Current concepts in unstable myocardial ischemia

Co-expression analysis to identify key modules and hub genes associated with COVID-19 in platelets

Corona virus disease 2019 (COVID-19) increases the risk of cardiovascular occlusive/thrombotic events and is linked to poor outcomes. The underlying pathophysiological processes are complex, and remain poorly understood. To this end, platelets play important roles in regulating the cardiovascular system, including via contributions to coagulation and inflammation. There is ample evidence that circulating platelets are activated in COVID-19 patients, which is a primary driver of the observed thrombotic outcome. However, the comprehensive molecular basis of platelet activation in COVID-19 disease remains elusive, which warrants more investigation. Hence, we employed gene co-expression network analysis combined with pathways enrichment analysis to further investigate the aforementioned issues. Our study revealed three important gene clusters/modules that were closely related to COVID-19. These cluster of genes successfully identify COVID-19 cases, relative to healthy in a separate validation data set using machine learning, thereby validating our findings. Furthermore, enrichment analysis showed that these three modules were mostly related to platelet metabolism, protein translation, mitochondrial activity, and oxidative phosphorylation, as well as regulation of megakaryocyte differentiation, and apoptosis, suggesting a hyperactivation status of platelets in COVID-19. We identified the three hub genes from each of three key modules according to their intramodular connectivity value ranking, namely: COPE, CDC37, CAPNS1, AURKAIP1, LAMTOR2, GABARAP MT-ND1, MT-ND5, and MTRNR2L12. Collectively, our results offer a new and interesting insight into platelet involvement in COVID-19 disease at the molecular level, which might aid in defining new targets for treatment of COVID-19–induced thrombosis.

Impaired tissue responsiveness to organic nitrates and nitric oxide: a new therapeutic frontier?

Nitric oxide (NO) is a physiologically important modulator of both vasomotor tone and platelet aggregability. These effects of NO are predominantly mediated by cyclic guanosine-3,'5'-monophosphate (cGMP) via activation of soluble guanylate cyclase. However, in patients with ischemic heart disease, platelets and coronary/peripheral arteries are hyporesponsive to the antiaggregatory and vasodilator effects of NO donors. NO resistance is also associated with a number of coronary risk factors and presents in different disease states. It correlates with conventional measures of "endothelial dysfunction," and represents a multifaceted disorder, in which smooth muscle and platelet NO resistance are equally important, as sites of abnormal NO-driven physiology. NO resistance results largely from a combination of "scavenging" of NO by superoxide anion radical (O(2)(-)) and of (reversible) inactivation of soluble guanylate cyclase. It constitutes an impaired physiological response to endogenous NO (endothelium-derived relaxing factor, EDRF) and, as such, may contribute to the increased risk of ischemic events. Impairment in responsiveness to NO in ischemic patients implies a potential problem that those patients, in greatest need of nitrate therapy, may be least likely to respond. The prognostic impact of NO resistance at vascular and platelet levels has been demonstrated in patients with ischemic heart disease, and it has been shown that a number of agents (angiotensin-converting enzyme [ACE] inhibitors, perhexiline, insulin, and possibly statins) ameliorate this anomaly. The current review examines different aspects of the "NO resistance" phenomenon and discusses some related methodological issues.

Pathophysiology and therapeutic modification of thrombin generation in patients with coronary artery disease

Thrombin plays a central role in thrombogenesis: it activates platelets, converts fibrinogen to fibrin, and activates factor XIII, which then crosslinks and stabilizes the fibrin clot. In addition, thrombin amplifies coagulation by activating factors VIII and V, key cofactors in the generation of activated factor X and thrombin, respectively. Even platelet function is influenced by thrombin. Hence, thrombin generation is most important both in the chronic progression of coronary atherosclerotic disease and in its conversion to acute events. To date, various therapeutic approaches capitalize on this knowledge by targeting specific thrombin-related pathways. Among the successful and carefully documented pharmacologic strategies in acute or chronic coronary heart disease are the use of unfractioned heparin, low-molecular-weight heparin, thrombolysis, hirudin, and/or inhibition of thrombin generation by glycoprotein IIb/IIIa antagonists, most often utilized on top of antiplatelet therapy (e.g., with acetylsalicylic acid) and/or vitamin K antagonism. The present review provides insights into the pathophysiology of thrombin generation in coronary atherosclerosis and gives an overview over the above mentioned therapeutic thrombin modifications.

New frontiers in the management of unstable coronary artery disease

Thrombotic occlusion is responsible for most acute manifestations of coronary artery disease, including unstable angina and non-Q-wave myocardial infarction. Antiplatelet therapy plays a major role in reducing the risk of ischemic events in such patients. Since thrombin generation is vital to the pathogenesis of thrombosis, recent studies have focused on thrombin inhibition in the management of acute ischemia. Heparin is the most widely used anticoagulant for acute management of thrombosis and is the treatment of choice in preventing and treating venous thromboembolism. Given in therapeutic doses intravenously, it is more effective than aspirin in reducing the risk of death or myocardial infarction in patients with unstable angina. Low-molecular-weight (LMW) heparins have improved pharmacologic and pharmacokinetic properties over standard heparin that may result in greater efficacy and safety. LMW heparins may be given in a fixed dose subcutaneously without monitoring, resulting in greater clinical utility and cost-effectiveness compared with standard heparin. Given subcutaneously in fixed, weight-adjusted doses they are more effective and safer than intravenous heparin in treating deep-vein thrombosis. Several studies have evaluated LMW heparins in unstable angina. In a small open trial, LMW heparin (nadroparin) reduced the risk of acute myocardial infarction compared with aspirin alone or a combination of aspirin and standard heparin. In 2 large clinical trials, LMW heparin (dalteparin) has been shown to be effective in the management of unstable angina with a 63% reduction in risk of death or acute myocardial infarction over patients treated with aspirin alone (Fragmin during Instability in Coronary Artery Disease; FRISC) and to be as effective as intravenous heparin (Fragmin in Unstable Coronary Artery Disease; FRIC).

Suppressed anti-aggregating and cGMP-elevating effects of sodium nitroprusside in platelets from patients with stable angina pectoris

Platelet hyperactivity plays an important role in the pathogenesis of cardio-vascular diseases. In patients with stable angina pectoris, we have recently demonstrated that nitroglycerin suppressed the increased platelet aggregability. The anti-aggregating effect of NTG and other nitrovasodilators is mediated by platelet guanylate cyclase, which generates cyclic GMP (cGMP) in response to nitric oxide (NO) liberated from the nitrovasodilator molecule. In the current study we utilised a more "direct" NO donor, sodium nitroprusside (SNP), to examine reversal of ADP-induced platelet aggregation in comparison with intraplatelet cGMP elevation in platelets from normal subjects (n = 22) and patients with stable angina pectoris (n = 23). Concentrations of SNP associated with 50% reversal of aggregation were 2.7 +/- 0.4 x 10(-7) mol/L with normal subjects and 4.5 +/- 0.5 x 10(-6) mol/L with patients (P < 0.01). SNP produced a concentration-dependent elevation of intraplatelet cGMP content: with 10(-4) mol/L SNP this was 17-fold for normals and 5-fold for patients (P < 0.01). An increase in cAMP content was seen only with 10(-4) mol/L SNP, and was 157 +/- 11% of baseline in platelets from normal subjects and 138 +/- 14% in patients. There was a strong interrelationship between cGMP-stimulating and anti-aggregating effects of SNP. The decrease in cGMP responsiveness to SNP was not related to a dysfunction of platelet guanylate cyclase; neither basal nor SNP-stimulated activity of the enzyme varied significantly between normal subjects and patients. Lipophilic derivatives of cGMP (db-cGMP) and cAMP (db-cAMP) caused reversal of aggregation; there was a nonsignificant trend towards decreased responsiveness of platelets from patients to both db-cGMP and db-cAMP. The observed decrease in responsiveness of platelets from angina patients to anti-aggregating effects of the exogenous NO donor, SNP, can therefore be attributed to suppressed cGMP accumulation. These results imply reduced platelet sensitivity to endogenous NO (endothelium-derived relaxing factor): this might contribute to platelet hyperaggregability observed in angina pectoris.

Stenosis enhances role of platelets in growth of regional thrombus and intimal wall thickening in rat carotid arteries

The authors present the results of a study in which stenosis was induced, resulting in either thrombus or intimal wall thickening, in rat carotid arteries. At > or = 75% stenosis in mildly denuded arteries, an acute and occlusive thrombus formation was induced, but the thrombus was significantly reduced in thrombocytopenia. Thrombus formation near the site of stenosis decreased with decreasing degree of stenosis, whereas the percent formation in the distal region (percent total thrombus) increased. Numerous mural platelet microthrombi were noted at the distal region of the stenosed arteries. After chronic 50% stenosis of the carotid artery for 2 weeks, significant intimal thickening was observed, without any occlusive thrombus formation. The combination with mild denudation was critical in eliciting the effect of stenosis. The magnitude of intimal growth in the stenosed artery was marked by day 6 and plateaued thereafter, whereas it was slight in nonstenosed arteries. The 5-bromodeoxyuridine index of the cells of the medial layer at day 3 was significantly increased by the stenosis, and the effect was reversed in thrombocytopenia. Complete reendothelialization of the intimal surface was observed by 7 to 10 days after surgery in the stenosed arteries. These findings suggest that the introduction of stenosis in these arteries enhances the interaction of platelets with the damaged arterial walls under abnormal fluid shear and that this enhancement leads to acute and occlusive thrombus formation associated with more marked stenosis as well as to sustained increase of intimal wall thickness in less marked stenosis.

Determinants of severity of left ventricular dysfunction in Australian men and women with coronary disease aged 65 years or less

BACKGROUND

The degree of left ventricular (LV) impairment is an important determinant of long term outcome in patients with coronary artery disease (CAD).

AIM

We aimed to determine variables predictive of the severity of LV dysfunction in men and women aged 65 years or less with CAD, and to quantitate their contributions.

METHODS

We documented atherogenic variables and extent of LV impairment and CAD severity at angiography in 521 consecutively studied men and women aged 65 years or less (381 males and 140 females). We assessed severity from an LV impairment score (Green Lane) and the ejection fraction. We related severity to quantitative and categorical variables which included the severity of angina (no angina, stable and unstable angina).

RESULTS

The LV impairment score correlated closely (negatively) with the ejection fraction (r = -0.783, p = 0.0001). There were eight variables independently predictive of the severity of LV impairment assessed by the LV score. The variables in descending order of relative importance in predicting the LV scores were past history of myocardial infarction (MI), number of significantly diseased vessels (> 50% luminal obstruction), life-time smoking dose, log-triglycerides, total cholesterol to HDL-C ratio, hypertension, age and Body Mass Index (BMI). They were all positive relationships. Together they correctly classified the LV scores of 52.6% of the patients. Gender was not an independent contributor to the LV score when other variables were controlled. When the contributions to the variance in LV scores of past history of MI (15.4%) and number of significantly diseased vessels (2.6%) were controlled, life-time smoking dose independently explained 2.1% (p < 0.01) of the variance. The LV impairment score was 55% higher in heavy smokers than in non-smokers (p = 0.01). When we compared patients with stable and unstable angina, LV scores are higher and ejection fraction lower in the unstable angina patients consistent with them having a greater degree of LV dysfunction.

CONCLUSION

We conclude that variables other than a history of MI and CAD severity contribute significantly to the variance of the degree in LV impairment in CAD patients among which the life-time smoking dose, triglycerides, TC/HDL-C, hypertension and increased BMI are all relevant to prevention, and that patients with unstable vs stable angina usually have more impaired LV function.

Risk stratification by early exercise testing after an episode of unstable coronary artery disease. The RISC Study Group

After stabilization of symptoms by medication a predischarge exercise test was performed in 855 men admitted with suspected unstable angina (54%) or non-Q-wave myocardial infarction (46%). Multiple logistic regression analysis demonstrated that the number of leads with ST-depression at exercise, low maximal work load, increasing age and ST-elevation in electrocardiogram at rest had independent prognostic value concerning the risk of myocardial infarction or death during the following year. Therefore a combination of extension of ST-depression and peak work load was used to define 'high and low risk response' at the exercise test. After 1 year the mortality in patients with 'high risk' compared to 'low risk' exercise response was 3.6% and 0% (P < 0.001) and the risk of either myocardial infarction or death was 15.4% and 3.9% (P < 0.0001), respectively. ST-depression, occurrence of angina and low peak load at exercise were independent predictors of future severe angina. After 1 year 29.5% of patients with any of these indicators at exercise had incapacitating symptoms that necessitated referral for coronary angiography compared to 4.8% in the group without these findings (P < 0.0001). The predictive value of the exercise test remained high in subgroups based on inclusion diagnosis, age or findings in electrocardiogram at rest and independently of treatment with beta-blockade, other antianginal medication or aspirin at the time of the exercise test.

Cyclic flow variations in a conscious dog model of coronary artery stenosis and endothelial injury correlate with acute ischemic heart disease syndromes in humans

OBJECTIVES

The purpose of this study was to test the hypothesis that episodes of cyclic flow variations (CFVs) in conscious dogs with coronary stenoses and endothelial injury correlate with acute ischemic heart disease syndromes in humans.

BACKGROUND

Although the canine model with CFVs has proved to be a useful model of coronary thrombosis, whether CFVs progress to these syndromes has not been clearly described.

METHODS

Cyclic flow variations were produced by an external constrictor placed at the site of the left anterior descending coronary artery with injured endothelium. Blood flow in this artery and 24-h Holter electrocardiogram (ECG) were recorded during the 1st 5 postoperative days.

RESULTS

Of 41 dogs that underwent the initial operative procedure successfully, 29 developed an episode of CFVs. In five dogs in which CFVs persisted throughout the monitoring period, the left anterior descending coronary artery flow decreased until day 3 and thereafter increased through day 5. Transient coronary occlusion during CFVs induced ST segment changes that returned to baseline after reflow. In 12 dogs, CFVs progressed to persistent coronary occlusion, and histologic examination revealed thrombus formation at the stenotic site and evidence of myocardial infarction. Four of these 12 dogs died suddenly of ventricular arrhythmias during persistent coronary occlusion; another 5 dogs died of reperfusion arrhythmias during CFVs with no evidence of myocardial infarction.

CONCLUSIONS

Conscious dogs with CFVs closely correlated with clinical acute ischemic heart disease syndromes, suggesting them to be a useful model for investigating the complex mechanisms of cellular interactions in the pathogenesis of these syndromes.

Role of nitrates in unstable angina pectoris

Unstable angina pectoris is a clinically heterogeneous process with patient symptoms varying between reduced threshold for exertional angina and the occurrence of multiple episodes of rest pain. The major factors in the pathogenesis of unstable angina appear to be intracoronary platelet aggregation and thrombus formation secondary to fissuring or rupture of atheromatous plaques, with associated coronary vasoconstriction due to release of constrictor materials from aggregating platelets and deficiency of endothelium-related vasodilator activity. The latter factor is of particular interest in view of the similar biochemical mechanisms of action of nitroglycerin (NTG) and endothelium-derived relaxing factor (EDRF). The efficacy of NTG in limiting platelet aggregation is also of particular interest in this condition. Medical therapy in patients with unstable angina usually requires use of multiple agents. In the short term, there is a strong case for the use of intravenous heparin both to relieve pain and to reduce the risk of acute myocardial infarction. Aspirin is perhaps less effective in the short term, but very useful in long-term treatment of such patients. Despite their widespread clinical use, beta-adrenoceptor antagonists are probably only marginally beneficial, whereas dihydropyridine calcium antagonists such as nifedipine are potentially harmful as monotherapy and of questionable use in combination with other drugs. Other agents that are effective in relieving ischemic symptoms are the nondihydropyridine calcium antagonists verapamil and diltiazem and the oxygen-sparing agent perhexiline maleate. Despite a paucity of controlled trial data, nitrates are used in the vast majority of patients with unstable angina.

Immediate and follow-up results of the conservative coronary angioplasty strategy for unstable angina pectoris

To assess the results of a conservative coronary angioplasty strategy in unstable angina pectoris, the records of 1,421 consecutive patients without previous myocardial infarction undergoing a first percutaneous transluminal coronary angioplasty (PTCA) between 1986 and 1990 were reviewed. Of these patients, 631 had unstable and 790 had stable angina pectoris. Only after an intense effort to medically control symptoms, the unstable patients underwent PTCA at an average of 15.4 days (range 1 to 76) after hospital admission. Primary clinical success was achieved in 91.7% of patients with unstable and in 94.4% of those with stable angina pectoris (p = not significant). In-hospital mortality rates were 0.3 and 0.1%, respectively (p = not significant). Nonfatal in-hospital event rates for acute myocardial infarction, cerebrovascular accident and coronary bypass surgery were only slightly higher in patients with unstable angina pectoris; however, the difference from the stable group was significant when all events were combined (9 vs 5.9%; p less than 0.04). During 6-month follow-up, no significant difference in adverse events was found between the groups. The respective rates for the unstable and stable groups were 0.4 and 0.2% for death, 5.5 and 5.1% for major nonfatal events, and 17.7 and 20.1% for repeat PTCA. These results suggest that use of a conservative PTCA strategy in the treatment of patients with unstable angina pectoris results in favorable and similar immediate and 6-month outcomes compared with those in patients with stable angina pectoris.

Early postoperative myocardial morbidity in patients with coronary artery disease undergoing major non-cardiac surgery: correlation with perioperative ischaemia

As a part of a study assessing early postoperative myocardial morbidity in 50 patients with active coronary artery disease undergoing major non-cardiac surgery, the ECG was monitored continuously for 24 hr after the onset of anaesthesia, using a frequency modulated (FM) Holter monitor. Concurrent automated blood pressure and pulse were measured non-invasively at three-minute intervals during anaesthesia and subsequently at five-minute intervals. Thirty patients were monitored with two-site ECG recordings, from modified V1 and V5 (Group A). Twenty patients had seventeen-site ECG monitoring, multiplexing a four by four array of precordial electrodes onto one channel of the frequency modulated recorder (Group B). Tapes were analyzed for noise, supraventricular and ventricular dysrythmias, runs of tachy- and bradycardia, and ST segment changes. These data were correlated with serial standard 12-lead ECGs and CK-MB assay in the 72 hr after surgery. Seven tapes from Group A could not be analyzed. Change (greater than 1 mm) on ST monitoring from both Groups A (14/23), B (14/20), correlated with serial 12-lead ECG and/or CK-MB changes. The majority of first ST change 19/28 (70%) occurred after anaesthesia. In 14/28 (50%) ST change occurred during episodes of tachycardia and elevated blood pressure (greater than 20% above baseline). Nine patients (9/23) in Group A had no ST change; however, six had serial 12-lead ECG and/or CK-MB changes. Six patients (6/20) in Group B had no ST changes, and none of these patients had any change of serial 12-lead ECGs or CK-MB assay. No patient complained of chest pain during the Holter monitoring period. Continual monitoring of heart rate and blood pressure and accurate ST monitoring are essential to detect and treat perioperative myocardial ischemia. A multiple-lead precordial system is substantially more sensitive than traditional two-lead ECG holter monitoring in detecting myocardial ischaemia.

Platelet response to the aggregatory effect of platelet activating factor (PAF) ex vivo in patients with acute myocardial infarction

Platelets from patients with acute myocardial infarction exhibit an increased sensitivity to the aggregatory effect of PAF, in vitro, the first 48 h after the onset of the symptoms. This sensitivity, expressed as PAF EC50 values, seems to be transient after the 2 day period. Also, a remarkable decreased sensitivity to the inhibitory effect of PGI2 against the aggregation induced by PAF appears to the platelets of those patients the first hours after the onset of the symptoms, and persists for at least 14 days. Treatment of patients by drugs with a known inhibitory effect on platelet aggregation in vivo and in vitro (aspirin, nifedipine, indomethacin), does not influence the increase in platelet sensitivity to PAF, but inhibits the secondary aggregation induced by the released aggregating factors from the PAF activated platelets. The increase in platelet sensitivity to PAF is not unique to the AMI since it is also observed in patients with acute bacterial pneumonia. However, we cannot support the theory that it is a general phenomenon of acute tissue injury since it is general phenomenon of acute tissue injury since it is not observed in patients with acute muscular injury.

Thiol-containing agents in the management of unstable angina pectoris and acute myocardial infarction

The development of unstable angina pectoris and acute myocardial infarction is a process of platelet aggregation and thrombus formation associated with local coronary vasoconstriction. Regional deficiencies in endothelial vasodilator function, due to reduced formation of endothelium-derived relaxing factor (EDRF), may predispose to platelet aggregation and coronary vasoconstriction. Nitroglycerin (NTG), frequently utilized in the management of unstable angina pectoris and acute myocardial infarction, undergoes bioconversion, via a sulfhydryl-dependent process, to nitric oxide, which is identical or closely related to EDRF. Other products of the nitrate bioconversion "cascade" are various S-nitrosothiols, which, like nitric oxide, activate soluble guanylate cyclase, inducing increased formation of cyclic guanosine monophosphate. NTG potentially may act to correct a localized deficiency of EDRF effect, at both the vasculature and platelet levels. In patients with unstable angina, hemodynamic effects and therapeutic efficacy of intravenously infused NTG may be attenuated within hours. Combined therapy with NTG and intravenously infused N-acetylcysteine (NAC) results in potentiation of hemodynamic responses to NTG, markedly augments the effects of NTG on platelet aggregation, and reduces the incidence of acute myocardial infarction in patients with severe unstable angina pectoris. The combination of NTG with intermittent NAC infusion may increase the risk of hypotensive episodes in such patients, whereas continuous coinfusion of the drugs is better tolerated. The combination of NTG with thiol-containing agents, such as NAC, may be of therapeutic value in unstable angina pectoris and in evolving acute myocardial infarction. This is currently under investigation.

Gradation of unstable angina based on a sensitive immunoassay for serum creatine kinase MB

A newly developed, highly sensitive immunoassay for creatine kinase MB isoenzyme was evaluated in 68 patients with or without different types of ischaemic heart disease. Patients were classified on the basis of clinical criteria in four groups: no ischaemic heart disease, stable angina, unstable angina, and acute myocardial infarction. Enzyme concentration in patients with stable angina was the same (even during exercise) as seen in the patients without ischaemic heart disease. Patients with unstable angina, however, could be divided into two groups. One group showed clear evidence of severe myocardial ischaemia by serial changes and higher mean values of creatine kinase MB up to 40 hours after the onset of symptoms, whereas in the remainder values were stable and resembled those seen in the patients without ischaemic heart disease. The changes in concentration correlated with signs of repetitive ischaemic episodes deduced from continuous ST segment monitoring during the first 24 hours after admission. These findings indicate that patients with unstable angina are a heterogenous group. In some, severe and prolonged ischaemia can be detected by a serological assay with high sensitivity.

Risk of myocardial infarction and death during treatment with low dose aspirin and intravenous heparin in men with unstable coronary artery disease. The RISC Group

796 men with unstable coronary artery disease (unstable angina or non-Q-wave myocardial infarction [MI] ), were randomised to double-blind placebo-controlled treatment with oral aspirin 75 mg/day and/or 5 days of intermittent intravenous heparin. The risk of MI and death was reduced by aspirin. After 5 days the risk ratio was 0.43 (confidence intervals, 0.21-0.91), at 1 month 0.31 (0.18-0.53), and at 3 months 0.36 (0.23-0.57). Aspirin reduced event rate in non-Q-wave MI and unstable angina, independently of electrocardiographic abnormalities or concurrent drug therapy. Heparin had no significant influence on event rate, although the group treated with aspirin and heparin had the lowest number of events during the initial 5 days. Treatment had few side-effects and high patient compliance.

Unstable angina. Approaching treatment with a rational plan

An appreciation of the pathogenesis of unstable angina forms the basis of rational therapy. The physician's task is to quickly reduce inappropriate myocardial oxygen demands, find and treat factors causing these increased demands, increase coronary blood flow, and prevent progressive thrombosis. Once the patient is stabilized, the physician can assess the risk of myocardial infarction. High-risk patients may benefit from percutaneous transluminal coronary angioplasty or coronary bypass surgery. The question is how to best accommodate accompanying factors (eg, associated health disorders, advanced age), not whether drug therapy, interventional therapy, or coronary bypass surgery is the best method. All three methods are, at different times, necessary for optimal management of unstable angina.