Prediction of mortality in hospital survivors of myocardial infarction. Comparison of predischarge exercise testing and radionuclide ventriculography at rest

Risk stratification after acute myocardial infarction in the reperfusion era

Historically, risk stratification for survivors of acute myocardial infarction (AMI) has centered on 3 principles: assessment of left ventricular function, detection of residual myocardial ischemia, and estimation of the risk for sudden cardiac death. Although these factors still have important prognostic implications for these patients, our ability to predict adverse cardiac events has significantly improved over the last several years. Recent studies have identified powerful predictors of adverse cardiac events available from the patient history, physical examination, initial electrocardiogram, and blood testing early in the evaluation of patients with AMI. Numerous studies performed in patients receiving early reperfusion therapy with either thrombolysis or primary angioplasty have emphasized the importance of a patent infarct related artery for long-term survival. The predictive value of a variety of noninvasive and invasive tests to predict myocardial electrical instability have been under active investigation in patients receiving early reperfusion therapy. The current understanding of the clinically important predictors of clinical outcomes in survivors of AMI is reviewed in this article.

Interrelation of left ventricular ejection fraction, pulmonary congestion and outcome in acute myocardial infarction

The interrelation of different grades of pulmonary congestion evaluated by chest roentgenogram in the coronary care unit, predischarge left ventricular (LV) ejection fraction (EF) and long-term prognosis was studied in 1,850 surviving patients of acute myocardial infarction (AMI). Pulmonary congestion was categorized as: none, mild or moderate, or severe; LVEF was classified as: greater than or equal to 40%, 25 to 39%, or less than 25%. The majority of patients (1,060; 57%) had an LVEF greater than or equal to 40% and no signs of pulmonary congestion. Severe pulmonary congestion was noted in 63 patients (3.4%), 17 with LVEF less than 25% and 16 with LVEF greater than or equal to 40%. One hundred twenty-five patients (6.8%) had an LVEF less than 25%, 49 of whom had no signs of pulmonary congestion. During a mean 2-year follow-up, cardiac mortality occurred in 212 patients (11.5%). The cardiac mortality rate was related to both predischarge LVEF impairment and severity of pulmonary congestion. Cardiac mortality hazard ratios (95% confidence intervals [CI]) for LVEF less than 25%, and 25 to 39% were 5.32 (CI 3.49, 8.13; p less than 0.0001) and 2.91 (CI 2.10, 4.02; p less than 0.0001), respectively, where a referent hazard ratio of 1 was assigned to patients with LVEF greater than or equal to 40% and to those with no pulmonary congestion. Development of pulmonary congestion during AMI significantly increased the cardiac mortality risk derived from LVEF, with a marked mortality effect in patients with severe pulmonary congestion; (hazard ratio 4.20; 95% CI 2.67, 6.62; p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

The value of exercise tests after acute myocardial infarction

The aim of the present study was to relate the clinical course in patients after a first acute myocardial infarction with the response to exercise-tests performed one month after discharge. 90 consecutive patients who suffered an acute myocardial infarction for the first time were followed-up after 12 months in general practice. Six patients had died, and nine patients had suffered another MI. 23 patients were being treated for heart failure, 51 for angina pectoris, and 8 for arrhythmias. 14 patients received treatment for both heart failure and angina pectoris. Of the patients at work, 17.6% did not return to work because of the heart disease. 80 patients were in function groups I-II and 10 in function groups III-IV (New York Heart Association's Classification). Occurrence of ST-segment displacements was without prognostic value. Left ventricular function index (dRPP) and working capacity (W) were predictive with respect to mortality, heart failure, and angina pectoris requiring drug treatment. Exercise tests following acute myocardial infarction could not predict the chances of returning to work.

Use of left ventricular function as an end point of thrombolytic therapy

In recent acute myocardial infarction, early reperfusion of the infarct-related artery by intracoronary or intravenous thrombolytic therapy induces a significant limitation of infarct size, provided reperfusion occurs within a time frame that myocardial salvage can still be expected. Limitation of infarct size reduces scar tissue formation, aneurysm formation, infarct zone expansion, left ventricular volume enlargement, and eventually results in higher left ventricular ejection fraction. Infarct size limitation and left ventricular function preservation occur with all thrombolytic agents currently in clinical use: streptokinase, alteplase and, more recently, anistreplase. When anistreplase is compared with conventional heparin therapy, a 31% reduction in infarct size is found (estimated from single photon emission computed tomography, or SPECT). This translates into a significant preservation of left ventricular ejection fraction as observed in anistreplase-treated patients compared with heparin-treated patients (0.53 +/- 0.13 vs 0.47 +/- 0.12, p less than 0.002). In comparative trials of 2 thrombolytic agents, anistreplase was demonstrated to be as efficient as alteplase on left ventricular ejection fraction preservation and infarct size limitation.

Prognostic significance of the Karnofsky Performance Status score in patients with acute myocardial infarction: comparison with the left ventricular ejection fraction and the exercise treadmill test performance. The MILIS Study Group

The prognostic significance of functional status has not been previously studied in the setting of acute myocardial infarction. We assessed the Karnofsky Performance Status (KPS) score, a simple functional status scale that is commonly used to categorize physical ability, in 849 patients with acute myocardial infarction who were enrolled in the Multicenter Investigation of the Limitation of Infarct Size (MILIS) study. We then compared the KPS score with other predictors of prognosis in these patients. In patients who presented with acute myocardial infarction, a lower KPS score (less than 8 on a scale of 1 to 10) 3 weeks before the index infarction was associated with a higher incidence of congestive heart failure, in-hospital cardiac arrest, and mortality during hospitalization, as compared with patients with KPS scores greater than or equal to 8 (each p less than 0.001). Cumulative 1-year and 4-year mortality rates were significantly higher in patients with KPS scores less than 8, as compared with patients with KPS scores greater than or equal to 8 (42.5% vs. 12.6% at 1 year and 61.6% vs 25.1% at 4 years, respectively; both p less than 0.001). The left ventricular ejection fraction on admission was significantly lower in patients with KPS scores less than 8, as compared with those with KPS scores greater than or equal to 8 (p less than 0.019). The cumulative mortality rate was equally well predicted by low KPS score and by left ventricular ejection fraction (both p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein A and prognosis after myocardial infarction in non-diabetic men

The implications of apolipoproteins A-I and A-II for the prognosis of 178 non-diabetic men after acute myocardial infarction were studied. During a mean follow-up period of 4 years, one or more "coronary events" (nonfatal myocardial infarction, fatal coronary heart disease, coronary artery bypass graft surgery, deterioration of exercise ECG) were recorded in 37 patients. Serum levels of apolipoproteins A-I and A-II did not discriminate between patients with and without coronary events. This applied to the entire sample as much as to subgroups defined by presence or absence of interventions (coronary artery bypass graft surgery, long-term therapy with beta-blockers or lipid-lowering drugs). We conclude that coronary events in the first years after myocardial infarction cannot be predicted by apolipoprotein A-I or A-II levels.

Predischarge maximal exercise test identifies risk for cardiac death in patients with acute myocardial infarction

A maximal exercise test was performed in 54 patients with acute myocardial infarction (AMI) before discharge and in 49 age-matched control subjects. The long-term prognosis was assessed after an average follow-up of 7.6 years in AMI patients and 5.8 years in control subjects. The maximal work capacity and systolic blood pressure increase in AMI patients was 59% that of control subjects (p less than 0.001). Seventeen AMI patients had significant ST-segment shifts, 13 with ST depression and 4 with ST elevation. In AMI patients experiencing a cardiac death during follow-up the maximal work capacity and systolic blood pressure increase were significantly lower than in survivors and those who died from noncardiac reasons (p less than 0.01; p less than 0.05), with no difference between these groups in the number of patients with ST-segment shifts. The average maximal work capacity of control subjects was 143 watts. A maximal work capacity half this (less than or equal to 72 watts) predicted long-term mortality in AMI patients (p less than 0.001). In addition a low increase in systolic blood pressure (less than 30 mm Hg) also predicted long-term mortality (p less than 0.005), whereas ST shifts were of no significant value. In this study maximal work capacity turned out to be the best single exercise variable for identifying groups of AMI patients with very low and relative high risk of cardiac death. When all 3 exercise variables were combined, the predischarge maximal exercise test was of great value in identifying AMI patients at low risk for cardiac death (predictive value of a negative test: 95%).

Thrombolytic agents in early myocardial infarction

The current revolution in the treatment of acute myocardial infarction by means of thrombolytic therapy has as its underlying strategy 3 aims: early restoration of the blood flow in order to salvage jeopardized but still viable tissues, limitation of the ultimate infarct size, and preservation, as far as possible, of ventricular function. The hope is that these 3 achievements will result in reduced short- and long-term mortality rates. The techniques used in this overall strategy are still under investigation. Three leading pharmacologic compounds vie for supremacy: streptokinase as well as its anisoylated form, recombinant technique tissue-type plasminogen activator and urokinase with or without prourokinase. In addition, the underlying anatomy may require early, or delayed, percutaneous transluminal coronary angioplasty where needed backed by coronary artery bypass grafting. Thus, the tactics of the intervention may vary from case to case and indeed from center to center depending on experience and facilities, but the conclusion is clearly the same: Early reperfusion is a must if one wishes to save ischemic but viable tissue. This report summarizes the current evidence for this new strategy.

Relative power of clinical, exercise test, and angiographic variables in predicting clinical outcome after myocardial infarction: the Newham and Tower Hamlets study

The interrelations of clinical, exercise test, and angiographic variables and their relative values in predicting specific clinical outcomes after myocardial infarction have not been fully established. Of 302 consecutive stable survivors of infarction, 262 performed a predischarge submaximal exercise test. In the first year after infarction patients with a "positive" exercise test were 13 times more likely to die, 2.8 times more likely to have an ischaemic event, and 2.3 times more likely to develop left ventricular failure than patients with negative tests. Patients with positive exercise tests underwent cardiac catheterization. Features of the history, 12 lead electrocardiogram, in-hospital clinical course, exercise test, and left ventricular and coronary angiograms that predicted these clinical end points were identified by univariate analysis. Then multivariable analysis was used to assess the relative powers of all variables in predicting end points. Certain features of the exercise test remained independent predictors of future ischaemic events and the development of overt left ventricular failure, but clinical and angiographic variables were more powerful predictors of mortality. Because the exercise test is also used to select patients for angiography, however, the results of this study strongly support the use of early submaximal exercise testing after infarction.

Which exercise test variables are of prognostic importance post-myocardial infarction?

The prognostic value of parameters noted on pre-discharge exercise testing was assessed in 300 survivors of acute myocardial infarction. Exercise testing was performed at a mean of 9 days post-infarction. Each patient's data were studied for the presence of ST-segment depression or elevation greater than or equal to 0.1 mV in any of the 12 leads recorded, angina pectoris, exertional hypotension and duration of exercise. The patients were followed for a mean of 12 months and the incidence of death, reinfarction, angina pectoris, heart failure and coronary revascularization procedures was noted. All variables studied, other than the presence of exercise-induced ST-segment elevation, were significantly associated with the occurrence of subsequent cardiac events (P less than 0.001). Exercise-induced ST-segment depression identified 80% of patients who developed complications and was significantly more sensitive than any of the other variables as a prognostic marker (P less than 0.05). The finding of angina pectoris, an abnormal blood pressure response or a limited exercise tolerance in association with exercise-induced ST-segment depression heightened the prognostic implications of this variable.

Limitations on the prognostic value of predischarge data after myocardial infarction

Clinical variables and those obtained by non-invasive techniques were studied prospectively in a series of 306 patients discharged from hospital after an acute myocardial infarction. The predictive value of the data at two and 12 months was assessed by univariate and multivariate analyses. The best correlation was found for age, hypertension, bundle branch block, early and late heart failure, x ray cardiothoracic ratio, digoxin use, the number of metabolic equivalents reached during the stress test, echocardiographic wall motion score index, left ventricular end diastolic diameter, left ventricular ejection fraction, and the presence of an aneurysm. The prognostic value of the same data at 12 months was studied in those surviving for two months. There was a noticeable decline in the relative risk of all but two of the factors (number of metabolic equivalents, ventricular arrhythmias). All of the predictive variables except the x ray cardiothoracic ratio, number of metabolic equivalents, and the presence of an aneurysm lost their discriminant power. The explanation for this is the strength of statistical relations of these variables with the outcome at two months. They continued to influence the score at 12 months even when the entire patient series was considered. In conclusion, the study shows that the predictive value of most of the predischarge variables usually taken into account in the assessment of risk in patients one year after infarction does not extend beyond the first two months.

Stratifying risk after a myocardial infarction

These discussions are selected from the weekly staff conferences in the Department of Medicine, University of California, San Francisco. Taken from transcriptions, they are prepared by Drs Homer A. Boushey, Professor of Medicine, and David G. Warnock, Associate Professor of Medicine, under the direction of Dr Lloyd H. Smith, Jr, Professor of Medicine and Associate Dean in the School of Medicine. Requests for reprints should be sent to the Department of Medicine, University of California, San Francisco, School of Medicine, San Francisco, CA 94143.

Left ventricular function of survivors of a first complicated acute myocardial infarction. A prehospital discharge cross-sectional echocardiographic study

To assess the left ventricular function of patients who suffer from post-infarction angina and left ventricular failure in the coronary care unit, 79 consecutive survivors (mean age 48 years) of a first acute myocardial infarction were prospectively studied and followed-up for a mean 18- (10-34) month period. Forty-seven had an uncomplicated infarction, 17 suffered from post-infarction angina and 15 had left ventricular failure. The left ventricular function of these patients prior to discharge from hospital was assessed by cross-sectional echocardiography and radionuclide angiography. Analysis of left ventricular wall motion was performed in all patients using a 11-segment model of the left ventricular. The ejection fraction was determined by echocardiography in 47 patients and by radionuclide angiography in 50. The mean echocardiographic wall motion score of post-infarction angina patients (4.8 +/- 0.8) (+/- SEM) was lower than that of patients with left ventricular failure (9.5 +/- 0.5) (P less than 0.001), but was not different from patients suffering uncomplicated infarctions (4.6 +/- 0.3). The mean echocardiographic ejection fraction was also similar in post-infarction angina (45.3 +/- 4.0; n = 16) and patients with uncomplicated infarction (51.9 +/- 2.7; n = 17), but was lowest in the group of patients with left ventricular failure (35.1 +/- 3.3; n = 14). Similarly, the radionuclide ejection fraction of patients with post-infarction angina (41.4 +/- 3.4; n = 17) and patients with uncomplicated infarction (45.6 +/- 2.7; n = 19) did not differ, but was lower in patients with left ventricular failure (25.9 +/- 2.8; n = 14). The echocardiographic ejection fraction correlated with that obtained by radionuclide angiography in all 46 patients (r = 0.71, P less than 0.001). The wall motion score correlated with the radionuclide ejection fraction in all 50 patients (r = -0.73, P less than 0.001) and with the echocardiographic ejection fraction in 47 patients (r = -0.55, P less than 0.001). During follow-up, 3 (18%) patients suffering post-infarction angina and 2 (13%) with left ventricular failure died. New infarction was seen in 2 (12%) and 1 (7%) patients in these groups, respectively. We conclude that the left ventricular function of patients who suffer from post-infarction angina in the coronary care unit is good, but is impaired in those with even transient left ventricular failure. Echocardiographic assessment of cardiac function prior to hospital discharge was highly successful and may be performed in all such patients.

Cost-effectiveness analysis of patient management alternatives after uncomplicated myocardial infarction: a model

Quantitative decision analyses provide a means whereby the effectiveness, in terms of patient outcome, and costs of diverse clinical approaches to the care of patients with cardiovascular disease can be made explicit and understandable. Increasingly, the profession is being required to justify the costs of clinical care to society, government and third party payers. Such justifications can be effectively presented when structured in decision analytic format. To demonstrate the utility of decision analysis and its extension--cost-effectiveness analysis--as a technique for presenting the rationale for clinical practices and technology utilization, the Cardiovascular Norms Committee of the American College of Cardiology sponsored a model cost-effectiveness analysis. Alternative management options, 6 month mortality and costs for the post-myocardial infarction patient were compared. The options included exercise electrocardiography, exercise thallium scintigraphy and coronary angiography, followed by coronary artery bypass surgery for patients with left main coronary disease only or patients with left main disease, three vessel disease or single or double vessel disease and a significant amount of myocardium in jeopardy. Within the constraints of the model, proceeding directly to angiography for risk stratification was the most effective approach, lowering expected mortality from 8% to approximately 3%. The marginal costs for this strategy, however, were high. The most cost-effective approach was to screen patients initially with exercise electrocardiography.

Arrhythmias as predictors of sudden death

Two methods are available for exploring arrhythmias in cardiac patients who are at risk of sudden death: Holter monitoring and invasive electrophysiology. Despite numerous studies, the predictive value of these techniques, in terms of prognosis, remains poor for many reasons. Neither technique considered individually can give reliable prognostic indications simply because each technique addresses different issues which are only partially involved in the mechanism of sudden death. Invasive electrophysiology, by artificially provoking an arrhythmia, detects the potential substrate which may ultimately lead to lethal arrhythmias. Although this is an important technique it is insufficient because merely identifying the substrate for an arrhythmia does not necessarily mean that arrhythmia will occur. On the other hand, ambulatory ECG allows monitoring of spontaneous arrhythmias which may be considered as potential initiating factors in arrhythmias. However, even if initiating factors and potential substrates are present, they are not sufficient conditions to cause lethal arrhythmias to occur. When there is an opportunity to scrutinize the mechanism of arrhythmias which are indeed lethal, as in sudden death, it appears that the lethal event results from the intervention of a new factor which was either absent or not considered during preceding investigations. In coronary patients, curiously, ischemia more often provokes cardiac arrest or an electromechanical dissociation rather than a ventricular tachycardia or fibrillation. Sudden death is not infrequently of iatrogenic origin, because of the arrhythmogenic effect of powerful antiarrhythmic drugs. More important, ventricular fibrillation often occurs in the setting of a progressively increased sympathetic tone, which explains either the particular seriousness of a previously known arrhythmia or the occurrence of an arrhythmia which was never before observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Relative prognostic value of rest thallium-201 imaging, radionuclide ventriculography and 24 hour ambulatory electrocardiographic monitoring after acute myocardial infarction

Rest thallium-201 scintigraphy, radionuclide ventriculography and 24 hour Holter monitoring are acceptable methods to assess myocardial necrosis, performance and electrical instability. This study examined the relative value of the three tests, when obtained a mean of 7 days after acute myocardial infarction, in predicting 1 year mortality in 93 patients. Planar thallium-201 images were obtained in three projections and were scored on a scale of 0 to 4 in 15 segments (normal score = 60). Patients were classified as having high risk test results as follows: thallium score less than or equal to 45 (33 patients), left ventricular ejection fraction less than or equal to 40% (51 patients) and complex ventricular arrhythmias on Holter monitoring (36 patients). During the follow-up of 6.4 +/- 3.4 months (mean +/- SD), 15 patients died of cardiac causes. All three tests were important predictors of survival by univariate Cox survival analysis; the thallium score, however, was the only important predictor by multivariate analysis. The predictive power of the thallium score was comparable with that of combined ejection fraction and Holter monitoring (chi-square = 21 versus chi-square = 22). Thus, rest thallium-201 imaging performed before hospital discharge provides important prognostic information in survivors of acute myocardial infarction which is comparable with that provided by left ventricular ejection fraction and Holter monitoring. Patients with a lower thallium score (large perfusion defects) are at high risk of cardiac death during the first year after infarction.

Acute coronary artery obstruction in myocardial infarction: overview of thrombolytic therapy

Pump failure, ranging from ventricular dysfunction to acute cardiogenic shock, is now the leading cause of cardiac death. Efforts at temporary mechanical or pharmacologic support of the heart have been largely unsuccessful so that attention is now directed toward prevention of ventricular failure and limitation of myocardial infarct size or even outright prevention of infarction itself. In particular, attention has been refocused on earlier reperfusion efforts with streptokinase. The effect of thrombolysis in acute myocardial infarction on enzymatic infarct size, left ventricular function and early mortality was studied in subsets of patients in a randomized trial (Netherlands Interuniversity Cardiology Institute). Early thrombolytic therapy with intracoronary streptokinase (152 patients) or with intracoronary streptokinase preceded by intravenous streptokinase (117 patients) was compared with conventional treatment (264 patients). All 533 patients were admitted to the coronary care unit within 4 hours after onset of symptoms indicative of acute myocardial infarction. Of the patients eligible for this detailed analysis, 245 were allocated to thrombolytic therapy and 243 to conventional treatment. Early angiography was preformed in 212 of the 245 patients allocated to thrombolytic therapy. Patency of the infarct-related artery was achieved in 181 patients (85%). Enzymatic infarct size, measured from cumulative alpha-hydroxybutyrate dehydrogenase release, was smaller in patients allocated to thrombolytic therapy (median 760 versus 1,179 U/liter in control subjects, p = 0.0001). Left ventricular ejection fraction measured by radionuclide angiography before discharge was higher after thrombolytic therapy (median 50% versus 43% in control subjects, p = 0.0001). Twelve month mortality was lower in patients allocated to thrombolytic therapy (8% versus 16% in the control group, p less than 0.01). In multivariate regression analysis infarct size limitation, improvement of left ventricular ejection fraction and 3 month mortality were predicted by sigma ST, time from onset of symptoms to admission and Killip class at admission. Thrombolysis was most useful in patients admitted within 2 hours after onset of symptoms and in patients with a sigma ST segment of 1.2 mV or more. On the other hand, no beneficial effects of streptokinase on enzymatic infarct size, left ventricular function or mortality were observed in the subset of patients with sigma ST less than 1.2 mV, admitted 2 to 4 hours after onset of symptoms.

Radionuclide cineangiography in acute myocardial infarction: role in prognostication

Radionuclide-based procedures have achieved frequent application in acute myocardial infarction (MI). While these methods can be employed in diagnosis and assessment of therapy, diagnosis usually can be made more easily and with less expense when other methods are employed. Assessment of therapy, while potentially of value, has not been evaluated in a manner which can provide practical guidelines for clinical application. Practical utility has been associated with the use of radionuclide-based techniques in prognostication after infarction; this application is crucial to the formulation and optimization of management decisions. While myocardial perfusion scintigraphy and infarct-avid-agent imaging have been employed in prognostication after infarction, the largest body of prognostic data are available in association with radionuclide cineangiography. When determined in the early hours after infarction, a left ventricular ejection fraction (LVEF) less than 30% indicates a high likelihood of in-hospital mortality, irrespective of the site of infarction. When determined shortly prior to hospital discharge, LVEF less than 30% indicates a high likelihood of posthospital mortality, perhaps as high as 25% during the first year, and reaching 30% by the end of 2 years after infarction. Conversely, LVEF greater than or equal to 30% indicates an 8% 2-year postinfarction mortality risk. While LVEF is a highly potent risk descriptor, considerable evidence suggests the LVEF determined during exercise prior to hospital discharge also provides risk stratification, and may be superior to, or at least additive to, LVEF at rest as a prognostic index.(ABSTRACT TRUNCATED AT 250 WORDS)

Prediction of 1-year outcome after complicated and uncomplicated myocardial infarction: Bayesian analysis of predischarge exercise test results in 300 patients

After myocardial infarction (MI), the additive prognostic value of exercise variables to clinical variables has been questioned. The merits of a symptom-limited predischarge exercise test were therefore evaluated in clinically defined subgroups of patients. Exercise tests were consecutively performed by 208 survivors of uncomplicated MI (no heart failure, postinfarction angina, recurrent infarction, or late arrhythmias) and by 92 survivors of complicated MI. After uncomplicated MI (1-year mortality rate 4%), an achieved workload greater than 70% of age-predicted maximum identified 145 patients at very low risk (predictive value for survival 98%). After complicated MI (1-year mortality rate 13%), an exaggerated heart rate response was the best predictor of outcome, but had low (92%) predictive value of survival at 155 bpm. It is concluded that stress testing has only limited value after complicated MI. After uncomplicated MI, exercise variables are extremely helpful in identifying patients at very low risk in whom further investigations are not warranted.

Prognostic significance of the treadmill exercise test performance 6 months after myocardial infarction

A submaximal treadmill exercise test performed before hospital discharge after an uncomplicated myocardial infarction is often utilized to estimate prognosis and guide management, but there is little experience with a maximal exercise test performed 6 months after infarction to identify prognosis later in the convalescent period. The performance characteristics during an exercise test 6 months after myocardial infarction were related to the development of death, recurrent nonfatal myocardial infarction and coronary artery bypass surgery in the subsequent 12 months (that is, 6 to 18 months after infarction) in 473 patients. Mortality was significantly greater in patients who exhibited any of the following: inability to perform the exercise test because of cardiac limitations, the development of ST segment elevation of 1 mm or greater during the exercise test, an inadequate blood pressure response during exercise, the development of any ventricular premature depolarizations during exercise or the recovery period and inability to exercise beyond stage I of the modified Bruce protocol. By utilizing a combination of four high risk prognostic features from the exercise test, it was possible to stratify patients in terms of risk of mortality, from 1% if none of these features were present to 17% if three or four were present. Recurrent nonfatal myocardial infarction was predicted by an inability to perform the exercise test because of cardiac limitations, but not by any characteristics of exercise test performance. Coronary artery bypass surgery was associated with the development of ST segment depression of 1 mm or greater during the exercise test. Although clinical evidence of angina and heart failure 6 months after infarction was predictive of subsequent mortality among all survivors, among the low risk group without severely limiting cardiac disease, the exercise test provided unique prognostic information not available from clinical assessment alone. Therefore, a maximal exercise test performed 6 months after myocardial infarction is a valuable, noninvasive tool to evaluate prognosis. It provides information that is independent of and additive to clinical evaluation performed at the same time.

Prognostic information from early post-infarction exercise testing

Early post-myocardial infarction exercise testing has proved surprisingly safe. S-T elevations portended a bad prognosis as did also marked S-T segment depressions, especially if combined with premature ventricular contractions or short duration of exercise. A poor prognosis was also seen if, at low workloads, blood pressure could not reach 130 mm Hg, the heart rate did not rise above 130 beats per minute, or if there was angina. Complex arrhythmias were only of prognostic value as an independent variable with ambulatory monitoring. Negative findings were of more predictive value than positive results and have important therapeutic implications.

Risk stratification for 1 year survival based on characteristics identified in the early hours of acute myocardial infarction. The Western Washington Intracoronary Streptokinase Trial

We evaluated the relationship between baseline factors defined at 4.6 +/- 2.1 hr after onset of acute myocardial infarction and 1 year survival in 245 patients entered in the Western Washington Intracoronary Streptokinase Trial. Univariate statistics identified a significant relationship between 10 of these factors and survival. Multivariate analysis identified three factors as being most closely related to survival: (1) left ventricular ejection fraction (LVEF) (p less than .0001), (2) treatment with streptokinase (p = .03), and (3) location of infarction (p = .04). Mathematic models based on this analysis and applied to our patients identified high- and low-risk subgroups for 1 year mortality. Patients receiving standard, not interventional, therapy with anterior infarction and an LVEF of 50% or less and those with inferior infarction and an LVEF of 39% or less comprised the high-risk group. For patients receiving standard therapy, 1 year mortality was 41% in the high-risk group and 4% in the low-risk group. The models illustrated the magnitude of benefit of streptokinase treatment and achievement of complete reperfusion for those at low and high risk. We conclude that LVEF determined in the first hours of acute myocardial infarction is the most important of all baseline factors for prediction of 1 year survival. Mathematic models based on left ventricular function measured as ejection fraction are useful for risk stratification in this setting.

Relative value of clinical variables, bicycle ergometry, rest radionuclide ventriculography and 24 hour ambulatory electrocardiographic monitoring at discharge to predict 1 year survival after myocardial infarction

The relative value of predischarge clinical variables, bicycle ergometry, radionuclide ventriculography and 24 hour ambulatory electrocardiographic monitoring for predicting survival during the first year in 351 hospital survivors of acute myocardial infarction was assessed. Discriminant function analysis showed that in patients eligible for stress testing the extent of blood pressure increase during exercise slightly improved the predictive accuracy beyond that of simple clinical variables (history of previous myocardial infarction, persistent heart failure after the acute phase of infarction and use of digitalis at discharge), whereas radionuclide ventriculography and 24 hour electrocardiographic monitoring did not. The predictive value for mortality was 12% with clinical variables alone and 15% with the stress test added. Radionuclide ventriculography and 24 hour electrocardiographic monitoring were slightly additive to clinical information in the whole group of patients independent of the eligibility for stress testing (predictive value for mortality 24% with clinical variables alone and 26% with radionuclide ejection fraction and 24 hour electrocardiographic monitoring added). It is concluded that the appropriate use of simple clinical variables and stress testing is sufficient for risk stratification in postinfarction patients, whereas radionuclide ventriculography and 24 hour electrocardiographic monitoring should be limited to patients not eligible for stress testing.

Use of radionuclide angiography and an electrocardiographic stress test to diagnose multivessel disease after a first episode of uncomplicated myocardial infarction

Sixty consecutive patients who were symptom free 2-12 months after an uncomplicated acute myocardial infarction underwent maximal treadmill exercise testing, radionuclide angiography before and during submaximal bicycle stress test, and coronary angiography. The results of the non-invasive procedures were compared with those of coronary angiography. The sensitivity and specificity of electrocardiogram stress test for detection of multivessel disease were 40% and 77% respectively. Failure of left ventricular ejection fraction to increase at least 5% with exercise identified 20 of the 25 patients with multivessel disease (sensitivity 80%) and 23 of the 35 patients with no additional coronary artery stenosis (specificity 66%). In patients with anterior Q waves the sensitivity was 78% and the specificity 50%, whereas in the presence of inferior Q waves these values were 81% and 87% respectively. Loss of left ventricle synchronicity during effort, as indicated by failure of the standard deviation of the phases to decrease during exercise, demonstrated a radionuclide angiography sensitivity of 80% (77% for anterior myocardial infarction and 81% for inferior myocardial infarction) and a specificity of 50% (33% for anterior myocardial infarction and 64% for inferior myocardial infarction). When the test was considered to be positive if either the ejection fraction or the standard deviation of the phases criteria were positive, the sensitivity was 100% and specificity 46% (30% for anterior myocardial infarction and 65% for inferior myocardial infarction). It is concluded that in patients who are free from angina 2-12 months after an episode of uncomplicated myocardial infarction, a simple exercise electrocardiogram cannot be relied upon to detect residual ischaemia. An abnormal ejection fraction response or an increased standard deviation of the phases during exercise nuclear angiography or both identified all the patients with multivessel disease. None of the patients in whom radionuclide angiographic criteria were negative had multivessel disease.

Exercise testing early after myocardial infarction: historic perspective and current uses

Exercise testing performed earlier than six weeks post-MI is accepted as "standard" medical practice. Although both heart rate-limited and symptom-limited exercise protocols are used with nearly equal frequency, the latter appears more valuable because the prognostic yield is greater without sacrificing patient safety. Treadmill or cycle ergometers are the preferred modes of testing because of higher exercise work loads imposed and increased sensitivity and specificity of results. The physiologic exercise responses to graded work loads among these acute MI survivors include a mean maximal heart rate range of 118 to 136 beats/min, a peak systolic blood pressure between 137 and 170 mmHg, a mean peak double product from 16,000 to 22,400, and a mean maximal work load between 4.8 and 7.0 METS. Exercise findings which are most clinically useful are greater than 1 mm ST segment depression from rest level, presence of angina pectoris during exercise, decrease in systolic blood pressure with increasing work, presence of complex or frequent VEBs, and exercise tolerance less than 4 METS. These exercise findings identify, in recent post-MI survivors, groups of patients that have significantly different estimated future cardiac morbidity and mortality rates. The most consistent indices of multi-vessel coronary heart disease are ST segment depression, angina pectoris, and poor exercise tolerance. The most important role of stress testing in this period post-MI is identification of individuals who urgently need evaluation for coronary bypass surgery. In addition to risk stratification, exercise testing provides valuable information regarding exercise prescription for cardiac rehabilitation, direct psychologic benefit for resuming an active lifestyle, and motivation for exercise participation. Although safety of the early post-MI stress test has not been systematically studied, reports from individual studies indicated low morbidity and mortality. Attesting to this is the frequency with which it is performed as a routine office procedure. Finally, there has been a growing use of this procedure not only among cardiologists but also among internists and family practice physicians.

Surgical versus non-surgical management of patients soon after acute myocardial infarction

Of 510 patients admitted to hospital with acute myocardial infarction, 34 had coronary artery bypass grafting before discharge (6-43 days (median 20) after infarction). The patients who were given grafts generally had a smaller infarction with less functional impairment than the 476 patients who were not. The outcome of coronary artery bypass grafting was investigated in a retrospective matched pair study. Patients were matched on the basis of the presence of postinfarction angina, left ventricular ejection fraction, location of the infarction, peak creatine kinase activity, Killip clinical class, and severity of coronary disease with 34 patients who were given medical treatment only. At one year follow up fewer of the operated patients had symptoms than did the matched non-operated patients. Survival at one year in the operated and non-operated groups respectively was 94% vs 91%; angina within one year occurred in 3% vs 68%; congestive heart failure in 3% vs 6%; and 0% vs 32% were referred for later bypass grafting or coronary angioplasty. It is concluded that coronary artery bypass grafting can be performed safely soon after myocardial infarction provided that left ventricular function is not seriously compromised. Such treatment is more effective than medical treatment for relief of angina during the first year after infarction.

Prediction of mortality during the first year after acute myocardial infarction from clinical variables and stress test at hospital discharge

The predictive value of a predischarge symptom-limited stress test was studied in 405 consecutive survivors of acute myocardial infarction (AMI). Three hundred patients performed bicycle ergometry; 105 could not perform it. Among these latter 105 patients, the stress test was contraindicated in 43 because of angina or heart failure and in 62 because of noncardiac limitations. One-year survival was 44% in the "cardiac-limited" group (19 of 43) and 92% in the "non-cardiac-limited" group (57 of 62). One-year survival among the patients who performed an exercise test at discharge was 93% (280 out of 300). The best stress test predictor of mortality by univariate analysis was the extent of blood pressure (BP) increase: 42 +/- 24 mm Hg in 280 survivors vs 21 +/- 14 mm Hg in 20 nonsurvivors (p less than 0.001). Among the 212 patients in whom BP increased 30 mm Hg or more, mortality was 3% (n = 6), while it was 16% (n = 14) among the 88 patients in whom BP increased less than 30 mm Hg. Angina, ST changes and arrhythmias were not as predictive. Stepwise discriminant function analysis showed inadequate BP increase to be an independent predictor of mortality. A high-risk group can be identified at discharge on clinical grounds in patients unable to perform a stress test, whereas intermediate- and low-risk groups can be identified by the extent of BP increase during exercise.