Post-infarction exercise testing in patients under 55 years. Relation between ischaemic abnormalities and the extent of coronary artery disease

Cost-effectiveness of routine coronary angiography after acute myocardial infarction

BACKGROUND

Coronary angiography is indicated for many patients after acute myocardial infarction (AMI). There are a number of subgroups of AMI patients, however, for whom the indication for coronary angiography is not well established.

METHODS AND RESULTS

We developed a decision-analytic model for AMI in representative patient subgroups based on relevant clinical characteristics. The model estimates quality-adjusted life expectancy and direct lifetime costs for two strategies: coronary angiography and treatment guided by its results versus initial medical therapy without angiography. Decision tree chance node probabilities were estimated with the use of pooled data from randomized clinical trials and other relevant literature, costs were estimated with the use of the Medicare Part A database, and quality of life adjustments were derived from a survey of 1051 patients who had had a recent AMI. In our analysis, incremental cost-effectiveness ratios for coronary angiography and treatment guided by its result, compared with initial medical therapy without angiography, ranged between $17,000 and > $1 million per quality-adjusted year of life gained. Patient subgroups with severe postinfarction angina or a strongly positive exercise tolerance test (ETT) typically had cost-effectiveness ratios of < $50,000 per quality-adjusted year of life gained. In addition, most patient subgroups with a prior AMI had cost-effectiveness ratios of < $50,000 per quality-adjusted year of life gained, even with a negative ETT result.

CONCLUSIONS

In many patient subgroups after AMI, the cost-effectiveness of routine coronary angiography and treatment guided by its results compares favorably with other treatment strategies for coronary heart disease.

Impact of treatment strategy on predischarge exercise test in the Thrombolysis in Myocardial Infarction (TIMI) II Trial

Predischarge supine bicycle ergometry was used to assess persistent myocardial ischemia in postinfarction patients who received thrombolytic therapy and were randomized to an invasive versus conservative strategy in the Thrombolysis in Myocardial Infarction (TIMI) II trial. The frequency of ischemic responses in both strategies, and the 1-year prognostic importance of the different exercise test outcomes were examined. At 14 days, the percentage of patients with any adverse outcome (including death, presence of exercise-induced ST-segment depression, or inability to perform the exercise test) was 33.7% of 1,681 randomly assigned to the invasive strategy compared with 34.6% of 1,658 randomly assigned to the conservative strategy (p = 0.57). The 1-year mortality was greater in patients who did not perform the predischarge exercise test (7.7%) than in those who did (1.8%) (p < 0.001); the former were older, and a greater proportion were women, had a more frequent history of myocardial infarction, and more extensive coronary artery disease (p < 0.01 for each comparison). The 1-year mortality in patients with exercise-induced ST-segment depression or chest pain was only 1.4% (3 of 22) among those randomly assigned to the conservative strategy where coronary angiography and revascularization were recommended if the test result was abnormal (relative risk compared with those without ST-segment depression or chest pain 0.6; 99% confidence interval 0.1 to 2.9).(ABSTRACT TRUNCATED AT 250 WORDS)

Degree of coronary artery disease predicted by exercise testing

The ability of exercise testing to predict the extent of coronary artery disease was examined in 268 male patients undergoing both coronary angiography and bicycle testing with electrocardiography before coronary artery bypass surgery. When maximal ST-depressions limited by symptoms increased from 0 to 4 mm or more, the percentage of patients with 'serious' coronary disease, defined as either triple vessel disease or left main stem stenosis, increased from 50% to 80% (P = 0.0001). The patients in the lowest third of physical work capacity showed only a slightly increased risk of serious disease. This tendency was abolished in patients who were using beta-blockers, whereas the relationship between ST-depression and disease was not affected by this medication. The probability of finding left main stem stenosis in a patient increased from 5 to 30% with increasing ST-depression: beta-blockers did not affect this relationship, but there was no additional predictive effect of implicating the level of physical work capacity. It is concluded that traditional electrocardiography during exercise is of value when selecting patients for angiography, but that the physical work level obtained during the test does not predict the degree of coronary pathology.

Prognostic value of an exercise test one year after myocardial infarction

An exercise test was performed in 306 patients who had had acute myocardial infarction one year previously. The five year cumulative coronary heart disease mortality was 40.0%, when the test had to be discontinued because of ventricular arrhythmias but only 13.0% if discontinued because of fatigue (P less than 0.05). If the maximum work load was less than 80 W the mortality was 30.7% compared with 16.6% in patients who exercised at least 80 W (P less than 0.01). If maximum systolic blood pressure was less than or equal to 150 mmHg mortality was 40.3% compared with 8.5% in patients with greater than 200 mgHg (P less than 0.001). The mortality was 38.2% in patients having single monoform ventricular ectopic beats at a rate of three or more per minute or multiform, paired or early cycle ventricular ectopic beats or ventricular tachycardias: this compared with 14.1% (P less than 0.001) in patients having no or only single monoform ventricular ectopic beats at a rate of less than three per minute. ST-segment depression in univariate testing had no prognostic value. When both exercise test and clinical variables were used in survival analysis (Cox's regression) the most important variable was heart volume and after that ventricular arrhythmias. In multivariate regression analysis ST segment depression also had additional prognostic value. Thus ventricular arrhythmias turned out to be the most important prognostic factor measured during exercise test.

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.

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.

Evidence of anaerobic metabolism during low-level exercise testing in high-risk postmyocardial infarction patients

Low-level exercise testing was performed on 31 patients 7.4 +/- 2.7 days following an acute myocardial infarction. Measurements of oxygen consumption (VO2) and arterial serum lactate were made at rest and during exercise in these patients and 15 normal subjects. The patients were subdivided into finishers (F) and nonfinishers (NF) of the low-level protocol. The NF group had 2.5 +/- 6 stenosed vessels and an ejection fraction of 44 +/- 11% compared to F subjects, who had 1.4 +/- 1 vessels stenosed (p less than .001) and an ejection fraction of 54 +/- 14% (p less than .05). Finishers had significantly higher VO2 than the nonfinishers (14.5 +/- 2.5 ml/kg/min vs. 11.2 +/- 3.5 ml/kg/min p less than .01). At the end of exercise serum lactate level was 1.18 +/- .59 mM in normals, 1.43 +/- .52 mM in finishers, and 2.15 +/- .9 mM in nonfinishers. The change in serum lactate from rest to end exercise divided by the change in VO2 from rest to end exercise was .039 +/- .038 mM/ml kg per min in normals, .075 +/- .045 mM/ml kg per min in finishers (p less than .03 vs. normal), and .210 +/- .189 mM/ml kg per min for nonfinishers (p less than .001 vs. normal). These results indicate that nonfinishers produce more lactate and use less oxygen during low-level exercise, suggesting that working muscles are deriving energy by anaerobic metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of the maximal ST/HR slope to estimate myocardial ischaemia after recent myocardial infarction

Fifty two patients were examined 4-6 weeks after myocardial infarction to assess whether factors other than coronary artery narrowing affect the maximal ST/HR slope which is used as an index of myocardial ischaemia. The slope was compared with indices of myocardial scarring or cardiac enlargement derived from x ray and echocardiographic and angio-cardiographic investigations. In 35 (67%) patients the slope failed to predict the severity of myocardial ischaemia attributable to coronary artery narrowing: in 14 (27%) patients the slope overestimated the findings of coronary angiography and in 21 (40%) patients the slope underestimated the findings of coronary angiography. In the remaining 17 (33%) patients the slope accorded with the assessment of myocardial ischaemia by coronary angiography. Underestimation by the slope was associated with significantly poorer left ventricular function and a lower ejection fraction, indicating a greater degree of myocardial scarring. To assess whether overestimation was related to cardiac enlargement with better preservation of ventricular function a follow up examination was performed six months after infarction. In the overestimated group 11 patients were followed up and seven of them showed a reduction in the maximal ST/HR slope which correlated with a reduction in the cardiothoracic ratio. This suggested that cardiac enlargement had contributed to myocardial ischaemia. The results suggest that if the maximal ST/HR slope is an index of exercise induced myocardial ischaemia after recent infarction, it is subject to the influences of coronary artery narrowing as well as those of scarring and cardiac enlargement.