Benign early repolarization: Electrocardiographic manifestations and differentiation from other ST segment elevation syndromes

Diagnostics

Benign Early Repolarization: Electrocardiographic Manifestations and Differentiation From Other ST Segment Elevation Syndromes WILLIAM J. BRADY, MD Early repolarization, also known as benign early repolarization (BER) or normal variant, is noted in approximately 1% of the population and in up to 48% of patients seen in the emergency department with chest pain. BER represents a benign variant of the normal electrocardiogram and is one of several syndromes producing electrocardiographic ST segment elevation. BER electrocardiographically includes diffuse or widespread ST segment elevation, upward concavity of the initial portion of the ST segment, notching or slurring of the terminal QRS complex, and concordant T waves of large amplitude. This article focuses on BER and includes a discussion of the electrocardiographic tools useful in making this diagnosis and in distinguishing BER from other ST segment elevation syndromes. (Am J Emerg Med 1998;16:592-597. Copyright © 1998 by W.B, Saunders Company) Approximately 2% of emergency department (ED) visits are for the chief complaint of chest pain. i-3 Depending on the patient population surveyed, approximately 20% of these patients will be experiencing an acute myocardial infarction (AMI). 4,5 The rapid and accurate diagnosis of AMI is a formidable challenge for the emergency physician. Patients presenting to the ED with acute chest pain potentially of ischemic origin are evaluated with three principle tools: the history of the event, the 12-lead electrocardiogram (ECG), and cardiac serum markers. The ECG is a powerful clinical tool in the evaluation of such patients and assists the physician in the selection of the proper therapy, in particular the application of treatment aimed at coronary reperfusion. 6 From the perspective of the acute coronary ischemic event, various electrocardiographic findings suggest the urgent consideration of certain evaluation and management strategies. In particular, ST segment elevation may indicate transmural AMI and remains an important criterion for the

From the Department of Emergency Medicine and Internal Medicine, University of Virginia Health Sciences Center, Charlottesville, VA. Manuscript received July 22, 1997; accepted August 1, 1997. Address reprint requests to Dr Brady, Department of Emergency Medicine, Box 523-21, University of Virginia Health Sciences Center, Charlottesville, VA 22906-0114. Key Words: Benign early repolarization, early repolarization, normal variant, ST segment, ST segment elevation, electrocardiogram. Copyright © 1998 by W.B. Saunders Company 0735-6757/98/1606-0011 $8.00/0 592

potential initiation of thrombolytic therapy, primary angioplasty, and/or other pharmacologic interventions. 7 ST segment elevation, however, is not a sensitive marker of AMI. 8 Numerous other noninfarction syndromes that occur in the chest pain patient will manifest ST segment elevation on the ECG (Figure 1, Table 1). Certain patterns, such as left bundle branch block (LBBB), left ventricular hypertrophy, and left ventricular aneurysm, occur with increased frequency in patients with known coronary artery disease; these patterns may confound the ED evaluation by mimicking AMI with ST segment elevation on the ECG. Other patterns, such as benign early repolarization (BER) and acute pericarditis, are not necessarily associated with ischemic heart disease, although they may resemble acute infarction ST segment waveforms. One prehospital study of adult chest pain patients found that the majority of patients manifesting ST segment elevation on the ECG did not have AMI as a final hospital diagnosis; left ventricular hypertrophy and LBBB followed by other syndromes such as BER accounted for the majority of the cases. 9 Among adult ED chest pain patients, ST segment elevation was encountered in 22% of cases. AMI infrequently was the cause of this ST segment elevation and was the final hospital diagnosis in only 15% of this population. BER was encountered almost as often as AMI (13%) (unpublished data). Furthermore, Miller et aP ° found that in patients admitted to the coronary intensive care unit with presumed AMI, ST segment elevation was diagnostic for acute infarct in only half of patients with a history of ischemic heart disease; LVA left ventricular aneurysm and other such ST segment elevation, non-AMI syndromes were responsible for the ST segment abnormalities resembling acute infarction in this patient group. These syndromes causing ST segment elevation not related to AMI are not infrequently misdiagnosed as acute infarction, which then may subject the patient to unnecessary and potentially dangerous therapies and procedures. For example, a report by Sharkey et al xa noted that 11% of patients receiving thrombolytic agents were not experiencing AMI. The electrocardiographic syndromes producing this pseudo-infarct ST segment elevation included BER (30%), left ventricular hypertrophy (30%), and various intraventricular conduction abnormalities (30%).

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farction syndrome, the correct diagnosis must be made not only to offer appropriate management for that particular illness but also to avoid the incorrect application of potentially dangerous therapies such as thrombolysis. The following discussion focuses on one such n o n - A M I cause of ST segment elevation BER--- and includes description of the electrocardiographic tools useful in making this diagnosis and in distinguishing B E R from other syndromes.

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CASE PRESENTATIONS Case 1

e

f

FIGURE 1. Various syndromes causing ST segment elevation with electrocardiographic examples: (a) benign early repolarization; (b) acute myocardial infarction; (c) acute myocardial infarction; (d) acute pericarditis (stage I); (e) left ventricular hypertrophy; (f) left bundle branch block; and (g) left ventricular aneurysm. Note the concave nature of the initial, up-sloping portion of the ST segment-T wave complex in the non-AMI examples (a, d, e, f, and g), compared with either the convex (b) or the flat (c) morphologies in the AMI cases. The widely recognized befits of early diagnosis and rapid revasculafization treatment o f A M I have only emphasized importance of emergency physician competence in electrocardiographic interpretation. The emergency physician, frequently the first physician to evaluate such chest pain patients, is charged with the responsibility of rapid, accurate diagnosis followed by appropriate therapy delivered expeditiously. In the case of A M I with ST segment elevation on the ECG, revascularization treatments and other therapies should be considered. In the instance of the chest pain patient demonstrating ST segment elevation resulting from a nonin-

TABLE1. Causes of ST Segment Elevation Cardiac Acute myocardial infarction Variant (Prinzmetal's) angina Acute pericarditis Left ventricular aneurysm Left ventricular hypertrophy Bundle branch blocks (LBBB, RI3BB, NSIVCD) Early repolarization Metabolic Hyperkalemia Hypothermia (Osborne or "J" waves) Hyperventilation Miscellaneous Acute abdominal disorders (pancreatitis, cholecystitis, peritonitis) Central nervous system hemorrhage Medications (type I anti-arrhythmic agents, isoproterenol) Body habitus Idiopathic ABBREVIATIONS:LBI3B, left bundle branch block; RBBB, right bundle branch block; NSIVCD, nonspecific intraventricular conduction delay.

A 39-year-old man without medical history presented to the ED with left chest pain that had appeared approximately 2 weeks earlier. The pain, intermittent in occurrence, was worse with inspiration and with upper extremity movement; no associated symptoms were noted. The physical examination was normal; no chest wall tenderness was found. A 12-lead ECG (Figure 2) revealed normal sinus rhythm with widespread ST segment elevation, believed to be consistent with BER. The patient's pain spontaneously resolved before any medical therapy. The patient was admitted to the ED-based chest pain center and underwent a "rule-out myocardial infarction" protocol with serial cardiac enzyme and ECG analysis, which did not reveal myocardial infarction; the repeat ECGs did not demonstrate change. Further, an ECG obtained 2 years earlier during a routine examination showed similar findings. The patient underwent a nuclear stress test, which was normal; he was discharged with a diagnosis of chest pain of unclear etiology and was doing well at follow-up.

Case 2 A 42-year-old man with a history of cocaine abuse presented via ambulance to the ED with dyspnea and substernal chest pain. He had recently smoked approximately 1 gram of cocaine. The examination revealed a middle-aged patient in considerable distress, clutching his chest; the remainder of the examination was unremarkable. A 12-lead ECG (Figure 3) demonstrated sinus rhythm with ST segment elevation. The patient received sublingual nitroglycerin and intravenous lorazepam. Serial ECGs were performed, every 3 to 5 minutes, which did not show change. With the above medications, the patient's pain resolved after approximately 15 minutes. He was admitted to the chest pain center with a "rule out myocardial infarction" protocol. No further pain was noted; the serial enzyme levels and ECGs did not demonstrate ischemia or infarction. The initial and serial ECGs were believed to represent BER. The patient was discharged from the ED against medical

FIGURE 2. A 12-lead ECG revealing normal sinus rhythm with widespread ST segment elevation noted in the anterior (V2-V4), lateral (V5 and V6), and inferior leads (II, III, aVF). The ST segment elevation is characterized by initial concavity in all leads. Prominent T waves were also encountered across the precordium. J point irregularity was seen in the inferior distribution. No ST segment depression (reciprocal change) was noted. The electrocardiographic findings were believed to represent BER.

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DISCUSSION

FIGURE 3. A 12-lead ECG demonstrating sinus rhythm with ST segment elevation in inferior (II, III, aVF) and anterolateral (V2 through V6) leads as well as notching of the J point and prominent T waves. The leads with ST segment elevation all demonstrate a concavity to the initial, up-sloping portion of the ST segment-T wave complex. The ECG suggests BER. Serial ECGs did not reveal evolution of the ST segment elevation; comparison with a past ECG revealed similar ST segment waveforms. advice before performance of a stress test. He did return to the cardiology clinic for a scheduled follow-up evaluation approximately 2 weeks later, and had a negative nuclear stress test.

Case3 A 38-year-old man who was a long-distance runner presented to the ED with chest pain of 2 hours' duration. The chest discomfort was described as left-sided in location, "sharp" in quality, and worse with inspiration. The physical examination was unremarkable; chest wall tenderness partially reproduced the patient's pain. A 12-lead ECG (Figure 4) revealed ST segment elevation in multiple leads. The findings on the ECG were believed to represent BER. The patient was discharged from the ED with recommended follow-up with his physician for musculoskeletal chest pain. At follow-up, the patient appeared well; a nuclear stress test did not reveal evidence of ischemic heart disease.

FIGURE 4. A 12-lead ECG demonstrating ST segment elevation in leads V2 through V6 (anterior) and in leads II, III, and aVF (inferior); the ST segment elevation ranged from 2 to 4 mm in the anterior distribution while the elevation was less pronounced in the inferior area (1 to 2 ram). The leads with ST segment elevation all demonstrate a concavity to the initial, up-sloping portion of the ST segment-T wave complex. Additionally, notching or irregularity of the J point was observed in several leads including leads II, III, aVF, V4, Vs, and V6. The T waves in the mid to right precordial leads were also prominent, potentially suggestive of the hyperacute T wave. Reciprocal ST segment depression was not noted on this ECG. The findings on the ECG were believed to represent BER.

The syndrome of benign early repolarization, first described in 1936 by Shipley and Hallaran, 12 is considered to be a normal variant, not indicative of underlying cardiac disease. BER electrocardiographically includes diffuse or widespread ST segment elevation, upward concavity of the initial portion of the ST segment, notching or slurring of the terminal QRS complex, and symmetric, concordant T waves of large amplitude. 13 BER has been reported in men and women of all age groups and in people of varying ethnic backgrounds. The general population will have early repolarization on the ECG in approximately 1% of cases. 14 Young military recruits demonstrate BER in 1% to 2% of individuals15; it is also a common finding in athletes. 16 Among adult ED chest pain patients, BER is seen at an increased frequency and is encountered in 13% of such cases (unpublished data). Hollander et ally noted that BER is seen on ECGs in 23% to 48% of adult ED chest pain patients who have used cocaine. In a large population-based study, the mean age of patients with BER was 39 years, with a range of 16 to 80; it was seen predominantly in patients younger than 50 years of age and rarely encountered in individuals older than 70 years (3.5%).14 Men manifest BER significantly more often than women. 14 This electrocardiographic pattern has been reported in Japanese, Indians, Africans, and American black and whites. 24 For unknown reasons, BER is more often encountered in black men from the ages of 20 to 40 years, 18 although other authors have disputed such a tendency in black Americans. 14 The physiologic basis for this electrocardiographic normal variant is poorly understood and is a subject of ongoing controversy. 19 Suggested mechanisms of BER include early repolarization of the subepicardium, relatively earlier repolarization of the anterior wall of the left ventricle compared to the posterior wall, regional differences in sympathetic tone, and sympathetic-parasympathetic tone imbalances. 21-2~ The term "early repolarization," however, may be a misnomer from the electrophysiologic perspective. An investigation by Mirvis 19 found no increase in the temporal overlap between termination of ventricular depolarization and onset of repolarization the theoretical basis of B E R - - i n "variant" subjects compared with "normal" patients. The ST segment of the cardiac electrical cycle represents the period between depolarization and repolarization of the left ventricle. In the normal state, the ST segment is isoelectric, meaning that it is neither elevated nor depressed relative to the TP segment. The electrocardiographic definition of BER (Figure 5, Table 2) includes the following characteristics: (1) ST segment elevation; (2) upward concavity of the initial portion of the ST segment; (3) notching or slurring of the terminal QRS complex; (4) symmetric, concordant T waves of large amplitude; (5) widespread or diffuse distribution of ST segment elevation on the ECG; and (6) relative temporal stability. I3 The ST segment elevation begins at the " J " (or junction) point--the portion of the electrocardiographic cycle where the QRS complex ends and the ST segment begins (Figure 6A). The degree of J point elevation is usually less than 3.5 ram. 14 This ST segment elevation morphologically appears as if the ST segment has been evenly lifted upwards from the isoelectric

WILLIAM J. BRADY • EARLY REPOLARIZATION

FIGURE 5. Representative examples of electrocardiographic complexes depicting BER. All three complexes demonstrate ST segment elevation with elevation of the J point. The initial portion of the ST segment-T wave complex is concave. The ST segments of BER appear to have been lifted evenly off the baseline, thereby preserving the normal upward concavity of the J point. The actual J point may demonstrate either smooth or notched contours--these examples all are smooth (see Figure 6B for an example of a notched J point). baseline at the J point. 13 This elevation results in a preservation of the normal concavity of the initial, up-sloping portion of the ST segment-T wave complex; this is a very important electrocardiographic feature used to distinguish BER-related ST segment elevation from ST segment elevation associated with AMI (Figure 5 and 6A). The ST segment elevation encountered in BER is usually less than 2 mm but may approach 5 m m in certain individuals. Eighty percent to 90% of individuals demonstrate ST segment elevation less than 2 mm in the precordial leads and less than 0.5 mm in the limb leads; only 2% of cases of BER manifest ST segment elevation greater than 5 ram. x4,23 The J point itself is frequently notched or irregular in contour and is considered highly suggestive, but not diagnostic, of BER (Figure 6B). 13A424 Prominent T waves of large amplitude and slightly asymmetric morphology are also encountered; the T waves may appear "peaked," suggestive of the hyperacute T wave encountered in patients with AMI. The T waves are concordant with the QRS complex and are usually found in the precordial leads (Figures 2 through 6). The height of the T waves in BER ranges from approximately 6.5 m m in the precordial distribution to 5 mm in the limb leads. 13,14,18,2~ The degree of ST segment elevation related to BER is usually greatest in the mid to left precordial leads (leads V2 to Vs). The ST segments of the remaining electrocardiographic leads are less often elevated to the extent observed in leads V2 through Vs. The limb leads (I, II, III, aVL, and aVF) show ST segment elevation less often. One large series reported that the limb leads revealed ST segment elevation in only 45% of cases of BER. Lead aVR does not show ST segment elevation caused by BER. 23 "Isolated" BER in the limb leads, ie, no precordial ST segment elevation, is a very TABLE2. Electrocardiographic Criteria Suggestive of BER Widespread ST segment elevation most prominent in midprecordial leads (precordial leads >> limb leads) J point elevation Concavity of initial up-sloping portion of ST segment Notching or irregular contour of J point Prominent, concordant T waves (large amplitude) Relatively fixed/constant pattern Reduction in ST segment elevation with sympathomimetic factors

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FIGURE 6. (A) Single electrocardiographic complex demonstrating BER and two characteristic features including J point elevation (arrow) and concavity of the initial, up-sloping portion of the ST segment (notched area). (B) Single electrocardiographic complex demonstrating BER and the characteristic notching or irregularity at the J point (indicated by arrow). rare finding. 14,23 Such "isolated" ST segment elevation in the inferior (II, III, and aVF) or lateral (I and aVL) leads should prompt consideration of another explanation for the observed ST segment abnormality. Lastly, the chronic nature of the ST segment elevation is helpful in the diagnosis of BER. Patients tend to demonstrate the BER pattern consistently over time in most cases. Exceptions to this statement, however, must be made. Certain individuals, when electrocardiographically observed over prolonged periods, will demonstrate a changing magnitude of ST segment elevation with transient fluctuations in the pattern. The magnitude of BER may also lessen over time as the patient ages. In 25% to 30% of patients with BER previously seen on the ECG, additional electrocardiographic analysis many years later will reveal a complete disappearance of the pattern? 4,23 The electrocardiographic differential diagnosis of ST segment elevation (Figure 1, Table 1) not only includes the benign variant BER but also potentially more malignant syndromes ranging from acute pericarditis and left ventricular hypertrophy to AMI and LBBB. The emergency physician is quickly able to discard LBBB or another intraventricular conduction abnormality as a cause of ST segment elevation in the chest pain patient with possible BER by noting a normal QRS complex duration, and can rule out left ventricular hypertrophy by noting the absence of significant forces (ie, large amplitude of Q and R waves in leads V1 and V6, respectively). The electrocardiographic differential diagnosis can be further narrowed by deleting left ventricular aneurysm from the list if the patient does not have a history of myocardial infarction. After such consideration, AMI, BER, and acute pericarditis are the remaining electrocardiographic syndromes on the list of possibilities responsible for ST segment elevation. Acute pericarditis and BER are often difficult to distinguish on the ECG. The ST segment elevation encountered in the two syndromes is similar; in both, there is a concavity of the initial, up-sloping portion of the ST segment-T wave complex. Therefore, an analysis of this portion of the cardiac electrical cycle will not be helpful in determining the electrocardiographic cause of the ST segment elevation between these two entities. The PR segment is not infrequently depressed in patients with early pericarditis, particularly in Iead V6; the PR segment is also elevated in lead aVR

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in such instances. The PR segment is usually normal in BLUR.25'26 The electrocardiographic changes associated with

early pericarditis--in particular, ST segment elevation commonly encountered in stage I--evolve in most cases over several hours to several days, whereas the ST segment elevation seen in BER remains relatively constant over this same time frame. 27 The ST segment elevation seen in acute pericarditis tends to be more widespread across the ECG with ST segment abnormalities noted in both the precordial and limb leads; isolated pericarditis, however, does occur. 25'26'28 The T wave in acute pericarditis frequently is of normal amplitude and morphology, whereas the T wave in BER is frequently altered as noted above. The ratio of the ST segment elevation to the height of the T wave (ST/T) is also a helpful guide; a ratio greater than 0.25 in lead V6 strongly suggests pericarditis, z8 In the setting of ST segment elevation, the distinction of BER from AMI is based on several electrocardiographic factors, including an analysis of the ST segment-T wave complex waveform, the presence of reciprocal change, and evolutionary changes. At times, this distinction is difficult; Sharkey et al la noted that approximately 30% of patients who incorrectly received thrombolytic therapy for presumed AMI actually had BER on the ECG and a noninfarction chest pain syndrome. The initial, up-sloping portion of the ST segment-T wave complex is concave in BER, compared with either a flattened or a convex pattern observed in the AMI patient. This rnorphologic observation should only be used as a guideline. As with most guidelines, it is not infallible; patients with ST segment elevation caused by AMI may demonstrate transient concavity of this portion of the waveform. 25 Reciprocal change, defined as ST segment depression in leads distant from the area of acute infarction, is a very useful electrocardiographic finding for identification of the AMI case. 9 Reciprocal change is not encountered in patients with BER; the electrocardiographic finding of ST segment depression greater than 1 mm in a patient with ST segment elevation on the ECG should suggest the possibility of AMI. 26 The combined findings of ST segment elevation greater than 1 mm in two anatomically contiguous leads and reciprocal ST segment depression increase the diagnostic accuracy to over 90% that the ST segment elevation is the result of AMI. 9 The addition of Q waves to the findings of reciprocal change and ST segment elevation also strongly suggests the possibility ofAMI. 26 Lastly, the performance of serial ECGs may demonstrate the dynamic electrocardiographic changes usually encountered in acutely ischemic patients, thus assisting in the identification of either AMI or BER. 25 Waveform abnormalities associated with BER are relatively stable and are unlikely to change over the short term in the ED, compared with the dynamic electrocardiographic findings associated with acute ischemic cardiac disease. Further, a comparison to previous ECGs, if available, provides an invaluable clue to the patient's current electrocardiographic status. Recall when making comparisons to past electrocardiographic studies that certain patients with BER will either have transient alterations, if not complete resolution, in the degree of BER expression on the ECG. Reliance on the timely availability of past ECGs as a

primary clinical tool rather than a sound knowledge of the ECG in patients with ST segment elevation and its various causes, however, is not advised.

CONCLUSION

The syndrome of BER is considered to be a normal variant, not indicative of underlying cardiac disease, and electrocardiographically includes diffuse or widespread ST segment elevation, upward concavity of the initial portion of the ST segment, notching or slurring of the terminal QRS complex, and symmetric, concordant T waves of large amplitude. BER has been reported in both sexes, in all age groups, and in persons of multiple ethnic backgrounds. The general population will reveal BER in approximately 1% of cases, whereas ED chest pain patients will demonstrate such ST segment elevation in up to 48% of instances. The emergency physician will encounter BER on the ECG on a daily basis. The importance of the pattern is found not in its presence--it does not indicate underlying cardiac disease. Rather, the emergency physician must recognize this pattern in chest pain patients as BER and not misidentify it as AMI--a not uncommon event. Lastly, BER is described as a normal variant pattern. Its presence, like the normal or nondiagnosfic ECG, does not rule out the possibility of an early acute coronary ischemic event in a patient experiencing chest pain or other anginal equivalent complaints. Disposition decisions and therapeutic judgments, short of thrombolysis, must be made based on the particular patient encountered, the history provided, and the examination observed.

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