Evaluation of ST segment elevation criteria for the prehospital electrocardiographic diagnosis fo acute myocardial infarction

Three, dynamic variants of ST segment elevations in a patient with osteosarcoma and cardiac metastasis

In the right clinical setting, ST segment elevation (STE) on electrocardiogram (ECG) is most concerning for acute injury due to transmural myocardial ischemia. This frequently points to significant epicardial coronary artery disease, mandating emergent cardiac intervention. In rare cases, cardiac metastases may cause transient STE. We present a case of a 28-year-old male patient with metastatic osteosarcoma with STE in three different ECG territories over ten months. Several transient, dynamic patterns of STE were noted: anteroseptal leads concerning for acute injury with reciprocal ST depressions in inferior leads, lateral leads, inferior leads with reciprocal ST depression in lateral leads, followed by STE again in lateral leads. Given the patient's young age, absence of cardiac history or symptoms, personal preference, bleeding risk, and cancer prognosis, cardiac catheterization was never pursued. We present this case to remind providers to include metastatic cancer in the differential diagnosis of STE on ECG, and that these changes can be dynamic.

Pneumomediastinum and ST-Segment Elevation

Although acute myocardial infarction is the most clinically significant cause of ST-segment elevation, other serious clinical conditions have been reported with this electrocardiographic abnormality. We report a patient with pneumomediastinum who presented with dyspnea and electrocardiographic changes mimicking ST-segment elevation myocardial infarction. Coronary angiography demonstrated no evidence of myocardial injury and the electrocardiographic abnormality promptly resolved with the resolution of the pneumomediastinum.

Abnormal repolarization in the acute myocardial infarction patients: a frequency-based characterization

Despite ST elevation having poor sensitivity for acute myocardial infarction (AMI), it remains the main electrocardiographic (ECG) repolarization index for AMI diagnosis. Aim of the present study was to propose a new f99 index, defined as the frequency at which the repolarization normalized cumulative energy reaches 99%, for ECG AMI discrimination from health with good sensitivity and good specificity. Evaluation of such f99 index was performed on 12-standard-lead (I, II, III, aV1, aVr, aVf, V1 to V6) ECG recordings of 47 healthy controls and 108 acute myocardial infarction (AMI) patients. Repolarization dispersion caused f99 distributions to be significantly lead dependent. In most leads (leads I, II, aVl, aVr, V2-V6), f99 median value was lower in the healthy controls (10-17 Hz) than in the AMI patients (12-38 Hz) indicating higher frequency components (i.e. a more fragmented repolarization) in the latter population. AMI patients from healthy controls discrimination by f99, evaluated in terms of sensitivity (Se) and specificity (Sp), was also lead dependent. Single-lead analysis indicated leads I (Se=80%, Sp=77%) and aVl (Se=84%, Sp=74%) as optimal. Instead, lead-system analysis, performed to overcome dispersion issues, provided the best results when averaging over the 6 precordial leads (Se= 81% and Sp=74%). In conclusion, our new f99 index appears as a promising tool for non-invasively and reliably discriminate AMI patients from healthy subjects.

Recurrent intraoperative silent ST depression responding to phenylephrine

Intraoperative myocardial ischemia is attributed to decreased myocardial oxygen supply. We present an unusual case of recurrent, symptomless inferior wall ischemia in an apparently healthy male with no history of coronary artery disease after a spinal block. The recurring episodes were linked to tachycardia and presented with significant ST depression in Lead II with reciprocal elevation in lead aVL. The episodes responded to phenylephrine and subsided without residual sequelae.

Evolving considerations in the management of patients with left bundle branch block and suspected myocardial infarction

Patients with a suspected acute coronary syndrome and left bundle branch block (LBBB) present a unique diagnostic and therapeutic challenge to the clinician. Although current guidelines recommend that patients with new or presumed new LBBB undergo early reperfusion therapy, data suggest that only a minority of patients with LBBB are ultimately diagnosed with acute myocardial infarction, regardless of LBBB chronicity, and that a significant proportion of patients will not have an occluded culprit artery at cardiac catheterization. The current treatment approach exposes a significant proportion of patients to the risks of fibrinolytic therapy without the likelihood of significant benefit and leads to increased rates of false-positive cardiac catheterization laboratory activation, unnecessary risks, and costs. Therefore, alternative strategies to those for patients with ST-segment elevation myocardial infarction are needed to guide selection of appropriate patients with a suspected acute coronary syndrome and LBBB for urgent reperfusion therapy. In this article, we describe the evolving epidemiology of LBBB in acute coronary syndromes and discuss controversies related to current clinical practice. We propose a more judicious diagnostic approach among clinically stable patients with LBBB who do not have electrocardiographic findings highly specific for ST-segment elevation myocardial infarction.

ST elevation: telling pathology from the benign patterns

Benefits of early reperfusion in patients presenting with acute ST elevation myocardial infarction (STEMI) are well known. The American College of Cardiology / American Heart Association guidelines recommend triage decisions are made within 10 minutes of performing initial electrocardiogram (ECG). Since many patients presenting with ischemic symptoms may have ST elevation (STE) at baseline, not all STE signify transmural ischemia. Benign patterns can be easy to find in some cases. However, patients with benign STE at baseline (left ventricular hypertrophy, early repolarization pattern) may have ongoing ischemia and present with Non-ST elevation myocardial infarction (NSTEMI) or even STEMI superimposed on the benign pattern. The ability of clinicians to distinguish between ischemic and non ischemic STE varies widely and is affected by prevalence of such changes in patient population. More studies need to be done to delineate the criteria to clearly distinguish between ischemic and non ischemic ST elevation.

The use of a 4-step algorithm in the electrocardiographic diagnosis of ST-segment elevation myocardial infarction by novice interpreters

The electrocardiographic (ECG) diagnosis of ST-segment elevation myocardial infarction (STEMI) represents a challenge to all health care providers, particularly so for the novice ECG interpreter. We have developed--and present in this article--a 4-step algorithm that will detect STEMI in most instances in the prehospital and other nonemergency department (ED) settings. The algorithm should be used in adult patients with chest pain or equivalent presentation who are suspected of STEMI. It inquires as to the presence of ST-segment elevation as well as the presence of STEMI confounding/mimicking patterns; the algorithm also makes use of reciprocal ST-segment depression as an adjunct in the ECG diagnosis of STEMI. If STEMI is detected by this algorithm, then management decisions can be made based upon this ECG diagnosis. If STEMI is not detected using this algorithm, then we can only note that STEMI is not "ruled in"; importantly, STEMI is not "ruled out." In fact, more expert interpretation of the ECG will be possible once the patient (and/or the ECG) arrive in the ED where ECG review can be made with the more complex interpretation used by expert physician interpreters.

Differentiating ST-elevation myocardial infarction from nonischemic ST-elevation in patients with chest pain

Current guidelines state that patients with compatible symptoms and ST-segment elevation (STE) in ≥2 contiguous electrocardiographic leads should undergo immediate reperfusion therapy. Aggressive attempts at decreasing door-to-balloon times have led to more frequent activation of primary percutaneous coronary intervention (pPCI) protocols. However, it remains crucial to correctly differentiate STE myocardial infarction (STEMI) from nonischemic STE (NISTE). We assessed the ability of experienced interventional cardiologists in determining whether STE represents acute STEMI or NISTE. Seven readers studied electrocardiograms of consecutive patients showing STE. Patients with left bundle branch block or ventricular rhythms were excluded. Readers decided if, based on electrocardiographic results, they would have activated the pPCI protocol. If NISTE was chosen, readers selected from 12 possible explanations as to why STE was present. Of 84 patients, 40 (48%) had adjudicated STEMI. The percentage for which readers recommended pPCI varied (33% to 75%). Readers' sensitivity and specificity ranged from 55% to 83% (average 71%) and 32% to 86% (average 63%), respectively. Positive and negative predictive values ranged from 52% to 79% (average 66%) and 67% to 79% (average 71%), respectively. Broad inconsistencies existed among readers as to the chosen reasons for NISTE classification. In conclusion, we found wide variations in experienced interventional cardiologists in differentiating STEMI with a need for pPCI from NISTE.

Appropriate cardiac cath lab activation: optimizing electrocardiogram interpretation and clinical decision-making for acute ST-elevation myocardial infarction

During the last few decades, acute ST-elevation on an electrocardiogram (ECG) in the proper clinical context has been a reliable surrogate marker of acute coronary occlusion requiring primary percutaneous coronary intervention (PPCI). In 2004, the American College of Cardiology/American Heart Association ST-elevation myocardial infarction (STEMI) guidelines specified ECG criteria that warrant immediate angiography in patients who are candidates for primary PPCI, but new findings have emerged that suggest a reappraisal is warranted. Furthermore, as part of integrated and efficient STEMI systems, emergency department and emergency medical services providers are now encouraged to routinely make the time-sensitive diagnosis of STEMI and promptly activate the cardiac catheterization laboratory (Cath Lab) team. Our primary objective is to provide a practical summary of updated ECG criteria for emergency coronary angiography with planned PPCI, thus allowing clinicians to maximize the rate of appropriate Cath Lab activation and minimize the rate of inappropriate Cath Lab activation. We review the evidence for ECG interpretation strategies that either increase diagnostic specificity for "classic" STEMI and left bundle-branch block or improve diagnostic sensitivity in identifying 4 STEMI-equivalents: posterior MI, acute left main occlusion, de Winter ST/T-wave complex, and certain scenarios of resuscitated cardiac arrest.

Utilization of ST-segment deviation sum and change scores to identify acute myocardial infarction

OBJECTIVE

No information is currently available regarding the optimal cutoff values of the baseline ST-segment deviation sum (STDsum(baseline)) and 60-minute ST-segment deviation change (STDchange(60 min)) for predicting acute myocardial infarction (AMI).

METHODS

A retrospective study was performed in 783 admitted patients with chest pain who had suspected acute coronary syndrome and absence of left ventricular hypertrophy or bundle branch block on the initial electrocardiogram (ECG). The STDsum(baseline) was defined as the sum in millimeters (1 mm = 0.1 mV) of the absolute value of ST-segment deviations in all 12 leads at the initiation of continuous 12-lead ECG monitoring session. The STDchange(60 min) was defined as the absolute value of the difference between the baseline and 60-minute STDsum. Three cutoff values are reported and represent the smallest values in which the positive likelihood ratio (+LR) for AMI was greater than or equal to 5, 10, and 20, respectively.

RESULTS

Acute myocardial infarction occurred in 162 (20.7%) patients. The smallest cutoff value of the STDsum(baseline) for AMI with a +LR equal to or greater than 5, 10, and 20 was 9.6, 12.4, and 14.1 mm, respectively. In the subset of 699 patients without ST-segment elevation AMI on initial ECG, the smallest cutoff value of the STDchange(60 min) for AMI with a +LR equal to or greater than 5, 10, and 20 was 2.4, 3.5, and 7.9 mm, respectively.

CONCLUSIONS

Clinical studies need to be performed to determine if STDsum and STDchange, in conjunction with physician pretest probability of AMI, can be used to select patients who may benefit from emergent reperfusion therapy and other aggressive medical management strategies.

The Positive Predictive Value of Paramedic Versus Emergency Physician Interpretation of the Prehospital 12-Lead Electrocardiogram

BACKGROUND

Obtaining a prehospital 12-lead ECG may improve triage and expedite care of patients with acute myocardial infarction (AMI). Whether the ECG should undergo physician review prior to activation of a percutaneous intervention (PCI) team is unclear.

OBJECTIVE

To document the positive predictive value (PPV) of the prehospital 12-lead ECG when interpreted by paramedics versus emergency physicians.

METHODS

This was a prospective, observational study. In November 2003, our local health care and emergency medical services (EMS) systems implemented a prehospital "cardiac alert" program in which patients suspected of having ST-elevation myocardial infarction (STEMI) based on the prehospital 12-lead ECG were diverted away from receiving facilities without emergent PCI capability and the PCI team was mobilized. For the first year, a cardiac alert was activated by paramedics (Phase I). After the first year, the ECG was transmitted to the ED, with the emergency physician (EP) responsible for activation (Phase II). The PPV for cardiac alerts in Phases I and II were compared by using three different "gold standards": cardiologist interpretation of the prehospital 12-lead ECG, disposition to emergent PCI, and coronary lesions on angiography or arrest prior to emergent PCI.

RESULTS

A total of 110 patients were enrolled (54 in Phase I, 56 in Phase II). Cardiologist confirmation of a STEMI on the prehospital 12-lead EKG was 42/54 (78%) in Phase I and 54/56 (96%) in Phase II. Disposition to emergent PCI occurred in 38/54 (70%) Phase I patients and 51/56 (91%) Phase II patients. Lesions at catheterization or arrest prior to emergent PCI were observed in 41/54 (69%) of Phase I patients and 50/56 (89%) of Phase II patients. All of these comparisons achieved statistical significance (p < 0.01).

CONCLUSIONS

Transmission to the ED for EP interpretation improves the PPV of the prehospital 12-lead ECG for triage and therapeutic decision-making.

Differentiating ST elevation myocardial infarction and nonischemic causes of ST elevation by analyzing the presenting electrocardiogram

Guidelines recommend that patients with suggestive symptoms of myocardial ischemia and ST-segment elevation (STE) in > or =2 adjacent electrocardiographic leads should receive immediate reperfusion therapy. Novel strategies aimed to reduce door-to-balloon time, such as prehospital wireless electrocardiographic transmission, may be dependent on the interpretation accuracy of the electrocardiogram (ECG) readers. We assessed the ability of experienced electrocardiographers to differentiate among STE, acute STE myocardial infarction (STEMI), and nonischemic STE (NISTE). A total of 116 consecutive ECGs showing STE were studied. Fifteen experienced cardiologists were asked to decide, based on the ECG and assuming that the patient had compatible symptoms, whether they would send each patient for primary percutaneous coronary intervention (PPCI). If NISTE was chosen, the reader selected 1 or more 12 possible options to explain the choice. Of 116 patients, only 8 had STEMI. The percentage of ECGs for which PPCI was recommended for the patient by the individual readers varied widely (7.8% to 33%). There was no significant difference between the North American and Other Countries readers (p = 0.13). The sensitivity and specificity of the individual readers ranged from 50% to 100% (average 75%) and 73% to 97% (average 85%), respectively. There were broad inconsistencies among the readers in the chosen reasons used to classify NISTE. In conclusion, we found wide variations among experienced electrocardiographers in reading ECGs with STE and differentiating STEMI with need for PPCI from NISTE. There is a need to revise our current electrocardiographic criteria for differentiating STEMI from NISTE.

A Bayesian sensitivity analysis of out-of-hospital 12-lead electrocardiograms: implications for regionalization of cardiac care

BACKGROUND

The effectiveness of out-of-hospital regionalization of ST-elevation myocardial infarction (STEMI) patients to hospitals providing primary percutaneous coronary intervention depends on the accuracy of the out-of-hospital 12-lead electrocardiogram (PHTL). Although estimates of sensitivity and specificity of PHTL for STEMI have been reported, the impact of out-of-hospital STEMI prevalence on positive predictive value (PPV) has not been evaluated.

OBJECTIVES

To describe the relationship between varying population STEMI prevalences and PHTL predictive values, using ranges of PHTL sensitivity and specificity.

METHODS

The authors performed a Bayesian analysis using PHTL, where values for sensitivities (60%-70%), specificities (98%), and two prevalence ranges (0.5%-5% and 5%-20%) were derived from a literature review. PPV prediction intervals were compared with three months of prospective data from the Los Angeles County Emergency Medical Services Agency STEMI regionalization program.

RESULTS

When the estimated prevalence of STEMI in the out-of-hospital population is 5%-20%, the median PPV of the PHTL is 83% (95% credible interval [CrI] = 53% to 97%). However, if the population prevalence of STEMI is between 0.5% and 5%, the median PPV is 43% (95% CrI = 12% to 86%). When the PPV prediction intervals were incorporated with the Los Angeles County Emergency Medical Services Agency data, the PPV was 66%.

CONCLUSIONS

Even when assuming high specificity for PHTL, the false-positive rate will be considerable if applied to a population at low risk for STEMI. Before broadening application of PHTL to low-risk patients, the implications of a high false-positive rate should be considered.

Electrocardiographic abnormalities mimicking myocardial infarction in a patient with intracranial haemorrhage: a possible pitfall for prehospital thrombolysis

The electrocardiogram, when applied in the prehospital setting, has a significant effect on a patient with chest pain. The potential effect includes both diagnostic and therapeutic issues, including the diagnosis of acute myocardial infarction and the indication for thrombolysis or invasive procedures. We report the case of a man who suffered from a syncope, with a prehospital electrocardiogram showing prominent ST-segment elevation. Out-of-hospital thrombolytic therapy was planned by the emergency department. Fortunately, thrombolysis did not start because the patient fared worse. He was taken to the emergency department and, because of mental status impairment, it was decided to perform a cranial computed tomographic scan. The diagnosis shifted to a haemorrhagic stroke. According to the guidelines, prehospital thrombolysis would have been inappropriate in this case because the patient did not have any chest discomfort. The pathophysiological mechanisms of electrocardiographic abnormalities in the setting of intracranial haemorrhage are reviewed, as well as the issue of thrombolysis administered or planned only on the basis of an electrocardiogram.

Upwardly concave ST segment morphology is common in acute left anterior descending coronary occlusion

ST elevation (STE) in anterior precordial leads, in association with upwardly convex morphology (M) or straightM, is associated with anterior acute myocardial infarction (aAMI). Upwardly concaveM is characteristic of pseudoinfarction patterns such as early repolarization. A retrospective review was done of diagnostic electrocardiograms (EKG) of consecutive patients presenting to our Emergency Department (ED) who underwent emergent primary percutaneous intervention (PCI) and had proven left anterior descending (LAD) occlusion. If all leads from V2-V6 were upwardly concave, the EKG was classified as concaveM. If one lead was convex, the EKG had convexM. If no leads were convex and at least one was straight, it had straightM. Non-concaveM was defined as either convexM or straightM. Borderline STE was defined if the EKG did not have 2 consecutive leads with >or= 2 mm of STE. "Subtle," as opposed to "diagnostic," morphology was defined as concaveM without terminal QRS distortion. Data were analyzed with descriptive statistics. There were 37 patients identified who met the inclusion criteria and whose records were available for review. ConcaveM was found in 16 of 37 (43%), 4 with terminal QRS distortion. Measurements resulted in a classification of borderline STE in 15 of 37 (41%) (9 of whom had subtle morphology) for Rater 1 and 12 of 37 (32%) (7 of whom had subtle morphology) for Rater 2, while 19% to 24% had both "subtle" morphology and borderline ST elevation. ConcaveM, as compared with convexM or terminal QRS distortion, was associated with a shorter duration of symptoms (p < 0.05). It is concluded that concave morphology cannot be used to exclude STEMI with LAD occlusion. Many patients with LAD occlusion have borderline ST elevation with subtle morphology. Concave morphology is associated with a shorter duration of symptoms.

Regionalization of ST-segment elevation acute coronary syndromes care: putting a national policy in proper perspective

A uniform policy for regionalization of ST-segment elevation myocardial infarction (STEMI) care raises several concerns. Transferring all STEMI patients to obtain primary percutaneous coronary intervention (PCI) may be less effective than transferring only high-risk STEMI patients. Delays in time to treatment >60 min associated with transferring patients for primary PCI may result in increased mortality for the average patient as compared with providing immediate fibrinolytic therapy at their initial hospital; yet more than 95% of patients transferred for primary PCI in the U.S. exceed this 60-min benchmark. Superior outcomes associated with treatment at higher-volume regional STEMI centers are inconsistent among centers, and there is no direct evidence that patients will benefit by a transfer to a high-volume hospital from a low-volume hospital. Published data suggest as many as 800 PCI patients would need to be transferred to a high-volume PCI hospital to avoid a single death at a low-volume PCI hospital. Although European randomized trial data suggest transferring patients with STEMI for primary PCI may be superior to immediate fibrinolytic therapy, these findings are unlikely to generalize to the U.S. health care system given size, geography, and organization. ST segment elevation myocardial infarction care regionalization would require a massive redistribution of health care resources, depriving several hospitals of advanced cardiac care facilities, expertise, and associated revenue. Clearer evidence of the benefits and discussion of potential harms are needed before adopting a national STEMI regionalization policy.

ST Segment and T Wave Abnormalities Not Caused by Acute Coronary Syndromes

This article reviews the ST segment and T wave abnormalities seen in non-acute coronary syndrome (ACS) electrocardiograph presentations. Particular emphasis is placed on the distinction of these non-ACS syndromes from acute coronary syndrome related ST segment and or T wave change.

Acute coronary syndromes

Despite technologic advances in many diagnostic fields, the 12-lead ECG remains the basis for early identification and management of an acute coronary syndrome. This article reviews the use of the ECG in acute coronary syndromes.

Pre-hospital 12-lead electrocardiography programs: a call for implementation by emergency medical services systems providing advanced life support--National Heart Attack Alert Program (NHAAP) Coordinating Committee; National Heart, Lung, and Blood Institute (NHLBI); National Institutes of Health

Emergency medical services (EMS) providers who administer advanced life support should include diagnostic 12-lead electrocardiography programs as one of their services. Evidence demonstrates that this technology can be readily used by EMS providers to identify patients with ST-segment elevation myocardial infarction (STEMI) before a patient's arrival at a hospital emergency department. Earlier identification of STEMI patients leads to faster artery-opening treatment with fibrinolytic agents, either in the pre-hospital setting or at the hospital. Alternatively, a reperfusion strategy using percutaneous coronary intervention can be facilitated by use of pre-hospital 12-lead electrocardiography (P12ECG). Analysis of the cost of providing this service to the community must include consideration of the demonstrated benefits of more rapid treatment of patients with STEMI and the resulting time savings advantage shown to accompany the use of P12ECG programs.

Real-time paramedic compared with blinded physician identification of ST-segment elevation myocardial infarction: results of an observational study

The aim of the study were to determine if paramedics can accurately identify ST-segment elevation myocardial infarction (STEMI) on prehospital 12-lead (PHTL) electrocardiogram and to compare paramedic with blinded physician identification of STEMI. Paramedics identified definite STEMI, or possible acute myocardial infarction but not definite, and nondiagnostic. Two blinded readers (cardiologist and emergency physician) independently categorized each PHTL. A third reviewer assigned final diagnoses and determined whether the PHTL met STEMI criteria. One hundred sixty-six PHTL were acquired over an 8-month period. Fifteen were excluded from analysis. Sixty-two percent of the patients (94/151) were male, mean age was 61.1 years (+/-14.8 SD, range 20-92 years), and 81% had chest pain. Twenty-five patients (16.6%; 95% confidence interval [CI], 11%-23.5%) had confirmed STEMI and 16 (10.6%) had confirmed non-STEMI acute myocardial infarction. Paramedic sensitivity was 0.80 (95% CI, 0.64-0.96); specificity was 0.97 (95% CI, 0.94-1.00) with positive likelihood ratio of 25.2 and negative likelihood ratio of 0.21. Overall accuracy was similar for paramedic and physician reviewers (0.94, 0.93, 0.95). Highly trained paramedics in an urban emergency medical services system can identify patients with STEMI as accurately as blinded physician reviewers.

Disagreement in the interpretation of electrocardiographic ST segment elevation: a source of error for emergency physicians?

Evaluation of the electrocardiogram (ECG) is a complex, subjective process with the potential for interobserver disagreement. The objective of this study was to determine the ECG patterns with discrepant interpretations, the rates of disagreement in the determination of both the presence of ST segment elevation (STE) and morphology. ECGs were reviewed in a retrospective fashion by attending EPs for STE and waveform morphology. Those ECGs that were interpreted in a discrepant fashion were then analyzed to detect patterns of disagreement. ECGs from 599 patients were reviewed. Two hundred eleven patients (35.2% of the total patient population surveyed) had STE as determined by at least one attending EP; 40 (19% of the STE population) patients had STE determined by 1 EP, 21 (10% of the STE population) patients by 2 EPs, and 150 (71% of the STE population) patients by 3 EPs. The STE of 61 (28.9%) ECGs were interpreted in a discrepant fashion. The average STE was 1.31 mm per lead for ECGs with disagreement and 2.93 mm per lead for ECGs with agreement (P<.05). ECGs with reciprocal ST depression were more likely to have agreement with regard to the STE (P<.05). Fourteen ECGs (8.2% of 171 ECGs with STE determined by at least 2 EPs) had ST segment morphology interpreted in a discrepant fashion. Disagreement in the determination of electrocardiographic ST segment elevation by EPs occurs frequently and is related to the amount of STE present on the ECG. Electrocardiographic patterns responsible for this interpretive disagreement of ST segment elevation can represent an unfortunate but potentially predictable source of error in emergency medical care.

Electrocardiographic ST segment elevation: a comparison of AMI and non-AMI ECG syndromes

Chest pain (CP) patients presenting to the ED may manifest electrocardiographic ST segment elevation (STE). AMI (acute myocardial infarction) is a less frequent cause of such abnormality and one of many patterns responsible for ST segment elevation in ED CP patients. We performed a retrospective comparative review of the electrocardiographic features of various STE syndromes, focusing on differences between AMI and non-AMI syndromes. The electrocardiograms (ECGs) of consecutive ED adult CP patients (with 3 serial troponin I determinations) were interpreted by 3 attending emergency physicians. These ECGs with STE represented the study population used for analysis. Various electrocardiographic features such as STE, ST segment depression (STD), STE morphology, anatomic distribution of STE, and the number of leads with STE were recorded; derived values such as total STE, total ST segment deviation, and average STE per lead were calculated. Interobserver reliability concerning STE morphology was determined. AMI was diagnosed by abnormal serum troponin I values (>0.1 mg/dL) followed by a rise and fall of the serum marker; STE diagnoses of non-AMI causes were determined by medical record review. Five hundred ninety-nine CP patients were entered in the study with 212 (35%) individuals showing STE, 55 (26%) with electrocardiographic AMI and 157 (74%) with non-AMI electrocardiographic syndromes. Anatomic location within the AMI group included 32 inferior and inferior variants, 18 anterior and anterior variants, and 5 lateral; non-AMI anatomic locations included 56 inferior and inferior variants, 98 anterior and anterior variants, and 3 lateral; anterior STE occurred significantly more often in non-AMI syndromes. Total STE was 15.3 mm in AMI patients and 7.4 mm in non-AMI patients (P =.0004). The number of leads with STE was not significantly different between the two groups, 3.4 mm in AMI and 4.1 in non-AMI syndromes. ST segment elevation per lead was not significantly different in the 2 groups, 4.4 mm in AMI versus 1.8 mm in non-AMI syndromes. Total ST segment deviation (sum of STE and STD) was significantly greater in AMI syndromes, 17.8 mm in AMI compared with 10.5 mm in non-AMI syndromes (P =.00009). The presence of STD occurred at statistically similar rates in both groups. The morphology of the STE occurred in significantly different rates between AMI and non-AMI patterns, concave more often in non-AMI patterns (P <.00001) and nonconcave more often in AMI (P <.00001). Non-AMI causes of STE account for the majority of electrocardiographic syndromes encountered in ED chest pain patients. These findings alone are not adequate to determine the electrocardiographic cause of the ST segment elevation in chest pain patients. When determining AMI versus non-AMI with the ECG, these various findings should be used in the consideration of the overall clinical picture (history, examination, and electrocardiogram) in chest pain patients with ST segment elevation.

The electrocardiographic differential diagnosis of ST segment depression

The importance of the electrocardiographic differential diagnosis of ST segment depression in patients presenting with acute chest pain is discussed.

Reciprocal ST segment depression: impact on the electrocardiographic diagnosis of ST segment elevation acute myocardial infarction

Acute myocardial infarction (AMI) is one of many causes of electrocardiographic ST segment elevation (STE) in ED chest pain (CP) patients; at times, the electrocardiographic diagnosis may be difficult. Coexistent ST segment depression has been reported to assist in the differentiation of non-infarction causes of STE from AMI-related ST segment elevation. The objective was to determine the effect of AMI diagnosis on the presence of STD among ED CP patients with electrocardiographic STE. Adult CP patients with electrocardiographic STE in at least 2 anatomically distributed leads were reviewed for the presence or absence of ST segment depression in at least 1 lead and separated into 2 groups, both with and without ST segment depression. A comparison of the 2 groups was performed in 2 approaches: all STE patients and then only with STE patients who lacked confounding electrocardiographic pattern (bundle branch block [BBB], left ventricular hypertrophy [LVH], or right ventricular paced rhythm [VPR]). All patients in the study underwent prolonged observation in the ED (at least 8 hours) with 3 serial troponin T determinations and 3 electrocardiograms (ECG). AMI was diagnosed by abnormal serum troponin T values (>0.1 mg/dL); electrocardiographic STE diagnoses of non-AMI causes were determined by medical record review. There were 171 CP patients with STE were entered in the study with 112 (65.5%) individuals show ST segment depression. When considering all study patients, ST segment depression was present at statistically equal rates in AMI and non-AMI situations (P = NS). The sensitivity, specificity, positive predictive value, and negative predictive value for the electrocardiographic diagnosis of AMI were 63%, 34%, 30%, and 67%, respectively. Patients with confounding patterns (LVH 46, BBB 19, and VPR 6) were removed from the analysis group, leaving 100 patients for analysis; 38 of these patients had ST segment depression. When considering this group of study patients, ST segment depression was present significantly more often in AMI patients (P <.0001). The sensitivity, specificity, positive predictive value, and negative predictive value for the electrocardiographic diagnosis of AMI were 69%, 93%, 93%, and 71%, respectively. Clinical diagnoses were as follows: 56 AMI, 50 USAP, and 65 noncoronary syndrome. When all CP patients with electrocardiographic STE are considered, the presence of ST segment depression is not helpful in distinguishing AMI from non-AMI. If one considers only patterns which lack electrocardiographic ST segment depression caused by altered intraventricular conduction, the presence of ST segment depression strongly suggests the diagnosis of AMI. In these cases, reciprocal ST segment depression is of considerable value in establishing the electrocardiographic diagnosis of STE AMI.

Recognition of ST elevation by paramedics

OBJECTIVE

To define the ability of UK paramedics to recognise ST segment elevation using a prehospital 12 lead electrocardiogram (ECG).

METHODS

Analysis of the diagnostic ability of seven paramedics 12 months after a two day training course, using interpretation of a 12 lead ECG by two cardiologists as the criterion standard. Comparison of paramedic and A&E SHO diagnosis to determine accuracy, specificity, sensitivity, negative predictive value, and positive predictive value of paramedic interpretation.

RESULTS

Paramedics showed a median accuracy of 0.95 (95% CI 0.88 to 0.98), a specificity of 0.91 (95% CI 0.53 to 1.0), a sensitivity of 0.97 (95% CI 0.94 to 0.99), a NPV of 0.77 (95% CI 0.62 to 0.92) and a PPV of 0.99 (95% CI 0.92 to 1.0). This was not significantly different from a group of experienced A&E SHOs.

CONCLUSIONS

UK paramedics can recognise ST elevation using a 12 lead ECG. Radio transmission of an ECG may not be necessary to pre-alert the hospital.

Electrocardiographic ST-segment elevation: the diagnosis of acute myocardial infarction by morphologic analysis of the ST segment

Acute myocardial infarction (AMI) is one of many causes of ST-segment elevation (STE) in emergency department (ED) chest pain (CP) patients. The morphology of STE may assist in the correct determination of its cause, with concave patterns in non-AMI syndromes and non-concave waveforms in AMI.

OBJECTIVES

To determine the impact of STE morphologic analysis on AMI diagnosis and the ability of this technique to separate AMI from non-infarction causes of STE.

METHODS

The electrocardiograms (ECGs) of consecutive ED adult CP patients (with three serial troponin I determinations) were interpreted in two-step fashion by six attending emergency physicians (EPs): 1) the determination of STE by three EPs followed by 2) STE morphologic analysis (either concave or non-concave) in those patients with STE. The impact of STE morphology analysis was investigated in the identification of AMI and non-AMI causes of STE. Acute myocardial infarction was diagnosed by abnormal serum troponin I values (>0.1 mg/dL) followed by a rise and fall of the serum marker; STE diagnoses of non-AMI causes were determined by medical record review. Interobserver reliability concerning STE morphology was determined. Study inclusion criteria included at least three troponin values performed in serial fashion no more frequently than every three hours, initial ED ECG, ED diagnosis, and final hospital diagnosis.

RESULTS

Five hundred ninety-nine CP patients were entered in the study, with 171 (29%) individuals having STE on their ECGs. Of the 171 patients who had STE, 56 had AMI, 50 had unstable angina pectoris (USAP), and 65 had non-coronary final diagnoses. Forty-nine patients had non-concave STE, 46 with AMI and three with USAP; no patient with a non-coronary diagnosis had a non-concave STE morphology. The sensitivity and specificity of the non-concave STE morphology for AMI diagnoses were 77% and 97%, respectively; the positive and negative predictive values for non-concave morphology in AMI diagnoses were 94% and 88%, respectively. Interobserver reliability in the STE morphology determination revealed a kappa coefficient of 0.87.

CONCLUSIONS

A non-concave STE morphology is frequently encountered in AMI patients. While the sensitivity of this pattern for AMI diagnosis is not particularly helpful, the presence of this finding in adult ED chest pain patients with STE strongly suggests AMI. This technique produces consistent results among these EPs.

Electrocardiographic ST segment depression

Traditionally, ST segment depression has been associated with acute coronary syndromes; this electrocardiographic pattern may also be found in patients with nonischemic events, such as left bundle branch block (LBBB), left ventricular hypertrophy (LVH), and those with therapeutic digitalis levels. Using the ECG as an adjunct in distinguishing those patients with acute coronary syndromes from those with more "benign," nonacute causes of STSD will obviously lead to divergent treatment and management plans. The following cases illustrate the use the ECG in patients presenting with chest pain and electrocardiographic ST segment depression attributable to an ACS, LVH, LBBB, or digitalis.

Accuracy and clinical effect of out-of-hospital electrocardiography in the diagnosis of acute cardiac ischemia: a meta-analysis

STUDY OBJECTIVE

We sought to evaluate quantitatively the evidence on the diagnostic performance of out-of-hospital ECG for the diagnosis of acute cardiac ischemia (ACI) and acute myocardial infarction (AMI) and the clinical effect of out-of-hospital thrombolysis.

METHODS

We conducted a systematic review and meta-analysis of the English-language literature published between 1966 and December 1998 on the diagnostic accuracy of out-of-hospital ECG and the clinical effect of out-of-hospital thrombolysis. Both prospective and retrospective studies qualified for the assessment of diagnostic performance. For clinical effect, data from prospective nonrandomized studies were synthesized separately from data from randomized trials. Diagnostic performance was assessed by using estimates of test sensitivity, specificity, and diagnostic odds ratios and was summarized by using summary receiver-operating characteristic curves. Measures of clinical effect included time savings, early ventricular function, early mortality, and long-term survival.

RESULTS

Diagnostic accuracy was evaluated in 11 studies with a total of 7,508 patients. Data were available for ACI in 5 studies and for AMI in 8 studies. For ACI, the random-effects pooled sensitivity was 76% (95% CI, 54% to 89%), the specificity was 88% (95% CI, 67% to 96%), and the diagnostic odds ratio was 23 (95% CI, 6.3 to 85). The respective figures for AMI were sensitivity of 68% (95% CI, 59% to 76%), specificity of 97% (95% CI, 89% to 92%), and diagnostic odds ratio of 104 (95% CI, 48 to 224). Both in nonrandomized (n=4, total 1,531 patients) and randomized (n=9, total 6,643 patients) studies, out-of-hospital thrombolysis shortened the time from onset of symptoms to thrombolytic treatment by 40 to 60 minutes. Data on short-term ejection fraction were sparse. Hospital mortality was reduced by 16% (95% CI, 2% to 27%) among randomized trials, and a similar estimate of effect was seen in nonrandomized studies. There was no clear effect on long-term mortality, but data were sparse.

CONCLUSION

Out-of-hospital ECG has excellent diagnostic performance for AMI and very good performance for ACI. Out-of-hospital thrombolysis achieves time savings and improves short-term mortality, but the effect on long-term mortality is unknown.

Differences in management and outcomes of acute myocardial infarction among four general hospitals in Japan

OBJECTIVE

To ascertain the differences among hospitals in Japan in the management patterns and outcomes of patients with acute myocardial infarction (AMI).

DESIGN

Retrospective cohort study by means of patient chart review.

SETTING

Four tertiary-care teaching hospitals in Japan observed over a 1-year period.

STUDY PARTICIPANTS

Consecutive patients (N=482) admitted for AMI.

MAIN OUTCOME MEASURES

Clinical characteristics, rates of diagnostic and therapeutic procedures performed, cardiac complications, and length of stay.

RESULTS

Patients' clinical characteristics differed significantly among the four hospitals in terms of age, gender, and prior cardiac history, but not in terms of comorbidity or infarct location. The frequency and type of diagnostic and therapeutic procedures were different, and in-hospital mortality varied (4-14%, P=0.022). Average length of hospital stay ranged from 15.8+/-12.6 days to 41.0+/-19.4 days (P=0.0001). After adjustment for the clinical characteristics, these differences remained significant among hospitals.

CONCLUSION

Considerable differences in the management and outcomes of patients with AMI exist in Japan.

Comparison of an automated thrombolytic predictive instrument to both diagnostic software and an expert cardiologist for diagnosis of an ST elevation acute myocardial infarction

Because the electrocardiograms (ECGs) of patients with symptoms suggesting an acute thrombotic coronary occlusion are typically read by physicians relatively inexperienced in this skill, it is important to develop automated decision support. A Thrombolytic Predictive Instrument (TPI) is now available along with the standard diagnostic software in a commercially available electrocardiograph. This study evaluates the performance of the predictive software in comparison to both an expert cardiologist and standard diagnostic software. True sensitivity and specificity cannot be determined because acute coronary angiography was not performed. The specificities determined by this study were excellent (98% and 99%), and the sensitivities were very good (72% and 78%). These results that the TPI will be only rarely applied to patients who do not indeed have an acute coronary thrombosis. However, the reasons for even this small number of presumably falsely TPI positive patients should be determined and analyzed. It is unlikely that alterations of the thresholds for TPI activation will significantly improve on this very good level of sensitivity, without prohibitively decreasing specificity.

ELECTROCARDIOGRAPHIC DIAGNOSIS OF ACUTE MYOCARDIAL INFARCTION

The widely recognized benefits of early diagnosis and treatment of acute myocardial infarction (AMI) have only emphasized the importance of emergency physician (EP) competence in electrocardiographic interpretation. As such, the EP must be an expert in the interpretation of the electrocardiogram (ECG) in the emergency department chest pain center patient. The ECG is a powerful clinical tool used in the evaluation of patients, assisting in making the diagnosis of AMI and other syndromes, selecting appropriate therapies (including thrombolysis and primary angioplasty), securing the location of an adequate inpatient disposition, and predicting the risk of cardiovascular complications and death. This article will discuss the appropriate uses of the ECG in the patient with possible or confirmed AMI and review the typical electrocardiographic findings of AMI, diagnostically confounding patterns, mimickers of infarction, and new techniques.

Can myocardial infarction be rapidly identified in emergency department patients who have left bundle-branch block?

STUDY OBJECTIVES

Fibrinolytic therapy is recommended for patients who have chest pain and left bundle-branch block (LBBB). However, the presence of baseline ECG abnormalities makes early accurate identification of acute myocardial infarction (AMI) difficult. The predictive ability of clinical and ECG variables for identifying patients with LBBB and AMI has not been well studied. We sought to determine the prevalence and predictors of myocardial infarction among patients presenting to the emergency department with LBBB on the initial ECG who were evaluated for myocardial infarction.

METHODS

All patients presenting to the ED were prospectively risk stratified on the basis of clinical and historical variables. ECGs from patients with LBBB were compared retrospectively with previously published criteria for identification of AMI. The ability of a new LBBB to predict AMI was also determined.

RESULTS

Twenty-four (13%) of the 182 patients with LBBB had AMI. Clinical and historical variables were similar in patients with and without AMI. A new LBBB had a sensitivity of 42% and a specificity of 65%. The presence of concordant ST-segment elevation or depression had specificities and positive predictive values of 100%; however, sensitivities were only 8% and 17%, respectively. The best diagnostic criterion was the presence of concordant ST-segment elevation or depression on the ECG or an initially elevated creatine kinase MB (sensitivity, 63%; specificity, 99%).

CONCLUSION

ECG criteria for identifying patients with AMI and LBBB identify only a small minority of patients with AMI. Treating all patients with LBBB and chest pain with fibrinolytics would result in treatment of a significant number of patients without AMI.

Electrocardiographic ST-segment elevation: correct identification of acute myocardial infarction (AMI) and non-AMI syndromes by emergency physicians

OBJECTIVE

To determine the emergency physician's (EP's) ability to identify the cause of ST-segment elevation (STE) in a hypothetical chest pain patient.

METHODS

Eleven electrocardiograms (ECGs) with STE were given to EPs; the patient in each instance was a 45-year-old male with a medical history of hypertension and diabetes mellitus with the chief complaint of chest pain. The EP was asked to determine the cause of the STE and, if due to acute myocardial infarction (AMI), to decide whether thrombolytic therapy (TT) would be administered (the patient had no contraindication to such treatment). Rates of TT administration were determined; appropriate TT administration was defined as that occurring in an AMI patient, while inappropriate TT administration was defined as that in the non-AMI patient.

RESULTS

Four hundred fifty-eight EPs completed the questionnaire; levels of medical experience included the following: postgraduate year 2-3, 193 (42%); and attending, 265 (58%). The overall rate of correct interpretation of the study ECGs was 94.9% (4,782 correct interpretations out of 5,038 instances). Acute myocardial infarction with typical STE, ventricular paced rhythm, and right bundle branch block were never misinterpreted. The remaining conditions were misinterpreted with rates ranging between 9% (left bundle branch block, LBBB) and 72% (left ventricular aneurysm, LVA). The overall rate of appropriate thrombolytic agent administration was 83% (1,525 correct administrations out of 1,832 indicated administrations). The leading diagnosis for which thrombolytic agent was given inappropriately was LVA (28%), followed by benign early repolarization (23%), pericarditis (21%), and LBBB without electrocardiographic AMI (5%). Thrombolytic agent was appropriately given in all cases of AMI except when associated with atypical STE, where it was inappropriately withheld 67% of the time.

CONCLUSIONS

In this survey, EPs were asked whether they would give TT based on limited information (ECG). Certain syndromes with STE were frequently misdiagnosed. Emergency physician electrocardiographic education must focus on the proper identification of these syndromes so that TT may be appropriately utilized.