Significance of Silent Myocardial lschemia After Coronary Artery Bypass Surgery Donald A. Weiner, MD
llm prevalence and prognostic signifkance of transient myocardial ischemia after coronary ar= tery bypass grafUng (CABG) were evaluated. In 3 studies, ischemla was found in an average of 24% of patients by ambulatorye kctrocardiographk monttoring at 3-12 months after CABG. An averageof3@?~ofpat&ntsIn3otherstudiesexperienced ischemk ST-segment depression during exercise testing at 4-66 months after CABG. Of the ischemk episodes, 77% were silent during exercise testing In the Coronary Artery Surgery Study (CASS) randomized patient subsets+ survlval at l2 years was signifkantly lower for patientswhohadeithersllentorsymptomatkischem& during exercise testhg at 6 months after CABG comparedwith those who had no ischemia. (Am J Cardiol1992;70:3SF-38F)
From the Evans Memorial Department of Clinical Research and the Department of Medicine, The University Hospital, Boston, Massachusetts. Address for reprints: Donald A. Weiner, MD, Section of Cardiology, The University Hospital, 88 East Newton Street, Boston, Massachusetts02118.
M
yocardial revascularization using coronary artery bypass grafting (CABG) usually provides excellent symptomatic relief for patients with angina pectoris.’ Amelioration of myocardial ischemia and improvement in exercise capacity after CABG have been well documented by exercise testing.2 Recent studies, however, have determined that transient myocardial ischemia may occur spontaneously or be precipitated by exercise testing in up to 33% of patients postoperatively.3-7 The probable mechanisms involved include graft occlusion, progression of coronary artery disease (CAD) in the native coronary blood vessels, and incomplete revascularization, but unknown factors may also be involved.‘j Because postoperative ischemia can be ameliorated or completely abolished by medication, percutaneous coronary angioplasty, or a second CABG, it is important to establish whether postoperative ischemia has an adverse effect on the survival of patients who have undergone CABG. This article will review the prevalence and prognostic significance of postoperative ischemia that has been documented by either exercise testing or ambulatory electrocardiographic (ECG) monitoring. PREVALENCE Earlier studies that used ambulatory ECG monitoring after CABG demonstrated that transient myocardial ischemia frequently occurs (Table I). Crea et a1,3using 48hour ambulatory ECG monitoring in 45 patients an average of 4 months after CABG, found that 68 ischemic episodes occurred in 7 patients (16%). Before CABG, 249 episodes of transient ST-segment depression were observed in 35 patients. Egstrup4 applied 36-hour ambulatory ECG monitoring 3 months after CABG in 36 patients who either were asymptomatic or had minimal symptoms and found 39 episodes of silent ischemia among 12 patients (33%). Finally, Kennedy et al6 employed ambulatory 24-hour ECG monitoring in 94 patients 3 months (early) after CABG and in 184 patients 12 months (late) after CABG. Silent ischemia was detected in 19 (20%) A SYMPOSIUM:
MECHANISMS
FOR MYOCARDIAL
INFARCTION
35F
TABLE I Prevalence of Myocardial lschemia During Ambulatory Electrocardiographic Monitoring After CABG Study
Patients (n)
Months After CABG
Prevalence
Crea et al3
45
4
16%
Egstrupk
36
3
33%
94 184
3 12
20% 27%
Kennedy et a16
CABG = coronary artery bypass grafting.
TABLE II Prevalence of Myocardial lschemia During Exercise Testing After CABG Study
Patients (n)
Months After CAEG
Prevalence
45
4
36%
Dubach et aI5
296
50
28%
Weiner et al7
174 137
6 18
36% 45%
Crea et al3
CABG = coronaty artery bypass grafting.
Crea et a1,3in accordance with a modified Bruce protocol, had 45 patients perform a treadmill test an average of 4 months after CABG; these researchers found ischemic ST-segment depression in 16 (36%) patients. All patients with an ischemic response were incompletely revascularized. Dubach et al5 found that 84 (28%) of 296 patients displayed ischemic ST-segment depression when tested according to a standard treadmill protocol an average of 4.2 years after CABG. Fifty (60%) of the 84 patients with ischemia did not have accompanying angina. In a subset of patients in the Coronary Artery Surgery Study (CASS) who were randomized to surgery, treadmill testing according to the Bruce protocol detected ischemic ST-segment depression in 62 (36%) of 174 patients at 6 months (early) after CABG and in 61(45%) of 137 patients at 18 months (late) after CABG.’ Silent ischemia during exercise testing occurred in 82% of the ischemic patients studied early and in 90% of the ischemic patients evaluated late after CABG.
TABLE Ill Prognosis for Myocardial lschemia During Ambulatory Electrocardiographic Monitoring After CABG Follow-Up
Rate of Cardiac Events
Egstrupe
9 months
50% in patients with SMI vs 8% in patients without SMI (p = 0.005)
Kennedy et al6
4 years
Early after CAEG: 11% in patients with SMI vs 24% In patients without SMI tp = NS)
Study
Late after CABG: 14% in patients with SMI vs 15% in patients without SMI (p = NS) CABG = coronary artery bypass grafbng; silent myocardial ischemia.
NS = difference
not slgnihcant;
SMI =
TABLE IV Prognosis for Myocardial lschemia During Exercise Testing After CABG Reference Dubach et al5
Weiner et al7
Follow-Up (years)
Results
2
Prevalence of ST-segment depression similar in patients with cardiac events (27%) and in total population (28%)
12
Survival worse in patients with symptomatic (45%) or silent (68%) ischemia vs those without ischemia (80%)
of 94 patients early and in 50 (27%) of 184 patients late after CABG. The mean frequency of episodes was in the range of 6-10 per 24-hour period, with a mean duration from 15-23 minutes. Myocardial ischemia can also be precipitated during exercise testing after CABG (Table II). 36F
THE AMERICAN
JOURNAL
OF CARDIOLOGY
VOLUME
70
PROGNOSIS Egstrup4 found that although 6 (50%) of the 12 patients who showed evidence of silent myocardial ischemia during ambulatory ECG monitoring after CABG experienced cardiac events during the following 9 months, only 2 (8%) of 24 patients without silent myocardial ischemia had such events (Table III). Silent ischemia was the most powerful predictor of cardiac events. In contrast, Kennedy et al6 did not find that silent myocardial &hernia predicted adverse clinical events during the first 4-5 years after CABG. The only variable that carried a slightly increased relative risk was younger age in the group tested l-3 months after CABG. Two recent studies evaluated the prognostic significance of exercise testing after CABG (Table IV). Dubach et al5 found that the prevalence of ST-segment depression was similar among patients who either died or had a nonfatal myocardial infarction (7 [27%] of 26 patients) compared with the total population (84 [28%] of 296). That study, however, was limited by both the long time (mean 4.2 years) that elapsed between CABG and performance of the exercise test and the short follow-up period (mean 2 years). Data from the CASS randomized population (n = 174) demonstrated that the 12-year survival rate after CABG was significantly different among patients grouped on the basis of the 6-month postoperative exercise test results.7 The survival rate was significantly higher for patients without ischemia (80%) than for paNOVEMBER
16, 1992
100 ST 1 Angina g al F 32 z 2 2m iii 5 5 0
FIGURE l. Cumulathfe survhml ratesforpatht6wRhsllentlschemha 6wuP 11, symptomatic lscheda(group?),andnols& emla (graup 2). n = total number ofpatlentqsl~ =STseIpnent depmssh. (Reprinted wRh perml&on from J Am Co/i CaMo/.~
~
813
80% Group 3
-
-
68% Group 1
+
-
45% Group 2
+
+
60 40 20
’ 0
2
4
6 Years
8
10
12
particular clinical importance because many treatment approaches, including use of antianginal medications, coronary artery angioplasty, and a second CABG, can successfullylessen or eliminate DISCUSSION Results from earlier studies show that exercise ischemia. The best strategy for lowering the risk of testing often produced inaccurate indications of adversecardiac events among patients with postopthe effectiveness of CABG revascularization. Mc- erative ischemia is uncertain at present. In conclusion, silent ischemia can often be seen Conahay et al8 found that only 32% of patients during ambulatory ECG monitoring or exercise with incomplete revascularization and 30% of patesting after CABG. Certain investigations have tients with no revascularization had positive exerdemonstrated that ischemia has an adverse effect cise test results. Dodek et al9 found that 33% of patients with complete revascularization had posi- on survival, which confirms similar results in studtive exercise tests, and 59% of patients with incom- ies of patients with stablenJ2 or unstable13J4anplete revascularization had negative tests. Block et gina and of postinfarction patients.15J6 allo found that 13 (68%) of 19 patients with unsuccessful revascularization had negative ST- REFERENCES L Rahimtoola SH. Coronary bypasssurgeryfor chronic angina-1981: a perspecsegment responsespostoperatively. tive. Circulation 1982;65:225-241. More recent studies evaluating the prevalence 2. Hossack KF, Bruce RA, Ivey TD, Kusumi F. Changesin cardiac functional and prognostic significance of ischemia after CABG capacity after coronary bypasssurgery in relation to adequaq of revascularizaJAm Co11Cardbl1984;3:47-54. demonstrate that ischemia occurs frequently after 3.tion.Crea F, Kaski JC, FragassnG, Hackett D, StanbridgeR, Taylor KM, Maseri CABG and is usually silent. Although the mecha- A. Usefulnessof Holter monitoring to improve the sensitivity of exercisetesting nisms underlying the occurrence of silent myocar- in determining the degree of myocardial revascularizationafter coronary artery bypassgrafting for stable anginapectoris.Am .I Cum?01 1987;60:4043. dial ischemia after CABG are unknown, they may 4. Egstmp K. Asymptomatic myocardial ischemia as a predictor of cardiac have a neurogenic basis or result from a reduction events after coronary artery bypass grafting for stable angina pectoris. Am J 1988;61:248-252. in the amount of jeopardized myocardium after Card01 5. Dubach P, Froelicher V, Klein J, Detrano R. Use of the exercise test to successfulrevascularization. In the CASS study, 24 predict prognmisafter coronary artery bypassgrafting.Am .I C&l 1989,63:53O(27%) of the 90 patients who demonstrated symp- 533. 6. Kennedy HL, Seiler SM, SpragueMK, Homan SM, Whitlock JA, Kern MJ, tomatic ischemia preoperatively had silent myocar- Vandormael MG, Bamer HB, Codd JE, Wiilman VL. Relation of silent dial ischemia during exercise testing 6 months after myocardial ischemiaafter coronary artery bypassgrafting to angiographiccompletenessof revascularizationand long-term prognosis.Am J Cardtil1990,65:14CABG.7 Therefore, patients who reveal only silent 22. myocardial ischemia postoperatively may be incom- 7. Weiner DA, Ryan TJ, ParsonsL, Fisher LD, Chaitman BR, Sheffield LT, pletely revascularized, despite the overall lessening Tristani FE. Prevalence and prognostic significanceof silent and symptomatic ischemia after coronary bypass surgery: a report from the coronary artery of their ischemic burden. surgery study (CA%) randomized population. J Am Coil Cam?01 1991;18:343Studies analyzing the prognostic significance of 348. DR, Valdes M, McCallister BD, Crockett JE, Corm RD, Reed postoperative ischemia have produced conflicting 8.WA,McConahay Killen DA. Accuracy of treadmill testing in assessmentof direct myocarresults. In the CASS subset followed up for as dial revascularization.Cirnrlarion 1977;56:54%.552. many as 12 years after CABG, the occurrence of 9. Dodek A, KassebamnDG, Griswold HE. Stresselectrocardiography in the evaluation of aortocoronary bypasssurgery.Am Hearf J 1973;86:292-307. ischemia during exercise testing predicted an ad- 10. Block TA, Murray JA, English MT. Improvement in exerciseperformance verse effect on survival.7 These results are of after unsuccessfulmyocardial revascularization.Am J Cardiol1977;40:673+80. tients with symptomatic &hernia (45%) or silent myocardial ischemia (68%) (Figure 1).
A SYMPOSIUM: MECHANISMS FOR MYOCARDIAL INFARCTION
37F
1l Roccn MB, Nabel EG, Campbell S, Goldman L, Barry J, Mead K, Selwyn l4. NademaneeK, Intarachot V, JosephsonMA, Rieders D, Mody Fv, Singh AP. Prognostic importance of myocardial ischemia detected by ambulatory BN. Prognostic significance of silent mywardial ischemia in patients with monitoring in patients with stable coronary artery disease.Circulation 1988,78: unstable angina.JAm Coil Cardiol 1987;1:1-9. 877-w. 15. Gottlieb SO, Gottlieb SH, Achuff SC, BaumgardnerR, Mellits ED, Weis12. Deedwania PC, Carbajal EV. Silent ischemiaduring daily life is an indepen- feldt ML, Gerstenblith G. Silent ischemiaon Halter monitoring predicts mortaldent predictor of mortality in stable angina.Circulation 1990,81:74~756. ity in high-risk postinfarction patients.J. 1988;259:103&1035. l3. Gottlieb SO, Weisfeldt ML, Ouyang P, Mellits ED, Gerstenblith G. Silent l6.Tzivoni D, Gavish A, Zm D, Gottlieb S, Moriel M, Keren A, Banai S, ischemiaas a marker for early unfavorable outcomesin patients with unstable Stem S. Prognostic significanceof ischemicepisodesin patients with previous angina.N EnglJ Med 1986;314:121b1219. myccardial infarction. Am .I Cardiol 1988;62:661-664.
38F
THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70
NOVEMBER 16, 1992
llm prevalence and prognostic signifkance of transient myocardial ischemia after coronary ar= tery bypass grafUng (CABG) were evaluated. In 3 studies, ischemla was found in an average of 24% of patients by ambulatorye kctrocardiographk monttoring at 3-12 months after CABG. An averageof3@?~ofpat&ntsIn3otherstudiesexperienced ischemk ST-segment depression during exercise testing at 4-66 months after CABG. Of the ischemk episodes, 77% were silent during exercise testing In the Coronary Artery Surgery Study (CASS) randomized patient subsets+ survlval at l2 years was signifkantly lower for patientswhohadeithersllentorsymptomatkischem& during exercise testhg at 6 months after CABG comparedwith those who had no ischemia. (Am J Cardiol1992;70:3SF-38F)
From the Evans Memorial Department of Clinical Research and the Department of Medicine, The University Hospital, Boston, Massachusetts. Address for reprints: Donald A. Weiner, MD, Section of Cardiology, The University Hospital, 88 East Newton Street, Boston, Massachusetts02118.
M
yocardial revascularization using coronary artery bypass grafting (CABG) usually provides excellent symptomatic relief for patients with angina pectoris.’ Amelioration of myocardial ischemia and improvement in exercise capacity after CABG have been well documented by exercise testing.2 Recent studies, however, have determined that transient myocardial ischemia may occur spontaneously or be precipitated by exercise testing in up to 33% of patients postoperatively.3-7 The probable mechanisms involved include graft occlusion, progression of coronary artery disease (CAD) in the native coronary blood vessels, and incomplete revascularization, but unknown factors may also be involved.‘j Because postoperative ischemia can be ameliorated or completely abolished by medication, percutaneous coronary angioplasty, or a second CABG, it is important to establish whether postoperative ischemia has an adverse effect on the survival of patients who have undergone CABG. This article will review the prevalence and prognostic significance of postoperative ischemia that has been documented by either exercise testing or ambulatory electrocardiographic (ECG) monitoring. PREVALENCE Earlier studies that used ambulatory ECG monitoring after CABG demonstrated that transient myocardial ischemia frequently occurs (Table I). Crea et a1,3using 48hour ambulatory ECG monitoring in 45 patients an average of 4 months after CABG, found that 68 ischemic episodes occurred in 7 patients (16%). Before CABG, 249 episodes of transient ST-segment depression were observed in 35 patients. Egstrup4 applied 36-hour ambulatory ECG monitoring 3 months after CABG in 36 patients who either were asymptomatic or had minimal symptoms and found 39 episodes of silent ischemia among 12 patients (33%). Finally, Kennedy et al6 employed ambulatory 24-hour ECG monitoring in 94 patients 3 months (early) after CABG and in 184 patients 12 months (late) after CABG. Silent ischemia was detected in 19 (20%) A SYMPOSIUM:
MECHANISMS
FOR MYOCARDIAL
INFARCTION
35F
TABLE I Prevalence of Myocardial lschemia During Ambulatory Electrocardiographic Monitoring After CABG Study
Patients (n)
Months After CABG
Prevalence
Crea et al3
45
4
16%
Egstrupk
36
3
33%
94 184
3 12
20% 27%
Kennedy et a16
CABG = coronary artery bypass grafting.
TABLE II Prevalence of Myocardial lschemia During Exercise Testing After CABG Study
Patients (n)
Months After CAEG
Prevalence
45
4
36%
Dubach et aI5
296
50
28%
Weiner et al7
174 137
6 18
36% 45%
Crea et al3
CABG = coronaty artery bypass grafting.
Crea et a1,3in accordance with a modified Bruce protocol, had 45 patients perform a treadmill test an average of 4 months after CABG; these researchers found ischemic ST-segment depression in 16 (36%) patients. All patients with an ischemic response were incompletely revascularized. Dubach et al5 found that 84 (28%) of 296 patients displayed ischemic ST-segment depression when tested according to a standard treadmill protocol an average of 4.2 years after CABG. Fifty (60%) of the 84 patients with ischemia did not have accompanying angina. In a subset of patients in the Coronary Artery Surgery Study (CASS) who were randomized to surgery, treadmill testing according to the Bruce protocol detected ischemic ST-segment depression in 62 (36%) of 174 patients at 6 months (early) after CABG and in 61(45%) of 137 patients at 18 months (late) after CABG.’ Silent ischemia during exercise testing occurred in 82% of the ischemic patients studied early and in 90% of the ischemic patients evaluated late after CABG.
TABLE Ill Prognosis for Myocardial lschemia During Ambulatory Electrocardiographic Monitoring After CABG Follow-Up
Rate of Cardiac Events
Egstrupe
9 months
50% in patients with SMI vs 8% in patients without SMI (p = 0.005)
Kennedy et al6
4 years
Early after CAEG: 11% in patients with SMI vs 24% In patients without SMI tp = NS)
Study
Late after CABG: 14% in patients with SMI vs 15% in patients without SMI (p = NS) CABG = coronary artery bypass grafbng; silent myocardial ischemia.
NS = difference
not slgnihcant;
SMI =
TABLE IV Prognosis for Myocardial lschemia During Exercise Testing After CABG Reference Dubach et al5
Weiner et al7
Follow-Up (years)
Results
2
Prevalence of ST-segment depression similar in patients with cardiac events (27%) and in total population (28%)
12
Survival worse in patients with symptomatic (45%) or silent (68%) ischemia vs those without ischemia (80%)
of 94 patients early and in 50 (27%) of 184 patients late after CABG. The mean frequency of episodes was in the range of 6-10 per 24-hour period, with a mean duration from 15-23 minutes. Myocardial ischemia can also be precipitated during exercise testing after CABG (Table II). 36F
THE AMERICAN
JOURNAL
OF CARDIOLOGY
VOLUME
70
PROGNOSIS Egstrup4 found that although 6 (50%) of the 12 patients who showed evidence of silent myocardial ischemia during ambulatory ECG monitoring after CABG experienced cardiac events during the following 9 months, only 2 (8%) of 24 patients without silent myocardial ischemia had such events (Table III). Silent ischemia was the most powerful predictor of cardiac events. In contrast, Kennedy et al6 did not find that silent myocardial &hernia predicted adverse clinical events during the first 4-5 years after CABG. The only variable that carried a slightly increased relative risk was younger age in the group tested l-3 months after CABG. Two recent studies evaluated the prognostic significance of exercise testing after CABG (Table IV). Dubach et al5 found that the prevalence of ST-segment depression was similar among patients who either died or had a nonfatal myocardial infarction (7 [27%] of 26 patients) compared with the total population (84 [28%] of 296). That study, however, was limited by both the long time (mean 4.2 years) that elapsed between CABG and performance of the exercise test and the short follow-up period (mean 2 years). Data from the CASS randomized population (n = 174) demonstrated that the 12-year survival rate after CABG was significantly different among patients grouped on the basis of the 6-month postoperative exercise test results.7 The survival rate was significantly higher for patients without ischemia (80%) than for paNOVEMBER
16, 1992
100 ST 1 Angina g al F 32 z 2 2m iii 5 5 0
FIGURE l. Cumulathfe survhml ratesforpatht6wRhsllentlschemha 6wuP 11, symptomatic lscheda(group?),andnols& emla (graup 2). n = total number ofpatlentqsl~ =STseIpnent depmssh. (Reprinted wRh perml&on from J Am Co/i CaMo/.~
~
813
80% Group 3
-
-
68% Group 1
+
-
45% Group 2
+
+
60 40 20
’ 0
2
4
6 Years
8
10
12
particular clinical importance because many treatment approaches, including use of antianginal medications, coronary artery angioplasty, and a second CABG, can successfullylessen or eliminate DISCUSSION Results from earlier studies show that exercise ischemia. The best strategy for lowering the risk of testing often produced inaccurate indications of adversecardiac events among patients with postopthe effectiveness of CABG revascularization. Mc- erative ischemia is uncertain at present. In conclusion, silent ischemia can often be seen Conahay et al8 found that only 32% of patients during ambulatory ECG monitoring or exercise with incomplete revascularization and 30% of patesting after CABG. Certain investigations have tients with no revascularization had positive exerdemonstrated that ischemia has an adverse effect cise test results. Dodek et al9 found that 33% of patients with complete revascularization had posi- on survival, which confirms similar results in studtive exercise tests, and 59% of patients with incom- ies of patients with stablenJ2 or unstable13J4anplete revascularization had negative tests. Block et gina and of postinfarction patients.15J6 allo found that 13 (68%) of 19 patients with unsuccessful revascularization had negative ST- REFERENCES L Rahimtoola SH. Coronary bypasssurgeryfor chronic angina-1981: a perspecsegment responsespostoperatively. tive. Circulation 1982;65:225-241. More recent studies evaluating the prevalence 2. Hossack KF, Bruce RA, Ivey TD, Kusumi F. Changesin cardiac functional and prognostic significance of ischemia after CABG capacity after coronary bypasssurgery in relation to adequaq of revascularizaJAm Co11Cardbl1984;3:47-54. demonstrate that ischemia occurs frequently after 3.tion.Crea F, Kaski JC, FragassnG, Hackett D, StanbridgeR, Taylor KM, Maseri CABG and is usually silent. Although the mecha- A. Usefulnessof Holter monitoring to improve the sensitivity of exercisetesting nisms underlying the occurrence of silent myocar- in determining the degree of myocardial revascularizationafter coronary artery bypassgrafting for stable anginapectoris.Am .I Cum?01 1987;60:4043. dial ischemia after CABG are unknown, they may 4. Egstmp K. Asymptomatic myocardial ischemia as a predictor of cardiac have a neurogenic basis or result from a reduction events after coronary artery bypass grafting for stable angina pectoris. Am J 1988;61:248-252. in the amount of jeopardized myocardium after Card01 5. Dubach P, Froelicher V, Klein J, Detrano R. Use of the exercise test to successfulrevascularization. In the CASS study, 24 predict prognmisafter coronary artery bypassgrafting.Am .I C&l 1989,63:53O(27%) of the 90 patients who demonstrated symp- 533. 6. Kennedy HL, Seiler SM, SpragueMK, Homan SM, Whitlock JA, Kern MJ, tomatic ischemia preoperatively had silent myocar- Vandormael MG, Bamer HB, Codd JE, Wiilman VL. Relation of silent dial ischemia during exercise testing 6 months after myocardial ischemiaafter coronary artery bypassgrafting to angiographiccompletenessof revascularizationand long-term prognosis.Am J Cardtil1990,65:14CABG.7 Therefore, patients who reveal only silent 22. myocardial ischemia postoperatively may be incom- 7. Weiner DA, Ryan TJ, ParsonsL, Fisher LD, Chaitman BR, Sheffield LT, pletely revascularized, despite the overall lessening Tristani FE. Prevalence and prognostic significanceof silent and symptomatic ischemia after coronary bypass surgery: a report from the coronary artery of their ischemic burden. surgery study (CA%) randomized population. J Am Coil Cam?01 1991;18:343Studies analyzing the prognostic significance of 348. DR, Valdes M, McCallister BD, Crockett JE, Corm RD, Reed postoperative ischemia have produced conflicting 8.WA,McConahay Killen DA. Accuracy of treadmill testing in assessmentof direct myocarresults. In the CASS subset followed up for as dial revascularization.Cirnrlarion 1977;56:54%.552. many as 12 years after CABG, the occurrence of 9. Dodek A, KassebamnDG, Griswold HE. Stresselectrocardiography in the evaluation of aortocoronary bypasssurgery.Am Hearf J 1973;86:292-307. ischemia during exercise testing predicted an ad- 10. Block TA, Murray JA, English MT. Improvement in exerciseperformance verse effect on survival.7 These results are of after unsuccessfulmyocardial revascularization.Am J Cardiol1977;40:673+80. tients with symptomatic &hernia (45%) or silent myocardial ischemia (68%) (Figure 1).
A SYMPOSIUM: MECHANISMS FOR MYOCARDIAL INFARCTION
37F
1l Roccn MB, Nabel EG, Campbell S, Goldman L, Barry J, Mead K, Selwyn l4. NademaneeK, Intarachot V, JosephsonMA, Rieders D, Mody Fv, Singh AP. Prognostic importance of myocardial ischemia detected by ambulatory BN. Prognostic significance of silent mywardial ischemia in patients with monitoring in patients with stable coronary artery disease.Circulation 1988,78: unstable angina.JAm Coil Cardiol 1987;1:1-9. 877-w. 15. Gottlieb SO, Gottlieb SH, Achuff SC, BaumgardnerR, Mellits ED, Weis12. Deedwania PC, Carbajal EV. Silent ischemiaduring daily life is an indepen- feldt ML, Gerstenblith G. Silent ischemiaon Halter monitoring predicts mortaldent predictor of mortality in stable angina.Circulation 1990,81:74~756. ity in high-risk postinfarction patients.J. 1988;259:103&1035. l3. Gottlieb SO, Weisfeldt ML, Ouyang P, Mellits ED, Gerstenblith G. Silent l6.Tzivoni D, Gavish A, Zm D, Gottlieb S, Moriel M, Keren A, Banai S, ischemiaas a marker for early unfavorable outcomesin patients with unstable Stem S. Prognostic significanceof ischemicepisodesin patients with previous angina.N EnglJ Med 1986;314:121b1219. myccardial infarction. Am .I Cardiol 1988;62:661-664.
38F
THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70
NOVEMBER 16, 1992
