The electrocardiogram in ST elevation acute myocardial infarction: correlation with coronary anatomy and prognosis

The electrocardiogram is considered an essential part of the diagnosis and initial evaluation of patients with chest pain. This review summarises the information that can be obtained from the admission electrocardiogram in patients with ST elevation acute myocardial infarction, with emphasis on: (1) prediction of infarct size, (2) estimation of prognosis, and (3) the correlations between various electrocardiographic patterns and the localisation of the infarct and the underlying coronary anatomy.

Frequency, characteristics, and clinical significance of transient ST segment elevation in patients with acute coronary syndromes

BACKGROUND

Prior investigations of transient myocardial ischaemia have focused on ST depression events. Therefore, the purpose of this analysis was to determine the frequency, characteristics, and clinical significance of transient ST segment elevation in patients with acute coronary syndromes.

METHODS

A secondary analysis from two prospective studies utilizing 12-lead ST segment monitoring was used to compare ST elevation vs ST depression events.

RESULTS

Of 868 patients, 177 (20%) had 574 events (242, ST elevation; 332, ST depression). Patients with ST elevation were more likely to have single vessel coronary artery disease, whereas patients with ST depression were more likely to have triple vessel coronary artery disease. ST elevation events were of shorter duration, more often associated with chest pain, and had greater ST changes than ST depression events. There was no difference in clinical outcome between patients with ST elevation vs depression; however, those with ST events were more likely to have adverse hospital outcomes (OR, 3.67) or death (OR, 2.03) than patients without ST events. After controlling for clinical prognostic factors, transient ST events observed with continuous ST monitoring predicted hospital death independently from signs of ischaemia on the initial standard 12-lead ECG.

CONCLUSIONS

Transient ST elevation is nearly as prevalent as transient ST depression in patients with acute coronary syndromes. Since the vast majority of ST events are brief and otherwise clinically silent, ST segment monitoring is more efficacious in detecting ischaemic events and in predicting adverse clinical outcomes than patients' symptoms or the initial standard 12-lead ECG.

Clinical consequences of ST-segment changes caused by body position mimicking transient myocardial ischemia: hazards of ST-segment monitoring?

A case is described in which an acute ST-segment change, presumably due to a change in body position, is erroneously interpreted as an acute ischemic event. Positional ST-segment changes during continuous, multi-lead electrocardiographic (ECG) monitoring are particularly challenging to distinguish from transient myocardial ischemia because 1) positional ECG templates are often not feasible to record at the beginning of monitoring in unstable patients; 2) positional ECG templates, if recorded, are often not readily accessible to clinicians for later comparison; 3) body position cannot be correlated with ST events because patients are out of the direct view of nurses during the event or clinicians review ST trends at a later time; 4) ST monitors typically do not store ECGs frequently enough to be able to observe on the ST trend the gradual ("ramp-like") onset of ST changes that is characteristic of transient ischemia; and 5) absence of chest pain with a ST event does not help clinicians identify false alarms because it is well understood that the majority of ischemic events are clinically silent.

Thoracic location of the lead with maximal ST-segment deviation during posterior and right ventricular ischemia: comparison of 18-lead ECG with 192 estimated body surface leads

By using our database of continuous 18-lead electrocardiographic (ECG) recordings (standard + V3-5R + V7-9) during coronary angioplasty, we selected 68 patients with left circumflex balloon occlusions (posterior ischemia model) or proximal right coronary artery balloon occlusions (right ventricular IRV] ischemia model). ST-segment amplitudes (J + 60 ms) at preangioplasty baseline were subtracted from maximal ST amplitudes during balloon inflation to create a positive or negative change score (deltaST) for each of the 18 leads. DeltaST elevation was used to describe a change in the ST level in the positive direction from baseline, whether or not actual ST elevation from the isoelectric line was present. DeltaST depression was used to describe a change in the ST level in the negative direction from baseline, whether or not actual ST depression from the isoelectric line was present. ST amplitudes from 8 of the 12 standard leads were then used to estimate ST amplitudes at 192 body surface sites spanning the entire anterior and posterior thorax using the transformation technique of Lux. Thoracic distributions of the DeltaST values were displayed on a torso figure, including locations of the 18 lead locations and points of maximal ST elevation and depression. The 192 estimated body surface unipolar leads were compared with 18-lead ECGs (bipolar and unipolar). During 53 left circumflex occlusions, the maximal deltaST elevation was always located in the 18-lead ECG, with the most frequent locations at leads III, II (41%), V7-8 (34%), and V5-6 (25%). The maximal deltaST depression was located outside the 18-lead ECG (89%), with the most frequent locations above standard lead V2 (67%) and V3 (14%). During 16 proximal right coronary artery occlusions, the maximal deltaST elevation was always located in the 18-lead ECG, with the most frequent locations at leads III (81%) and V2-3R (13%). The maximal deltaST depression was located outside the 18-lead ECG (93%), with the most frequent locations above standard lead V2 (50%), V3 (14%), and V4 (14%). We conclude that maximal deltaST elevation is always located in the 18-lead ECG and maximal deltaST depression is frequently located outside of 18-lead ECG during left circumflex and proximal right coronary artery occlusions. Future studies are required to determine the bipolar leads for the 192 estimated body surface potential mapping leads.

New electrocardiographic criteria for posterior wall acute myocardial ischemia validated by a percutaneous transluminal coronary angioplasty model of acute myocardial infarction

The standard 12-lead electrocardiogram (ECG) fails to detect ST-segment elevation in patients with posterior wall acute myocardial ischemia. However, additional posterior leads V(7-9) provide limited additional diagnostic information to the standard 12-lead ECG when an ischemic criterion of 1-mm ST elevation is used. No study is available to delineate the ischemic criteria in the posterior electrocardiographic leads. Continuous 15-lead ECGs (standard 12 lead + V(7-9)) were recorded in 53 subjects undergoing elective left circumflex coronary angioplasty (posterior ischemia model). ST amplitudes (J + 60 ms) at preangioplasty baseline were subtracted from maximal ST amplitudes during balloon occlusion to create a positive or negative change score (DeltaST) for each of the 15 leads. During 53 left circumflex occlusions, 26 subjects (49%) had DeltaST elevation of > or = 1 mm and 24 subjects (45%) had DeltaST elevation ranging from 0.5 to 0.95 mm in > or = 1 posterior leads. Five subjects (9%) had DeltaST elevation of > or = 1 mm in the posterior leads without DeltaST elevation anywhere in any of the 12 leads. The sensitivity in detecting myocardial ischemia using 15-lead ECGs (58%) was not statistically different from the standard 12-lead ECG (49%) (p = 0.06). Adjusting the ischemic criterion from 1 to 0.5 mm in V(7-9) significantly improved the sensitivity from 49% in the 12-lead ECG to 94% in the 15-lead ECG (p = 0.000). In addition, 12 subjects (23%) had posterior ST-segment elevation without anterior ST-segment depression. Thus, posterior leads V(7-9) contribute significant additional diagnostic information above and beyond the standard 12-lead ECG only when a new ischemic criterion of 0.5 mm instead of 1 mm ST elevation is applied to the posterior leads.

Prehospital delay time in acute myocardial infarction: an exploratory study on relation to hospital outcomes and cost

BACKGROUND

Short prehospital delay is associated with improved outcomes in myocardial infarction, but the impact on cost has not been tested. Shortening delay time could reduce health care expenditures.

METHODS AND RESULTS

Two hundred ninety-eight patients were examined with the use of a historic prospective design at 2 hospital sites. A secondary analysis was performed that used patients with confirmed myocardial infarction from the National Register of Myocardial Infarction and direct and indirect costs from the accounting system at the hospitals. Chi-square, Mann Whitney U, and Fisher exact tests were used for comparisons. Delay and 4 sets of variables were regressed on cost with the significant predictors used to construct a final model. The mean age was 71 +/- 14 years old; 62% were men. There were no major differences in demographics, cardiac history, risk factors, and admission characteristics between short and long delayers. Resource utilization and clinical outcomes were similar between the 2 groups; there was no difference in cost. Additional diagnostic procedures (odds ratio 2.92; 95% confidence interval 1.65-5.15) and complications (odds ratio 3.43; 95% confidence interval 2.03-5.82) were significant predictors of cost. Delay was not a predictor of high cost.

CONCLUSIONS

Short prehospital delay was not associated with improved clinical outcomes, nor did it predict cost. Explanations include (1) the low utilization of early reperfusion therapy in the short delay group, (2) the study lacked sufficient power to detect a difference in cost between short and long delayers, and (3) the severity of illness could not be adequately measured. This issue warrants further study because of the potential impacts on health care expenditures.

Accuracy of the EASI 12-lead electrocardiogram compared to the standard 12-lead electrocardiogram for diagnosing multiple cardiac abnormalities

This study was performed to compare a derived 12-lead electrocardiogram (ECG) using a simple 5-electrode lead configuration (EASI 12-lead) with the standard ECG for multiple cardiac diagnoses. Accurate diagnosis of arrhythmias and ischemia often require analysis of multiple (ideally, 12) ECG leads; however, continuous 12-lead monitoring is impractical in hospital settings. EASI and standard ECGs were compared in 540 patients, 426 of whom also had continuous 12-lead ST segment monitoring with both lead methods. Independent standards relative to a correct diagnosis were used whenever possible, for example, echocardiographic data for chamber enlargement-hypertrophy, and troponin levels for acute infarction. Percent agreement between the 2 methods were: cardiac rhythm, 100%; chamber enlargement-hypertrophy, 84%-99%; right and left bundle branch block, 95% and 97%, respectively; left anterior and posterior fascicular block, 97% and 99%, respectively; prior anterior and inferior infarction, 95% and 92%, respectively. There was very little variation between the 2 lead methods in cardiac interval measurements; however, there was more variation in P, QRS, and T-wave axes. Of the 426 patients with ST monitoring, 138 patients had a total of 238 ST events (26, acute infarction; 62, angioplasty-induced ischemia; 150, spontaneous transient ischemia). There was 100% agreement between the 2 methods for acute infarction, 95% agreement for angioplasty-induced ischemia, and 89% agreement for transient ischemia. EASI and standard 12-lead ECGs are comparable for multiple cardiac diagnoses; however, serial ECG changes (eg, T-wave changes) should be assessed using one consistent 12-lead method.

Multilead ST-segment monitoring in patients with acute coronary syndromes: a consensus statement for healthcare professionals. ST- Segment Monitoring Practice Guideline International Working Group

BACKGROUND

ST-segment monitoring is underused by healthcare professionals for patients with acute coronary syndromes treated in emergency departments and intensive care units.

OBJECTIVE

To provide clinically practical consensus guidelines for optimal ST-segment monitoring.

METHODS

A working group of key nurses and physicians met in Dallas, Tex, in November 1998.

RESULTS

Consensus was reached on who should and should not have ST monitoring, goals and time frames for ST monitoring in various diagnostic categories, what electrocardiographic leads should be monitored, what equipment requirements are needed, what strategies improve accuracy and clinical usefulness of ST monitoring, and what knowledge and skills are required for safe and effective ST monitoring.

CONCLUSIONS

Because changes in the ST segment can shift among various electrocardiographic leads in the same person over time owing to different ischemic mechanisms, 12-lead ST monitoring is recommended. Recommended monitoring times are as follows: myocardial infarction or unstable angina, 24 to 48 hours or until patient is event-free for 12 to 24 hours; chest pain prompting a visit to an emergency department, 8 to 12 hours; catheter-based interventions with less definitive interventional outcomes requiring monitoring in an intensive unit, 6 to 12 hours; and cardiac surgery or noncardiac surgery in patients with coronary disease or risk factors, 24 to 48 hours. An ST measurement point of J + 60 ms makes it unlikely that measurement will coincide with the upslope of the T wave, even in patients with sinus tachycardia. Accurate and consistent lead placement and careful electrode and skin preparation are imperative to improve the clinical usefulness of ST monitoring.

Multilead ST-segment monitoring in patients with acute coronary syndromes: a consensus statement for healthcare professionals. ST- Segment Monitoring Practice Guideline International Working Group

BACKGROUND: ST-segment monitoring is underused by healthcare professionals for patients with acute coronary syndromes treated in emergency departments and intensive care units. OBJECTIVE: To provide clinically practical consensus guidelines for optimal ST-segment monitoring. METHODS: A working group of key nurses and physicians met in Dallas, Tex, in November 1998. RESULTS: Consensus was reached on who should and should not have ST monitoring, goals and time frames for ST monitoring in various diagnostic categories, what electrocardiographic leads should be monitored, what equipment requirements are needed, what strategies improve accuracy and clinical usefulness of ST monitoring, and what knowledge and skills are required for safe and effective ST monitoring. CONCLUSIONS: Because changes in the ST segment can shift among various electrocardiographic leads in the same person over time owing to different ischemic mechanisms, 12-lead ST monitoring is recommended. Recommended monitoring times are as follows: myocardial infarction or unstable angina, 24 to 48 hours or until patient is event-free for 12 to 24 hours; chest pain prompting a visit to an emergency department, 8 to 12 hours; catheter-based interventions with less definitive interventional outcomes requiring monitoring in an intensive unit, 6 to 12 hours; and cardiac surgery or noncardiac surgery in patients with coronary disease or risk factors, 24 to 48 hours. An ST measurement point of J + 60 ms makes it unlikely that measurement will coincide with the upslope of the T wave, even in patients with sinus tachycardia. Accurate and consistent lead placement and careful electrode and skin preparation are imperative to improve the clinical usefulness of ST monitoring.

Frequency of ischemia during intracoronary ultrasound in women with and without coronary artery disease

Myocardial ischemia is common during ICUS imaging in women with and without CAD. Although no long-term adverse effects occurred in our small sample, a larger sample of women is required to confirm our observations and to determine the precise mechanisms of ischemia. Such studies may determine whether the smaller diameter of coronary vessels in women makes the women more vulnerable than men to the occurrence of chest pain and ischemia during ICUS. Although ICUS is valuable in guiding coronary interventions, disposable catheters are costly. Studies are required to assess the cost-benefit ratio of incorporating ICUS with coronary interventional procedures. Until more is known, we recommend that nurses educate patients about ICUS, monitor them closely for ischemia and arrhythmias during the procedure, and consider obtaining 12-lead ECGs when patients undergo and ICUS procedure.

Frequency of ischemia during intracoronary ultrasound in women with and without coronary artery disease

Myocardial ischemia is common during ICUS imaging in women with and without CAD. Although no long-term adverse effects occurred in our small sample, a larger sample of women is required to confirm our observations and to determine the precise mechanisms of ischemia. Such studies may determine whether the smaller diameter of coronary vessels in women makes the women more vulnerable than men to the occurrence of chest pain and ischemia during ICUS. Although ICUS is valuable in guiding coronary interventions, disposable catheters are costly. Studies are required to assess the cost-benefit ratio of incorporating ICUS with coronary interventional procedures. Until more is known, we recommend that nurses educate patients about ICUS, monitor them closely for ischemia and arrhythmias during the procedure, and consider obtaining 12-lead ECGs when patients undergo and ICUS procedure.

Frequency of silent myocardial ischemia with 12-lead ST segment monitoring in the coronary care unit: are there sex-related differences?

BACKGROUND

Ischemia that occurs in the coronary care unit (CCU), whether symptomatic or silent, is associated with significant in-hospital and out-of-hospital complications. Studies have reported that more than 90% of ischemic episodes are silent in patients with unstable angina who are treated in the CCU with maximal medical therapy. Prior reports indicate that women complained more frequently of chest pain than men did.

PURPOSE

The aim of this study was to compare the frequency of silent myocardial ischemia in men versus women with use of continuous 12-lead ST segment monitoring in the CCU. A secondary goal was to determine whether silent ischemia was associated with less ST segment deviation as compared with symptomatic ischemia.

METHOD

Patients admitted for treatment of acute coronary syndrome in the CCU and who subsequently had 1 or more ischemic events during their monitoring period were selected for this analysis. All patients were continuously monitored (42.5 hours +/- 37.6) in the CCU with the EASI (Zymed Medical Instruments, Camarillo, Calif) 12-lead electrocardiogram (ECG) system that derives 12 leads with use of 3 information channels and 5 electrodes.

RESULTS

Of 491 patients, 128 (91 men and 37 women) had at least 1 episode of transient myocardial ischemia. Men and women did not differ in their proportion of chest pain during ischemia (men 27% and women 21%, NS). For both men and women, ST segment deviation was significantly greater during symptomatic ischemia compared with silent ischemia.

CONCLUSION

There are no sex-related differences in ischemic events in the CCU in regards to the variables of chest pain and ST magnitude. Therefore, because chest pain is not a reliable indicator of myocardial ischemia in the CCU, regardless of sex, patients should be adequately monitored for ischemic events.

Peak time of occurrence of myocardial ischemia in the coronary care unit

BACKGROUND: The onset of acute myocardial infarction and sudden cardiac death has a circadian variation, with the peak occurrence between 6 AM and 12 noon. OBJECTIVES: To determine if a circadian variation exists for transient myocardial ischemia in patients admitted to the coronary care unit with unstable coronary syndromes. METHODS: The sample was selected from patients enrolled in a prospective clinical trial who had had ST-segment monitoring for at least 24 hours and had had at least one episode of transient ischemia. The 24-hour day was divided into 6-hour periods, and comparisons were made between the 4 periods. RESULTS: In 99 patients, 61 with acute myocardial infarction and 38 with unstable angina, a total of 264 (mean +/- SD, 3 +/- 2) ischemic events occurred. Patients were more likely to have ischemic events between 6 AM and noon than at other times. A greater proportion of patients complained of chest pain between 6 AM and noon than during the other 3 periods. However, more than half the patients never complained of chest pain during ischemia between 6 AM and noon. CONCLUSION: Transient ischemia occurs throughout the 24-hour day; however, ischemia occurs more often between 6 AM and noon. An important nursing intervention for detecting ischemia is continuous electrocardiographic monitoring of the ST segment, even during routine nursing care activities, which are often at a peak during the vulnerable morning hours.

Peak time of occurrence of myocardial ischemia in the coronary care unit

BACKGROUND

The onset of acute myocardial infarction and sudden cardiac death has a circadian variation, with the peak occurrence between 6 AM and 12 noon.

OBJECTIVES

To determine if a circadian variation exists for transient myocardial ischemia in patients admitted to the coronary care unit with unstable coronary syndromes.

METHODS

The sample was selected from patients enrolled in a prospective clinical trial who had had ST-segment monitoring for at least 24 hours and had had at least one episode of transient ischemia. The 24-hour day was divided into 6-hour periods, and comparisons were made between the 4 periods.

RESULTS

In 99 patients, 61 with acute myocardial infarction and 38 with unstable angina, a total of 264 (mean +/- SD, 3 +/- 2) ischemic events occurred. Patients were more likely to have ischemic events between 6 AM and noon than at other times. A greater proportion of patients complained of chest pain between 6 AM and noon than during the other 3 periods. However, more than half the patients never complained of chest pain during ischemia between 6 AM and noon.

CONCLUSION

Transient ischemia occurs throughout the 24-hour day; however, ischemia occurs more often between 6 AM and noon. An important nursing intervention for detecting ischemia is continuous electrocardiographic monitoring of the ST segment, even during routine nursing care activities, which are often at a peak during the vulnerable morning hours.

12-lead ST-segment monitoring vs single-lead maximum ST-segment monitoring for detecting ongoing ischemia in patients with unstable coronary syndromes

BACKGROUND: 12-lead ECG monitoring of the ST segment is more sensitive than patients' symptoms for detecting ischemia after thrombolytic therapy or catheter-based interventions, but it is unclear whether monitoring of the single lead showing maximum ST deviation would be as efficacious. OBJECTIVE: To determine whether monitoring all 12 ECG leads for changes in the ST segment is necessary to detect ongoing ischemia in patients with unstable coronary syndromes. METHODS: Continuous 12-lead ST segment monitoring was performed in 422 patients from the onset of myocardial infarction or during balloon inflation in catheter-based interventions until the patient's discharge from the cardiac care unit. Computer-assisted techniques were used to determine (1) which lead showed the maximum ST deviation at the onset of myocardial infarction or during balloon inflation and (2) what proportion of later ischemic events were associated with ST deviation in this lead. RESULTS: The lead with the maximum ST deviation could be determined in 312 patients (74%). The remaining 110 (26%) had non-Q wave infarction without ST deviation or no ST changes during balloon inflation. During 18,394 hours of 12-lead ST monitoring, 118 (28%) of the 312 patients had a total of 463 ischemic events, 80% of which were silent. Of 377 ischemic events in which a maximum ST lead was detected, 159 (42%) did not show ST deviation in this lead (sensitivity, 58%; 95% CI, 53%-63%). Routine monitoring of leads V1 and II showed ST deviation in only 152 of the 463 events (sensitivity, 33%; 95% CI, 29%-37%). CONCLUSIONS: Monitoring of all 12 ECG leads for changes in the ST segment is necessary to detect ongoing ischemia in patients with unstable coronary syndromes.

12-lead ST-segment monitoring vs single-lead maximum ST-segment monitoring for detecting ongoing ischemia in patients with unstable coronary syndromes

BACKGROUND

12-lead ECG monitoring of the ST segment is more sensitive than patients' symptoms for detecting ischemia after thrombolytic therapy or catheter-based interventions, but it is unclear whether monitoring of the single lead showing maximum ST deviation would be as efficacious.

OBJECTIVE

To determine whether monitoring all 12 ECG leads for changes in the ST segment is necessary to detect ongoing ischemia in patients with unstable coronary syndromes.

METHODS

Continuous 12-lead ST segment monitoring was performed in 422 patients from the onset of myocardial infarction or during balloon inflation in catheter-based interventions until the patient's discharge from the cardiac care unit. Computer-assisted techniques were used to determine (1) which lead showed the maximum ST deviation at the onset of myocardial infarction or during balloon inflation and (2) what proportion of later ischemic events were associated with ST deviation in this lead.

RESULTS

The lead with the maximum ST deviation could be determined in 312 patients (74%). The remaining 110 (26%) had non-Q wave infarction without ST deviation or no ST changes during balloon inflation. During 18,394 hours of 12-lead ST monitoring, 118 (28%) of the 312 patients had a total of 463 ischemic events, 80% of which were silent. Of 377 ischemic events in which a maximum ST lead was detected, 159 (42%) did not show ST deviation in this lead (sensitivity, 58%; 95% CI, 53%-63%). Routine monitoring of leads V1 and II showed ST deviation in only 152 of the 463 events (sensitivity, 33%; 95% CI, 29%-37%).

CONCLUSIONS

Monitoring of all 12 ECG leads for changes in the ST segment is necessary to detect ongoing ischemia in patients with unstable coronary syndromes.

Bedside diagnosis of myocardial ischemia with ST-segment monitoring technology: measurement issues for real-time clinical decision making and trial designs

Monitoring of the ST segment is a valuable tool for guiding clinical decision making and evaluating anti-ischemia interventions in clinical trials; however, measurement issues hamper its diagnostic accuracy. This study reports the frequency and type of false positives and other measurement issues we have encountered during 12-lead ST-segment monitoring of patients in a cardiac care unit. Of 292 patients, 117 (40%) had one or more false positive events during an average of 41 hours of ST-segment monitoring, for a total of 506 false positive events. The 506 false positive events included 167 (36%) due to body positional change; 132 (26%) due to sudden increase in QRS complex/ST-segment voltage; 96 (19%) due to transient arrhythmia or pacing; 80 (16%) due to heart rate change in steeply sloped ST-segment contours; 26 (5%) due to a noisy signal; and 5 (1%) due to lead misplacement. It is concluded that many conditions in addition to myocardial ischemia can cause transient ST-segment deviation in patients with unstable coronary syndromes. Accurate ST-segment monitoring requires expertise in electrocardiogram interpretation, an understanding of the patient's clinical situation, and knowledge of the functions and limitations of the ST-segment monitoring system.

Estimating ischemic burden: comparison of two formulas

BACKGROUND: Complex formulas based on elevations of the ST segment on the ECG allow noninvasive estimation of ischemic burden. However, the formulas require elaborate computations that make them clinically useless, particularly in critical and emergent situations. Estimation of the amount of ischemic myocardium is useful in monitoring effects of therapeutic interventions. OBJECTIVE: To compare a simplified formula that sums ST-segment deviations in 12 ECG leads with formulas widely validated in clinical trials: anterior ischemic area = 3[1.5(number of leads ST increases) -0.4]; inferior ischemic area = 3[0.6(sigma ST increases II, III, aVF) +2.0]. METHODS: Data were collected from 46 patients undergoing angioplasty of the left anterior descending branch of the coronary artery or the right coronary artery who had changes in the ST segment denoting ischemia during balloon inflation. Absolute values of ST-segment elevations or depressions in the 12 standard ECG leads with a minimum deviation of 0.5 mm were added to determine the sum of the ST-segment deviations during ischemia of the left anterior descending branch of the coronary artery and ischemia of the right coronary artery. This sum was compared with the anterior and inferior ischemic area scores. The Pearson Product-Moment Correlation Coefficient was used to measure the association between the scores. RESULTS: The sum of ST-segment deviations for the left anterior descending branch correlated with the anterior ischemic area score, and the sum of ST-segment deviations for the right coronary artery correlated with the inferior ischemic area score. CONCLUSIONS: The complex, but validated, formulas for anterior ischemic area and inferior ischemic area correlate well with the simpler sum of ST-segment deviations. Because the simpler sum is more clinically useful, it may provide an alternative for monitoring ischemic burden.

Estimating ischemic burden: comparison of two formulas

BACKGROUND

Complex formulas based on elevations of the ST segment on the ECG allow noninvasive estimation of ischemic burden. However, the formulas require elaborate computations that make them clinically useless, particularly in critical and emergent situations. Estimation of the amount of ischemic myocardium is useful in monitoring effects of therapeutic interventions.

OBJECTIVE

To compare a simplified formula that sums ST-segment deviations in 12 ECG leads with formulas widely validated in clinical trials: anterior ischemic area = 3[1.5(number of leads ST increases) -0.4]; inferior ischemic area = 3[0.6(sigma ST increases II, III, aVF) +2.0].

METHODS

Data were collected from 46 patients undergoing angioplasty of the left anterior descending branch of the coronary artery or the right coronary artery who had changes in the ST segment denoting ischemia during balloon inflation. Absolute values of ST-segment elevations or depressions in the 12 standard ECG leads with a minimum deviation of 0.5 mm were added to determine the sum of the ST-segment deviations during ischemia of the left anterior descending branch of the coronary artery and ischemia of the right coronary artery. This sum was compared with the anterior and inferior ischemic area scores. The Pearson Product-Moment Correlation Coefficient was used to measure the association between the scores.

RESULTS

The sum of ST-segment deviations for the left anterior descending branch correlated with the anterior ischemic area score, and the sum of ST-segment deviations for the right coronary artery correlated with the inferior ischemic area score.

CONCLUSIONS

The complex, but validated, formulas for anterior ischemic area and inferior ischemic area correlate well with the simpler sum of ST-segment deviations. Because the simpler sum is more clinically useful, it may provide an alternative for monitoring ischemic burden.

Body position effects on the ECG: implication for ischemia monitoring

Rotation of the heart in relation to surface electrocardiographic (ECG) electrodes when a patient turns to one side has been reported to cause ST-segment shifts, triggering false alarms with continuous ST-segment monitoring. We prospectively analyzed ST-segment and QRS complex changes in both standard and derived ECGs in 40 subjects (18 with heart disease and 22 healthy) in supine, right- and left-lying positions. Of the 40 subjects, 6 (4 cardiac, 2 healthy) developed positional ST deviations of 1 mm or more on the standard ECG. In the derived method, five of the same six subjects showed ST-segment deviation of which most occurred in the left-lying position. Positional ST changes were most frequent for males and for cardiac patients (33%). Changes in QRS complex morphology were common on the standard (28 of 40, 70%) and less frequent on the derived ECGs (17 of 40, 43%), occurring in both healthy and cardiac subjects. QRS axis changes occurred only on the standard ECG. It was concluded that (1) right and left side-lying positions frequently induce clinically significant ECG changes; (2) positional ST-segment deviation is less frequent than previously reported and is most likely to occur in males with cardiac disease; and (3) the derived method is less prone to positional QRS changes than the standard ECG.

Frequency, duration, magnitude, and consequences of myocardial ischemia during intracoronary ultrasonography

To determine the frequency, duration, magnitude, and possible adverse effects of ischemia during intracoronary ultrasonography, real-time standard 12-lead electrocardiograms were recorded before, during, and after ultrasonography. Ischemia was defined as new-onset ST segment deviation of > or = 1 mm in one or more leads, measured at J + 80 msec. The magnitude of ischemia was expressed as the sum of absolute ST segment deviations across 12 leads. Eighteen (67%) of 27 patients had ischemia during intracoronary ultrasonography. The electrocardiogram resembled the characteristic pattern observed with occlusion of the vessel under study, involving ST segment elevation in contiguous leads in 89% of patients. A higher proportion of women (88%) had ischemia than men (58%), and women had smaller arterial lumenal areas compared with men (6.3 vs 9.1 mm2; p < 0.05). Individuals with ischemia were smaller than those without ischemia (body surface area = 1.99 vs 1.79 m2; p = 0.01). The mean duration of ischemia was 4 minutes and the mean 12-lead ST segment deviation score was 8.5 mm (maximum 20.5 mm). No patient with ischemia during ultrasonography had complications. Ischemia is common during intracoronary ultrasonography, particularly in women and individuals with smaller vessels; however, no adverse outcomes occur as a result.

Risk of thromboembolism in chronic atrial flutter

Anticoagulant therapy is not conventionally used in the treatment of patients with atrial flutter. This recommendation has been based on sparse clinical experience, and recent preliminary reports suggest a significant risk of thromboembolism for these patients. A retrospective study was undertaken to assess the frequency of thromboembolic events as well as potential risk factors for these events in a cohort of patients with atrial flutter referred for radiofrequency ablation treatment. Eighty-six consecutive patients with a primary diagnosis of atrial flutter were evaluated. A history of embolic events was noted in 12 of 86 patients (14%) with atrial flutter, with an annual risk of approximately 3%. There were no differences in the prevalence of coronary artery disease, cardiomyopathy, valvular disease, or atrial fibrillation between the 2 groups of patients having an embolic event and those of patients without embolic events. Left ventricular function and left atrial size were also similar between the 2 groups. The only significant risk factor was hypertension (p < 0.05). However, in a regression model with other clinical variables (i.e., age, gender, left atrial size, presence or absence of any cardiac disease, length of time in flutter, left ventricular function, type of flutter, flutter cycle length, type of secondary arrhythmias) no significant predictors were found. Patients with transient ischemic attacks or pulmonary emboli were then excluded from the analysis in order to compare the thromboembolic risk in the present study to that reported in major atrial fibrillation trials. The overall risk becomes 7% (6 of 86), which over a mean follow-up period of 4.5 years yields an annual risk of approximately 1.6%. Although this risk is only 1/3 of that for patients with atrial fibrillation, this risk is higher than previously recognized for patients with chronic atrial flutter. Anticoagulant therapy should be seriously considered for these patients.

Computer versus manual measurement of ST-segment deviation

Total ST scores (sum of absolute deviations in all 12 electrocardiographic [ECG] leads) have been used for research purposes to estimate total ischemic burden and to predict reperfusion after thrombolytic therapy. Computerized monitoring systems are capable of measuring ST deviation to the 10-microV level, whereas humans are incapable of such precise resolution. The purpose of this study was to compare computer versus manual ST scores in 12-lead ECGs exhibiting ischemia and to compare interrater reliability of manual measurements between two experts. A total of 58 subjects with 100 microV or more ST deviation in one or more leads during percutaneous transluminal coronary angioplasty balloon inflation were selected for analysis. ST measurements were made at J + 80 ms, using the isoelectric line as a reference, and summed across all 12 leads. Manual measurements were made to a minimum of 50 microV by two independent reviewers blinded to the computer scores. Total ST scores were compared using paired t-tests, and Pearson coefficients were used to test the correlations. A high correlation was observed between the manual and computer measurements (r = .96, P < .00) and between the two reviewers (r = .96, P < .00). A high degree of interrater reliability is possible with manual measurements of ST deviation. Computer measurements are consistently greater than manual measurements, presumably because humans "round down" to the nearest 50 microV. As such, computers may detect ischemia that is missed by humans. However, computer and manual measurements of ST deviation should not be mixed when used as a variable for research.

Comparison of standard and derived 12-lead electrocardiograms for diagnosis of coronary angioplasty-induced myocardial ischemia

To determine whether a derived 12-lead electrocardiogram (ECG) would demonstrate typical ST-segment changes of ischemia during percutaneous transluminal coronary angioplasty (PTCA), 207 patients were monitored with continuous 12-lead ST-segment monitoring during angioplasty. Additionally, to compare the derived and standard ECGs during known periods of ischemia with PTCA balloon inflation, 151 patients were recorded with both electrocardiographic methods during the procedure. Of the 207 patients recorded with the derived ECG, 171 (83%) had typical ischemic ST-segment changes during PTCA balloon inflation. The amplitudes of these ST deviations were similar to those observed during transient myocardial ischemia observed in clinical settings (median peak ST deviation, 225 microV). There was agreement regarding presence or absence of ischemia in 150 of the 151 patients recorded with both derived and standard electrocardiographic methods (> 99% agreement). With use of the standard ECG as the "gold standard" for ischemia diagnosis, there were no false-positive results and only 1 false-negative result with the derived ECG. Furthermore, there was nearly perfect agreement between the two 12-lead methods in terms of anterior versus inferior wall patterns of ischemia. Future studies are required to determine whether continuous monitoring with a derived ECG would improve diagnosis and lead to better patient outcomes.

Frequency of disabling symptoms in supraventricular tachycardia

The purposes of this study were to describe: clinical symptoms in a sample of consecutive patients with supraventricular tachycardia (SVT); incidence of sudden death, syncope, and other disabling symptoms; whether these symptoms differ by tachycardia mechanism; and to identify predictor variables of syncope in patients with SVT. Data were collected from chart reviews of 167 consecutive patients with SVT admitted for radiofrequency ablation. Three patients (2%) had nonlethal cardiac arrest, and a total of 16% (26 of 183) received at least 1 external direct-current shock for arrhythmia management. Twenty percent of subjects (33 of 167) reported at least 1 episode of syncope which was preceded by palpitations. The most frequent symptoms were: palpitations (96%), dizziness (75%), and shortness of breath (47%). We found atrioventricular nodal reentrant tachycardia (AVNRT) in 64 patients, atrioventricular-reciprocating tachycardia (AVRT) in 59, atrial tachycardia in 22, and atrial flutter in 22. The symptom profiles of patients with AVNRT, AVRT, and atrial tachycardia were very similar, but differed significantly (p <0.05) from those reported in the atrial flutter group. Multivariate analysis showed that heart rate > or = 170 beats/min was the only independent risk factor for syncope. Chi-square analysis demonstrated that SVT patients with heart rate > or = 170 beats/min had significantly more dizziness and syncope. Thus, despite a low incidence of associated heart disease, and good left ventricular function, there was a high frequency of disabling, potentially life-threatening symptoms associated with episodes of SVT in this sample. SVT can have potentially lethal consequences, and is more disruptive than previously thought.

Chest pain is an unreliable measure of ischemia in men and women during PTCA

OBJECTIVE

To investigate the differences between men and women in ischemia-induced pain, the amount of ST-segment deviation (the "ST deviation score"), and the relation between pain intensity and ST deviation score.

DESIGN

Retrospective, comparative descriptive.

SETTING

Cardiac catheterization laboratory of a large, urban, university-affiliated medical center with full cardiac services.

PATIENTS

Adults who underwent percutaneous transluminal coronary angioplasty (PTCA) and had electrocardiographic (ECG) evidence of myocardial ischemia during balloon inflation.

METHODS

Continuous 12-lead ECGs were recorded during balloon inflation in patients undergoing PTCA. Patients rated pain on a scale of 0 to 10. The total ST deviation score equaled baseline ECG ST minus maximal ST deviation; absolute deviations were totaled. Frequencies, measures of central tendency, or chi-square or t tests were used for data analysis with significance established at p < 0.05.

RESULTS

There were no difference in the degree of chest pain between men and women during balloon inflation, nor was ST deviation score associated with pain in either gender. Pain intensity did not correlate with total ST deviation in men (r = 0.02) or women (r = -0.07).

CONCLUSIONS

In this study, pain was a poor indicator of ischemia in both sexes during PTCA, and the degree of pain did not correlate with the magnitude of ST deviation. More than one third of men and more than one fourth of women experienced no chest pain during balloon inflation. Clinicians should consider continuous ST-segment monitoring and patient symptoms to monitor accurately for ischemia.

ST segment monitoring with a derived 12-lead electrocardiogram is superior to routine cardiac care unit monitoring

BACKGROUND

Prior studies have shown that a derived 12-lead electrocardiogram with a simple electrode configuration is comparable with the standard electrocardiogram for arrhythmia analysis.

METHODS

A prospective, comparative, within subjects design was used to compare the value of the derived 12-lead electrocardiogram with that of routine monitoring of leads V1 and II for detection of transient myocardial ischemia in 250 patients treated for unstable angina or myocardial infarction.

RESULTS

During 11,532 hours of derived 12-lead ST segment monitoring, 55 (22%) of 250 patients had 176 episodes of ischemia. Of the 55 patients with ischemia, 75% reported no chest pain and 64% had no ischemic ST changes with routine monitoring leads. All five patients who developed angiographically confirmed abrupt reocclusion after percutaneous transluminal coronary angioplasty had ischemic ST changes with the derived electrocardiogram (sensitivity, 100%), compared with only two patients with routine monitoring (sensitivity, 40%). Serious complications occurred in 17% of angina patients with ischemic events compared to 3% of those without ischemia. Length of stay in the cardiac care unit was twice as long in angina patients who had ischemic events. In patients with acute myocardial infarction, ischemic events were not associated with a more complicated hospital course; however, length of stay in the cardiac care unit was longer in patients with recurrent ischemia.

CONCLUSIONS

The findings show that derived 12-lead ST monitoring is superior to routine monitoring of leads V1 and II for detecting transient myocardial ischemia. ST monitoring of the derived 12-lead electrocardiogram may identify high-risk patients with unstable angina and provide prognostic information that would not be otherwise available from the usual clinical measures.

ST segment monitoring with a derived 12-lead electrocardiogram is superior to routine cardiac care unit monitoring

BACKGROUND: Prior studies have shown that a derived 12-lead electrocardiogram with a simple electrode configuration is comparable with the standard electrocardiogram for arrhythmia analysis. METHODS: A prospective, comparative, within subjects design was used to compare the value of the derived 12-lead electrocardiogram with that of routine monitoring of leads V1 and II for detection of transient myocardial ischemia in 250 patients treated for unstable angina or myocardial infarction. RESULTS: During 11,532 hours of derived 12-lead ST segment monitoring, 55 (22%) of 250 patients had 176 episodes of ischemia. Of the 55 patients with ischemia, 75% reported no chest pain and 64% had no ischemic ST changes with routine monitoring leads. All five patients who developed angiographically confirmed abrupt reocclusion after percutaneous transluminal coronary angioplasty had ischemic ST changes with the derived electrocardiogram (sensitivity, 100%), compared with only two patients with routine monitoring (sensitivity, 40%). Serious complications occurred in 17% of angina patients with ischemic events compared to 3% of those without ischemia. Length of stay in the cardiac care unit was twice as long in angina patients who had ischemic events. In patients with acute myocardial infarction, ischemic events were not associated with a more complicated hospital course; however, length of stay in the cardiac care unit was longer in patients with recurrent ischemia. CONCLUSIONS: The findings show that derived 12-lead ST monitoring is superior to routine monitoring of leads V1 and II for detecting transient myocardial ischemia. ST monitoring of the derived 12-lead electrocardiogram may identify high-risk patients with unstable angina and provide prognostic information that would not be otherwise available from the usual clinical measures.

Computer versus manual measurement of ST-segment deviation

Total ST scores (sum of absolute deviations in all 12 electrocardiographic [ECG] leads) have been used for research purposes to estimate total ischemic burden and to predict reperfusion after thrombolytic therapy. Computerized monitoring systems are capable of measuring ST deviation to the 10-microV level, whereas humans are incapable of such precise resolution. The purpose of this study was to compare computer versus manual ST scores in 12-lead ECGs exhibiting ischemia and to compare interrater reliability of manual measurements between two experts. A total of 58 subjects with 100 microV or more ST deviation in one or more leads during percutaneous transluminal coronary angioplasty balloon inflation were selected for analysis. ST measurements were made at J + 80 ms, using the isoelectric line as a reference, and summed across all 12 leads. Manual measurements were made to a minimum of 50 microV by two independent reviewers blinded to the computer scores. Total ST scores were compared using paired t-tests, and Pearson coefficients were used to test the correlations. A high correlation was observed between the manual and computer measurements (r = .96, P < .00) and between the two reviewers (r = .96, P < .00). A high degree of interrater reliability is possible with manual measurements of ST deviation. Computer measurements are consistently greater than manual measurements, presumably because humans "round down" to the nearest 50 microV. As such, computers may detect ischemia that is missed by humans. However, computer and manual measurements of ST deviation should not be mixed when used as a variable for research.

ECG criteria to distinguish between aberrantly conducted supraventricular tachycardia and ventricular tachycardia: practical aspects for the immediate care setting

To reevaluate ECG criteria for distinguishing supraventricular tachycardia (SVT) with aberrant conduction from ventricular tachycardia (VT), 133 wide QRS tachycardias were recorded in patients undergoing invasive electrophysiological (EP) study. Surface ECG leads (standard 12-lead and MCL leads) were compared to EP recordings to provide a standard for correct diagnosis. Criteria from six studies were pooled to select QRS morphology agreed to be highly specific for SVT or VT (specificity > 90%). Some morphological criteria were modified to simplify analysis for the immediate care setting.

RESULTS

Although the 12-lead ECG was useful in distinguishing aberrancy from VT, 13 tachycardias (10%) were misdiagnosed or could not be diagnosed. The MCL1 lead recorded clearly different QRS morphology than lead V1 in 40% of VT cases and was diagnostically inferior to V1. Most established criteria were highly specific for a diagnosis, but not very sensitive as individual criteria. Neither a QRS width of > 0.14 seconds nor a monophasic R wave pattern in lead V1 were valuable in diagnosing VT.

CONCLUSIONS

In distinguishing SVT with aberrant conduction from VT: (1) Although the 12-lead ECG is valuable, about 1 in 10 wide QRS tachycardias defy differentiation; (2) tachycardias > 190 beats/min often do not exhibit unequivocal criteria with which to make a certain diagnosis; (3) multiple leads are required for accurate assessment of QRS width, presence of AV dissociation or VA block, QRS axis, and morphological criteria; and (4) the MCL1 lead cannot be substituted for V1 in the use of morphological criteria for VT.