Impact of increased infarct transmurality on remodeling and function during healing after anterior myocardial infarction in the dog

Differentiation of transmural and nontransmural infarction using speckle tracking imaging to assess endocardial and epicardial torsion after revascularization

Assessment of transmural extent (TME) of necrosis after acute myocardial infarction (MI) remains a major problem in clinical practice. The study sought to determine whether speckle tracking imaging (STI) could differentiate transmural from nontransmural acute MI by assessment of endocardial and epicardial torsion. TME of infarct was measured by contrast-enhanced magnetic resonance imaging. Patients were divided into two groups according to TME (transmural MI group [TME ≥ 50%, n = 36] and nontransmural MI group [TME < 50%, n = 35]). As a control group, 30 subjects without evidence of structural heart disease were included. Conventional echocardiography and STI were done in controls and patients before and 1 month after percutaneous coronary intervention. Compared with control subjects, endocardial and epicardial torsion in patients with transmural and nontransmural MI were all extremely decreased (all P < 0.01). One month after percutaneous coronary intervention, there was no significant increase in endocardial and epicardial torsion in transmural MI patients. However, apical rotation and left ventricular torsion resumed slightly but significantly in the epicardium (but not endocardium) in patient with nontransmural MI (3.11 ± 0.81 vs. 4.37 ± 1.15°, P < 0.01; 3.69 ± 1.07 vs. 5.52 ± 1.89°, P < 0.01, respectively). The combined evaluation of endocardial and epicardial torsion by STI may be used to differentiate transmural from nontransmural MI after revascularization.

Ischemia/Infarction

Myocardial infarction (MI) accounts for most incidences of heart failure (HF) and low ejection fraction. Evidence suggests that acute MI leads to early cardiac remodeling, with changes in ventricular geometry and structure that in turn lead to a vicious cycle of ventricular dilation, increased wall stress, hypertrophy and more ventricular dilation and dysfunction, and worsening of HF. The early geometric and structural changes contribute to early mechanical complications and subsequent progressive ventricular remodeling and the development of chronic HF. A clear understanding of the underlying mechanisms is helpful in developing optimal preventive and therapeutic strategies for HF.

Impact of coronary revascularization and transmural extent of scar on regional left ventricular remodelling

AIMS

Transmural extent (TME) of myocardial scar, contractile reserve, and perfusion all predict improvement in regional myocardial function after coronary revascularization. We sought their association with regional remodelling after infarction.

METHODS AND RESULTS

We studied 89 patients (age 62 +/- 10 years) with left ventricular (LV) dysfunction, at least 1 month post infarction. Viability was identified by TME < 75% on contrast-enhanced magnetic resonance imaging (ce-MRI), augmentation at low-dose dobutamine echocardiography (DbE), or >60% uptake on delayed redistribution on TI-201 SPECT (single photon emission computed tomography). Coronary revascularization was performed in 36 patients. Regional LV end-diastolic volume (EDV) and end-systolic volume, and ejection fraction were measured with MRI at baseline and after a median follow-up of 18 months. Of 357 segments identified with subendocardial infarction (TME 0-25%) on ce-MRI, 176 were revascularized. Subendocardial scar segments were associated with reverse regional remodeling during follow-up. Revascularization was an independent correlate of change in EDV, but TME and revascularization showed no interaction with respect to their influence on regional volumes. Contractile reserve was present on DbE in 228 segments, of which 129 were TME 0-25%; remodelling was associated with intervention in non-transmural infarcts showing viability by DbE. Viability was identified by TI-201 SPECT in 381 segments (233 with TME 0-25%), but viability by SPECT was not associated with reverse remodelling. No significant reverse remodelling occurred in segments with intermediate scar thickness (TME 26-75%) or transmural scar, independent of revascularization or viability by DbE or TI-SPECT.

CONCLUSION

Reverse regional remodelling is associated with subendocardial infarction, especially in the setting of contractile reserve and revascularization.

Pleiotropic effects of cardiac drugs on healing post-MI. The good, bad, and ugly

Healing after myocardial infarction (MI) is a well-orchestrated time-dependent process that involves inflammation, tissue repair with extracellular collagen matrix (ECCM) deposition and scar formation, and remodeling of myocardial structure, matrix, vasculature, and function. Rapid early ECCM degradation followed by slow ECCM replacement and maturation during post-MI healing results in a prolonged window of enhanced vulnerability to adverse remodeling. Decreased ECCM results in adverse ventricular remodeling, dysfunction, and rupture. Inflammation, a critical factor in normal healing, if impaired results in adverse remodeling and rupture. Several therapeutic drugs prescribed after MI exert pleiotropic effects that suppress ECCM and inflammation during healing and may have good, bad, or ugly consequences. This article reviews the potential impact of pleiotropic effects of some prototypic cardiac drugs such as renin-angiotensin-aldosterone system (RAAS) inhibitors, statins, and thrombolytics during healing post-ST-segment-elevation MI (STEMI), with special focus on inflammation, ECCM and remodeling, and implications in the elderly.

Sequential Changes of Myocardial Function During Acute Myocardial Infarction, in the Early and Chronic Phase After Coronary Intervention Described by Ultrasonic Strain Rate Imaging

OBJECTIVE

The aim of this prospective clinical study was to follow up patients with acute myocardial infarction from the ischemic event, over the primary coronary intervention (PCI), up to the chronic phase after survived myocardial infarction by noninvasive strain rate (SR) imaging and to determine its role in the assessment of transmurality of infarction.

METHODS

In all, 41 patients with acute S-T elevation infarction were examined immediately before, 3 days after, and 5 months after PCI. Regional myocardial function was assessed by the use of ultrasonic SR imaging and peak systolic SR and systolic strain were extracted. In addition, late-enhancement (LE) imaging with magnetic resonance imaging was done after 5 months to assess the transmurality of residual scar distribution.

RESULTS

Magnetic resonance imaging showed that 8 patients had no LE (complete recovery = no-scar group), 16 patients had subendocardial LE (nontransmural infarction = NT group), and 17 patients had a transmural LE (transmural infarction = T group) in the region of interest. Before PCI both SR and strain were markedly reduced in the ischemic segments compared with the nonischemic remote region in all 3 groups (SR: ischemia = -0.6 +/- 0.3 s(-1); remote = -1.3 +/- 0.4 s(-1), P < .001). Three days after PCI, systolic SR only increased significantly in the regions that were not transmurally infarcted. After 5 months the measurement of systolic strain could accurately distinguish the different groups. (no-scar group = -24 +/- 5%, NT group = -13 +/- 4%, T group = -1 +/- 3%).

CONCLUSIONS

This clinical study shows that with SR imaging: (1) the ischemic segment can be precisely detected; (2) the absence of transmurality early after coronary intervention can be predicted; and (3) in the chronic phase the transmurality of scar distribution can be assessed.

An Echocardiographic Left Ventricular Wall Area Index for Functional Detection of Myocardial Injury in Hemodynamically Unloaded Hearts

Functional assessment of the left ventricle is affected by loading conditions. Detection of rejection-mediated myocardial injury in a heterotopic heart transplant model is a challenge for the echocardiographer because the heart is in an unloaded state. We examined the relationship of a novel left ventricular (LV) wall area index (LVWAI) and serum cardiac troponin T (cTnT) levels. The LVWAI, based on prior methods of determining LV mass, was defined as the difference between epicardial and endocardial areas divided by the epicardial area. The biphasic morphometric response of LVWAI reflected changes in the cTnT levels and allowed echocardiographic detection of myocardial injury in hemodynamically unloaded hearts.

MR imaging of spatial extent of microvascular injury in reperfused ischemically injured rat myocardium: value of blood pool ultrasmall superparamagnetic particles of iron oxide

PURPOSE

To (a) assess the value of a blood pool magnetic resonance (MR) imaging contrast agent (Clariscan) for characterizing microvascular injury in ischemically injured rat myocardium and (b) compare the extent of microvascular injury at Clariscan-enhanced MR imaging with infarction and areas at risk seen with histochemical staining.

MATERIALS AND METHODS

Twenty rats underwent 45 minutes of coronary artery occlusion and 3 hours of reperfusion. Sequential T1-weighted spin-echo MR images were acquired in 10 rats to assess leakage of Clariscan into myocardium over time. Ten other rats underwent the same duration of occlusion and reperfusion (3 hours) so that the extent of microvascular injury in the entire heart could be measured and correlated with infarction and area at risk at necropsy. The Student t test and Bland-Altman method were used for data analysis.

RESULTS

Clariscan improved visualization of regions with transmural and nontransmural microvascular injury. Accumulation of Clariscan was best reflected by the mean ratios of signal intensity in injured myocardium to that in normal myocardium measured before (0.98 +/- 0.01 [standard error of the mean]) and after (1.34 +/- 0.04) injection. At 15 minutes after injection, the size of the enhanced region remained constant over the course of observation. The mean size of the hyperenhanced region (44% of the left ventricle +/- 2) was significantly (P <.001) larger than the mean size of true infarction at necropsy (29% +/- 3) but smaller than the mean size of the area at risk (50% +/- 2).

CONCLUSION

Clariscan has potential for estimating the spatial extent of microvascular injury in ischemically injured myocardium and may be useful as a marker of microvascular injury after thrombolytic therapy.

Myocardial viability: impact on left ventricular dilatation after acute myocardial infarction

OBJECTIVE

To evaluate whether the presence of viable myocardium, detected by low dose dobutamine echocardiography, limits the likelihood of left ventricular dilatation in patients with acute myocardial infarction.

PATIENTS

107 patients were studied by low dose dobutamine echocardiography at (mean (SD)) 3 (1) days after acute myocardial infarction. Cross sectional echocardiography was repeated three months later. Patients were divided in two groups based on the presence (n = 47) or absence (n = 60) of myocardial viability.

RESULTS

Baseline characteristics were comparable between the two groups, except for infarct location. Left ventricular end diastolic volume index (EDVI) was stable in patients with viability, but end systolic volume index (ESVI) decreased significantly (p = 0.006). Patients without viability had a significant increase in both EDVI (p < 0.0001) and ESVI (p = 0.0007). Subgroup analysis in patients with small and large infarcts (peak creatine kinase < or = 1000 v > 1000 IU/l) showed that ventricular dilatation occurred only in patients with large infarcts without viability. This resulted in larger ESVI values at three months in that group compared with patients with large infarcts plus viability (p < 0.05). Multivariate regression analysis identified myocardial viability as an independent predictor of left ventricular dilatation, along with wall motion score index on low dose dobutamine echocardiography and the number of pathological Q waves.

CONCLUSIONS

The presence of viability early after acute myocardial infarction is associated with preservation of left ventricular size, whereas the absence of viability results in ventricular dilatation, particularly in large infarcts.

Matrix metalloproteinase inhibition after myocardial infarction: a new approach to prevent heart failure?

Increased activity of matrix metalloproteinases (MMPs) has been implicated in numerous disease processes, including tumor growth and metastasis, arthritis, and periodontal disease. It is now becoming increasingly clear that extracellular matrix degradation by MMPs is also involved in the pathogenesis of cardiovascular disease, including atherosclerosis, restenosis, dilated cardiomyopathy, and myocardial infarction. Administration of synthetic MMP inhibitors in experimental animal models of these cardiovascular diseases significantly inhibits the progression of, respectively, atherosclerotic lesion formation, neointima formation, left ventricular remodeling, pump dysfunction, and infarct healing. This review focuses on the role of MMPs in cardiovascular disease, in particular myocardial infarction and the subsequent progression to heart failure. MMPs, which are present in the myocardium and capable of degrading all the matrix components of the heart, are the driving force behind myocardial matrix remodeling. The recent finding that acute pharmacological inhibition of MMPs or deficiency in MMP-9 attenuates left ventricular dilatation in the infarcted mouse heart led to the proposal that MMP inhibitors could be used as a potential therapy for patients at risk for the development of heart failure after myocardial infarction. Although these promising results encourage the design of clinical trials with MMP inhibitors, there are still several unresolved issues. This review describes the biology of MMPs and discusses new insights into the role of MMPs in several cardiovascular diseases. Attention will be paid to the central role of the plasminogen system as an important activator of MMPs in the remodeling process after myocardial infarction. Finally, we speculate on the use of MMP inhibitors as potential therapy for heart failure.

Tissue Doppler imaging differentiates transmural from nontransmural acute myocardial infarction after reperfusion therapy

BACKGROUND

The evaluation of transmural extent of necrosis after acute myocardial infarction remains a major problem in clinical practice. We sought to determine whether color M-mode tissue Doppler imaging (TDI) could differentiate transmural from nontransmural myocardial infarction.

METHODS AND RESULTS

Twenty-one anesthetized open-chest dogs underwent 90 or 120 minutes of left anterior descending coronary artery occlusion followed by 180 minutes of reperfusion. The transmural extension of infarct was measured by triphenyltetrazolium chloride (TTC) staining. Segment shortening in the endocardium and epicardium of the anterior and posterior walls was assessed by sonomicrometry. Regional myocardial blood flow was measured by radioactive microspheres. TDI was obtained from an epicardial short-axis view. We calculated systolic and diastolic velocities within the endocardium and epicardium of myocardial walls and the subsequent myocardial velocity gradient (MVG). TTC staining could identify 2 groups according to the transmural extent of necrosis: 15 dogs had a nontransmural (NT) necrosis (42+/-3% of wall thickness), and 6 dogs developed a transmural (T) infarct (81+/-4% of wall thickness). In both groups, ischemia resulted in a significant and similar reduction in endocardial and epicardial velocities, with a resulting low systolic MVG in the anterior wall (0.10+/-0.07 in NT and 0.10+/-0.08 s(-1) in T). At 60 minutes of reperfusion, systolic MVG failed to change significantly in the transmural group (-0.20+/-0.09 s(-1)). In contrast, it increased significantly after reflow in the NT group compared with ischemic values (-0.99+/-0.20 versus 0.10+/-0.07 s(-1), P:<0.05).

CONCLUSIONS

TDI can differentiate transmural from nontransmural myocardial infarction early after reperfusion.

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.

Effects of acute myocardial ischemia on intramyocardial contraction heterogeneity: A study performed with ultrasound integrated backscatter during transesophageal atrial pacing

BACKGROUND

[corrected] Subendocardial thickening is greater than subepicardial thickening and acute myocardial ischemia mainly impairs the former. Integrated backscatter cyclic variations (IBScv) reflect regional myocardial contractility and are blunted during myocardial ischemia. We hypothesized that stress-induced myocardial ischemia mainly affects subendocardial IBScv.

METHODS AND RESULTS

Multiplane transesophageal echocardiography and simultaneous atrial pacing were performed in 12 patients without coronary artery disease (CAD) and in 25 with significant CAD. In a transgastric 2-chamber view, we calculated IBScv in subendocardium and subepicardium and a heterogeneity index, both at rest and at peak-pacing. In 27 myocardial segments of patients with normal coronary arteries, and in 16 myocardial segments supplied by coronary artery without significant stenosis in patients with CAD, there was a transmural gradient of IBScv at rest and the heterogeneity index did not change during all the protocol steps. In the 53 myocardial segments related to a significantly narrowed coronary artery, the transmural gradient of IBScv, present at rest, significantly decreased at peak-pacing because of subendocardial blunting, but promptly recovered 5 seconds after pacing interruption. Moreover, the myocardial thickening at rest and peak pacing correlated with the subendocardial IBScv behavior and not with the subepicardial one.

CONCLUSIONS

IBScv are greater in the subendocardium than in the subepicardium. Atrial pacing stress test does not affect IBScv in segments supplied by nonstenotic coronary arteries, whereas it affects segments supplied by diseased coronary arteries, blunting exclusively subendocardial IBScv. Heterogeneity of IBScv intramyocardial changes caused by stress-induced ischemia must be taken into account when using IBScv for investigating myocardial ischemia.

Long-term implications of reocclusion on left ventricular size and function after successful thrombolysis for first anterior myocardial infarction

BACKGROUND

Successful thrombolysis can prevent left ventricular dilatation after acute myocardial infarction. However, in almost 30% of patients, reocclusion occurs. The aim of this study was to assess the long-term implications of reocclusion on left ventricular size and function.

METHODS AND RESULTS

Fifty-six patients were studied with two-dimensional echocardiography at baseline (2 +/- 1.6 days) and 5.0 +/- 1.4 years after first anterior myocardial infarction. All patients (a subset of those enrolled in the APRICOT trial) had a patent infarct-related artery when studied < 48 hours after thrombolysis and underwent repeat coronary angiography at 3 months. Baseline characteristics were comparable in patients with (n = 17) and without reocclusion (n = 39). Left ventricular volume indexes were stable in patients without reocclusion. Patients with reocclusion, however, showed a significant increase in end-diastolic volume index (EDVI; P = .008) and end-systolic volume index (ESVI; P = .039). Furthermore, patients without reocclusion demonstrated improvement in wall motion score index (WMSI; P = .0001) and ejection fraction (EF; P = .016), whereas patients with reocclusion did not. After 5 years, patients with reocclusion had significantly larger volume indexes (EDVI, 99 +/- 41 versus 76 +/- 22 mL/m2, P = .007; ESVI, 59 +/- 40 versus 39 +/- 20 mL/m2, P = .017) and more compromised left ventricular function (WMSI, 1.63 +/- 0.33 versus 1.39 +/- 0.32, P = .013; EF, 45 +/- 13% versus 51 +/- 11%, P = .077) than patients without reocclusion. Multivariate analysis identified baseline WMSI and reocclusion as significant independent predictors of left ventricular dilatation.

CONCLUSIONS

Reocclusion of the infarct-related artery within 3 months of successful thrombolysis is associated with left ventricular dilatation and is detrimental to functional recovery of left ventricular function 5 years after first anterior myocardial infarction.

Rate of collagen deposition during healing and ventricular remodeling after myocardial infarction in rat and dog models

BACKGROUND

We hypothesized that the rate and amount of infarct collagen deposition during healing after myocardial infarction might influence ventricular remodeling in rat and dog models. The purpose of this study was to compare rates of infarct collagen deposition and ventricular remodeling in the two models.

METHODS AND RESULTS

Infarcted rat and dog hearts were removed at fixed time intervals between 1 and 50 days for measuring remodeling parameters and infarct and noninfarct collagen content (mg/g hydroxyproline). Collagen was less in sham rat (n=29) than dog (n=30) ventricles (3.32 versus 4.57 mg/g, P<.001) and markedly lower in the rat (n=48) than dog (n=59) infarcts throughout healing and by 50 days (9.98 versus 56.74 mg/g, P<.0001). Infarct collagen leveled off earlier and healing (histology) was completed sooner in the rat. Infarct scars were also thinner in the rat, with more (P<.0001) thinning and bulging (mm/g), and greater increase in ventricular volume. Although the mass to volume ratio decreased (P<.001) in both models, global remodeling was different, with greater transverse axis widening and globularity in the dog. Although infarct size, transmurality, heart rate, filling pressure, and blood pressure were greater in the rat, infarcts 10% to 30% in size in both models showed similar differences in infarct collagen and remodeling.

CONCLUSIONS

Compared with dog infarcts, rat infarcts exhibited faster healing and infarct collagen deposition and markedly lower infarct collagen. In addition to larger, more transmural, and thinner infarcts, and greater hemodynamic load, the lower infarct collagen in that model might be an important factor in the greater regional remodeling.

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.

Impact of left ventricular unloading after late reperfusion of canine anterior myocardial infarction on remodeling and function using isosorbide-5-mononitrate

BACKGROUND

Late reperfusion during acute myocardial infarction results in delayed recovery of ventricular function and less remodeling, whereas ventricular unloading with nitrates improves function and attenuates remodeling. Whether late reperfusion combined with prolonged unloading with isosorbide-5-mononitrate (ISMN) might produce greater functional recovery and less remodeling than late reperfusion alone is not known.

METHODS AND RESULTS

In vivo left ventricular function and topography (echocardiograms), postmortem topography (planimetry), and collagen (hydroxyproline) were measured in dogs that were randomized to reperfusion 2 hours after left anterior descending coronary artery ligation, and ISMN (n = 12) or placebo (n = 12) was given as 25 mg IV over 4 hours followed by 50 mg PO QID for 6 weeks. Compared with placebo, the ISMN group had similar heart rate but lower left atrial pressure, mean arterial pressure, and rate-pressure products. Although in vivo baseline remodeling and functional parameters were similar in the two groups, by 6 weeks the ISMN group had smaller (P < or = .05) infarct and noninfarct segment lengths, ventricular volumes, and mass; less (P < .001) asynergy; and greater (P < .001) ejection fraction. More important, by 2 days, ejection fraction was 18% greater (P < .025) and asynergy 26% less (P < .05) with ISMN. At 6 weeks, ISMN showed less (P < or = .05) scar size, scar collagen, cavity dilation, noninfarct wall thickness, and apical bulging than placebo. In another 4 dogs, acute ISMN produced less improvement in function and remodeling than prolonged ISMN.

CONCLUSIONS

Late reperfusion of acute anterior myocardial infarction combined with prolonged ISMN unloading results in greater and earlier recovery of ventricular function and less remodeling than late reperfusion alone.

Combined captopril and isosorbide dinitrate during healing after myocardial infarction. Effect on ventricular remodeling, function, mass and collagen

OBJECTIVES

We sought to compare the effects of captopril plus isosorbide dinitrate versus monotherapy on infarct collagen content and left ventricular remodeling and function during healing after myocardial infarction.

BACKGROUND

Captopril or isosorbide dinitrate monotherapy can limit postinfarction dilation. Whether captopril inhibits infarct collagen content, or whether captopril plus isosorbide dinitrate might be more beneficial, is not known.

METHODS

In vivo remodeling variables and function (echocardiography), hemodynamic variables, postmortem topography (planimetry) and collagen content (hydroxyproline) were measured in 48 chronically instrumented dogs that were randomized 2 days after left anterior descending coronary artery ligation to 6 weeks of therapy with captopril, isosorbide dinitrate, captopril plus isosorbide dinitrate or placebo.

RESULTS

Compared with placebo, the three active therapies decreased blood pressure and left atrial pressure; limited infarct expansion, infarct thinning, noninfarct wall stretching and thickening; limited left ventricular dilation and increase in left ventricular mass; and decreased regional bulging, aneurysm frequency and left ventricular dysfunction. However, the decrease in asynergy and increase in volume ejection fraction were less with captopril or captopril plus isosorbide dinitrate than with isosorbide dinitrate. Infarct thinning and bulging at 6 weeks was also less with isosorbide dinitrate than with captopril. Although initial left ventricular asynergy, final scar sizes and noninfarct collagen content at 6 weeks were similar among the groups, collagen in the center of the infarct scar was less with captopril or captopril plus isosorbide dinitrate than with placebo or isosorbide dinitrate.

CONCLUSIONS

Monotherapy with captopril or isosorbide dinitrate, or their combination, improved all remodeling variables, but isosorbide dinitrate improved function more than captopril or captopril plus isosorbide dinitrate. Inhibition of infarct collagen content by captopril suggests that benefits with captopril represent a balance between positive and negative effects, and its combination with isosorbide dinitrate might be advantageous.

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.