The pathogenesis of coronary artery disease and the acute coronary syndromes (2)

Benefit of adding low molecular weight heparin to the conventional treatment of stable angina pectoris. A double-blind, randomized, placebo-controlled trial

BACKGROUND

Patients with chronic coronary artery disease exhibit a dysfunctioning endothelium, which may be responsible for exercise-induced platelet activation and expression of a procoagulant moiety. In this study, we evaluated the therapeutic efficacy of a low molecular weight heparin (Parnaparin) in patients with stable angina pectoris.

METHODS AND RESULTS

According to a double-blind, randomized, placebo-controlled trial, 29 patients with stable exercise-induced angina pectoris and angiographically proven coronary artery disease received a single daily subcutaneous injection of Parnaparin or placebo on top of aspirin and conventional antianginal medication over 3 months. Patients randomized to Parnaparin showed a significant decrease in the fibrinogen level (P = .035) and an improvement in both the time to 1-mm ST segment depression (P = .008) and the peak ST segment depression (P = .015). The Canadian Cardiovascular Society class for angina pectoris was also improved by Parnaparin (P = .016). Parnaparin did not affect ADP and collagen-induced platelet aggregation, whereas thrombin-induced aggregation was reduced (P = .0001). The bleeding time was slightly prolonged, but this was not associated with any significant bleeding.

CONCLUSIONS

Patients with stable angina pectoris may be treated with Parnaparin in addition to aspirin and conventional antianginal medication. Side effects are negligible, and compliance is excellent.

Different effects of two methods of low-density lipoprotein apheresis on the coagulation and fibrinolytic systems

OBJECTIVE

Immunoadsorption (IMA) and dextran sulfate adsorption (DSA) are two methods for selective extracorporeal elimination of low-density lipoproteins which are known as LDL apheresis. Their influence on haemostasis until now is widely unknown.

DESIGN

The effects of both LDL apheresis procedures on the coagulation and fibrinolytic systems were compared amongst five patients treated with IMA and four patients who received a DSA therapy.

SUBJECTS

All patients with severe heterozygous familial hypercholesterolaemia were participants in a long-term LDL apheresis programme with treatments every 1-2 weeks.

INTERVENTION

Combined anticoagulation with heparin and citrate in IMA, and also heparin exclusively in DSA were used for the extracorporeal circulation.

MEASURES

Blood samples were taken immediately before and after a single LDL apheresis and five times during the weekly interval until the next therapy.

RESULTS

DSA had a significantly greater effect on standard clotting tests than IMA at the end of plasma therapy despite identical dosages of heparin. DSA caused a considerable reduction of the coagulation factors V, VIII:C, vWF:Ag, XI, XII, and prekallikrein by 48-99% at the end of apheresis treatment whereas only factor VIII:C showed a marked decrease of 72% after IMA. All abnormalities of the global coagulation tests and of most clotting factors were restored 1 day after treatment in both procedures followed by a moderate rebound phenomenon of single coagulation factors during the next few days in IMA-treated patients.

CONCLUSION

DSA exerts a more profound effect on the coagulation system than IMA by a substantial co-elimination of various clotting factors in addition to the desired removal of atherogenic lipoproteins.

The vascular endothelium. A new horizon

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Lowering blood lipids to treat atherosclerosis: vascular tone, plaques, events, and mortality

Hypercholesterolemia has been associated with an increase in vascular tone, mainly because of an impairment of endothelium-dependent relaxation. This endothelial dysfunction occurs before any definite atherosclerotic lesion is demonstrated. In both animal models and humans the correction of hypercholesterolemia has been associated with hemodynamic improvement. Several controlled trials have demonstrated that long-term treatment with cholesterol-lowering drugs is effective in blocking progression and in some cases in inducing regression of angiographically detected arterial lesions. Arteriographies produce a negative image of the arterial lumen but do not provide sufficient information on vessel wall status. Noninvasive B-mode ultrasound has allowed a direct visualization of the arterial wall in superficial vascular districts, such as the carotid bifurcation. Wall and lesion measures are increasingly used as end points for clinical trials of antiatherosclerotic drugs. In secondary prevention, cholesterol reduction is associated with a lower incidence of coronary heart disease, although the cholesterol reduction should be at least 8-9% to have an impact on total mortality.

Calcium antagonists differently inhibit proliferation of human coronary smooth muscle cells in response to pulsatile stretch and platelet-derived growth factor

BACKGROUND

Vascular smooth muscle cell proliferation is the key event of coronary artery disease. Mechanical forces, in particular, pulsatile stretch and platelet-derived growth factor, may play an important role.

METHODS AND RESULTS

Vascular smooth muscle cells were cultured from the media of human left descending coronary arteries obtained from organ donors using the explant method. To study effects of pulsatile stretch on vascular smooth muscle cell proliferation, a computer-controlled in vitro pulsatile stretch device was used. Cells were seeded onto Flex I culture plates with deformable membranes and exposed to pulsatile stretch (60 cycles per minute) and/or growth factors. Proliferation of smooth muscle cells was determined by 3H-thymidine incorporation. Pulsatile stretch markedly stimulated 3H-thymidine incorporation of coronary smooth muscle cells (180 +/- 15 to 432 +/- 27 cpm/10(5) cells; P < .05) after 24 hours and increased cell number after 6 days (10.3 +/- 0.7 x 10(4)/mL; P < .05). Platelet-derived growth factor-AB (0.01 to 10 ng/mL) concentration-dependently stimulated 3H-thymidine incorporation in coronary smooth muscle cells (EC50, 0.1 ng/mL) and had additive effects with pulsatile stretch. The Ca2+ antagonist verapamil (10(-7) to 10(-5) M) concentration-dependently inhibited proliferation stimulated by platelet-derived growth factor back to control levels (P < .05 to .01) but not that induced by pulsatile stretch.

CONCLUSIONS

Pulsatile stretch and platelet-derived growth factor are potent stimuli for proliferation of coronary smooth muscle cells. The selective inhibitory effect of a Ca2+ antagonist on smooth muscle cell proliferation stimulated by platelet-derived growth factor but not by pulsatile stretch may explain why the drugs have only modest antiatherogenic effects in patients with coronary artery disease.

Endogenous tissue-type plasminogen activator and risk of myocardial infarction

Endogenous tissue-type plasminogen activator (tPA) has been hypothesised to be a marker of baseline fibrinolytic capacity. We therefore tested whether tPA antigen is associated with the occurrence of future myocardial infarction (MI) among apparently healthy individuals. tPA antigen concentrations were measured at baseline in plasma samples from 231 apparently healthy men from the Physicians' Health Study cohort who later developed MI, and in an equal number of controls matched for age and smoking habit who remained free of reported cardiovascular disease during a follow-up of 60.2 months. In crude matched-pair analyses, baseline concentrations of tPA antigen were higher in cases than controls (p = 0.03) and strongly associated with risk of future MI. Specifically, the relative risks of developing a first MI from lowest (referent) to highest quintiles of tPA antigen were 1.00, 1.27, 1.75, 1.88, and 2.81 (p for trend 0.0008, 95% CI for the relative risk in the fifth as compared with first quintile 1.47 to 5.37, p = 0.002). Analyses which adjusted for risk factors that affect progression of atherosclerosis, particularly HDL-cholesterol, abolished the statistical significance of this association, a finding which suggests that elevations of tPA antigen are a result rather than a cause of atherosclerotic coronary disease. These prospective data suggest that endogenous tPA concentrations increase as a consequence of important preclinical atherosclerosis and therefore may be a marker for risk of future MI.

Risk of thrombosis in human atherosclerotic plaques: role of extracellular lipid, macrophage, and smooth muscle cell content

OBJECTIVE

To assess the size of the lipid pool and the number of smooth muscle cells and monocyte/macrophages in human aortic plaques that were intact and to compare the results with those in aortic plaques undergoing ulceration and thrombosis.

DESIGN

The lipid pool was measured as a percentage of the total cross sectional area of the plaque. Immunohistochemistry was used to identify cell types (monocytes/macrophages (M phi) by EBM11 and HAM56, smooth muscle cells by alpha actin). The area of the tissue occupied by each cell type was measured by quantitative microscopy in the peripheral (shoulder) area of the plaque and the plaque cap. Absolute counts of each cell type were expressed as the ratio of SMC:M phi.

MATERIAL

Aortas were obtained at necropsy from men aged less than 69 years who died suddenly (within 6 hours of the onset of symptoms) of ischaemic heart disease. 155 plaques from 13 aortas were studied. Four aortas showed intact plaques only (group A, n = 31). Nine aortas showed both intact plaques (group B, n = 79) and plaques that were undergoing thrombosis (group C, n = 45).

RESULTS

In 41 (91.1%) of the 45 plaques undergoing thrombosis (group C) lipid pools occupied more than 40% of the cross sectional area of the plaque. Only 12 (10.9%) of the 110 intact plaques (groups A + B) had lipid pools of this size. The mean size of the lipid pool in plaques of groups A, B, and C was 12.7%, 27.3% and 56.7% respectively. Compared with intact plaques those undergoing thrombosis contained a smaller volume of smooth muscle cells (2.8% v 11.8%) and a larger volume of monocyte/macrophages (13.7% v 2.9%) in the plaque cap. The ratio of the number of smooth muscle cells to monocytes/macrophages was 7.8 in group A plaques, 4.1 in group B plaques, and 1.0 in group C plaques. This gradient was the result of an absolute increase in monocyte/macrophages and an absolute decrease in smooth muscle cells.

CONCLUSIONS

In the aorta ulceration and thrombosis were characteristic of plaques with a high proportion of their volume occupied by extracellular lipid, and in which there was a shift toward a preponderance of monocyte/macrophages compared with smooth muscle cells in the cap.

PADGEM/GMP-140 expression on platelet membranes from homozygous beta thalassaemic patients

Thromboembolic events, which are associated with significant morbidity and mortality, occur in beta-thalassaemia. We studied the expression of the platelet selectin PADGEM/GMP-140 on intact cells from thalassaemic patients, as a marker of in vivo platelet activation. The mean of positive cells (%) was 38.143 +/- 20.65 in the patients versus 5.048 +/- 1.8 in the controls, n = 21, P < 0.001. No correlation was found between GMP-140 expression and splenectomy, platelet counts, plasma ferritin and natural coagulation inhibitors. Instead an indirect correlation was found between GMP-140 expression and HDL-cholesterol. Moreover platelet activation was directly correlated with pre-beta lipoproteins. Our data indicate that thalassaemic patients present an in vivo platelet activation, which possibly depends on the dyslipidaemia, which is now regarded as a frequent feature of this disease.

Natural history of coronary atherosclerosis using quantitative angiography in men, and implications for clinical trials of coronary regression. The Harvard Atherosclerosis Reversibility Project Study Group

Previous studies of the natural history of coronary disease generally relied on estimates of percent stenosis derived from visual assessment of the coronary angiogram. In a study of 26 patients, serial quantitative angiography was performed 3 years apart to determine changes in both absolute measurements of the luminal diameter and relative percent stenosis. Initially, the mean minimal diameter of 74 coronary obstructions was 1.94 +/- 0.09 mm, the mean "normal" reference diameter was 3.06 +/- 0.11 mm, and the mean percent stenosis was 37%. At follow-up, there was a mild reduction of 0.12 +/- 0.04 mm (6%) in the minimal diameter (p < 0.005), and an increase in percent stenosis to 39% (p = 0.03). The average diameter of 85 arterial segments without a focal obstruction either initially or at follow-up showed mild but significant progression (-0.11 +/- 0.04 mm; p = 0.02). Using a minimal change of 0.27 mm in arterial diameter as a categoric variable, progression occurred in 26% of 74 arterial segments, no significant change in 65%, and regression in 9%. The only significant determinant of disease progression was the initial severity of disease. Obstructed arteries with a larger initial minimal diameter and presumably milder disease progressed more rapidly than did those with a smaller diameter (r = -0.42; p = 0.0002). There was no effect of age on the rate of progression (r = 0.02; p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium-channel antagonists for prevention of atherosclerosis

OBJECTIVE

To critically evaluate the current literature regarding the role of calcium-channel antagonists in preventing atherosclerosis.

DATA SOURCES

English language clinical studies, abstracts, conference proceedings, and review articles pertaining to calcium-channel antagonists and atherosclerosis.

STUDY SELECTION

Relevant animal and human studies examining the role of calcium-channel antagonists in atherosclerosis prevention and treatment.

DATA EXTRACTION

Potential mechanisms for the development of atherosclerosis and the use of calcium antagonists for preventing and treating coronary artery disease are discussed. Animal studies are summarized; next, significant data from human clinical studies are presented.

DATA SYNTHESIS

Available studies are described and discussed.

CONCLUSIONS

Results from animal and clinical trials in humans suggest that calcium antagonists may retard the development and progression of atherosclerosis. However, most clinical trials to date have been conducted in patients with proven atherosclerotic plaques. Further studies examining the role of calcium-channel antagonists in preventing and treating atherosclerosis are needed, but may be difficult to conduct because of the large numbers of patients required, long trial duration, and associated costs.

Angioscopy, coronary thrombi and acute coronary syndromes

Coronary angioscopy is a new diagnostic imaging technique in which optic fibres are used to directly observe the intracoronary lumen. Angioscopy provides a full colour, high resolution, three-dimensional image of the intracoronary artery surface morphology. Studies using angioscopy revealed that the frequency of coronary thrombi in patients with acute coronary syndromes was higher than previous studies, based on arteriography, had reported. Arteriographic recognition of thrombus in unstable angina was from 1.3% to 52%. On the other hand, thrombi were observed in 88% by angioscopy in patients with rest angina in our study. Whereas ordinary arteriography provides only two-dimensional black and white images, angioscopy can distinguish between a thrombus and a plaque, even if the clot is very small. In a study of 17 unstable angina and 22 myocardial infarction patients, the frequencies of coronary thrombi in the two groups were essentially the same. Grayish-white thrombi were observed in most of the unstable angina patients but in none of the infarction patients. On the other hand, red or mixed red and white thrombi were observed in all infarction patients but in only a few unstable angina patients. This difference may account for the contrasting results of thrombolytic therapy.

Atherosclerosis: what is it and why does it occur?

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The prognostic value, clinical, and angiographic characteristics of patients with early postinfarction angina after a first myocardial infarction

To evaluate the prognostic value of early postinfarction angina and its relationship to clinical and angiographic variables, 231 consecutive patients who had a first myocardial infarction were studied. All underwent cardiac catheterization within 10 weeks after admission to the hospital. There were no differences in basic characteristics or in ejection fraction, extent or severity of coronary artery disease, or collateral circulation between the patients with early postinfarction angina (n = 27) and those without early postinfarction angina (n = 204) except for the incidence of angina before myocardial infarction. Patients with early postinfarction angina had exercise-induced angina (42% vs 21%; p < 0.025) more frequently and shorter exercise duration (6.9 +/- 2.5 minutes vs 8.3 +/- 2.5 minutes; p = 0.007). Early postinfarction angina was associated with a significantly higher event rate (15% vs 4%; p < 0.025) and a significantly higher mortality rate (15% vs 3%; p < 0.005) in the first year after infarction but not during the subsequent 4-year follow-up. In patients with early postinfarction angina, stress test results had no predictive value for future cardiac events in contrast to patients without early postinfarction angina in whom ST-segment depression as observed on the stress test ECG and exercise duration had predictive value for future cardiac events. In patients with early postinfarction angina there was no relationship between the incidence of events and the number of diseased vessels in contrast to patients without early postinfarction angina who had a high incidence of events when three-vessel disease was present (16% vs 62%; p < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of unstable angina pectoris

Unstable angina pectoris may be manifested as new-onset angina, a change in the anginal pattern, pain at rest with associated electrocardiographic (ECG) changes, or postinfarction angina. Of these, pain at rest with ischemic ECG changes is known to be associated with the poorest prognosis. The pathogenesis of unstable angina pectoris involves a combination of a fixed atherosclerotic obstruction and a dynamic component related to coronary vasoconstriction, thrombus formation, or both. Long-acting nitrates, inhibitors of platelet aggregation, beta blockers, and calcium antagonists are among the agents that have been shown to be effective in the medical management of unstable angina. A study now in progress is evaluating the routine use of thrombolytic therapy for this indication. Although alleviation of symptoms and prevention of death and myocardial infarction are important therapeutic goals, the overall efficacy of a particular medical therapy can best be assessed by objective evaluation of its ability to control ischemia, using such techniques as exercise scintigraphy and ambulatory ECG monitoring. Cardiac catheterization and revascularization are indicated for patients with unstable angina who continue to experience symptoms or who show evidence of silent ischemia despite medical therapy. A study is under way to determine the advisability of routine revascularization of such patients. Revascularization will provide symptomatic relief in most patients with unstable angina and may prolong survival and improve left ventricular function in certain subsets.

Randomized trial of thrombolysis versus heparin in unstable angina

BACKGROUND

The clinical usefulness of intravenous thrombolytic therapy in unstable angina is currently unknown, despite the pathogenetic similarity of this entity to acute myocardial infarction, for which thrombolysis has enjoyed great success. To compare the clinical benefit of intravenous urokinase with that of conventional antithrombotic therapy in preventing the progression of unstable angina to new myocardial infarction, intractable angina, or death within the first 96 hours after hospitalization, 149 patients with unstable angina were randomized to one of two intravenous thrombolytic strategies.

METHODS AND RESULTS

Forty-nine patients received 3 million units urokinase i.v. over 90 minutes plus intravenous heparin (group A); 47 patients received unblinded 3 million units urokinase i.v. plus 325 mg aspirin p.o. daily (group B); and 53 patients received placebo thrombolytic infusion plus full-dose heparin (group C). The primary end point of this trial was 96-hour clinical status. There were no significant differences in the baseline characteristics (age, sex, previous myocardial infarction, hypertension prevalence, diabetes, tobacco use, or previous revascularization) among the three groups. Despite an excess of minor untoward reactions for the urokinase groups (chills, 26.5% and 23.4% for groups A and B versus 0% for group C; p < 0.01), there was no significant difference with respect to major bleeds (two, none, and two for groups A, B, and C, respectively; p = NS). At 96 hours after presentation, no significant difference emerged in the incidence of new cardiac events: new myocardial infarctions developed in 10.2% of group A, 6.4% of group B, and 3.8% of group C (p = NS); intractable angina occurred in 6.1% of group A, 10.6% of group B, and 9.4% of group C (p = NS). There were no deaths. All three groups encountered a similar incidence of overall cardiac events: 16.3%, 17.0%, and 13.2% for groups A, B, and C, respectively (p = NS). Although trial enrollment was to extend to 600 patients, interim analysis led to early cessation of enrollment due to a negative trend in respect to outcome after thrombolysis.

CONCLUSIONS

High-dose intravenous urokinase followed by either heparin or aspirin can be safely administered to a broad, unselected group of patients with unstable angina. However, this study suggests that no clinical advantage is conferred by urokinase, with either adjunctive antithrombotic therapy over standard heparin therapy alone, when given relatively late (mean, 8.7 hours) after admission for unstable angina. A possible detrimental effect cannot be excluded.

Deletion polymorphism in the gene for angiotensin-converting enzyme is a potent risk factor for myocardial infarction

Factors involved in the pathogenesis of atherosclerosis, thrombosis and vasoconstriction contribute to the development of coronary heart disease. In a study comparing patients after myocardial infarction with controls, we have explored a possible association between coronary heart disease and a variation found in the gene encoding angiotensin-converting enzyme (ACE). The polymorphism ACE/ID is strongly associated with the level of circulating enzyme. This enzyme plays a key role in the production of angiotensin II and in the catabolism of bradykinin, two peptides involved in the modulation of vascular tone and in the proliferation of smooth muscle cells. Here we report that the DD genotype, which is associated with higher levels of circulating ACE than the ID and II genotypes, is significantly more frequent in patients with myocardial infarction (n = 610) than in controls (n = 733) (P = 0.007), especially among subjects with low body-mass index and low plasma levels of ApoB (P < 0.0001). The ACE/ID polymorphism seems to be a potent risk factor of coronary heart disease in subjects formerly considered to be at low risk according to common criteria.