Prompt improvement of left ventricular function and preservation of topography with combined reperfusion and intravenous nitroglycerin in acute myocardial infarction

Postconditioning with Nitrates Protects Against Myocardial Reperfusion Injury: A New Use for an Old Pharmacological Agent

Early reperfusion remains the key therapy to salvage viable myocardium and must be applied as soon as possible following an acute myocardial infarction (AMI) to attenuate the ischemic insult. However, reperfusion injury may develop following reintroduction of blood and oxygen to vulnerable myocytes, which results in more severe cell death than in the preceding ischemic episode. Ischemic postconditioning (I-PostC) provides a cardioprotective effect in combination with pharmacological agents. Although nitrates have been tested in many experimental and clinical studies of acute AMI to evaluate the cardioprotective effect, few investigations have been focused on nitrates postconditioning in patients undergoing percutaneous coronary intervention (PCI). This review presents the manifestations of myocardial reperfusion injury (RI) and potential mechanisms underlying it, and provides the mechanisms involved in the cardioprotection of I-PostC. We also present a new therapeutic approach to attenuate RI by use of an ‘old’ agent – nitrates – in AMI patients.

Challenges with nitrate therapy and nitrate tolerance: prevalence, prevention, and clinical relevance

Nitrate therapy has been an effective treatment for ischemic heart disease for over 100 years. The anti-ischemic and exercise-promoting benefits of sublingually administered nitrates are well established. Nitroglycerin is indicated for the relief of an established attack of angina and for prophylactic use, but its effects are short lived. In an effort to increase the duration of beneficial effects, long-acting orally administered and topical applications of nitrates have been developed; however, following their continued or frequent daily use, patients soon develop tolerance to these long-acting nitrate preparations. Once tolerance develops, patients begin losing the protective effects of the long-acting nitrate therapy. By providing a nitrate-free interval, or declining nitrate levels at night, one can overcome or reduce the development of tolerance, but cannot provide 24-h anti-anginal and anti-ischemic protection. In addition, patients may be vulnerable to occurrence of rebound angina and myocardial ischemia during periods of absent nitrate levels at night and early hours of the morning, and worsening of exercise capacity prior to the morning dose of the medication. This has been a concern with nitroglycerin patches but not with oral formulations of isosorbide-5 mononitrates, and has not been adequately studied with isosorbide dinitrate. This paper describes problems associated with nitrate tolerance, reviews mechanisms by which nitrate tolerance and loss of efficacy develop, and presents strategies to avoid nitrate tolerance and maintain efficacy when using long-acting nitrate formulations.

Nitric oxide donor agents for the treatment of ischemia/reperfusion injury in human subjects: a systematic review

In animal models, administration of nitric oxide (NO) donor agents has been shown to reduce ischemia/reperfusion (I/R) injury. Our aim was to systematically analyze the biomedical literature to determine the effects of NO-donor agent administration on I/R injury in human subjects. We hypothesized that NO-donor agents reduce I/R injury. We performed a search of Cochrane Library, PubMed, CINAHL, conference proceedings, and other sources with no restriction to language using a comprehensive strategy. Study inclusion criteria were as follows: (a) human subjects, (b) documented periods of ischemia and reperfusion, (c) treatment arm composed of NO-donor agent administration, and (d) use of a control arm. We excluded secondary reports, reviews, correspondence, and editorials. We performed a qualitative analysis to collate and summarize treatment effects according to the recommended methodology from the Cochrane Handbook. Twenty-six studies involving multiple etiologies of I/R injury (10 cardiopulmonary bypass, six organ transplant, seven myocardial infarction, three limb tourniquet) met all inclusion and no exclusion criteria. Six (23%) of 26 were considered high-quality studies as per the Cochrane criteria for assessing risk of bias. In 20 (77%) of 26 studies and four (67%) of six high-quality studies, patients treated with NO-donor agents experienced reduced I/R injury compared with controls. Zero clinical studies to date have tested NO-donor agent administration in patients with cerebral I/R injury (e.g., cardiac arrest, stroke). Despite a paucity of high-quality clinical investigations, the preponderance of evidence to date suggests that administration of NO-donor agents may be an effective treatment for I/R injury in human subjects.

Nitric oxide and cardiovascular protection

Nitric oxide (NO) plays a critical role in ischemic heart disease and ischemia-reperfusion. There is an increasing body of evidence to support the role of NO in myocardial and vascular protection in disease. The finding that NO might act as a trigger of late ischemic preconditioning (IPC) might lead to the development of novel anti-ischemic therapy. The role of NO signaling in the cardioprotective effects of ACE inhibitors and angiotensin II type 1 receptor(AT(1)) receptor antagonists is an active area of study.

Nitric oxide and cardioprotection during ischemia-reperfusion

Coronary artery reperfusion is widely used to restore blood flow in acute myocardial infarction and limit its progression. However, reperfusion of ischemic myocardium results in reperfusion injury and persistent ventricular dysfunction even when achieved after brief periods of ischemia. Normally, small amounts of nitric oxide (NO) generated by endothelial NO synthase (eNOS) regulates vascular tone. Ischemia-reperfusion triggers the release of oxygen free radicals (OFRs) and a cascade involving endothelial dysfunction, decreased eNOS and NO, neutrophil activation, increased cytokines and more OFRs, increased inducible NO synthase (iNOS) and marked increase in NO, excess peroxynitrite formation, and myocardial injury. Low doses of NO appear to be beneficial and high doses harmful in ischemia-reperfusion. eNOS knock-out mice confirm that eNOS-derived NO is cardioprotective in ischemia-reperfusion. iNOS overexpression increases peroxynitrite but did not cause severe dysfunction. Increased angiotensin II (AngII) after ischemia-reperfusion inactivates NO, forms peroxynitrite and produces cardiotoxic effects. Beneficial effects of angiotensin-converting-enzyme inhibition and AngII type 1 (AT(1)) receptor blockade after ischemia-reperfusion are partly mediated through AngII type 2 (AT(2)) receptor stimulation, increased bradykinin and NO. Interventions that enhance NO availability by increasing eNOS might be beneficial after ischemia-reperfusion.

Beneficial effects of therapy on the progression of structural remodeling during healing after reperfused and nonreperfused myocardial infarction: different effects on different parameters

BACKGROUND

Structural left ventricular remodeling after myocardial infarction is a complex process with several pathophysiologic descriptors that can be modified by pharmacotherapy. However, the possibility that different classes of antiremodeling agents might exert different effects on different remodeling parameters after reperfused and nonreperfused myocardial infarction has not been systematically studied.

METHODS AND RESULTS

We measured detailed left ventricular remodeling parameters in vivo (echocardiograms) repeatedly over 6 weeks and ex vivo (planimetry) at 6 weeks after myocardial infarction in 36 dogs randomized (factorial design) after reperfused or nonreperfused myocardial infarction to 6 weeks of twice daily oral therapy with the calcium channel blocker amlodipine (5 mg), the angiotensin-converting enzyme inhibitor enalapril (5 mg) or placebo, and 18 matching sham or control animals. Compared to placebo and control groups over 6 weeks, both agents reduced left ventricular loading and limited overall remodeling in both reperfused and nonreperfused groups, but there were pertinent differences. Enalapril limited the increase in left ventricular asynergy in the reperfused group. Both enalapril and amlodipine limited infarct zone thinning in the nonreperfused groups but increased infarct zone thinning in the reperfused groups, despite preserved infarct zone collagen with amlodipine. Enalapril decreased left ventricular diastolic volume and mass more than amlodipine in the reperfused group and increased left ventricular ejection fraction in the nonreperfused group. Both agents limited regional and global shape deformation in reperfused and non-reperfused groups. Diastolic wall stress in the infarct zone decreased with amlodipine, and increased with enalapril and reperfusion.

CONCLUSIONS

Different antiremodeling therapies may exert different effects on different remodeling parameters during healing after reperfused myocardial infarction. Significant interactions occur during reperfusion. More than one variable may be needed for the comprehensive assessment of the antiremodeling efficacy of different therapies.

A double-blind, randomized study of the effect of immediate intravenous nitroglycerin on the incidence of postprocedural chest pain and minor myocardial necrosis after elective coronary stenting

BACKGROUND

Anginal chest pain without creatine kinase (CK) elevation is frequently observed in the first hours after coronary stenting. Possible causes of ischemic episodes are microembolism, side branch occlusion, coronary vasospasm, and disturbances of microvascular circulation. In a prospective, double-blind, randomized trial, we tested the effect of intravenous nitroglycerin on the incidence of angina and minor myocardial necrosis (MMN), as detected by cardiac troponin I increase, after elective coronary stenting.

METHODS AND RESULTS

One hundred patients were randomly assigned to intravenous nitroglycerin (group A: n = 50, goal dose 100 microgram/min) or placebo (group B: n = 50, NaCl 0.9%) during 12 hours after stenting. Patients with acute myocardial infarction, known intolerance to nitrates, and hemodynamic instability during angioplasty were excluded. The 2 groups were comparable in respect to baseline and interventional variables, except for age (group A: 60 +/- 9 years, group B: 56 +/- 10 years; P =.04). The incidence of chest pain was not influenced by nitroglycerin (group A: 18%, group B: 22%; P = not significant). However, the occurrence of MMN was significantly reduced by nitroglycerin (group A: 5%, group B: 19%, P =.036). A rise in CK with significant CK-MB fraction was observed in only 2 patients in group B (both less than twice upper limit). Only 4 of the 10 patients with MMN also had chest pain.

CONCLUSIONS

Routine use of intravenous nitroglycerin after coronary stenting significantly reduced the occurrence of minor myocardial necrosis. However, the incidence of postprocedural chest pain remained unchanged.

Nitrates in myocardial infarction

Until two decades ago nitroglycerin was contraindicated in acute myocardial infarction (MI). Studies in the canine model demonstrated that low-dose intravenous (i.v.) infusion, carefully titrated to decrease mean blood pressure by 10% but not below 80 mmHg, during early stages of acute MI produced marked reduction of left ventricular (LV) preload, improvement in regional perfusion, and limitation of infarct size and remodeling. However, more i.v. nitroglycerin to decrease blood pressure further resulted in a paradoxical J-curve effect, with hypoperfusion and increased infarct size. Clinical studies have confirmed that low-dose i.v. nitroglycerin infusion for the first 48 hours after acute MI is safe, not only for improving performance in LV failure, but also for limiting ischemic injury, infarct size, remodeling, and infarct-related complications, including deaths in-hospital and up to 1 year. Recent studies suggest that more prolonged therapy with nitrates spanning the healing phase of acute anterior Q-wave MI can further limit LV remodeling and preserve function. Preliminary results of the recently completed ISIS-4 megatrial suggest, however, that long-term nitrate in patients with suspected MI in the 1990s does not improve survival significantly.