The ST segment of the ambulatory electrocardiogram in a normal population.

The behaviour of the ST segment in everyday life was studied by ambulatory electrocardiography in 111 normal volunteers. Fifteen were excluded because of abnormal exercise responses (10 subjects) and significant postural ST segment shifts (five subjects). This left 62 men and 34 women, mean (SD) age 40.5 (12.6) years (range 20-67 years). Ambulatory monitoring of leads CM5 and CC5 for 24 hours was followed by a maximal treadmill exercise test. The tapes of the ambulatory monitoring were analysed by a computer aided system. The computer printed trend plots of the ST segment (measured both at the J point and at J + 60 ms) to detect episodes of ST segment elevation and depression, which were confirmed by visual analysis of real time printouts. Twelve subjects showed "ischaemic" ST segment depression and nine subjects showed ST segment elevation. Eight people with ambulatory ST segment changes were studied during exercise by radionuclide ventriculography and thallium-201 imaging scans. Although seven of the eight thallium studies were normal, radionuclide ventriculography showed functional impairment in five cases. Seven of the 10 subjects with abnormal exercise tests were similarly investigated and their results followed the same pattern, with normal thallium images in six and functional impairment in four. Ambulatory electrocardiography was repeated in 20 people after a median of 20 days. The ST segment changes were reproducible. ST segment changes of an apparently ischaemic nature occur even in a carefully defined normal population but they do not necessarily represent latent clinically significant coronary artery disease. This indicates that ST segment changes seen in patients with known obstructive coronary artery disease should be interpreted with caution.     

The haemodynamic response to myocardial ischaemia in ambulant patients with variant angina

The haemodynamic response to myocardial ischaemia in patients with variant angina during ambulatory activity is unknown. Ambulatory pulmonary artery pressure monitoring with a transducer tipped catheter and simultaneous frequency modulated electrocardiograms was used to assess changes in left ventricular function in five male patients (mean age 51.8 years) during variant angina; four patients had coronary artery stenosis and one had normal coronary arteries. Two hundred and seventy hours of ambulatory recordings were analysed. Twenty episodes (12 painful, 8 silent) of ST segment change greater than 1 mm occurred. Episodes tended to occur more frequently in the early morning hours. Six episodes of painful ST elevation were associated with a rise in pulmonary artery diastolic pressure. In the remaining episodes ST segment elevation was of shorter duration and there was no rise in pulmonary artery diastolic pressure. Pain was usually a late feature. Silent ST segment elevation occurred at rest and pulmonary artery diastolic pressure increased in all but one episode. Silent exertional ST segment depression was associated with a greater increase in pulmonary artery diastolic pressure than that seen during ST segment elevation. ST segment depression preceded or followed ST segment elevation in two episodes. The onset of ST segment elevation nearly always preceded the onset of a rise in pulmonary artery diastolic pressure. Ergometrine maleate provocation produced a rise in pulmonary artery diastolic pressure in three patients. In one there was no response to 1000 micrograms but spontaneous episodes of ST segment elevation were recorded during ambulatory monitoring. Treadmill exercise resulted in both ST segment elevation and depression with a similar haemodynamic response during both types of electrocardiographic change. When there is important coronary artery disease in two or more vessels ST segment changes may occur in different territories during treadmill exercise and during spontaneous episodes. Ambulatory pulmonary artery diastolic pressure monitoring is a useful technique for the investigation of variant angina.     

The haemodynamic response to myocardial ischaemia in ambulant patients with variant angina.

The haemodynamic response to myocardial ischaemia in patients with variant angina during ambulatory activity is unknown. Ambulatory pulmonary artery pressure monitoring with a transducer tipped catheter and simultaneous frequency modulated electrocardiograms was used to assess changes in left ventricular function in five male patients (mean age 51.8 years) during variant angina; four patients had coronary artery stenosis and one had normal coronary arteries. Two hundred and seventy hours of ambulatory recordings were analysed. Twenty episodes (12 painful, 8 silent) of ST segment change greater than 1 mm occurred. Episodes tended to occur more frequently in the early morning hours. Six episodes of painful ST elevation were associated with a rise in pulmonary artery diastolic pressure. In the remaining episodes ST segment elevation was of shorter duration and there was no rise in pulmonary artery diastolic pressure. Pain was usually a late feature. Silent ST segment elevation occurred at rest and pulmonary artery diastolic pressure increased in all but one episode. Silent exertional ST segment depression was associated with a greater increase in pulmonary artery diastolic pressure than that seen during ST segment elevation. ST segment depression preceded or followed ST segment elevation in two episodes. The onset of ST segment elevation nearly always preceded the onset of a rise in pulmonary artery diastolic pressure. Ergometrine maleate provocation produced a rise in pulmonary artery diastolic pressure in three patients. In one there was no response to 1000 micrograms but spontaneous episodes of ST segment elevation were recorded during ambulatory monitoring. Treadmill exercise resulted in both ST segment elevation and depression with a similar haemodynamic response during both types of electrocardiographic change. When there is important coronary artery disease in two or more vessels ST segment changes may occur in different territories during treadmill exercise and during spontaneous episodes. Ambulatory pulmonary artery diastolic pressure monitoring is a useful technique for the investigation of variant angina.     

Relation between left ventricular function at rest and with exercise and silent myocardial ischemia.

The prognostic value of radionuclide measures of left ventricular function at rest and exercise is well established. Some studies have suggested that the frequency and duration of silent ischemia during ambulatory monitoring provide similar prognostic information; however, studies comparing these two techniques have not been performed. This study examines the relation between left ventricular function at rest and exercise-induced ischemia assessed by radionuclide ventriculography with myocardial ischemia during ambulatory electrocardiographic (ECG) monitoring. Of the 155 patients with coronary artery disease studied, 88% had left ventricular dysfunction with exercise, defined as failure of the ejection fraction to increase by greater than 4% with exercise, and 33% of patients had left ventricular dysfunction at rest (ejection fraction less than 45%); 52% had transient episodes of ST segment depression during 48-h ambulatory ECG monitoring. Exercise-induced left ventricular dysfunction during radionuclide ventriculography was extremely sensitive (94%) in detecting patients with ischemic episodes during ambulatory ECG monitoring; however, only 55% of patients with exercise-induced left ventricular dysfunction had ST segment depression during ambulatory monitoring. Moreover, patients with left ventricular dysfunction at rest had a lower prevalence of transient episodes of ST segment depression (31%) than did patients with normal left ventricular function at rest (62%) (p = 0.008). The relation between prognostically important variables during exercise radionuclide ventriculography and the number and duration of transient episodes of ST depression was examined.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prognostic significance of transient myocardial ischaemia after first acute myocardial infarction: five year follow up study.

OBJECTIVE--To assess the five year prognostic significance of transient myocardial ischaemia on ambulatory monitoring after a first acute myocardial infarction, and to compare the diagnostic and long term prognostic value of ambulatory ST segment monitoring, maximal exercise testing, and echocardiography in patients with documented ischaemic heart disease. DESIGN--Prospective study. SETTING--Cardiology department of a teaching hospital. PATIENTS--123 consecutive men aged under 70 who were able to perform predischarge maximal exercise testing. INTERVENTIONS--Echocardiography two days before discharge (left ventricular ejection fraction), maximal bicycle ergometric testing one day before discharge (ST segment depression, angina, blood pressure, heart rate), and ambulatory ST segment monitoring (transient myocardial ischaemia) started at hospital discharge a mean of 11 (SD 5) days after infarction. MAIN OUTCOME MEASURES--Relation of ambulatory ST segment depression, exercise test variables, and left ventricular ejection fraction to subsequent objective (cardiac death or myocardial infarction) or subjective (need for coronary revascularisation) events. RESULTS--23 of the 123 patients had episodes of transient ST segment depression, of which 98% were silent. Over a mean of 5 (range 4 to 6) years of follow up, patients with ambulatory ischaemia were no more likely to have objective end points than patients without ischaemic episodes. If, however, subjective events were included an association between transient ST segment depression and an adverse long term outcome was found (Kaplan-Meier analysis; P = 0.004). The presence of exercise induced angina identified a similar proportion of patients with a poor prognosis (Kaplan-Meier analysis; P < 0.004). Both exertional angina and ambulatory ST segment depression had high specificity but poor sensitivity. The presence of exercise induced ST segment depression was of no value in predicting combined cardiac events. Indeed, patients without exertional ST segment depression were at increased risk of future objective end points (Kaplan-Meier analysis; P < 0.0045). These findings may be explained in part by a higher prevalence of left ventricular dysfunction in patients without ischaemic changes in the exercise electrocardiogram (P < 0.05). CONCLUSION--There seem to be limited reasons to perform ambulatory ST segment monitoring in survivors of a first myocardial infarction who can perform exercise tests before discharge. Patients at high risk of future myocardial infarction or death from cardiac causes are not identified. Ambulatory monitoring and exertional angina distinguish a small subset of patients who will develop severe angina pectoris demanding coronary revascularisation during follow up. Patients without exercise induced ST segment depression comprise a high risk subgroup in terms of subsequent objective end points. The role of ambulatory ST segment monitoring performed in unselected patients immediately after infarction when risk is maximal remains to be clarified.     

Hyperventilation test in coronary disease: a comparison with a bicycle ergometer exercise test. Report of 100 cases]

A hundred cases have been studied and divided into three categories:--60 normal subjects;--30 coronary subjects with a positive exercise test;--10 subjects with defective nervous control of the circulation; using the exercise test, we studied the effects of hyperventilation on repolarisation of the ventricle. In the normal subjects there was no ischaemic depression of the ST segment, but there were minor changes in repolarisation which affected the T wave in 73% of subjects and were essentially posterior in distribution. In the coronary subjects, we found three with ischaemic depression of the ST segment and one with ST elevation of 2.5 mm (6.7% of the coronary subjects). This last finding is evidence against the commonly held hypothesis that reproduction of ST depression by hyperventilation during the exercise test indicates a false positive test. In the patients with defective nervous control of the circulation, 9 had an ischaemic type of ST depression, either as a new feature or as a more severe one compared with that found at rest. The mechanism by which these depressions are produced has not been totally explained:--in the cases with defective nervous control of the circulation, it appears that latent increased sympathetic activity is increased by the hyperventilation;--in the coronary subjects, it may be caused by true ischaemia or by an associated defect in nervous control of the circulation.     

Symptomatic and silent myocardial ischaemia in hypertensive patients with left ventricular hypertrophy.

OBJECTIVE--To assess the prevalence of symptomatic and silent myocardial ischaemia in patients with hypertensive left ventricular hypertrophy. DESIGN--Cross sectional study. SETTING--University department of medical cardiology. PATIENTS--90 patients (68 men and 22 women; mean age 57 (range 25 to 79)) with left ventricular hypertrophy due to essential hypertension. INTERVENTIONS--48 hour ambulatory ST segment monitoring (all patients), exercise electrocardiography (n = 79), stress thallium scintigraphy (n = 80), coronary arteriography (n = 35). RESULTS--43 patients had at least one episode of ST segment depression on ambulatory electrocardiographic monitoring. The median number of episodes was 16 (range 1 to 84) with a median duration of 8.6 (range 2 to 17) min. Over 90% of these episodes were clinically silent. 26 patients had positive exercise electrocardiography and 48 patients had reversible thallium perfusion defects despite chest pain during exercise in only five patients. 18 of the 35 patients who had coronary arteriography had important coronary artery disease. Seven of these patients gave no history of chest pain. CONCLUSIONS--Symptomatic and silent myocardial ischaemia are common in hypertensive patients with left ventricular hypertrophy, even in the absence of epicardial coronary artery disease.     

The Value of Exercise Electrocardiography and Exercise Thallium-201 Myocardial Perfusion Scanning in Determining the Presence of Single Vessel Coronary Artery Obstruction

Summary: In 39 patients with single vessel coronary artery disease and no previous myocardial infarction, exercise thallium-207 myocardial perfusion scanning and 12 lead exercise electrocardiography (ECG) were compared to see how reliably each method identified the site of coronary artery obstruction. Significant (≥ 70% diameter) stenosis was present in the left anterior descending (LAD) coronary artery in 21 patients, in the right coronary artery (RCA) in 14 patients and in the left circumflex (LCX) in four patients. Thallium defects on the scan in the septa1 (SEPT), anteroseptal (ANT SEPT) and anterior (ANT) segments correlated (P < 0.0005) with LAD disease and defects in the inferior (INF), posteroinferior (POST INF), and posterior (POST) segments correlated (P < 0.0005) with RCA or LCX disease. Exercise induced ST segment elevation in VI and/or AVL correlated with LAD disease. The site of ischaemic ST depression did not correlate with disease in any vessel. ST segment depression in leads L2, 3, AVF (67%) and in leads V4–6 (67%) was most sensitive for detecting patients with LAD disease and ST depression in leads V4–6 was most sensitive (56%) for detecting patients with RCA or LCX disease but neither differentiated LAD from RCAILCX disease.
During exercise induced ischaemia, the site of ST segment depression on the 12 lead exercise ECG will not identify the area of ischaemia in patients with single vessel disease but thallium defects will. In contrast to ST depression, ST elevation in V1 and/or AVL may identify LAD stenosis.     

Symptomatic and silent myocardial ischaemia in hypertensive patients with left ventricular hypertrophy.

OBJECTIVE--To assess the prevalence of symptomatic and silent myocardial ischaemia in patients with hypertensive left ventricular hypertrophy. DESIGN--Cross sectional study. SETTING--University department of medical cardiology. PATIENTS--90 patients (68 men and 22 women; mean age 57 (range 25 to 79)) with left ventricular hypertrophy due to essential hypertension. INTERVENTIONS--48 hour ambulatory ST segment monitoring (all patients), exercise electrocardiography (n = 79), stress thallium scintigraphy (n = 80), coronary arteriography (n = 35). RESULTS--43 patients had at least one episode of ST segment depression on ambulatory electrocardiographic monitoring. The median number of episodes was 16 (range 1 to 84) with a median duration of 8.6 (range 2 to 17) min. Over 90% of these episodes were clinically silent. 26 patients had positive exercise electrocardiography and 48 patients had reversible thallium perfusion defects despite chest pain during exercise in only five patients. 18 of the 35 patients who had coronary arteriography had important coronary artery disease. Seven of these patients gave no history of chest pain. CONCLUSIONS--Symptomatic and silent myocardial ischaemia are common in hypertensive patients with left ventricular hypertrophy, even in the absence of epicardial coronary artery disease.     

Thallium-201 scintigraphy after dipyridamole infusion with low-level exercise. III. Clinical significance and additional diagnostic value of ST segment depression and angina pectoris during the test

Intravenous dipyridamole thallium testing is a useful alternativeprocedure for assessing coronary artery disease (CAD) in patientswho are unable to perform maximal exercise tests. IschaemicST segment depression and angina pectoris are frequently observedduring the test, in particular when exercise is added to dipyridamoleinfusion. To establish the clinical significance and additionaldiagnostic value of these markers of ischaemia during dipyridamolelow-level exercise testing (DXT) 57 patients with CAD (groupA), 21 patients with normal or near-normal coronary arteriesat coronary arteriography (group B), and 20 healthy subjectswith low likelihood of CAD (group C) were studied. During DXT ischaemic ST segment depression was observed in 28patients (47%) of group A and in two patients (10%) of groupB. Angina pectoris was experienced by 35 patients (61%) of groupA and by five patients (24%) of group B. The positive predictivevalue of both ST depression and angina pectoris was high (88and 93%, respectively), but the negative predictive values werelow (42 and 40%, respectively). Combining ST segment analysiswith the findings of thallium imaging significantly increasedthe diagnostic accuracy of the test. ST segment depression, angina pectoris, and thallium abnormalitieswere highly specific findings if the study population consistedof asymptomatic subjects with a low likelihood of CAD (groupC). Sensitivity for the detection of the presence of CAD increasedwith the extent of CAD for all parameters studied. Thus, STdepression and angina pectoris, alone or in combination, duringDXT have little diagnostic significance, although sensitivityis increased in patients with triple-vessel CAD. Analysis ofthe ST segment provides additional information and should thereforebe included in the overall interpretation of the test results.A marked difference in the false positive rates for all parameterswas observed between asymptomatic subjects and angiographicallynormal patients with chest pain syndromes, which can be explainedby selection bias.     

A method for praecordial surface mapping of the exercise electrocardiogram.

A technique for praecordial surface mapping of the exercise electrocardiogram is described. This showed the area, time course, and severity of ST segment depression as projected onto the front of the chest after exercise. Twenty normal volunteers and 20 patients with coronary artery disease have been studied. No changes were seen after exercise in the normal subjects but areas of ST segment depression appeared in all 20 patients with angina pectoris. In 5 of the 20 patients with coronary artery disease, the exercise test was repeated on a later date. There were no significant differences in the area of severity of electrocardiographic abnormalities recorded during the two tests. This technique may prove to be useful for diagnosis and assessing medical and surgical treatments in patients with ischaemic heart disease.     

Haemodynamic response to myocardial ischaemia during unrestricted activity, exercise testing, and atrial pacing assessed by ambulatory pulmonary artery pressure monitoring

Ambulatory pulmonary artery pressure monitoring by means of a transducer tipped catheter with a simultaneous frequency modulated electrocardiogram and a miniaturised tape recorder was used to study the haemodynamic implications of ST segment depression in patients with coronary artery disease. Nineteen male patients (mean (SD) age 58 (11) years) with clinical and angiographic evidence of coronary artery disease were studied together with six controls. Changes in the ST segment and pulmonary artery diastolic pressure during treadmill exercise, atrial pacing, and unrestricted ambulant activity were analysed. During exercise, pulmonary artery diastolic pressure rose significantly in patients with coronary artery disease but not in the controls. One patient with ST depression greater than 1 mm did not have a rise in pulmonary artery diastolic pressure on exercise; two had a rise in pulmonary artery diastolic pressure with no ST segment change despite severe angina. The pulmonary artery diastolic pressure tended to rise before or simultaneously with the onset of ST segment depression. The haemodynamic response to atrial pacing was similar in normal controls and patients with coronary artery disease. During ambulatory monitoring there were 29 episodes of ST segment depression all of which were associated with a rise in pulmonary artery diastolic pressure and chest pain. The onset of ST segment depression occurred before a rise in pulmonary artery diastolic pressure in 11 episodes, was simultaneous with it in 11, and followed it in seven episodes. During exercise and ambulatory monitoring there was a correlation between the magnitude of ST segment depression and the rise in pulmonary artery diastolic pressure. Pain was a late feature during exercise, atrial pacing, and anginal episodes. This technique for the first time allows the relation between ST segment changes and haemodynamic alterations in left ventricular function to be assessed in ambulant patients with coronary artery disease.     

Haemodynamic response to myocardial ischaemia during unrestricted activity, exercise testing, and atrial pacing assessed by ambulatory pulmonary artery pressure monitoring.

Ambulatory pulmonary artery pressure monitoring by means of a transducer tipped catheter with a simultaneous frequency modulated electrocardiogram and a miniaturised tape recorder was used to study the haemodynamic implications of ST segment depression in patients with coronary artery disease. Nineteen male patients (mean (SD) age 58 (11) years) with clinical and angiographic evidence of coronary artery disease were studied together with six controls. Changes in the ST segment and pulmonary artery diastolic pressure during treadmill exercise, atrial pacing, and unrestricted ambulant activity were analysed. During exercise, pulmonary artery diastolic pressure rose significantly in patients with coronary artery disease but not in the controls. One patient with ST depression greater than 1 mm did not have a rise in pulmonary artery diastolic pressure on exercise; two had a rise in pulmonary artery diastolic pressure with no ST segment change despite severe angina. The pulmonary artery diastolic pressure tended to rise before or simultaneously with the onset of ST segment depression. The haemodynamic response to atrial pacing was similar in normal controls and patients with coronary artery disease. During ambulatory monitoring there were 29 episodes of ST segment depression all of which were associated with a rise in pulmonary artery diastolic pressure and chest pain. The onset of ST segment depression occurred before a rise in pulmonary artery diastolic pressure in 11 episodes, was simultaneous with it in 11, and followed it in seven episodes. During exercise and ambulatory monitoring there was a correlation between the magnitude of ST segment depression and the rise in pulmonary artery diastolic pressure. Pain was a late feature during exercise, atrial pacing, and anginal episodes. This technique for the first time allows the relation between ST segment changes and haemodynamic alterations in left ventricular function to be assessed in ambulant patients with coronary artery disease.     

Differences in the frequency of ST segment depression during upright and supine exercise: assessment in normals and in patients with coronary artery disease

Increased utilization of ambulatory ST segment monitoring mandates an appreciation of nonischemic variables that may influence the ST segment. While a greater frequency of ST segment depression has been reported with supine vs upright exercise, the relative false positive rate in both positions is not known. Thus, we compared the frequency of exercise ECG abnormalities during upright and supine bicycle exercise in two groups--17 normals and 46 patients with coronary artery disease. Exercise was performed in combination with radionuclide ventriculographic imaging. Peak exercise heart rate, peak systolic blood pressure, and exercise duration time were all slightly higher in the upright vs supine position (p less than 0.05). Nevertheless, the frequency of positive ST segment responses was more common in the supine position, both in the patients with coronary artery disease (54% vs 30%, p less than 0.05) and in the normal subjects (29% vs 6%, p = NS). The corresponding radionuclide ventriculographic responses, however, were normal during upright and supine exercise in 6 of the 11 CAD patients and in all five of the normal subjects with an abnormal ST segment response during supine exercise only. The frequency of exercise-induced chest pain was also similar in the two positions. Thus, we theorize that nonischemic factors may govern some positive ST segment responses in the supine position. This finding is of relevance for understanding the potential sources of physiologic false positive ST segment responses for ambulatory ST segment monitoring.     

Noninvasive testing in the evaluation of myocardial ischemia: agreement among tests

The purpose of this study was to investigate the relations among four exercise-induced phenomena--angina, ST segment depression, decrease in ejection fraction and thallium perfusion defects--and to determine their impact on aerobic capacity. One hundred fifty-six men (mean age 52 +/- 8 years) with documented coronary heart disease were studied with radionuclide ventriculography during supine bicycle exercise, thallium scintigraphy and treadmill testing with computerized electrocardiography and maximal oxygen uptake. Of 624 administered tests, 243 results (39%) were considered to indicate ischemia. The average number of abnormal tests was 1.6 per patient and, when considered as continuous variables, their results correlated poorly. Correlations did not improve when adjusting for heart rate achieved or by eliminating patients with coronary artery bypass surgery or myocardial infarction. Statistical methods of comparing degree of interest agreement yielded surprisingly weak relations among the four tests of ischemia. Treadmill performance was markedly impaired by angina, but much less impaired by other indicators of ischemia. It is concluded that the usual test responses implying ischemia have weak agreement when uniformly applied to patients with known coronary artery disease.     

Characteristics of episodes of ST elevation or ST depression during ambulatory monitoring in patients subsequently undergoing coronary angiography

Transient ischaemic ST segment changes were studied in 296 consecutive patients with coronary heart disease attending hospital for coronary arteriography. They underwent two channel, frequency modulated ambulatory monitoring for 24 hours. During this time 221 episodes of transient ST elevation (n = 56) or ST depression (n = 165) with a horizontal deviation of at least 1 mm lasting at least 1 min were found in 70 patients (23.6%). Only 34% of episodes were associated with pain. The duration of the episode, the heart rate at the beginning of the episode, or the extent of ST deviation were not related to the occurrence of pain. Episodes of ST elevation were of significantly shorter duration, occurred significantly more often during the early morning, and at significantly lower heart rates than episodes of ST depression. The considerable overlap between the characteristics of episodes of ST elevation and ST depression suggests that in many instances a combination of factors is responsible for transient ischaemic ST segment changes.     

Prognostic value of ambulatory ST segment monitoring compared with exercise testing at 1-3 months after acute myocardial infarction

The relative value of ambulatory ST segment monitoring for assessingprognosis following acute myocardial infarction is currentlyuncertain. Ambulatory monitoring was performed in 177 patientsat a mean of 38 days (range 22–93) post-myocardial infarctionand its prognostic value was compared with exercise treadmilltesting (n=170). Cardiac events (myocardial infarction, cardiacdeath or coronary revascularisation) were noted during at least1 year of follow-up. The presence or absence of ST depressionon ambulatory nonitoring did not predict increased fatal ornon-fatal cardiac events although more severe ST depressionhad some predictive power: after adjusting for clinical variablesand coronary prognostic indices, the duration/24 h (P=0·03)and magnitude (P=0·007) of ST depression had independentvalue. ST deviation on exercise testing was associated (P<0·05)with increased events (19/90; 21% vs 7/80; 9%) and in patientswith a positive exercise test ST depression on ambulatory monitoringdid not identify any additional events (8/41; 20% vs 11/49;22%). No factor available from ambulatory monitoring was predictiveof outcome once variables from exercise testing were taken intoaccount. Ambulatory ST segment monitoring performed in the laterecovery phase (1–3 months) after acute myocardial infarctionis inferior to exercise testing for predicting prognosis anddoes not increase the predictive power of an exercise test.Ambulatory monitoring may only be indicated in patients unableto perform an exercise test.     

Characteristics of episodes of ST elevation or ST depression during ambulatory monitoring in patients subsequently undergoing coronary angiography.

Transient ischaemic ST segment changes were studied in 296 consecutive patients with coronary heart disease attending hospital for coronary arteriography. They underwent two channel, frequency modulated ambulatory monitoring for 24 hours. During this time 221 episodes of transient ST elevation (n = 56) or ST depression (n = 165) with a horizontal deviation of at least 1 mm lasting at least 1 min were found in 70 patients (23.6%). Only 34% of episodes were associated with pain. The duration of the episode, the heart rate at the beginning of the episode, or the extent of ST deviation were not related to the occurrence of pain. Episodes of ST elevation were of significantly shorter duration, occurred significantly more often during the early morning, and at significantly lower heart rates than episodes of ST depression. The considerable overlap between the characteristics of episodes of ST elevation and ST depression suggests that in many instances a combination of factors is responsible for transient ischaemic ST segment changes.     

Value of the bipolar lead CM5 in electrocardiography.

Only bipolar lead recording are available during ambulatory monitoring. Their sensitivity in detecting ST segment changes in relation to standard electrocardiographic leads is not known. The magnitude and direction of ST segment changes in the bipolar lead CM5 were compared with those in standard electrocardiographic leads in patients during exercise testing and percutaneous transluminal coronary angioplasty. Thirty patients with coronary artery disease were studied during exercise tests in which ST segment depression (greater than 0.5 mm) occurred in one or more standard electrocardiographic leads and 13 patients were studied during angioplasty that resulted in ST segment change in one or more leads (I, II, III, V2, V5, and CM5). Lead CM5 was the most sensitive lead (93%) during exercise testing and also showed the greatest magnitude of ST segment change below the isoelectric line in 93% of the patients. Only two patients, one with ST segment elevation in inferior leads and one with changes restricted to septal leads, had no ST segment depression in lead CM5. When ST segment shift from the baseline electrocardiogram was measured the magnitude of depression was greatest in lead CM5 in only 63% of the patients. During angioplasty of the left anterior descending coronary artery, lead CM5 showed ST segment depression in seven patients, ST segment elevation in two, and a biphasic response in one. Two of the three patients with balloon inflation in right coronary artery developed ST segment elevation in lead CM5. Thus lead CM5 is a reliable lead for detecting subendocardial ischaemia experienced during everyday activities in anginal patients. During total occlusion of coronary arteries (as in variant angina or myocardial infarction) lead CM5 commonly shows ST segment depression and changes due to right coronary artery occlusion may not be detected.     

Ambulatory electrocardiographic ST segment changes in healthy volunteers.

Twenty four hour ambulatory monitoring was performed on 120 healthy volunteers using a frequency modulated recorder: 50 men and 50 women below 40 years and 20 men between 40 and 60 years were studied. Twenty eight subjects had episodes of ST segment elevation (range 1-3 mm), which occurred almost invariably at night with a slow heart rate 62.4 +/- 10.4 beats/min). ST segment elevation occurred most often in men, and was not found in subjects over the age of 37. Also in 10 subjects horizontal or downsloping ST segment depression (range 1-2 mm) was recorded, usually in association with tachycardia (135 +/- 10.5 beats/min). Nine of these exercised on a bicycle ergometer, and widespread ST segment depression was observed in eight. Thus ST segment changes, which are often interpreted as myocardial ischaemia in patients with ischaemic heart disease, are commonly seen in 24 hour electrocardiographic monitoring of healthy volunteers.