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Value of negative predischarge exercise testing in identifying patients at low risk after acute myocardial infarction treated by systemic thrombolysis
Value of Negative Predischarge Exercise Testing in Identifying Patients at Low Risk After Acute Myocardial Infarction Treated by Systemic Thrombolysis Giacomo Piccalb, MD, Salvatore Pirelli, MD, Daria Massa, MD, Manlio Cipriani, MD, Filippo Maria Sarullo, MD, and Claudio De Vita, MD
Aithough thrombotytic therapy reduces mortality in patients with acute myecardial infarctton (AMI), it is assoctated wtth a greater inctdence of successive coronary events, and there is still no ideal diagnostk and therapeutic strategy for such patients. The present study vertfies the value of negative predischarge exercise testing in identifying low-risk patients treated with thrombotyds after AMI. One hundred fifty-seven comecutive patients with an uncompltcated clinical course underwent maximal or symptom-limited exercise testing (Bruce treadmill protocoi) within 15 days of AMI in the absence of therapy. The iecation of the AMI was anterior in 51 patients, inferior in 85 and non-Q-wave in 21. All of the pattents were followed for 6 months. Death and nonfatal retnfarction were considered as major coronary events, and the recurrence of angina as a minor event. Exerctse test results were negative in 166 patients (group 1) and postttve for angina or ST depression 20.1 mV in 62 (group 2). No deaths occurred during follow-up; there were 3 reinfarctions (3%) and 7 cases (7%) of postinfarction angina in group 1, and 2 retnfarcttons (4%) and 21 cases (46%) of posttnfarctton angina in group 2. By the end of follow-up, 90% of the patients with negative exercise test results were event-free (97% in the case of major events). These results show that thrombotytic therapy does not affect the value of negative postfnfarction exercise testing in identifying low-risk patients. (Am J Cardiol lSS2;70:31-33)
From the Department of Cardiology, Niguarda Hospital, Milan, Italy. Manuscript receivedOctober 15,1991;revisedmanuscriptreceivedand acceptedFebruary 26,1992. Address for reprints: Giacomo Piccal~, MD, Via Rapaccioli 6, 29100Piacenza,Italy.
F
ibrinolytic therapy hasradically changedthe natural history of patients with acute myocardial infarction (AMI). Studies involving large numbers of patients have shown that such treatment leads to a significant reduction in hospital mortality and that this advantage continues over the long term.1-4 Neverthe less, a high percentageof patients also have important coronary stenosesat the site of the infarct and this may limit myocardial recovery in the acute phaseand cause early or late reocclusion.5*6Before the introduction of thromturlytic therapy, exercise testing was the most widely used method of evaluating uncomplicated AMI, given that <2% of patients with a negative maximal exercise test result died within 1 year and that there was usually no need for further diagnostic evaluation.7-10 However, it is possible that what is true for patients treated with conventional therapy may not be true for patients treated with thrombolytic therapy.11112The present study verifies whether a negative exercise test responseis still capable of identifying patients at low risk after uncomplicated AM1 in the era of thrombolytic therapy. METHODS
Study population: The characteristics of the study population are shown in Figure 1. Between January 1988 and October 1990, 708 patients were admitted to our intensive coronary care unit for AMI. The presence of 12 of the following criteria led to a diagnosis of AMI: typical chest pain lasting for >30 minutes; Q waves that were abnormal according to the Minnesota Code,13with evolutionary ST and T waves changeson serial tracings; an increase in total serum creatine kinase, with a peak level of more than twice the upper limit of the normal values for our laboratory; and the presenceof an MB isoenzymefraction >5% of total cre atine kinase. Of the 708 admitted patients, 292 received intravenous systemicthrombolytic treatment (streptokinase 1,500,OOO U over 60 minutes or recombinant tissue-type plasminogen activator 100 mg over 3 hours). Thrombolytic treatment was administered to all of patients admitted within 6 hours of the onset of symptoms and who had typical chest pain persisting for >30 minutes and ST-segmentelevation >l mm in 12 adjacent electrocardiographic leads. During the acute phase.,17 of these patients died (mortality 5.8%); the remaining 275 were consideredeligible for the present prospective study. Of these 275 patients, 157 underwent exercise EXERCISE TESTING AFTER THROMBOLYSIS
31
and then every 3 minutes until the electrocardiogram returned to normal. During exercise,3 leads were continuously monitored. End-point criteria were: (1) angina, (2) ST depression>0.2 mV, (3) dyspnea,(4) complex ventricular arrhythmias, (5) a decreasein systolic blood pressure>lO mm Hg in 2 consecutivesteps,and (6) fatigue. The presenceof angina or ST-segmentdepression10.1 mV, measuredat 80 ms from the J point, were consideredas criteria of positivity. Follow-up: Patients were controlled by means of clinical visits 6 months after AMI. All were treated with /I blockers and aspirin if these were well tolerated. Death and nonfatal reinfarction were classifiedas major events,and postinfarction angina as a minor event. Angioplasty and coronary artery bypassgrafting, although not consideredeventsas such, were also taken into account. Follow-up was concluded in all patients. StatiatIeaI -sib: Values are presentedas mean f standard deviation. The chi-square test was used to compare the incidence of discrete variables between groups. A p value <0.05 was consideredsignificant.
PTS admittedto CCUfor AMI
t- 0 416
t cn-r 1
NOT ITl-
292
0Deaths t 17
q 275
CCU survivors
RESULTS Of the 157 enrolled patients, 136 were men (86%) and 21 women (14%) (mean age 55 f 11 years [range 34 to 761); the location of the AM1 was anterior in 51 157 118 patients (32%), inferior in 85 (54%) and non-Q-wave in NOT prediscargeET 21 (14%). Exercise test results were negative in 105 patients FlGUREl.Sludypqddbn.AMI=aa&emyoaddhfuc(group 1) and positive for angina or ST depressionin 52 cweunH;~=exerdsetes&llT=hiiOlQCCU=UUOnUY (group 2). Mean duration of exercisewas 7 f 2 minb---WV. utes, peak heart rate 135 f 15 beats/min, and peak testing and 118 were excluded from the study for the systolic blood pressure 170 f 29 mm Hg. No deaths following reasons:postinfarction angina in 36, clinical occurred during the 6-month follow-up period, 5 pasigns of left ventricular dysfunction in 19, complex ven- tients (4%) experienceda reinfarction, angina appeared tricular arrhythmias in 2, constant pacemaker rhythm in 28 (18%) and 19 (12%) underwent revascularization. in 2, stable left bundle branch block in 7 and physical In group 1, there were 3 reinfarctions (3%) and 7 cases limitations precluding maximal testing in 52. Advanced of angina (7%); in group 2, there were 2 reinfarctions age was not consideredan exclusion criterion; none of (4%) and 21 casesof angina (40%) (Figure 2). There were no differencesbetweenthe 2 groups with regard to the patients underwent angiography before the test. Bxerdse! testis: All of the patients performed a reinfarction, but there was a significant difference in the maximal or symptom-limited treadmill exercisetest ac- appearanceof angina (p
+
0
0
2(4%)
-
-
P *s - -
rn Reinfarction
-
30%) 0 Reinfarction
1 FIGURE 2. F&w-up resutb at 6 months. ~=exer&etesQns=netdgdkmt.
PTS with positive ET
L~----j-cqJ Angina
=
p
PTS with negative l?T
Angina
THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70
JULY 1. 1992
DISCUSSION Although systemic thrombolytic therapy has been shown to be capable of limiting the extension of AM1 and reducing both hospital and long-term mortality, it is also associatedwith an increasedrisk of successivecoronary events.1-4The ideal diagnostic approach to adopt for patients treated with thrombolytic therapy is not yet known. In particular, it is not known whether a negative exercisetest result is sufficiently indicative of patients at low risk for cardiac events, as is the case with conventionally treated patients.l2 Our study showsthat the enrolled population, consisting of a consecutive series of patients treated with thrombolytic therapy with an uncomplicated clinical course,had good prognosisas far as major events were concerned. Thii is attributable not only to thrombolysis but also to the combination of 2 selection factors: (1) Among patients surviving an infarct, those eligible for an early predischarge exercise test (629’0in our series)have a particularly good prognosis9J4J5;and (2) acceptedexclusion criteria ensure that patients eligible for thrombolysis have a lower rate of mortality than the global population of patients with AMI.16 The exercise test results from our study show that patients with a negative exercise test responsehave an excellent prognosis with an overall negative prediction of cardiac events of 90% (97% in major events). Only 3 patients (3%) underwent revascularization within 6 months, and so it is unlikely that recourseto revascularization significantly modiied the prognosisin these patients. Our results are similar to those relating to pub lished studies on a large number of patients during the prethrombolytic era. These studies have demonstrated that patients with a negative exercisetest result have a l-year mortality rate X2%, and that the negative predictive value for cardiac events(death and reinfarction) is 95%.9,15,17
During follow-up of patients with positive exercise test results, one should rememberthat it was beyondthe scopeof the present study to verify the predictive value of postinfarct positivity. Historical studies have clearly shown that positive results identify a group of patients with a high mortality rate8 and that this can be favorably modified by revascularization,18which may distort the relation between parameters such as ST-segment depressionand cardiac mortality. As expected, in our study population, a positive exercisetest responsecorra lated with the appearanceof postinfarction angina and revascularization, but there was no correlation with major clinical events (death or reinfarction). Thii agrees with the results of more recent studies demonstrating
that a positive postinfarction exercisetest is not predictive of mortality or reinfarction: mortality is correlated with indexesof ventricular dysfunction, such as exercise duration and the behavior of blood pressure,and no ergometric index is predictive of reinfarction.14J5J7J9,20
REFERENCES
1. Gruppo ltaliano per lo Studio della Stre.ptc&iii nell’ Infarto miocardico (GISSI). Effectivenessof intravenousthrombolytic treatmentin acutemyocardial infarction. Lancer 1986;1:397-401. 2. ISIS-2 (SecondInternational Study of Infarct Survival) Collaborative Group. Randomizedtrial of intravenousstreptokinase,oral aspirin, both or neither among 17,187casesof suspectedacute myocardial infarction: ISISZ. Lancer 1988;2: 349-360. 3. Rovelli F, De Vita C, Feruglio GA, Lotto A, Selvini A, Tognoni G and GISSI investigators.GISSI trial: early results and late follow-up. J Am CoN tirdiol 1987;1O(suppl):33B-39B. 4. Gruppo Italiano per lo Studio della Streptochiii nell’ Infarto miocardico (GISSI): Long-term-effect of intravenous thrombolysis in acute myocardiil infarction: final report of the GISSI study. Lancer 1987;2:871-874. 5. Harrison DG, FergusonDW, Collins SM. Skorton DJ. EricksenEE, Kioschos JM, Marcus ML, Withe CW. Rethrombcsisafter reperfusionwith streptokinase: importance of geometry of residual lesions.Circulation 1984;69:99-999. 6. Gash AK, SpannJF, Sherry S, Belber AD, Carabello BA, McDonough MT, Mann RH, McCann WD, Gault JD, Gentxler RD, Kent RL. Factorsinfluencing reocclusionafter coronary thrombolysis for acute myocardial infarction. Am J Cardiol 1986;57:175-177. 7. Weiner DA. Role of exercisetesting after myocardial infarction. J Am Co11 Cordial 1986;8:1020-1021. 8. Thtroux P, Waters DD, Halphen C, DebasieuxJC, Mixgala MF. Prognostic value of exercisetesting soon after acute myocardial infarction. N Engl J Med 1979;301:341-345. 9. De Busk RF, Kraemer HC, Nash E. Stepwise risk stratification soon after acute myocardial infarction. Am J Cardiol 1983;52:1161-1166. 10. Cohn PF. The role of noninvasivecardiac testing after an uncomplicated myccardial infarction. N Engl J Med 1983;308:9&93. 11. Waters DD. Exercisetestingafter myocardial infarction: a perspective.J Am Co11Cardiol 1986;8:1018-1019. 12. Moss AJ, Benhorin J. Prognosisand managementafter a first myocardial infarction. N Engl J Med 1990;322:743-753. 13. BlackburnH. Electrocardiographicclassificationfor populationcomparisons: the Minnesota Code. J Elecrrocardiol 1969;2:5-9. 14. Fioretti P, Brewer RW, Siioons ML, Bos RS, Baardman T, Beelen A, HugenholtzP. Predictionof mortality during the fust year after acutemyocardial infarction from clinical variables and stress test at hospital discharge. Am J Cardiol 1985;55:1313-1318. 15. Krone RS, Gillespie JA, Weld FM, Miller JP, Moss AJ and the Multicenter Postinfarction Research Group. Low-level exercise testing after myocardial infarction: usefulness in enhancing clinical risk stratification. Circularion 1985;71:80-89. 16. Grines CL, De Maria A. Optimal utilization of thrombolytic therapy for acute myocardial infarction: concepts and controversies.J Am Co11 Cardiol 1990;16:223-231. 17. Nielsen JR, Mickley H, DamsgaardEM, Froland A. Predischargemaximal exercise teat identities risk for cardiac death in patients with acute myocardial infarction. Am J Cardiol 1990;65:149-153. 18. Williams DB, Ivey TD, Bailey WW, Irey SJ, Rideout JT, Stewart D. Postinfarction angina: results of early revascularixation. J Am Coil Cardiol 1983;2: 859-864. 19. Pilate L, Silberger J, LisbonaR, SnidermanA. Prognosisin Patientswith low left ventricular ejection fraction after myocardial infarction. Importanceof exercise capacity. Circularion 1988;80:1636-1641. 20. MadsenEB, Gilpin E, Ahnve S, Henning H, RossJ. Prediction of functional capacity and use of exercise testing for predicting risk after acute myocardial infarction. Am J Cardiol 1985;56:839-845.
EXERCISE TESTING AFTER THROMBOLYSIS
33
Aithough thrombotytic therapy reduces mortality in patients with acute myecardial infarctton (AMI), it is assoctated wtth a greater inctdence of successive coronary events, and there is still no ideal diagnostk and therapeutic strategy for such patients. The present study vertfies the value of negative predischarge exercise testing in identifying low-risk patients treated with thrombotyds after AMI. One hundred fifty-seven comecutive patients with an uncompltcated clinical course underwent maximal or symptom-limited exercise testing (Bruce treadmill protocoi) within 15 days of AMI in the absence of therapy. The iecation of the AMI was anterior in 51 patients, inferior in 85 and non-Q-wave in 21. All of the pattents were followed for 6 months. Death and nonfatal retnfarction were considered as major coronary events, and the recurrence of angina as a minor event. Exerctse test results were negative in 166 patients (group 1) and postttve for angina or ST depression 20.1 mV in 62 (group 2). No deaths occurred during follow-up; there were 3 reinfarctions (3%) and 7 cases (7%) of postinfarction angina in group 1, and 2 retnfarcttons (4%) and 21 cases (46%) of posttnfarctton angina in group 2. By the end of follow-up, 90% of the patients with negative exercise test results were event-free (97% in the case of major events). These results show that thrombotytic therapy does not affect the value of negative postfnfarction exercise testing in identifying low-risk patients. (Am J Cardiol lSS2;70:31-33)
From the Department of Cardiology, Niguarda Hospital, Milan, Italy. Manuscript receivedOctober 15,1991;revisedmanuscriptreceivedand acceptedFebruary 26,1992. Address for reprints: Giacomo Piccal~, MD, Via Rapaccioli 6, 29100Piacenza,Italy.
F
ibrinolytic therapy hasradically changedthe natural history of patients with acute myocardial infarction (AMI). Studies involving large numbers of patients have shown that such treatment leads to a significant reduction in hospital mortality and that this advantage continues over the long term.1-4 Neverthe less, a high percentageof patients also have important coronary stenosesat the site of the infarct and this may limit myocardial recovery in the acute phaseand cause early or late reocclusion.5*6Before the introduction of thromturlytic therapy, exercise testing was the most widely used method of evaluating uncomplicated AMI, given that <2% of patients with a negative maximal exercise test result died within 1 year and that there was usually no need for further diagnostic evaluation.7-10 However, it is possible that what is true for patients treated with conventional therapy may not be true for patients treated with thrombolytic therapy.11112The present study verifies whether a negative exercise test responseis still capable of identifying patients at low risk after uncomplicated AM1 in the era of thrombolytic therapy. METHODS
Study population: The characteristics of the study population are shown in Figure 1. Between January 1988 and October 1990, 708 patients were admitted to our intensive coronary care unit for AMI. The presence of 12 of the following criteria led to a diagnosis of AMI: typical chest pain lasting for >30 minutes; Q waves that were abnormal according to the Minnesota Code,13with evolutionary ST and T waves changeson serial tracings; an increase in total serum creatine kinase, with a peak level of more than twice the upper limit of the normal values for our laboratory; and the presenceof an MB isoenzymefraction >5% of total cre atine kinase. Of the 708 admitted patients, 292 received intravenous systemicthrombolytic treatment (streptokinase 1,500,OOO U over 60 minutes or recombinant tissue-type plasminogen activator 100 mg over 3 hours). Thrombolytic treatment was administered to all of patients admitted within 6 hours of the onset of symptoms and who had typical chest pain persisting for >30 minutes and ST-segmentelevation >l mm in 12 adjacent electrocardiographic leads. During the acute phase.,17 of these patients died (mortality 5.8%); the remaining 275 were consideredeligible for the present prospective study. Of these 275 patients, 157 underwent exercise EXERCISE TESTING AFTER THROMBOLYSIS
31
and then every 3 minutes until the electrocardiogram returned to normal. During exercise,3 leads were continuously monitored. End-point criteria were: (1) angina, (2) ST depression>0.2 mV, (3) dyspnea,(4) complex ventricular arrhythmias, (5) a decreasein systolic blood pressure>lO mm Hg in 2 consecutivesteps,and (6) fatigue. The presenceof angina or ST-segmentdepression10.1 mV, measuredat 80 ms from the J point, were consideredas criteria of positivity. Follow-up: Patients were controlled by means of clinical visits 6 months after AMI. All were treated with /I blockers and aspirin if these were well tolerated. Death and nonfatal reinfarction were classifiedas major events,and postinfarction angina as a minor event. Angioplasty and coronary artery bypassgrafting, although not consideredeventsas such, were also taken into account. Follow-up was concluded in all patients. StatiatIeaI -sib: Values are presentedas mean f standard deviation. The chi-square test was used to compare the incidence of discrete variables between groups. A p value <0.05 was consideredsignificant.
PTS admittedto CCUfor AMI
t- 0 416
t cn-r 1
NOT ITl-
292
0Deaths t 17
q 275
CCU survivors
RESULTS Of the 157 enrolled patients, 136 were men (86%) and 21 women (14%) (mean age 55 f 11 years [range 34 to 761); the location of the AM1 was anterior in 51 157 118 patients (32%), inferior in 85 (54%) and non-Q-wave in NOT prediscargeET 21 (14%). Exercise test results were negative in 105 patients FlGUREl.Sludypqddbn.AMI=aa&emyoaddhfuc(group 1) and positive for angina or ST depressionin 52 cweunH;~=exerdsetes&llT=hiiOlQCCU=UUOnUY (group 2). Mean duration of exercisewas 7 f 2 minb---WV. utes, peak heart rate 135 f 15 beats/min, and peak testing and 118 were excluded from the study for the systolic blood pressure 170 f 29 mm Hg. No deaths following reasons:postinfarction angina in 36, clinical occurred during the 6-month follow-up period, 5 pasigns of left ventricular dysfunction in 19, complex ven- tients (4%) experienceda reinfarction, angina appeared tricular arrhythmias in 2, constant pacemaker rhythm in 28 (18%) and 19 (12%) underwent revascularization. in 2, stable left bundle branch block in 7 and physical In group 1, there were 3 reinfarctions (3%) and 7 cases limitations precluding maximal testing in 52. Advanced of angina (7%); in group 2, there were 2 reinfarctions age was not consideredan exclusion criterion; none of (4%) and 21 casesof angina (40%) (Figure 2). There were no differencesbetweenthe 2 groups with regard to the patients underwent angiography before the test. Bxerdse! testis: All of the patients performed a reinfarction, but there was a significant difference in the maximal or symptom-limited treadmill exercisetest ac- appearanceof angina (p
+
0
0
2(4%)
-
-
P *s - -
rn Reinfarction
-
30%) 0 Reinfarction
1 FIGURE 2. F&w-up resutb at 6 months. ~=exer&etesQns=netdgdkmt.
PTS with positive ET
L~----j-cqJ Angina
=
p
PTS with negative l?T
Angina
THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70
JULY 1. 1992
DISCUSSION Although systemic thrombolytic therapy has been shown to be capable of limiting the extension of AM1 and reducing both hospital and long-term mortality, it is also associatedwith an increasedrisk of successivecoronary events.1-4The ideal diagnostic approach to adopt for patients treated with thrombolytic therapy is not yet known. In particular, it is not known whether a negative exercisetest result is sufficiently indicative of patients at low risk for cardiac events, as is the case with conventionally treated patients.l2 Our study showsthat the enrolled population, consisting of a consecutive series of patients treated with thrombolytic therapy with an uncomplicated clinical course,had good prognosisas far as major events were concerned. Thii is attributable not only to thrombolysis but also to the combination of 2 selection factors: (1) Among patients surviving an infarct, those eligible for an early predischarge exercise test (629’0in our series)have a particularly good prognosis9J4J5;and (2) acceptedexclusion criteria ensure that patients eligible for thrombolysis have a lower rate of mortality than the global population of patients with AMI.16 The exercise test results from our study show that patients with a negative exercise test responsehave an excellent prognosis with an overall negative prediction of cardiac events of 90% (97% in major events). Only 3 patients (3%) underwent revascularization within 6 months, and so it is unlikely that recourseto revascularization significantly modiied the prognosisin these patients. Our results are similar to those relating to pub lished studies on a large number of patients during the prethrombolytic era. These studies have demonstrated that patients with a negative exercisetest result have a l-year mortality rate X2%, and that the negative predictive value for cardiac events(death and reinfarction) is 95%.9,15,17
During follow-up of patients with positive exercise test results, one should rememberthat it was beyondthe scopeof the present study to verify the predictive value of postinfarct positivity. Historical studies have clearly shown that positive results identify a group of patients with a high mortality rate8 and that this can be favorably modified by revascularization,18which may distort the relation between parameters such as ST-segment depressionand cardiac mortality. As expected, in our study population, a positive exercisetest responsecorra lated with the appearanceof postinfarction angina and revascularization, but there was no correlation with major clinical events (death or reinfarction). Thii agrees with the results of more recent studies demonstrating
that a positive postinfarction exercisetest is not predictive of mortality or reinfarction: mortality is correlated with indexesof ventricular dysfunction, such as exercise duration and the behavior of blood pressure,and no ergometric index is predictive of reinfarction.14J5J7J9,20
REFERENCES
1. Gruppo ltaliano per lo Studio della Stre.ptc&iii nell’ Infarto miocardico (GISSI). Effectivenessof intravenousthrombolytic treatmentin acutemyocardial infarction. Lancer 1986;1:397-401. 2. ISIS-2 (SecondInternational Study of Infarct Survival) Collaborative Group. Randomizedtrial of intravenousstreptokinase,oral aspirin, both or neither among 17,187casesof suspectedacute myocardial infarction: ISISZ. Lancer 1988;2: 349-360. 3. Rovelli F, De Vita C, Feruglio GA, Lotto A, Selvini A, Tognoni G and GISSI investigators.GISSI trial: early results and late follow-up. J Am CoN tirdiol 1987;1O(suppl):33B-39B. 4. Gruppo Italiano per lo Studio della Streptochiii nell’ Infarto miocardico (GISSI): Long-term-effect of intravenous thrombolysis in acute myocardiil infarction: final report of the GISSI study. Lancer 1987;2:871-874. 5. Harrison DG, FergusonDW, Collins SM. Skorton DJ. EricksenEE, Kioschos JM, Marcus ML, Withe CW. Rethrombcsisafter reperfusionwith streptokinase: importance of geometry of residual lesions.Circulation 1984;69:99-999. 6. Gash AK, SpannJF, Sherry S, Belber AD, Carabello BA, McDonough MT, Mann RH, McCann WD, Gault JD, Gentxler RD, Kent RL. Factorsinfluencing reocclusionafter coronary thrombolysis for acute myocardial infarction. Am J Cardiol 1986;57:175-177. 7. Weiner DA. Role of exercisetesting after myocardial infarction. J Am Co11 Cordial 1986;8:1020-1021. 8. Thtroux P, Waters DD, Halphen C, DebasieuxJC, Mixgala MF. Prognostic value of exercisetesting soon after acute myocardial infarction. N Engl J Med 1979;301:341-345. 9. De Busk RF, Kraemer HC, Nash E. Stepwise risk stratification soon after acute myocardial infarction. Am J Cardiol 1983;52:1161-1166. 10. Cohn PF. The role of noninvasivecardiac testing after an uncomplicated myccardial infarction. N Engl J Med 1983;308:9&93. 11. Waters DD. Exercisetestingafter myocardial infarction: a perspective.J Am Co11Cardiol 1986;8:1018-1019. 12. Moss AJ, Benhorin J. Prognosisand managementafter a first myocardial infarction. N Engl J Med 1990;322:743-753. 13. BlackburnH. Electrocardiographicclassificationfor populationcomparisons: the Minnesota Code. J Elecrrocardiol 1969;2:5-9. 14. Fioretti P, Brewer RW, Siioons ML, Bos RS, Baardman T, Beelen A, HugenholtzP. Predictionof mortality during the fust year after acutemyocardial infarction from clinical variables and stress test at hospital discharge. Am J Cardiol 1985;55:1313-1318. 15. Krone RS, Gillespie JA, Weld FM, Miller JP, Moss AJ and the Multicenter Postinfarction Research Group. Low-level exercise testing after myocardial infarction: usefulness in enhancing clinical risk stratification. Circularion 1985;71:80-89. 16. Grines CL, De Maria A. Optimal utilization of thrombolytic therapy for acute myocardial infarction: concepts and controversies.J Am Co11 Cardiol 1990;16:223-231. 17. Nielsen JR, Mickley H, DamsgaardEM, Froland A. Predischargemaximal exercise teat identities risk for cardiac death in patients with acute myocardial infarction. Am J Cardiol 1990;65:149-153. 18. Williams DB, Ivey TD, Bailey WW, Irey SJ, Rideout JT, Stewart D. Postinfarction angina: results of early revascularixation. J Am Coil Cardiol 1983;2: 859-864. 19. Pilate L, Silberger J, LisbonaR, SnidermanA. Prognosisin Patientswith low left ventricular ejection fraction after myocardial infarction. Importanceof exercise capacity. Circularion 1988;80:1636-1641. 20. MadsenEB, Gilpin E, Ahnve S, Henning H, RossJ. Prediction of functional capacity and use of exercise testing for predicting risk after acute myocardial infarction. Am J Cardiol 1985;56:839-845.
EXERCISE TESTING AFTER THROMBOLYSIS
33