Antithrombotic properties of transdermal nitroglycerin in stable angina pectoris

Antianginal Therapy for Stable Ischemic Heart Disease

Chronic angina pectoris is associated with considerable morbidity and mortality, especially if treated suboptimally. For many patients, aggressive pharmacologic intervention is necessary in order to alleviate anginal symptoms. The optimal treatment of stable ischemic heart disease (SIHD) should be the prevention of angina and ischemia, with the goal of maximizing both quality and quantity of life. In addition to effective risk factor modification with lifestyle changes, intensive pharmacologic secondary prevention is the therapeutic cornerstone in managing patients with SIHD. Current guidelines recommend a multifaceted therapeutic approach with β-blockers as first-line treatment. Another important pharmacologic intervention for managing SIHD is nitrates. Nitrates can provide both relief of acute angina and can be used prophylactically before exposure to known triggers of myocardial ischemia to prevent angina. Additional therapeutic options include calcium channel blockers and ranolazine, an inhibitor of the late inward sodium current, that can be used alone or in addition to nitrates or β-blockers when these agents fail to alleviate symptoms. Ranolazine appears to be particularly effective for patients with microvascular angina and endothelial dysfunction. In addition, certain antianginal therapies are approved in Europe and have been shown to improve symptoms, including ivabradine, nicorandil, and trimetazidine; however, these have yet to be approved in the United States. Ultimately, there are several different medications available to the physician for managing the patient with SIHD having chronic angina, when either used alone or in combination. The purpose of this review is to highlight the most important therapeutic approaches to optimizing contemporary treatment in response to individual patient needs.

Stable Ischemic Heart Disease

Classical angina refers to typical substernal discomfort triggered by effort or emotions, relieved with rest or nitroglycerin. The well-accepted pathogenesis is an imbalance between oxygen supply and demand. Goals in therapy are improvement in quality of life by limiting the number and severity of attacks, protection against future lethal events, and measures to lower the burden of risk factors to slow disease progression. New pathophysiological data, drugs, as well as conceptual and technological advances have improved patient care over the past decade. Behavioral changes to improve diets, increase physical activity, and encourage adherence to cardiac rehabilitation programs, are difficult to achieve but are effective.

Concomitant nitrates enhance clopidogrel response during dual anti-platelet therapy

BACKGROUND

Despite advances in modern anti-platelet strategies, clopidogrel still remains the cornerstone of dual anti-platelet therapy (DAPT) in patients undergoing percutaneous coronary interventions (PCI). There is some inconclusive evidence that response after clopidogrel may be impacted by concomitant medications, potentially affecting clinical outcomes. Sustained released nitrates (SRN) are commonly used together with clopidogrel in post-PCI setting for mild vasodilatation and nitric oxide-induced platelet inhibition.

METHODS

We prospectively enrolled 458 patients (64.5 ± 9.6 years old, and 73.4% males) following PCI undergoing DAPT with clopidogrel and aspirin. Platelet reactivity was assessed by the VerifyNow™ P2Y12 assay at the maintenance outpatient setting.

RESULTS

Concomitant SRN (n=266) significantly (p=0.008) enhanced platelet inhibition after DAPT (251.6 ± 80.9PRU) when compared (232.1 ± 73.5PRU) to the SRN-free (n=192) patients. Multivariate logistic regression analysis with the cut-off value of 253 PRU for defining heightened platelet reactivity confirmed independent correlation of more potent platelet inhibition during DAPT and use of SRN (Relative risk=1.675; Odds ratio [1.059-2.648]; p=0.027). In contrast, statins, calcium-channel blockers, beta blockers, angiotensin receptor blockers, ACE-inhibitors, diuretics, and anti-diabetic agents did not significantly impact platelet inhibition following DAPT.

CONCLUSION

The synergic ability of SRN to enhance response during DAPT may have important clinical implications with regard to better cardiovascular protection, but extra bleeding risks, requiring further confirmation in a large randomized study.

Stable ischemic heart disease

Classical angina refers to typical substernal discomfort triggered by effort or emotions, relieved with rest or nitroglycerin. The well-accepted pathogenesis is an imbalance between oxygen supply and demand. Goals in therapy are improvement in quality of life by limiting the number and severity of attacks, protection against future lethal events, and measures to lower the burden of risk factors to slow disease progression. New pathophysiological data, drugs, as well as conceptual and technological advances have improved patient care over the past decade. Behavioral changes to improve diets, increase physical activity, and encourage adherence to cardiac rehabilitation programs, are difficult to achieve but are effective.

Nitroglycerin and sodium nitroprusside: potential contributors to postoperative bleeding?

Postoperative bleeding is common in patients undergoing cardiac surgery with cardiopulmonary bypass. Most cases of severe postoperative bleeding not due to incomplete surgical hemostasis are related to acquired transient platelet dysfunction mediated by platelet activation during contact with the synthetic surfaces of the cardiopulmonary bypass equipment. Antihypertensive agents nitroglycerin and sodium nitroprusside have been shown to have platelet inhibitory properties, yet the clinical consequence in terms of postoperative bleeding has been little studied. Knowing that cardiopulmonary bypass causes platelet dysfunction, it is prudent for physicians to be aware of the additional platelet inhibition caused by these commonly used antihypertensive agents.

Recent advances in the management of chronic stable angina II. Anti-ischemic therapy, options for refractory angina, risk factor reduction, and revascularization

The objectives in treating angina are relief of pain and prevention of disease progression through risk reduction. Mechanisms, indications, clinical forms, doses, and side effects of the traditional antianginal agents - nitrates, β-blockers, and calcium channel blockers - are reviewed. A number of patients have contraindications or remain unrelieved from anginal discomfort with these drugs. Among newer alternatives, ranolazine, recently approved in the United States, indirectly prevents the intracellular calcium overload involved in cardiac ischemia and is a welcome addition to available treatments. None, however, are disease-modifying agents. Two options for refractory angina, enhanced external counterpulsation and spinal cord stimulation (SCS), are presented in detail. They are both well-studied and are effective means of treating at least some patients with this perplexing form of angina. Traditional modifiable risk factors for coronary artery disease (CAD) - smoking, hypertension, dyslipidemia, diabetes, and obesity - account for most of the population-attributable risk. Individual therapy of high-risk patients differs from population-wide efforts to prevent risk factors from appearing or reducing their severity, in order to lower the national burden of disease. Current American College of Cardiology/American Heart Association guidelines to lower risk in patients with chronic angina are reviewed. The Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation (COURAGE) trial showed that in patients with stable angina, optimal medical therapy alone and percutaneous coronary intervention (PCI) with medical therapy were equal in preventing myocardial infarction and death. The integration of COURAGE results into current practice is discussed. For patients who are unstable, with very high risk, with left main coronary artery lesions, in whom medical therapy fails, and in those with acute coronary syndromes, PCI is indicated. Asymptomatic patients with CAD and those with stable angina may defer intervention without additional risk to see if they will improve on optimum medical therapy. For many patients, coronary artery bypass surgery offers the best opportunity for relieving angina, reducing the need for additional revascularization procedures and improving survival. Optimal medical therapy, percutaneous coronary intervention, and surgery are not competing therapies, but are complementary and form a continuum, each filling an important evidence-based need in modern comprehensive management.

Attenuated severity of new acute ischemic events in patients with previous coronary heart disease receiving long-acting nitrates

BACKGROUND

Platelet aggregation and secondary vasoconstriction are key events in the genesis of acute coronary syndromes.

HYPOTHESIS

Since nitrates have vasodilatory and antiaggregant effects, treatment with long-acting nitrates at the time of onset of acute coronary syndromes could be associated with attenuation of their severity.

METHODS

A consecutive series of 533 patients with acute coronary syndrome and past history of coronary artery disease admitted to the Cardiology Service of a general hospital was studied. A specific questionnaire assessed the use of nitrates and other relevant drugs, as well as other clinical variables. The diagnosis of unstable angina or acute myocardial infarction (MI) was established according to clinical, electrocardiographic, and enzymatic criteria.

RESULTS

In the whole cohort, 169 patients had MI and 364 had unstable angina. Previous use of long-acting nitrates was significantly more common in patients with unstable angina (56%) than in those with MI (37%) (p < 0.0001). Multivariate analysis identified being a nonsmoker [odds ratio: 95%, confidence limits (CL) 0.37, 0.23-0.59], previous unstable angina (CL 0.62, 0.41-0.92), use of aspirin (CL 0.58, 0.41-0.92), and use of long-acting nitrates (CL 0.61, 0.40-0.93) as the independent predictors of the development of unstable angina rather than MI; of these the combination of nitrates and aspirin was the strongest predictor.

CONCLUSIONS

Long-acting nitrates as well as aspirin are suggested to have a protective or modifying effect on the development of acute coronary syndromes, favoring unstable angina rather than acute MI.

Ivabradine: the evidence of its therapeutic impact in angina

INTRODUCTION

Stable angina pectoris (SAP) is a widely prevalent disease affecting 30 000 to 40 000 per million people in Europe and the US. SAP is associated with reductions in quality of life and ability to work, and increased use of healthcare resources. Ivabradine is a drug with a unique therapeutic target, the I(f) current of the sinus node, developed for the treatment of cardiovascular diseases including SAP. It has an exclusive heart rate reducing effect, without any negative effect on left ventricular function or coronary vasodilatation.

AIMS

The aim of this paper is to review the evidence concerning the use of ivabradine in the treatment of SAP.

EVIDENCE REVIEW

Ivabradine is an effective antianginal and antiischemic drug, not inferior to the beta blocker atenolol and the calcium channel antagonist (CCA) amlodipine. It decreases the frequency of angina attacks and increases the time to anginal symptoms during exercise. Because of its exclusive chronotropic effect, ivabradine is not associated with the typical adverse reactions associated with beta blockers or other antianginal drugs.

CLINICAL VALUE

Clinical evidence shows that ivabradine is a very good antiischemic and antianginal agent, being as effective as beta blockade and CCA therapy in controlling myocardial ischemia and symptoms of stable angina. Ongoing studies will determine the potential of ivabradine to improve morbidity and mortality in coronary artery disease and heart failure.

Pharmacological modulation of platelet function in hypertension

Platelets exert a considerable influence on human morbidity and mortality. The rationale for their study in hypertension follows the observation that the major consequences of hypertension are stroke and myocardial infarction. However, the etiology of these consequences in hypertension is, paradoxically, not hemorrhagic (as might be expected from the effects of high blood pressure), but occlusive, with thrombus being the culprit lesion. Mechanisms of platelet activation include high shear force, activation of the renin-angiotensin system, endothelial changes, and the presence of comorbidity, such as atrial fibrillation. The treatment of high blood pressure brings about a reversal of the changes seen in the cell. This could be in part due to the direct effect of the drug on the megakaryocyte and/or the platelets themselves, or it might simply be due to the reduction in blood pressure. Some drugs, such as calcium channel antagonists and angiotensin II receptor blockers, however, might have direct effects on platelet biochemistry other than reducing blood pressure. Finally, antiplatelet drugs are becoming an important part of the management of high-risk hypertensives, which aim to minimize vascular complications.

Acute and delayed antithrombotic effects of alcohol in humans

Alcohol intake, especially in the form of red wine, has been shown to inhibit platelet function. However, whether alcohol in spirits may inhibit platelet-dependent thrombosis in humans up to 6 hours after ingestion is unknown and was assessed in this study. Platelet thrombus that is formed on exposure of an aortic media (simulating deep arterial injury or plaque rupture) to flowing blood was assessed in an ex vivo Badimon's superfusion chamber at shear rates of 754 or 2,546 seconds(-1) (simulating flow in normal or stenosed arteries). Twelve healthy subjects were studied before and at 20 minutes and 6 hours after consumption of 2 ounces of 40% alcohol. Blood alcohol level was 1.1+/-0. 1, 8.2+/-0.7, and 1.3+/-0.2 mmol/L at baseline, 20 minutes and 6 hours, respectively, after alcohol consumption (analysis of variance [ANOVA] p = 0.0001). Compared with baseline, platelet thrombus formation at the low shear rate flow was significantly decreased by 57% and 61% at 20 minutes and 6 hours, respectively, after alcohol intake (ANOVA p = 0.0001). Platelet thrombus deposition at the high shear rate was similarly inhibited to 68% and 64% of baseline values at 20 minutes and 6 hours, respectively (ANOVA p = 0.003). Men and women showed equal benefit. Thus, moderate alcohol intake in humans significantly inhibited platelet thrombus deposition under low and high shear rates of arterial flow conditions. This antithrombotic effect of a single alcohol drink, persisting for 6 hours and even after blood alcohol level has returned to baseline, may be clinically relevant to the cardioprotective effects of alcohol in men and women.

Nitroglycerin rebound associated with vascular, rather than platelet, hypersensitivity

OBJECTIVES

The purpose of this study was to determine whether acute withdrawal of nitroglycerin (NTG) during hemodynamic tolerance is associated with platelet hypersensitivity.

BACKGROUND

Nitroglycerin is an effective antianginal medication but its use is limited by the development of tolerance and rebound. We have previously demonstrated a sustained inhibition of platelet function during continued use of NTG, but whether cessation of NTG is associated with an increase in platelet function that may contribute to rebound is unknown.

METHODS

Normal porcine aortic media were exposed to flowing arterial blood from pigs (n = 8) treated continuously with NTG patches (Nitrodur 0.8 mg/h) for 48 h. Platelet function, blood pressure and the responses to angiotensin II infusion were evaluated before, during and after NTG treatment.

RESULTS

Mean arterial pressure fell by 15% after 3 h of treatment compared with control, returned to baseline by 48 h and increased significantly 2 h after drug removal. Autologous 51Cr-labelled platelet deposition on the aortic media was reduced by 30% after 48 h of continuous NTG administration compared with baseline (p = 0.02) and remained decreased 2 h after cessation of NTG therapy. Platelet aggregation to thrombin decreased in parallel to the decrease in platelet deposition. Blood pressure increase after intravenous injection of 10 microg of angiotensin II was blunted during treatment with NTG but increased significantly 2 h after cessation of nitrate therapy when compared with baseline.

CONCLUSIONS

Supersensitivity of the vessel wall to vasoconstrictors such as angiotensin 11, but not platelet hyperactivity, may contribute to the rebound phenomenon after acute nitrate withdrawal.

A perspective on the potential problems with aspirin as an antithrombotic agent: a comparison of studies in an animal model with clinical trials

Aspirin is the most widely prescribed agent to reduce the platelet-mediated contributions to atherosclerosis, coronary thrombosis and restenosis after angioplasty. While aspirin treatment has led to significant reductions in morbidity and mortality in many clinical trials, there are several scenarios in which aspirin may fail to provide a full antithrombotic benefit. The cyclic flow model of experimental coronary thrombosis suggests that elevations of plasma catecholamines, high shear forces acting on the platelets in the stenosed lumen and the presence of multiple, input stimuli can activate platelets through different mechanisms that may lead to thrombosis despite aspirin therapy. Aspirin therapy is limited because it only blocks some of the input stimuli, leaving aspirin-independent pathways through which coronary thrombosis can be precipitated. These include thrombin and thrombogenic arterial wall substrates such as tissue factor. New agents that block the adenosine diphosphate (ADP) receptor, or regulate platelet free cytosolic calcium, such as direct nitric oxide donors, may be more potent overall than aspirin. Agents that block the platelet integrin GPIIb-IIIa receptor inhibit the binding of fibrinogen to platelets regardless of which input stimuli activate the platelet and, thus, as demonstrated in the cyclic flow model, would be much more potent than aspirin as an antithrombotic agent. The cyclic flow model has been useful in predicting which agents are likely to be of benefit in clinical trials.

Contribution of vascular tissue to the antiplatelet activity of sodium nitroprusside

We tested whether or not platelet inhibition by sodium nitroprusside (SNP) was enhanced by vascular tissue production of nitric oxide (NO) and calcitonin gene-related peptide (CGRP) release. Platelet aggregation was determined with whole blood impedance aggregometry after incubations of SNP in the presence or absence of rat aortic tissue (AT) or AT + CGRPS(8-37) (a specific CGRP antagonist). SNP alone had no effect on platelet aggregation until 100 microM was used (2.3 + 1.5 omega vs. control aggregation of 9.9 +/- 2.0 omega; p < 0.001). Co-incubation of AT with SNP significantly enhanced platelet inhibition at 1 (1.6 +/- 1.3 omega; p < 0.001), 10 (0.7 +/- 0.4 omega; p < 0.001), and 100 microM (0.3 +/- 0.3 omega; p < 0.001). CGRP(8-37) did not significantly antagonize aggregation by SNP + AT (p > 0.05). The inhibition of platelet aggregation by 10 microM SNP was inhibited by methylene blue (MB) (9.0 +/- 1.7 omega at 10 microM; 11.7 +/- 2.4 omega at 100 microM; p < 0.001) but not by 30 microM L-N(upsilon)-monomethyl-L-arginine (L-NMMA; 2.9 +/- 1.8 omega; p > 0.05). These results indicate that vascular tissue significantly contributes to the ability of SNP to inhibit platelet aggregation, probably through greater vascular enzymatic production of NO, but not by releasing CGRP, in contrast to nitroglycerin.

Persistent inhibition of platelets during continuous nitroglycerin therapy despite hemodynamic tolerance

BACKGROUND

Nitroglycerin has been shown to possess antiplatelet properties in both animals and humans. Tolerance to the hemodynamic effects of nitroglycerin develops with continuous therapy, but it is unclear whether there is tolerance to its antiplatelet effect.

METHODS AND RESULTS

Tolerance to nitroglycerin was studied by exposing porcine aortic media to flowing arterial blood from control pigs (n = 9) or pigs treated with continuous nitroglycerin patches (Nitro-dur, 0.8 mg/h; n = 11) at a shear rate of 3397 s-1 for 3 minutes. Relative to baseline, mean arterial pressure fell by approximately 10% at 3 and 24 hours (P < .05) but returned to baseline at 48 hours of continuous nitroglycerin treatment, whereas no significant changes were observed in control animals. Autologous 51Cr-labeled platelet deposition (x 10(6)/cm2) on the aortic media at baseline and 3, 24, and 48 hours remained stable in control animals, with mean values of 94.8 +/- 5.9, 89.4 +/- 8.3, 89.3 +/- 8.8, and 84.3 +/- 5.7, respectively. However, in pigs treated continuously with nitroglycerin for 48 hours, platelet deposition was reduced significantly at 3 (65.9 +/- 4.8), 24 (63.8 +/- 6.4), and 48 hours (56.5 +/- 7.3) of nitroglycerin treatment compared with baseline (93.1 +/- 3.6). Platelet aggregation induced by thrombin also decreased at 3 (12.4 +/- 1.3), 24 (12.6 +/- 1.7), and 48 hours (10.8 +/- 1.6) of nitroglycerin treatment compared with baseline (16.3 +/- 1.4) but remained unchanged in the control group. Also, nitroglycerin treatment increased intraplatelet cGMP at 3, 24, and 48 hours compared with baseline.

CONCLUSIONS

This study demonstrates the persistent inhibition of platelet function and platelet deposition on an injured arterial wall by continuous nitroglycerin therapy despite hemodynamic tolerance.

Hyperlipidemia and coronary disease. Correction of the increased thrombogenic potential with cholesterol reduction

BACKGROUND

Hypercholesterolemia is a risk factor for coronary disease, and platelet reactivity is increased with hypercholesterolemia, suggesting a prethrombotic risk. The aim of this study was to measure mural platelet thrombus formation on an injured arterial wall in a model simulating vessel stenosis and plaque rupture in hypercholesterolemic coronary disease patients before and after cholesterol reduction.

METHODS AND RESULTS

Thirty-two patients with stable coronary disease were studied. Platelet thrombus formation and serum lipids were measured in 16 hypercholesterolemic patients (cholesterol > 5.2 mmol/L) before and after a mean of 2.5 months of pravastatin therapy (40 mg/d) and in 16 normocholesterolemic control patients. Thrombus formation was assessed by exposing porcine aortic media to the patient's flowing venous blood for 3 minutes at a shear rate of 754 or 2546 s-1 at 37 degrees C in an ex vivo superfusion chamber. Quantitative morphometric platelet thrombus formation at baseline was higher in the hypercholesterolemic patients at both the high and low shear rates: 4.8 +/- 1.0 and 3.3 +/- 0.7 micron 2/mm, respectively, compared with normocholesterolemic patients: 2.1 +/- 0.5 and 1.6 +/- 0.4 micron 2/mm (both P < .05). In the hypercholesterolemic patients, pravastatin decreased total cholesterol from 6.5 +/- 0.2 to 4.5 +/- 0.2 mmol/L and LDL cholesterol from 4.5 +/- 0.2 to 2.8 +/- 0.1 mmol/L (both P < .05). Platelet thrombus formation at high and low shear rates decreased to 2.0 +/- 0.3 and 1.3 +/- 0.3 micron 2/mm, respectively (both P < .05).

CONCLUSIONS

Thus, hypercholesterolemia is associated with an enhanced platelet thrombus formation on an injured artery, increasing the propensity for acute thrombosis. Platelet thrombus formation at both high and low shear rates decreased as total and LDL cholesterol levels were reduced with pravastatin. Cholesterol lowering may therefore reduce the risk of acute coronary events in part by reducing the thrombogenic risk.

Cigarette smoking acutely increases platelet thrombus formation in patients with coronary artery disease taking aspirin

BACKGROUND

Smoking is associated with an increased risk of myocardial infarction and sudden death. Platelet activation and thrombosis at sites of vessel stenosis and injury or plaque disruption play a crucial role in these acute coronary events. Thus, the aim of this study was to determine whether cigarette smoking acutely increases platelet thrombus formation on an injured arterial surface at local shear rates typical of a stenotic artery.

METHODS AND RESULTS

Twelve habitual smokers with stable coronary disease, on aspirin 325 mg/d, were studied immediately before and 5 minutes after smoking two cigarettes each. Ex vivo platelet thrombus formation on porcine arterial media (simulating deep arterial injury) was measured after exposure to the patient's circulating venous blood for 3 minutes in cylindrical flow chambers at 37 degrees C. The flow chambers were designed to produce shear rates of 754 or 2546 s-1, the latter being typical of the high shear rates produced by vessel stenosis. Plasma catecholamine, thromboxane B2, and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) levels and whole blood platelet aggregation responses to thrombin were also measured before and after smoking. Compared with before smoking, morphometrically measured platelet thrombus formation on arterial media at shear rates of 754 and 2546 s-1 increased by an average of 48% (P = .19) and 64% (P = .014), respectively, after smoking. Plasma epinephrine increased by more than twofold after smoking (P = .026). Plasma thromboxane B2 and 6-keto-PGF1 alpha levels did not change. Smoking also increased whole blood platelet aggregation to thrombin (P < or = .05).

CONCLUSIONS

These results suggest that smoking-enhanced platelet thrombosis may be an important contributory mechanism for acute coronary events in smokers that is not prevented by aspirin treatment. Catecholamine release and heightened platelet aggregation response to in vivo agonists may contribute to the prothrombotic effects of smoking.