Platelet aggregates in peripheral and coronary-sinus blood in patients with spontaneous coronary-artery spasm

Apolipoprotein (a)/Lipoprotein(a)-Induced Oxidative-Inflammatory α7-nAChR/p38 MAPK/IL-6/RhoA-GTP Signaling Axis and M1 Macrophage Polarization Modulate Inflammation-Associated Development of Coronary Artery Spasm

Objective. Apolipoprotein (a)/lipoprotein(a) (Lp(a)), a major carrier of oxidized phospholipids, and α7-nicotinic acetylcholine receptor (α7-nAChR) may play an important role in the development of coronary artery spasm (CAS). In CAS, the association between Lp(a) and the α7-nAChR-modulated inflammatory macrophage polarization and activation and smooth muscle cell dysfunction remains unknown. Methods. We investigated the relevance of Lp(a)/α7-nAChR signaling in patient monocyte-derived macrophages and human coronary artery smooth muscle cells (HCASMCs) using expression profile correlation analyses, fluorescence-assisted cell sorting flow cytometry, immunoblotting, quantitative real-time polymerase chain reaction, and clinicopathological analyses. Results. There are increased serum Lp(a) levels (3.98-fold, $p=0.011$ ) and macrophage population (3.30-fold, $p=0.013$ ) in patients with CAS compared with patients without CAS. Serum Lp(a) level was positively correlated with high-sensitivity C-reactive protein ( $r^2=0.48$ , $p<0.01$ ), IL-6 ( $r^2=0.38$ , $p=0.03$ ), and α7-nAChR ( $r^2=0.45$ , $p<0.01$ ) in patients with CAS, but not in patients without CAS. Compared with untreated or low-density lipoprotein- (LDL-) treated macrophages, Lp(a)-treated macrophages exhibited markedly enhanced α7-nAChR mRNA expression ( $p<0.01$ ) and activity ( $p<0.01$ ), in vitro and ex vivo. Lp(a) but not LDL preferentially induced CD80+ macrophage (M1) polarization and reduced the inducible nitric oxide synthase expression and the subsequent NO production. While shRNA-mediated loss of α7-nAChR function reduced the Lp(a)-induced CD80+ macrophage pool, both shRNA and anti-IL-6 receptor tocilizumab suppressed Lp(a)-upregulated α7-nAChR, p-p38 MAPK, IL-6, and RhoA-GTP protein expression levels in cultures of patient monocyte-derived macrophages and HCASMCs. Conclusions. Elevated Lp(a) levels upregulate α7-nAChR/IL-6/p38 MAPK signaling in macrophages of CAS patients and HCASMC, suggesting that Lp(a)-triggered inflammation mediates CAS through α7-nAChR/p38 MAPK/IL-6/RhoA-GTP signaling induction, macrophage M1 polarization, and HCASMC activation.

Angina due to coronary artery spasm (variant angina): diagnosis and intervention strategies

INTRODUCTION

Since Prinzmetal first described a 'variant' form of angina pectoris, with predominantly resting episodes of pain and cyclic severity variations, it has gradually become apparent that this clinical presentation is caused by episodes of coronary artery spasm (CAS) involving focal or diffuse changes in large and/or small coronary arteries in the presence or absence of 'fixed' coronary artery stenoses. However, most clinicians have only limited understanding of this group of disorders.

AREAS COVERED

We examine the clinical presentation of CAS, associated pathologies outside the coronary vasculature, impediments to making the diagnosis, provocative diagnostic tests, available and emerging treatments, and the current understanding of pathogenesis.

EXPERT OPINION

CAS is often debilitating and substantially under-diagnosed and occur mainly in women. Many patients presenting with CAS crises have non-diagnostic ECGs and normal serum troponin concentrations, but CAS can be suspected on the basis of history and association with migraine, Raynaud's phenomenon and Kounis syndrome. Definitive diagnosis requires provocative testing at coronary angiography. Treatment still centers around the use of calcium antagonists, but with greater understanding of pathogenesis, new management options are emerging.

Impairment of platelet NO signalling in coronary artery spasm: role of hydrogen sulphide

BACKGROUND AND PURPOSE

The pathophysiology of coronary artery spasm (CAS), with its associated ischaemic crises, is currently poorly understood and treatment is frequently ineffective. In view of increasing evidence that platelet-based defects may occur in CAS patients, we investigated platelet reactivity in CAS patients and whether symptomatic crises reflect activation of platelet-endothelial interactions.

EXPERIMENTAL APPROACH

CAS patients were evaluated during acute and/or chronic symptomatic phases and compared with healthy control subjects. Inhibition of ADP-induced platelet aggregation by the NO donor sodium nitroprusside (SNP) and plasma concentrations of syndecan 1 (glycocalyx shedding marker), tryptase (mast cell activation marker) and platelet microparticles were measured.

KEY RESULTS

Inhibition of platelet aggregation by SNP was diminished in chronic CAS, with further (non-significant) deterioration during symptomatic crises, whereas plasma concentrations of syndecan 1, tryptase and platelet microparticles increased. Treatment of patients with high-dose N-acetylcysteine (NAC) plus glyceryl trinitrate rapidly increased platelet responsiveness to SNP and decreased plasma syndecan 1 concentrations. The effect of NAC on platelet responsiveness to SNP was confirmed in vitro and mimicked by the H₂ S donor NaHS. Conversely, inhibition of enzymatic production of H₂ S attenuated NAC effect.

CONCLUSION AND IMPLICATIONS

CAS is associated with substantial impairment of platelet NO signalling. During acute symptomatic exacerbations, platelet resistance to NO is aggravated, together with mast cell activation and damage to both vasculature and platelets. NAC, via release of H₂ S, reverses platelet resistance to NO and terminates glycocalyx shedding during symptomatic crises: This suggests that H₂ S donors may correct the pathophysiological anomalies underlying CAS.

Coronary artery disease with and without angina--two different entities?

Coronary heart disease (CHD), previously neither diagnosed nor suspected, was strongly suspected in 115 of 2014 men aged 40-59 years during a cardiovascular survey examination. Sixty-nine of 105 men who underwent diagnostic coronary angiography had pathologic angiograms. Twenty-six of these 69 had angina pectoris (AP) with and without pathologic exercise ECGs and 43 had pathologic exercise ECG as the only indicator of CHD. The extent of coronary artery changes was similar in the two groups. The men without AP were in almost all respects similar to 1832 men labelled as normals. The men with AP differed in several respects from their non-AP angiographic counterparts and from their non-AP angiographic counterparts and from the normals: they had more dyspepsia, a higher stress score, higher serum cholesterol and triglycerides, lower antithrombin III levels in the blood and lower blood platelet retention values. These results indicate that coronary artery disease with and without AP may represent somewhat different pathogenetic entities.

Continuous long-term dosing with oral slow-release isosorbide dinitrate does not reduce incidence of cardiac events in patients with healed myocardial infarction

BACKGROUND

In the short term, isosorbide dinitrate (ISDN) is considered to be therapeutically effective. The long-term effects of treatment with slow-release ISDN are less clear.

HYPOTHESIS

The study was undertaken to investigate the effects of continuous, long-term dosing with oral slow-release ISDN on the incidence of cardiac events in patients with healed myocardial infarction (MI). The study was carried out in accordance with the intention-to-treat principle.

METHODS

In all, 1.102 in- and outpatients, of either gender, with healed MI were randomly divided into groups treated with ISDN (n = 470) and not treated with ISDN (n = 632). Patients in the ISDN group received a continuous regimen of 20 mg of oral, long-acting ISDN three times a day, after meals. The mean observation period was 15.0 +/- 18.5 months. The primary endpoints were nonfatal and fatal recurrent MI, death from congestive heart failure, and sudden death.

RESULTS

There were no significant differences in the baseline characteristics of the patients in the ISDN and no-treatment groups; nevertheless, significantly more patients in the ISDN group experienced cardiac events. In the ISDN group, 35 patients (7.4%) experienced cardiac events during the observation period, versus only 28 patients (4.4%) in the no-treatment group (p < 0.05; odds ratio 1.74; 95% confidence interval 1.04-2.90).

CONCLUSION

Continuous long-term dosing with oral, slow-release ISDN does not reduce and probably increases the incidence of cardiac events among patients with healed MI.

Comparison of clinical and angiographic features and longterm follow-up events between patients with variant angina and patients with ST elevation myocardial infarction

We investigated to what extent patients with variant angina and significant coronary stenosis (>or=70%) present a clinical and angiographic profile similar to patients with ST elevation myocardial infarction. Thus, the clinical and angiographic features as well as follow-up events of 200 patients were prospectively analyzed and were compared with those of 422 patients with a first ST elevation myocardial infarction survivors of the early phase (3 days) and those of 70 patients with variant angina and non significant stenosis. Age and incidence of smoking, systemic hypertension, diabetes and maximum ST elevation were similar in the 2 groups. Furthermore, among patients with significant coronary stenosis, stenosis severity and the proportion of eccentric lesions were also comparable. Incidence of recent-within 30 days prior to admission-angina at rest was higher in variant angina patients with significant stenosis (67% vs. 27%, p<0.001) than in those with myocardial infarction but long standing angina at rest (>30 days) was low and comparable in these 2 groups (15% vs. 11%, ns). Also, in a 5-year follow-up most patients from these 2 groups were free from angina at rest (86% vs. 84%) which in variant angina patients was largely attributable to a high revascularization rate (72%). Moreover, the rate of myocardial infarction/cardiac death (20% vs. 19%) was also similar. Patients with variant angina and non-significant stenosis, however, had longer antecedent angina, more frequent follow-up angina and a lower incidence of cardiac events than the other 2 groups. Thus, these findings suggest that patients with variant angina and significant coronary stenosis generally behave as an acute coronary syndrome-likely associated with an acutely complicated plaque-rather than as recurrent vasospastic angina, and should be managed accordingly.

Eccentric Dosing of Nitrates Does Not Increase Cardiac Events in Patients with Healed Myocardial Infarction

This study was performed to investigate the risk of cardiac events by eccentric or continuous dosing of nitrates in patients with healed myocardial infarction. A total of 573 patients with healed myocardial infarction were assigned to one of two groups: a nitrate-treatment (n =239) and a nontreatment (n =334) group. The nitrate-treatment group was further subdivided into a group receiving eccentric dosing of nitrates (n =153) and a group receiving continuous dosing of nitrates (n =86). The mean observation period was 11.2+/-8.2 months. The cardiac events investigated were nonfatal and fatal recurrent myocardial infarction, death from congestive heart failure, sudden death, worsening angina and rebound angina. Baseline characteristics were also compared among the three groups to determine any effects on outcome. Among the patients receiving eccentric or continuous dosing of nitrates, the rates of cardiac events were 12.7/1,000 person.year and 67.4/1,000 person.year, respectively, whereas the rate was 19.7/1,000 person.year in the nontreated patients. The incidence of cardiac events was significantly greater in patients receiving continuous dosing of nitrates than in the nontreated patients (p <0.05). Continuous dosing of nitrates thus increases cardiac events, and while eccentric dosing of nitrates does not increase them, it is also not effective at preventing them in patients with healed myocardial infarction.

Intracoronary administration of a thromboxane A2 synthase inhibitor relieves acetylcholine-induced coronary spasm

This study sought to clarify the effectiveness of intracoronary administration of a thromboxane (TX) A2 synthase inhibitor, Ozagrel Na, to relieve coronary spasms induced by intracoronary injection of acetylcholine (ACh). An ACh spasm provocation test was performed in 92 consecutive patients with coronary spastic angina using incremental doses of 20, 50, and 80 microg into the right coronary artery, and 20, 50, and 100 microg into the left coronary artery within 20s. A coronary spasm was defined as TIMI 0 or 1 flow and an intracoronary injection of 20 mg Ozagrel Na was administered when it was provoked. Within 2 min of the administration of the TXA2 synthase inhibitor, ACh-induced coronary spasms were relieved (TIMI 3 flow) in 88.1% of procedures without complications. In only 4 cases (4.3%), it took more than 3 min to relieve the coronary spasms. Intracoronary administration of 20mg Ozagrel Na when ACh-induced spasms occurred, shortened the spasm relief time in all 7 patients (200 +/- 59s vs 111 +/- 23s, p < 0.01), improved the maximal ST segment elevation in 5 of them (3.9 +/- 3.7 mm vs 0.7 +/- 1.5 mm, p < 0.05), and stopped chest pain in 4 patients. In 4 patients who had ACh-induced coronary spasm of the left anterior descending artery, the TXB2 concentration in the coronary sinus decreased after intracoronary administration of Ozagrel Na into the left coronary artery (463 +/- 562 vs 96 +/- 45, p < 0.01). In conclusion, intracoronary administration of a TXA2 synthase inhibitor can relieve ACh-induced coronary spasms by inhibiting TXA2 synthesis in the local coronary circulation.

In vivo platelet activation in atherothrombotic stroke is not determined by polymorphisms of human platelet glycoprotein IIIa or Ib

Platelet membrane glycoprotein polymorphisms are candidate risk factors for thrombosis, but epidemiological data are conflicting. Thus, demonstration of a genotype-dependent alteration in function is desirable to resolve these inconsistencies. We investigated in vivo platelet activation in acute thrombosis and related this to platelet genotype. Frequencies of the 1b and 2b alleles of the HPA 1a/1b and HPA 2a/2b platelet glycoprotein polymorphisms were determined in 150 (52 men/98 women, mean age 58.3 years) patients with atherothrombotic stroke, and the influence of genotype on markers of platelet activation was assessed. Platelet P-selectin (CD62P) expression and fibrinogen binding was measured using whole blood flow cytometry within 24 h of stroke and 3 months later in 77 patients who provided a repeat blood sample. Results were compared with matched controls. Neither the 1b allele [allele frequency 0.11 vs. 0.13, odds ratio (OR) confidence interval (CI) 0.8 (0.5-1.3)] nor the 2b allele [0.09 vs. 0.07, OR (CI) 1.4 (0.8-2.4)] was significantly over-represented in patients. Increased numbers of activated platelets were found following stroke (acute mean P-selectin expression 0.64% vs. control 0.35%, P < 0.001; acute mean fibrinogen binding 1.6% vs. control 0.9%, P < 0.001). Activation persisted in the convalescent phase (P < 0.001 and P = 0.005 vs. controls for P-selectin and fibrinogen respectively). Expression of P-selectin and fibrinogen was not influenced by either the HPA 1a/1b genotype (P > 0.95 for each marker, Scheffe's test) or the 2a/2b genotype (P > 0.95 for each). Although persisting platelet activation is seen in atherothrombotic stroke, it is independent of HPA 1a/1b and 2a/2b genotypes. These data suggest an underlying prothrombotic state, but do not support the polymorphisms studied as risk factors for thrombotic stroke in this population.

Transcardiac 5-hydroxytryptamine release and impaired coronary endothelial function in patients with vasospastic angina

1. The present study was designed to test the hypotheses whether platelet degranulation across the coronary bed is detectable during non-ischaemic periods in patients with vasospastic angina (VSA) and whether the exogenous nitric oxide (NO) donor nitroglycerin (GTN) is able to modify platelet degranulation, reflecting an impaired endothelial production of NO. 2. We studied 13 patients with VSA and 10 controls. The time course of coronary sinus (CS) plasma 5-hydroxytryptamine (5-HT) levels was evaluated every 4 h before and after intravenous infusion of GTN over a period of 40 h. Coronary sinus plasma 5-HT levels were significantly higher at any measured time point in patients with VSA compared with control and were significantly decreased in patients with VSA following treatment with GTN, but not in controls. Femoral artery plasma 5-HT levels remained almost constant throughout the study. The ratio of CS:aorta 6-keto-prostaglandin F1 alpha was significantly and inversely correlated with the transcardiac plasma 5-HT difference only in patients with VSA (r = -0.68; P < 0.02; n = 13). 3. The time course of CS 5-HT levels confirmed significant platelet degranulation across the coronary bed supplied by the spasming artery in patients with VSA and this was modified by GTN. The present data suggest that platelet degranulation occurs during non-ischaemic periods in patients with VSA and that prostacyclin biosynthesis may be a compensatory response to an impaired endothelial release of NO, limiting the degree of the effects of platelet degranulation.

Stent placement for recurrent vasospastic angina resistant to medical treatment

The successful stent placement for treatment of recurrent vasospastic angina in a patient with nonstenotic coronary arteries is described. Use of the Palmaz-Schatz stent resulted in successful vasodilation that completely prevented anginal attacks. This procedure represents an alternative treatment for patients with vasospastic angina refractory to aggressive medical therapy.

Increased serotonin release across the coronary bed during a nonischemic interval in patients with vasospastic angina

BACKGROUND

Platelet activation and coagulation abnormality have been observed during coronary spasm. It is crucial whether platelet activation occurs even during a nonischemic period.

HYPOTHESIS

This study was designed to determine whether platelets might be activated across the coronary bed during a nonischemic interval in patients with vasospastic angina.

METHODS

Plasma levels of serotonin, 6-keto-prostaglandin F1 alpha, and catecholamines in the aorta and the coronary sinus were simultaneously measured in 16 patients with vasospastic angina and 13 control patients with nonischemic heart disease.

RESULTS

None of these patients showed myocardial ischemia during sampling. The difference in transcardiac plasma levels of serotonin in patients with vasospastic angina was significantly higher than that in controls (1.48 +/- 1.08 ng/ml vs. 0.07 +/- 0.12 ng/ml, respectively, p < 0.001). Coronary sinus plasma norepinephrine levels in these two groups were almost the same (204.8 +/- 110.8 pg/ml vs. 190.4 +/- 131.6 pg/ml, respectively). The ratio of 6-keto-prostaglandin F1 alpha in the coronary sinus and the aorta was not different between the two groups (1.17 +/- 0.96 in patients with vasospastic angina vs. 1.15 +/- 0.68 in controls).

CONCLUSIONS

These data suggest that platelet activation across the coronary bed should be ascribed to endothelial dysfunction. Lack of compensatory enhancement of prostacyclin production might be concerned with dysfunction of coronary endothelial cells in these patients.

Platelet Aggregation, Thromboxane A(2), Prostacyclin Generation and Platelet Sensitivity to Prostacyclin during the First Month after Myocardial Infarction

This study was designed to investigate platelet aggregation, plasma thromboxane A, and prostacyclin concentration and platelet sensitivity to prostacyclin simultaneously during the first month after myocardial infarction (MI). Spontaneous platelet aggregation and aggregation responses to ADP and adrenaline were low on the day of admission, increased rapidly by the 7th day post-MI, remained elevated during the second week post-MI and reached the level of chronic coronary artery disease patients but not healthy persons at the end of the fourth week of illness. An increase in plasma thromboxane B, the spontaneous and stable breakdown product of thromboxane A, level and enhanced prostacyclin production, with a maximum on the third post-MI day, were observed. We also demonstrated a significant platelet resistance to prostacyclin in MI patients. Thrombocyte sensitivity to prostacyclin normalized by the end of the fourth post-MI week. These results indicate the need for therapy with platelet inhibitors in patients with MI.

Platelet activation in stable coronary artery disease

To elucidate the role of physical activity in the pathogenesis of acute ischemic syndromes in patients with coronary artery disease (CAD), we hypothesized that platelet activation occurs when coronary blood flow velocity and shear stress increase across an atherosclerotic vascular bed. We measured platelet aggregation by using angiologic catheterization to obtain simultaneous samples of whole blood from the coronary sinus and the aorta while at rest, 2 minutes after the onset of rapid atrial pacing, and 10 minutes after termination of pacing. Of 82 consecutive patients included in our study, 36 had stenosis of the left coronary artery, 12 had stenosis of the right coronary artery only, and 34 had no evidence of CAD. Samples taken at rest revealed no arteriovenous difference in platelet aggregation between patients with CAD and those without CAD. In patients with significant stenosis (> or = 50%) of the left coronary artery, atrial pacing caused platelet aggregation to increase in samples from the coronary sinus (64 +/- 9% increase; p < 0.01) but not in blood from the aorta (2 +/- 8% decrease; difference not significant). This increase was transient, with aggregation returning almost to resting values 10 minutes after pacing ended. Atrial pacing elicited no change in platelet aggregation in samples from either the coronary sinus or aorta of patients with nonsignificant stenosis (< 50%) of the left coronary artery, patients with significant stenosis of the right coronary artery only, and patients free of CAD. Thus, under resting conditions, no evidence of platelet activation across the coronary bed was seen regardless of CAD status.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet hyperaggregability across the coronary bed in response to rapid atrial pacing in patients with stable coronary artery disease

BACKGROUND

Platelet aggregation is believed to contribute to the precipitation of acute ischemic syndromes. Because physical activity has been proposed as one possible trigger in converting a patient with chronic coronary artery disease to one with an acute ischemic syndrome, we examined the hypothesis that platelets become activated when coronary blood flow velocities (and thereby shear stress) increase across an atherosclerotic bed.

METHODS AND RESULTS

During catheterization, 82 patients (36 with left coronary artery disease, 12 with only right coronary artery disease, and 34 with normal coronary arteries) had measurement of whole blood platelet aggregation performed on blood samples obtained simultaneously from the coronary sinus and aorta at rest, 2 minutes after onset of rapid atrial pacing, and 10 minutes after pacing was terminated. There was no arteriovenous difference in platelet aggregation under resting conditions in patients with versus those without coronary artery disease. Atrial pacing in patients with left coronary artery disease (greater than or equal to 50% stenosis in a major epicardial vessel) caused an increase in platelet aggregation in the coronary sinus blood (+64 +/- 9%, p less than 0.01) but not in arterial blood (2 +/- 8% decrease, p = NS). This increase was transient and returned nearly to baseline 10 minutes after termination of pacing. Patients with nonsignificant left coronary artery disease, those with normal coronary arteries, and patients with significant disease only in the right coronary artery (venous drainage not into the coronary sinus) did not show any changes in either the coronary sinus or arterial blood with atrial pacing.

CONCLUSIONS

There is no evidence of platelet activation across a normal or an atherosclerotic coronary bed at rest. When coronary blood flow increases in the presence of significant (greater than or equal to 50%) narrowing of epicardial coronary arteries, however, platelets are activated and aggregate more easily. This mechanism may play a role in the precipitation of acute ischemic syndromes in patients with coronary artery disease.

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.

Transcoronary platelet activation and consumption in coronary artery disease: studies at rest

The platelet count(PC), plasma platelet factor 4 (PF4) and plasma beta-thromboglobulin(beta TG) have been measured in blood obtained from a peripheral vein, the aortic root and the coronary sinus in 7 patients with normal coronary arteries, 9 patients with lesser degrees of coronary artery disease(CAD) and in 13 patients with severe CAD under resting conditions. In each patient group values obtained in the peripheral venous blood were similar to those obtained in normal subjects. In each group values obtained in blood from the coronary sinus were similar to those obtained in blood from the coronary aortic root and in most instances these were similar to values obtained in peripheral venous blood. for example, in the 13 subjects with hemodynamically significant 3-vessel or 2-vessel CAD the mean values in blood from a peripheral vein, the aorta and the coronary sinus respectively were: PC-194, 205, and 208 x 10(9)/1; PF4-3.3, 3.7, and 3.5 ng/ml; and beta TG-15.5, 23.0 and 18.6 ng/ml. These findings provide no support for the occurrence of continuous platelet activation or platelet consumption in the coronary vessels or elsewhere in patients with stable CAD, under resting conditions, regardless of its severity.

Aspirin and other antiplatelet drugs in the prophylaxis of thrombosis

Aspirin is of proven value as an antithrombotic drug. In unstable angina it reduces the risk of death and myocardial infarction by half. After a myocardial infarction it reduces the risk of death by about 10% and of coronary incidence (coronary death or definite myocardial infarction) by about 25%. These effects appear to be additive with those of beta-blocking drugs. Aspirin also reduces the risk of occlusion of aortocoronary saphenous vein grafts by about half. In transient cerebral ischaemia, aspirin may reduce the risk of stroke and death by 50%. In most clinical trials to date the daily dose of aspirin ranges from 325 mg to 1400 mg. Interest in very low doses of aspirin (less than 60 mg daily) is considerable but has yet to be translated into proven clinical benefit. Dipyridamole has not been shown to be effective as an antithrombotic when used alone. Its antiplatelet action ex vivo may be enhanced by combination with aspirin but clinical trials have shown relatively little advantage of the combination over aspirin alone. Sulphinpyrazone has not become established as a first line antithrombotic drug. Epoprostenol is useful in extracorporeal circulations to prevent platelet consumption and possibly in severe inoperable peripheral vascular disease.

Resting angina with fixed coronary artery stenosis: nocturnal decline in ischemic threshold

Atrial pacing was performed in 16 patients with angina at rest and significant coronary artery stenosis (greater than 70%) over 2 consecutive days in the morning (10 A.M. to 1 P.M.), in the afternoon (4 to 7 P.M.), and at night (12 midnight to 3 A.M.) to assess possible circadian variations of their ischemic threshold. Overall, the incidence of resting angina was highest at night. All pacing results were positive (greater than or equal to 1.0 mm ST segment shift) and tended to be reproducible in nine patients, whereas some or all were negative in seven. Among all positive results, ischemic thresholds at night were significantly lower than those in the morning and in the afternoon (125 +/- 3 vs 138 +/- 3 and 139 +/- 2 beats/min, mean +/- SEM; p less than .005). In nine patients, 19 pacing tests produced ST segment elevation, of which 13 were performed at night (68%). We conclude that patients with resting angina and severe coronary stenosis often exhibit a nocturnal decline in their ischemic threshold, which seems to facilitate development of transmural ischemia during atrial pacing.

Effects of thromboxane analog U46619 on endothelial damaged canine coronary arteries in vivo

We studied the effects of the thromboxane analog, U46619, infused into the left anterior descending (LAD) artery of intact dogs before and after producing endothelial denudation of the mid portion of the LAD. Proximal artery cross-sectional area (CSA) decreased by 47% with 0.1 microgram/min infusion of U46619 with intact and denuded endothelium, while resting CSA reduced spontaneously following denudation. Coronary resistance vessels demonstrated a marked constrictor response to U46619 with a rise in resistance and a fall in flow and myocardial O2 consumption. U46619 produces significant narrowing of proximal epicardial coronary arteries as well as resistance coronary vessels. This effect could cause ischemia in patients with moderate coronary atherosclerosis.

Increased thromboxane A2 generation and altered membrane fatty acid composition in platelets from patients with active angina pectoris

Lipid composition of platelet membranes and thromboxane A2 (TxA2) generation by platelets were investigated in eighty-seven anginal patients (forty-two with resting angina in active phase and forty-five with effort stable angina or rest angina in inactive phase) and in forty-five clinically healthy subjects of similar age. All subjects were on the same dietary regimen and the adherence to diet was checked by analysis of red blood cell lipids. Platelets from active angina patients produced more TxA2 than platelets from both inactive patients and controls (p less than 0.001). Moreover patients with active angina had higher arachidonic acid (AA, p less than 0.001) and lower eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) levels in phosphatidylcholine (PC, p less than 0.001), than inactive patients and controls. AA and EPA changes in membrane PC significantly correlated with TxA2 production (p less than 0.001) but not with coronary pathoanatomy. Plasma lipids, content of cholesterol, total phospholipids (and their saturated and unsaturated fatty acids) and the different phospholipid fractions in platelet membrane were not different in the three groups. Present results indicate that in platelets from anginal patients phospholipid fatty acid composition is at least in part independent of plasma composition and that in active angina there are modifications leading to increased TxA2 formation and possibly contributing to the occurrence of ischemic attacks.

Platelet function and coagulation studies in patients with mitral valve prolapse

Twenty-eight consecutive patients with mitral valve prolapse (MVP), seven of whom had previous cerebrovascular disorders (CVD), were studied for platelet function and coagulation tests. While platelet function tests were found to be normal with the exception of platelet aggregation rate (PAR), there was a significant rise of factors VIII vWF:Ag (Von Willebrand) and (FPA) fibrinopeptide A. Six cases had high levels of both these factors, suggesting the existence of a particular subset of patients with MVP, with a higher risk of thromboembolic episodes, although only three out of seven patients with previous CVD had either FPA or VIII vWF:Ag levels. The broad spectrum of subjects with MVP probably explains the different results obtained when studying platelet function and coagulation factors. Therefore, larger population studies and prolonged follow-up of cases with either coagulation abnormalities similar to the ones found in the present report and/or altered platelet function tests are suggested to discover if it is possible to detect patients with a potential for thromboembolism.

Acute myocardial infarction: an episodic event of several coronary spasms followed by dilatation?

Acute myocardial infarction (AMI) can no longer be considered as a single event, but as a series of episodes. In most of the cases, the initial event may be the induction of a severe spasm of the coronary artery by vasoconstrictive substance released from aggregated platelets. These spasms are followed by dilatation, which is caused by substances set free from the ischemic tissue. Dilatation then results in a washing-out of vasoactive mediators (as well as myoglobin) and platelets, which is reflected as a peak in the blood myoglobin concentration-time curve. The local depletion of vasodilative metabolites allows a further contraction of the coronary vessel. A new accumulation of platelets then stimulates another spasm. This vicious circle (thrombo-ischemic re-entry-mechanism) is repeated several times and can be interrupted by the systemic administration of thrombolytic drugs (streptokinase).

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.

Beta-thromboglobulin release within coronary circulation--a potential role of platelets in ergonovine-induced coronary vasospasm

The role of platelets in the pathogenesis of acute myocardial ischemia is not yet agreed upon. In this study, the gradient of plasma beta-thromboglobulin concentration between coronary sinus and aorta was used as an indicator of platelet activation within the coronary circulation. Blood samples were drawn before and after injection of ergonovine maleate in patients without fixed coronary stenosis in whom significant coronary spasm was induced by ergonovine (n = 8, Group 1), patients with significant stenosis (greater than or equal to 75%) of the left anterior descending artery and positive ergonovine test (n = 7, Group 2) and patients with significant stenosis of left anterior descending coronary artery and negative ergonovine test (n = 11, Group 3). Fifteen patients with normal coronary arteries who were negative in the ergonovine test served as controls (Group 4). After the ergonovine test, all Group 1 patients revealed a significant increase of beta-thromboglobulin gradient (P less than 0.001), while those in other groups did not. Additionally, the gradient after the ergonovine test of Group 1 patients was larger than those of the other groups (P less than 0.01). All blood samples after the ergonovine test were collected before or at the onset of angina attacks. These results suggest that platelet activation within the coronary circulation has some pathogenic role, probably as an aggravating factor, in coronary artery spasm.

Histamine-induced spasm not significantly modulated by prostanoids in a swine model of coronary artery spasm

The role of prostanoids in a swine model of coronary artery spasm was examined. Eighteen miniature pigs underwent endothelial denudation of the left coronary artery (left circumflex branch in 14 pigs and left anterior descending branch in 4 pigs) followed by high cholesterol feeding. Three months after the denudation, when coronary artery spasm was repeatedly provoked along the denuded portion of the coronary artery by histamine, the vasoconstrictive effect of thromboxane A2 and the preventive effects of indomethacin and prostacyclin against histamine-induced coronary artery spasm were examined. Intracoronary administration of thiothromboxane A2, 200 micrograms, a stable thromboxane A2 analog, failed to provoke coronary artery spasm (seven of seven cases) but nonselectively constricted the coronary artery by 33%. Intravenous administration of indomethacin, 2 mg/kg, or continuous intravenous infusion of prostacyclin, 50 ng/kg per min, failed to prevent histamine-induced coronary artery spasm (four of four and eight of eight cases, respectively), yet the spasm was all but prevented by intravenous pretreatment with diphenhydramine at a dose of 1 mg/kg. Thus, in this swine model, prostanoids may not play a primary role in the occurrence of coronary artery spasm.

Enhanced in vivo platelet activation in subtypes of ischemic stroke

It remains uncertain whether platelet activation in ischemic stroke is contributory or secondary to brain ischemia. The efficacy of aspirin (ASA) in stroke prevention suggests that platelet activation contributes to the occurrence of stroke. On the other hand, platelet activation may be simply a generalized consequence of cerebral ischemic damage. To examine this issue, plasma levels of the platelet specific proteins beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4) were measured in fifty-eight patients with various defined types of acute ischemic strokes. beta-TG was a broader indicator of platelet activation than PF4. Compared with an age-matched control group, thromboembolic and cardioembolic stroke patients had significantly elevated beta-TG levels (p less than 0.001). Also, beta-TG levels in these stroke categories were significantly higher in samples drawn within the first week after the event than in those drawn later (p less than 0.001). In contrast, beta-TG levels in lacunar stroke patients and in most TIA patients were normal. beta-TG levels did not correlate with the volume of cerebral infarction as measured by planimetry from CT scans. Moreover, beta-TG levels in patients on chronic ASA therapy at the time of stroke did not differ from those in patients of the same diagnostic categories not taking aspirin. These data indicate that platelet activation may be important in some, but not all, subtypes of ischemic stroke and that platelet activation can occur in stroke even though the platelet cyclooxygenase pathway is suppressed.

Abnormal cardiocoronary thromboxane A2 production in patients with unstable angina

Thromboxane B2 (TXB2), the stable metabolite of thromboxane A2 (TXA2), was measured in the coronary sinus and in aortic blood before and after cold pressor test (CPT) in 21 patients suffering from ischemic heart disease (7 affected by stable effort angina and 14 by unstable angina) and in 12 patients not suffering from myocardial ischemia (control group) during coronary angiography. Aspirin (10 mg/kg intravenously) was administered before catheterization in order to prevent platelet and leukocyte TXA2 formation. Control subjects and patients with effort angina had TXB2 resting levels lower than unstable angina patients without a transcardiac gradient which, on the contrary, was found in unstable angina patients. Only in these patients CPT resulted in a significant TXB2 increase more marked in the coronary sinus (from 50.0 +/- 18.9 pg/ml to 73.0 +/- 35.1 pg/ml, p less than 0.001) than in the aorta (from 33.4 +/- 17.1 pg/ml to 42.6 +/- 24.0 pg/ml, p less than 0.05), so that the transcardiac TXB2 gradient significantly increased. In all but two unstable angina patients, TXB2 elevation was not associated with a fall of cardiac lactate extraction. The resting and CPT-induced TXB2 gradients were unrelated to the presence and severity of coronary angiographic lesions. These results indicate that unstable angina patients show an abnormal cardiocoronary capacity to synthesize TXA2, which seems not to be elicited by the occurrence of myocardial ischemia.

Endogenous biosynthesis of prostacyclin during cardiac catheterization and angiography in man

The potent platelet inhibitory and vasodilator properties of prostacyclin suggest that levels of this substance may be of relevance to drug action and pathologic processes in the coronary vascular bed. Attempts to estimate the coronary secretion rate of prostacyclin have relied on measurements of metabolites obtained via cardiac catheter, usually as an adjunct to coronary angiography. To test the hypothesis that such procedures might themselves perturb endogenous biosynthesis of prostacyclin we used mass spectrometry to measure plasma levels of 6-keto-prostaglandin (PG) F1 alpha across the coronary vascular bed, as well as to assess the excretion of a major urinary metabolite, 2,3-dinor-6-keto-PGF1 alpha (PGI-M), in patients undergoing cardiac catheterization. PGI-M excretion increased variably from a median 100 to 205 pg/mg creatinine (p less than .01) during catheterization with angiography and remained elevated 2 to 4 hr after initiation of the procedure. However, cardiac catheterization without angiography also stimulated metabolite excretion, perhaps reflecting catheter-induced vascular trauma. The direct effect of radiocontrast media on vascular release of prostacyclin was indicated by increased PGI-M excretion in healthy volunteers administered intravenous radiocontrast and by studies of the canine coronary artery and jugular vein in vitro. Measurement of plasma 6-keto-PGF1 alpha after left heart catheterization showed that levels in aortic (21 +/- 8 pg/ml) and coronary sinus (14 +/- 2 pg/ml) blood were increased compared with peripheral venous levels (less than or equal to 4 + 1 pg/ml) determined before this procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary artery spasm--1984

Coronary artery spasm was virtually unknown not long ago, but the intense, ongoing interest it has generated in the past decade has produced a number of specific diagnostic techniques and therapeutic approaches, as well as considerable insight into mechanisms of coronary vascular tone and various coronary syndromes. There is growing evidence that coronary artery spasm is involved in unstable angina, stable angina, myocardial infarction, and sudden death. It is by no means a benign process and is associated with significant morbidity or mortality if misdiagnosed or untreated. It seems clear that what started as a mere clinical curiosity involving a minority of patients with the so-called Prinzmetal's variant angina is snowballing into a major arena for research, diagnosis, and treatment in the field of ischemic coronary artery disease.

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)

Reversal of acute experimental cerebral vasospasm by calcium antagonism with verapamil

Acute vasospasm of the transclivally exposed basilar artery of anesthetised cats was produced by the subarachnoid injection of platelet-rich plasma (PRP) treated with enough adenosine diphosphate (ADP) to induce platelet aggregation and secretion. Vasorelaxation was produced by the topical application of the calcium antagonist verapamil. Changes in the internal diameter of the basilar artery were determined by measuring the blood column diameter from photomicrographs taken sequentially, at 5 minute intervals, through the operating microscope. Changes in blood vessel diameter are expressed as a plus or minus percentage of the pretreatment diameter. Arterial blood pressure and blood gas values were kept in the physiological range for the cat. The subarachnoid injection of PRP-ADP produced severe constriction of the basilar artery (mean constriction at 5 minutes after injection: -40.7% +/- 2.8 SEM). Platelet-free plasma, ADP alone and Elliott's A solution had no spasmogenic effect when injected into the subarachnoid space. The topical application of the calcium channel blocker verapamil (0.1 mg per kg) 30 minutes after the injection of PRP-ADP, with the basilar artery still in spasm (mean constriction: -23% +/- 3.5 SEM), produced prompt and dramatic vasodilation (mean dilation at 5 minutes after application: +52.7% +/- 18.1 SEM). This spasmolytic effect persisted in a decremental fashion for the 60 minute period of observation, by which time the previously constricted vessel had returned to its normal size. These observations indicate that the platelet fraction of whole blood may be involved in the genesis of acute vasospasm following subarachnoid hemmorrhage and that this phenomenon can be readily reversed by calcium antagonism.

Platelet activation caused by cardiac catheter blood collection, and its prevention

The study of platelet changes occurring across the coronary circulation is important in the investigation of the platelet's role in ischemic heart disease. It requires blood sampling through cardiac catheters. This could activate platelets and alter the results of tests of platelet activation and reactivity. This study was designed to examine this problem and to devise satisfactory methods for obtaining blood for platelet studies through long catheters. Blood collected through catheters introduced with a guide-wire had a much higher plasma heparin neutralising activity (HNA), platelet factor 4(PF4) and beta-thromboglobulin (beta TG) than peripheral venous blood, and lower platelet count(PC). Blood collected through catheters introduced via a sheath, and kept filled with anticoagulant/antiplatelet solution until blood sampling, gave results similar to peripheral venous blood for the PC, platelet aggregate ratio, platelet fluorescent granule count, and for plasma HNA, PF4 and beta TG. It is concluded that platelets are activated during blood collection through cardiac catheters; however, with appropriate precautions, blood which is satisfactory for platelet studies can be obtained.

Prostacyclin produced by the pericardium and its influence on coronary vascular tone

To determine the influence of pericardial fluid prostacyclin on coronary blood flow, the latter was measured in the circumflex artery of anesthetized dogs. Intraaortic infusions of angiotensin II (25 ng . kg-1 . min-1) reduced blood flow and released prostacyclin into pericardial fluid. Epicardial and pericardial superfusion with indomethacin (1 micrograms/ml) abolished prostacyclin release and significantly increased the coronary vasoconstrictor effect of angiotensin II; this treatment did not appear to affect vascular synthesis of prostacyclin. Pericardial prostacyclin may modulate the coronary vasoconstrictor effect of angiotensin, but its general role as a regulator of coronary vascular resistance is probably limited. A more important effect of pericardial prostacyclin may be exerted on the large coronary vessels in the epicardial surface. Release of prostacyclin into pericardial fluid represents a potential mechanism for opposing coronary vasospasm, especially if platelet activation is found to be a contributory factor in vasotonic angina pectoris.

Arterial and coronary sinus catecholamines in the course of spontaneous coronary artery spasm

We studied plasma catecholamine levels in 10 patients with frequent spontaneous episodes of coronary artery spasm to evaluate the role of the sympathetic nervous system. Peripheral venous norepinephrine in supine and upright postures, urinary excretion of catecholamines, and functional testing of the sympathetic nervous system did not differ from the same measurements in control subjects. Arterial and coronary sinus levels of norepinephrine and epinephrine drawn early in ischemia were not elevated over baseline; coronary sinus norepinephrine levels were higher than those in arterial samples and rose from 315 +/- 32 (pg/ml +/- SE) at the onset of ST elevation to 490 +/- 49 pg/ml late in ischemia (p less than 0.05). Plasma epinephrine levels, higher in arterial than coronary sinus samples, also rose significantly only late in ischemia, from 44 +/- 14 pg/ml to 148 +/- 35 pg/ml (p less than 0.05) in arterial blood and from 33 +/- 10 pg/ml to 108 +/- 29 pg/ml in coronary sinus samples (p less than 0.05). Generalized sympathetic nervous system activation is not likely to be the sole cause of coronary artery spasm.

The significance of platelet-vessel wall prostaglandin equilibrium during exercise-induced stress

Alterations in platelet-generated thromboxane A2 (TXA2) and vessel wall-generated prostacyclin (PGI2) have been associated with myocardial ischemia. To examine TXA2-PGI2 equilibrium at rest and during exercise stress, we studied 13 normal subjects and 15 coronary artery disease patients. Plasma TXB2 and 6-keto-PGF1 alpha were measured as stable metabolites of TXA2 and PGI2, respectively, by radioimmunoassay. In normal subjects, plasma TXB2 levels increased 24% during exercise from 135 +/- 30 to 168 +/- 42 pg/ml (p = NS). Plasma 6-keto-PGF1 alpha levels increased 224% from 54 +/- 17 to 175 +/- 57 pg/ml (p less than 0.05). In coronary artery disease patients, although resting plasma TXB2 levels (mean 136 +/- 43 pg/ml) were comparable to levels in normal subjects, a greater increase (82%) occurred during exercise (mean 248 +/- 70 pg/ml; p less than 0.02 compared to resting levels). Resting plasma 6-keto-PGF1 alpha levels (mean 94 +/- 28 pg/ml) were also similar to normal subjects but increased only by 43% during exercise (mean 134 +/- 53 pg/ml; p = NS compared to resting levels). These data suggest that: in normal subjects TXA2 and PGI2 increase during exercise, PGI2 increasing more than TXA2, and although coronary disease patients have resting TXA2 and PGI2 levels in the normal range, TXA2 levels increase more than PGI2 levels during exercise. These observations may have a bearing on the mechanism of exercise-induced angina pectoris in certain coronary artery disease patients.

The beriberi analogy to myocardial infarction

Two pandemics of heart attack deaths have plagued the world's population during the past 130 years. The first pandemic, induced by beriberi, was caused by the industrial revolution altering the nutritional composition of rice. By 1892 a simple working knowledge, then at hand, could have terminated the beriberi plague; however, orthodox medicine being then enchanted with the false concept that all disease was caused by germs, permitted millions of Asians to die needlessly of beriberi by refusing to tell them to eat rice bran or to drink rice bran tea. A second pandemic of heart attack deaths, called myocardial infarction (MI), struck the developed nations of the Western World in full force after 1930. As a hypothesis, it is suggested that this MI pandemic, still raging today, was caused by a change in food processing that occurred after 1920, when the new oil seed industry introduced into our food three greatly harmful lipid substances. The unnatural trans-trans isomer of linoleic acid, which had never been in human food prior to 1920 and which entered our food in margarines and refined oils, blocked the conversion of natural cis-cis linoleic acid to prostaglandin E1, which tends to prevent MI, both by acting as a vasodilator and by minimizing platelet aggregation. Harmful lactones were also introduced into our food, increasing the risk of MI by decreasing the fibrinolytic activity of our blood. The oil seed industry also introduced into our diet free radical lipid peroxides that make the myocardium more vulnerable to infarction. It is suggested that except for the one in 500 of us who is afflicted by familial hypercholesterolemia, the cholesterol concept of MI is as false today as was the concept in 1900 that germs caused beriberi. It is further suggested that a working knowledge is at hand today that can make death from MI just as rare as death is now from a beriberi-induced heart attack.

Haemodynamic and metabolic effects of dazoxiben at rest and during atrial pacing

1 Thromboxane B2 (TXB2) levels were measured in three sites (coronary sinus, pulmonary artery, and femoral artery) at rest and during atrial pacing in 11 patients with stable angina pectoris. 2 There was a highly significant increase in arterial TXB2 on pacing (by up to 820 pg/ml) but there was no change in the thromboxane levels at the other two sites. 3 Dazoxiben 200 mg orally abolished the increase in arterial TXB2, but had no effect on systemic, pulmonary or coronary haemodynamics, no effect on myocardial metabolism and a variable effect on atrial pacing time to angina.

Platelet reactivity and its dependence on alpha-adrenergic receptor function in patients with ischaemic heart disease

We studied 57 patients admitted to hospital with ischaemic heart disease, including nine patients with variant angina, to evaluate platelet reactivity and its dependence on alpha-adrenergic receptor function. The threshold concentration for biphasic platelet aggregation in response to adrenaline and adenosine diphosphate was measured in fresh platelet rich plasma. There were age related alterations in platelet responsiveness to adrenaline. In 27 age matched control subjects platelets showed adrenaline induced aggregation at a concentration higher than 0.1 mumol. The threshold concentrations for adrenaline and adenosine diphosphate were 0.91 mumol and 4.68 mumol. In 16 patients with acute infarction, 14 with old infarction, nine with effort angina, and nine with rest angina, mean values of platelet aggregation threshold for both adrenaline and adenosine diphosphate were not altered significantly when compared with control subjects. In contrast, the values for adrenaline and adenosine diphosphate in nine patients with variant angina were 0.012 mumol and 2.24 mumol and seven of them showed obvious platelet hyperactivity to adrenaline at a concentration lower than 0.1 mumol. The threshold concentration for adrenaline induced aggregation did not correlate with serum cholesterol and triglyceride levels.

Effects of dazoxiben on transcardiac thromboxane levels and haemodynamics in coronary heart disease

1 Plasma thromboxane levels were obtained from both the coronary sinus and aorta in patients with stable angina pectoris paced to angina, and in unstable angina patients before and after dazoxiben 100 mg. 2 Although there was a wide range of values in the different groups, dazoxiben significantly reduced plasma thromboxane levels in all patients. 3 Dazoxiben had no adverse effect on coronary and systemic haemodynamics, and atrial pacing time to angina was increased from 245 +/- 41 to 308 +/- 48s (P less than 0.01).

Thallium-201 uptake in variant angina: probable demonstration of myocardial reactive hyperemia in man

Myocardial thallium scintigraphy was performed in four subjects with variant angina and in one subject with isolated, fixed coronary obstruction. Three subjects with variant angina had short episodes of ischemic ST-segment elevation that lasted 20--100 seconds. Thallium scintigrams demonstrated excess uptake in regions judged to be ischemic by angiographic and electrocardiographic criteria. Two subjects, one with variant angina and the other with a fixed coronary lesion, had prolonged episodes of ischemia that lasted 390--900 seconds. Both had reduced thallium uptake in the ischemic regions. We conclude that myocardial reactive hyperemia is the cause of excess thallium uptake in patients with variant angina who have short episodes of myocardial ischemia.

Influence of blood sampling site and technique on thromboxane concentrations in patients with ischemic heart disease

Thromboxane A2 may play a role in coronary arterial spasm, unstable angina, myocardial infarction, cardiac arrhythmias, and sudden death. Although previous studies have examined peripheral, aortic, and coronary sinus concentrations of its stable metabolite, thromboxane B2 (TxB2), it is unknown, first, if blood sampling through long catheters alters the concentration of TxB2 and second, if peripheral levels of this prostanoid reflect its intracoronary production and release. In order to answer these questions, paired blood samples were obtained through an 18-gauge needle and a No. 7 or 8 French 110 to 125 cm catheter from the arterial (14 patients) and venous (16 patients) circulations; in addition, coronary sinus and peripheral venous samples were obtained in 16 patients and aortic samples were obtained in 14 of these patients. All samples were analyzed to TxB2 by radioimmunoassay. Blood sampling through long catheters did not systematically alter the concentrations of arterial TxB2 (needle, 85.5 +/- 67.5 pg/ml [mean +/- SD]; catheter, 62.3 +/- 40.9 pg/ml; p = 0.20) or venous TxB2 (needle, 182.5 +/- 170.5 pg/ml; catheter, 521.4 +/- 1536.0 pg/ml; p = 0.39). Peripheral venous TxB2 levels did not correlate with TxB2 levels in coronary sinus (r = 0.01) or the TxB2 coronary sinus/aortic ratios (r = 0.21). Thus blood sampling through long catheters across the coronary bed is both a reliable and necessary method for assessing intracoronary TxB2 production in patients with ischemic heart disease.

Lack of thromboxane A2 involvement in the arrhythmias occurring during acute myocardial ischemia in dogs

Coronary artery occlusion (CAO) followed by reperfusion of the ischemic myocardium has been associated with the onset of ventricular arrhythmias. It has been suggested that platelet aggregates in the ischemic area may release thromboxane A2 (TxA2) which may then be responsible for the arrhythmias that occur during reperfusion. To study this possibility, the effect of TxA2 synthetase inhibition on arrhythmias was examined in anesthetized dogs during occlusion and for 60 minutes following release. Imidazole (30 mg/kg) was infused intravenously for 10 minutes, followed by continuous infusion of 100 mg/kg/hr for 125 minutes. The left anterior descending coronary artery was occluded, 5 minutes after the initial dose, for 60 minutes. Three minutes after release of CAO, TxB2 concentrations were significantly higher in the arterial blood of vehicle-treated animals (2.06 +/- 0.53 pmoles/ml) than in either CAO + imidazole (0.66 +/- 0.16 pmoles/ml) or sham-CAO animals receiving imidazole (0.66 +/- 0.09 pmoles/l). However, CAO dogs whether receiving imidazole or 0.9% NaCl generated a significantly greater number of ectopic beats during and after occlusion than sham-CAO animals. Therefore, release of TxA2 does not appear to be a major causative factor in the generation of reperfusion arrhythmias in dogs following coronary artery occlusion.