Evaluation of patients with acute myocardial infarction: which test, for whom and why?

[Risk stratification after acute myocardial infarction]

In recent years, the characteristics of patients who suffer acute myocardial infarction without complications during hospitalization have changed. In addition, the range of non-invasive studies available for evaluating left ventricular systolic function, residual myocardial ischemia, and myocardial viability in these patients has improved. Left ventricular systolic function and residual ischemia should be evaluated in all patients before release. The non-invasive technique used (exercise test, echocardiography, nuclear cardiology, magnetic resonance imaging) depends on availability, experience, and results at each institution. Coronary arteriography should be performed in patients with significant ischemia or severe left ventricular systolic dysfunction in non-invasive studies. In these cases coronary angiography must be performed to determine if coronary arteries are suitable for revascularization before performing a test of myocardial viability.

Uncomplicated first myocardial infarction: strategy for comprehensive prognostic studies

To evaluate the prognostic role of combined cardiac studies (submaximal exercise test, thallium-201 scintigraphy, radionuclide exercise ventriculography, two-dimensional echocardiography, Holter monitoring and cardiac catheterization) in patients with a first acute myocardial infarction without complications during hospital admission, 115 consecutive patients aged less than 65 years were prospectively evaluated. The studies were carried out before hospital discharge and the patients were then clinically followed up for 12 months. During the follow-up period, 69 patients (60%) developed complications, which were severe in 23 (20%). Half of all complications and 70% of severe complications developed during the 1st follow-up month. Logistic regression analysis disclosed that the combination of studies with the highest predictive power for complications (probability of complications 99%) and severe complications (probability of severe complications 95%) was the association of exercise test + thallium-201 + echocardiogram. Four decision models (exercise test + echocardiography, exercise test + radionuclide ventriculography, thallium-201 scintigraphy + echocardiography, thallium-201 scintigraphy + radionuclide ventriculography) allowed the stratification of all patients in a particular risk category (high, intermediate or low). The best decision model was the association of thallium-201 scintigraphy + radionuclide ventriculography (probability of complications if both tests were positive 84%; probability of absence of severe complications if both tests were negative 88%), but there were no significant differences with the other models. Any association of a test detecting residual ischemia or functional capacity, or both (exercise test or thallium-201) and a test assessing ventricular function (echocardiography or radionuclide ventriculography) results in significant prognostic information in patients with an uncomplicated first acute myocardial infarction. Additional cardiac catheterization does not improve the predictive power of noninvasive studies, which should ideally be performed before hospital discharge because most complications develop during the 1st follow-up month.

Trends in use of coronary angiography in subacute phase of myocardial infarction

BACKGROUND

Most patients do not undergo acute reperfusion after myocardial infarction, and which of these patients should undergo coronary angiography is still debated.

METHODS AND RESULTS

We analyzed the 1-year clinical outcomes and rates of coronary angiography performed as late as 60 days after myocardial infarction in 3,804 patients admitted between 1979 and 1988 and followed in six different centers. Patients less than 75 years old were classified into low-, medium-, and high-risk groups using a multivariate analysis of historical and clinical variables gathered during the first 8 hospital days. Patients who underwent early reperfusion (17%, all after 1984) were analyzed separately. To analyze time trends, patients were compared before and after mid-1984. Mortalities from day 9 through 1 year were similar for the two time periods in the low- (3.3% versus 2.5%) and medium-risk (7.4% versus 5.6%) groups, but mortality was lower for the high-risk group after 1984 (31.6% versus 20.0%). The proportion of patients undergoing coronary angiography increased dramatically in each group after 1984 (low risk, 18% versus 48%; medium risk, 23% versus 49%; high risk, 10% versus 32%, before and after 1984, respectively). Furthermore, a large percentage of patients (more than 40%) in the low-risk group did not have at least one of the indications for coronary angiography recently recommended by a joint task force. Among patients undergoing coronary angiography, the proportion of patients with three-vessel coronary artery disease decreased after 1984, whereas the proportion undergoing mechanical revascularization in the year after infarction increased in all risk groups.

CONCLUSIONS

Despite the recent development of noninvasive techniques with high sensitivity for detecting high-risk patients after myocardial infarction, coronary angiography is being performed increasingly in all patients, including those determined to be at low risk for complications based on clinical data. The economic consequences of such a trend could be considerable, and its impact requires careful analysis.

Six year follow up of a consecutive series of patients presenting to the coronary care unit with acute chest pain: prognostic importance of the electrocardiogram

In a retrospective 6 year follow up data were obtained for 536 of 566 (95%) consecutive patients admitted to a coronary care unit with acute chest pain. Their diagnoses were acute myocardial infarction in 290 (54%), myocardial ischaemia in 164 (31%), pericarditis in 16 (3%), and non-cardiac in 66 (12%). Six year mortality was 36%, 24%, 0%, and 16% respectively. In patients with acute myocardial infarction a higher mortality rate during follow up was associated with a higher than average age, a higher than average creatine kinase, previous myocardial infarction, Q wave infarction, and the presence of reciprocal changes. The presence of reciprocal changes was associated with higher than average concentration of serum creatine kinase, indicating more extensive infarction. Infarction complicated by ventricular fibrillation or left bundle branch block was associated with a higher death rate. The electrocardiogram recorded at the time of acute myocardial infarction contains much useful prognostic information.

Interobserver agreement and accuracy of bedside estimation of right and left ventricular ejection fraction in acute myocardial infarction

Ninety-eight patients with acute myocardial infarction were examined by 3 clinicians who, independently of each other, gave an estimate of left ventricular (LV) and right ventricular (RV) ejection fraction (EF) in each patient. Their estimates were based on physical examination, chest x-ray, electrocardiogram, patient history and clinical course during admission. Ejection fractions were estimated as belonging to 1 of 4 categories: normal (LVEF greater than or equal to 0.53, RVEF greater than or equal to 0.57), mildly reduced (LVEF 0.40 to 0.52, RVEF 0.45 to 0.56), moderately reduced (LVEF 0.30 to 0.39, RVEF 0.35 to 0.44) or severely reduced (LVEF less than 0.30, RVEF less than 0.35). Radionuclide ventriculography was carried out immediately after the physical examination. LVEF was correctly estimated in 43% of all examinations, deviated from radionuclide LVEF by 1 LVEF category in 45% and by 2 LVEF categories in 12%. The 3 clinicians agreed on estimated LVEF in only 32% of the patients. RVEF was correctly estimated in 67% of the examinations, but none of the clinicians identified greater than 43% of the relatively few patients with reduced radionuclide RVEF and they greatly disagreed as to who among the patients had a reduced RVEF. Previous myocardial infarction, electrocardiographic infarct location, Killip class, physical signs of left- and right-sided heart failure, radiographic pulmonary congestion and cardiomegaly were analyzed to determine which were the most helpful in predicting LVEF and RVEF. The results disclosed that several variables, traditionally believed to be reliable indexes of reduced ventricular function, were surprisingly poor predictors of LVEF and RVEF.

A decision scheme for coronary angiography after acute myocardial infarction

It is important to select patients in the convalescent phase of acute myocardial infarction in whom knowledge of coronary anatomy may identify those potentially suitable for intervention aimed at improving prognosis. However, differing guidelines have been proposed, and by applying some of these guidelines to our large database of patients after acute myocardial infarction, several problem areas were identified. These include lack of considering patients with resting ischemia beyond day 5 of hospitalization, management of patients with reduced ventricular function or patients not exercise tested, and the role of coronary angiography in the elderly. Based on this experience and further analysis in 1,848 patients surviving beyond day 5 of hospitalization, a modified decision scheme for coronary angiography was developed and then tested in a second population (n = 780). In the new scheme, patients over 75 years of age are considered individually. Those under 75 years of age with severe resting ischemia in the hospital at any time beyond the first 24 hours (18% mortality between day 6 and year 1), and hospital survivors with a history of previous myocardial infarction and clinical or radiographic signs of left ventricular failure in the hospital (25% 1-year mortality after discharge), are recommended for coronary angiography. Among the remaining patients, some will perform an exercise test, and those with an ischemic response or poor workload (11% 1-year mortality) are also assigned to coronary angiography. When an exercise test is not performed, a resting radionuclide left ventricular ejection fraction is recommended, and coronary angiography is considered if the value lies between 0.20 and 0.44 (12% 1-year mortality). This relatively simple scheme does not make general recommendations in the elderly, considers patients with in-hospital left ventricular failure or reduced left ventricular function or both, and approaches the problem of patients who do not perform an exercise test. This general approach would avoid early coronary angiography in patients with an average 1-year mortality risk after discharge of 3% and recommend coronary angiography in those at increased risk (average mortality rate, 16%) who make up about 55% of this population under 75 years of age.

Current practice patterns in the management of acute myocardial infarction. Survey of the American College of Chest Physicians

Over the past decade, the management of patients with acute myocardial infarction has undergone remarkable change due in part to the availability of new diagnostic and therapeutic modalities. Many of these techniques have gained widespread acceptance and use without the benefit of studies demonstrating efficacy. A survey of 391 members of the Section on Clinical Cardiology of the American College of Chest Physicians was conducted to assess current practice patterns in the management of acute myocardial infarction. Significant differences in the routine (greater than or equal to 50 percent of the time) use of various management approaches were found, with exercise tolerance testing, echocardiography, Holter monitoring, and cardiac rehabilitation frequently employed, whereas electrophysiologic studies, pyrophosphate scans, pulmonary artery catheterization, and cardiac pacing were infrequently used. Significant differences in the use of these procedures were noted with regard to the age of the physician and his or her geographic location of practice. These differences in practice patterns indicate that physicians have not reached consensus with regard to the value of these new diagnostic procedures and therapeutic approaches in the treatment of patients with acute myocardial infarction. Given the incremental costs of these procedures, clinical trials to assess their efficacy are clearly indicated.

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.

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.