Functional significance of hypertrophy of the noninfarcted myocardium after myocardial infarction in humans

Effects of oral amino acid supplements on cardiac function and remodeling in patients with type 2 diabetes with mild-to-moderate left ventricular dysfunction

The aim of this study was to evaluate the effects of an oral special mixture of amino acid (AA) supplements alongside angiotensin-converting enzyme (ACE) inhibitor therapy on left ventricular (LV) function and symptoms in patients with type 2 diabetes mellitus with mild-to-moderate LV dysfunction. It is established that the remodeling process is associated with late onset of heart failure and decreased survival. ACE inhibitor therapy reduces progressive increases in LV dimensions and significantly improves the clinical course of a broad spectrum of patients with LV dysfunction. Moreover, AA supplements prevent myocardial dysfunction caused by exercise in patients with type 2 diabetes. In addition to ACE inhibitor therapy, patients with diabetes were randomly assigned to receive AA supplements or placebo. LV function and dimensions were assessed with quantitative echocardiographic tests at intake into the study and after 6 months of follow-up. In patients with type 2 diabetes, LV end-diastolic index was reduced significantly during the 6-month period of AA consumption (89 +/- 9 mL/m2 vs 76 +/- 8 mL/m2; p <0.01), and LV ejection fraction (LVEF) improved (0.46 +/- 0.07 vs 0.52 +/- 0.05; p <0.001). No significant changes in LVEF or LV end-diastolic index occurred in the placebo group. These findings suggest that AA supplementation, together with ACE-inhibitor therapy, may have a beneficial effect on the LV remodeling process in patients with type 2 diabetes with mild-to-moderate LV dysfunction.

B-Type Natriuretic Peptide Enhances Mild Hypoxia-Induced Apoptotic Cell Death in Cardiomyocytes

In the case of left ventricle remodeling after myocardial infarction, cardiomyocyte apoptosis is attributed to increased cardiac workload by the stimulus such as chronic hypoxia. B-Type natriuretic peptide, being known as a reliable prognostic of cardiovascular pathology, plays an important role in the myocardial infarction. However, the action of B-type natriuretic peptide on cardiomyocytes undergoing apoptosis is unclear. In the present study, B-type natriuretic peptide have exhibited the enhancive effects on the mild hypoxia-induced cardiomyocyte apoptosis with the manifestation of facilitating phosphatidylserine evagination and increasing typical fragmented nuclei. In addition, B-type natriuretic peptide aggravated the dissipation of delta psi(m), the depletion of intracellular ATP and the increase of caspase-3 activity. 8-Bromo-cGMP, which increased cGMP independent of B-type natriuretic peptide, could mimic B-type natriuretic peptide's effects; whereas cGMP-dependent protein kinase inhibitor, Rp-8-br-cGMP inhibited that. Further study revealed the enhancive effect of BNP on down-regulation of Bcl-2 mRNA expression in the presence of mild hypoxia. In conclusion, the present study demonstrated that B-type natriuretic peptide aggravated the cardiomyocyte apoptosis by influencing hypoxia-induced mitochondrial death pathway, which is true at least in this oxygen deprivation model; and this effect was partially realized through intracellular cGMP.

Influence of gender on the response to hemodynamic overload after myocardial infarction

After myocardial infarction (MI), the left ventricle (LV) undergoes ventricular remodeling characterized by progressive global dilation, infarct expansion, and compensatory hypertrophy of the noninfarcted myocardium. Little attention has been given to the response of remodeling myocardium to additional hemodynamic overload. Studies have indicated that gender may influence remodeling and the response to both MI and hemodynamic overload. We therefore determined 1) structural and function consequences of superimposing hemodynamic overload (systemic hypertension) on remodeling myocardium after a MI and 2) the potential influence of gender on this remodeling response. Male and female Dahl salt-sensitive and salt-resistant rats underwent coronary ligation, resulting in similar degrees of MI. One week post-MI, all rats were placed on a high-salt diet. Four groups were then studied 4 wk after initiation of high-salt feeding: MI female, MI female + hypertension, MI male, and MI male + hypertension. Hypertension-induced pressure overload resulted in additional comparable degrees of myocardial hypertrophy in both females and males. In females, hypertension post-MI resulted in concentric hypertrophy with no additional cavity dilation and no measurable scar thinning. In contrast, in males, hypertension post-MI resulted in eccentric hypertrophy, further LV cavity dilation, and scar thinning. Physiologically, concentric hypertrophy in post-MI hypertensive females resulted in elevated contractile function, whereas eccentrically hypertrophied males had no such increase. Female gender influences favorably the remodeling and physiological response to hemodynamic overload after large MI.

Prognostic value of left ventricular hypertrophy and geometry in patients with a first, uncomplicated myocardial infarction

BACKGROUND

The prognostic impact of left ventricular (LV) geometry on cardiovascular risk for patients with a first, uncomplicated acute myocardial infarction (AMI), and echocardiographic ejection fraction > or =50% has not been well described.

METHODS AND RESULTS

Accordingly, 111 AMI consecutive patients (mean age 59.3+/-10 years) performed echocardiographic examination at predischarge. LV mass was calculated by means of Devereux's formula and subsequently indexed by body surface area. Fifty-three patients had LV hypertrophy and 58 patients had normal LV mass. The two groups were homogeneous for demographic, clinical and angiographic variables as well as for the incidence of residual ischemia on predischarge stress testing. During follow-up period there were 24 cardiac events (cardiac death, unstable angina and non-fatal reinfarction) in the 53 patients with LV hypertrophy and only four events in the remaining 58 patients without LV hypertrophy (RR=2.45; CI=1.76-3.41; P<0.0001). The patients with concentric LV hypertrophy showed a higher incidence of events (64%) than patients with eccentric LV hypertrophy (32%, P<0. 05) and patients with normal geometry and mass (6%, P<0.0001). Multivariate Cox regression model identified concentric geometry as the most powerful predictor of combined end-points (chi(2)=32.7, P<0. 0001).

CONCLUSIONS

An increased LV mass and concentric geometry resulted important independent markers of an adverse outcome in patients with a first, uncomplicated myocardial infarction and good LV function.

Remote myocardial dysfunction after acute anterior myocardial infarction: impact of left ventricular shape on regional function: a magnetic resonance myocardial tagging study

OBJECTIVES

We sought to evaluate regional morphology and function in patients in their first week after having a reperfused anterior myocardial infarction (MI) using magnetic resonance (MR) myocardial tagging.

BACKGROUND

The mechanism of myocardial dysfunction in the remote, noninfarct-related regions is an unresolved issue to date.

METHODS

Sixteen patients with a first reperfused transmural anterior MI were studied with MR tagging at 5 +/- 2 days after the event, and the results were compared with those of an age-matched control group regions. The left ventricle (LV) was divided into infarct, adjacent and remote regions. Magnetic resonance tagging provided information on the regional ventricular morphology and function.

RESULTS

Morphologically, an increase of the circumferential radius of curvature was found in the remote myocardium, whereas the longitudinal radius of curvature was increased in all regions of the LV. A significant increase in apical sphericity was also found. A significant reduction in strain and function was found not only in the infarct region, but also in the adjacent and remote myocardium. The loss in regional ejection fraction in the remote myocardium (61.4 +/- 11.7% in patients vs. 68.7 +/- 10.0% in control subjects, p < 0.0001) was related to a significant reduction of the longitudinal and circumferential strain, whereas systolic wall thickening was preserved.

CONCLUSIONS

Remote myocardial dysfunction contributes significantly to the loss in global ventricular function. This could be secondary to morphologic changes in the infarct region, leading to an increased systolic longitudinal wall stress without loss of intrinsic contractility in the remote regions.

Functional impact of an increase in ventricular mass after myocardial damage and its attenuation by converting enzyme inhibition

BACKGROUND

A increase in left ventricular mass after ventricular damage has been identified as an initial response to injury. However, the functional significance of this response has not been clearly established and is the focus of this study.

METHODS AND RESULTS

Twelve mongrel dogs underwent transmyocardial direct current shock to produce transmural left ventricular damage. Six were assigned to converting enzyme inhibitor therapy initiated 24 hours after damage and continued for 4 weeks. The remaining six dogs served as a control group. Left ventricular structure (mass and end diastolic volume) and systolic function (regional and global ejection fraction at rest and during afterload stress) were assessed by magnetic resonance imaging before damage and at the end of the 4-week period. After myocardial damage, left ventricular mass increased from 93.6 +/- 4.0 to 107.5 +/- 3.4 gm in the control group (P < .01) with no change in ventricular volume. Ramipril-treated dogs displayed a reduction in mass (83.2 +/- 2.2 to 74.6 +/- 2.9 gm, P < .05). In the control group, there was greater reduction in global ejection fraction in response to afterload stress at 4 weeks compared with baseline (-16 +/- 4 vs -4 +/- 3%, P = .03). Ejection fraction response to afterload stress was maintained at 4 weeks in the converting enzyme inhibitor-treated group (-5 +/- 3 vs - 1 +/- 4%) and was different at 4 weeks from the control group (-1 +/- 4 vs -16 +/- 4%, P = .004).

CONCLUSION

The increase in left ventricular mass noted after direct current shock was associated with the impairment of systolic function during afterload stress. Inhibition of this mass increase results in preservation of function, thus further supporting the concept that attenuation of ventricular remodeling should be a therapeutic goal.

Frequency of sudden cardiac death and profiles of risk

The epidemiology of ventricular tachycardia/fibrillation (VT/VF) and sudden cardiac death (SCD) must be explored from multiple aspects, each of which contributes insights into the problem and no one of which exerts exclusive dominance for preventive or therapeutic strategies. These include: (1) population dynamics, using conventional epidemiologic approaches; (2) risk as a function of time from an index event; (3) conditioning risk factors, based on the presence of underlying disease states; (4) transient risk factors that are dynamic and trigger a potentially fatal event at a specific point in time; and (5) "response risk," which refers to individual susceptibility (possibly determined genetically) to the adverse effects of longitudinal and/or dynamic risk factors. Major inroads into profiling individual or population risk of SCD will require better understanding of each of these epidemiologic-clinical-physiologic interactions. The disciplines range from epidemiology, through clinical medicine, to membrane channel physiology, genetic determinants, and molecular biology.

Regional gradation of L-type calcium currents in the feline heart with a healed myocardial infarct

INTRODUCTION

Abnormal action potentials in myocytes adjacent to > 2-month-old feline LV myocardial infarcts (MI) may reflect alterations in Ca2+ currents (Ica).

METHODS AND RESULTS

We compared ICa, at 36 degrees C, in subendocardial myocytes isolated from areas adjacent to MI and to ICa in cells from remote areas (> 4 mm away; REM) and control cells from similar regions in normal hearts. Control (CON) myocytes had membrane capacitance of 234 +/- 10 pF (n = 81 cells) compared to 305 +/- 14 pF in REM (71 cells; P < 0.05 from CON) and 237 +/- 11 pF (n = 55 cells) in MI (not different from CON). From Vh = -40 mV; peak ICa elicited by test potentials (-35 to +70 mV) were significantly larger in CON (-1746 +/- 123 pA) and REM (-1795 +/- 142 pA) compared to MI (-1352 +/- 129 pA) (P < 0.05). Peak ICa density was significantly reduced in REM (-6.0 +/- 0.4 pA/pF) or MI (-5.7 +/- 0.4 pA/pF, P < 0.05) compared to CON (-7.5 +/- 0.4 pA/pF). Double exponential ICa decay was similar among groups. Half-inactivation potential (V0.5) was significantly shifted (hyperpolarizing direction) for MI (-29.1 +/- 2.6 mV) and REM (-24.6 +/- 1.2 mV) myocytes compared to -20.3 +/- 1.0 mV in CON. MI slope factor (k; 9.0 +/- 0.5) was significantly different from CON (6.8 +/- 0.3) and REM (7.3 +/- 0.4). No differences in time course of recovery from inactivation were noted. Five millimolar Ba2+o produced significant increases in ICa in CON and REM but an attenuated response in MI. Bay K8644 (1 microM) produced similar ICa increase in all groups. ICa increase due to isoproterenol (1 microM) in MI and REM was half that in CON, but there were no differences in increased ICa responses among groups following phenylephrine (10 microM).

CONCLUSION

Reduced ICa density in REM reflects cell hypertrophy, whereas altered ICa of MI may reflect altered channel structure and/or function.

Angiotensin-converting enzyme inhibitor therapy affects left ventricular mass in patients with ejection fraction > 40% after acute myocardial infarction

OBJECTIVES

We tested the hypothesis that angiotensin-converting enzyme (ACE) inhibitor therapy decreases left ventricular (LV) mass in patients with a left ventricular ejection fraction (LVEF) > 40% and no evidence of heart failure after their first acute Q wave myocardial infarction (MI).

BACKGROUND

Recently, ACE inhibitor therapy has been shown to have an early mortality benefit in unselected patients with acute MI, including patients without heart failure and a LVEF > 35%. However, the effects on LV mass and volume in this patient population have not been studied.

METHODS

Thirty-five patients with a LVEF > 40% after their first acute Q wave MI were randomized to titrated oral ramipril (n = 20) or conventional therapy (control, n = 15). Magnetic resonance imaging (MRI) performed an average of 7 days and 3 months after MI provided LV volumes and mass from summated serial short-axis slices.

RESULTS

Left ventricular end-diastolic volume index did not change in ramipril-treated patients (62 +/- 16 [SD] to 66 +/- 17 ml/m2) or in control patients (62 +/- 16 to 68 +/- 17 ml/m2), and stroke volume index increased significantly in both groups. However, LV mass index decreased in ramipril-treated patients (82 +/- 18 to 73 +/- 19 g/m2, p = 0.0002) but not in the control patients (77 +/- 15 to 79 +/- 23 g/m2). Systolic arterial pressure did not change in either group at 3-month follow-up.

CONCLUSIONS

In patients with a LVEF > 40% after acute MI, ramipril decreased LV mass, and blood pressure and LV function were unchanged after 3 months of therapy. Whether the decrease in mass represents a sustained effect that is associated with a decrease in morbid events requires further investigation.

Pathophysiologic aspects of end-stage heart failure

Heart failure is not a distinct disease, but rather a complex clinical syndrome that can result from virtually any form of heart disease. The so-called "end stages" of heart failure do not respect etiologic boundaries. Patients are characterized clinically by extreme cardiomegaly, breathlessness, and fluid retention. Despite recent advances in the pharmacologic management of congestive heart failure, it remains a highly lethal and disabling disorder. Only through an improved understanding of the basic biology of the early stages of the syndrome can heart failure be prevented or at least forestalled. There is now intense interest in understanding the mechanisms operative in early left ventricular remodeling, which has the potential to culminate in end-stage heart failure. The study of animal models has been particularly useful in this regard, as have clinical studies performed in the early stages of acute myocardial infarction. The remodeling process is characterized by myocyte loss and segmental scarring, interstitial fibrosis, myocardial slippage, and myocyte hypertrophy. Although the mechanisms responsible for these topographic changes are as yet unclear, the net result is progressive enlargement of the heart, culminating in severe left ventricular dysfunction. A long-held view that cardiomegaly is a necessary adaptive process that maintains stroke volume in the presence of a falling ejection fraction has been challenged, although undoubtedly the early responses to myocardial injury in the form of myocyte hypertrophy and maintenance of wall stress are useful adaptations. However, as the left ventricle continues to dilate and hypertrophy over time, a form of overadjustment occurs that perhaps is an important contributory factor toward end-stage failure.

Ventricular dilatation and remodeling after myocardial infarction

OBJECTIVE

To discuss the important predictors of ventricular enlargement after myocardial infarction and the appropriate time frame for the initiation of medical and pharmacologic therapy.

DESIGN

A review of the important contributions relative to the process known as "postinfarction ventricular remodeling" is provided; current clinical implications and areas for future investigation are discussed.

MATERIAL AND METHODS

Ventricular dilatation is an important factor in the prognosis after infarction. Stretching and thinning of the myocardium within the infarct region can be seen within hours after the acute event and may be accompanied by delayed but potentially progressive stretching and thinning in the noninfarct regions. Development of left ventricular hypertrophy in the nonischemic myocardium, in response to increased wall stress, can be observed but may be insufficient for proper compensation. This process is referred to as postinfarction remodeling and can result in progressive and long-term changes in ventricular architecture and function in the absence of additional ischemic injury.

RESULTS

The most effective way to limit the extent of postinfarction ventricular remodeling is to limit infarct size by prompt medical intervention within the first few hours. In addition to traditional post-infarction medications such as beta-blockers, nitrates, and aspirin, long-term benefit may be derived by use of adjunctive pharmacologic therapy such as angiotensin converting enzyme inhibitors, which have been shown to be valuable in limiting the extent of ventricular chamber dilatation after infarction. Studies in animal models and conclusions from clinical trials have shown that angiotensin converting enzyme inhibitors also decrease late mortality and cardiac morbidity after infarction, likely through favorable effects on both hemodynamic and neurohumoral factors specific to this class of medication.

CONCLUSION

These investigations notwithstanding, further studies are necessary for a complete understanding of the pathogenesis of postinfarction ventricular remodeling and the appropriate timing of specific pharmacologic therapy intended to limit ventricular dilatation. The hemodynamic and neurohumoral interactions on and within the heart must be thoroughly understood relative to microscopic and macroscopic changes in cardiac size, shape, and function after myocardial infarction.

Effect of prolonged nitrate therapy on left ventricular remodeling after canine acute myocardial infarction

BACKGROUND

Prolonged nitrate therapy during healing between 2 days and 6 weeks after anterior myocardial infarction has the potential for limiting further left ventricular remodeling (or changes in topography) and preserving function. Longterm therapy throughout healing over 6 weeks might be more beneficial than short-term therapy over the first 2 weeks after infarction.

METHODS AND RESULTS

The effect of prolonged nitrate therapy between 2 days and 6 weeks during healing after infarction on serial parameters of ventricular remodeling (scar expansion, scar thinning, ventricular dilation, and hypertrophy) and function (asynergy or akinesis plus dyskinesis and ejection fraction) by serial two-dimensional echocardiography, hemodynamics, postmortem topography (computerized planimetry, geometric maps, and radiographs), and collagen content (hydroxyproline) was studied in 64 instrumented dogs randomized 2 days after left anterior descending coronary artery ligation to various nitrate regimens (n = 32) over the first 2 weeks (subgroup 1: 2% transdermal nitroglycerin at 8 AM and 4 PM, n = 6; subgroup 2: 2% transdermal nitroglycerin plus 2.6 mg of sustained-release oral nitroglycerin at 8 AM, 3 PM, and 10 PM, n = 5; subgroup 3: oral isosorbide dinitrate, 30 mg at 8 AM and 4 PM, n = 11) or 6 weeks (subgroup 4: isosorbide dinitrate, n = 10) and in matching controls (n = 32). Nitrate therapy reduced left atrial pressure, mean arterial pressure, and the rate-pressure product compared with controls over the 6 weeks. Postmortem scar mass and hydroxyproline were similar in control and nitrate groups. However, scar stretching and thinning, cavity dilation, noninfarct wall hypertrophy, and apical bulging were less with nitrates, especially in the long-term subgroup 4. In vivo remodeling parameters between 2 days and 6 weeks after ligation showed that, compared with controls, nitrate therapy prevented further stretching of the asynergic segment, decreased the expansion index, decreased further scar thinning, prevented the increase in ventricular volumes, reduced the frequency of ventricular aneurysm, prevented the increase in ventricular mass, reduced the extent of asynergy, and improved ejection fraction. Although the beneficial effect on topography and function was seen in all nitrate subgroups, the overall benefit was greater with long-term therapy over 6 weeks (subgroup 4) than short-term therapy confined to the first 2 weeks (subgroups 1, 2, and 3).

CONCLUSIONS

Prolonged nitrate therapy, in various regimens during healing after infarction, effectively reduced left ventricular loading and prevented infarct thinning, further infarct expansion, progressive ventricular dilation, and the increase in mass. These effects were associated with decreased asynergy and improved ejection fraction. The beneficial effects were greater with long-term therapy over 6 weeks than short-term therapy over the first 2 weeks.

Coronary collateral circulation and diastolic function

Patients with coronary artery disease reportedly have an impaired left ventricular filling. To evaluate the effects of coronary collaterals on diastolic function in patients with effort-induced angina, resting radionuclide ventriculography was performed in 14 patients with severe isolated (> or = 90% diameter) stenosis of the left anterior descending coronary artery and in seven normal subjects. Contrast ventriculography showed normal wall motion in all patients. Functional indices obtained by radionuclide ventriculography were compared between those patients with collateral vessels, Rentrop classification grades 1 (n = 7) and 3 (n = 1), and those patients without (n = 6) collateral vessels. Global peak filling rate was significantly (P < 0.01) reduced in the patients with collaterals. The septal, apical and lateral peak filling rates were also reduced in patients with collateral vessels, with the reduction in lateral peak filling rate being statistically significant (P < 0.05). The indices of systolic function and the temporal diastolic asynchronous index were similar, irrespective of the presence of collaterals. The exercise tolerance as evaluated by the rate-pressure product at peak treadmill exercise stress testing in 12 patients was significantly (P < 0.01) lower in those with collateral vessels. Angiographically visible collaterals could be a marker for more severe coronary stenosis in patients with effort-induced angina, and an indicator of the severity of deterioration in left ventricular diastolic function.

Prognostic value of left ventricular mass in uncomplicated acute myocardial infarction and one-vessel coronary artery disease

This study assesses the relative prognostic value of increased left ventricular (LV) mass compared with residual ischemic myocardium and angiographic characteristics of the diseased vessel in 76 patients with uncomplicated acute myocardial infarction associated with 1-vessel coronary artery disease (CAD). All patients underwent symptom-limited treadmill exercise testing, resting and dipyridamole echocardiography and coronary angiography before discharge, and were followed-up for 32 +/- 6 months. LV measurements were obtained in diastole according to the Penn convention. Measurements of LV mass were divided by body surface area to obtain LV mass index. A cut-off value of 135 g/m2 body surface area for men and 112 g/m2 for women was prospectively selected. The individual effects of clinical, stress testing and angiographic variables were evaluated by using the Cox regression model. Echocardiographic LV mass index was increased in 43 patients and normal in 33. There was no intergroup difference with respect to baseline clinical and angiographic variables, ejection fraction and prevalence of stress-induced ischemia. During follow-up there were 23 cardiac events in the 43 patients with increased LV mass index and only 5 in the 33 with normal LV mass index (p < 0.001). No patient died or had nonfatal reinfarction among patients with normal LV mass. Cox survival analysis identified an increased LV mass index as the only independent predictor of cardiac events (chi-square = 7.9; p < 0.005; RR = 5.4). Thus, these data suggest that LV mass is an important independent risk factor in patients with uncomplicated acute myocardial infarction associated with 1-vessel CAD.

Structural basis of end-stage failure in ischemic cardiomyopathy in humans

BACKGROUND

Ischemic cardiomyopathy is characterized by myocyte loss, reactive cellular hypertrophy, and ventricular scarring. However, the relative contribution of these tissue and cellular processes to late failure remains to be determined.

METHODS AND RESULTS

Ten hearts were obtained from individuals undergoing cardiac transplantation as a result of chronic coronary artery disease in its terminal stage. An identical number of control hearts were collected at autopsy from patients who died from causes other than cardiovascular disease, and morphometric methodologies were applied to the analysis of the left and right ventricular myocardium. Left ventricular hypertrophy evaluated as a change in organ weight, aggregate myocyte mass, and myocyte cell volume per nucleus showed increases of 85%, 47%, and 103%, respectively. Corresponding increases in the right ventricle were 75%, 74%, and 112%. Myocyte loss, which accounted for 28% and 30% in the left and right ventricles, was responsible for the difference in the assessment of myocyte hypertrophy at the ventricular, tissue, and cellular levels. Left ventricular muscle cell hypertrophy was accomplished through a 16% and 51% increase in myocyte diameter and length, whereas right ventricular myocyte hypertrophy was the consequence of a 13% and 67% increase in these linear dimensions, respectively. Moreover, a 36% reduction in the number of myocytes included in the thickness of the left ventricular wall was found. Collagen accumulation in the form of segmental, replacement, and interstitial fibrosis comprised an average 28% and 13% of the left and right ventricular myocardia, respectively. The combination of cell loss and myocardial fibrosis, myocyte lengthening, and mural slippage of cells resulted in 4.6-fold expansion of left ventricular cavitary volume and a 56% reduction in the ventricular mass-to-chamber volume ratio.

CONCLUSIONS

These results are consistent with the contention that both myocyte and collagen compartments participate in the development of decompensated eccentric ventricular hypertrophy in the cardiomyopathic heart of ischemic origin.

Hemodynamic effects of captopril and isosorbide mononitrate started early in acute myocardial infarction: a randomized placebo-controlled study

OBJECTIVES

The aim of this study was to study the hemodynamic effects of orally administered captopril and isosorbide mononitrate in suspected acute myocardial infarction.

BACKGROUND

Early treatment with converting enzyme inhibitors and nitrates in acute myocardial infarction may limit infarct expansion and prevent left ventricular dilation.

METHODS

In a double-blind study, 81 patients were randomized within 36 h of the onset of symptoms of suspected acute myocardial infarction to 1 month of oral captopril (6.25 mg initial dose, followed 2 h later by 12.5 mg and continuing with 12.5 mg three times daily), isosorbide mononitrate (initial dose 20 mg followed by 20 mg three times daily) or matching placebo. The effects of treatment on changes from baseline in mean arterial blood pressure, heart rate, stroke volume, cardiac output and systemic vascular resistance were assessed noninvasively using Doppler echocardiography 1 h after the first dose, 1 week after infarction and at 6 weeks (that is, 2 weeks after the scheduled end of trial treatment).

RESULTS

One hour after the start of treatment, blood pressure was reduced by approximately 10% with both captopril and isosorbide mononitrate, but this difference did not persist at 1 week. Captopril was associated with a significant increase in cardiac output compared with placebo of 13 +/- 3% at 1 h (p < 0.01), 23 +/- 5% at 1 week (p < 0.001) and 22 +/- 6% (p < 0.05) at 6 weeks (2 weeks after the end of trial treatment). This increase in cardiac output with captopril was mainly due to a substantial and sustained increase in stroke volume, although there was also a small increase in heart rate at 1 week. Both captopril and isosorbide mononitrate reduced systemic vascular resistance within 1 h of the start of treatment, but only the effect of captopril was sustained (perhaps because the three-times daily nitrate regimen induced tolerance). Study treatment was well tolerated, and the incidence of withdrawal of study treatment for hypotension was not significantly different from that with placebo.

CONCLUSIONS

This study indicates that the hemodynamic effects of both captopril and isosorbide mononitrate are well tolerated in the acute phase of myocardial infarction and that captopril favorably influences cardiac function.

Chronic effects of a cardiac assist device on the bulk and regional mechanics of the failed left ventricle in goats

Pneumatically driven, diaphragm-type left ventricular assist devices (LVADs) were implanted into 8 goats with profound induced infarction to the left ventricle by using multiple ligations of the left anterior descending (LAD) coronary artery as well as small arteries in the LAD distribution area. Left ventricular diameters, regional myocardial segment lengths, and wall thicknesses were measured by sono-micrometers. After left ventricular function seemed to be recovered, the goats were weaned off the LVADs after a gradual decrease of pump bypass flow over several days. Thereafter, hemodynamic and cardiac parameters were observed for about 1 month more. Three animals recovered successfully owing to the LVAD pumping. Before starting pump-weaning procedures, the bulk mechanical work (BMW) done by the left ventricle during LVAD pumping and under temporary pump-off conditions was 0.08 +/- 0.01 (mean +/- SE) and 0.22 +/- 0.01 W/100 g left ventricular weight (LVW), respectively, while the regional mechanical work done by the normal myocardium (RMWn) was 1.5 +/- 0.4 and 4.3 +/- 0.9 mW/cm3 during pumping and under temporary pump-off conditions, respectively. BMW and RMWn values obtained under pump-on conditions both increased gradually during the weaning process. Even after pump removal, they continued to increase and reached constant values of about 0.3 W/100 g LVW and 10 mW/cm3, respectively, around 2 weeks after pump removal. Although the myocardium in the infarction area did no work for the first several days after surgery, it recovered to do some external work with the aid of LVAD pumping. However, recovery of left ventricular function owed more to compensatory increases in pumping ability of the remaining normal myocardium than to recovery of the damaged myocardium. The LVAD could salvage severely damaged hearts unless the infarction area exceeded 50% of the left ventricular wall.

Cardioreparation and the concept of modulating cardiovascular structure and function

Hypertension and atherosclerotic cardiovascular disease represent major global health problems. Practising physicians are challenged daily by patients suffering adverse cardiovascular events, such as myocardial infarction, stroke, heart failure and sudden cardiac death. Major risk factors have been identified of which the most important is left ventricular hypertrophy. In recent years, growth factors, regulatory peptides and effector hormones of the renin-angiotensin-aldosterone system have been identified as important modulators of cell growth and behaviour. It therefore follows that a major emphasis has been placed on the importance of abnormalities in organ structure as the primary basis for impaired function of the heart and vasculature, including large and medium sized arteries and resistance vessels, or arterioles. The concept of reparation recognizes the importance of abnormalities in tissue structure to the functional basis of disease. It suggests that the structurally remodelled heart and vasculature can be restored to, or toward, normal structure and function by suitable therapy. Experimental and clinical trials which address this premise are reviewed herein.

Altered left ventricular remodeling with beta-adrenergic blockade and exercise after coronary reperfusion in rats

BACKGROUND

beta-Adrenergic blockade is known to improve the survival of patients after acute myocardial infarction and to reduce myocardial infarct size in experimental coronary occlusion. However, the effects of beta-blockade on global and regional left ventricular (LV) remodeling have not been characterized after coronary occlusion with reperfusion. In rats subjected to coronary occlusion and reperfusion, we have demonstrated beneficial effects of reperfusion in sedentary rats with a hypertrophic response to exercise in the surviving outer wall of the infarcted zone, and in this study we investigated whether such remodeling is modified by beta-blockade in both sedentary and exercised rats.

METHODS AND RESULTS

Female Sprague-Dawley rats were randomized into groups at 5 days after 45 minutes of left coronary artery occlusion followed by reperfusion to produce nontransmural infarction. Animals completing the experiment included a propranolol-treated sedentary group (750 mg/l drinking water) (n = 20) and a propranolol-treated exercised group (n = 19), and these groups were compared with two groups of simultaneously randomized rats (which were also part of a separate study): an untreated sedentary group (n = 21) and an untreated exercised group (n = 20). After 3 weeks of intervention, global and regional LV morphological changes were analyzed in 78 completed experiments from midventricular transverse slices of hearts after perfusion fixation. Compared with sedentary untreated rats, propranolol-treated sedentary rats showed significantly increased LV cavity area (41.6 versus 31.5 mm2, p < 0.001) and reduced wall thicknesses in the noninfarcted (1.77 versus 1.95 mm, p < 0.01) and infarcted regions (1.29 versus 1.36 mm, p < 0.01) (two-way ANOVA). In the propranolol-treated rats, exercise further increased the LV cavity area (44.6 versus 39.1 mm2, p < 0.001), reduced the noninfarcted wall thickness (1.62 versus 1.81 mm, p < 0.01), and increased the LV dimension/wall thickness ratio in the noninfarcted region (4.7 versus 3.95 mm, p < 0.001). Whereas exercise in the reperfused group in the absence of beta-blockade significantly increased the viable subepicardial area of the infarcted zone, as reported elsewhere, propranolol treatment prevented this exercise-induced increase of subepicardial area (7.8 rest versus 7.7 mm2 exercise, NS), and there was a significant reduction of total myocardial area in the propranolol-treated exercised group compared with the untreated exercised group (p < 0.05). Corresponding trends in LV weights were not statistically significant.

CONCLUSIONS

These findings provide evidence for altered LV remodeling, including LV cavity dilation and reduced wall thickness, after 3 weeks of propranolol treatment in sedentary rats after coronary artery occlusion and reperfusion to produce nontransmural infarction. In addition, after 3 weeks of exercise together with propranolol treatment, morphological changes were consistent with suppression of exercise-induced myocardial hypertrophy globally and in the viable outer wall of the infarcted region, accompanied by further LV cavity dilation.

Long-term oral nitrate therapy prevents chronic ventricular remodeling in the dog

OBJECTIVES

The purpose of this experiment was to assess the long-term effects of oral nitrate therapy on ventricular remodeling in a canine model of discrete myocardial damage.

BACKGROUND

A progressive increase in left ventricular mass and volume has been documented after experimental and clinical myocardial infarction. This ventricular remodeling has been associated with the development of congestive heart failure. Nitrate therapy, especially when combined with hydralazine, is effective in the management of clinical heart failure. Moreover, nitrates inhibit infarct expansion, one of the earliest manifestations of ventricular remodeling. Whether nitrates can attenuate chronic left ventricular remodeling is unknown.

METHODS

Dogs with discrete myocardial necrosis produced 24 h earlier by transmyocardial direct current shock were randomized to receive isosorbide mononitrate, 30 mg twice daily (n = 10), or no treatment (n = 4); the latter group was augmented by 13 control dogs from a prior study in which an identical protocol was used. Ventricular structure was assessed with nuclear magnetic resonance imaging at baseline and at 1 and 16 weeks after myocardial damage.

RESULTS

Left ventricular mass increased at 1 week in the control group (mean +/- SD 68.1 +/- 10.7 g to 80.1 +/- 12.1 g, p = 0.0001) but not in the nitrate-treated group (70.2 +/- 7.7 g to 69.6 +/- 7.3 g, p = NS). No change in left ventricular volume was observed in either group during the 1st week after myocardial damage. After 16 weeks of follow-up left ventricular mass had increased by 12.7 +/- 7.1 g (p = 0.001) in the control group and had decreased by 1.2 +/- 7.7 g in the nitrate group. Left ventricular volume was increased at 16 weeks by 14.2 +/- 10.3 ml in the control group but was decreased by 3.7 +/- 7.5 ml in the nitrate group. Isosorbide mononitrate produced transient hemodynamic effects with a return of most measured variables toward baseline within 2 h after administration of the drug. At 1 week there was no intergroup difference in rest hemodynamic variables assessed 12 h after drug administration. At 16 weeks, pulmonary capillary wedge pressure (15 +/- 4 vs. 8 +/- 3 mm Hg, p = 0.0001), pulmonary artery pressure (24 +/- 5 vs. 16 +/- 3 mm Hg, p = 0.0001) and right atrial pressure (10 +/- 3 vs. 6 +/- 3 mm Hg, p = 0.008) were all higher in the control group.

CONCLUSIONS

Long-term oral nitrate therapy attenuates the early and late manifestations of ventricular remodeling after myocardial damage in the dog. Hemodynamic observations suggest the possibility that drug-induced preload or afterload reduction does not completely explain this effect.

Ventricular remodeling after myocardial infarction. Experimental and clinical studies

Changes of ischemic myocardium following coronary occlusion, including active and passive functions, and adaptive changes of non-ischemic surviving myocardium have been summarized under the term "left ventricular remodeling" post myocardial infarction. An increase in left ventricular volume may be a consequence, and associated with an adverse prognosis. Although left ventricular dilatation may increase stroke volume and, thus, be compensatory at first, in about one-fifth of patients it ultimately results in progressive dysfunction and heart failure. Major determinants of this process are time, infarct size, infarct location, global left ventricular function assessed 4 days after infarction by radionuclide ejection fraction and right heart catheter (stroke volume), and morphology of the infarct-associated coronary artery. The surviving myocardium hypertrophies and may also dilate structurally. Depression of left ventricular ejection fraction chronically after the infarct is due to deterioration of wall motion of chamber segments initially classified normal by radionuclide analysis. Biochemical changes may also occur, including reduction of phosphocreatine, prolongation of time to peak Cai2+, and changes in myosin isoforms. Systemic or local humoral factors may be involved in these changes, however, clear evidence is still lacking. Perfusion of surviving myocardium may be altered under various conditions due to morphologic and functional changes of coronary vasculature. Successful prevention of heart failure and death by angiotensin converting enzyme inhibitors in asymptomatic patients with left ventricular dysfunction post-myocardial infarction has supported the pathophysiologic concepts of remodeling.

Myocardial cell hypertrophy after myocardial infarction with reperfusion in dogs

BACKGROUND

The potential role of myocardial cell hypertrophy in the ischemic zone in the mechanism of late recovery of regional contractile function after myocardial infarction followed by reperfusion has not been examined.

METHODS AND RESULTS

Eight chronically instrumented, conscious dogs were subjected to 90-120 minutes of circumflex coronary artery occlusion followed by reperfusion. The thickness and function of the anterior (AT) and posterior (PT) walls was measured by ultrasonic gauges at control, during occlusion, and after reperfusion. After 3 weeks, cross-sectional areas of surviving cells were determined from subepicardial (epi), midwall (mid), and subendocardial (endo) regions in six dogs and compared with those from six animals without infarction, including three sham-operated control dogs. PT systolic wall thickening showed dyskinesia during occlusion but recovered after reperfusion to 48% of control at 1 week and 67% at 3 weeks. End-diastolic thickness of the PT wall increased markedly after reperfusion, but AT and PT walls were only slightly thicker (p = NS) than in control dogs at 3 weeks. Cross-sectional areas of reperfused dogs in the infarct region averaged 279 (PTepi), 291 (PTmid), and 317 microns 2 (PTendo) and were significantly larger than in control animals (237 [PTepi], 241 [PTmid], and 233 microns 2 [PTendo]). PT cell areas were significantly larger than AT cells, ENDO cell areas were larger than EPI cells (both p < 0.05), and ENDO cells of the AT wall were larger than those of noninfarcted dogs (p < 0.05).

CONCLUSIONS

In dogs with myocardial infarction followed by reperfusion, the cross-sectional areas of cells in the infarcted PT wall were larger than those in the noninfarcted AT wall, and within both the infarcted and noninfarcted zones, cell areas were larger in the endocardial than the epicardial region. In all regions of the infarcted wall and in the ENDO region of the noninfarcted wall, cell areas were generally larger than those of control dogs without infarction, and the control dogs showed no transmural differences in cell areas. The mechanisms responsible for this significant remodeling of the reperfused infarcted zone, which involves myocardial cellular hypertrophy, are unknown, but it is possible that hypertrophy of surviving regions of the infarcted wall played a role in the late recovery of regional function that accompanied this hypertrophic response.

Ventricular loading is coupled with DNA synthesis in adult cardiac myocytes after acute and chronic myocardial infarction in rats

To determine whether the overload associated with myocardial infarction and ventricular failure in rats is coupled with activation of DNA synthesis in the remaining left and right ventricular myocytes, flow cytometric analysis was performed on myocyte nuclei prepared from both ventricles 7 and 30 days after coronary occlusion. In addition, oral captopril was administered in separate groups of control and experimental rats to establish whether a relation existed between attenuation of ventricular loading and magnitude of DNA synthesis in myocytes. Results demonstrated that left ventricular failure and right ventricular dysfunction at 7 days after infarction were biventricularly associated with marked increases in the number of myocyte nuclei in the G2M phase of the cell cycle. In contrast, the fraction of nuclei in the G0+G1 phase decreased. In comparison with the earlier time point, the 30-day interval was characterized by a significant magnitude of cardiac hypertrophy, a moderate amelioration of ventricular pump function, and a decrease in the percentage of myocyte nuclei in the G2M phase in both ventricles. However, 30 days after infarction, the number of right ventricular myocyte nuclei in the S and G2M phases remained elevated with respect to control animals. Captopril therapy reduced the extent of ventricular loading and the population of myocyte nuclei in the cell cycle at 7 days. In conclusion, DNA synthesis in myocyte nuclei may represent an important adaptive component of the myocardial response to infarction.

Decreased concentration of myofibrils and myofiber hypertrophy are structural determinants of impaired left ventricular function in patients with chronic heart diseases: a multiple logistic regression analysis

OBJECTIVES

The aim of this study was to perform a multiple logistic regression analysis to identify independent structural determinants of impaired left ventricular function.

BACKGROUND

The association between contractile failure and structural alterations of the myocardium has been demonstrated in several studies, and multiple interactions between myocardial structure and cardiac performance are likely.

METHODS

Morphometric data assessed from 130 left ventricular biopsy specimens were analyzed. The endomyocardial specimens were obtained from 57 patients with normal coronary arteries (17 with normal left ventricular ejection fraction and 40 with impaired left ventricular function [dilated cardiomyopathy]), 15 patients with hypertrophic cardiomyopathy and 32 patients with aortic valve disease. Transmural biopsy specimens were assessed in 6 donor hearts before heart transplantation and in 20 patients with left anterior descending coronary artery disease whose specimens were obtained from the left ventricular anterior wall during aortocoronary bypass surgery. Global or regional left ventricular function was evaluated from left cineventriculograms. The volume fraction of cardiac fibrous tissue, intracellular volume fraction of myofibrils, volume fraction of myofibrils related to myocardial tissue (including fibrosis) and myofiber diameters were determined from semithin sections of the biopsy specimens with the use of light microscopic morphometry.

RESULTS

Multiple logistic regression analysis revealed decreased volume fraction of myofibrils (p < 0.005) and increased fiber diameter (p < 0.002) as independent determinants of impaired left ventricular function.

CONCLUSIONS

These data indicate that, independent of the underlying heart disease, both decreased concentration of contractile proteins and myocyte hypertrophy are independently associated with impaired left ventricular function.

Rapid, accurate and simultaneous noninvasive assessment of right and left ventricular mass with nuclear magnetic resonance imaging using the snapshot gradient method

Left ventricular, and possibly also right ventricular, mass is an important determinant of prognosis in cardiovascular disease. Consequently, noninvasive estimation of ventricular mass may be an important clinical investigation. The ideal technique for this purpose would be widely available and accurate, employ short study times and avoid exposure to contrast agents and radiation. Conventional nuclear magnetic resonance (NMR) imaging fulfills most of these criteria, but it is time-consuming and expensive. Moreover, its accuracy in estimating right ventricular mass has yet to be assessed. Accordingly, high speed NMR imaging using the snapshot gradient echo technique was used to assess right and left ventricular mass in 10 dogs and the results were compared with values obtained at autopsy, which ranged from 26.1 to 52.9 and 61 to 119.8 g, respectively. The mean absolute difference between the NMR imaging estimates and autopsy findings was 2 +/- 1.2 g (range 0.4 to 4.2) for right ventricular mass and 4.4 +/- 1.7 g (range 1.8 to 6.6) for left ventricular mass. Total NMR imaging time was less than or equal to 5 min. These data demonstrate that high speed NMR imaging can be used to accurately estimate right as well as left ventricular mass.

Functional significance of post-myocardial infarction left ventricular hypertrophy: a beneficial response

Hypertrophy of noninfarcted myocardium occurs as a chronic response to myocardial infarction, but no previous study has related the changes in wall thickness to serial changes in left ventricular function. Thus the functional significance of postinfarction hypertrophy is unknown. The purpose of this study was to determine the relationship between the development of postinfarction hypertrophy and the resting left ventricular ejection fraction measured by two-dimensional echocardiography. After occlusion of the proximal left anterior descending coronary artery in 11 dogs, the ejection fraction fell acutely (0.63 +/- 0.08 to 0.33 +/- 0.10, p less than 0.001) and rose at 3.5 months to 0.62 +/- 0.12. End-diastolic thickness of the noninfarcted left ventricle increased (11 +/- 1.0 mm to 13 +/- 1.4 mm, p less than 0.01) as did left ventricular mass (101 +/- 18 gm to 134 +/- 21 gm, p less than 0.0001). Restoration of the ejection fraction toward the baseline value correlated with the increases in left ventricular mass (r = 0.79, p = 0.007) and wall thickness (r = 0.71, p = 0.025). Hypertrophy of the noninfarcted myocardium correlated with the magnitude and approximately paralleled the time course of the improvement in the ejection fraction and therefore may have had a beneficial effect on resting left ventricular function as a chronic adaptation to myocardial infarction.

The clinical pharmacology of angiotensin converting enzyme inhibitors in chronic heart failure

ACE inhibitors (ACEIs) have now been shown to improve symptoms and survival in patients with mild, moderate and severe chronic heart failure. Their mechanism of action is thought to be a combination of RAAS suppression and augmentation of bradykinin and prostaglandins. Although ACE inhibitors improve hemodynamics post myocardial infarction, we do not yet have consistent data on their effects on symptoms or survival in these particular patients. One other potential benefit is their effects on reperfusion injury and free radicals. As yet only minor differences have been found to exist between different ACEIs but increasing attention is now being focussed in this direction.

Cellular basis of ventricular remodeling after myocardial infarction

To determine whether acute left ventricular failure associated with myocardial infarction leads to architectural changes in the spared nonischemic portion of the ventricular wall, large infarcts were produced in rats, and the animals were sacrificed 2 days after surgery. Left ventricular end-diastolic pressure was increased, whereas left ventricular dP/dt and systolic pressure were decreased, indicating the presence of severe ventricular dysfunction. Absolute infarct size, determined by measuring the fraction of myocyte nuclei lost from the left ventricular free wall, averaged 63%. Transverse midchamber diameter increased by 20%, and wall thickness diminished by 33%. The number of mural myocytes in this spared region of the left ventricular free wall decreased by 36% and the capillary profiles by 40%. Thus, side-to-side slippage of myocytes in the myocardium occurs acutely in association with ventricular dilation after a large myocardial infarction. In order to analyze the chronic consequences of myocardial infarction on ventricular remodeling, a second group of experiments was performed in which the left coronary artery was ligated and the functional and structural properties of the heart were examined 1 month later. In infarcts affecting an average 38% of the free wall of the left ventricle (small infarcts), reactive hypertrophy in the spared myocardium resulted in a complete reconstitution of functioning tissue. However, left ventricular end-diastolic pressure was increased, left ventricular dP/dt was decreased, and diastolic wall stress was increased 2.4-fold. After infarctions resulting in a 60% loss of mass (large infarcts), a 10% deficit was present in the recovery of viable myocardium. Functionally, ventricular performance was markedly depressed, and diastolic wall stress was increased 9-fold. The alterations in loading of the spared myocardium were due to an increase in chamber volume and a decrease in the myocardial mass/chamber volume ratio that affected both infarct groups. Thus, decompensated eccentric ventricular hypertrophy develops chronically after infarction and growth processes in myocytes are inadequate for normalization of wall stress when myocyte loss involves nearly 40% or more of the cells of the left ventricular free wall. The persistence of elevated myocardial and cellular loads may sustain the progression of the disease state toward end-stage congestive heart failure.

Induction of myocardial hypertrophy after coronary ligation in rats decreases ventricular dilatation and improves systolic function

BACKGROUND

Previous studies have shown that hypertrophy of surviving myocytes after myocardial infarction (MI) is limited. Progressive ventricular dilatation after MI may occur when compensatory hypertrophy cannot restore left ventricular (LV) wall stress to normal.

METHODS AND RESULTS

To test whether induction of additional myocyte hypertrophy might prevent pathological LV remodeling after large MI, we administered 2-tetradecylglycidic acid (TDGA) 20 mg/kg/day to sham-operated (n = 12) and MI (n = 10) rats for 10 days, beginning the third day after infarction. We have previously shown that chronic inhibition of long-chain fatty acid oxidation with TDGA in rats results in myocardial hypertrophy without any apparent impairment of LV systolic function. When compared with untreated MI rats (n = 9), we found that TDGA-treated MI rats had increases in LV weight/body wt, myocyte cross-sectional area, and peak developed LV pressure during abrupt aortic occlusion. MI rats treated with TDGA had lower LV end-diastolic pressures and smaller end-diastolic volumes, whereas stroke volume was maintained. The ex vivo passive LV pressure-volume relation was shifted toward the pressure axis compared with untreated infarct rats. In sham-operated rats, TDGA caused increases in LV weight/body wt, myocyte size, peak developed LV pressure, cardiac index, and stroke volume index, and a shift of the passive LV pressure-volume relation toward the pressure axis.

CONCLUSIONS

Induction of myocardial hypertrophy with an inhibitor of long-chain fatty acid oxidation retarded the process of LV dilatation and produced beneficial effects on systolic function after large myocardial infarction. These data support the hypothesis that inadequate hypertrophy of residual myocardium after infarction may contribute to LV dilatation and the development of congestive heart failure.

Early and late effects of captopril treatment after large myocardial infarction in rats

The early (after 21 days) and late (after 4 months) effects of continuous treatment with captopril on left ventricular performance, weight and volumes were studied in rats with myocardial infarction. Early effects were examined in rats subjected to coronary ligation and randomized to either immediate treatment with captopril (2 g/liter drinking water) starting 2 h after surgery or no treatment. After 21 days, the treated group showed reductions in mean arterial, left ventricular systolic and left ventricular end-diastolic pressures compared with untreated rats. Right and left ventricular weight and left ventricular volumes were decreased and the ejection fraction index was increased by captopril treatment. To study the late effects of captopril, a second group of rats was randomized to immediate captopril treatment (starting 2 h after surgery), delayed captopril treatment (starting 21 days after surgery) or no treatment. When studied after 4 months of treatment, rats started on captopril treatment 2 h after infarction showed no differences compared with rats started on treatment 21 days after infarction. Treatment with captopril for 4 months produced changes that were similar to those in rats treated for 21 days. Captopril treatment improved hemodynamic function after myocardial infarction in rats examined after either 21 days or 4 months of treatment. The extent of the benefit was similar in the two treatment periods. Initiation of captopril therapy immediately after infarction did not appear to produce a greater effect than treatment started at 21 days after infarction in rats studied after the drug had been administered for 4 months.