Circulating platelet products in unstable angina pectoris

The Effects of Platelet-Activating Factor on Uterine Contractility, Perfusion, Hypoxia, and Pain in Mice

It is widely hypothesized that menstrual pain is triggered by prostaglandin synthesis that evokes high-pressure uterine contractions and ischemia. However, the effects of molecules implicated in menstrual pain on uterine contractility, perfusion, and oxygenation in vivo have been rarely demonstrated. Studies in women that do not respond to nonsteroidal anti-inflammatory drugs (NSAIDs) have reported elevated levels of platelet-activating factor (PAF). To establish in vivo evidence of PAF's capability to impair uterine homeostasis and to elicit visceral pain, we examined the effects of the PAF receptor agonist (carbamyl PAF [CPAF]) in comparison to other molecules hypothesized to play a role in uterine pain in mice. Uterine pressure was increased by oxytocin, prostaglandin F2α (PGF2α), and CPAF. Even in the absence of inflammatory molecules, uterine contractions reduced uterine oxygenation by 38%. CPAF reduced uterine perfusion by 40% ± 8% and elicited further oxygen desaturation approaching hypoxia (9.4 ± 3.4 mm Hg Pao₂). Intraperitoneal injections of CPAF and PGF2α evoked visceral pain and pelvic hyperalgesia in awake wild-type mice. However, pain was not observed in identically injected PAF-receptor knockout mice. Thus, our model provides a demonstration that a molecule implicated in NSAID-resistant dysmenorrhea has a detrimental effect on uterine homeostasis and is capable of causing visceral pain. Our results support the general hypothesis that menstrual cramps are caused by uterine contractions, impaired perfusion, and reduced oxygenation. Since this study was limited to mice, confirmation of these results in humans would be valuable for development of novel therapeutics targeted at inflammatory precursors, contractility, perfusion, and tissue oxygenation.

Chronic Platelet Activation and Acute Coronary Syndromes in 13 Middle-Aged Patients

We report on clinical, laboratory, and angiographic findings that appear to characterize a group of 13 middle-aged patients who suffered acute coronary syndromes (ACS) despite little angiographic evidence of atherosclerotic heart disease (ASHD) or other risk factors. Nine of the 13 were ≤46 years of age and the rest ranged to 59 years. All had evidence of platelet disorders (PD): seven had chronic immune thrombocytopenia (ITP), one had familial thrombocytopenia, and five had other disorders affecting platelets. Evidence of long-standing chronic platelet activation was the common feature of the group, as found by (i) elevated platelet microparticles (PMP), (ii) thrombocytopenia, and (iii) enhanced procoagulant activity of plasma. Data on the 7 with ITP were compared to 20 ITP without ACS: the former had higher PMP (p < 0.01) and platelet-associated IgM (p < 0.05) relative to the ITP patient controls. Another set of patient controls consisted of 20 ACS with documented ASHD: although activation indicators were abnormal also in this group relative to normal controls (p < 0.01), the PD group of 13 had more marked abnormalities in all tests (p < 0.03), particularly in PMP and thrombocytopenia (p < 0.01). The seven youngest in the PD group appeared to respond to antiplatelet therapy since no recurrence of coronary ischemia was seen in up to 3 years of observation. It is suggested that chronic platelet activation by antibodies or immune complex may predispose those in the PD group to ACS (e.g., when under stress) despite the absence of ASHD and few other known risk factors. The true incidence of this syndrome is unknown but may be substantial. Key Words: Chronic platelet activation-Platelet microparticles-Platelet.associated IgM-Immune thrombocytopenia-Acute coronary syndromes-Middle age.

Coronary Angioplasty in Patients with Unstable Angina, with Special Reference to Preceding Treatment with Antithrombin III and Heparin

Seventy-nine patients undergoing percutane ous transluminal coronary angioplasty (PTCA) for unsta ble angina were analyzed with respect to preceding an tithrombin treatment; group I comprised patients (n = 26) without antecedent antithrombin therapy; group II, pa tients (n = 30) with heparin infusion for ≥24 h, and group III patients (n = 23) with ongoing heparin infusion and given antithrombin III concentrate immediately before the procedure because of plasma antithrombin III <85%. Immediate results were 89% (70 of 79) angiographic suc cess, five (6%) subacute occlusions (two subsequent non-Q wave infarctions), no emergency coronary artery bypass grafting (CABG), and no immediate mortality. There were no differences between the groups. From dis charge to 4 months, one patient died, one had a nonfatal infarction, and 24 (30%) had repeated PTCA or CABG. The cumulative 4-month event rate was 11 of 26 (42%) in group I, 10 of 30 (33%) in group II, and 7 of 23 (30%) in group III (NS). During PTCA, heparin bolus administra tion was guided by activated clotting time (ACT), aiming at>300 s. Baseline ACT was significantly less in patients not treated with heparin (129 ± 34 s in group I vs. 179 ± 38 and 162 ± 29 s in groups II and III, respectively; p < 0.05), but during the procedure, patients from all groups required the same amount of heparin (13,900 ± 4,800, 13,000 ± 6,800, and 13,000 ± 5,700 IU, respectively; NS) to reach similar maximum ACT levels (334 ± 36, 312 ± 32, and 319 ± 44 s, respectively; NS). Patients receiving warfarin ( n = 8) responded with a higher ACT (456 ± 110 s; p < 0.05) on lower doses of heparin (10,000 ± 3,800 IU). In conclusion, patients with unstable angina receiv ing individualized antithrombotic therapy can be success fully treated with PTCA, with an acute complication rate and long-term results comparable with those expected in patients undergoing elective procedures. The value of an tithrombin III substitution must be evaluated in random ized trials. Preprocedural heparin infusion does not re duce the need of extra heparin during the procedure. Key Words: Antithrombin III—Heparin—PTCA (percutane ous transluminal coronary angioplasty)—Unstable angina pectoris.

High platelet reactivity is associated with myocardial infarction in premenopausal women: a population-based case-control study

SUMMARY BACKGROUND

Platelets are involved in the occlusion of coronary arteries after rupture of an atherosclerotic plaque. Furthermore, activated platelets release large quantities of growth factors, chemokines and interleukins that regulate inflammatory reactions. Therefore, we hypothesized that high basal platelet reactivity may contribute to an increased risk of myocardial infarction (MI) in premenopausal women.

METHODS

We assessed the relation between high platelet reactivity and MI in a population-based case-control study among premenopausal women (aged < 50 years). We used multivariable logistic regression to quantify the effect of high platelet reactivity, adjusted for potential confounders. Platelet reactivity was estimated by plasma levels of neutrophil activating peptide 2 (NAP-2), CXC chemokine ligand (CXCL)4, soluble glycoprotein 1b (sGPIb) and soluble P-selectin.

RESULTS

High platelet reactivity (i.e. levels >or= 90th percentile control subjects) was associated with a 2- to 3-fold increased incidence of MI: the adjusted odds ratios (ORs) were 3.0 [95% confidence interval (CI) 1.4-6.4] for NAP-2, 2.2 (0.9-5.1) for CXCL4, 1.9 (0.7-4.6) for sP-selectin and 2.5 (1.1-5.7) for sGPIb. The incidence of MI dose-dependently increased when more markers were elevated. High platelet reactivity according to both NAP-2 and sGPIb was associated with an up to tenfold increased incidence (9.9, 95% confidence interval 2.0-48.3).

CONCLUSIONS

High basal platelet reactivity was associated with a 2- to 3-fold higher incidence of MI compared with normal platelet reactivity in premenopausal women. Our results suggest that high basal platelet reactivity may contribute to a higher risk of MI.

Caffeine stimulates in vivo platelet reactivity

The effect of coffee drinking on platelet reactivity was studied in 12 healthy subjects. Plasma beta-thromboglobulin concentration was determined before and one hour after administration of 100 mg of caffeine, corresponding to one cup of coffee. Mean values were 47.0 +/- 19.3 and 179.3 +/- 85.5 ng/ml before and after caffeine administration respectively. The increase, 298 +/- 150%, is highly significant (p less than 0.001).

Increased platelet reactivity in unstable angina patients is not related to C-reactive protein levels

Platelets are a major component of thrombi, and coronary thrombosis plays a key role in the pathogenesis of unstable angina (UA). Whether platelet aggregability is increased in UA patients however, is not known. Furthermore, no study has investigated the relationship between platelet reactivity and inflammation in UA patients In this study, venous blood samples were collected at admission in coronary care unit in 37 patients with unstable angina (Braunwald class IIIB) and in 37 sex- and age-matched patients with chronic stable angina (CSA). Patients taking thienopyridine or anticoagulant drugs were excluded from the study, as also were excluded patients with a history of acute myocardial infarction in the previous 12 months. Platelet aggregability was measured on flowing blood as time to occlude a ring coated with collagen-adenosine diphosphate (ADP), using the platelet function analyzer (PFA-100) system. By this method, the time to occlusion (closure time) is taken as a measure of platelet adhesion/aggregability, with shorter times indicating greater platelet reactivity. There were 23 men and 14 women in both groups, and age was 67.7 +/- 8 and 67.5 +/- 8 years in UA and SA, respectively (P = 0.93). Closure time was significantly reduced in UA patients (78.8 +/- 14 s), compared to SA patients (93.3 +/- 19 s, P < 0.001). Among UA patients, serum C-reactive protein (CRP) levels had a median value of 5.1 mg/l (bottom and top quartile levels, 1.50-7.95). There was no significant correlation between closure time and CRP levels (r = 0.22, P = 0.29). Our data show that, in patients with unstable angina there is an increase of platelet reactivity in response to ADP/collagen stimulation, which is not related to inflammation.

Evaluation of platelet function in aspirin treated patients with CAD

BACKGROUND

Studies of platelet function in the acute coronary syndrome (ACS) have revealed both increased and unchanged platelet activation. To obtain a better understanding of platelet function in coronary artery disease in the setting of aspirin therapy, we performed platelet functional testing in patients with ACS and compared results to patients without CAD.

METHODS

We measured platelet aggregation and activation in response to ADP and epinephrine in 80 age and gender matched hospitalized patients (40 with ACS, 40 with non-cardiac chest pain (NCCP)). All subjects received ASA (81-325 mg). Platelet aggregation was performed using standard light transmission in platelet-rich plasma and activation was measured via flow cytometric analyses. We also studied platelet function under high shear rates measured by the platelet function analyzer (PFA-100).

RESULTS

ASA effect was found to be present in all subjects by blunted platelet aggregation in response to arachidonic acid. Patients with ACS showed significantly higher levels of platelet aggregation to epinephrine compared to patients with NCCP (p = 0.001). Other measures of platelet function including ADP aggregation, Pselectin, activated glycoprotein IIb/IIIa expression, and PFA-100 were unchanged between the two groups.

CONCLUSIONS

We have found conflicting results of platelet functional testing in ACS. Specifically aspirin therapy in patients with ACS is effective in suppressing the platelet release response and is effective in the partial suppression of platelet aggregation; however, it appears that ACS patients have increased platelet aggregation to adrenergic stimuli when compared to age and gender matched controls without CAD despite the use of aspirin. In some studies, because ACS patients have an accentuated response to adrenergic stimuli this might be interpreted as aspirin resistance. Our study suggests that depending on the assay used to determine aspirin resistance, not all patients with this label are resistant to the biological effects of aspirin but they may have higher than normal baseline platelet sensitivity to adrenergic stimuli.

Comparison of platelet activation in unstable and stable angina pectoris and correlation with coronary angiographic findings

We sought to investigate the relation between platelet activation and the angiographic evidence of ruptured plaque in patients presenting with unstable and stable angina pectoris. We prospectively enrolled 25 consecutive patients (5 women and 20 men, mean age 62 +/- 3 years), 17 with unstable angina and 8 with stable angina. Systemic venous blood samples were collected within 4 to 6 hours of admission for flow cytometry analysis. Activation-dependent epitope CD63 and glycoprotein IIb/IIIa on the platelet membrane were assayed. Fibrinogen levels were also measured. All patients with unstable angina underwent cardiac catheterization and had angiographic evidence of ruptured plaque. Of the patients with stable angina, 5 underwent coronary angiography with smooth noncomplex lesions and 3 had negative technetium-99m sestamibi stress tests. Patients with unstable angina were characterized by 39% higher levels of fibrinogen than patients with stable angina (423 +/- 304 vs 304 +/- 51 mg/dl, p = 0.004). The percentage of platelets positive for the activation-dependent epitope CD63 was 5 times higher in patients with unstable than stable angina (14.6 +/- 5.6% vs 2.75 +/- 1.6%, p = 0.0026). They also had a 15% higher expression of their glycoprotein IIb/IIIa (517 +/- 79 vs 449 +/- 50 mean fluorescence intensity, p = 0.038). Thus, this study establishes a direct relation between the morphology of ruptured plaque and platelet activation in patients with unstable angina. This may allow for further risk stratification. Patients with unstable complex lesions had a fivefold higher expression of the platelet activation epitope CD63 than patients with stable angina. Furthermore, they had 15% more glycoprotein IIb/IIIa aggregation sites expressed on their platelet membrane, thus indicating an intense thrombogenic potential.

NPC 15669, an Antiinflammatory Leucine Derivative, Reduces In Vitro Platelet Aggregability in Both Swine and Human Plasma

Background: Leumedins inhibit cell adhesion to endothelium via blockage of integrin binding. We tested a hypothesis that the novel leucine derivate NPC 15669 will affect in vitro platelet aggregability (PA) in both human and swine plasma. Methods and Results: Platelet-rich plasma (PRP) was incubated with 200 µ g and 400 µ g of NPC 15669. Then PA was induced by ADP, collagen, thrombin, and ristocetin in the PRP without NPC 15669 and in NPC 15669-treated samples. We have found that PRP incubation with 200 µ g of NPC 15669 significantly decreases PA compared to baseline in all three experimental groups in response to all agonists tested. When PRP was treated with 400 µ g of NPC 15669, dose-dependent reduction of PA was observed only in the human control and swine groups, but not in patients with coronary atherosclerosis. Conclusions: Leumedins, known for their antiinflammatory properties, may have clinical applications related to their effect on platelet function. The mechanism of these effects is unknown, but may be related to the inhibition of platelet-endothelial binding.

Prothrombin fragments F1+2, thrombin-antithrombin III complexes, fibrin monomers and fibrinogen in patients with coronary atherosclerosis

We determined the plasma levels of prothrombin fragment F1+2, thrombin-antithrombin III complexes (TAT), fibrin monomers (FM), D-dimers (DD) and fibrinogen in 57 patients with angiographically verified graded coronary artery disease (CAD) free of concomitant peripheral atherosclerosis, cerebrovascular disease or diabetes mellitus and a group of 21 apparently healthy controls. Blood was collected from the antecubital vein through atraumatic venipuncture prior to the angiographic procedure. Plasma levels of hemostatic markers were related to the presence and graded severity of CAD. The levels of prothrombin fragment F1+2 (1.74+/-0.11 vs. 1.0+/-0.07 nmol/l, P<0.001), FM (41.6+/-5.5 vs. 7.42+/-3.05 nmol/l, P<0.001), TAT (15.6+/-2.7 vs. 2.96+/-0.32 microg/l, P<0.001) and fibrinogen (3.64+/-1.3 vs. 3.08+/-0.33 g/l, P<0.01) were significantly higher in patients with CAD compared to controls, while there was no difference regarding the fibrinolytic system represented by DD (441.6+/-58.9 vs. 337.4+/-42.05 microg/l, n.s.). Within the CAD group, patients with extensive coronary atherosclerosis (> or =2 vessel disease) had significantly higher values for prothrombin fragment F1+2 (1.89 vs. 1.57 nmol/l, P = 0.04), FM (50.7 vs. 29.8 nmol/l, P = 0.03), and a trend to significance was noted for fibrinogen (3.9 vs. 3.3 g/l, P = 0.07) suggesting that blood coagulability was related to the severity of the disease and that hemostatic markers of thrombin activity represent a useful tool to identify patients with a latent hypercoagulable state with a higher susceptibility to sustain coronary thrombosis.

Increased platelet reactivity and circulating monocyte-platelet aggregates in patients with stable coronary artery disease

OBJECTIVES

We sought to examine whether patients with stable coronary artery disease (CAD) have increased platelet reactivity and an enhanced propensity to form monocyte-platelet aggregates.

BACKGROUND

Platelet-dependent thrombosis and leukocyte infiltration into the vessel wall are characteristic cellular events seen in atherosclerosis.

METHODS

Anticoagulated peripheral venous blood from 19 patients with stable CAD and 19 normal control subjects was incubated with or without various platelet agonists and analyzed by whole blood flow cytometry.

RESULTS

Circulating degranulated platelets were increased in patients with CAD compared with control subjects (mean [+/- SEM] percent P-selectin-positive platelets: 2.1 +/- 0.2 vs. 1.5 +/- 0.2, p < 0.01) and were more reactive to stimulation with 1 micromol/liter of adenosine diphosphate (ADP) (28.7 +/- 3.9 vs. 16.1 +/- 2.2, p < 0.01), 1 micromol/liter of ADP/epinephrine (51.4 +/- 4.6 vs. 37.5 +/- 3.8, p < 0.05) or 5 micromol/liter of thrombin receptor agonist peptide (TRAP) (65.7 +/- 6.8 vs. 20.2 +/- 5.1, p < 0.01). Patients with stable CAD also had increased circulating monocyte-platelet aggregates compared with control subjects (percent platelet-positive monocytes: 15.3 +/- 3.0 vs. 6.3 +/- 0.9, p < 0.01). Furthermore, patients with stable CAD formed more monocyte-platelet aggregates than did control subjects when their whole blood was stimulated with 1 micromol/liter of ADP (50.4 +/- 4.5 vs. 28.1 +/- 5.3, p < 0.01), 1 micromol/liter of ADP/epinephrine (60.7 +/- 4.3 vs. 48.0 +/- 4.8, p < 0.05) or 5 micromol/liter of TRAP (67.6 +/- 5.7 vs. 34.3 +/- 7.0, p < 0.01).

CONCLUSIONS

Patients with stable CAD have circulating activated platelets, circulating monocyte-platelet aggregates, increased platelet reactivity and an increased propensity to form monocyte-platelet aggregates.

Changes in hemostatic function at times of cyclic variation in occupational stress

In this study we demonstrated, in the same healthy subjects, a significant elevation in coagulation factors VII and VIII, fibrinogen, thrombocyte count, and thrombin and adenosine diphosphate-induced platelet aggregation during a period of increased workload compared with a calm work period. These findings may add to the understanding of the mechanism that links mental stress to coronary disease.

Increased number of thromboxane A2-prostaglandin H2 platelet receptors in active unstable angina and causative role of enhanced thrombin formation

The current study was designed to investigate the number and affinity of platelet thromboxane A2/prostaglandin H2 (TxA2/PGH2) receptors in patients with unstable angina and, if any, the role played by the increased thrombin formation that is a common finding in these patients. Measurements taken during active unstable angina but not those taken during inactive angina showed an increase number (p < 0.001), without changes in affinity, of platelet TxA2/PGH2 receptors, evaluated as the binding capacity of iodine 125-PTA-OH, a stable TxA2 analogue. Moreover patients with active angina had higher plasma concentrations of fibrinopeptide A (FPA) (p < 0.0001), which were significantly related to the number of platelet TxA2/PGH2 receptors (r = 0.76; p < 0.01). Heparin infusion but not aspirin treatment promptly normalized the number of TxA2/PGH2 receptors and significantly reduced plasma FPA concentrations. In an in-vitro study thrombin in a concentration similar to that found in vivo significantly increased the number of platelet TxA2/PGH2 receptors (p < 0.01), whereas heparin did not affect TxA2/PGH2 receptors. These results have important therapeutic implications and indicate the preferential use of heparin rather than aspirin during the acute phase of unstable angina.

Myocardial ischemia after orthotopic liver transplantation

A hypercoagulable state exists after orthotopic liver transplantation. This hematologic abnormality may predispose patients to coronary thrombosis and unstable angina. The incidence of postoperative myocardial ischemia in such patients is unknown. Suitable electrocardiograms and clinical events of consecutive patients undergoing orthotopic liver transplantation (n = 45) and major intraabdominal surgery (n = 28) during a 3-month period at a major university teaching hospital and transplant center were examined retrospectively. Clinical myocardial ischemia or ischemic electrocardiographic changes, or both, occurred in 6 transplant patients compared with no patient in the nontransplant or comparison group. In 4 of the 6 patients with dramatic electrocardiographic changes and ischemic events, coronary arteriography failed to demonstrate significant obstructive disease. It is concluded that severe myocardial ischemia may occur in patients after orthotopic liver transplantation in the absence of significant coronary disease. A hypercoagulable state may predispose to coronary thrombosis in this setting, providing insight (and a future model for study) into the development of unstable angina.

Antithrombotic properties of transdermal nitroglycerin in stable angina pectoris

Nitroglycerin provides an external source of nitric oxide which stimulates guanylate cyclase and produces vasodilatation and inhibition of platelet function. The antithrombotic effects of intravenous nitroglycerin were recently documented in various experimental models and in patients with unstable angina. This protocol was designed to evaluate whether these effects could also be detected with transdermal nitroglycerin in patients with stable angina. In a randomized, double-blind, controlled parallel trial, 22 patients received transdermal nitroglycerin, 0.6 mg/hour (11 patients), or placebo (11 patients). Platelet aggregation to adenosine diphosphate (ADP) and to thrombin was measured in whole blood. Thrombus formation was assessed on porcine aortic media exposed to the patient's venous blood for 3 minutes at shear rates of 2,546 and 754 s-1. Platelet aggregation to ADP decreased from 7.7 +/- 0.8 to 5.3 +/- 0.8 ohms (p < 0.05) with nitroglycerin, and to thrombin from 15.6 +/- 1.2 to 12 +/- 1.2 ohms (p < 0.05). Thrombus size at the high-shear rate decreased from 2.8 +/- 0.7 to 1.0 +/- 0.3 microns 2 (p < 0.05), and at the low-shear rate from 2.5 +/- 0.5 to 1.0 +/- 0.2 microns 2 (p < 0.05). Placebo had no significant effect on platelet aggregation and platelet thrombus deposition. These parameters were all reduced by > or = 20% in 8 patients taking nitroglycerin but only in 3 patients taking placebo (p < 0.05). Transdermal nitroglycerin significantly inhibits platelet aggregation and mural thrombus formation in patients with angina pectoris.

Haemostatic variables in patients with unstable angina

To assess the contribution of thrombus formation in the pathogenesis of unstable angina, we employed the recently developed assays of small fragments which reflect the degree of activation of various components of the haemostatic system. Such haemostatic measurements were undertaken in patients with unstable angina (n = 47) from the time of their admission to the coronary care unit (CCU) at 8-h intervals in the first 24 h and then daily for a total of 5 days. The results obtained were compared with healthy control values. Patients exhibited lower ATIII, prolongation of the APTT and TT, but not PT or the reptilase time, which is a consequence of heparinization. There was significant elevation of fibrinogen, factor VIII:C, von Willebrand factor:antigen and von Willebrand factor:ristocetin cofactor throughout the study period. There was also evidence of thrombin generation as indicated by the elevated levels of fibrinopeptide A (FPA) and thrombin-antithrombin complexes. The platelet release proteins, beta-thromboglobulin (BTG) and platelet factor 4 (PF4), were markedly elevated in the first 2 days and dropped gradually thereafter. The fibrinolytic inhibitor, plasminogen activator inhibitor (PAI), levels were elevated throughout. Proteins C and S, plasminogen and alpha 2-antiplasmin remained unchanged. It was concluded that in patients with unstable angina, there is significant activation of the clotting system and inhibition of fibrinolysis which confirms the existence of a tendency towards thrombus formation in patients with unstable angina.

Circulating aggregated platelets, number of platelets per aggregate, and platelet size during acute myocardial infarction

Circulating aggregated platelets (total, reversibly and irreversibly aggregated), the number of platelets per aggregate and "big" platelets were measured by a modification of the Wu and Hoak method in 42 patients on the first, second and fifth day of acute myocardial infarction (AMI). Among them, 30 had an uncomplicated course and 12 patients had complications that occurred between the 5th and 10th day of hospitalization (7 patients had reinfarction and 5 died). In all patients the measured parameters were elevated compared with those of control subjects. There was a significant increase, especially after the first observation day, in the values of total aggregated platelets (37 +/- 11% vs 26 +/- 12%, p < 0.001), reversibly aggregated platelets (27 +/- 9% vs 17 +/- 8%, p < 0.001) and the average platelets per aggregate (8.6 +/- 0.3 vs. 2.3 +/- 0.4) in patients with versus without complications. In considering the role of platelets in the development of AMI, these findings may add information to the role of platelets in determining the course of AMI.

Unstable angina: role of silent ischemia and total ischemic time (silent plus painful ischemia), a 6-year follow-up

To assess the long-term prognostic significance of total ischemic time (silent plus painful ischemia) and silent ischemia in patients with unstable angina whose condition stabilized with medical treatment, 76 patients were studied. All patients underwent Holter ambulatory electrocardiographic (ECG) monitoring for greater than or equal to 48 h beginning within the 1st 12 h of the hospital stay. Forty-three patients (Group A) had a total ischemic time greater than or equal to 60 min, whereas 33 patients (Group B) had a total ischemic time less than 60 min. More than 78% of the ischemic episodes in patients in Group A and 62% of those in Group B were silent (p less than 0.05); nine patients in Group A and six in Group B had only silent episodes. Patients in Group A frequently showed three-vessel disease (65% vs. 18%, p less than 0.01), angiographic findings of subtotal occlusion of the coronary arteries (TIMI grade I) (76.7% vs. 42.4%, p less than 0.01) and ischemic alterations in the rest ECG (51.2% vs. 30.3%, p less than 0.05). During a 6-year follow-up period, 15 patients in Group A and 8 in Group B experienced myocardial infarction (p less than 0.05); 9 patients in Group A and 4 in Group B required coronary artery surgery (p less than 0.05) and 10 patients in Group A and 4 in Group B died of cardiac causes (p less than 0.01). Multivariate analysis showed three-vessel disease to be the most important predictor of cardiac mortality and morbidity (p = 0.025); it was followed in predictive power by a total ischemic time greater than or equal to 60 min and by left ventricular dysfunction. The presence of silent ischemia was not shown to be an independent predictor of long-term morbidity and mortality. In conclusion, patients with unstable angina and a total ischemic time greater than or equal to 60 min frequently have silent ischemic episodes on Holter ECG monitoring, a greater extent of coronary atherosclerosis and ischemic alterations of the rest ECG. The long-term prognosis of patients with unstable angina whose condition stabilizes with medical treatment depends on the extent of coronary atherosclerosis and on the longer duration of total ischemic time but not on the presence of silent ischemia.

Spontaneous platelet aggregation, tourniquet ischaemia, and aspirin in survivors of myocardial infarction

Platelet number, plasma beta-thromboglobulin (beta-TG), spontaneous platelet aggregation (SPA), serum thromboxane B(2) (TXB(2)), and 6-keto-PGF(101) were assessed in 9 males with proven atherosclerosis (survivors of myocardial infarction, (MI) in a stable condition) and compared with values for 9 young, healthy controls. Results were obtained before and after 3-day treatment with aspirin. In addition, SPA was assessed before and after a tourniquet test. MI survivors had higher beta-TG (p < 0.01) and SPA values (p < 0.05), and a lower platelet count (p < 0.05) than controls. Aspirin significantly attentuated all these changes. These data suggest that platelet function is increased in survivors of MI. Tourniquet-induced ischaemia significantly (p < 0.05) enhanced SPA in MI survivors but not in controls. Aspirin did not inhibit SPA following ischaemia in contrast to its effect under pre-ischaemic conditions or in controls. It seems that the proaggregatory threshold is decreased in MI survivors. The results challenge the assumption that an acute coronary event with underlying atherosclerosis is due to an interaction between atherosclerosis plaque and normal platelets.

Flow cytometric assessment of platelet function in patients with peripheral arterial occlusive disease

This study compared new and traditional measures of platelet function in 16 patients with severe peripheral arterial occlusive disease and 15 age-matched controls. Circulating platelets were characterized by the use of fluorescence flow cytometry to assess platelet aggregate formation and expression of the secretion-dependent alpha granule membrane protein GMP-140, by measurement of plasma beta-thromboglobulin (beta-TG), and by performance of platelet-rich plasma aggregation studies. In addition, blood samples were treated with graded concentrations of adenosine diphosphate (ADP; 0 to 10 mumols/L) to characterize by fluorescence flow cytometry the secretory and aggregatory responses to mild stimulation. No differences were detected between the two groups with regard to platelet function in unstimulated circulating blood by use of these techniques. Values (mean +/- SEM) observed were: GMP-140-positive platelets, 11% +/- 3% versus 13% +/- 2%; platelet aggregates in circulating whole blood, 4% +/- 1% versus 9% +/- 3%; plasma beta-TG, 92 +/- 12 versus 94 +/- 22 ng/ml; and ED50 (concentration of ADP required to produce half maximal aggregation), 3.8 +/- 1.1 versus 3.1 +/- 0.5 mumol/L in the patients with peripheral arterial occlusive disease and controls, respectively. Treatment with ADP caused a dose-related increase in GMP-140 expression in both groups, without significant differences in this parameter between the groups at any given concentration. However, stimulation with ADP concentrations greater than 1 mumol/L resulted in more frequent aggregate formation in the control than in the peripheral arterial occlusive disease group (25% +/- 4% versus 11% +/- 2%, respectively at 5.0 mumols/L, p = 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Pathophysiology of acute coronary syndromes

The natural history of coronary artery disease is punctuated by clinical manifestations of unstable angina, acute myocardial infarction, and ischemic sudden death. These acute coronary syndromes share common pathophysiologic mechanisms that include fissuring of a plaque followed by varying degrees of dynamic coronary obstruction, which is due to vasoconstriction and coronary thrombosis. The response to plaque fissure is likely to be modulated by local and/or systemic procoagulant and anticoagulant-fibrinolytic activities. The key role of coronary thrombosis in acute coronary syndromes has substantial implications for prevention and treatment of complications of coronary atherosclerosis.

Platelet activation in the pathogenesis of unstable angina: importance in determining the response to plasminogen activators

Unstable angina is a clinical syndrome of recurrent myocardial ischemia. In some cases, this reflects episodic platelet activation and coronary thrombosis. Thus, the biosynthesis of thromboxane A2, which is largely derived from activated platelets, is increased, often coincident with chest pain. The major role of platelets in unstable angina may influence the response to plasminogen activators. Platelets increase the resistance of thrombi to lysis, by inducing clot retraction and cross-linking and by releasing inhibitors. Thus, coronary thrombi in unstable angina may be resistant to lysis. Furthermore, both t-PA and streptokinase cause platelet activation and thrombin formation in vivo, possibly via plasmin. Plasmin can activate platelets and factor V directly. These prothrombotic effects of plasminogen activators may limit their activity in unstable angina. At the very least, their therapeutic efficacy may be highly dependent on the coadministration of potent antiplatelet agents and anticoagulants.

Concurrent nitroglycerin administration decreases thrombolytic potential of tissue-type plasminogen activator

Dynamic coronary vasoconstriction may play a role in coronary artery reocclusion after successful thrombolysis. The effect of nitroglycerin on the thrombolytic effects of recombinant tissue-type plasminogen activator (rt-PA) was examined in dogs with an electrically induced occlusive coronary artery thrombus. Eleven dogs were randomly given rt-PA alone and seven rt-PA with nitroglycerin. The dose of rt-PA was 0.75 mg/kg body weight given over 20 min and the dose of nitroglycerin was 125 micrograms/min for 40 min. The reperfusion rate in the dogs given rt-PA alone was 73% (8 of 11 dogs) and that in the rt-PA plus nitroglycerin group was 57% (four of seven dogs) (p = NS). The time to thrombolysis (or reperfusion) in dogs receiving rt-PA plus nitroglycerin was 70% greater than in those receiving rt-PA alone (means +/- SD/29.8 +/- 9.9 versus 17.6 +/- 5.9 min, p less than 0.02), and the duration of reperfusion much shorter (11 +/- 17 versus 42 +/- 16 min, p less than 0.02). Peak coronary blood flow after reperfusion in dogs receiving rt-PA plus nitroglycerin was also less than in those receiving rt-PA alone (36 +/- 52 versus 63 +/- 20 ml/min, p less than 0.02). Reocclusion occurred in all dogs given rt-PA with nitroglycerin and in six of eight given rt-PA alone (p = NS). Plasma concentrations of rt-PA were lower when nitroglycerin was given with rt-PA alone (427 +/- 279 versus 1,471 +/- 600 ng/ml, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Unstable angina

Unstable angina can manifest as an array of symptom complexes. In some patients, medical therapy will stabilize the episodes of angina, and only predismissal exercise testing or angiography (or both) will be necessary. At the other end of the spectrum are patients with rest angina or multiple episodes of silent ischemia who are refractory to medical therapy and experience undetected microinfarction. Most of these patients require immediate catheterization and subsequent intervention with intra-aortic balloon pulsation, percutaneous transluminal coronary angioplasty, or coronary artery bypass grafting. An entire spectrum of manifestations exists between these two extremes. One challenge during the 1990s will be better stratification of patients with unstable angina so that safe, efficient, cost-effective treatment strategies can be appropriately applied to all patients.

Dipyridamole for coronary artery bypass surgery

A randomized trial to compare the effects of oral and intravenous dipyridamole was conducted in 58 patients undergoing coronary artery bypass graft (CABG) surgery. Preoperative oral administration of dipyridamole resulted in lower plasma drug concentrations in the early postoperative period than perioperative intravenous administration. Postoperative platelet counts were highest in the patients receiving intravenous dipyridamole, intermediate in those receiving oral dipyridamole and lowest in the control group. Postoperative blood loss was significantly reduced with both oral and intravenous dipyridamole. A second randomized trial was conducted in an additional 40 patients undergoing CABG surgery to evaluate the effects of dipyridamole on myocardial platelet and leukocyte deposition and the cardiac release of thromboxane. Twenty patients received intravenous dipyridamole perioperatively. Autologous platelets and leukocytes were labeled with 111In and 99mTc respectively and were infused before release of the crossclamp. Myocardial biopsies were obtained after aortic declamping and indicated that platelets and leukocytes were deposited in the myocardium during reperfusion. Dipyridamole reduced both platelet and leukocyte deposition. Cardiac release of thromboxane B2 occurred in the early postoperative period and was reduced by dipyridamole. In conclusion, dipyridamole preserved platelets and reduced postoperative bleeding and blood product transfusions in patients undergoing CABG surgery. Dipyridamole also reduced cardiac platelet deposition and thromboxane release and may reduce perioperative ischemic injury.

Alpha 2-adrenoceptors and platelet function in patients with variant angina

We have previously reported that platelets of patients with variant angina exhibited pronounced hyperactivity to epinephrine, as assessed by aggregation study. To determine whether this is associated with a change in surface alpha-adrenoceptor status, we investigated the capacity and affinity of binding sites for [3H]dihydroergocryptine, a potent alpha-antagonist, of platelet lysates prepared from 22 patients with ischemic heart disease and 13 control subjects of similar age. [3H]DHE binding capacity to platelets from control subjects, 6 patients with acute myocardial infarction, 9 with effort angina and 7 with variant angina were 233 +/- 44 (SD), 226 +/- 53, 252 +/- 58 and 348 +/- 48 fmol/mg protein and its affinity were 2.05 +/- 1.40, 0.98 +/- 0.46, 1.59 +/- 0.37 and 1.49 +/- 0.66 nM, respectively. The patients with variant angina had significantly higher capacity of platelet alpha-adrenoceptor than controls (49% increase) or patients with other types of ischemic heart disease. In contrast, the affinity for [3H]DHE was not significantly different as compared with other three groups. Similar increments in the binding capacity for [3H]-rauwolscine, alpha 2 antagonist, were found in platelet lysates prepared from 6 patients with variant angina. These results suggest that increased capacity of platelet alpha-adrenoceptor may explain enhanced reactivity to epinephrine in patients with variant angina.

Cardiac ischemia and endothelial function in the isolated rabbit heart

Truly effective prevention of reperfusion myocardial damage is precluded in part by a lack of understanding of the earliest events which accompany ischemia. The purpose of this study was to assess the coronary endothelial response to two forms of ischemic injury in an isolated crystalloid perfused rabbit heart. Global cardiac ischemia, confirmed by NADH fluorescence photography, was induced either by mechanically reducing coronary flow by 90% (MRCF, N = 11) or by an infusion of N-formyl-methionyl-leucyl-phenylalanine (fMLP, N = 11), a known stimulus for leukotriene synthesis and coronary vasospasm. Compared with control, MRCF resulted in an increase in effluent concentrations of both prostacyclin (152 +/- 22 pg/ml vs 951 +/- 214 pg/ml, P less than 0.05) and plasminogen activator (0.8 +/- .3 IU/ml vs 1.4 +/- 0.5, P less than 0.05) but no detectable increase in effluent thromboxane B2 or leukotriene C4 concentrations. fMLP infusion resulted in an immediate reduction in coronary flow coincident with diffuse myocardial ischemia. In contrast to MRCF, however, fMLP-induced ischemia resulted in a significant but smaller increase in effluent prostacyclin concentration (210 +/- 47 pg/ml vs 606 +/- .55 pg/ml, P = 0.05) and a marked increase in both thromboxane B2 (less than or equal to 33 +/- 4 pg/ml vs 1141 +/- 375 pg/ml, P less than 0.05) and leukotriene C4 (less than 0.25 ng/ml vs 3.3 +/- 1.2 ng/ml, P less than 0.05) concentrations. Additionally, fMLP caused a reduction in effluent plasminogen activator activity (0.5 +/- 0.1 IU/ml vs 0.39 +/- 0.1 IU/ml, N = 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Role of resting thallium201 perfusion in predicting coronary anatomy, left ventricular wall motion, and hospital outcome in unstable angina pectoris

We performed quantitative thallium scintigraphy in 66 unstable angina patients, 5.6 +/- 5.1 hours after rest pain, to predict coronary anatomy, left ventricular wall motion, and hospital outcome. Thallium defects and/or washout abnormalities were present in 5 of 10 (50%) patients with coronary stenoses less than 50%, 27 of 33 (82%) patients with coronary stenosis greater than or equal to 50% and no history of previous myocardial infarction, and in 23 of 23 patients (100%) with histories of previous infarction. Defects were uncommon in the territory of vessels with less than 50% (13 of 61, 21%), but significantly more common in the territory of vessels with greater than or equal to 50% stenosis (57 of 137, 42%), p less than 0.005. With the addition of washout abnormalities to defect analysis, sensitivity for detection of coronary stenoses improved to 67% (92 of 137), p less than or equal to 0.005, but specificity fell to 59% (36 of 61), p less than 0.01. Segmental wall motion abnormalities were less common in segments with normal perfusion (21%) or in those with washout abnormalities alone (19%), than in segments with thallium defects (45%, p less than 0.005). Defects in patients with previous infarction were common in both segments, with normal (26 of 66, 40%) or abnormal (24 of 45, 53%) wall motion. Eleven of 18 patients with in-hospital cardiac events, but no history of myocardial infarction, had resting thallium defects, whereas only 8 of 25 patients without cardiac event had thallium defect (p = 0.056).(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of platelet binding of heparins and other glycosaminoglycans

The binding of glycosaminoglycans to intact washed human platelets was studied. The platelet binding of a 3H-labeled unfractionated heparin was saturable and reached equilibrium in 10-15 minutes. Heparin binding was specific: a 50-fold molar excess of an equivalent unlabeled heparin displaced up to 90% of labeled heparin, while chondroitin sulfate A and hyaluronic acid minimally displaced the binding of labeled heparin. Low molecular weight heparin fragments showed intermediate efficacy in displacing the binding of unfractionated [3H]heparin. Dextran sulfate (Mr 8,000, sulfation 17%) was as potent as unfractionated heparin in displacing binding, while neutral dextrans were ineffective. We observed that platelet activation by the calcium ionophore A23187 increased heparin binding by 2 to 3-fold, principally by enhancement of binding capacity not binding affinity. This process of heparin binding to the platelet surface may mediate some of the reported effects of heparin on platelet behavior.

Lack of association between haemostatic variables and the presence or the extent of coronary atherosclerosis

Blood samples were taken for haemostatic analysis from 225 patients with angina pectoris who were admitted to hospital for coronary angiography. beta thromboglobulin, platelet factor 3, platelet factor 4, factor VII:C, factor VIII:C, von Willebrand factor antigen, activated partial thromboplastin time, fibrinogen, antithrombin III, protein C:Ag, plasminogen, and antiplasmin were measured before angiography. Patients who had had a myocardial infarction in the two months before the investigation were excluded from the study. Multiple linear regression analysis showed that none of the haemostatic variables contributed independently to the prediction of an angiographic score that indicated the extent of coronary atherosclerosis. History of myocardial infarction, male sex, worsening of angina pectoris, serum triglycerides, and ejection fraction were independently associated with the angiographic score. There were some significant correlations between haemostatic variables and conventional risk factors for coronary heart disease. Thus data obtained from haemostatic analyses of peripheral venous blood do not permit the presence or the extent of atherosclerosis in coronary arteries to be predicted.

Electrocardiographic manifestations and in-hospital prognosis of transient acute myocardial ischemia at rest

From January 1970 to June 1985, transient electrocardiographic changes at rest were documented in 652 patients admitted to our coronary care unit. Patients were stratified according to the type of electrocardiographic alteration at rest: 295 had ST-segment elevation (group 1), 106 T-wave changes (group 2) and 251 ST-segment depression (group 3). Patients in group 3, compared with groups 1 and 2, were more likely to have symptoms of coronary artery disease dating back many years (p less than 0.01 and p less than 0.01, respectively), a previous myocardial infarction (p less than 0.05 and difference not significant), a positive exercise test (p less than 0.01 and p less than 0.01), transient ST-T changes occurring in a higher number of electrocardiographic leads (p less than 0.01 and p less than 0.01), multivessel disease (p less than 0.001 and p less than 0.01) and poor ventricular function (p less than 0.01 and p less than 0.05). Despite these differences, the occurrence of acute myocardial infarction and cardiac death during hospitalization was much more frequent in group 1 compared with groups 2 (p less than 0.02) and 3 (p less than 0.05). However, death occurred in those patients who had poor ventricular function and severe atherosclerosis. A greater susceptibility of group 1 patients to severe vasoconstriction documented by the ergonovine test and by the occurrence of spontaneous spasm seems to account for different in-hospital outcome.

Influence of anti-platelet drugs on platelet-vessel wall interactions

The influence of in vitro treatment of platelets with antiplatelet drugs on the interaction of these cells with the subendothelium was studied using citrated human blood obtained from normal control donors. Reconstituted blood following drug treatment was circulated through a special chamber which housed everted segments of de-endothelialized rabbit aorta. The wall shear rate used in these studies was 800 sec-1. Surface coverage of platelets on the subendothelium were morphometrically evaluated. Aspirin, Ibuprofen, Prostaglandin E1 and 13-Azaprostanoic acid significantly reduced platelet thrombi on exposed subendothelium. The calcium antagonists, Quin 2 and Diltiazem, exerted similar inhibitory effects, whereas Verapamil was a poor inhibitor. Aspirin treatment significantly enhanced platelet adhesion to the exposed vascular surface. Salicylate and Salicylamide did not enhance platelet adherence. Only Aspirin enhanced the formation of lipoxygenase metabolites of radiolabeled arachidonate. Results suggest that drugs which inhibit platelet aggregation and secretion of granule contents reduce formation of platelet thrombi. However, these drugs may or may not have a similar influence on platelet interaction with the subendothelium leading to spreading, adherence or formation of aggregates.

Fibrin and fibrinogen-related antigens in patients with stable and unstable coronary artery disease

Coronary-artery thrombosis may be important in the pathogenesis of unstable angina at rest. To study this possibility, we measured the serum concentrations of fibrin-related antigen, D dimer (the principal breakdown fragment of fibrin), and fibrin monomer (an intermediate product of fibrin formation) in the serum of five groups of subjects. These included 10 healthy controls, 10 controls with noncardiac pain, and three groups of 10 patients each with chronic stable angina, unstable angina at rest, or acute myocardial infarction. The concentration of fibrin-related antigen (normal range, 48 to 184 ng per milliliter) was normal in the control patients with noncardiac pain (63 to 202 ng per milliliter) and in patients with chronic stable angina (95 to 186), but it was increased in patients with unstable angina (401 to 2507) or acute myocardial infarction (470 to 1930) (P less than 0.001). D dimer concentrations in patients with unstable angina (178.3 to 310.6 ng per milliliter) or acute myocardial infarction (103.9 to 321.6) were higher than those in patients with chronic stable angina (28.6 to 52.1), in controls with noncardiac pain (44.7 to 53.1), and in healthy controls (40.4 to 50.3) (P less than 0.001). Concentrations of fibrin monomer were highest in patients with acute myocardial infarction (247.5 to 571.3 ng per milliliter) (P less than 0.001), intermediate in those with unstable angina (54.7 to 241.7) (P less than 0.001), and normal (normal range, 14.5 to 19.8 ng per milliliter) in controls with noncardiac pain (12.0 to 18.4). and patients with chronic stable angina (10.7 to 17.6). These findings suggest the presence of an active thrombotic process in patients with unstable angina at rest or acute myocardial infarction. The data do not prove that the coronary arteries were the site of the thrombotic process, but the observations are consistent with the hypothesis that thrombus formation may have an important role in the pathogenesis of these conditions.

Biochemical evidence of platelet activation in patients with persistent unstable angina

Thromboxane released from activated platelets and prostacyclin of the vessel wall may act as potent antagonistic modulators of platelet aggregability and coronary vascular tone. Therefore, urinary excretion of their major metabolites, 2,3-dinor-thromboxane B2 and 2,3-dinor-6-ketoprostaglandin F1 alpha, was studied in 16 patients presenting with prolonged angina at rest. The 10 patients whose condition did not improve under vigorous antianginal treatment within 48 hours exhibited higher thromboxane metabolite excretion than did the 6 patients who responded to therapy (2,208 +/- 1,542 versus 609 +/- 312 ng/g creatinine; p less than 0.001). Elevated values were also found in four of eight patients with sustained postinfarction angina. Enhanced thromboxane metabolite excretion was frequently associated with angiographic evidence of thrombus formation. When nine patients were restudied in a stable phase after 11 +/- 5 months, thromboxane metabolite excretion was consistently normal or high normal. Excretion of prostacyclin metabolites was not depressed in any patient but correlated weakly with thromboxane (r = 0.41). Thus, enhanced thromboxane production as an index of platelet activation may identify patients with active thrombus formation who could benefit most from platelet inhibitory treatment.

Circulating aggregated platelets in coronary artery disease

Circulating aggregated platelets were assessed in 30 patients with stable angina, 22 with unstable angina and 50 with acute myocardial infarction (AMI). Fifty healthy volunteers and 20 noncardiac patients served as controls. One milliliter of venous blood was separated into 2 solutions: 1 composed of ethylenediamine tetraacetic acid (EDTA) and formalin containing reversible and aggregates and 1 composed of EDTA alone containing irreversible aggregates only. By direct microscopic readings the percentage of platelets forming aggregates/1,000 counted platelets was determined in the 2 solutions. The number of reversibly aggregated platelets was estimated by subtracting the percentage of aggregated platelets in the second solution from that in the first solution. In patients with stable angina the percentage of aggregated platelets was higher than in control subjects (15 +/- 4% vs 7 +/- 2%, p less than 0.001). Most aggregated platelets (72% and 76%, respectively) were irreversibly aggregated. In the unstable angina group the percentage of aggregated platelets was similar to that of the AMI group (24 +/- 13% and 24 +/- 10%) and significantly higher than in the stable angina group. Only 11% and 17% of aggregated platelets in patients with stable angina and AMI were irreversibly aggregated and 89% and 83% of them were reversibly aggregated. Participation of platelets in the pathogenesis of unstable angina and AMI may be related to the early reversible phase of platelet activation.