The role of platelets in the genesis of ischemia

Gender-specific correlation of platelet ionized magnesium and serum low-density-lipoprotein cholesterol concentrations in apparently healthy subjects

We previously found an inverse correlation between platelet ionized magnesium concentration ((Mg2+)i) and serum total cholesterol concentration in normal male but not female subjects. In the present study, we determined the platelet (Mg2+)i by using a fluorescent ionized magnesium (Mg2+) indicator, FURAPTRA, and measured the serum concentrations of the following: total cholesterol; very-low-density lipoprotein cholesterol (VLDL-C); low-density lipoprotein cholesterol (LDL-C); high-density lipoprotein cholesterol (HDL-C); antioxidized low-density lipoprotein (LDL) autoantibodies; lipoprotein(a); apolipoproteins A-I (apo A-I) and B (apo B); triglycerides; estradiol-17 (E2); ceruloplasmin (Cp); and selected electrolytes, including total and ionized magnesium and calcium and total protein and albumin. In men, but not in women, platelet (Mg2+)i significantly inversely correlated with serum total cholesterol (r = -0.52, p < 0.02), LDL-C (r = -0.54, p < 0.009 by a "direct" method; r = -0.40, p < 0.05 by an electrophoretic method), and apo B (r = -0.42, p < 0.04). We found no significant correlations between platelet (Mg2+)i and any other variables, including serum total and ionized magnesium, antioxidized LDL autoantibodies, Cp, and E2. We speculate that decreased platelet (Mg2+)i is a possible marker for platelet membrane alterations that may affect platelet involvement in thrombosis and atherogenesis.

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.

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.

Myocardial infarction in young adults under 30 years: risk factors and clinical course

The clinical features and course of 30 patients (26 men and 4 women) under 30 years of age (mean age 27.3 years) with an acute myocardial infarction (MI) are described. The most common risk factor among this group of patients was smoking in 20 patients (66%). The prevalence of the other risk factors was low: hyperlipidemia in four patients and family history of ischemic disease in another four patients, diabetes mellitus, hypertension, and obesity each in one patient. Seven patients (23%) had none of the conventional risk factors. Three patients were exerting themselves prior to the onset of their MI pain; all of them had normal coronaries. Five patients experienced chest pain prior to MI, among them only two experienced classical angina pectoris. Eighteen patients underwent uncomplicated MI. The complications in the other 12 during the acute MI were rhythm disturbances in eight and congestive heart failure in four. Cardiac catheterization was performed in 25 patients. The occurrence of zero, one, or multivessel disease was equal. The 30 patients were followed up from six months to 15 years (mean 7 years). In 18 patients circulating aggregated platelets were measured one year after the MI. Elevated values were found in all of them (mean +/- SD 34.9 +/- 9.1%). In 6 of the 18, all heavy smokers, extreme values were found in the range of 39-55%. Three out of the 30 patients died within five years after their first MI. The other 15 patients developed complications, most of them angina pectoris. Five patients were hospitalized for reinfarction. None of the 30 underwent aortocoronary bypass operation.(ABSTRACT TRUNCATED AT 250 WORDS)

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.