Effect of captopril and enalapril on left ventricular geometry, function and collagen during healing after anterior and inferior myocardial infarction in a dog model

Testing the Translational Power of the Zebrafish: An Interspecies Analysis of Responses to Cardiovascular Drugs

The zebrafish is rapidly emerging as a promising alternative in vivo model for the detection of drug-induced cardiovascular effects. Despite its increasing popularity, the ability of this model to inform the drug development process is often limited by the uncertainties around the quantitative relevance of zebrafish responses compared with nonclinical mammalian species and ultimately humans. In this test of concept study, we provide a comparative quantitative analysis of the in vivo cardiovascular responses of zebrafish, rat, dog, and human to three model compounds (propranolol, losartan, and captopril), which act as modulators of two key systems (beta-adrenergic and renin–angiotensin systems) involved in the regulation of cardiovascular functions. We used in vivo imaging techniques to generate novel experimental data of drug-mediated cardiovascular effects in zebrafish larvae. These data were combined with a database of interspecies mammalian responses (i.e., heart rate, blood flow, vessel diameter, and stroke volume) extracted from the literature to perform a meta-analysis of effect size and direction across multiple species. In spite of the high heterogeneity of study design parameters, our analysis highlighted that zebrafish and human responses were largely comparable in >80% of drug/endpoint combinations. However, it also revealed a high intraspecies variability, which, in some cases, prevented a conclusive interpretation of the drug-induced effect. Despite the shortcomings of our study, the meta-analysis approach, combined with a suitable data visualization strategy, enabled us to observe patterns of response that would likely remain undetected with more traditional methods of qualitative comparative analysis. We propose that expanding this approach to larger datasets encompassing multiple drugs and modes of action would enable a rigorous and systematic assessment of the applicability domain of the zebrafish from both a mechanistic and phenotypic standpoint. This will increase the confidence in its application for the early detection of adverse drug reactions in any major organ system.

Protective Effect of Adansonia digitata against Isoproterenol-Induced Myocardial Injury in Rats

The baobab fruit (Adansonia digitata) was analyzed for proximate composition, amino acids, and minerals. The fruit pulp was found to be a good source of carbohydrates, proteins, phenols, and substantial quantities of K, Ca, and Mg. Amino acid analyses revealed high glutamic and aspartic acid, but the sulfur amino acids were the most limited. The present study was designed to investigate the role of Adansonia digitata (Baobab fruit pulp) against isoproterenol induced myocardial oxidative stress in experimental rats by demonstrating the changes in tissue cardiac markers, some antioxidant enzymes, interleukin-1 β (IL-1 β), monocyte chemoattractant protein-1(MCP-1), myeloperoxidase (MPO), Collagen-1, galectin-3, and serum corticosterone. The activities of enzymatic antioxidant glutathione peroxidase (GPX) and non-enzymatic antioxidant reduced glutathione (GSH) in the heart tissue; additionally, histopathological examination of the heart was estimated. Male albino rats were randomly divided into four groups of ten animals each. Group I served as normal control animal. Group II animals received isoproterenol (ISP) (85 mg/kg body weight intraperitonealy (i.p.) to develop myocardial injury. Group III were myocardial oxidative animals treated with Baobab fruit pulp (200 µg/rats/day) for 4 weeks. Group IV received Baobab fruit pulp only. The data suggested an isoproterenol increase in levels of cardiac marker enzymes [creatine kinase MB (CK- MB), lactate dehydrogenase (LDH), and aspartate aminotransferase (AST)], IL-1ß, MCP-1, MPO, Collagen, and galectin-3, with concomitant decrease in the activities GPX and GSH in heart tissue as well as corticosterone in serum. Baobab fruit pulp brings all the parameters to near normal level in ISP-induced myocardial infarction in rats. Histopathological examination of heart tissue of ISP-administered model rat showed infiltration of inflammatory cells and congestion in the blood vessels. However, treatment with Baobab fruit pulp (200 µg/rats/day) showed predominantly normal myocardial structure and no inflammatory cell infiltration. It has been concluded that Baobab fruit pulp has cardio protective effect against ISP-induced oxidative stress in rats.

Myocardial repair/remodelling following infarction: roles of local factors

Heart failure is a global health problem, appearing most commonly in patients with previous myocardial infarction (MI). Cardiac remodelling, particularly fibrosis, seen in both the infarcted and non-infarcted myocardium is recognized to be a major determinant of the development of impaired ventricular function, leading to a poor prognosis. Elucidating cellular and molecular mechanisms responsible for the accumulation of extracellular matrix is essential for designing cardioprotective and reparative strategies that could regress fibrosis after infarction. Multiple factors contribute to left ventricular remodelling at different stages post-MI. This review will discuss the role of oxidative stress and locally produced angiotensin II in the pathogenesis of myocardial repair/remodelling after MI.

Therapeutic drugs during healing after myocardial infarction modify infarct collagens and ventricular distensibility at elevated pressures

We investigated whether therapeutic drugs given during healing following acute myocardial infarction (AMI) modify infarct collagens and left ventricular (LV) distensibility. We treated dogs with drugs from major classes (i.e., indomethacin, ibuprofen, captopril, enalapril, verapamil, amlodipine, propranolol, isosorbide dinitrate [ISDN] and digoxin) between day 2 and 6 weeks and measured hemodynamics, LV remodeling and function during healing over 6 weeks after transmural anterior AMI, and regional collagens, LV distensibility under increasing pressure, rupture threshold (RT), and topography at 6 weeks. Relative to sham, AMI controls showed infarct zone (IZ) expansion and thinning, 9.3-fold increase in IZ collagen, LV dilation and dysfunction, and no change in distensibility and RT. Relative to controls, indomethacin as well as enalapril, captopril and amlodipine decreased IZ collagen. Infarct expansion was attenuated by ibuprofen, captopril, amlodipine and ISDN but augmented by indomethacin. Infarct thinning was prevented by captopril, amlodipine and ISDN but enhanced by indomethacin. Importantly, indomethacin and enalapril enhanced LV distensibility and lowered RT. Distensibility correlated positively with IZ type III collagen and negatively with type I/III collagen ratio and pyridinoline cross-links whereas RT correlated positively with IZ type I collagen. Systolic volume and ejection fraction deteriorated with indomethacin but were improved or preserved with other therapies. The results demonstrate that different therapeutic drugs may produce different effects on IZ collagens during healing post-AMI: drugs that attenuate or adversely alter IZ collagens also enhance LV distensibility, augment adverse remodeling and lower RT, suggesting that testing for these effects post-AMI is warranted.

Macrophage Colony-Stimulating Factor Treatment After Myocardial Infarction Attenuates Left Ventricular Dysfunction by Accelerating Infarct Repair

OBJECTIVES

We aimed to determine the effects of macrophage colony-stimulating factor (M-CSF) and granulocyte colony-stimulating factor (G-CSF) treatment on both the repair process and ventricular function after myocardial infarction (MI).

BACKGROUND

The M-CSF and G-CSF have multiple potential effects on cells involved in wound repair.

METHODS

Myocardial infarction was induced by 45- or 90-min coronary occlusion and reperfusion in rats with or without subsequent injection of M-CSF (10(6) IU/kg/day) or G-CSF (50 microg/kg/day) for five days. We examined histology and messenger ribonucleic acid (mRNA), and assessed left ventricular function in situ using a conductance catheter.

RESULTS

Five days after MI, M-CSF increased the number of ED-1-positive cells, mRNA levels of transforming growth factor-beta-1, collagen I and III, and collagen fibers within the infarct. Fourteen days after MI, induced by 45-min ischemia, left ventricular end-systolic elastance (Ees) was reduced (1,191 +/- 87 mm Hg/ml vs. 1,812 +/- 150 mm Hg/ml) and both isovolumic relaxation time constant (tau) (11.9 +/- 0.9 ms vs. 8.5 +/- 0.4 ms) and left ventricular end-diastolic volume (LVEDV) (0.225 +/- 0.014 ml vs. 0.172 +/- 0.011 ml) increased versus sham-operated rats. These alterations after MI were attenuated by M-CSF (Ees = 1,650 +/- 146, tau = 9.7 +/- 0.7, LVEDV = 0.199 +/- 0.012) but not by G-CSF. This beneficial effect of M-CSF on Ees was also detected in hearts with MI induced by 90-min ischemia. Furthermore, M-CSF increased collagen content within infarcts and reduced the proportion of thin collagen fibers 14 days after MI. The Ees significantly correlated with infarct collagen content. Nevertheless, neither M-CSF nor G-CSF modified infarct size.

CONCLUSIONS

The M-CSF treatment attenuates deterioration of left ventricular function after MI by accelerating infarct repair.

RAS and connective tissue in the heart

Circulating angiotensin (Ang) II has well-known endocrine properties in the cardiovasculature. AngII, produced de novo within the heart, has various autocrine and paracrine properties on resident cells expressed via AT(1) receptor-ligand binding. Herein, we review the heart's renin-angiotensin system and its role in connective tissue turnover involving heart valve leaflets and fibrous tissue that appears at sites of injury, such as following myocardial infarction.

Myocardial infarct expansion and matrix metalloproteinase inhibition

BACKGROUND

A potential mechanism for left ventricular (LV) remodeling after myocardial infarction (MI) is activation of the matrix metalloproteinases (MMPs). This study examined the effects of MMP inhibition (MMPi) on regional LV geometry and MMP levels after MI.

METHODS AND RESULTS

In pigs instrumented with radiopaque markers to measure regional myocardial geometry, MI was created by ligating the obtuse marginals of the circumflex artery. In the first study, pigs were randomized to MMPi (n=7; PD166793, 20 mg x kg(-1) x d(-1)) or MI only (n=7) at 5 days after MI, and measurements were performed at 2 weeks. Regional MI areas were equivalent at randomization and were increased in the MI-only group at 2 weeks after MI compared with the MMPi group. In the second study, pigs randomized to MMPi (n=9) or MI only (n=8) were serially followed up for 8 weeks. At 8 weeks after MI, LV end-diastolic dimension was lower with MMPi than in the MI-only group (4.7+/-0.1 versus 5.1+/-0.1 cm, P<0.05). Regional MI area was reduced with MMPi at 8 weeks after MI (1.3+/-0.1 versus 1.7+/-0.1 cm2, P<0.05). MMPi reduced ex vivo MMP proteolytic activity. In the MI region, membrane-type MMP levels were normalized and levels of the endogenous tissue inhibitor of MMPs (TIMP-1) were increased compared with normal levels with MMPi. These effects were not observed in the MI-only group.

CONCLUSIONS

MMPi attenuated the degree of post-MI LV dilation and expansion of the infarct during the late phase of MI healing. In addition, exogenous MMPi caused region-specific modulation of certain MMP and TIMP species.

Collagen accumulation after myocardial infarction: effects of ETA receptor blockade and implications for early remodeling

OBJECTIVES

Endothelin A (ETA) receptor blockade started early after myocardial infarction (MI) promotes adverse left ventricular (LV) dilatation. We tested the hypothesis that inhibition of ETA receptors during the early phase of healing affects collagen synthesis and accumulation, and induces expansion of infarcted myocardium.

METHODS

Starting 3 h after coronary ligation, female Wistar rats were treated with the selective ETA receptor antagonist LU 135252 (30 mg/kg body wt/day) or placebo. A period of 7 days after MI, hemodynamic, morphometric and biochemical studies were performed.

RESULTS

ET(A) receptor blockade enhanced infarct expansion index and decreased LV systolic function. Infarct scar of LU 135252-treated rats displayed decreased gene expression of fibrillar type I/III collagens and of transforming growth factor-beta(1) (TGF-beta(1)). Collagen content in the infarct scar and border regions was lower after ETA inhibition. In addition, Western blot analysis revealed, after ETA receptor blockade, enhanced matrix metalloproteinases MMP-13, and MMP-2 expression in the infarcted LV myocardium.

CONCLUSIONS

These data demonstrate that endothelin stimulates collagen accumulation at the site of infarction. Decreased collagen and TGF-beta(1) gene expression, associated with enhanced infarct expansion and MMP up-regulation likely contributes to ETA receptor blockade-mediated deleterious effects on ventricular remodeling after infarction.

Vascular remodeling during healing after myocardial infarction in the dog model: effects of reperfusion, amlodipine and enalapril

OBJECTIVES

We sought to determine whether reperfusion and the calcium channel blocker amlodipine or the angiotensin-converting enzyme inhibitor enalapril, during healing over six weeks after myocardial infarction (MI), limit structural vascular remodeling in the noninfarct zone (NIZ).

BACKGROUND

The effect of reperfusion and amlodipine or enalapril on structural vascular remodeling during healing of MI has not been determined.

METHODS

We randomly assigned 54 dogs to reperfused or nonreperfused MI, followed by twice-daily doses of oral placebo, amlodipine (5 mg) or enalapril (5 mg) for six weeks and three days off treatment, or to three matching sham groups. We measured in vivo hemodynamic data and left ventricular (LV) function and remodeling (by echocardiography) over the six weeks, as well as ex vivo structural vascular, ventricular and collagen remodeling in the hearts after six weeks.

RESULTS

Compared with placebo and sham groups, both amlodipine and enalapril with or without reperfusion produced LV unloading and limited structural LV remodeling and dysfunction over six weeks in vivo, and also decreased the NIZ resistance vessel media/lumen area ratio at six weeks ex vivo. In addition, amlodipine, but not enalapril, preserved infarct scar collagen and increased the border zone collagen volume fraction and perivascular fibrosis, as well as NIZ resistance vessel media thickness. Enalapril, but not amlodipine, decreased transforming growth factor-beta in the border zone and NIZ.

CONCLUSIONS

The results indicate that therapy with amlodipine and enalapril during healing after reperfused MI limits structural vascular remodeling in the NIZ, probably by different mechanisms.

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.

Ventricular remodeling after myocardial infarction and effects of ACE inhibition on hemodynamics and scar formation in SHR

The effect of ACE inhibition after myocardial infarction (MI) on MI healing and remodeling in the presence of hypertension is not exactly known. Therefore, the effect of quinapril on scar formation, remodeling and hemodynamics was studied in spontaneously hypertensive rats (SHR). Nine weeks after moderate and large MI, left ventricular end-diastolic pressure (LVEDP) and passive pressure-volume relations were similar in 28-week-old hypertensive and normotensive rats. Chronic therapy with quinapril (6 mg/kg/day, started 30 min post-MI) reduced LVEDP and LV to body weight ratio, yet did not affect pressure-volume relations. Quinapril increased MI size and reduced the content and brightness of collagen fibers in the scar examined by polarized light microscopy. In conclusion, ventricular dilatation after MI was not accelerated in SHR, probably due to LV hypertrophy. Quinapril produced beneficial hemodynamic effects similar to that observed in the normotensive rat model. The significance and timing of ACE inhibitor-induced impairment of scar formation need further evaluation.

Inhibition of collagen synthesis with prolyl 4-hydroxylase inhibitor improves left ventricular function and alters the pattern of left ventricular dilatation after myocardial infarction

Background- Left ventricular (LV) remodeling after myocardial infarction (MI) is associated with fibrosis, dilatation, and dysfunction. We postulated that prevention of fibrosis after MI with a prolyl 4-hydroxylase inhibitor (P4HI) would preserve LV function and attenuate LV enlargement. Methods and Results- Adult female rats (200 to 250 g) had experimental MI and were then randomized to treatment with P4HI (MI-FG041, n=29) or vehicle (MI-control, n=29) 48 hours after MI for 4 weeks in 2 phases. Echocardiograms were performed weekly with a 15-MHz linear transducer, and at 4 weeks, collagen isoform determinations and in vivo hemodynamics were performed. At randomization, the infarct size and LV function and size were similar in MI-FG041 and MI-control but significantly different from shams (n=9). At week 4, the LV function in MI-FG041 was significantly better than in MI-controls (fractional shortening 21% versus 16%, P=0.01; fractional area change 30% versus 19%, P=0.002; ejection fraction 35% versus 23%, P=0.001). In the FG041 group, LV area in systole was less (P<0.05), the dP/dt(max) after isoproterenol was higher (P<0.05), and types I and III collagen in noninfarcted LV were less than in MI-control. The hydroxyproline/proline ratio was increased by 64% in MI-control and reduced to the sham value in MI-FG041 rats. In the scar tissue, it was reduced by 24% in MI-FG041. Conclusions- This study demonstrates that prevention of interstitial fibrosis with a P4H inhibitor alters the pattern of LV enlargement and produces partial recovery of LV function after MI.

Recruitable ACE and tissue repair in the infarcted heart

Constitutive angiotensin-converting enzyme (ACE) is bound to endothelial cells where it serves to regulate circulating concentrations of angiotensin II (Ang II) that normally contribute to circulatory homeostasis. Recruitable ACE, bound to macrophage and myofibroblast cell membrane, regulates local concentrations of Ang II involved in tissue repair. De novo generation of Ang II modulates expression of TGF-beta1 whose autocrine/paracrine properties regulate collagen turnover at sites of fibrous tissue formation that appear in response to various forms of injury in diverse tissues. Persistent myofibroblasts and their ACE activity at the infarct site contribute to a sustained metabolic activity that can account for a progressive fibrosis at, and remote to, sites of myocardial infarction. Activation of the circulating renin-angiotensin-aldosterone system with sustained elevations in plasma Ang II and aldosterone induce a pro-inflammatory vascular phenotype of small arteries and arterioles. This further promotes the appearance of recruitable ACE bound to macrophages and myofibroblasts involved in vascular remodelling. Locally produced Ang II from these vascular sites leads to perivascular fibrosis of intramural coronary vasculature of non-infarcted myocardium. At these sites, remote to the infarct, such adverse structural remodelling by fibrous tissue eventuates in ICM, a major aetiologic factor involved in the appearance of chronic cardiac failure and contributes to its progressive nature.

Cardiac remodeling--concepts and clinical implications: a consensus paper from an international forum on cardiac remodeling. Behalf of an International Forum on Cardiac Remodeling

Cardiac remodeling is generally accepted as a determinant of the clinical course of heart failure (HF). Defined as genome expression resulting in molecular, cellular and interstitial changes and manifested clinically as changes in size, shape and function of the heart resulting from cardiac load or injury, cardiac remodeling is influenced by hemodynamic load, neurohormonal activation and other factors still under investigation. Although patients with major remodeling demonstrate progressive worsening of cardiac function, slowing or reversing remodeling has only recently become a goal of HF therapy. Mechanisms other than remodeling can also influence the course of heart disease, and disease progression may occur in other ways in the absence of cardiac remodeling. Left ventricular end-diastolic and end-systolic volume and ejection fraction data provide support for the beneficial effects of therapeutic agents such as angiotensin-converting enzyme (ACE) inhibitors and beta-adrenergic blocking agents on the remodeling process. These agents also provide benefits in terms of morbidity and mortality. Although measurement of ejection fraction can reliably guide initiation of treatment in HF, opinions differ regarding the value of ejection fraction data in guiding ongoing therapy. The role of echocardiography or radionuclide imaging in the management and monitoring of HF is as yet unclear. To fully appreciate the potential benefits of HF therapies, clinicians should understand the relationship between remodeling and HF progression. Their patients may then, in turn, acquire an improved understanding of their disease and the treatments they are given.

Secondary prevention of myocardial infarction: role of beta-adrenergic blockers and angiotensin-converting enzyme inhibitors

beta-Blockers reduce cardiovascular death and reinfarction in patients with a history of myocardial infarction (MI), and angiotensin-converting enzyme (ACE) inhibitors provide an overall survival benefit in patients with signs or symptoms of left ventricular (LV) dysfunction and a history of acute MI. Despite this, these agents remain underused in clinical practice. Appropriate patient selection in standard clinical practice should be encouraged in order to achieve a mortality rate reduction comparable to that seen in clinical trials. It appears from the findings of recent studies that the greatest benefit from beta-blocker therapy is achieved in patients who are more than 60 years of age and in patients at moderate or high risk for reinfarction and death (eg, patients with LV dysfunction or arrhythmias or both). Patients with class I-IV heart failure treated with ACE inhibitors have fewer recurrent infarctions, a lower incidence of severe congestive heart failure, and a reduced incidence of total cardiovascular death and sudden cardiac death. In addition to the studies completed in patients with MI, there are ongoing studies evaluating whether or not ACE inhibitors can reduce myocardial ischemic events in patients without a prior infarction who have coronary artery disease or hypertension and preserved LV function. There is also growing evidence that concomitant therapy with a beta-blocker and an ACE inhibitor may reduce mortality rates beyond that observed with ACE inhibitors alone in survivors of MI who have LV dysfunction.

Early captopril prevents myocardial infarction-induced hypertrophy but not angiogenesis

Delayed captopril, started after the healing phase of myocardial infarction, improves perfusion by reducing tissue weight without affecting the vascular capacity of the heart. Early captopril, during the healing phase, prevents reactive hypertrophy, but the effects on angiogenesis are unknown. Therefore, the effects of early captopril (2 g/l drinking water, from 1 day until 3 weeks after myocardial infarction) on regional coronary flow related to tissue mass, were studied in isolated perfused hearts from rats, subjected to coronary artery ligation. Regional maximal vascular capacity was measured during nitroprusside-induced vasodilation, using radioactive microspheres. Maximal vascular capacity was not changed by captopril. Reactive hypertrophy in infarcted hearts only reached statistical significance in the left ventricular free wall. Since captopril prevented hypertrophy but did not affect regional capacity, peak tissue perfusion was improved. Indicating effects on metabolism, captopril restored the increased lactate/purine ratio in infarcted hearts. Thus, early captopril treatment prevented post-myocardial infarction hypertrophy but did not suppress angiogenesis, thus beneficially influencing the vascularization/tissue mass ratio, probably reflected by preservation of aerobic metabolism.

Risk stratification after myocardial infarction using signal-averaged electrocardiographic criteria adjusted for sex, age, and myocardial infarction location

BACKGROUND

The objectives were to investigate the factors influencing signal-averaged ECGs (SAECGs) recorded in patients after myocardial infarction (MI) and to develop criteria for predicting arrhythmic events (AEs) that account for these factors.

METHODS AND RESULTS

SAECGs were recorded 5 to 15 days after MI in 2461 patients without bundle-branch block. The duration (QRSd), terminal potential (VRMS), and terminal duration (LAS) of the filtered QRS were measured. During follow-up (17 +/- 8 months), AEs (arrhythmic death; ventricular tachycardia, VT; ventricular fibrillation, VF) occurred in 80 patients (3.3%). Receiver operating characteristic curves showed that QRSd discriminated patients with all types of AEs, but VRMS and LAS discriminated only VT patients; QRSd minus LAS also discriminated AE patients. Sex, age, and MI location significantly affected the SAECG; survivors without VT or VF were divided into subgroups (2 sex x 4 age x 2 MI), and QRSd values exceeding the 70th percentile in each subgroup predicted AEs with a sensitivity of 65.4%. An unadjusted QRSd criterion showed the same overall sensitivity and specificity but with less uniform values for each subgroup. A Cox model was constructed by use of multiple prognostic indicators, and in rank order, QRSd, previous MI, and Killip class were predictive of AEs.

CONCLUSIONS

SAECG adjustments for sex, age, and MI location did not improve sensitivity and specificity but produced a more uniform predictive performance. The proposed criteria are based only on QRSd, because late potentials (VRMS and LAS) did not discriminate patients with sudden death. Duration of high-level activity during QRS (QRSd-LAS) can predict AEs, suggesting that the arrhythmogenic substate involves a large mass of myocardium.

Effects of afterload-reducing drugs on pathogenesis of antioxidant changes and congestive heart failure in rats

OBJECTIVES

The present study sought to evaluate the effects of the afterload-reducing drugs captopril and prazosin on changes in antioxidants as well as oxidative stress in relation to hemodynamic function in congestive heart failure (CHF) subsequent to myocardial infarction (MI).

BACKGROUND

Afterload reduction therapy has been shown to reduce morbidity and mortality in patients with MI. CHF subsequent to MI in rats is associated with a decrease in myocardial endogenous antioxidants and an increase in oxidative stress.

METHODS

The left anterior descending coronary artery in male Sprague-Dawley rats was ligated. Sham and experimental (post-MI [PMI]) animals were assessed for hemodynamic function as well as lung and liver weights at 1, 4 and 16 weeks after operation. At 4 weeks, some rats were also treated with captopril (2 g/liter in drinking water daily) or prazosin (0.2 mg/kg body weight subcutaneously daily) and assessed at 16 weeks. Hearts were isolated to study the activity of superoxide dismutase (SOD), glutathione peroxidase (GSHPx) and catalase as well as for thiobarbituric acid reactive substances (TBARS).

RESULTS

CHF at 4 and 16 weeks in the infarcted rats was indicated by an increase in left ventricular end-diastolic pressure and wet/dry weight lung and liver ratios and depressed left ventricular systolic pressure and dyspnea. All these changes were attenuated in both the captopril- and prazosin-treated groups. SOD, GSHPx and catalase activity in the untreated PMI groups was decreased at 4 and 16 weeks. However, treatment with captopril resulted in a significant improvement in SOD, GSHPx and catalase activity in the 16-week PMI group. With prazosin, only SOD activity was improved in the treated 16-week PMI group. Lipid peroxidation as indicated by TBARS was significantly increased in the 16-week PMI group, and both captopril and prazosin modulated this increase.

CONCLUSIONS

Occurrence of an antioxidant deficit and an increase in oxidative stress in the myocardium may play a role in the pathogenesis of CHF subsequent to MI. Attenuation of these changes in antioxidant activity with vasodilator (or antioxidant?) therapy mitigates the process of heart failure.

Protective effect of captopril on ischemic myocardium

The protective effect and mechanism of action of the angiotensin-converting enzyme inhibitor (ACE-I) captopril was investigated in organelles from ischemic myocardial cells in a canine coronary ligation model. Sarcoplasmic reticulum (SR) and mitochondrial fractions were extracted from ischemic and nonischemic myocardial cells from captopril- and saline-treated (control) hearts. Heart rate, cardiac output, and right ventricular systolic blood pressure were similar in the captopril-treated and control groups. Left ventricular systolic blood pressure (LVPs) decreased gradually to 89% of the baseline value after captopril administration, and to 78% of the baseline value after ligation. Ca-ATPase activity in the SR, the respiratory control ratio (RCR) in the mitochondria, and dinitrophenol (DNP)-stimulated ATPase activity were significantly higher in ischemic myocardium from the captopril-treated group than from the saline-treated (control) group. The SH group content of both organelles was higher in the captopril-treated group. Our results suggest that, in addition to their hemodynamic effects, ACE-I agents containing SH groups protect the myocardium from ischemic damage by preventing enzyme oxidation.

Effect of nitrates on myocardial remodeling after acute myocardial infarction

Nitrates are effective for the therapy of acute coronary syndromes, including acute myocardial infarction. Their application in acute infarction has established that vasodilators are beneficial provided hypotension is avoided. Nitrates limit early ventricular remodeling in infarction. New dosing strategies and formulations that permit chronic use after infarction with less tolerance might limit late remodeling. Over the last decade, the demonstrated effectiveness of angiotensin-converting enzyme (ACE) inhibitors in limiting ventricular dilation postinfarction has generated controversy over the usefulness of nitrates for that indication. The uncertainty has been intensified by 2 large mortality trials that tested both agents as adjuncts to conventional therapy. These trials were not designed to test whether nitrates might limit remodeling. Mechanistic experimental and clinical studies that tested whether nitrates or ACE inhibitors could effectively limit ventricular remodeling showed that both improved remodeling endpoints. However, experimental studies raise some concern about the decrease in infarct collagen associated with ACE inhibition and emphasize the fact that final outcome represents a balance of effects. That nitrates do not decrease infarct collagen could be important. Nitrate-induced early recruitment of ventricular function after late reperfusion of acute infarction might also be important. In the mortality trials, >50% of patients received open-label nitrates as per indication. Thus, the trial results to date do not suggest that nitrates are ineffective for remodeling, but rather that ACE inhibitors can confer added benefit. There has been no large clinical trial to test the efficacy of nitrates for remodeling as there has been for ACE inhibitors.

Mechanisms of subcellular remodelling in post-infarct heart failure

Occlusion of a coronary artery results in myocardial ischemia and subsequent myocardial infarction. Whenever the infarct size is more than 30% of the ventricular wall, the remaining myocardium attempts to compensate for the loss of muscle mass by changing the size and shape of cardiocytes in addition to developing cardiac hypertrophy, cardiac dilatation and congestive heart failure. This remodeling of the heart is associated with changes in the extracellular matrix including collagen proteins and is most probably due to the activation of both sympathetic nervous system and renin-angiotensin system as well as increased formation of various growth factors. Alterations in contractile function of the infarcted heart are associated with remodelling of the sarcoplasmic reticulum with respect to Ca(2+)-pump and Ca(2+)-release channels as well as contractile and regulatory proteins of the myofibrils. Myocardial infarction has also been shown to result in remodelling of the sarcolemmal membrane with respect to Ca(2+)-channels, Ca(2+)-transport systems, cardiac receptors and signal transduction mechanisms. Although information regarding remodelling of mitochondria in the infarcted heart is limited, alterations in energy yielding and Ca(2+)-accumulating systems are suspected. Accordingly, it is suggested that changes in cardiac contractile dysfunction due to myocardial infarction are associated with remodeling of both extracellular matrix and subcellular organelles in the heart.