Value of ambulatory ST segment monitoring in patients with chronic stable angina: does measurement of the "total ischaemic burden" assist with management?

[Long term electrocardiography (Holter monitoring)]

During the past almost 50 years Holter monitoring has become an established non-invasive diagnostic tool in clinical electrophysiology. It allows ECG recording independent of stationary monitoring facilities during daily life and, therefore, contains much information. In the beginning the main interest was directed towards quantitative and qualitative assessment of arrhythmias, their circadian behaviour, and the circadian behaviour of the heart rate. With advances in technology the analysis spectrum of Holter monitoring expanded, and it was used also for detection of silent myocardial ischaemia. New digital recorders and computers with large capacities made it possible to measure every single heart beat very accurately, which was a prerequisite for heart rate variability and QT-interval analysis, which provided new knowledge about the autonomic modulation of the heart rate and the circadian dynamicity of the QT interval, respectively. Beyond arrhythmia analysis Holter monitoring was increasingly used to assess prognosis in different cardiac conditions. It can also be valuable in assessing transient symptoms possibly related to arrhythmias or device dysfunction, which will not necessarily be revealed by simple device control.

Predictive value of silent myocardial ischemia for cardiac events in diabetic patients: influence of age in a French multicenter study

OBJECTIVE

Silent myocardial ischemia (SMI) in asymptomatic subjects with no history of myocardial infarction or angina is a frequent condition in diabetic patients. The aim of the study was to examine the predictive value of SMI for cardiac events in a multicenter cohort and to determine whether this value is higher in patients with a particular clinical profile.

RESEARCH DESIGN AND METHODS

A total of 370 asymptomatic diabetic patients with at least two additional cardiovascular risk factors was recruited in four departments of diabetology. SMI was assessed by either exercise or dipyridamole single-photon emission-computed tomography myocardial perfusion imaging with thallium-201. If dipyridamole stress was used, an electrocardiogram stress test was performed separately on another day. Follow-up duration was 3-89 months (38 +/- 23 months).

RESULTS

There was evidence of SMI in 131 patients (35.4%) on at least one positive noninvasive test. The patients with SMI were significantly older and had significantly higher serum triglycerides and lower HDL cholesterol levels. Cardiac events occurred in 53 patients (14.3%). Major cardiac events (death or myocardial infarction) occurred in 38 patients (10%) and other events (unstable angina, heart failure, or coronary revascularization) occurred in 15 patients. The patients who had cardiac events were older and had higher serum triglyceride levels at baseline. There was a significant association between SMI and cardiac events (hazard ratio 2.79 [95% CI 1.54-5.04]) and in particular major cardiac events (3 [1.53-5.87]). In the patients >60 years of age, the prevalence of SMI was higher (43.4 vs. 30.2% in those <60 years). SMI was associated with a significant risk of cardiac events (2.89 [1.31-6.39]) and in particular major cardiac events (3.66 [1.36-9.87]) for the patients >60 years old but not for those <60 years old.

CONCLUSIONS

In asymptomatic diabetic patients with additional cardiovascular risk factors, SMI is a potent predictor of cardiac events and should be assessed preferably in the patients >60 years of age.

ST segment depression criteria and the prevalence of silent cardiac ischemia in hypertensives

The reported prevalence of silent cardiac ischemia as assessed by ambulatory electrocardiographic recording varies widely. The influence of the stringency of the analysis criteria has never been reported. We performed 24-hour, 12-lead ambulatory electrocardiographic recording in patients with hypertension but without proven coronary artery disease. The recordings were analyzed according to strict ST segment depression criteria adapted from the American College of Cardiology/American Heart Association guidelines and according to basic ST segment depression criteria adapted from studies with only concise descriptions of ambulatory electrocardiographic recording analysis. Also, we performed 24-hour ambulatory blood pressure monitoring. More than 4400 hours of ambulatory electrocardiographic recording and ambulatory blood pressure monitoring in 194 patients with hypertension were analyzed. Medication was withdrawn in 45% of the patients. The average systolic blood pressure during the day was 152+/-13 (mean+/-SD); diastolic blood pressure was 94+/-17 mm Hg. According to the basic ST segment depression criteria, we found a prevalence of silent ischemia of 11.3%, and with the strict criteria the prevalence was 5.2%. The patients who were considered positive according to the basic criteria but not according to the strict criteria (false-positive) in the majority of cases (58%) had depression of an elevated baseline ST segment. We found a lower prevalence of silent cardiac ischemia as assessed by ambulatory electrocardiographic recording than generally reported. The stringency of applied analysis criteria appear to play an important role in this outcome.

Correlation of ST-segment depression during ambulatory electrocardiographic monitoring with myocardial perfusion and left ventricular function

To assess the relation between silent ischemia and objective markers of ischemia we compared ambulatory electrocardiographic (AECG) monitoring, exercise stress testing, and technetium-99m methoxyisobutyl isonitrile single-photon emission computed tomography (SPECT) in 68 patients with coronary artery disease. ST-segment depression at AECG monitoring occurred in 40%, exercise testing was positive in 88%, and SPECT was abnormal in 98% of patients. Patients with ST-segment depression had a higher incidence of 3-vessel disease (70% vs 45%, p = 0.04), shorter duration of exercise (267 +/- 109 vs 416 +/- 167 seconds, p < 0.01), lower workload achieved (5.1 +/- 1.9 vs 7.6 +/- 2.8 METs, p < 0.0002), and a greater extent of ischemia at scintigraphy (p = 0.01). Patients with a total ischemic time of >30 minutes in a 24-hour period had a lower ejection fraction (48 +/- 21% vs 70 +/- 9%, p = 0.001), a higher perfusion index at rest (2.4 +/- 0.6 vs 1.6 +/- 0.6, p = 0.001), and a greater number of segments with fixed perfusion defects (4.1 +/- 3.7 vs 1.3 +/- 1.8, p = 0.02) in comparison with those who had a shorter ischemic time. We conclude that AECG monitoring fails to identify a substantial proportion of patients with objective markers of ischemia; however, ST-segment depression reflects more significant disease. Longer total ischemic time correlates with the area of myocardial damage but not with other markers of ischemia.

Predictive value of cardiac autonomic neuropathy in diabetic patients with or without silent myocardial ischemia

OBJECTIVE

The aim of this study was to determine the predictive value of silent myocardial ischemia (SMI) and cardiac autonomic neuropathy (CAN) in asymptomatic diabetic patients.

RESEARCH DESIGN AND METHODS

We recruited 120 diabetic patients with no history of myocardial infarction or angina, a normal 12-lead electrocardiogram (ECG), and two or more additional risk factors. SMI assessment was carried out by means of an ECG stress test, a thallium-201 myocardial scintigraphy with dipyridamole, and 48-h ECG monitoring. CAN was searched for by standardized tests evaluating heart rate variations. Accurate follow-up information for 3-7 years (mean 4.5) was obtained in 107 patients.

RESULTS

There was evidence of SMI in 33 patients (30.7%). CAN was detected in 33 of the 75 patients (38.9%) who were tested, and a major cardiac event occurred in 11 of them. Among these 75 patients, the proportion of major cardiac events in the SMI+ patients was not significantly higher than that in the SMI- patients (6 of 25 vs. 5 of 50 patients), whereas it was significantly higher in the CAN+ patients than in the CAN- patients (8 of 33 vs. 3 of 42 patients; P = 0.04), with a relative risk of 4.16 (95% CI 1.01-17.19) and was the highest in the patients with both SMI and CAN (5 of 10 patients). After adjusting for SMI, there was a significant association between CAN and major cardiac events (P = 0.04).

CONCLUSIONS

In asymptomatic diabetic patients, CAN appears to be a better predictor of major cardiac events than SMI. The risk linked to CAN appears to be independent of SMI and is the highest when CAN is associated with SMI.

Silent ischaemia and hypertension

For many years now, silent ischaemia has been recognized as a distinct clinical entity, and its relevance in different patient groups has been established. However, a number of basic questions have not been answered. In explaining the pathophysiology of silent ischaemia, factors affecting both the demand and the supply side are now being recognized. With the exception of certain well-defined groups, it is not clear why some patients are mostly symptomatic, while other patients are predominantly asymptomatic. There appear to be many factors influencing the ischaemic pain threshold. Studies investigating the prevalence of silent ischaemia show a remarkably high prevalence of silent ischaemia in different patient groups. Patients with hypertension but without coronary artery disease form a specific and vulnerable high-risk population that is particularly prone to silent ischaemia. Since changes at the macrovascular level are not responsible, various factors negatively influencing either cardiac supply or demand have been investigated. A reduced coronary reserve is central in explaining the increased prevalence of silent ischaemia in hypertensives. Left ventricular hypertrophy renders meaningful detection of ST segment changes difficult, but a possible solution dealing with this problem is offered by applying more stringent criteria in terms of minimal ST depression in the definition of ischaemia. The treatment of silent ischaemia is largely the same as for angina pectoris, but whether therapy should be directed at elimination of all ischaemic episodes or only of symptomatic episodes depends on further prospective work addressing this question.

Prediction of late cardiac events by dipyridamole thallium scintigraphy in patients with intermittent claudication and occult coronary artery disease

Concomitant coronary artery disease often occurs in patients with peripheral vascular disease, but it may be asymptomatic. Despite being asymptomatic, cardiovascular events are the main source of morbidity and mortality in this group of patients. Dipyridamole thallium scintigraphy has been shown to be of prognostic value in patients with peripheral vascular disease and symptomatic coronary artery disease, but its effect on the long-term outcome in the asymptomatic group of patients is less defined. Eighty-four consecutive patients with peripheral vascular disease and no symptoms of coronary artery disease were therefore evaluated by clinical assessment, dipyridamole thallium imaging, radionuclide ventriculography, and cardiac catheterization and followed for a mean of 66 months. Abnormal perfusion patterns were found on thallium scintigraphy in 48 patients (57%); fixed, mixed, and reversible defects were present in 14 (17%), 11 (13%), and 23 (27%) patients, respectively. Significant coronary artery disease was present in 52 patients (69%) and mean left ventricular ejection fraction was 44%. During the follow-up period, 23 patients had a cardiac event (nonfatal myocardial infarction or cardiac death). Univariate analysis of 15 clinical, scintigraphic, radionuclide, and angiographic variables revealed that age, angiographic extent of coronary artery disease, and an abnormal thallium scan were significant predictors of subsequent cardiac events. Multivariate stepwise logistic regression analyses selected fixed and mixed thallium defects and diffuse coronary artery disease as the only significant independent predictors of outcome. Thus, the present study shows the value of dipyridamole thallium scintigraphy as a valuable prognostic indicator for long-term event-free survival in a cohort of patients with peripheral vascular disease and no history or symptoms of coronary artery disease.

Nitrates in silent ischemia

In recent years it has become clear that episodes of transient myocardial ischemia commonly occur in patients with coronary artery disease in the absence of chest pain or angina equivalent. These episodes of "silent myocardial ischemia" are particularly well documented during continuous ambulatory electrocardiographic monitoring in daily life. Evidence suggests that these episodes represent true ischemia, and appear to be a marker of unfavorable outcome. While the pathophysiology is not completely understood, it appears as though the mechanisms of angina and silent ischemia are the same. Both forms of ischemia respond to conventional antianginal medication. While long-acting nitrates are effective in reducing or preventing myocardial ischemia, because of their propensity to cause tolerance they should be used intermittently and in association with either beta-blockers or calcium antagonists. Nitrates are safe and comparatively inexpensive, and will continue to play an important role in the treatment and prevention of angina. However, in the light of current knowledge, there is no specific indication for the treatment of silent ischemia by nitrates.

Silent ischemia after uncomplicated myocardial infarction: lack of incremental clinical significance

To determine the potential utility of the detection of silent myocardial ischemia after acute myocardial infarction for clinical decision making, we investigated the hypothesis that the occurrence of silent myocardial ischemia on ambulatory electrocardiographic (EGG) monitoring after acute myocardial infarction is independently predictive of adverse outcome in patients in whom conventional clinical and investigative parameters indicate favourable prognosis on medical therapy. Among 465 consecutive patients admitted to our Coronary Care Unit with acute myocardial infarction, 42 patients (39% of those eligible) were randomly selected for study. Twenty-four hour ambulatory ECG monitoring was carried out 13 +/- 10 (standard deviation) days post-acute myocardial infarction. Ninety-eight percent of patients were receiving prophylactic anti-ischemic medications and 81% on aspirin. Silent myocardial ischemia was detected in 14%. During the follow-up period of 16 +/- 3 months, acute ischemic events occurred in 33% of those with silent myocardial ischemia and 19% of those without previous silent myocardial ischemia (P = 0.59). The sensitivity of the test for prediction of future acute ischemic events was 22% (95% confidence interval: 3-60%), specificity 87% (95% confidence interval: 72-97%), positive predictive value 33% (95% confidence interval: 4-78%) and negative predictive value 81% (95% confidence interval: 64-92%). Therefore the detection of ambulatory silent myocardial ischemia after acute myocardial infarction is not of sufficient incremental value as a predictor of the occurrence of adverse cardiac events to justify its routine clinical use in this subgroup of patients.

Comparison of the prognostic values of ischemia during daily life and ischemia induced by treadmill exercise testing

Although silent ischemia is common in patients with stable coronary artery disease (CAD), controversy surrounds the issue regarding the most appropriate method for detection. Routinely performed exercise tolerance testing provides important prognostic information. However, ambulatory electrocardiographic monitoring (AEM) has the distinct advantage of enabling evaluation of silent ischemia during daily life. Although numerous AEM studies have found a greater occurrence of silent ischemia than symptomatic ischemia in patients with stable angina pectoris, the independent prognostic value of AEM findings has not been definitively established. Several recent studies have addressed the question of whether AEM supplies additional information beyond that obtained from exercise testing. The results of these studies revealed that myocardial ischemia during daily life that is detected by AEM provides additional and independent prognostic information in patients with stable CAD who have evidence of ischemia during exercise testing.

Characteristics and clinical significance of ambulatory myocardial ischemia in men and women in the general population presenting with angina pectoris

OBJECTIVES

The aim of this study was to determine the frequency and prognostic importance of ambulatory myocardial ischemia and its association with cardiovascular risk factors in men and women in the general population presenting for the first time with typical angina pectoris.

BACKGROUND

Previous studies in selected "low" and "high" risk patients with stable coronary heart disease report a wide range in the frequency of ischemia (24% to 82%) and there is no agreement about whether ambulatory ischemia is of prognostic importance for the generality of patients with stable angina.

METHODS

Consecutive patients < or = 70 years of age from a randomly selected population with no previous coronary heart disease were assessed prospectively, and 96 patients with typical angina and 95 age-, gender- and practice-matched asymptomatic control subjects underwent 24-h ambulatory ST segment monitoring before antianginal therapy. All recordings were analyzed in blinded fashion. Follow-up evaluation of patients with angina to assess for revascularization, myocardial infarction and death was undertaken at a mean of 15.8 months (range 7 to 30) after the initial evaluation.

RESULTS

Transient episodes of ischemic ST segment depression were detected in 50 patients (52%) with angina and 9 control subjects (9%). In patients with angina, 159 episodes (71%) were silent, median duration of ischemia was 66 min (range 1 to 782) and mean +/- SD ST depression was 2.4 +/- 1.1 mm. In logistic regression analysis, serum cholesterol (p < 0.05) and ischemia on exercise (p < 0.01) were independently associated with the presence of ambulatory ischemia in men with angina, but only the latter was significant in women; this may reflect a different pathophysiologic basis for ambulatory ischemia in women. During follow-up, there were 29 events. Kaplan-Meier survival analysis revealed no significant difference in event-free survival between patients with angina who did and did not have ischemic episodes (66% vs. 72%, p = NS).

CONCLUSIONS

This is the first study representative of new patients with angina pectoris in the general population and shows that ischemia during daily living activities is present in > 50% of these patients but appears to be of no prognostic value.

Prognostic significance of transient ST segment changes after coronary artery bypass surgery: a long-term (4-10 year) follow up study

OBJECTIVE

To assess the long-term (four to 10 years) prognostic significance of transient ST segment changes on ambulatory ST segment monitoring after coronary artery bypass grafting (CABG).

PATIENTS AND METHODS

76 patients (67 men, nine women) underwent CABG between 1982 and 1984 (n = 31) and between 1987 and 1988 (n = 45) and at a mean age of 57. All underwent 48 hours of ambulatory ST segment monitoring at a mean of 19 weeks after surgery. The results were available for assessment. All general practitioners were contacted and patients' notes reviewed. Patients were contacted by telephone. Details were recorded of intervening events (acute myocardial infarction, unstable angina, need for further revascularisation, and deaths). Event free survival curves were produced for those with and without transient ST segment changes during routine postoperative ambulatory ST segment monitoring.

RESULTS

During 3213 hours of monitoring after CABG, 21 (27.6%) of 76 patients had transient ST segment changes, of which 70% were silent. Over a mean 70 month follow up period, patients with such ischaemic changes were no more likely to have either an objective (myocardial infarction or cardiac death) or subjective (unstable angina or another revascularisation) event than those patients without ischaemic changes. This finding was the same in patients operated on between 1987 and 1988 and between 1982 and 1984.

CONCLUSIONS

Although ambulatory ST segment monitoring is becoming increasingly popular in some countries as a routine investigation for ischaemia in various coronary subgroups, the findings of such an investigation, when performed after CABG, do not help to identify a subgroup more likely to have an adverse outcome during up to 10 years of follow up. There seems to be no reason to perform this investigation after surgery, and particularly to refer patients for reinvestigation because of the detection of predominantly silent ST segment changes of uncertain relevance.

Prognostic implications of myocardial ischemia during daily life in low risk patients with coronary artery disease

OBJECTIVES

The purpose of this study was to determine the incidence and prognostic importance of myocardial ischemia detected by ambulatory monitoring in low risk, medically managed patients with coronary artery disease.

BACKGROUND

Previous studies have demonstrated that certain high risk subsets of patients with coronary artery disease have improved survival with revascularization. The remaining low risk medically managed patients may still have episodes of silent ischemia during daily living, but the frequency and prognostic implications of such episodes in this group are unknown.

METHODS

We prospectively studied the incidence and prognostic significance of ST segment changes recorded during daily activities in 116 asymptomatic or mildly symptomatic low risk patients with native coronary artery disease who were followed up for 29 +/- 13 months. Low risk patients were selected after excluding patients with 1) left main disease; 2) three-vessel coronary artery disease and left ventricular dysfunction at rest; 3) three-vessel disease and inducible ischemia during exercise; and 4) two-vessel disease, left ventricular dysfunction and inducible ischemia.

RESULTS

Forty-five patients (39%) had transient episodes of ST segment depression during 48-h electrocardiographic (ECG) monitoring (total 217 episodes, lasting 7,223 min, 82% of episodes silent). There were eight acute cardiac events (seven myocardial infarctions, one episode of unstable angina) and nine patients underwent elective revascularization. Seven of the eight acute events occurred in patients without silent ischemia during monitoring. Kaplan-Meier survival analysis revealed no significant differences in event-free survival from either acute or total events in subgroups with or without silent ischemia during ambulatory ECG monitoring. None of the clinical, treadmill exercise, radionuclide ventriculographic or cardiac catheterization variables were predictive of outcome by Cox multivariate proportional hazard function analysis. Analysis of coronary arteriograms before and after acute cardiac events revealed that in five of the six patients studied, acute occlusion occurred in a coronary artery different from the artery with the severest stenosis on initial angiography.

CONCLUSIONS

In patients categorized as at low risk on the basis of the results of cardiac catheterization and stress testing, silent myocardial ischemia during daily life was not uncommon, and its presence failed to predict future coronary events.

Comparison of ST depression recorded by Holter monitors and 12-lead ECGs during coronary angiography and exercise testing

Data from previous studies are debatable regarding whether Holter monitors are a reliable electrocardiographic indicator of ischemia, for which the 12-lead electrocardiogram (ECG) is the standard. Simultaneous 12-lead and Holter ECGs were performed on 30 patients with typical angina pectoris during coronary angiography or exercise testing. ST depression recorded by both methods was directly compared, using the 12-lead ECG as the reference. The Holter tapes were also scanned by two automated ST analysis programs and the results were compared to 12-lead ECGs. Only 66 of the 178 12-lead ECG ST depression events were also present on the Holter recordings (37.1% Holter sensitivity). ST depression was underestimated by the Holter recordings compared to the 12-lead ECGs (p < 0.0001). The majority (67.0%) of ST depression events identified by one computer program were false positive events. The degree of ST depression was overestimated compared to 12-lead ECGs by the second program (p = 0.0033). Holter-detected ST depression may not be a reliable ECG indicator of myocardial ischemia.