solution containing PGE1 results in the inhibition of release of cardiac-derived TXA2 and in a better preservation of cardiac function after ischaemic arrest.

Use of a direct thrombin inhibitor (argatroban) during pulse-spray thrombolysis in experimental thrombosis

PURPOSE

To evaluate the effectiveness of intravenous and intrathrombic injection of the thrombin inhibitor argatroban during pulse-spray pharmacomechanical thrombolysis (PSPMT) in experimental venous thrombosis.

MATERIALS AND METHODS

Clots were produced in the inferior vena cava in 52 rabbits by placement of steel coils and balloon injury to the vessel wall. Two days later, clots were treated with PSPMT. Several treatment methods were used: intrathrombic saline, intrathrombic tissue plasminogen activator (t-PA), intrathrombic t-PA with intrathrombic and intravenous heparin, intrathrombic t-PA with intravenous argatroban, and intrathrombic t-PA with intrathrombic and intravenous argatroban at two different doses. After treatment, the rabbits were killed and residual clot was weighed. Pretreatment clot weight was estimated and clot lysis was assessed.

RESULTS

PSPMT with t-PA and adjunctive intrathrombic heparin resulted in greater lysis than PSPMT with only t-PA (percentage of residual clot, 59% +/- 14 vs 81% +/- 28; P = .02). Addition of intravenous argatroban did not increase lysis, but adjunctive intrathrombic argatroban significantly increased lysis at low doses (37% +/- 16; P = .02) and high doses (34% +/- 6; P = .006) compared with t-PA and intrathrombic heparin.

CONCLUSION

In a rabbit model of venous thrombosis, the use of intrathrombic argatroban during PSPMT with t-PA significantly improved clot lysis.

Enhanced thrombolysis, reduced coronary reocclusion and limitation of infarct size with liposomal prostaglandin E1 in a canine thrombolysis model

OBJECTIVES

The purpose of this study was to test the hypothesis that liposomal prostaglandin E1 (TLC C-53) would result in more rapid thrombolysis, less reocclusion and smaller infarct size when administered with heparin and streptokinase in a canine thrombolysis model.

BACKGROUND

In experimental animals, prostaglandin E1 has been shown to augment thrombolysis, improve coronary flow and reduce infarct size when infused directly into the left atrium. TLC C-53 is a stable preparation of prostaglandin E1 bound by phospholipid microspheres that produces fewer adverse hemodynamic effects during intravenous use.

METHODS

To investigate the effects of TLC C-53 on coronary patency and infarct salvage, we studied 30 conditioned open chest dogs. After coil-induced left anterior descending coronary artery occlusion and 1 h of clot maturation, the dogs were randomly assigned to receive a 10-min intravenous infusion of either TLC C-53 (2 micrograms/kg body weight) or placebo. Both groups then received intravenous heparin and streptokinase. Hemodynamic variables and Doppler coronary flow were monitored, and myocardial blood flow was determined using radioactive microspheres. Infarct size was assessed with triphenyltetrazolium chloride staining.

RESULTS

Thrombolysis time was accelerated from 79 +/- 38 to 47 +/- 9 min (mean +/- SD), and coronary patency was greater (100% vs. 50%) with TLC C-53 than with placebo (p < 0.05). Moreover, for arteries that recanalized, coronary Doppler flow and myocardial perfusion were more severely impaired with placebo. Infarct size as a percent of the area at risk was higher (p < 0.05) with placebo (51 +/- 15%) than with TLC C-53 (33 +/- 14%). Neutrophil infiltration into ischemic myocardium determined by myeloperoxidase assay was also significantly greater in the placebo group.

CONCLUSIONS

TLC C-53 administered intravenously before thrombolytic therapy resulted in a significant acceleration of thrombolysis time, improvement in coronary patency and blood flow during reperfusion and a reduction in infarct size.

Prostaglandin E1 does not accelerate rTPA-induced thrombolysis in acute myocardial infarction

Fifteen patients who arrived between 6 and 24 hours after the onset of acute myocardial infarction and who were found to have totally occluded coronary arteries, received aspirin, heparin, and tissue plasminogen activator given over 3 hours. Eight patients were randomly assigned to receive intravenous prostaglandin E1, 20 ng/kg/min for 6 hours, while seven patients received placebo infusion. Coronary arteriography begun immediately before the start of tissue plasminogen activator and repeated every 15 minutes revealed restoration of antegrade flow in two of eight (25%) patients treated with prostaglandin E1 and in two of seven (28%) patients receiving placebo. Pharmacologic sampling of tissue plasminogen activator levels were performed at baseline and 30, 45, 60, 75, 90, 135, 180, 190, 210, and 240 minutes afterwards for assessment of tissue plasminogen activator antigen. There was no difference in fibrinogen levels and no difference in tissue plasminogen activator antigen levels at these time periods. Clearance values of tissue plasminogen activator were calculated and were not different between the two groups. These data do not support the use of prostaglandin E1 for the acceleration of reperfusion in patients receiving tissue plasminogen activator for acute myocardial infarction.

Activation of the hemostatic system during thrombolytic therapy

Activation of the hemostatic mechanism has been described during thrombolytic therapy. This phenomenon has been detected by new methods of assessing hemostatic system function, based on immunoenzymatic or radioimmunoassays. However, these methods are extremely sensitive and, unless they are performed in expert laboratories, carefully following the recommended procedures, they generate in vitro artifacts. A description of these methods is provided, as well as a critical review of the available studies. The correct use of these methods will provide us with an understanding of the complex response of the hemostatic system to pharmacologic thrombolysis.

Profound inhibition of platelet aggregation with monoclonal antibody 7E3 Fab after thrombolytic therapy. Results of the Thrombolysis and Angioplasty in Myocardial Infarction (TAMI) 8 Pilot Study

OBJECTIVES

This study was undertaken to establish evidence for physiologic activity and to study the safety of murine-derived monoclonal antibody 7E3 Fab (m7E3 Fab) in patients receiving recombinant tissue-type plasminogen activator (rt-PA).

BACKGROUND

Platelet aggregation is believed to be a significant factor in the failure of pharmacologic reperfusion. By binding to the glycoprotein IIb/IIIa receptor, m7E3 Fab inhibits platelet aggregation and has been shown experimentally to decrease the time required for lysis and to prevent reocclusion. However, the safety of profound platelet inhibition after thrombolysis for acute myocardial infarction has not been tested in humans.

METHODS

Sixty patients receiving rt-PA, aspirin and heparin for acute myocardial infarction received m7E3 Fab bolus injections in ascending doses at 3, 6 and 15 h after initiation of the thrombolytic infusion. Ten patients treated with rt-PA but not m7E3 Fab were studied as control subjects.

RESULTS

Receptor site blockade and inhibition of platelet aggregation to 20 mumol/liter adenosine diphosphate were maximal at a dose of 0.25 mg/kg body weight of m7E3 Fab. Fifteen (25%) m7E3 Fab-treated patients and five (50%) control patients had major bleeding; eight of these events in seven m7E3 Fab-treated patients and one in a control patient occurred at the time of aortocoronary bypass surgery. Recurrent ischemia occurred in eight (13%) m7E3 Fab-treated patients and two (20%) control subjects. Coronary angiography was performed in 43 patients; the infarct-related coronary artery was patent in 5 of 9 (56%) control patients and 34 (92%) of 37 patients receiving m7E3 Fab.

CONCLUSIONS

Profound inhibition of platelet aggregation after thrombolysis was associated with bleeding rates comparable to those in control patients and a low rate of recurrent ischemia. The combination of m7E3 Fab and rt-PA, heparin and aspirin appears to be a promising and safe combination that should be evaluated in further studies of patients with acute myocardial infarction.

Comparison of vasodilatory prostaglandins with respect to cAMP-mediated phosphorylation of a target substrate in intact human platelets

The recent purification of a vasodilator-stimulated phosphoprotein (VASP) from human platelets and the development of a specific antiserum against VASP made it possible to study the quantitative effects of cAMP-elevating prostaglandins on cAMP-mediated phosphorylation of VASP in intact human platelets. Prostacyclin (PG-I2), prostaglandin-E1 (PG-E1) and the stable prostacyclinanalog Iloprost, all agents used for the treatment of peripheral vascular disease, induced rapid, stoichiometric and reversible phosphorylation of VASP in human platelets mediated by the cAMP-dependent protein kinase. However, there were substantial differences between these three cAMP-elevating prostaglandins with respect to their effects on extent, duration and reversibility of VASP phosphorylation. Maximal VASP phosphorylation was induced both by PG-I2 and Iloprost, but the PG-I2 effect was only of short duration in comparison to that of Iloprost. The extent of PG-E1-induced VASP phosphorylation was less than that observed with PG-I2 and Iloprost. In endothelial cell-platelet coincubations, an endothelial cell-derived, indomethacin-sensitive factor caused a rapid elevation of platelet cAMP level and VASP phosphorylation. These results provided direct evidence that human endothelial cells are capable of producing biologically active quantities of cAMP-elevating prostaglandins sufficient to induce stoichiometric cAMP-mediated protein phosphorylation in human platelets. VASP-phosphorylation induced by PG-I2 and PG-E1 was completely reversible after removal of the prostaglandins whereas this was only partially the case with Iloprost. In addition, evidence is presented that the prostaglandin-regulated adenylate cyclase system but not the cAMP-mediated protein phosphorylation desensitizes in human platelets after prolonged treatment with cAMP-elevating prostaglandins. VASP phosphorylation is proposed as a marker for quantitating aspects of vessel wall-platelet interaction.

In vivo thrombin inhibition enhances and sustains arterial recanalization with recombinant tissue-type plasminogen activator

The effects of heparin and the synthetic competitive thrombin inhibitor (2R,4R)-4-methyl-1-[N2-(3-methyl-1,2,3,4-tetrahydro-8-quinolinesulfon yl)-L-arginyl]-2-piperidinecarboxylic acid monohydrate (Argatroban) on thrombolysis with recombinant tissue-type plasminogen activator (rt-PA) was studied in groups of six or seven rabbits with arterial thrombosis. The model consisted of a whole-blood clot produced in a 1-cm isolated femoral arterial segment with superimposed endothelial damage and distal high-grade stenosis. rt-PA was injected as an intravenous bolus of 0.45 mg/kg body wt at 15-minute intervals until recanalization, or up to a maximum of four boluses. In seven rabbits given an intravenous injection of 17 mg/kg aspirin, rt-PA induced transient reflow in only one animal. In seven rabbits that received intravenous heparin (200 units/kg over 60 minutes), rt-PA administration produced reflow in five animals, which was persistent in two rabbits. Combined administration of aspirin and heparin in seven rabbits was associated with similar rt-PA-induced recanalization. rt-PA administration in six rabbits given intravenous Argatroban (100 micrograms/kg/min for 60 minutes) caused recanalization in five, with persistent patency in three. In six rabbits given aspirin and Argatroban, rt-PA caused recanalization in all, with persistent patency in five animals. Reflow occurred significantly more rapidly with Argatroban (14 +/- 7 minutes) than with heparin (35 +/- 11 minutes), reflow was obtained with fewer boluses of rt-PA in combination with Argatroban (median value of one bolus) than with heparin (median value, three boluses), and reocclusion after reflow was less frequent with Argatroban (0 of 11 versus 5 of 10 rabbits). Furthermore, the degree of thrombolysis determined by pathological analysis was significantly more extensive with Argatroban than with heparin, and patency persisted during a 3-hour observation period, despite elimination of Argatroban from the circulation. Thus, Argatroban, relative to heparin, enhances and sustains thrombolysis with rt-PA. It may offer promise as an adjunctive agent for thrombolytic therapy of arterial thrombosis.

Comparative effects of aspirin, a synthetic thrombin inhibitor and a monoclonal antiplatelet glycoprotein IIb/IIIa antibody on coronary artery reperfusion, reocclusion and bleeding with recombinant tissue-type plasminogen activator in a canine preparation

The comparative effects of intravenous aspirin, the synthetic thrombin inhibitor (2R,4R)-4-methyl-1-[N2-(3-methyl-1,2,3,4-tetrahydro-8- quinolinesulfonyl)-L-arginyl]-2-piperidinecarboxylic acid monohydrate (Argatroban) and F(ab')2 fragments of monoclonal antibody 7E3 against platelet glycoprotein IIb/IIIa (7E3-F[ab']2) on thrombolysis, reocclusion and bleeding associated with 0.45 mg/kg body weight bolus injections of recombinant tissue-type plasminogen activator (rt-PA) were studied in a canine coronary artery thrombosis model. Coronary patency was monitored for 2 h both by flow probe and by coronary angiography. Four groups were studied: Group I = pretreated with 17 mg/kg intravenous aspirin (n = 6), Group II = pretreated with 200 micrograms/kg per min intravenous Argatroban for 60 min (n = 5), Group III = pretreated with aspirin and Argatroban (n = 5) and Group IV = pretreated with 0.8 mg/kg intravenous 7E3-F(ab')2 (n = 5). In Group I, reflow occurred in four of six dogs, but did not persist; reflow was induced in Group II in four of five dogs, persisting in one; in Group III, reflow occurred in all five dogs, persisting in four; in Group IV reflow was achieved in four of five dogs, persisting in two. The frequency of persistent reflow in Group III was significantly higher than in the combined Groups I and II (p = 0.012), whereas the time to reflow was significantly shorter in the groups receiving Argatroban than in the aspirin group (median 25 versus 55 min, p = 0.04). There were no significant differences between Groups III and IV.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiologic effects and side effects of prostaglandin E1 in the adult respiratory distress syndrome

Because PGE1 previously has been reported to increase survival of patients with ARDS, we evaluated physiologic effects and side effects of PGE1 in a prospective open-label study of patients with ARDS. Seventeen patients with ARDS who did not have significant renal or hepatic dysfunction received PGE1 by continuous central venous infusion (30 ng/kg/min). Seventeen control patients with ARDS without renal or hepatic dysfunction who had similar APACHE II and ARDS scores and causes of ARDS did not receive PGE1. Prostaglandin E1 significantly decreased the SVRI and oxygen extraction ratio. Concentrations of total and polymorphonuclear leukocytes, but not platelets, increased significantly during PGE1 infusion, but did not change in control patients. There was no change in the Do2I and Vo2I during the course of the PGE1 infusion. There were no differences in Do2I and Vo2I during PGE1 infusion between survivors and nonsurvivors. Prostaglandin E1 was infused for a mean of 5.9 +/- 1.8 days (+/- SD) and was discontinued on ten occasions in seven patients because of supraventricular dysrhythmias (n = 4), hypotension (n = 3), thrombocytopenia (n = 3), and cardiac arrest (n = 2). Nonsurvivors had PGE1 discontinued prematurely more frequently than survivors (56 percent [5/9] vs 25 percent [2/8], respectively). The prevalence of multiple-system organ failure and the in-hospital mortality of both PGE1-treated and control patients were not different. Although PGE1 causes significant systemic vasodilation and possibly decreased intrapulmonary polymorphonuclear leukocyte sequestration, PGE1 does not influence multiple-system organ failure or mortality of patients with ARDS without renal or hepatic dysfunction.

Effect of prostacyclin on coronary occlusion in acute myocardial infarction

Prostacyclin is a powerful inhibitor of platelet aggregation and induces relaxation of vascular smooth muscle. We have studied the coronary effects of high local concentrations of prostacyclin in 17 patients during the early stages of acute myocardial infarction. We infused graded concentrations of intracoronary prostacyclin and compared the effects to those of intracoronary isosorbide dinitrate before and after an intracoronary infusion of streptokinase. Considerable dilation of the infarct-related stenosis may follow local infusions of prostacyclin in some patients. In general, however, dilation of the infarct-related stenosis or coronary recanalization did not result from infusion of prostacyclin.

Prostaglandin E1 attenuates postischemic contractile dysfunction after brief coronary occlusion and reperfusion

We have previously demonstrated that administration of the prostacyclin analogue iloprost improved postischemic functional recovery in reversibly injured ischemic-reperfused myocardium. The present study investigated the effects of administering an endogenous vasodilator prostanoid, prostaglandin E1 (PGE1), in the stunned myocardium (15 minutes of coronary artery occlusion and 3 hours of reperfusion) of anesthetized dogs. The percentage of regional myocardial segment shortening (%SS) after administration of PGE1 by two routes, intravenously (1 microgram/kg/min) or intraatrially (0.1 microgram/kg/min), to avoid pulmonary metabolism, 15 minutes before and throughout the period of occlusion, was compared to %SS in a control group treated with saline solution. Nearly equivalent reductions in mean arterial pressure during occlusion compared to pretreatment control (PTC) values were produced by intravenous (33%) or intraatrial (25%) PGE1. There was no difference in transmural myocardial blood flow (radioactive microsphere technique) in the ischemic region between the PGE1-treated and control groups at any time. Although there were no differences in %SS in the nonischemic region between groups throughout the experiment, postischemic recovery of segment function in the ischemic-reperfused area was significantly improved (p less than 0.05) at all times during reperfusion by intravenous PGE1 (%SS of PTC: 30 minutes = 65 +/- 8; 3 hours = 58 +/- 7) or intraatrial PGE1 (%SS of PTC: 30 minutes = 57 +/- 12; 3 hours = 50 +/- 4) compared to the control group (%SS of PTC: 30 minutes = 25 +/- 13; 3 hours = 10 +/- 13). Thus treatment with PGE1 attenuates postischemic contractile dysfunction in the stunned myocardium.2+ both.

Effects of aspirin and prostaglandin E1 on in vitro thrombolysis with urokinase. Evidence for a possible role of inhibiting platelet activity in thrombolysis

The formation of thrombi in vivo includes the activation of both platelets and the coagulation cascade. Conventional thrombolytic therapy is primarily directed toward the dissolution of fibrin. To evaluate the possibility that platelet activity impairs the lysis of thrombi, we studied the effects of aspirin and platelet-deaggregating prostaglandin E1 on thrombolysis with urokinase. Combined platelet and fibrin thrombi were produced in vitro by adding CaCl2 and collagen (1 microgram/ml) to citrated platelet-rich plasma (250,000 platelets per microliters). Urokinase (500-10,000 units/ml) caused a dose-dependent weight loss of the thrombi that was maximal at 2,000 units/ml. The addition of aspirin (10-200 micrograms/ml) to platelet-rich plasma before thrombus formation markedly enhanced thrombolysis with urokinase. This effect was most pronounced at 20 micrograms/ml aspirin. However, when aspirin was added after completion of thrombus formation, no significant effect on thrombolysis was noted. Prostaglandin E1 (1-100 mumol/l) improved the lysis with urokinase of the combined platelet and fibrin thrombi. This effect was maximal at 20 mumol/l prostaglandin E1. When pure fibrin thrombi were produced in platelet-free plasma, prostaglandin E1 was without effect on lysis. Thus, in vitro lysis with urokinase of combined platelet and fibrin thrombi was enhanced by the addition of platelet-deaggregating prostaglandin E1 and by pretreatment with aspirin.

Hemodynamic and angiographic effects of prostaglandin E1 in coronary artery disease

The effects of prostaglandin E1 (PGE1) were assessed in 24 patients with coronary artery disease. Quantitative coronary angiography was performed in 15 patients. PGE1 was found to produce dilation of coronary stenoses (6 +/- 12% to intravenous PGE1, difference not significant, 19 +/- 22% to intracoronary PGE1, p less than 0.05), but usually no change in the diameter of angiographically normal segments. In these patients intracoronary nitroglycerin consistently dilated the normal segments not altered with PGE1 and often led to further dilation of the stenoses. In 9 other patients who were undergoing coronary angioplasty, hemodynamics and the time to ischemia induced by coronary occlusion were measured. In both patient groups PGE1 led to decreases in aortic, pulmonary artery and pulmonary arterial wedge pressures and an increase in heart rate (all p less than 0.05). Before coronary occlusion PGE1 produced coronary vasodilation manifested by preservation in coronary sinus flow (130 +/- 41 to 126 +/- 42 ml/min, difference not significant); as aortic pressure declined coronary resistance decreased (0.9 +/- 0.3 to 0.8 +/- 0.3 mm Hg/ml/min, p less than 0.05). During coronary occlusion residual flow to the affected region was usually similar to control occlusions (37 +/- 20 to 36 +/- 25 ml/min, difference not significant) and collateral resistance was decreased (3.2 +/- 2.9 to 2.9 +/- 2.6 mm Hg/ml/min, p less than 0.05). However, time to ischemia usually remained unchanged. PGE1 shows an interesting angiographic and hemodynamic profile in patients with coronary artery disease. Although no obvious clinical benefit was seen, PGE1 was safely administered both intravenously and directly into narrowed coronary arteries.

Platelets and antiplatelet therapy in ischemic heart disease

Blood platelets have been shown to play an important role not only in thrombosis, but also in the pathogenesis of coronary artery disease and its complications. Drugs that affect platelets have been shown to reduce mortality in survivors of acute myocardial infarction, to reduce the risk of myocardial infarction in patients with unstable angina, and to preserve the potency of saphenous venous grafts used to bypass obstructed coronary arteries. The drugs may also play a role in the primary prevention of arteriosclerosis and in preventing thrombotic complications following coronary angioplasty.

Eicosanoids and myocardial ischaemia

The available data clearly suggest large alterations in myocardial eicosanoid generation during myocardial ischaemia and demonstrate important actions of eicosanoids on myocardial function during ischaemic conditions. These actions include direct effects on the injured myocardium as well as influences on other target cells, such as platelets and leukocytes. Selective modifications of eicosanoid generation, for example by providing exogenous PGI2 or by inhibiting oxygen toxicity are most challenging approaches for the design of new and potentially valuable cardioprotective agents. Antagonism of thromboxane formation and/or action might be of some value in ischaemia but appears to be less important for reperfusion injury. Leukotrienes and other noncyclic fatty acid peroxidation products are another group of potentially deleterious agents and there is a definite need for more selective inhibitors of leukotriene formation and/or action to establish their role in ischaemia.