Peripheral venous platelet aggregates in patients with unstable angina pectoris and acute myocardial infarction

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.

Circulating platelet aggregate size in ischemic heart disease

Platelet aggregate size was measured in 178 patients with ischemic heart disease, among whom 56 had stable angina, 42 suffered from unstable angina, and 80 had had uncomplicated acute myocardial infarction. A group of 50 healthy volunteers and 20 hospitalized noncardiac patients served as controls. Venous blood (0.5 cc) was introduced into a solution containing 11.7 mM EDTA and 1.0 g formaldehyde. Platelet aggregate size was determined by microscopic reading as the number of platelets forming aggregates (per 1000 counted platelets) divided by the number of aggregates. Mean aggregate size was found not significantly different in both control groups, as well as in patients with stable angina and acute myocardial infarction (2.21 +/- 0.36 platelets, 2.20 +/- 0.58 platelets, 2.28 +/- 0.19 platelets, 2.76 +/- 1.07 platelets, respectively, p = NS). The highest value was found in the unstable angina group: 4.00 +/- 1.40 platelets (p less than 0.001 vs other studied groups). Platelet aggregate size was found not to be related to sex, age, medication, or coronary risk factors. Unstable angina may thus be a unique entity in ischemic heart disease concerning its platelet behavior, demonstrated in this study by the increased size of peripheral platelet aggregates, which may have pathogenetic, diagnostic, and eventual therapeutic implications.

Differential transmyocardial platelet behavior in response to pacing and ergonovine-induced myocardial ischemia

In 17 anginal patients with critical narrowing of the left anterior descending artery, we studied the effects of acute ischemia, either induced by atrial pacing or by ergonovine, on transmyocardial platelet behavior. Six other patients with atypical chest pain and normal coronary arteries served as controls. Simultaneous arterial and great cardiac vein samples were drawn during control and ischemia to measure the levels of platelet factor four (PF4) and beta-thromboglobulin (BTG). During pacing-induced ischemia the great cardiac vein-arterial differences of PF4 and BTG decreased significantly, indicating a reduced platelet aggregability; no significant changes were observed in the control patients. By contrast, when ischemia resulted from ergonovine-induced spasm of the left anterior descending artery (five patients), the great cardiac vein-arterial differences increased, indicating enhanced platelet aggregability. Again no differences were observed in the patients with a negative ergonovine test. The results of our study suggest that the transcardiac platelet behavior may vary during different ischemic conditions. When ischemia is due to increased myocardial demands and flow is normal or increased, myocardial metabolites released from the ischemic area may oppose platelet aggregation. By contrast, spasm and the stagnant flow resulting from it may enhance platelet aggregation.

Intracoronary platelet activation in ischemic heart disease: effects of ticlopidine

Plasma levels of platelet factor 4 have been measured in the aortic and coronary sinus blood of 35 patients: group I (n = 12) with normal coronary arteriograms; group II (n = 15) with angiographically proven coronary artery disease; and group III (n = 8) composed of patients with ischemic heart disease who were being treated with the antiaggregant agent ticlopidine at the time of cardiac catheterization. The mean increase in platelet factor 4 levels through the coronary circulation was 27.4 +/- 21.9 ng/ml (mean +/- standard deviation) in group II, compared with -1 +/- 4.5 ng/ml in group I (p less than 0.01). In group III plasma levels of platelet factor 4 in aortic and coronary sinus samples were all within the normal range. Thus, we conclude that platelet activation constantly occurs in the coronary circulation of patients with stable coronary artery disease, and can be prevented with ticlopidine.

Evaluation of the effects of catheter sampling for the study of platelet behavior in the pulmonary and coronary circulation

To study the effects of sampling through cardiac catheters on indices of platelet function, we measured the levels of platelet factor 4 (PF4), beta thromboglobulin (BTG), and platelet aggregate ratio (PAR) in 10 patients with atrioventricular accessory pathway (AVNAP), six patients with primary pulmonary hypertension (PPH), and six patients with critical narrowing of the left anterior descending artery (LAD). In AVNAP and LAD patients samples were drawn simultaneously from a peripheral vein, coronary sinus, and brachial artery; in AVNAP patients samples were also obtained from the axillary vein before the coronary sinus was entered. In PPH patients samples were drawn from pulmonary artery, aorta, and a peripheral vein; in these patients the effects of an intravenous infusion of prostacyclin (PGI2) (2 to 8 ng/kg/min) on PF4, BTG, and PAR were also studied at all sampling sites. In all patients arterial, coronary sinus, pulmonary arterial, and axillary venous levels of PF4, BTG, and PAR significantly exceeded those measured in the peripheral vein. PGI2 infusion resulted in a significant decrease of PF4 at all sampling sites, while no consistent BTG changes were observed and PAR levels did not decrease in the peripheral vein. Although a considerable interpatient variability in PF4 levels was observed, a significant (r = 0.91) correlation was found in patients with AVNAP between simultaneous coronary sinus and arterial PF4 levels. The value of PF4 coronary sinus-arterial difference in LAD patients was consistently higher than that calculated in AVNAP patients (54.5 +/- 28.9 vs 4.2 +/- 3.8 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Coagulant activities of platelets in coronary artery disease

Platelets have been implicated in the pathogenesis of coronary artery disease, and a number of studies have examined platelet function and coagulation parameters in such patients. We have examined platelet coagulant activities, volumes, and aggregate ratios in 23 patients with chest pain, seven of whom had normal coronary angiograms (group I) and 16 of whom had angiographically proven coronary artery disease (group II). There were no significant differences in the mean values for platelet volume or platelet aggregate ratios between the two groups. The platelet coagulant activities concerned with initiation and the early stages of intrinsic coagulation were significantly increased in patients in group II as compared with those in group I. No significant differences were noted between the two groups with respect to prothrombin time, partial thromboplastin time, and plasma levels of fibrinogen and coagulation factors V and VIII. However, the mean activity in plasma of antithrombin III (but not the level of antithrombin III antigen) was significantly lower in patients of group II compared with group I. Overall, our observations provide evidence for an enhanced contribution of platelets to the intrinsic coagulation system in patients with coronary artery disease. The platelet coagulant hyperactivity noted in these patients may reflect a role of platelets in the pathogenesis of coronary artery disease or may be secondary to the underlying arterial disease.

In vivo platelet aggregation and plasma catecholamines in acute myocardial infarction

In vivo platelet aggregation assessed with the Filtragometer and potential correlates were compared among (1) patients with acute myocardial infarction (AMI), (2) normal controls, (3) patients with acute chest pain in whom AMI was eventually ruled out (ROMI), and (4) chronic outpatients (Cardiac Clinic group) with a history of myocardial infarction and/or angina pectoris. The measure was independent of sex, age, platelet count, immediate food intake, serum cholesterol, and triglyceride levels. The AMI group showed higher in vivo platelet aggregation than any of the other three groups (p less than 0.01). Least in vivo aggregation was seen in the normal group. Despite lack of correlation with the platelet aggregation measure, plasma epinephrine and norepinephrine showed statistically significant differences between the AMI and each of the other three groups. Our data support an association between platelet function and AMI, although not necessarily a cause and effect relationship.

Role of blood platelets and prostaglandins in coronary artery disease

In the last decade, several studies evaluating blood platelet function in patients with coronary heart disease have been reported. Although several platelet function abnormalities such as enhanced platelet aggregation, decreased platelet survival and increase in platelet release reaction in the stable condition and during stress in patients with myocardial ischemia have been recognized, the mechanism of these abnormalities is just beginning to be understood. Discovery of certain platelet and endothelium-generated prostaglandins has provided some information as to the possible mechanism of platelet dysfunction. Abnormalities of prostaglandin production and platelet sensitivity to various prostaglandins may have an important bearing on the enhanced platelet aggregation in vivo, genesis of atherosclerosis and probably precipitation of acute ischemic events. Since the discovery of these prostaglandins, the precise mode of action of several commonly used platelet-active drugs has been clarified. Development of new drugs acting at selective steps in the prostaglandin pathways may provide some exciting novel therapeutic procedures in patients with coronary heart disease.

Relationships of the platelet aggregate ratio to serum cholesterol concentration, smoking and age

The platelet aggregate ratio has been found to be decreased in some patients with vascular diseases suggesting the presence of increased circulating platelet aggregates. It has also been reported that hypercholesterolaemia is associated with an enhanced response of platelets to aggregating agents in platelet-rich plasma. The primary purpose of this investigation was to determine correlation of the platelet aggregate ratio with the serum cholesterol concentration of men with vascular diseases. For 52 men referred because of known or suspected coronary artery disease, cerebrovascular disease, or venous thromboembolism, the correlation coefficient of 0·06 suggested that the serum cholesterol concentration within the range observed (135-360 mg/dl) was not a factor influencing the platelet aggregate ratio. There was not a statistically significant difference between the mean platelet aggregate ratios or the mean serum cholesterol concentrations of the 21 non-smokers and the 31 smokers studied. A correlation coefficient of 0·03 between the platelet aggregate ratio and age of the patient suggested that the platelet aggregate ratio was independent of age in men with occlusive vascular diseases.

Circulating platelet products in unstable angina pectoris

In 19 patients with unstable angina pectoris at rest, plasma levels of the platelet-derived proteins beta-thromboglobulin and platelet factor 4 were significantly elevated in blood samples obtained during or within 4 hours after episodes of angina, but were usually normal during quiescent intervals. Plasma levels of the arachidonic acid metabolite thromboxane B2 were less clearly related to angina, and there was no association of angina with levels of the coagulation product fibrinopeptide A. This demonstration of an association of platelet activation and secretion with unstable angina pectoris by radioimmunoassay of circulating platelet constituents offers a new approach to assessment of therapy in ischemic heart disease and suggests that agents that alter platelet function should be evaluated in patients with unstable angina.

Abnormalities of platelet aggregation in sickle cell disease

In vitro platelet aggregation responses to epinephrine and ADP were significantly lower in patients with sickle cell disease when compared to age- and sex-matched normal subjects. Platelet aggregation responses were reduced in all patients regardless of clinical status. Measurement of circulating platelet aggregates showed normal values in patients with sickle cell disease in steady state or with infection alone, but a significant increase in others with acute vaso-occlusive crises. Recovery from vaso-occlusion was associated with a decline in circulating platelet aggregates. This study suggests that in vivo platelet activation may result in "tired" platelets which are refractory to epinephrine and ADP stimulation in vitro.

Platelet activation during exercise-induced myocardial ischemia

Because platelet activation may be important in the worsening of coronary atherosclerosis, we used a radioimmunoassay for platelet factor 4 to study platelet behavior in patients with coronary-artery disease. Forty patients had paired blood samples withdrawn for measurement of the plasma level of platelet factor 4 before and after a standardized exercise-tolerance test. Twenty patients had positive tests, and 19 of those 20 had clinical or angiographic evidence of coronary-artery disease. Eleven of the 20 had a greater than 50 per cent increase in platelet factor 4 after exercise. The remaining nine had positive exercise tests without rises in platelet factor 4. Elevated levels returned to normal within 15 minutes of exercise. Eighteen of 20 patients with negative exercise tests had no rise in platelet factor 4 after exercise. We conclude that a subset of patients with coronary-artery disease and exercise-induced myocardial ischemia had evidence of platelet activation and secretion. (N Engl J Med 302:193-197, 1980).

Platelet function studies in coronary artery disease. V. Evidence for enhanced platelet microthrombus formation activity in acute myocardial infarction

Circulating platelet microthrombi were evaluated during the acute and convalescent phases of illness in 44 patients admitted to the hospital for chest pain. Similar studies were performed in 10 healthy volunteers and 6 patients with infection. Circulating platelet microthrombi were significantly increased during the acute phase in 22 patients with transmural myocardial infarction compared with values in the other 22 patients without myocardial infarction, the healthy volunteers and the patients with infection alone. This increase in circulating platelet microthrombi declined to normal levels by the 7th hospital day in all but two patients who had evidence of extension of myocardial infarction and died. In contrast, circulating platelet microthrombi were similar in acute and convalescent phases of patients with chest pain but without myocardial infarction and were comparable with values in healthy volunteers. This study suggests that increased circulating platelet microthrombi may be related to tissue necrosis associated with transmural myocardial infarction.