Drug-induced expansion of infarct: morphologic and functional correlations

Pericardial Involvement in ST-Segment Elevation Myocardial Infarction as Detected by Cardiac MRI

Background

Post myocardial infarction pericarditis is considered relatively rare in the current reperfusion era. The true incidence of pericardial involvement may be underestimated since the diagnosis is usually based on clinical and echocardiographic parameters.

Objectives

This study aims to document the incidence, extent, and prognostic implication of pericardial involvement in ST-segment elevation myocardial infarction (PISTEMI) using cardiac MRI (CMR).

Methods

One hundred and eighty-seven consecutive ST-segment elevation myocardial infarction patients underwent CMR on day 5 ± 1 following admission, including steady-state free precession (SSFP) and late Gadolinium enhancement (LGE) sequences. Late Gadolinium enhancement and microvascular obstruction (MVO) were quantified as a percentage of left ventricular (LV) mass. Late Gadolinium enhancement was graded for transmurality according to the 17 AHA left ventricle (LV) segment model (LGE score). Late pericardial enhancement (LPE), the CMR evidence of pericardial involvement, was defined as enhanced pericardium in the LGE series and was retrospectively recorded as present or absent according to the 17 AHA segments. Late pericardial enhancement was evaluated adjacent to the LV, the right ventricle, and both atria. Clinical, laboratory, angiographic, and echocardiographic data were collected. Clinical follow-up for major adverse cardiac events (MACE) was documented and correlated with CMR indices, including LGE, MVO, and LPE.

Results

Late pericardial enhancement (LPE+) was documented in 77.5% of the study cohort. A strong association was found between LPE and the degree and extent of myocardial injury (LGE, MVO). Both LGE and MVO were significantly correlated with increased MACE on follow-up. On the contrary, LPE presence, either adjacent to the LV or the other cardiac chambers, was associated with a lower MACE rate in a median of 3 years of follow-up HR 0.39, 95% CI (0.21–0.7), p = 0.002, and HR 0.48, 95% CI (0.26–0.9), p = 0.02, respectively.

Conclusions

Prognostic implication of pericardial involvement in ST-segment elevation myocardial infarction was documented by CMR in 77.5% of our STEMI cohort. Late pericardial enhancement presence correlated significantly with the extent and severity of the myocardial damage. Unexpectedly, it was associated with a considerably lower MACE rate in the follow-up period.

Kounis syndrome secondary to nimesulide ingestion: a case report

Background

Kounis syndrome, also known as "allergic myocardial infarction," is a rare co-occurrence of acute coronary syndrome (ACS) in the setting of hypersensitivity reaction to any agent. Non-steroidal anti-inflammatory drugs (NSAIDs) like are often implicated in causing allergic reactions. Here, we present a case of anterior wall myocardial infarction (AWMI) occurred following angioedema secondary to intake of Nimesulide, not described earlier in literature.

Case presentation

A 45-year-old female developed generalized pruritic, erythematous maculopapular rash, facial puffiness, oral ulcers and hoarseness of voice within few hours following consumption of Nimesulide for fever and body-ache. Due to development of hypotension, electrocardiogram (ECG) was done, which revealed ST elevation in V2–V6, with marked elevation of troponin (TnI) and creatine kinase (CK-MB). He had no chest pain or shortness of breath. Echocardiography showed regional wall motion (RWMA) abnormality in left anterior descending artery (LAD) territory with an ejection fraction of 25%. Coronary angiography showed a complete thrombotic cutoff of LAD, for which Tirofiban infusion was started to decrease thrombus burden. Repeat angiography on next day showed 80% lesion in proximal LAD for which she underwent revascularization with a drug-eluting stent. The patient later showed improvement in cardiac function at 8 months of follow-up.

Conclusions

The occurrence of ACS requiring percutaneous coronary intervention (PCI) in the setting of allergic reactions is rarely reported in the literature. One should be aware of the rare possibility of Kounis syndrome in the setting of hypersensitivity reaction when accompanying features of symptoms suggestive of coronary artery disease co-exists. When indicated, ECG monitoring and cardiac biomarkers in patients with allergic responses help to identify this rare and treatable condition.

Late primary angioplasty (beyond 12 h): are we sure it should be avoided?

Optimal management for patients with ST-segment elevation myocardial infarction (STEMI) who arrive at a hospital late remains uncertain since evidence and real-world data are limited. Patients who present late with a STEMI are a heterogeneous population, and the clinical decision regarding percutaneous coronary intervention (PCI) should not be the same for all. One randomized clinical trial, multiple mechanistic studies, and contemporary registries suggest a presumed benefit for a prompt restoration of coronary flow even in late presenting STEMI. Crucial elements in decision-making are the presence of haemodynamic or electrical instability, and ongoing ischaemic signs or symptoms to tip the scales toward PCI. Among clinically stable, late-presenting patients, myocardial viability assessment and functional testing can identify yet another subgroup that may benefit from late PCI

Does the Heart Want What It Wants? A Case for Self-Adapting, Mechano-Sensitive Therapies After Infarction

There is a critical need for interventions to control the development and remodeling of scar tissue after myocardial infarction. A significant hurdle to fibrosis-related therapy is presented by the complex spatial needs of the infarcted ventricle, namely that collagenous buildup is beneficial in the ischemic zone but detrimental in the border and remote zones. As a new, alternative approach, we present a case to develop self-adapting, mechano-sensitive drug targets in order to leverage local, microenvironmental mechanics to modulate a therapy's pharmacologic effect. Such approaches could provide self-tuning control to either promote fibrosis or reduce fibrosis only when and where it is beneficial to do so.

Hurdles to Cardioprotection in the Critically Ill

Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.

Anti-inflammatory therapies in myocardial infarction: failures, hopes and challenges

In the infarcted heart, the damage-associated molecular pattern proteins released by necrotic cells trigger both myocardial and systemic inflammatory responses. Induction of chemokines and cytokines and up-regulation of endothelial adhesion molecules mediate leukocyte recruitment in the infarcted myocardium. Inflammatory cells clear the infarct of dead cells and matrix debris and activate repair by myofibroblasts and vascular cells, but may also contribute to adverse fibrotic remodelling of viable segments, accentuate cardiomyocyte apoptosis and exert arrhythmogenic actions. Excessive, prolonged and dysregulated inflammation has been implicated in the pathogenesis of complications and may be involved in the development of heart failure following infarction. Studies in animal models of myocardial infarction (MI) have suggested the effectiveness of pharmacological interventions targeting the inflammatory response. This article provides a brief overview of the cell biology of the post-infarction inflammatory response and discusses the use of pharmacological interventions targeting inflammation following infarction. Therapy with broad anti-inflammatory and immunomodulatory agents may also inhibit important repair pathways, thus exerting detrimental actions in patients with MI. Extensive experimental evidence suggests that targeting specific inflammatory signals, such as the complement cascade, chemokines, cytokines, proteases, selectins and leukocyte integrins, may hold promise. However, clinical translation has proved challenging. Targeting IL-1 may benefit patients with exaggerated post-MI inflammatory responses following infarction, not only by attenuating adverse remodelling but also by stabilizing the atherosclerotic plaque and by inhibiting arrhythmia generation. Identification of the therapeutic window for specific interventions and pathophysiological stratification of MI patients using inflammatory biomarkers and imaging strategies are critical for optimal therapeutic design.

Kounis syndrome: A concise review with focus on management

Kounis syndrome is defined as the co-incidental occurrence of an acute coronary syndrome with hypersensitivity reactions following an allergenic event and was first described by Kounis and Zavras in 1991 as an allergic angina syndrome. Multiple causes have been described and most of the data in the literature are derived from the description of clinical cases - mostly in adult patients - and the pathophysiology remains only partly explained. Three different variants of Kounis syndrome have been defined: type I (without coronary disease) is defined as chest pain during an acute allergic reaction in patients without risk factors or coronary lesions in which the allergic event induces coronary spasm that electrocardiographic changes secondary to ischemia; type II (with coronary disease) includes patients with pre-existing atheromatous disease, either previously quiescent or symptomatic, in whom acute hypersensitive reactions cause plaque erosion or rupture, culminating in acute myocardial infarction; more recently a type-III variant of Kounis syndrome has been defined in patients with preexisting coronary disease and drug eluting coronary stent thrombosis. The pathogenesis of the syndrome is discussed, and a therapeutic algorithm is proposed.

Modifying the mechanics of healing infarcts: Is better the enemy of good?

Myocardial infarction (MI) is a major source of morbidity and mortality worldwide, with over 7 million people suffering infarctions each year. Heart muscle damaged during MI is replaced by a collagenous scar over a period of several weeks, and the mechanical properties of that scar tissue are a key determinant of serious post-MI complications such as infarct rupture, depression of heart function, and progression to heart failure. Thus, there is increasing interest in developing therapies that modify the structure and mechanics of healing infarct scar. Yet most prior attempts at therapeutic scar modification have failed, some catastrophically. This article reviews available information about the mechanics of healing infarct scar and the functional impact of scar mechanical properties, and attempts to infer principles that can better guide future attempts to modify scar. One important conclusion is that collagen structure, mechanics, and remodeling of healing infarct scar vary so widely among experimental models that any novel therapy should be tested across a range of species, infarct locations, and reperfusion protocols. Another lesson from past work is that the biology and mechanics of healing infarcts are sufficiently complex that the effects of interventions are often counterintuitive; for example, increasing infarct stiffness has little effect on heart function, and inhibition of matrix metalloproteases (MMPs) has little effect on scar collagen content. Computational models can help explain such counterintuitive results, and are becoming an increasingly important tool for integrating known information to better identify promising therapies and design experiments to test them. Moving forward, potentially exciting new opportunities for therapeutic modification of infarct mechanics include modulating anisotropy and promoting scar compaction.

Physiological Implications of Myocardial Scar Structure

Once myocardium dies during a heart attack, it is replaced by scar tissue over the course of several weeks. The size, location, composition, structure, and mechanical properties of the healing scar are all critical determinants of the fate of patients who survive the initial infarction. While the central importance of scar structure in determining pump function and remodeling has long been recognized, it has proven remarkably difficult to design therapies that improve heart function or limit remodeling by modifying scar structure. Many exciting new therapies are under development, but predicting their long-term effects requires a detailed understanding of how infarct scar forms, how its properties impact left ventricular function and remodeling, and how changes in scar structure and properties feed back to affect not only heart mechanics but also electrical conduction, reflex hemodynamic compensations, and the ongoing process of scar formation itself. In this article, we outline the scar formation process following a myocardial infarction, discuss interpretation of standard measures of heart function in the setting of a healing infarct, then present implications of infarct scar geometry and structure for both mechanical and electrical function of the heart and summarize experiences to date with therapeutic interventions that aim to modify scar geometry and structure. One important conclusion that emerges from the studies reviewed here is that computational modeling is an essential tool for integrating the wealth of information required to understand this complex system and predict the impact of novel therapies on scar healing, heart function, and remodeling following myocardial infarction.

OPC-28326, a selective peripheral vasodilator with angiogenic activity, mitigates postinfarction cardiac remodeling

Although OPC-28326, 4-(N-methyl-2-phenylethylamino)-1-(3,5-dimethyl-4-propionyl-aminobenzoyl) piperidine hydrochloride monohydrate, was developed as a selective peripheral vasodilator with α2-adrenergic antagonist properties, it also reportedly exhibits angiogenic activity in an ischemic leg model. The purpose of this study was to examine the effect of OPC-28326 on the architectural dynamics and function of the infarcted left ventricle during the chronic stage of myocardial infarction. Myocardial infarction was induced in male C3H/He mice, after which the mice were randomly assigned into two groups: a control group receiving a normal diet and an OPC group whose diet contained 0.05% OPC-28326. The survival rate among the mice (n = 18 in each group) 4 wk postinfarction was significantly greater in the OPC than control group (83 vs. 44%; P < 0.05), and left ventricular remodeling and dysfunction were significantly mitigated. Histologically, infarct wall thickness was significantly greater in the OPC group, due in part to an abundance of nonmyocyte components, including blood vessels and myofibroblasts. Five days postinfarction, Ki-67-positive proliferating cells were more abundant in the granulation tissue in the OPC group, and there were fewer apoptotic cells. These effects were accompanied by activation of myocardial Akt and endothelial nitric oxide synthase. Hypoxia within the infarct issue, assessed using pimonidazole staining, was markedly attenuated in the OPC group. In summary, OPC-28326 increased the nonmyocyte population in infarct tissue by increasing proliferation and reducing apoptosis, thereby altering the tissue dynamics such that wall stress was reduced, which might have contributed to a mitigation of postinfarction cardiac remodeling and dysfunction.

Anti-inflammatory strategies for ventricular remodeling following ST-segment elevation acute myocardial infarction

Acute myocardial infarction (AMI) leads to molecular, structural, geometric, and functional changes in the heart in a process known as ventricular remodeling. An intense organized inflammatory response is triggered after myocardial ischemia and necrosis and involves all components of the innate immunity, affecting both cardiomyocytes and noncardiomyocyte cells. Inflammation is triggered by tissue injury; it mediates wound healing and scar formation and affects ventricular remodeling. Many therapeutic attempts aimed at reducing inflammation in AMI during the past 3 decades presented issues of impaired healing or increased risk of cardiac rupture or failed to show any additional benefit in addition to standard therapies. More recent strategies aimed at selectively blocking one of the key factors upstream rather than globally suppressing the response downstream have shown some promising results in pilot trials. We herein review the pathophysiological mechanisms of inflammation and ventricular remodeling after AMI and the results of clinical trials with anti-inflammatory strategies.

Non-genomic effect of glucocorticoids on cardiovascular system

Glucocorticoids (GCs) are essential steroid hormones for homeostasis, development, metabolism, and cognition and possess anti-inflammatory and immunosuppressive actions. Since glucocorticoid receptor II (GR) is nearly ubiquitous, chronic activation or depletion of GCs leads to dysfunction of diverse organs, including the heart and blood vessels, resulting predominantly from changes in gene expression. Most studies, therefore, have focused on the genomic effects of GC to understand its related pathophysiological manifestations. The nongenomic effects of GCs clearly differ from well-known genomic effects, with the former responding within several minutes without the need for protein synthesis. There is increasing evidence that the nongenomic actions of GCs influence various physiological functions. To develop a GC-mediated therapeutic target for the treatment of cardiovascular disease, understanding the genomic and nongenomic effects of GC on the cardiovascular system is needed. This article reviews our current understanding of the underlying mechanisms of GCs on cardiovascular diseases and stress, as well as how nongenomic GC signaling contributes to these conditions. We suggest that manipulation of GC action based on both GC and GR metabolism, mitochondrial impact, and the action of serum- and glucocorticoid-dependent kinase 1 may provide new information with which to treat cardiovascular diseases.

Current understanding of Kounis syndrome

Inflammatory mediators, adhesion molecules of neutrophils and monocytes, have been shown to be increased in the plasma of patients presenting with acute coronary syndromes. Anaphylaxis is a systemic, immediate hypersensitivity reaction caused by rapid IgE-mediated release of mediators from mast cells and basophils. Kounis syndrome is the coincidental occurrence of these two distinct conditions accompanied by clinical and laboratory findings of angina pectoris caused by inflammatory mediators released during an allergic insult. Allergic angina can progress to acute myocardial infarction, which is termed 'allergic myocardial infarction'. There are several causes reported to be capable of inducing Kounis syndrome. These include a number of conditions, several drugs, foods and insect stings, among others. In this article, the clinical aspects, diagnosis, pathogenesis, incidence and epidemiology, related conditions and therapeutic management of this important syndrome are discussed.

Treatment of Kounis syndrome

Kounis syndrome is potentially a life-threatening medical emergency with both a severe allergic reaction and acute coronary syndrome. Most of the information about this syndrome has come from the case reports. The management of these patients may be challenging for clinicians, and unfortunately guidelines have not been established yet. In this article, we review the current guidelines of acute coronary syndromes and anaphylaxis along with the published cases with Kounis syndrome secondary to beta-lactam antibiotics. We have summarized our recommendations for the work-up and treatment of Kounis syndrome from available data. Obviously, larger prospective studies are needed to establish definitive treatment guidelines for these patients.

Dexamethasone-induced cardioprotection: a role for the phosphatase MKP-1?

AIMS

Previous studies suggested that p38 MAPK activation during sustained myocardial ischaemia and reperfusion was harmful. We hypothesize that attenuation of p38MAPK activity via dephosphorylation by the dual-specificity phosphatase MKP-1 should be protective against ischaemia/reperfusion injury. Since the glucocorticoid, dexamethasone, induces the expression of MKP-1, the aim of this study was to determine whether upregulation of this phosphatase by dexamethasone protects the heart against ischaemia/reperfusion injury.

MAIN METHODS

Male Wistar rats were treated with dexamethasone (3 mg/kg/day ip) for 10 days, before removal of the hearts for Western blot (ip Dex-P) or perfusion in the working mode (ip Dex+P). Hearts were subjected to 20 min global or 35 min regional ischaemia (36.5 degrees C) and 30 or 120 min reperfusion. In a separate series, dexamethasone (1 microM) was added to the perfusate for 10 min (Pre+Dex) before or after (Rep+Dex) ischaemia.

KEY FINDINGS

Dexamethasone, administered intraperitoneally or added directly to the perfusate, significantly improved post-ischaemic functional recovery and reduced infarct size compared to untreated controls (p<0.05). These were associated with enhanced up-regulation of MKP-1 protein expression (arbitrary units (mean+/-SD): Untreated: 1; ip Dex-P: 2.59+/-0.22; ip Dex+P: 1.51+/-0.22; Pre+Dex: 4.11+/-0.73, Rep+15'Dex: 1.51+/-0.14; untreated vs. all groups, p<0.05) and attenuation of p38 MAPK activation (p<0.05) in all dexamethasone-treated groups, except for Rep+10'Dex. ERK and PKB/Akt activation were unchanged.

SIGNIFICANCE

Dexamethasone-induced cardioprotection was associated with upregulation of the phosphatase MKP-1 and inactivation of pro-apoptotic p38 MAPK.

Benefits of reperfusion beyond infarct size limitation

The most critical determinant of prognosis in patients with acute myocardial infarction (MI) is infarct magnitude, which can be established within several hours of an attack. The importance of the subsequent healing process is not negligible, however. In fact, much experimental and clinical evidence suggests that late reperfusion of the infarct-related coronary artery--i.e. at times too late to salvage the myocardium within the area at risk-is beneficial for reducing left ventricular remodelling and decreasing mortality ('open artery hypothesis'). For instance, one recent study highlighted the beneficial effects of late reperfusion therapy on the infarct tissue cell dynamics following acute MI. Nonetheless, several recent large, randomized clinical trials have failed to provide evidence of such benefits, refuting the clinical efficacy of late reperfusion. In addition, they also underscore the need for revised clinical studies in which there is less heterogeneity in the timing of reperfusion and in the initial infarct size, as well as the need for sustained patency of the recanalized artery. This review focuses on the effects of late reperfusion on the pathophysiology of MI in the context of the infarct tissue dynamics and clinical outcomes. We also discuss the issues that need to be resolved to improve clinical application.

Effects of timed administration of doxycycline or methylprednisolone on post-myocardial infarction inflammation and left ventricular remodeling in the rat heart

The development of strategies to ameliorate post-myocardial infarction (MI) remodeling and improve function continues to be an area of clinical importance. Use of steroids for this purpose is controversial since the effects of timed treatment on relevant inflammatory, biochemical and structure/function endpoints are unclear. In a previous report, we demonstrated that use of doxycycline pre-treatment improves post-MI remodeling and passive left ventricular (LV) function. However, the effects of timed doxycycline post-MI treatment are unknown. To examine these issues, we performed a study using a rat MI model. Animals were administered one of the following: doxycycline (DOX), the corticosteroid methylprednisolone (MP), or aqueous vehicle. Treatment was given early, short-term (at time of MI to 24 h post-MI) or late, long term (2-7 days post-MI). Animals were sacrificed at 3, 7 or 42 days post-surgery. We assessed LV hemodynamics, pressure-volume, and pressure-scar strains, histomorphometry, inflammation via measurements of myeloperoxidase activity, and matrix metalloproteinase (MMP) activity. Late MP treatment yielded a robust right-shifted pressure-volume curve, which was accompanied by increased scar strains. Late DOX treatment yielded reduced average heart weight and size and preserved scar thickness. DOX treatment did not suppress inflammation, which contrasts with the suppressive effects of MP. Use of early or late MP yielded increased MMP activity in infarcted and non-infarcted regions. Early and late treatment with DOX yielded infarct-associated MMP activity levels comparable to those of vehicle-treated animals. In conclusion, results indicate that late use of MP yields adverse post-MI structure/function outcomes that correlate with suppression of inflammation and increased MMP activity. These observations contrast with those of DOX, in particular, late treatment where improved outcomes were observed in LV structure and were accompanied by the lack of suppression of inflammation.

Improvement in left ventricular function following coronary stenting in patients with acute myocardial infarction: 6-month and 3-year follow-up

BACKGROUND

This study assesses hemodynamic and angiographic changes in patients with a patent infarct-related artery (IRA) after acute myocardial infarction (AMI).

METHODS

One hundred and seventy-seven patients with first AMI, who received a predischarge stenting to the IRA and sustained a patent IRA over 3 years, were stratified into 3 groups according to the baseline left ventricular ejection fraction (LVEF): group A included 63 patients with a LVEF of >49%, group B 73 patients with a LVEF of 40%-49%, and group C 41 patients with a LVEF of <40%. The hemodynamic and angiographic parameters were compared at baseline, 6-month and 3-year follow-up.

RESULTS

The LV end-diastolic volume index increased 1, 4 and 4 ml/m(2) at 6 months and 4, 5 and 10 ml/m(2) at 3 years, respectively in group A, B and C. The LVEF increased 4%, 7% and 12% at 6 months and 6%, 8% and 14% at 3 years, respectively in group A, B and C. The stroke volume index increased 3, 7 and 12 ml/m(2) at 6 months and 6, 8 and 15 ml/m(2) at 3 years, respectively in group A, B and C. The LV wall motion score decreased 2, 3 and 3 at 6 months and was unchanged at 3 years, respectively in group A, B and C. The LV end-diastolic pressure decreased 2, 3 and 4 mm Hg, respectively in group A, B and C, at 6-month follow-up and remained stable at 3 years.

CONCLUSIONS

Long-term beneficial effects in patients receiving a late predischarge intracoronary stenting following first AMI were seen and these may be related to patent IRA. A progressive improvement in left ventricular remodeling occurs in all patients regardless of their initial left ventricular function and the improvement continues for at least 3 years.

Bradykinin B2receptor antagonism attenuates inflammation, mast cell infiltration and fibrosis in remote myocardium after infarction in rats

Bradykinin may interfere with myocardial remodelling by promoting inflammation and mast cell activation or, alternatively, by counteracting angiotensin II-dependent collagen accumulation. The aim of the present study was to investigate the role of bradykinin B2 receptor antagonism in inflammatory and mast cell infiltration, fibroplasia and fibrosis accumulation following myocardial infarction (MI). Myocardial infarction was produced by the ligature of the left coronary artery in male Wistar rats that were 10 weeks of age. Immediately after MI, rats received the B2 receptor antagonist Hoe140 (0.5 microg/kg per min, s.c.) or saline over a period of 3 days, 1 week or 4 weeks, constituting three separate groups and their respective controls. Coronal myocardial tissue sections underwent haematoxylin and eosin, Giemsa and picrosirius red staining, as well as immunohistochemistry for alpha-smooth muscle actin (SMA). Morphometric studies were undertaken in three different myocardial regions: MI, remote non-infarcted subendocardium (non-MI SE) and remote non-infarcted interventricular septum (non-MI IVS). The MI size was comparable between Hoe140-treated groups and their respective controls (day 3: 42 +/- 4%, n = 8, vs 43 +/- 3%, n = 6; week 1: 37 +/- 5%, n = 5, vs 39 +/- 2%, n = 5; week 4: 35 +/- 3%, n = 9, vs 36 +/- 3%, n = 7). At day 3, Hoe140 treatment reduced inflammatory cell reaction within the MI (585 +/- 59 vs 995 +/- 170 cells/mm2; P = 0.02), non-MI SE (77 +/- 12 vs 214 +/- 57 cells/mm2; P = 0.02) and non-MI IVS (93 +/- 16 vs 135 +/- 14 cells/mm2; P = 0.03) regions. Mast cells were reduced within the non-MI IVS region (0.8 +/- 0.1 vs 2.5 +/- 0.4 cells/mm2; P = 0.006), but not within the MI region. In non-MI SE, mast cells were rarely found. At week 1, Hoe140 treatment reduced alpha-SMA-positive myofibroblast infiltration within the MI (2535 +/- 383 vs 5636 +/- 968 cells/mm2; P = 0.01) and non-MI SE (222 +/- 33 vs 597 +/- 162 cells/mm2; P = 0.03) regions. In the non-MI IVS region, alpha-SMA-positive myofibroblasts were rarely found. At week 4, Hoe140 treatment reduced collagen volume fraction within the MI (37 +/- 4 vs 53 +/- 4%; P = 0.03), non-MI SE (1.3 +/- 0.2 vs 2.6 +/- 0.3%; P = 0.001) and non-MI IVS (1.1 +/- 0.2 vs 1.8 +/- 0.2%; P = 0.01) regions. Bradykinin promotes inflammation, fibroplasia and fibrosis after MI. Mast cells may have a role in fibrosis deposition through a bradykinin-related mechanism.

Structure and Mechanics of Healing Myocardial Infarcts

Therapies for myocardial infarction have historically been developed by trial and error, rather than from an understanding of the structure and function of the healing infarct. With exciting new bioengineering therapies for myocardial infarction on the horizon, we have reviewed the time course of structural and mechanical changes in the healing infarct in an attempt to identify key structural determinants of mechanics at several stages of healing. Based on temporal correlation, we hypothesize that normal passive material properties dominate the mechanics during acute ischemia, edema during the subsequent necrotic phase, large collagen fiber structure during the fibrotic phase, and cross-linking of collagen during the long-term remodeling phase. We hope these hypotheses will stimulate further research on infarct mechanics, particularly studies that integrate material testing, in vivo mechanics, and quantitative structural analysis.

Corticosteroid receptors, 11 beta-hydroxysteroid dehydrogenase, and the heart

Mineralocorticoid and glucocorticoid hormones are known as corticosteroid hormones and are synthesized mainly in the adrenal cortex; however, more recently the enzymes involved in their synthesis have been found in a variety of cells and tissues, including the heart. The effects of these hormones are mediated via both cytoplasmic mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs), which act as ligand-inducible transcription factors. In addition, rapid, nongenomically mediated effects of these steroids can occur that may be via novel corticosteroid receptors. The lipophilic nature of these hormones allows them to pass freely through the cell membrane, although the intracellular concentration of mineralocorticoids and glucocorticoids is dependent on several cellular factors. The main regulators of intracellular glucocorticoid levels are 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) isoforms. 11 beta HSD1 acts predominantly as a reductase in vivo, facilitating glucocorticoid action by converting circulating receptor-inactive 11-ketoglucocorticoids to active glucocorticoids. In contrast, 11 beta HSD 2 acts exclusively as an 11 beta-dehydrogenase and decreases intracellular glucocorticoids by converting them to their receptor-inactive 11-ketometabolites. Furthermore, P-glycoproteins, by actively pumping steroids out of cells, can selectively decrease steroids and local steroid synthesis can increase steroid concentrations. Receptor concentration, receptor modification, and receptor-protein interactions can also significantly impact on the corticosteroid response. This review details the receptors and possible mechanisms involved in both mediating and modulating corticosteroid responses. In addition, direct effects of corticosteroids on the heart are described including a discussion of the corticosteroid receptors and the mechanisms involved in mediating their effects.

Acute cardiovascular protective effects of corticosteroids are mediated by non-transcriptional activation of endothelial nitric oxide synthase

Corticosteroids have been shown to exert beneficial effects in the treatment of acute myocardial infarction, but the precise mechanisms underlying their protective effects are unknown. Here we show that high-dose corticosteroids exert cardiovascular protection through a novel mechanism involving the rapid, non-transcriptional activation of endothelial nitric oxide synthase (eNOS). Binding of corticosteroids to the glucocorticoid receptor (GR) stimulated phosphatidylinositol 3-kinase and protein kinase Akt, leading to eNOS activation and nitric oxide dependent vasorelaxation. Acute administration of pharmacological concentrations of corticosteroids in mice led to decreased vascular inflammation and reduced myocardial infarct size following ischemia and reperfusion injury. These beneficial effects of corticosteroids were abolished by GR antagonists or eNOS inhibitors in wild-type mice and were completely absent in eNOS-deficient (Nos3(-/-)) mice. The rapid activation of eNOS by the non-nuclear actions of GR, therefore, represents an important cardiovascular protective effect of acute high-dose corticosteroid therapy.

Limiting lipid peroxidation in the nonischemic zone of infarcted rat hearts by indomethacin improves left ventricular function without affecting myocardial healing and remodeling

We recently showed that indomethacin reduces lipoperoxidation occurring in the nonischemic zone (right ventricle + septum; RVS) of rat hearts with permanent coronary occlusion. The purpose of this study was to determine whether this biochemical effect is associated with an improvement of residual cardiac function or with modifications of delayed ventricular remodeling, or both. Rats received either indomethacin (1 mg/kg i.p.) or a placebo 5 min before coronary occlusion, and then twice a day for 48 hours. Six hours after ligation, myeloperoxidase (MPO) activity (leukocyte infiltration index) was measured in the ischemic zone (left ventricle; LV) and in RVS. Forty-eight hours after ligation, left ventricular function was assessed in vivo. Alterations in myocardial geometry were estimated 21 days after ligation on histologic cross-sections. In the indomethacin group, cardiac function was improved compared with that with placebo, and the indexes of ventricular remodeling were not affected by the treatment. Finally, indomethacin at the dose used did not affect MPO activity in the LV. It is concluded that indomethacin treatment leads to a better maintenance of residual nonischemic tissue contractility without worsening late ventricular shape changes. These results could in part be explained by the ability of the treatment to decrease inflammatory mediator-induced oxidative stress in RVS without affecting infarct healing caused by leukocyte infiltration in LV.

Ventricular enlargement and remodeling following acute myocardial infarction: mechanisms and management

Severe myocardial ischemia, when sustained, leads to a predictable sequence of events, including myocardial necrosis, expansion of the infarct, and later its replacement by scar tissue. The nonischemic tissue sustains ventricular function, but it frequently adapts to the extra load placed on it by dilating. The enlargement and remodeling of the left ventricle may lead to ventricular failure and arrhythmias. Rational management to prevent these complications includes restoration of the patency of the occluded vessel and ventricular unloading. These two interventions may be useful both early and late in the course of infarction.

Effect of atenolol on myocardial infarct expansion in a nonreperfused rat model

Acute myocardial infarct expansion is associated with a poor prognosis. This study was performed to assess potential beneficial effects of beta-blockers on inhibiting expansion. A pilot study showed that atenolol (10 mg/kg) achieved sustained beta-blockade in rats. In the main study, following left coronary ligation, 36 rats received atenolol and 18 rats received placebo daily for 7 days. Infarct size was similar in treated and control rats (25 +/- 13% versus 28 +/- 11%). Expansion grades and a quantitative index of expansion were similar for both groups. Infarct size and expansion index were significantly related, but linear regression lines were similar for treated and control rats. We conclude that atenolol has no significant effect on infarct expansion in this nonreperfused rat model.

Left ventricular dilatation and failure post-myocardial infarction: pathophysiology and possible pharmacologic interventions

An important antecedent to the development of late congestive heart failure is left ventricular dilatation and remodeling following myocardial infarction, which occurs in 30-40% of acute anterior transmural infarcts. Dilatation and remodeling commence within the first 24 hours following myocardial infarction and may be steadily progressive over months to years. Both the infarcted and uninfarcted regions of the myocardium are equally involved in the process. The remodeling process comprises left ventricular wall thinning (mainly due to cell slippage), chamber dilatation, and compensatory hypertrophy of the uninfarcted segment of the myocardium. The hypertrophy may initially be physiologic but may ultimately become a pathologic process, and thereby contribute to pump dysfunction. The possible reasons why the ventricular hypertrophy may ultimately be dysfunctional include alterations in local architecture and their sequelae alone or in concert with local changes in the beta-adrenergic, alpha-adrenergic, or renin angiotensin systems. At the present time, there are encouraging data to suggest that nitroglycerin, or the angiotensin converting enzyme inhibitor captopril, may ameliorate this process.

Mechanical and electrical complications of acute myocardial infarction

Although much of the current enthusiasm in the management of acute myocardial infarction is related to revascularization strategies, mechanical and electrical complications continue to pose a major threat to recovery in some patients. Some of the major complications of acute myocardial infarction are cardiogenic shock, rupture of the free wall and pseudoaneurysm, rupture of the ventricular septum, acute mitral regurgitation, right ventricular myocardial infarction, infarct expansion or extension, pericarditis and tamponade, peri-infarction hypertension, and tachyarrhythmias and bradyarrhythmias. For each of these complications, general guidelines for diagnosis and management are offered. Early, aggressive, and judicious treatment of these complications may substantially decrease the morbidity and mortality associated with acute myocardial infarction.

The prevention of congestive heart failure: left ventricular dilation and its management

Left ventricular dilation and remodelling occur in 35-40% of anterior transmural myocardial infarcts and these events are important antecedents to the development of late congestive heart failure. This process commences within the first 24 hours following myocardial infarction and may be steadily progressive over months to years. Both the infarcted and the uninfarcted regions of myocardium are equally involved in the process. Thinning of the left ventricular wall occurs mainly as a result of cell slippage. In addition, compensatory hypertrophy occurs in the uninfarcted segment of the myocardium. While this hypertrophy may initially be physiological, it ultimately appears to become a pathological process and thereby contributes to pump dysfunction. At the present time there are encouraging data to suggest that nitroglycerin, administered in the setting of the acute infarction, or the angiotensin converting enzyme inhibitor captopril, may ameliorate this process. Whether a patent infarct related artery further limits dilation is uncertain and is currently under investigation.

Identification of patients prone to infarct expansion by the degree of regional shape distortion on an early two-dimensional echocardiogram after myocardial infarction

Early detection of potential expanders (patients who develop clinically significant infarct expansion with acute left ventricular (LV) dilatation and failure but no necrosis) after acute myocardial infarction (AMI) is necessary in order to apply preventive therapy. To determine whether the degree of regional shape distortion (RSD), or dilatation, on early two-dimensional echocardiogram (2-D echo) after AMI can identify potential expanders, serial clinical and echocardiographic data were studied prospectively in 244 consecutive patients with a first Q-wave AMI. Initial (mean 2 days) and final (mean 10 days) two-dimensional echocardiograms were compared for regional LV asynergy, RSD, and conventional indices of expansion measured on endocardial diastolic outlines of mid-LV short-axis sections. Analysis of clinical and 2-D echo data revealed 51 expanders and 193 nonexpanders. Expanders showed greater LV dysfunction and more inhospital deaths (27% vs. 8%, p less than 0.001) compared with nonexpanders; conventional indices of expansion showed more marked increase between initial and final two-dimensional echo in expanders, but initial indices were not predictive. In contrast, the new RSD index Pk, a measure of the outward bulge, was markedly greater in expanders than nonexpanders on both initial (16.5 vs. 2.4 mm, p less than 0.001) and final echo. Furthermore, expanders with greater than or equal to 30% increase in Pk (to 21 mm) developed rupture of the ventricular septum (n = 10) or free wall (n = 2). Also, 50 of 51 expanders compared with 3 of 193 nonexpanders had a Pk greater than or equal to 10 mm on the initial echo. A simpler index, the depth of RSD (rd), provided similar discrimination as Pk. Thus, the degree of diastolic RSD on an early 2-D echo after AMI can identify potential expanders.

Left ventricular topographic alterations in the completely healed rat infarct caused by early and late coronary artery reperfusion

Topographic changes in the completely healed (6 weeks) left ventricle of the rat, caused by early (30 minutes) and delayed (90 minutes) coronary artery reperfusion, were examined. With early reperfusion the extent of the scar, as a percentage of left ventricular (LV) circumference, was reduced compared to the extent of the scar in rats with permanent occlusion (27 +/- 3% vs 42 +/- 2%, p less than 0.01). Early reperfusion also preserved LV topography by preventing dilation of the LV cavity and thinning of the healed free wall. Late reperfusion (90 minutes) did not reduce the extent of the scar (35 +/- 3% vs 42 +/- 2% of LV circumference, p = NS) or prevent dilation of the LV cavity compared with permanent occlusion. However, the healed free wall/noninfarcted septum ratio was significantly greater in rats with late reperfusion than in those with permanent occlusion (0.98 +/- 0.06 vs 0.73 +/- 0.07, p less than 0.05). Thus early reperfusion completely inhibited scar thinning and dilation of the LV cavity, maintaining normal LV topography. Late reperfusion, too late to reduce infarct size, still contributed to improved healing of the myocardium by resulting in a thicker scar.

Increased afterload aggravates infarct expansion after acute myocardial infarction

After acute transmural myocardial infarction, the heart may undergo major remodeling characterized by thinning and dilation of the infarct zone and overall enlargement of the heart. The effect of increased left ventricular pressure on infarct expansion and the extent to which it alters postinfarction remodeling were studied in a rat model. Rats with either aortic banding or a sham operation and a survival period of 3 weeks were further randomized to sham thoracotomy or left coronary ligation. Surviving rats were killed 7 days later and the hearts were fixed in diastole for morphologic analysis. Hearts with aortic banding had a mean peak to peak gradient of 20.7 +/- 4.9 mm Hg across the aortic band at death and a significantly thicker heart than that of the comparison group without an aortic band. Infarct size, as a percent of total left ventricular mass, at the time of death was less in the group with aortic banding, yet infarct expansion was more marked. However, when original infarct size was estimated taking into account the effects of aortic banding, scar formation, infarct expansion and infarct-induced hypertrophy, it was found to be similar in both infarct groups (45.50 +/- 4.2 versus 47.90 +/- 3.1%). Infarct expansion, as measured by cavity dilation and infarct thinning, occurred in both infarct groups but was greater in the group with aortic banding.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise training after anterior Q wave myocardial infarction: importance of regional left ventricular function and topography

To determine whether the extent of left ventricular dysfunction and the degree of shape distortion can predict outcome in survivors of moderate-sized anterior Q wave myocardial infarction who are undergoing exercise training, these variables were measured by two-dimensional echocardiography before and after 12 weeks of a low level exercise training program starting 15 weeks after infarction in 13 patients (7 in group 1 and 6 in group 2) and 12 weeks apart in 24 matched control patients without training. By the end of training, the functional class score had increased in group 2 (from 2.25 to 2.67, p less than 0.005) but had not changed in group 1. Further discrimination of groups 1 and 2 was provided by an initial asynergy (akinesia or dyskinesia, or both) less than 18% or greater than or equal to 18%. Compared with group 1, group 2 had greater initial asynergy (32 versus 6%, p less than 0.001), expansion index (asynergic/normal endocardial segment length: 1.8 versus 1.6, p less than 0.025) and peak shape distortion index (12.2 versus 1.0 mm, p less than 0.005) but lower ejection fraction (43 versus 59%, p less than 0.05) and thinning ratio (asynergic/normal wall thickness: 0.61 versus 0.74, p less than 0.05). These variables did not change with training in group 1. However, in group 2, training caused significant increase in asynergy (from 32 to 40%, p less than 0.05), expansion index (from 1.8 to 2.0, p less than 0.01) and peak shape distortion (from 12.2 to 20.9 mm, p less than 0.05) associated with a decrease in thinning ratio (from 0.61 to 0.51, p less than 0.001) and ejection fraction (from 43 to 30%, p less than 0.005). Initial values for these variables were similar for corresponding control groups but did not change over the 12 weeks. Thus, patients with greater than or equal to 18% left ventricular asynergy on the initial echocardiogram showed more shape distortion, expansion and thinning before exercise training and developed further functional and topographic deterioration with training.

Functional infarct expansion, left ventricular dilation and isovolumic relaxation time after coronary occlusion: a two-dimensional echocardiographic study

Left ventricular dilation and infarct expansion after acute myocardial infarction are associated with an increased morbidity and mortality. The purpose of this study was to determine whether angiotensin-converting enzyme inhibition could reverse left ventricular dilation and improve the diastolic properties of the left ventricle very early after coronary occlusion. The acute time course of left ventricular dilation and infarct expansion (as determined by two-dimensional echocardiography) and early diastolic isovolumic relaxation time were studied in 20 dogs subjected to 3 h of coronary occlusion. End-diastolic area before occlusion was 8.4 +/- 0.5 and 8.9 +/- 0.7 cm2 (p = NS) in the captopril- and the saline-treated group, respectively. At 30 min after occlusion (pretreatment), end-diastolic area increased to 12.6 +/- 0.8 cm2 in the captopril-treated group (p less than 0.01) and 11.3 +/- 0.9 cm2 (p less than 0.05) in the saline-treated group. Three hours after occlusion and after captopril treatment, end-diastolic area decreased to 9.4 +/- 0.6 cm2 (p less than 0.05 versus 30 min after occlusion), whereas it was unchanged in the saline-treated group. Functional infarct expansion (as assessed by end-systolic anterior to posterior endocardial segment length ratio) occurred early after occlusion, and captopril reduced this expansion. Pretreatment values for early diastolic isovolumic relaxation time increased from 29.1 +/- 2.4 to 50.5 +/- 2.9 ms in captopril-treated dogs (p less than 0.01) and from 34.3 +/- 3.4 to 46.9 +/- 2.7 ms in saline-treated dogs (p less than 0.01) after coronary occlusion, implying a worsening of diastolic function.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukocytes, oxygen radicals, and myocardial injury due to ischemia and reperfusion

Ischemic myocardium generates stimuli for neutrophil chemotaxis before the final extent of irreversible ischemic injury is attained. Reperfusion accelerates the infiltration of ischemic myocardium by neutrophils. Oxygen radicals released by the activated neutrophils may exacerbate the tissue damage caused by ischemia. Neutrophil depletion by antiserum was shown to limit infarct size in dogs undergoing coronary occlusion for 90 minutes followed by reperfusion for 6 or 72 hours, but not in dogs undergoing occlusion for 4 hours. Prostacyclin, which inhibits the generation of superoxide anions by neutrophils, also limited canine myocardial injury despite no effect on collateral blood flow. Iloprost, an analogue of prostacyclin that inhibits neutrophils also reduced infarct size, while SC39902, an analogue that does not inhibit neutrophils, did not alter infarct size. The results suggest that oxygen radicals released by activated neutrophils play a role in the pathophysiology of myocardial injury due to ischemia followed by reperfusion.

Myocardial infarct expansion, infarct extension, and reinfarction: pathophysiologic concepts

Infarct expansion and infarct extension are events early in the course of myocardial infarction with serious short- and long-term consequences. Infarct expansion, disproportionate thinning, and dilatation of the infarct segment probably begin within hours of acute infarction and usually reach peak extent within seven to 14 days. Clinical data suggest that infarct expansion occurs in approximately 35% to 45% of anterior transmural myocardial infarctions and to a lesser extent in infarctions at other sites. Although expansion usually develops in large infarcts, the extent of transmural necrosis rather than absolute infarct size predicts its occurrence. Expansion has an adverse effect on infarct structure and function for several reasons. Functional infarct size is increased because of infarct segment lengthening, and expansion results in over-all ventricular dilatation. Thus, patients with expansion of an infarct have poorer exercise tolerance, more congestive heart failure symptoms, and greater early and late mortality than those without expansion. Infarct rupture and late aneurysm formation are two additional structural consequences of infarct expansion. Experimental and clinical data suggest that the incidence and severity of expansion can be modified by interventions. Increased ventricular loading conditions and steroidal and nonsteroidal antiinflammatory agents make expansion more severe. Reperfusion of the infarct segment and pharmacologic interventions that decrease ventricular afterload lessen the severity of expansion. Previous myocardial infarction and preexisting ventricular hypertrophy may also limit the development of infarct expansion. Infarct extension is defined clinically as early in-hospital reinfarction after a myocardial infarction. The pathologic finding of infarct extension is necrotic and healing myocardium of several different recent ages within the same vascular territory. Although this pathologic criterion usually cannot be verified, studies employing invasive and noninvasive assessment of patients with early reinfarction provide evidence that the new myocardial injury is usually in the same vascular risk region as the original infarction. A variety of different criteria have been applied in the clinical diagnosis of infarct extension, and this has resulted in a large range of estimated frequencies from under 10% to as high as 86%. High estimates are found in studies using one or two nonspecific criteria such as ST segment shift or reelevation of total CK. The lowest rates have been found when combinations of criteria are used.(ABSTRACT TRUNCATED AT 400 WORDS)

Steroid administration after myocardial infarction promotes early infarct expansion. A study in the rat

Whether steroids lead to thinner scars and larger aneurysms by delaying collagen deposition or worsening infarct expansion before significant collagen deposition begins is unknown. Rats underwent either transmural infarction by left coronary ligation or sham operation. Both infarct and sham rats were randomized to methylprednisolone 50 mg/kg i.p. X 4 or saline treatment within 24 h after operation. Sacrifice occurred before (3 d) or after (7 d) collagen deposition typically begins. Despite similar infarct size, infarct wall thickness was 1.35 +/- 0.08 mm in the saline and 0.99 +/- 0.12 mm in the methylprednisolone group (P less than 0.001) at 3 d. This decrease in wall thickness was explained by a decrease in the number of myocytes across the infarct wall (r = 0.99; P less than 0.001), suggesting that steroids promote myocyte slippage. Furthermore, methylprednisolone caused no further infarct thinning or cavity dilatation beyond 3 d. Thus, high-dose methylprednisolone given within 24 h after transmural infarction worsens infarct expansion before collagen is laid down by promoting the slippage of necrotic myocytes.