Persistent reduction in left ventricular asynergy in patients with acute myocardial infarction by intravenous infusion of nitroglycerin

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.

Effect of early treatment with anti-hypertensive drugs on short and long-term mortality in patients with an acute cardiovascular event

BACKGROUND

Acute cardiovascular events represent a therapeutic challenge. Blood pressure lowering drugs are commonly used and recommended in the early phase of these settings. This review analyses randomized controlled trial (RCT) evidence for this approach.

OBJECTIVES

To determine the effect of immediate and short-term administration of anti-hypertensive drugs on all-cause mortality, total non-fatal serious adverse events (SAE) and blood pressure, in patients with an acute cardiovascular event, regardless of blood pressure at the time of enrollment.

SEARCH STRATEGY

MEDLINE, EMBASE, and Cochrane clinical trial register from Jan 1966 to February 2009 were searched. Reference lists of articles were also browsed. In case of missing information from retrieved articles, authors were contacted.

SELECTION CRITERIA

Randomized controlled trials (RCTs) comparing anti-hypertensive drug with placebo or no treatment administered to patients within 24 hours of the onset of an acute cardiovascular event.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data and assessed risk of bias. Fixed effects model with 95% confidence intervals (CI) were used. Sensitivity analyses were also conducted.

MAIN RESULTS

Sixty-five RCTs (N=166,206) were included, evaluating four classes of anti-hypertensive drugs: ACE inhibitors (12 trials), beta-blockers (20), calcium channel blockers (18) and nitrates (18). Acute stroke was studied in 6 trials (all involving CCBs). Acute myocardial infarction was studied in 59 trials. In the latter setting immediate nitrate treatment (within 24 hours) reduced all-cause mortality during the first 2 days (RR 0.81, 95%CI [0.74,0.89], p<0.0001). No further benefit was observed with nitrate therapy beyond this point. ACE inhibitors did not reduce mortality at 2 days (RR 0.91,95%CI [0.82, 1.00]), but did after 10 days (RR 0.93, 95%CI [0.87,0.98] p=0.01). No other blood pressure lowering drug administered as an immediate treatment or short-term treatment produced a statistical significant mortality reduction at 2, 10 or >/=30 days. There was not enough data studying acute stroke, and there were no RCTs evaluating other acute cardiovascular events.

AUTHORS' CONCLUSIONS

Nitrates reduce mortality (4-8 deaths prevented per 1000) at 2 days when administered within 24 hours of symptom onset of an acute myocardial infarction. No mortality benefit was seen when treatment continued beyond 48 hours. Mortality benefit of immediate treatment with ACE inhibitors post MI at 2 days did not reach statistical significance but the effect was significant at 10 days (2-4 deaths prevented per 1000). There is good evidence for lack of a mortality benefit with immediate or short-term treatment with beta-blockers and calcium channel blockers for acute myocardial infarction.

Evaluation of effects of nitroglycerin therapy by echocardiography

Echocardiography (Echo) is a convenient method in diagnosing and in quantification of cardiac abnormalities, although dependent on registration quality. M-mode and two-dimensional Echo give adequate information regarding heart dimensions and cavity volume but only indirect information of pressures. M-mode Echo gives an ideal opportunity to study left ventricular wall motion as an expression of systolic and diastolic function. Both inter and intra patient comparisons will be possible to perform. Improved wall function after intake of nitroglycerin and other nitrate preparations, has been reported in Echo studies both in resting state and in induced acute myocardial ischemia during exercise in man or in acute coronary occlusion in dogs.

Nitric oxide and cardiovascular protection

Nitric oxide (NO) plays a critical role in ischemic heart disease and ischemia-reperfusion. There is an increasing body of evidence to support the role of NO in myocardial and vascular protection in disease. The finding that NO might act as a trigger of late ischemic preconditioning (IPC) might lead to the development of novel anti-ischemic therapy. The role of NO signaling in the cardioprotective effects of ACE inhibitors and angiotensin II type 1 receptor(AT(1)) receptor antagonists is an active area of study.

Validation of three-dimensional echocardiography for quantifying the extent of dyssynergy in canine acute myocardial infarction: comparison with two-dimensional echocardiography

OBJECTIVES

This study was designed to compare the accuracy of three- and two-dimensional echocardiography for quantifying the extent of abnormal wall motion in experimental acute myocardial infarction, as correlated with the pathologic determination of infarct size.

BACKGROUND

Two-dimensional echocardiographic estimations of the fraction of myocardium showing abnormal wall motion are often used as an index of infarct size even though they rely on image plane positioning and geometric assumptions that may not be valid. Three-dimensional echocardiographic reconstruction of the endocardial surface eliminates the need for these assumptions and may improve echocardiographic estimates of infarct size.

METHODS

Coronary ligation was performed in 14 open chest dogs, and echocardiographic imaging of the ventricle was performed 6 h later. Three-dimensional echocardiography used seven or eight spatially registered short-axis images to measure percent of endocardial surface and mass showing abnormal wall motion. Three two-dimensional echocardiographic methods using multiple, nonpatially registered images were evaluated. One method used seven or eight-axis slices and a summation of discs algorithm for computing surface area. The second method used the same images and a conical model for the left ventricle. The third used basal, middle and apical short-axis plus apical four- and two-chamber views comparing summed endocardial lengths showing abnormal wall motion with the total of the endocardial dimensions, expressed as percent. The percent of left ventricular mass and surface area infarcted was determined by staining with triphenyltetrazolium chloride.

RESULTS

Three-dimensional echocardiographic measurements of endocardial surface and correlated more closely with infarct mass (r = 0.94, SEE +/- 3.6%) than did the two-dimensional method using the summation of discs algorithm (r = 0.85, SEE +/- 6.6%), he summation of conical sections algorithm (r = 0.82, SEE +/- 5.4%) or the method using summed endocardial lengths (r = 0.79, SEE +/- 7.4%). Limits of agreement analysis comparing mass showing abnormal wall motion with anatomic infarct mass surface area showing abnormal wall motion with anatomic infarct surface area showed the smallest limits for three-dimensional echocardiography.

CONCLUSIONS

Three-dimensional echocardiography is a more accurate means of noninvasively estimating myocardial infarct size in this canine model than two-dimensional echocardiography.

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.

Medical therapy of acute myocardial infarction: Part II. The role of adjunctive medical therapy

The second part of this review summarizes the role of other classes of pharmacological therapy in treatment of acute myocardial infarction (MI). The goals of pharmacological therapy are to alleviate symptoms, to stabilize hemodynamic status, and to prevent arrhythmias. These agents have been utilized primarily because of their ability to limit infarct size. Other beneficial properties may include their effects on neurohormonal activation, hemodynamics, and arrhythmias. In an individual patient, age, associated medical conditions, and hemodynamic status are important considerations in choosing a specific class of drug therapy. The beta-adrenergic blocking agents have modest effects on mortality, and they are useful when used alone and in combination with thrombolytic agents. Calcium antagonists have a limited role in acute MI. Diltiazem reduces the incidence of reinfarction in patients with non-Q MI. Oral nitrate therapy has not been shown to reduce mortality. Data from recent trials suggest that prophylactic administration of antiarrhthymic therapy is also not useful in acute MI. The role of angiotensin-converting enzyme inhibitors when administered in the acute phase of MI needs to be evaluated further. These agents are safe and well tolerated, and they offer greatest benefit when given in patients with left ventricular dysfunction.

Effect of nitrates on the frequency of left ventricular free wall rupture complicating acute myocardial infarction: a case-controlled study

Although up to 33% of all deaths from acute myocardial infarction are attributable to left ventricular free wall rupture, data showing a beneficial effect of drugs on this complication are scarce and contradictory. The aim of our study was to investigate the effect of nitrate therapy (intravenous or oral) during the first days after acute myocardial infarction on the frequency of free wall rupture in human beings. In a retrospective case-controlled study, 91 patients with free wall rupture complicating acute myocardial infarction demonstrated on autopsy or operation were compared with 182 control patients with acute myocardial infarction without rupture. The risk of sustaining free wall rupture was approximately 30% lower in patients receiving nitrates: (crude odds ratio 0.62; adjusted odds ratio 0.73 p 0.038). The data analysis demonstrates a possible association between nitrate use and frequency of left ventricular free wall rupture in patients with acute myocardial infarction. Nitrates seem to reduce the risk of rupture by approximately 30%.

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.

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.

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.

Effects of nitrates on mortality in acute myocardial infarction and in heart failure

1. Seven randomized controlled trials of intravenous nitroglycerin in a total of about 850 patients have been reported. Overall, there were 51 deaths (12.5%) in the nitroglycerin group and 87 (20%) in the control group. This indicates a 48% reduction in the odds of death (P less than 0.001, 95% confidence limits (25% to 64%)). 2. There are five randomized trials of oral nitrates after acute myocardial infarction. In these trials, 11.8% of the patients in the nitrate group compared with 13.3% in the control group died. This indicates a nonsignificant 12% reduction in the odds of death but the 95% confidence interval overlaps widely with the i.v. trials. If all trials of i.v. or oral nitrates are considered the reduction in the odds of death is 32% (P less than 0.01). 3. Nitrates have a beneficial effect on haemodynamics in heart failure but the data on mortality effects are sparse. In combination with hydralazine, however, long-term mortality was reduced in the V-HEFT trial of chronic heart failure.

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.

The golden hours of the myocardial infarction: nonthrombolytic interventions

Emergency care of patients with acute myocardial infarction requires active decision making to use agents that may improve morbidity and mortality. Thrombolysis remains the primary tool to accomplish this goal. Other pharmacologic agents, including lidocaine, nitrates, calcium channel blockers, beta-blockers, and aspirin, have been used acutely in myocardial infarction in the hopes of preventing death and salvaging myocardium. The decision to select one or all of these agents requires a knowledge of the clinical evidence of their efficacy and risk-to-benefit ratios. The clinical studies of the use of these agents acutely in the management of myocardial infarction are reviewed.

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.

Effects of nitroglycerin at therapeutic doses on platelet aggregation in unstable angina pectoris and acute myocardial infarction

The platelet aggregation response to adenosine diphosphate (ADP) and to thrombin was quantified in 10 patients, 5 with unstable angina pectoris and 5 with acute myocardial infarction, before, during and after a 45-minute infusion of nitroglycerin. An impedance aggregometer allowing rapid bedside studies in whole blood was used. The reproducibility of the methods was documented to be within 10%. Doses of nitroglycerin were titrated for a 10 mm Hg decrease in mean arterial blood pressure with mean doses being 1.2 +/- 0.2 (standard error of the mean) micrograms/kg/min. Nitroglycerin decreased the area under the aggregation curve induced by ADP from 43 +/- 3.6 to 30 +/- 6.3 cm2 (p = 0.007) and by thrombin from 8.9 +/- 1.7 to 4.1 +/- 0.9 cm2 (p = 0.003). Peak responses to ADP were decreased from 13.3 +/- 1 to 9.1 +/- 1.7 ohms (p = 0.005) and to thrombin from 9.3 +/- 2 to 5.0 +/- 1.2 ohms (p = 0.003). All patients had greater than or equal to 50% inhibition with 1 agent or the other and the inhibition was greater than 50% with each of the 2 aggregating agents in 6 patients. Analyses performed on blood withdrawn 15 minutes after the discontinuation of nitroglycerin showed a return to baseline before nitroglycerin results. When analyses were delayed and performed on blood preserved at room temperature for 30 minutes, no effect of nitroglycerin could be detected. Thus, bedside platelet aggregation studies document a significant and reversible effect of nitroglycerin at therapeutic doses on platelet function.

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.

Prospective two-dimensional echocardiographic evaluation of left ventricular thrombus and embolism after acute myocardial infarction

To determine whether two-dimensional echocardiography can identify patients with left ventricular thrombus after myocardial infarction who are prone to embolism, clinical and echocardiographic variables in 541 patients with a first infarction between 1979 and 1983 were studied prospectively. The first echocardiogram showed definite thrombus in 115 patients (Group 1, 21%) and no thrombus in 426 (Group 2, control). In Group 1, 27 patients (23%) had clinical evidence of systemic embolism related to the thrombus before referral (Group 1a) and 88 did not (Group 1b); these two groups were similar in age, gender and infarct location, but more Group 1a patients were within 1 month of the acute infarction. In both Groups 1a and 1b, the thrombus was found in apical views over asynergic zones, with no difference (p greater than 0.05) between the two groups in the size (average area from two views being 5.3 versus 4.5 cm2), type (protruding in apical views 30% versus 27%), location (apical 83% versus 86%; septal 11% versus 11%; posterior 4% versus 2%), extent of asynergy (31% versus 33%) and ejection fraction (33% versus 34%). However, the frequency of anticoagulant therapy was less (26% versus 63%, p less than 0.005), adjacent hyperkinesia greater (100% versus 49%, p less than 0.005) and thrombus mobility greater (81% versus 19%, p less than 0.005) in Group 1a than in Group 1b. Serial echocardiograms revealed a decreased size of the thrombus by 6 months in both Groups 1a and 1b, and little or no trace in 85% by 24 months. Thus, ventricular thrombus size, location and protrusion in apical views on echocardiography did not correlate with embolism. In contrast, thrombus mobility, the presence of adjacent hyperkinesia and thrombus protrusion assessed in multiple views appeared to be strong discriminators of thrombus prone to embolism. These echocardiographic features might provide a guide for the duration of anticoagulant therapy.

Myocardial infarction: is bepridil, a new calcium antagonist, able to improve the course of the acute phase?

Several calcium antagonists are useful in the treatment of ischemic heart disease. This open randomized study was designed to determine the effects of bepridil, a new long-acting calcium antagonist with antiarrhythmic properties, on the course of acute myocardial infarction (AMI). Two hundred patients with AMI of less than 48 hours duration (average 10.9 hours) were randomly assigned to two treatment groups: The first one was treated with bepridil (BEP, n = 100), and the second one was considered as a control group, using isosorbide dinitrate at a low dosage (ISDN, n = 100). BEP was administered intravenously for 48 hours at a dosage of 4 mg/kg/day; at the same time, an oral dose of 200 mg t.i.d. was started and continued for 21 days. In the control group, ISDN was given orally at the low dosage of 5 mg every 4 hours for 21 days. An uneventful course was seen in 28 BEP patients versus 15 in the control group (p less than 0.05). Mortality and recurrence of angina were lower in the BEP group than in the control group, but the difference is not significant. On the other hand, moderate and severe hemodynamic complications did not occur in 80 BEP patients versus 65 in the control group (p less than 0.05). Ventricular arrhythmias occurred in 36 BEP patients versus 50 in the control group (p less than 0.05). Antiarrhythmic therapy was required in 14 BEP patients versus 61 in the control group (p less than 0.001). These results show that bepridil seems capable of improving the hemodynamics and arrhythmologic course of AMI.

Myocardial salvage with streptokinase combined with nitroglycerine and verapamil in acute myocardial infarction

We tested the hypothesis that preservation of left ventricular function results from treatment with intravenous streptokinase given in the first 2 hours from onset of acute transmural myocardial infarction together with nitroglycerine and verapamil. Thirty-three consecutive patients with onset of pain less than 2 hours prior to admission, received intravenous streptokinase 1.5 x 10(6) units with intravenous nitroglycerine and verapamil; 23 concurrently admitted "control" patients with pain onset 2-4 hours received intravenous nitroglycerine and verapamil only. Radionuclide ventriculographic assessment at 2 days revealed a significantly greater left ventricular ejection fraction in the streptokinase-treated patients (54.5 +/- 2.8 vs 46.1 +/- 2.9; P less than 0.05), which persisted at 28-35 days (50.1 +/- 2.3 vs 41.2 +/- 2.9; P less than 0.05). Streptokinase-treated patients had a significantly increased incidence of ischaemic events in the 35 days following infarction, but a lower incidence of death, congestive cardiac failure and non-fatal ventricular tachycardia than control group patients. Infarct-related artery patency assessed at 3-5 days was 94% in streptokinase-treated patients. We conclude that early presentation and treatment with intravenous streptokinase, nitroglycerine and verapamil is associated with a high incidence of successful thrombolysis and significant preservation of left ventricular function. Nitroglycerine and verapamil may augment the efficacy of streptokinase in this group of patients.

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

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

Early natural history of regional left ventricular dysfunction after experimental myocardial infarction

Existing studies provide conflicting information concerning the natural history of regional dysfunction after subacute myocardial infarction. The purpose of this study was to use quantitative computer-assisted two-dimensional echocardiography to define the natural history of abnormal wall motion in a subacute canine infarct model within individual short-axis echocardiographic planes, and in the entire ventricle as well. Serial short-axis echocardiograms were obtained from 10 closed-chest dogs before occlusion and at 0.5, 6, 24, 48, and 72 hours after ligation of the circumflex (six dogs) or left anterior descending (four dogs) coronary artery. The circumferential extent of abnormal wall motion was quantified by two different computer-assisted methods: the first, a derived correlation method, examined wall motion throughout the systolic contraction sequence; the second method examined the fractional radial change in endocardial ray length from end-diastole to end-systole. The study shows that for individual planes there is a slight but not statistically significant increase in the circumferential extent of abnormal wall motion from 0.5 to 72 hours after coronary artery occlusion; however, when the total extent of left ventricular asynergy was used to define a global functional infarct size, we observed a small (3.6% to 5.4%) but significant increase in the circumferential extent of abnormal wall motion.

Nitrates

Nitroglycerin and the long-acting nitrates are playing an increasingly important role in cardiovascular medicine. These agents are recommended in all of the various anginal syndromes and are as effective as the beta-blockers and calcium channel antagonists. There is a definite place for nitrate therapy in treating the complications of acute myocardial infarction. These drugs are also highly effective as unloading therapy in congestive heart failure. The mechanisms of action of the nitrates are reviewed in this article. Information is provided regarding nitrate efficacy in all the major clinical syndromes in which these drugs are used. Finally, appropriate dosing strategies are suggested that should eliminate the potential problem of nitrate tolerance.

Comparison of different pharmacological interventions on enzymatic parameters during acute myocardial infarction

The concept that acute myocardial infarction is a dynamic event and that different interventions can modify the extent of the necrosis, has led to renewed interest in early pharmacological and surgical treatments designed to reduce the ischemic injury. To evaluate the effects of different pharmacological interventions aimed to reduce the extent of necrosis, we studied 166 patients (138 male and 28 female, mean age of 59.4 +/- 11.3 years) admitted within 6 h after chest pain and treated with a single therapy during the first 72 h. Enzymatic infarct size (IS) was calculated by serial creatine kinase isoenzyme MB determinations using a compartmental model. Six groups of patients were evaluated: 33 patients were treated only with antiplatelet drugs, 38 with anticoagulants, 34 with intravenous thrombolytic therapy, 20 with calcium channel blockers, 25 with nitrates, and 16 with beta-blockers. Estimated IS (gEq/m2) and elimination constant (Kd, U/L/h) did not differ in the six groups, but patients treated with streptokinase had higher release constant (Ka, U/L/h) and shorter time to peak CK-MB value. Early treatment (less than or equal to 2 h after chest pain) had a favourable effect on the enzymatic IS only in patients treated with calcium channel blockers (p less than 0.005).

Role of infarct expansion in rupture of the ventricular septum after acute myocardial infarction: a two-dimensional echocardiographic study

To verify the role of infarct expansion (IE) in ventricular septal rupture (VSR) after transmural acute myocardial infarction (TAMI), topographic parameters were measured using tomographic imaging with two-dimensional echocardiography (2-D echo) and computer-aided analysis in four groups of patients: 8 patients with VSR (Group 1); 24 patients with TAMI but no mechanical complications (Group 2); 11 normal athletes (Group 3); 5 adults with congenital ventricular septal defect (Group 4). Measurements made on end-diastolic outlines of mid-left ventricular (LV) short-axis images included: LV asynergy (akinesis and/or dyskinesis), expansion index (asynergy/nonasynergy-containing endocardial segment length), thinning ratio (asynergic/nonasynergic wall thickness), and new indexes of regional shape distortion (RSD) by quantifying the deviation of the actual asynergic segment from the ideal asynergic arc constructed using the nearly circular nonasynergic contour. In Group 1, clinical IE (hypotension, congestive heart failure, no signs of new infarction) preceded detection of the VSR and portable 2-D echo showed the VSR associated with LV asynergy, marked IE, and RSD. Although Groups 1 and 2 had similar LV asynergy (28.7 vs. 26.9% LV) and ejection fraction (38.9 vs. 41.8%), Group 1 had higher expansion index (1.50 vs. 1.17, p less than 0.05), lower thinning ratio (0.54 vs. 0.67, p less than 0.005), and higher RSD parameters (e.g., peak distortion, Pk or maximum radial distance from the ideal arc, 19.3 vs. 3.9 mm, p less than 0.01; area of distortion, Ad, 7.4 vs. 1.1 cm2, p less than 0.05) than Group 2. Groups 3 and 4 had normal regional and global function and no evidence of expansion, thinning, or RSD. Thus, IE with marked diastolic RSD on an early 2-D echo after TAMI might identify patients at risk for VSR.

The role of transdermal nitroglycerin in the treatment of coronary heart disease

Nitroglycerin has long been a mainstay of the treatment of ischemic cardiac pain. The introduction of transdermal formulations and in particular the development of controlled methods of delivery have been responsible for the renaissance of clinical interest in this simple and effective treatment. The pathophysiologic abnormality accompanying myocardial ischemia affords a natural theater for the exhibition of the therapeutic utility of these preparations and methods. The means whereby nitrates induce relaxation of vascular smooth muscle are not entirely clear, but their pharmacodynamic activities are perfectly plain. In the doses used in clinical practice, nitrates exert their predominant hemodynamic effects and therapeutic benefits through their peripheral vasodilator activities. This is particularly marked in veins, although in higher doses nitrates also dilate the larger systemic and coronary arteries. Criticisms of the efficacy of transdermal formulations of nitrates in the treatment of angina pectoris have arisen largely from uncritical acceptance of a small number of studies of questionable methodologic validity. Large-scale general practice studies have invariably found that transdermal nitrate delivery systems improve the quality of life in ambulant patients: anginal attacks are reduced with a minimum of side effects. The widespread acceptance of this novel form of drug delivery has stimulated its application in other therapeutic avenues. The efficacy of transdermal nitroglycerin in the suppression of silent ischemic attacks has been demonstrated. The maintenance of benefit initiated by intravenous nitroglycerin in patients with unstable angina also broadens the use of this method of nitrate delivery. In patients with acute myocardial infarction, whether complicated by left ventricular failure or not, the nitrates, and transdermal nitroglycerin in particular, appear to hold considerable promise. Improvement of hemodynamic abnormalities may cause reduction in infarct size and fewer life-threatening arrhythmias. Even survival may be extended. The utility of transdermal nitrates in the treatment of severe chronic heart failure is less certain. But the use of higher doses and an interval regimen of administration may hold promise for such patients. Naturally, more information is required before the overall therapeutic profile of this new method of controlled nitroglycerin delivery across the whole spectrum of coronary heart disease can be fully described. Fortunately, the high level of efficacy and safety of transdermal nitroglycerin demonstrated in the majority of reported studies encourages the pursuit of such an important therapeutic target.

Congestive heart failure

A review of the epidemiology, pathophysiology, and treatment of congestive heart failure is presented, with particular attention given to newer modalities of therapy.

Results of a randomized prospective trial of intraaortic balloon counterpulsation and intravenous nitroglycerin in patients with acute myocardial infarction

A randomized prospective clinical trial compared combined treatment with intraaortic balloon pumping and intravenous nitroglycerin for 4 to 5 days with routine clinical management in 20 patients with extensive myocardium at risk for infarction as evidenced by a thallium defect score of 7.0 units or greater. No significant differences in mortality or clinical outcome were observed between the 10 patients receiving the combined treatment and the 10 receiving routine management. In 14 patients two-dimensional echocardiograms obtained 6 to 24 hours after the onset of symptoms and at follow-up 6 to 16 days later (after completion of combined intraaortic balloon pumping plus nitroglycerin therapy) were analyzed to determine whether infarct segment or noninfarct segment lengths were affected by therapy. Among these 14 patients, 5 (3 receiving the combined therapy and 2 receiving routine management) demonstrated an increase in infarct segment length of greater than 1.0 cm. Mean infarct segment length increased 0.30 +/- 0.44 cm in patients receiving the combined therapy and 0.29 +/- 0.36 cm in patients on routine management (p = NS). In contrast, noninfarct segment length increased greater than 1.0 cm (mean increase 1.20 +/- 0.39) in five of seven patients on routine management but in none of 7 patients receiving intraaortic balloon pumping plus nitroglycerin therapy (mean decrease 0.22 +/- 0.20 cm) (p less than 0.05). No significant differences were noted in left ventricular ejection fraction, as measured by gated blood pool scintigraphy, or thallium perfusion defect score in a comparison of day 1 (pretreatment) with day 4 thallium or day 7 to 14 gated blood pool scintigrams. Thus, in patients with extensive myocardium at risk, it is unlikely that a reduction in mortality or a significant improvement in myocardial perfusion or ventricular function can be obtained by early intervention with intraaortic balloon pumping in combination with nitroglycerin. Although this combined therapy failed to prevent infarct segment lengthening (infarct expansion), the combined afterload-lowering effects of intraaortic balloon pumping and nitroglycerin did appear to prevent dilation or remodeling of noninfarcted segments during the first 2 weeks after acute myocardial infarction.

Evaluation of biventricular involvement in hypotensive patients with transmural inferior infarction by two-dimensional echocardiography

Hypotension in inferior myocardial infarction (IMI) may be due to extensive involvement of the right ventricle (RV), left ventricle (LV), or both. We verified this hypothesis in 24 patients with IMI and hypotension (systolic blood pressure less than 100 mm Hg), within 48 hours of admission, by means of two-dimensional echocardiography (2DE). We measured the extent of regional RV and LV asynergy (akinesis and/or dyskinesis) in parasternal short-axis sections at mitral, chordal, midpapillary muscle, and low papillary muscle levels. Initial right heart catheterization revealed predominant RV dysfunction in 16 patients (group 1) and predominant LV dysfunction in eight patients (group 2). For all patients, the initial 2DE revealed: (1) biventricular asynergy involving the posterior RV, posterior LV, and posterior interventricular septum; (2) a wide range of values for the extent of asynergy (RV 21% to 90%; LV 19% to 48%); and (3) a direct correlation between peak creatine kinase levels and percentage of LV asynergy (r = 0.80, p less than 0.001) or percentage of RV plus LV asynergy (r = 0.72, p less than 0.001). Although the extent of LV asynergy was similar in the two groups (34% vs 34%, NS), the extent of RV asynergy was greater in group 1 than in group 2 (57% vs 30%, p less than 0.001). More important, the ratio of RV/LV asynergy was greater for group 1 than group 2 (1.75 vs 0.89, p less than 0.001), and this difference in ratios between the two groups was also found in 2DE studies at 10 days and 6 months. A RV/LV asynergy ratio value of 1.1 provided clear separation between the groups. Thus, the RV/LV asynergy ratio on an initial 2DE can clarify the clinical syndrome of hypotension in patients with IMI. An increased asynergy ratio might identify those patients with predominant RV involvement.

Effect of nitroglycerin on coronary collateral flow and pressure during acute coronary occlusion

Coronary collateral function was evaluated in 21 conscious, unsedated patients by measuring aortic and distal coronary pressures and great cardiac vein flow during transient (1 minute) balloon occlusion of the anterior descending artery in the course of coronary angioplasty. Measurements were made before and during administration of intravenous nitroglycerin (NTG). Clinical, electrocardiographic and hemodynamic events of transient myocardial ischemia occurred in 10 patients before and 6 patients during NTG administration (p = 0.11). The NTG infusion consistently decreased pressure determinants of myocardial oxygen demand without increasing heart rate. NTG also decreased a calculated coronary collateral resistance index in 13 patients. Responsiveness to NTG did not appear to depend on the presence or absence of collateral vessels detected by angiography or on any other angiographic variable assessed. Measurement of coronary collateral function during coronary angioplasty is a new technique with the potential to assess the ability of interventions to prevent transient myocardial ischemia and improve myocardial perfusion during acute coronary occlusion in humans.

Mechanism of action of nitrates. Role of changes in venous capacitance and in the left ventricular diastolic pressure-volume relation

Nitroglycerin, when administered to patients with heart failure, causes a marked reduction in left ventricular filling pressure but often an increase in stroke volume and stroke work; based on the Frank-Starling principle, such a reduction in "preload" would be expected to result in a decrease in left ventricular end-diastolic volume and, therefore, a decline in stroke volume. Assessment of pressure-volume coordinates, however, has revealed that nitroglycerin produces a downward shift in the pressure-volume relationship. This apparent improvement in left ventricular compliance cannot be attributed to alterations in the elastic properties of the myocardium but rather appear to reflect a reduction in left ventricular external constraint. Recent animal and clinical investigations in our laboratory suggest that nitroglycerin causes venous dilatation (particularly in the mesenteric bed), thereby decreasing venous pressure at any given vascular volume. This decrease in cardiac filling pressure results in a decrease in heart size and, therefore, a reduction in pericardial pressure. Left ventricular transmural (intracavitary minus pericardial) pressure is little changed, however, so that end-diastolic volume and stroke volume are maintained.

Nitrate delivery systems in perspective. A decade of progress

In recent years the use of nitroglycerin and long-acting nitrate compounds in clinical practice has been increasing. Only 10 to 15 years ago these drugs, at least in oral formulation, were felt to have no clinical utility because of concern that potent hepatic enzyme activity would degrade sufficient amounts of the nitrate compounds from reaching the systemic circulation. However, it is now recognized that oral nitrate administration when given in sufficient amounts achieves therapeutic plasma concentrations and desired clinical effects. Nitrates are routinely used for the treatment of stable and unstable angina and also play a role in therapy for complications of myocardial infarction. Nitrates are very effective agents for preload reduction in vasodilator therapy of congestive heart failure. A wide variety of nitrate delivery systems, including the standard oral and sublingual formulations, and as well as the new transdermal nitroglycerin discs and buccal nitroglycerin, are now available. Sublingual nitroglycerin, isosorbide dinitrate, and buccal nitroglycerin are used for acute treatment of attacks of ischemic chest pain. For ambulatory patients, long-acting therapy can be administered by oral, topical ointment, transdermal disc, and buccal nitroglycerin formulations. Each compound has a slightly different onset and duration of action, which is in part dose-dependent. The relative merits and problems with each of the formulations are reviewed. Intravenous nitroglycerin is now commercially available and plays an increasing role in the intensive care units. It is an ideal drug for acute chest pain syndromes, including acute myocardial infarction. Specialized tubing does not need to be employed. The wide variety of nitrate delivery systems available to physicians makes use of this tried and true therapy practical and easy to carry out for clinicians.