Myocardial salvage by intravenous nitroglycerin in conscious dogs: loss of beneficial effect with marked nitroglycerin-induced hypotension

The utility of thrombophilia and hematologic screening in live liver donation

BACKGROUND

Most centers perform some degree of hematologic screening, including thrombophilia testing, on prospective live liver donors. The nature and extent of such screens are not standardized, and there is limited evidence regarding hematologic risk stratification.

METHODS AND RESULTS

We present an experience of hematologic screening among prospective liver donors. Five-hundred-eightyfour patients were screened for liver donation between 1/2013 and 1/2020, of whom 156 (27%) proceeded to donor hepatectomy. Thirty-three of 428 (8%) declined patients were excluded for hematologic indications. Hematologic indications were the 2nd most frequent medical indications for exclusion (trailing only hepatologic indications). The most common reason for hematologic exclusion was concern regarding thrombophilia. Nevertheless, 21 patients with evidence of possible thrombophilia proceeded to donor hepatectomy, and none incurred hematologic complications. Similarly, seven patients with screening findings concerning for increased bleeding risk (most often thrombocytopenia) underwent donor hepatectomy without hematologic complication. Three of 156 (2%) of patients who underwent donor hepatectomy incurred a hematologic complication (all thrombotic, none fatal). None of these patients had any evident hematologic risk factor on screening.

CONCLUSION

This study underscores the difficulty of hematologic risk stratification among prospective living donors, however, suggests that some patients with relatively mild risk factors may be safe for donation.

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.

Clinical effectiveness of telmisartan alone or in combination therapy for controlling blood pressure and vascular risk in the elderly

Elderly patients (age ≥ 65 years) with hypertension are at high risk for vascular complications, especially when diabetes is present. Antihypertensive drugs that inhibit the renin-angiotensin system have been shown to be effective for controlling blood pressure in adult and elderly patients. Importantly, renin-angiotensin system inhibitors were shown to have benefits beyond their classic cardioprotective and vasculoprotective effects, including reducing the risk of new-onset diabetes and associated cardiovascular effects. The discovery that the renin-angiotensin system inhibitor and angiotensin II type 1 (AT(1)) receptor blocker (ARB), telmisartan, can selectively activate the peroxisome proliferator-activated receptor-γ (PPARγ, an established antidiabetic drug target) provides the unique opportunity to prevent and treat cardiovascular complications in high-risk elderly patients with hypertension and new-onset diabetes. Two large clinical trials, ONTARGET (Ongoing Telmisartan Alone in combination with Ramipril Global Endpoint Trial) and TRANSCEND (Telmisartan Randomized AssessmeNt Study in ACE-I iNtolerant subjects with cardiovascular disease) have assessed the cardioprotective and antidiabetic effects of telmisartan. The collective data suggest that telmisartan is a promising drug for controlling hypertension and reducing vascular risk in high-risk elderly patients with new-onset diabetes.

Effect of systemic blood pressure on microcollateral circulation evaluated by real-time contrast echocardiography

BACKGROUND

In acute myocardial infarction, residual collateral-derived myocardial blood flow (CBF) within the ischemic area is one of the major determinants of infarct size. Management of systemic blood pressure (sBP) related to maintain collateral circulation is still difficult. The aim of this study was to reveal the influence of sBP on the rescue of area at risk by collateral circulation.

METHODS

Real-time myocardial contrast echocardiography just after the onset of complete occlusion of the left circumflex coronary artery was performed in collateral-rich open-chest dogs. The video intensity of the ischemic area was evaluated during the occlusion and the CBF (A x beta) was calculated from a replenishment curve: y = A (1 - e(-beta t)). To analyze the effect of sBP on the collateral circulation, sBP was altered by infusion of nitroglycerin or etilefrine hydrochloride. To evaluate the defect size (%DS), every end-systolic myocardial contrast echocardiography image after left circumflex coronary artery occlusion was converted into binary images using custom offline software.

RESULTS

The %DS increased and CBF slightly decreased at low sBP. The %DS decreased and CBF increased at high sBP. At excessively high sBP, %DS increased and CBF decreased again.

CONCLUSION

Real-time myocardial contrast echocardiography, which is a useful noninvasive method to evaluate the collateral perfusion quantitatively, has a crucial role in the decision of patient treatment and management strategy of acute myocardial infarction.

Valsartan in the treatment of heart attack survivors

Survivors of myocardial infarction (MI) are at high risk of disability and death. This is due to infarct-related complications such as heart failure, cardiac remodeling with progressive ventricular dilation, dysfunction, and hypertrophy, and arrhythmias including ventricular and atrial fibrillation. Angiotensin (Ang) II, the major effector molecule of the renin–angiotensin–aldosterone system (RAAS) is a major contributor to these complications. RAAS inhibition, with angiotensin-converting enzyme (ACE) inhibitors were first shown to reduce mortality and morbidity after MI. Subsequently, angiotensin receptor blockers (ARBs), that produce more complete blockade of the effects of Ang II at the Ang II type 1 (AT₁) receptor, were introduced and the ARB valsartan was shown to be as effective as an ACE inhibitor in reducing mortality and morbidity in high-risk post-MI suvivors with left ventricular (LV) systolic dysfunction and and/or heart failure and in heart failure patients, respectively, in two major trials (VALIANT and Val-HeFT). Both these trials used an ACE inhibitor as comparator on top of background therapy. Evidence favoring the use of valsartan for secondary prevention in post-MI survivors is reviewed.

C-type natriuretic peptide, a novel antifibrotic and antihypertrophic agent, prevents cardiac remodeling after myocardial infarction

OBJECTIVES

We assessed the hypothesis that in vivo administration of C-type natriuretic peptide (CNP) might attenuate cardiac remodeling after myocardial infarction (MI) through its antifibrotic and antihypertrophic action.

BACKGROUND

Recently, we have shown that CNP has more potent antifibrotic and antihypertrophic effects than atrial natriuretic peptide (ANP) in cultured cardiac fibroblasts and cardiomyocytes.

METHODS

Experimental MI was induced by coronary ligation in male Sprague-Dawley rats; CNP at 0.1 mug/kg/min (n = 34) or vehicle (n = 35) was intravenously infused by osmotic mini-pump starting four days after MI. Sham-operated rats (n = 34) served as controls. After two weeks of infusion, the effects of CNP on cardiac remodeling were evaluated by echocardiograpic, hemodynamic, histopathologic, and gene analysis.

RESULTS

C-type natriuretic peptide markedly attenuated the left ventricular (LV) enlargement caused by MI (LV end-diastolic dimension, sham: 6.7 +/- 0.1 mm; MI+vehicle; 8.3 +/- 0.1 mm; MI+CNP: 7.7 +/- 0.1 mm, p < 0.01) without affecting arterial pressure. Moreover, there was a substantial decrease in LV end-diastolic pressure, and increases in dP/dt(max), dP/dt(min), and cardiac output in CNP-treated MI rats compared with vehicle-treated MI rats. Importantly, CNP infusion markedly attenuated an increase in morphometrical collagen volume fraction in the noninfarct region (sham: 3.1 +/- 0.2%; MI+vehicle: 5.7 +/- 0.5%; MI+CNP: 3.9 +/- 0.3%, p < 0.01). In addition, CNP significantly reduced an increase in cross-sectional area of the cardiomyocytes. These effects of CNP were accompanied by suppression of MI-induced increases in collagen I, collagen III, ANP, and beta-myosin heavy chain messenger ribonucleic acid levels in the noninfarct region.

CONCLUSIONS

These data suggest that CNP may be useful as a novel antiremodeling agent.

Moderate Systemic Hypotension During Reperfusion Reduces the Coronary Blood Flow and Increases the Size of Myocardial Infarction in Pigs

STUDY OBJECTIVE

s: To examine the effects of low arterial BP (ABP) during reperfusion on the extent of myocardial infarction and on coronary blood flow (CBF) in an occlusion/reperfusion experimental model.

DESIGN

Prospective, randomized animal study.

SETTING

University hospital.

PARTICIPANTS

Normal pigs that were anesthetized, intubated, and mechanically ventilated.

INTERVENTIONS

Twenty-seven open-chest pigs underwent occlusion of the mid left anterior descending (LAD) coronary artery for 1 h followed by reperfusion for 2 h. During reperfusion, the animals were randomly assigned to either continuous infusion of nitroglycerin in therapeutic doses and fluid infusion at rates to maintain a mean ABP >or= 80 mm Hg (group 1, n = 13), or continuous nitroglycerin infusion at rates to maintain a mean ABP between 60 mm Hg and 75 mm Hg (group 2, n = 14).

MEASUREMENTS AND RESULTS

The hemodynamics and the coronary ABP distal to the occlusion were recorded throughout the experiment. In addition, the LAD CBF and peak hyperemia CBF before occlusion and during reperfusion periods were measured by transit-time flowmetry. At the end of the experiment, the infarcted left ventricular myocardial size was measured. There were no significant hemodynamic differences, including the distal coronary arterial pressure, between the two groups before or during the LAD artery occlusion period. During reperfusion, mean ABP was 90 +/- 3 mm Hg in group 1 vs 69 +/- 3 mm Hg in group 2 (p < 0.001). In group 1, the infarcted myocardium represented 50.3 +/- 4.3% of the myocardium at risk, vs 69.4 +/- 7.2% in group 2 (p < 0.001). During reperfusion, CBF and peak hyperemia CBF were significantly higher in group 1 than in group 2.

CONCLUSIONS

Low ABP during reperfusion increases the size of myocardial infarction and decreases CBF.

Nitric oxide in heart failure: friend or foe

Nitric oxide (NO) is a controversial molecule. It is either beneficial or deleterious. As with NO donors, one reason for this duality is related to the dose. Small doses are highly beneficial, maintaining blood flow in vessels and blood pressure, and protecting against foreign invaders. In high doses, it results in hypotension, forms peroxynitrite which is cytotoxic, and contributes to heart failure.

Pharmacokinetics of ITF 296 (Sinitrodil) a novel organic nitrate, in healthy volunteers

ITF 296 is a new orally active nitrate acting selectively on large arterial vessels over a wide range of doses. In healthy volunteers it causes less reduction in vascular resistance and less venodilatation than classic nitrates. Its pharmacokinetic profile was evaluated after intravenous infusion and oral (solution and immediate-release tablet) administration in a randomised cross-over design on 11 healthy volunteers. The plasma levels of ITF 296 and its metabolite ITF 1124 were determined by a HPLC method. The drug is rapidly distributed (mean steady-state distribution volume 53+/-17 liters) and eliminated (half-life of about 25 minutes) both after intravenous and oral administration. The total clearance is 2. 31+/-0.46 l/min. The oral solution of ITF 296 is well absorbed (Cmax=0.057 microg/ml, tmax=30 min) but it undergoes a first-pass effect (F=25%). The tablet, developed only for Phase 1 clinical studies, is characterised by an immediate release (Cmax=0.057 microg/ml, tmax=30 min). The extent of its absolute and relative bioavailability is about 14% and 53% respectively.

Safety, tolerability, and antiischaemic efficacy of ITF-296, a nitric oxide donor, in patients with chronic stable angina

A double-blind, placebo-controlled, parallel-group, dose-escalation study was performed to evaluate ITF-296, a new nitric oxide donor, in chronic stable angina. Twenty-four male patients underwent exercise electrocardiography in conjunction with echocardiography on three separate occasions within 2 weeks. After two reproducibility tests, the third exercise test was immediately preceded by a 30-min intravenous infusion of either placebo or 0.3, 1.0, or 3.0 microg/kg/min of ITF-296, with six patients in each treatment group. During ITF-296 infusion, systolic blood pressure decreased by a mean of 12 mm Hg compared with a 2 mm Hg increase in the placebo group [difference, -14; 95% confidence interval (CI), -23 to -6 mm Hg]. ITF-296 administration was followed by consistent increases in total exercise time, time to angina threshold, and time to 1-mm ST-segment depression. The mean change in total exercise time was 39 s on placebo and 94 s on ITF-296 (mean difference, 54 s; 95% CI, -48 to 157 mm Hg). The 1.0- and 3.0-microg/kg/min doses increased exercise time by >2 min with no important change in peak rate-pressure product compared with baseline. The trends exhibited in this small preliminary study were consistently pharmacologically plausible and indicate that ITF-296 shows potential antiischaemic efficacy in patients with chronic stable angina.

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.

Cardiovascular disease in elderly patients

OBJECTIVE

To provide an overview of the cardiovascular consequences of the normal aging process in humans and to review unique aspects of the diagnosis and management of heart disease in the elderly population.

DESIGN

We reviewed relevant published articles and summarized the diagnostic approaches and treatment recommendations for congestive heart failure, coronary artery disease, cardiac valvular disease, and arrhythmias in elderly patients.

RESULTS

The aging process is associated with predictable anatomic and physiologic alterations in the cardiovascular system. consequently, the manifestations of heart disease in the geriatric population differ from those found in younger patients. Additionally, outcomes of cardiac diseases and therapeutic options change with advancing age because of such factors as alterations in drug metabolism.

CONCLUSION

Age-related changes in the cardiovascular system result from intrinsic cardiac aspects of human senescence, primary cardiac disease, and influence of comorbid conditions on the heart. The natural history of heart disease is generally adversely affected by age. Although many treatment strategies with demonstrated efficacy in younger patients are relevant in the elderly age-group, careful attention to the influence of concomitant illness, the unique physiologic and pharmacologic changes, and the assessment of the potential effect of therapy on survival and quality of life is essential in treating elderly patients.

Cardiovascular effects of NT-1, a new patch form of nitroglycerin, alone and in combination with nifedipine in conscious dogs

The cardiovascular effects of NT-1, a new patch form of nitroglycerin, alone and in combination with nifedipine in conscious dogs were examined. NT-1 (2.5 mg kg-1 nitroglycerin) decreased systolic blood pressure by 10-15%, while diastolic blood pressure and heart rate were not affected. Coronary blood flow and calculated rate-pressure product were decreased. These parameter changes occurred at 30 min after NT-1 application and remained constant for 8 h until NT-1 was removed. After administration of NT-1 in combination with nifedipine, systolic blood pressure was significantly decreased to a greater extent, and heart rate and coronary blood flow showed a tendency to increase compared with nifedipine alone. Rate-pressure product was not changed compared with that obtained on administration of nifedipine alone. These results suggest that NT-1 may be applicable as a transdermal sustained release medication, and show that in combination with nifedipine, NT-1 can induce a large increase in coronary blood flow without further increasing rate-pressure product.

Nitrates in myocardial infarction: influence on infarct size, reperfusion, and ventricular remodelling

OBJECTIVE

To assess the possible benefits of intravenous isosorbide dinitrate in acute myocardial infarction and oral isosorbide mononitrate in subacute myocardial infarction.

METHODS

316 patients presenting with acute myocardial infarction were entered into double blind placebo controlled clinical trials assessing infarct size by enzyme release, ventricular size and function by echocardiography, reperfusion by continuous 12 lead ST segment monitoring and late potentials by high resolution electrocardiography.

RESULTS

301 patients, of whom 292 (97%) received thrombolytic treatment, were randomised on admission to intravenous isosorbide dinitrate or placebo. Overall, there was no significant effect of treatment on infarct size, ST segment resolution, ventricular remodelling, or late potentials at day 3. A trend was observed towards a reduction in infarct size in patients with non-Q wave infarction treated with isosorbide dinitrate. Heterogeneity of nitrate effect was observed in relation to the degree of ST segment elevation on presentation with a clear benefit of isosorbide dinitrate in patients with moderate ST segment elevation (472 U/l v 704 U/l, P = 0.003) and a trend towards a deleterious effect in patients with marked ST segment elevation (1152 U/l v 1058 U/l, P = 0.2). ST segment re-elevation was more common among patients receiving nitrate treatment than in those assigned to placebo (29 v 16, P < 0.05). Some 160 patients underwent a further randomisation to sustained release isosorbide mononitrate or placebo on day 3. Echocardiographic volumes after 6 weeks of treatment were similar in the two groups.

CONCLUSIONS

No benefit was observed with administration of nitrates in the treatment groups as a whole for either acute or subacute infarction. There was, however, evidence of heterogeneity of effect in the different subgroups of acute infarction, and the possibility that nitrates may have differing actions in different groups of patients should be considered.

Nitrates in myocardial infarction

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

Antiischemic effects of pirsidomine, a new nitric oxide donor

The antiischemic effect of pirsidomine (CAS 936 (3-(cis-2,6-dimethylpiperidino)-N-(4-methoxybenzoyl))-sydnon imine), a new nitric oxide donor, was investigated in a model of myocardial infarction in the dog. Dogs were anaesthetised, thoracotomized, and the left descending coronary artery was occluded for 6 h. Pirsidomine was given intraduodenally (i.d.) at the dose of 1.0 mg/kg to 11 dogs 30 min prior to coronary occlusion. Eleven dogs received the solvent i.d. and served as controls. Pirsidomine administration completely prevented the increase in left ventricular end-diastolic pressure and pulmonary artery pressure induced by the coronary occlusion and resulted in a marked decrease in systolic and diastolic blood pressure, cardiac output, left ventricular contractility, left ventricular work and left ventricular oxygen consumption. Additionally, pirsidomine completely prevented the occlusion-induced increase in flow in the non-occluded circumflex coronary artery. Regional blood flow measurements (with radioactive microspheres) revealed that pirsidomine induced a significant reduction in blood flow in the non-ischemic areas (both epi- and endocardial) but in the course of the ischemia, significantly increased flow in the ischemic epicardial areas. Infarct-size (triphenyltetrazolium chloride technique) in control dogs was 45% of the area at risk, but only 26% (P < 0.05) in pirsidomine-treated dogs. Thus, pirsidomine had a marked antiischemic effect in this model. This was probably due to the hemodynamic unloading of the heart as well as to redistribution of blood from the non-ischemic to the ischemic areas of the myocardium.

Use of nitroglycerin for the treatment of acute myocardial infarction

After a decade of warnings against the use of nitrates in acute myocardial infarction (MI), they are becoming recognized for their potential to salvage left ventricular (LV) myocardium, geometry and function. Low-dose intravenous (IV) nitroglycerin (NTG) infusion for the first 48 h after acute MI, titrated to lower mean blood pressure by 10% to 30%, but not below 80 mmHg, has been shown to be safe, to improve hemodynamics, and to decrease infarct size, infarct expansion, complications, and deaths in a prospective, randomized, single-blind study of 310 patients. In addition, low-dose NTG infusion for the first 48 h, followed by prolonged buccal NTG given during healing after acute MI in an eccentric dose schedule to minimize tolerance, was found to limit further progressive remodeling and preserve LV function. Meta-analysis of nitrate studies in acute MI indicate that they improve survival. Preliminary and ongoing studies suggest that prolonged NTG therapy post MI can produce further benefit.

Effects of nitrate therapy on ventricular remodeling and function

The hypothesis that nitrates might effectively limit left ventricular remodeling and improve function after acute myocardial infarction has been tested in experimental and clinical models, with special attention to the pathophysiologic evolution of remodeling. In 1 clinical study, before the thrombolytic era, the effects of low-dose intravenous nitroglycerin infusion for the first 48 hours during acute myocardial infarction was evaluated in a prospective, randomized, single-blinded, placebo-controlled study of 310 patients (154 nitroglycerin; 156 placebo). Nitroglycerin proved to be safe and produced several benefits compared with placebo: (1) smaller infarct size; (2) less left ventricular dysfunction; (3) less infarct expansion and thinning; (4) better functional status; (5) fewer in-hospital complications such as left ventricular failure, left ventricular thrombus, cardiogenic shock, and infarct extension; and (6) fewer deaths up to 1 year. Two subsequent clinical studies in the thrombolytic era, with low-dose intravenous nitroglycerin infusion during infarction over the first 48 hours followed by buccal nitrate (eccentric dose regimen) or placebo during healing over 6 weeks postinfarction, indicated that prolonged nitrate therapy effectively limited left ventricular remodeling and improved function further compared with placebo.

Attenuation of left ventricular dilatation after acute myocardial infarction by early initiation of enalapril therapy. CONSENSUS II Multi-Echo Study Group

This trial investigated the effect of enalapril, administered early, on left ventricular (LV) volumes after myocardial infarction. Four hundred twenty-eight patients included in the Cooperative New Scandinavian Enalapril Survival Study (CONSENSUS II) were examined with echocardiography within 5 days, at 1 month and at 6 months after myocardial infarction. Enalaprilat (1 mg) or placebo infusion was initiated within 24 hours after infarction, followed by oral treatment to a target dose of 20 mg/day. A significant attenuation of LV dilatation was noted at 1 month in patients treated with enalapril compared with those receiving placebo. Changes in LV end-diastolic volume indexes during the first month were (mean +/- SEM) 5.7 +/- 1.0 ml/m2 for the placebo group and 1.9 +/- 0.8 ml/m2 for the enalapril group (p < 0.02). Changes in LV end-systolic volume indexes were 3.1 +/- 0.8 and 0.5 +/- 0.6 ml/m2, respectively (p < 0.02). The between-group difference was most marked in patients with anterior wall infarction (p < 0.005). Volume changes beyond the first month were similar in both groups but the differences observed at 1 month were maintained. The larger volumes in the placebo versus enalapril group were significant or borderline significant at 1 and 6 months. Thus, enalapril treatment initiated early after myocardial infarction and continued for 6 months can attenuate LV dilatation during the first month resulting in smaller LV volumes after 1 and 6 months.

Reduced infarct size in nonreperfused myocardial infarction by combined infusion of isosorbide dinitrate and streptokinase

The value of thrombolytic therapy in myocardial infarction is well established, while any beneficial effect of adjunct therapy is more uncertain. In a double-blind, randomized, parallel-group study the effect of combined intravenous infusions of streptokinase and isosorbide dinitrate (ISDN) on enzyme-estimated infarct size was investigated. One hundred consecutive patients with strong clinical and electrocardiographic suspicion of myocardial infarction, admitted to the coronary care unit within 8 hours after the onset of symptoms, were given a streptokinase infusion of 1.5 million units for 1 hour and a titrated dose of ISDN or placebo for 48 hours. From isoenzyme B of creatine kinase (CK-B) values measured every 4 hours, the infarct size was calculated and the possible presence of reperfusion was evaluated. The infarct size in patients receiving ISDN infusion was reduced (p = 0.04, one-sided test) compared with placebo. By subdividing the patients according to whether or not reperfusion had occurred, the infarct size appeared to be similar following ISDN and placebo in patients with reperfusion (419 versus 369 U/L), whereas the infarct size in patients not reperfused was markedly reduced after treatment with ISDN (223 versus 1320 U/L, p = 0.003). In conclusion, the present study demonstrates that the infarct size may be reduced by other means than reperfusion and it supports the use of combined infusion of thrombolytic agents and nitrates in patients with suspected myocardial infarction.

Role of nitrates after acute myocardial infarction

Apart from their ability to relieve myocardial ischemia, nitrates have an important role to play on preservation of left ventricular (LV) geometry and function after acute myocardial infarction (MI). In the first 48 hours after acute MI, intravenous nitroglycerin infusion titrated to a low-dose regimen produces multiple benefits, including smaller infarct size, better regional and global LV function, less remodeling, fewer in-hospital complications, and fewer deaths in-hospital and up to 1 year. This regimen might be an effective adjunct during reperfusion therapy for salvaging ischemic myocardium, LV geometry, and function. Recent studies indicate that prolonged therapy with nitrates during the healing phase after acute MI can effectively further limit progressive LV remodeling (less LV dilation, expansion, thinning, and aneurysm formation) and preserve LV function. Tolerance with chronic therapy is avoided by an eccentric dose regimen to provide a nitrate-free interval.

Effect of long-term captopril therapy on left ventricular remodeling and function during healing of canine myocardial infarction

To determine whether the long-term reduction of preload and afterload by captopril during healing after acute anterior myocardial infarction might attenuate left ventricular remodeling and improve function, 30 chronically instrumented dogs with infarction produced by left anterior descending coronary artery ligation were randomized 2 days later to oral therapy with placebo (n = 15) or captopril, 50 mg twice daily (n = 15), for 6 weeks. Serial hemodynamic as well as topographic and functional variables (two-dimensional echocardiography) were measured over 6 weeks. Scar topography (planimetry), occluded bed size (coronary arteriography) and collagen (hydroxyproline) content were measured at 6 weeks. Between 2 days and 6 weeks, captopril decreased (p less than 0.001) mean arterial pressure and mean left atrial pressure more than did placebo, but it did not influence heart rate. Infarct scar mass, transmurality and collagen content at 6 weeks were similar in the two groups but scars showed less (p less than 0.001) thinning and expansion with captopril than with placebo. Echocardiograms showed similar infarct expansion and thinning in the two groups at 2 days but less aneurysm with captopril at 6 weeks. Between 2 days and 6 weeks, expansion index (infarct-/noninfarct-containing segment length) decreased (p less than 0.001) with captopril but increased (p less than 0.001) with placebo. Also, thinning ratio (infarct/normal wall thickness) decreased (p less than 0.001) with placebo but did not change (p = NS) with captopril. By 6 weeks, left ventricular asynergy and volumes showed a greater decrease (p less than 0.01) and global ejection fraction a greater increase (p less than 0.05) with captopril.(ABSTRACT TRUNCATED AT 250 WORDS)

Intravenous nitroglycerin unloading in acute myocardial infarction

Low-dose intravenous nitroglycerin infusion can be safely administered during acute myocardial infarction to unload the left ventricle and salvage ischemic myocardium and left ventricular geometry and function. In an experimental conscious dog model, low-dose infusion titrated to decrease mean blood pressure by 10% over the first 6 hours after coronary artery ligation resulted in 51% decrease in infarct size, 54% decrease in preload, and more than 50% increase in collateral blood flow. The same benefits were seen when methoxamine was given to counteract that 10% decrease in blood pressure. Similar short-term nitroglycerin infusion also limited remodeling in the dog model. More important, no myocardial salvage was seen with excessive nitroglycerin-induced hypotension to levels less than 80 mm Hg. Clinically, prolonged low-dose nitroglycerin infusion was evaluated in a prospective, randomized, single-blinded, placebo-controlled study of 310 patients with acute infarction: 154 received nitroglycerin and 156 received placebo. Nitroglycerin was titrated to reduce mean blood pressure by 10% in normotensive patients and up to 30% in hypertensive (blood pressure greater than 140/90 mm Hg) patients, but not to less than 80 mm Hg. Nitroglycerin produced several benefits compared with placebo: (1) smaller creatine kinase infarct size; (2) less regional left ventricular dysfunction, better global ejection fraction, and less infarct expansion and thinning; (3) better clinical functional status and hemodynamics; (4) fewer inhospital complications such as acute left ventricular failure and dilation due to marked infarct expansion, left ventricular thrombus, cardiogenic shock, and infarct extension; and (5) fewer deaths up to 1 year in patients with anterior Q-wave infarction.

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

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

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

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

Tolerance with low dose intravenous nitroglycerin therapy in acute myocardial infarction

The question of vascular tolerance was examined in 154 patients with acute myocardial infarction (64 anterior, 90 inferior) who were treated with prolonged low dose intravenous nitroglycerin in a recent randomized placebo-controlled study. The dose of nitroglycerin was carefully titrated to decrease mean blood pressure by 10% in normotensive patients and 30% in hypertensive (blood pressure greater than 140/90 mm Hg) patients, but not less than 80 mm Hg. Tolerance was defined as the need to increase the dose to maintain this hemodynamic effect. It was labelled "true" if chest pain was absent and "apparent" if chest pain was present. Group analysis of dose, pain scores, hemodynamic, 2-dimensional echocardiographic and clinical parameters monitored serially before and after therapy indicated benefit with nitroglycerin over placebo despite equalizing of blood pressures after 10 hours. Reversal of blood pressures and volumes after discontinuing nitroglycerin suggested lack of significant tolerance. However, detailed individual analysis suggested significant hemodynamic tolerance in 37 patients (24%), both in the true tolerance (12%) and apparent tolerance (12%) subgroups. Tolerance appeared early, requiring the dose to be increased by 30 +/- 39 micrograms/min within 11 +/- 9 hours. The dose was greater (p less than 0.001) in the tolerance than in the no tolerance subgroup, both before (60 vs 27 micrograms/min) and after (90 vs 38 micrograms/min) 10 hours. Tolerance blunted the beneficial effect on infarct size, but positive effects on function, topography and complications persisted.

Calcium-channel blockers in acute myocardial infarction

The calcium-channel blockers are useful in treating a variety of cardiovascular disorders. Due to their antiischemic and spasmolytic properties, these agents have been studied in the prophylaxis and treatment of acute myocardial infarction. This article reviews this application with respect to reduction of mortality, infarct size, and reinfarction rate. Of the agents currently available for clinical use, nifedipine has been studied most extensively. This agent shows no beneficial effects in this setting and its use may in fact be harmful. Of the few trials that have been conducted with verapamil, none have shown decreased mortality. Verapamil may reduce infarct size although further confirmation is required. Diltiazem is the only agent that has been shown to have short- and long-term benefits in the patient with acute myocardial infarction. Proper patient selection is of utmost importance in ensuring successful therapy. In particular, those patients with non-Q-wave infarctions and/or normal left ventricular function can be expected to derive the most benefit in terms of reducing mortality and reinfarction rate associated with the acute event.

Effect of intravenous nitrates on mortality in acute myocardial infarction: an overview of the randomised trials

About 2000 patients have been randomised in ten trials of intravenous nitroglycerin or nitroprusside in acute myocardial infarction. Taken separately, the individual trials have all been too small to provide a reliable estimate of the effects of treatment on mortality, but collectively they provide strong evidence of benefit. In total there have been 136 nitrate and 193 control deaths, and an appropriate overview of the separate trial results indicated a "typical" reduction of 35% (SD 10) in the odds of death (2p less than 0.001, with 95% confidence limits of about one-sixth to one-half). Both nitroglycerin and nitroprusside reduced mortality, the reduction being non-significantly greater with nitroglycerin than with nitroprusside. The greatest reduction in mortality occurred during the first week or so of follow-up, with a non-significant further reduction after this early period. This suggests that the early benefit is not rapidly lost.

The effect of arterial pressure alterations during halothane anesthesia on residual flow and infarct size with transient regional ischemia of the dog

The present study was designed to determine if infarct size under halothane anesthesia could be reduced by increasing the pressure gradient across the collateral vascular bed, thereby increasing flow within the occluded vascular bed. Forty-nine mongrel dogs were anesthetized with halothane under identical physiologic conditions with the exception of systemic arterial blood pressure. The control group of 18 animals anesthetized with halothane was compared to two experimental groups. In one group of 15 dogs, the mean systemic pressure was raised 25% above control with phenylephrine (BP25). In the second group of 15 dogs, systemic pressure was raised 50% above control (BP50). Adjacent marginal branches of the left circumflex coronary artery were ligated for 90 minutes followed by 90 minutes of reflow. The area of the occluded vascular bed was similar in all groups, but the area of infarction as a percentage of the occluded vascular bed was reduced from 47.7 +/- 4.7% to 25.4 +/- 4.3% in the BP25 group (P < or = .05 v control) and to 33.1 +/- 5.0% in the BP50 group. Flow measurements using microspheres showed a larger zone of ischemic tissue receiving adequate residual flow in the BP25 and BP50 groups compared to the control. It is concluded that infarct size during halothane anesthesia in the dog can be reduced by increasing systemic blood pressure with phenylephrine.

Healing after myocardial infarction in the dog: changes in infarct hydroxyproline and topography

Temporal changes in infarct collagen and left ventricular topography during healing after myocardial infarction were studied in 132 dogs with coronary artery ligation: 8 sham dogs and 13 with no infarction (controls) and 111 with infarction (3 at 1 day, 54 at 2 days, 25 at 7 days, 3 at 2 weeks, 9 at 4 weeks and 17 at 6 weeks). Myocardial hydroxyproline (a marker of collagen) was measured by spectrophotometry and pathologic infarct size, arteriographic occluded bed size and topography by computerized planimetry of weighed left ventricular rings. Over 6 weeks, hydroxyproline was unchanged in normal regions (average 4.20 mg/g dry weight) but increased progressively between 7 days and 6 weeks (9.94 versus 55.55 mg/g, p less than 0.001) in infarct zones. Progressive infarct contraction occurred over 6 weeks, with infarct size at 6 weeks being 40% less than at 2 days (9.7 versus 16.3% of the left ventricle, p less than 0.001), although total infarct hydroxyproline was directly related to infarct size at each time period (r = 0.73 to 0.81, p less than or equal to 0.05). Significant (p less than or equal to 0.05) left ventricular topographic changes in infarct hearts compared with control hearts included: 1) increase in cavity area (5.0 versus 3.9 cm2), endocardial circumference (8.8 versus 7.4 cm) and expansion index (infarct/normal endocardial segment length, 1.21 versus 1.02) by 7 days; and 2) decrease in thinning ratio (infarct/normal wall thickness, 0.71 versus 0.98) by 6 weeks. Also, compared with 2 day infarcts, by 6 weeks infarct area was decreased (1.8 versus 3.4 cm2) and the noninfarcted segment length increased (6.9 versus 5.4 cm). Changes in hydroxyproline and topography were similar for anterior (n = 54) and posterior (n = 57) infarcts. Thus, healing in canine infarcts is associated with cavity dilation and infarct expansion within 7 days followed by infarct contraction and thinning by 6 weeks, whereas collagen increases between 7 days and 6 weeks. Collagen deposition in expanded and thinned infarct segments explains the permanent regional shape distortion associated with ventricular aneurysms.

Different relations between infarct size and occluded bed size in barbiturate-anesthetized versus conscious dogs

The relation between infarct size and occluded bed size in barbiturate-anesthetized (n = 32) and conscious (n = 34) dogs was compared using models of the left anterior descending (n = 43) and circumflex (n = 23) coronary arteries with 2 day old infarcts. Infarct and occluded bed (postmortem coronary arteriography) masses were measured by computerized planimetry of weighed left ventricular rings. For either type of occlusion, infarcts were larger in anesthetized than in conscious dogs (56 versus 33% occluded bed, p less than 0.001), with greater slopes of the linear regressions between infarct size and occluded bed size (p less than 0.001) and less epicardial sparing (p less than 0.05) on topographic mapping. Although arterial and left atrial pressures were similar in the two groups, heart rates were higher in the anesthetized dogs, both before (127 versus 88 beats/min, p less than 0.001) and after (151 versus 109 beats/min, p less than 0.001) occlusion. Myocardial blood flow distribution (radioactive microspheres, n = 33) favored the epicardium in anesthetized dogs, with lower endocardial-epicardial flow ratios pre- and postocclusion. Also, the level of total plasma catecholamines (radioenzymatic assay) was higher in barbiturate-anesthetized (n = 5) than in conscious (n = 5) dogs. Increasing the heart rate in conscious dogs (n = 18) to that of the anesthetized group (139 beats/min) by pacing produced larger infarcts and greater linear regression slopes, as seen in anesthetized dogs. Decreasing the heart rate in anesthetized dogs (n = 7) to that of the conscious group (98 beats/min) by sinoatrial node destruction and pacing resulted in smaller infarcts and lower linear regression slope, as seen in conscious dogs. Thus, the larger infarcts in barbiturate-anesthetized dogs appeared to be related mainly to the tachycardia, although transmural maldistribution of flow and increased circulating catecholamines might have contributed.

Effects of nitroglycerin-induced hypotension on myocardial blood flow in a two vessel occlusion-stenosis anesthetized canine model

The effects of acute occlusion of the left anterior descending coronary artery on regional blood flow (microspheres) to the remote bed supplied by either an unstenosed or a stenosed circumflex coronary artery were assessed during the infusion of intravenous nitroglycerin in 11 open chest barbiturate-anesthetized mongrel dogs. Left anterior descending coronary artery occlusion in the presence of an unstenosed left circumflex artery during nitroglycerin infusion caused systolic aortic and distal circumflex pressure to decrease significantly from 98 +/- 4 to 91 +/- 3 and from 99 +/- 4 to 92 +/- 3 mm Hg, respectively. Remote circumflex bed flow was unchanged. The infusion of intravenous nitroglycerin in the presence of a left circumflex stenosis (gradient 31 +/- 3 mm Hg) reduced systolic aortic and distal circumflex pressure to 98 +/- 2 (p = 0.001) and 71 +/- 4 mm Hg (p = 0.001), respectively, and lowered remote circumflex bed endocardial flow from 1.00 +/- 0.08 to 0.79 +/- 0.07 ml/min per g (p = 0.001). When the left anterior descending coronary artery was occluded under these conditions, systolic aortic and distal left circumflex pressure decreased to 89 +/- 3 (p = 0.005) and 62 +/- 4 mm Hg (p = 0.08), respectively. Remote circumflex artery bed endocardial and transmural flow were significantly reduced to 0.58 +/- 0.07 (p = 0.01) and 0.65 +/- 0.07 ml/min per g (p = 0.03), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Potential deleterious haemodynamic effects of glyceryl trinitrate on myocardial ischaemia in man

The potential adverse effects of glyceryl trinitrate on myocardial ischaemia were studied using low and high dose infusions in 10 patients with coronary heart disease. Cardiac venous flow was measured by the thermodilution technique and blood was sampled for metabolic studies. Angina pectoris was provoked by atrial pacing before drug infusion and the same heart rate was regained with low and high doses of glyceryl trinitrate. Both doses reduced myocardial ischaemia equally. The low dose of glyceryl trinitrate reduced mean systolic aortic pressure from 145(23) to 128(23) mm Hg and the high dose further to 103(9) mm Hg. Myocardial oxygen uptake decreased owing to a combined reduction in preload and afterload with the low dose and was substantially more reduced with the high dose owing to a further afterload reduction. Transmural perfusion gradient did not change with the low dose of glyceryl trinitrate but fell significantly with the high dose. This fall in myocardial perfusion probably accounts for the lack of further reduction in ischaemia with the high dose. Thus the adverse effects of glyceryl trinitrate infusion are small and do not increase myocardial ischaemia.