Abolition of Holter monitor-detected silent myocardial ischemia after percutaneous transluminal coronary angioplasty

Assessment and significance of ST-segment changes detected by ambulatory electrocardiography after acute myocardial infarction

This study assessed the prognostic value of ST-segment changes detected by ambulatory electrocardiographic monitoring during the early in-hospital period after acute myocardial infarction. New methods for defining the ST-segment reference level and for measuring ST-segment elevation were used. ST-segment depression was defined as a change in ST level by > or = 0.1 mV 80 ms after the J point, elapsing > or = 1 minute. ST-segment elevation was defined as a deviation by > or = 0.15 mV, elapsing > or = 1 minute, and measured at the J point. An interval of > or = 2 minutes was required before another discrete episode was counted. Four ST-segment reference levels were automatically calculated: (1) "isoelectric," (2) "nearest to normal," (3) "24-hour median," and (4) "first-hour median." During a mean follow-up period of 3 years (mean 36 +/- 15 months), 47 cardiac events occurred in 38 patients: 18 deaths, 9 nonfatal reinfarctions, and 20 revascularization procedures. More deaths occurred in patients with than without ST elevation-24-hour median (22% vs 5%, p = 0.03), and in patients with than without ST depression-isoelectric (61% vs 32%, p = 0.02), and in patients with than without ST-depression-24-hour median (61% vs 23%, p = 0.003). "All cardiac events" (deaths, infarctions, or revascularization procedures) occurred more often in patients with than without ST depression-isoelectric (55% vs 22%, p = 0.003), and in patients with than without ST-depression-24-hour median (47% vs 17%, p = 0.004). Sensitivity, specificity, and accuracy of ST depression/elevation-24-hour median to assess mortality were 78%, 71%, and 73%, respectively.

Daily life cardiac ischaemia. Should it be treated?

Daily life cardiac ischaemia is defined as reversible myocardial cellular hypoxia that occurs during activities of daily living, without artificial provocation. Most of these daily life ischaemic episodes are not associated with symptoms. However, it is not practical to distinguish silent versus symptomatic daily life ischaemia as both are associated with haemodynamic abnormalities and future adverse outcomes. Daily life cardiac ischaemia is best detected using ambulatory electrocardiogram (ECG) monitoring; however, there are other diagnostic tools (e.g. exercise treadmill) that can be used. Once detected, the optimal therapy for daily life myocardial ischaemia has yet to be identified. However, it does appear that usual antianginal medications including nitrates, beta-blockers, calcium antagonists and antiplatelet drugs are effective in reducing the incidence and severity of daily life myocardial ischaemia. Medical therapy and revascularisation should be utilised to obliterate all episodes of daily life cardiac ischaemia to prevent future cardiac events. Moreover, the efficacy of the chosen therapeutic regimen for each patient should be documented with follow-up objective testing. The diagnosis and management of daily life myocardial ischaemia is continually evolving. Future research as well as economic considerations will shape future management strategies.

[Silent ischemia]

Silent myocardial ischaemia is a very common phenomenon in patients with coronary artery disease. It may occur in patients with clinical manifestations of angina, be detected during the post-myocardial infarction period or in patients totally asymptomatic. Whatsoever, it is well demonstrated that silent myocardial ischaemia has a very potent prognostic value. Therapeutic implications are similar to those in symptomatic ischaemia. Indications for myocardial revascularization by mean of angioplasty or bypass grafting may be discussed and depend on ventricular function and extension of coronary lesions.

Significance of ST-segment elevation during ambulatory monitoring after acute myocardial infarction

The significance of ST segment elevation during ambulatory monitoring after acute myocardial infarction was examined in 203 patients. Ambulatory monitoring was performed both early (mean 6.4 days [range 3 to 15]; N = 201) and late (38 days [range 22 to 93]; N = 177), and 174 patients underwent exercise treadmill testing (38 days [range 22 to 93]). Cardiac events (death, reinfarction, and coronary revascularization) were documented during a 1-year follow-up period. ST elevation (all silent) occurred in 25 of 201 patients (12%) on early monitoring but in only 4 of 177 (2%) on late monitoring (p < 0.001). Compared with patients (N = 148) without any ST deviation, those with early ST elevation had more pericarditis (8/25 [32%] vs 23/148 [16%]; p = 0.089) but no more angina or exercise ischemia. The mortality rate tended to be higher in patients with early ST elevation (4/25 [16%] vs 10/148 [7%]; p = 0.24), but ST elevation was too infrequent to be a valuable prognostic indicator. ST elevation is not uncommon during ambulatory monitoring early after myocardial infarction but is rare during later monitoring. Such ST elevation is almost always silent, does not usually reflect myocardial ischemia, and is not a useful prognostic indicator.

Noninvasive testing of asymptomatic patients for the detection of silent ischemia after an infarction. A decision analysis

This decision analysis estimates the overall gain in life expectancy and the relative efficacy of predischarge submaximal exercise electrocardiography, ambulatory cardiac monitoring, and thallium-201 scintigraphy for the identification of silent ischemia in asymptomatic postinfarct patients. A small, virtually equal increase in life expectancy can be obtained from any of the noninvasive tests (as compared to no testing). Large differences in life expectancy may result only when the prevalence of residual coronary artery disease and the probability of left-main and three-vessel lesions are high.

Role of increases in heart rate in determining the occurrence and frequency of myocardial ischemia during daily life in patients with stable coronary artery disease

OBJECTIVES

The goal of this study was to investigate the role of increases in heart rate in the development of ischemic episodes recorded during ambulatory electrocardiographic (ECG) monitoring in patients with stable coronary artery disease and to establish the importance of such increases in determining the frequency of ambulatory myocardial ischemia.

BACKGROUND

The factors that determine the occurrence and frequency of episodes of myocardial ischemia that patients with stable coronary artery disease experience during daily life have not been clearly defined. In particular, the role of increases in heart rate in the development of myocardial ischemia is controversial.

METHODS

To address these issues, 54 patients (42 men and 12 women, mean age 60.5 +/- 8 years) with proved coronary artery disease who had > or = 1 mm ST segment depression during exercise testing underwent an exercise treadmill test with use of the National Institutes of Health combined protocol and a 48-h period of ambulatory ECG monitoring. The exercise ischemic threshold was determined as the heart rate at the onset of ST segment depression during exercise testing.

RESULTS

During monitoring, 48 (89%) of the 54 patients had at least one episode of ST segment depression (mean +/- SD 6.6 +/- 5 episodes, range 0 to 22). The majority (320 of 359 or 89%) of ischemic episodes were preceded by an increase in heart rate > or = 10 beats/min; the most significant increase (22.3 +/- 10 beats/min) occurred during the 5-min period before the onset of the episode. An ischemic episode occurred 80% of the times the heart rate reached the exercise ischemic threshold. A strong correlation was observed between the number of times the exercise ischemic threshold was reached during monitoring and both the number and the duration of ischemic episodes (r = 0.90 and 0.71, respectively, p < 0.0001).

CONCLUSIONS

Increases in heart rate that exceed the exercise ischemic threshold are commonly observed before the onset of episodes of ambulatory myocardial ischemia in patients with stable coronary artery disease. Moreover, such increases constitute an important determinant of the frequency of myocardial ischemia during daily life. These findings may explain the variability observed in the number of ischemic episodes and may have important implications for the mechanisms that contribute to myocardial ischemia in daily life and for the clinical evaluation of patients with coronary artery disease.

Effects of coronary artery bypass surgery and angioplasty on the total ischemic burden: a study of exercise testing and ambulatory ST segment monitoring

To assess the effects of standard therapeutic interventions on the total ischemic burden, 86 patients with stable angina underwent 48 hours of ambulatory ST segment monitoring and treadmill exercise testing before and at a mean of 10 weeks after coronary artery bypass surgery (CABG) (group 1, N = 46) or percutaneous transluminal coronary angioplasty (PTCA) (group 2, N = 40). There were 72 male and 14 female patients with a mean age of 56.4 years. All patients had documented coronary artery disease (24, single-vessel; 28, two-vessel; 34, three-vessel disease). Both groups were characteristically similar apart from more severe coronary artery disease (p less than 0.001) and more previous myocardial infarctions (p less than 0.05) in group 1. Groups with CABG and PTCA had significant prolongation of exercise time after intervention (group 1: 7.6 to 9.8 minutes, p less than 0.0001; group 2: 8.1 to 10.0 minutes, p less than 0.001), and both interventions led to a significant reduction in ischemic responses (group 1: 33 to 4, p less than 0.001; group 2: 20 to 13, p less than 0.05) to exercise. During a total of 7643 hours of ST segment monitoring, 253 episodes of ischemia were recorded in 3768 hours before and 44 ischemic episodes in 3875 hours after intervention (group 1, 113 episodes in 24 patients and 21 episodes in 10 patients; group 2, 140 episodes in 13 patients and 23 episodes in six patients). Both interventions reduced the mean frequency of ischemia per 24 hours (group 1: 1.24 to 0.22 episodes per 24 hours; p less than 0.01; group 2: 1.9 to 0.3 episodes per 24 hours; p less than 0.05). Almost 28% (N = 24) of resting electrocardiographic findings were altered as a result of intervention.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of diltiazem on symptomatic and asymptomatic episodes of ST segment depression occurring during daily life and during exercise

BACKGROUND

Silent myocardial ischemia is an adverse prognostic marker in patients with coronary disease; however, controlled data on the effect of treatment are sparse and contradictory, and the relations among the occurrence of ST segment depression, drug efficacy, and heart rate are unclear.

METHODS AND RESULTS

Sixty patients with stable coronary artery disease, a positive treadmill exercise test and asymptomatic ST segment depression on ambulatory electrocardiographic recording were assessed in a multicenter, double-blind, placebo-controlled, cross-over trial. Treadmill exercise tests and 72-hour electrocardiographic recordings were obtained at the end of two 2-week treatment periods with sustained-release diltiazem 180 mg b.i.d. or equivalent placebo. Episodes of asymptomatic ST depression decreased by 50% or more in 70% of the patients from a median number of 4.5 (range, 0-19) to 1.5 (range, 0-13) (p = 0.0001); their cumulative duration also decreased from 78.5 (range, 0-60) to 24.5 (range, 0-411) minutes (p = 0.001). No circadian variation was found in the efficacy of diltiazem. The occurrence of ischemic type ST segment depression was modulated by changes in heart rate rather than by absolute heart rate. Diltiazem also improved exercise test end points but to a lesser extent. Time to ST segment depression increased to 341 +/- 148 from 296 +/- 154 seconds (p = 0.005). Although less frequent with diltiazem administration (45 versus 54 patients, p less than 0.03), exercise-induced ST depression was more often asymptomatic (98% versus 72% of patients, p less than 0.0001).

CONCLUSIONS

Diltiazem reduces the frequency and severity of ischemic type ST depression in patients with stable coronary artery disease.

Transient myocardial ischemia during Holter registration before and after coronary angioplasty

PURPOSE

Revascularizing procedures like percutaneous transluminal coronary angioplasty (PTCA) aim at reducing the incidence and severity of myocardial ischemia. To evaluate this, continuous Holter ST analysis is a possible method.

DESIGN

41 patients (35 men, 6 women) with stable angina pectoris had continuous twenty-four-hour two-channel Holter registration (V5/aVF-analogous leads) recorded before and after PTCA. Transient myocardial ischemia (TM) was defined as 0.1 mV ST depression or more 80 msec after the J point for one minute or more.

FINDINGS

PTCA was successful for 37 patients (90%). Eleven of these had a total of 53 episodes of TM, 36 (68%) before and 17 (32%) after PTCA (p less than 0.05). Fifteen episodes (28%) were symptomatic, and 38 (72%) were asymptomatic. Six patients had TM after successful PTCA, 5 of whom had one-vessel disease and a clinically uncomplicated course. One patient had multivessel disease, with only one vessel dilated. Follow-up angiograms for 9 of the 11 patients with TM revealed 5 restenoses. There was no significant correlation between TM after PTCA and subsequent restenosis (p greater than 0.05).

IMPLICATIONS

TM is common in patients with stable angina pectoris. The incidence significantly decreases after successful PTCA, but TM is seen also with a clinically uncomplicated course. In multivessel disease this is consistent with incomplete revascularization, whereas in single-vessel disease the most likely cause is intermittent spasm or thrombosis. TM after successful PTCA does not seem to be a predictor of restenosis.

Silent ischaemia in the 1990s

Silent myocardial ischaemia (significant ST depression without chest pain) is a common occurrence in most forms of coronary heart disease and can be associated with permanent changes in myocardial structure. The haemodynamic and ECG manifestations of silent episodes are similar to those observed in painful ischaemia. Exercise testing is the most appropriate method for assessing the severity of coronary artery disease; increased sensitivity can be obtained by combining it with radionuclide scintigraphy or ventriculography. Ambulatory ECG monitoring may fail to detect ischaemic changes revealed by exercise provocation. The treatment approach should depend on the degree of ischaemia. Numerous clinical investigations in stable and unstable angina and in patients with a previous myocardial infarction indicate that the prognosis of patients with myocardial ischaemia does not depend on whether the ischaemia is silent or symptomatic. Silent and symptomatic episodes alone represent the same degree of coronary disease. Moreover, it appears that ischaemic episodes are a more powerful adverse prognostic influence than left ventricular function or the extent of coronary artery disease. All anti-ischaemic agents, such as beta-blockers, calcium antagonists and nitrates, and interventions such as coronary balloon angioplasty or coronary bypass surgery, are very effective treatments for myocardial ischaemia. All efforts should be made to prevent ischaemic episodes, whether silent or symptomatic, since the severity of disease rather than the presence or absence of symptoms more accurately reflects the need for intervention.

Long-term follow-up of patients with silent ischemia during exercise radionuclide angiography

A retrospective 5 year follow-up study was performed in 140 patients with unequivocal ischemia during exercise radionuclide angiography (greater than or equal to 10% decrease in left ventricular ejection fraction or greater than or equal to 5% decrease in ejection fraction together with a distinct regional wall motion abnormality). In 84 patients (60%), ischemia during radionuclide angiography was silent (silent ischemia group), whereas 56 patients experienced angina during the test (symptomatic group). Work load and antianginal medication were similar in both groups. Critical cardiac events (unstable angina, myocardial infarction, cardiac death) occurred in 27% of patients in the silent ischemia group and 16% of those in the symptomatic group (p = NS); however, myocardial infarction or death was more frequent in patients with silent ischemia (22% versus 9%; p less than 0.05). If there was additional exercise-induced ST segment depression, the rate of critical events was further increased (p less than 0.05). The difference in critical cardiac events seemed to be influenced by the higher incidence of revascularization procedures in symptomatic patients, whereas medical therapy had no similar effect. Thus, these findings suggest that patients with documented severe ischemia should undergo left heart catheterization and revascularization irrespective of symptoms to improve their prognosis.

Usefulness of coronary angioplasty in asymptomatic patients

Of 6,545 patients who had elective coronary angioplasty procedures performed over a 7.5-year period from June 1980 through December 1987, 114 (1.7%) never had symptoms of myocardial ischemia. Exercise-induced silent myocardial ischemia was documented before angioplasty in 94% of these asymptomatic patients. Angioplasty was successful in 87%, whereas emergency coronary artery bypass grafting was required in 4%, and a further 2% had myocardial infarctions after the procedures. The remaining 7% had unsuccessful angioplasty procedures but experienced no in-hospital cardiac events. The follow-up period after hospital discharge averaged 43 +/- 20 months (range 5 to 93). There were no deaths. In the group of 99 patients with initially successful angioplasty procedures the follow-up interval ranged from 5 to 92 months. During that period, 7 patients underwent coronary bypass surgery, 4 patients had myocardial infarction and 30 patients had repeat angioplasty procedures for restenosis. The cumulative probability of event-free survival over 5 years for the group with successful angioplasty was: 100% freedom from death, 95% freedom from myocardial infarction, 87% freedom from myocardial infarction or coronary bypass surgery and 61% freedom from myocardial infarction, coronary bypass surgery or repeat angioplasty. Thus, coronary angioplasty performed in 114 asymptomatic patients, most with exercise-induced silent myocardial ischemia, achieved very good primary success and was accompanied by low cardiac event rates and no deaths over several years of patient follow-up.

Usefulness of percutaneous transluminal coronary angioplasty in alleviating silent myocardial ischemia in patients with absent or minimal painful myocardial ischemia

To examine the role of percutaneous transluminal coronary angioplasty (PTCA) in patients with silent ischemia, 50 consecutive patients (mean age 54 years, 88% men) with 1-vessel disease and absent or minimal symptoms who underwent PTCA were identified. Nineteen patients (38%) were asymptomatic and 31 patients (62%) had minimal angina (at most 1 episode/month, and with marked exertion only). Exercise-induced ischemia was present in 45 of 49 patients (92%) tested. The remaining 5 patients had a critical stenosis in a vessel supplying a large myocardial territory. A total of 75 lesions were dilated, 71 successfully (95%). There were no procedural deaths or infarctions. The single complication was an urgent bypass operation. After PTCA, only 3 of 46 patients exercised (7%) had inducible ischemia (p less than 0.0005 vs before PTCA). At a mean follow-up of 36 months, 46 of 49 patients alive (94%) were asymptomatic (p less than 0.0005 vs before PTCA). The 3-year actuarial survival and infarct-free survival were 98 and 96%, respectively. However, 5 patients (10%) crossed over to bypass surgery and 14 patients (28%) underwent repeat PTCA. Progression of native coronary disease was present in 9 of these patients (47%). As in symptomatic patients, elective PTCA can be performed safely and with a high success rate in patients with silent ischemia, and can markedly reduce the incidence of exercise-induced ischemia. With this approach, greater than 90% of the patients were asymptomatic at the 3-year follow-up; however, 34% required a further revascularization procedure for restenosis or progression of native disease or both.(ABSTRACT TRUNCATED AT 250 WORDS)

Ambulatory (Holter) electrocardiography and myocardial ischemia

Ambulatory (Holter) electrocardiography has evolved over the past two decades to allow accurate assessment of the cardiac rhythm, and more recently, accurate detection and measurement of ST segment changes. These ambulatory ECG ST segment changes that occur with and without symptoms, although thought to be of questionable clinical value for many years, have recently been clearly documented in coronary artery disease patients to represent true myocardial ischemia. Concurrent with these technologic developments has been an evolution of the pathophysiologic understanding of myocardial ischemia, and the relative role and sequential nature that ECG ST segment changes have in its development. This review examines from a clinical perspective the current understanding of the pathophysiologic sequence of development of myocardial ischemia, emphasizes the ECG diagnostic methods that detect this sequential change, examines the criteria that define ambulatory ECG myocardial ischemia, and discusses those nonischemic factors that affect the ECG ST segment and its interpretation. Moreover, an ever increasing number of ambulatory ECG studies of coronary artery disease and normal patients have defined unique characteristics of the ambulatory ECG ST segment changes observed with regard to its diagnostic, prognostic, and therapeutic assessment value in the study of myocardial ischemia.

Silent myocardial ischemia: an update

Silent myocardial ischemia is diagnosed by several different techniques and has been documented in all the anginal syndromes. In addition to other factors, its presence may be related to increased pain threshold and increased pain tolerance. Although some patients with painless ischemia may have less extensive coronary artery disease, cumulative evidence indicates that silent myocardial ischemia does not necessarily signify a lesser degree of cardiac ischemia or a less severe coronary abnormality. As judged by ambulatory monitoring studies, it shows circadian variation; occurs more frequently than symptomatic ischemia; and appears to depend, in large part, on activation of the sympathetic nervous system. Frequent silent ischemic events during ambulatory monitoring are worrisome because they reflect the disease "activity" of single or multiple coronary atherosclerotic lesions. Thus, there may be a direct association between the severity of ischemia seen during Holter monitoring, the extent of underlying coronary artery disease or disease activity, and prognosis. When diagnosed by exercise testing, silent myocardial ischemia may be associated with significant coronary involvement. In this regard, patients with three vessel coronary disease, impaired left ventricular function, and silent ischemia during stress testing should benefit from coronary revascularization. Compared with symptomatic patients, other evidence suggests that patients with exercise-induced asymptomatic ischemia have at least the same or perhaps even a worse outlook; this may be related to the lack of symptoms that would prompt evaluation and therapy. Awareness of the possibility of silent myocardial ischemia and use of commonly available tests, both to establish its presence and severity and to guide treatment, are emerging as new clinical goals. Further data, however, are necessary to determine how vigorously this should be pursued in different patient subgroups. In association with unstable angina or post-myocardial infarction, the added risk of silent myocardial ischemia warrants a more aggressive approach.