Special Feature

Benign Early Repolarization

By William J. Brady, MD

The syndrome of benign early repolarization (BER) electrocardiographically includes diffuse ST segment elevation (STE), 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.1

BER is a normal variant and is not indicative of underlying cardiac disease. The physiologic basis is poorly understood and remains a subject of ongoing controversy. In fact, the term "early repolarization" may be a misnomer from the electrophysiologic perspective in that one investigation found no increase in the temporal overlap between termination of ventricular depolarization and onset of repolarization—the theoretical basis of BER—in patients with the electrocardiographic pattern. Suggested mechanisms of BER include early subepicardial repolarization, earlier repolarization of the anterior wall of the left ventricle (LV) compared to the posterior wall, and regional differences in sympathetic/parasympathetic tone. BER has been reported in men and women of all age groups and in people of varying ethnic backgrounds. The mean age is approximately 40 years, with men manifesting BER significantly more often; usually, BER is seen in patients younger than 50 years and is rarely encountered in individuals older than 70 years.2 For unknown reasons, BER may be encountered more often in young black males. The general population will have early repolarization on the ECG in approximately 1% of cases; this pattern is seen in adult emergency department (ED) patients with an increased frequency, including: 1) young males, 1-2% of cases; 2) chest pain patients, 13% of cases; and 3) chest pain patients using cocaine, 23-48% of cases.2,3

The ST segment of the cardiac electrical cycle represents the period between depolarization and repolarization of the LV. 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 includes the following characteristics: 1) STE; 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.2,4,5

The STE begins at the "J" (or junction) point—the portion of the electrocardiographic cycle where the QRS complex ends and the ST segment begins. (See Figure 1.) The degree of J point elevation is usually less than 3.5 mm; the J point itself is frequently notched or irregular in contour and is considered highly suggestive of BER. The STE morphologically appears as if the ST segment has been evenly lifted upward from the isoelectric baseline at the J point, with preservation of the normal concavity of the initial, up-sloping portion of the ST segment/T wave complex—an important electrocardiographic feature used to distinguish BER-related STE from STE associated with acute myocardial infarction (MI). The STE encountered in BER is usually less than 2 mm, but may approach 5 mm in certain individuals, with 90% of individuals demonstrating less than 2 mm STE in the precordial leads and less than 0.5 mm in the limb leads. The degree of STE related to BER is usually greatest in the mid- to left precordial leads (leads V2 to V5) with less pronounced elevations in the remaining electrocardiographic leads. "Isolated" BER in the limb leads (i.e., no precordial STE) is a rare finding and should prompt consideration of another explanation for the observed ST segment abnormality. Prominent T waves of large amplitude and slightly asymmetric morphology are also encountered; the waves may appear "peaked," suggestive of the hyperacute T wave encountered in patients with acute MI. The T waves are concordant with the QRS complex and are usually found in the precordial leads. The height of the T waves in BER ranges from approximately 6.5 mm in the precordial distribution to 5 mm in the limb leads.2,4,5 (See Figure 2.)

The electrocardiographic differential diagnosis of STE not only includes the benign variant BER but also potentially more malignant syndromes ranging from acute pericarditis and LVH to acute MI and LBBB. The emergency physician is quickly able to discard certain causes of STE in the chest pain patient with possible BER: 1) LBBB and other intraventricular conduction abnormalities by noting a normal QRS complex duration; 2) LVH with the absence of significant electrical forces in leads V1 and V6; and 3) left ventricular aneurysm if the patient lacks a history of MI. Acute pericarditis and BER are often difficult to distinguish on the ECG in that the STE encountered in the two syndromes is similar, both demonstrating a concavity of the initial, up-sloping portion of the ST segment/T wave complex.6,7 Electrocardiographic features suggestive of BER of potential use in making this distinction include: 1) a normal PR segment (the PR segment is often depressed in patients with early pericarditis, particularly in lead V6, with reciprocal PR segment elevation in lead aVR); 2) the static nature of the electrocardiographic changes (changes in the STE and other abnormalities evolve relatively rapidly in early pericarditis); 3) prominent, hyperacute T waves (the T wave in acute pericarditis frequently is of normal amplitude and morphology); and 4) the STE/T wave height ratio of less than 0.25 in lead V6 (a ratio greater than 0.25 strongly suggests pericarditis).6,7 The differentiation of STE due to BER from that associated with MI (yet another challenge) is made using several electrocardiographic issues, all suggestive of the early repolarization pattern, including: 1) the initial, up-sloping portion of the ST segment/T wave complex is concave in BER (compared to the either flattened or convex pattern observed in the acute MI patient); 2) reciprocal change is not encountered in patients with BER (considering the ECG of a patient with STE, ST segment depression greater than 1 mm in leads distant from the area of acute infarction should suggest the possibility of acute MI; and 3) the lack of evolving changes in the STE/T wave morphology (the performance of serial ECGs may demonstrate the dynamic electrocardiographic changes usually encountered in acute MI patients.6,7 (See Figure 3.)

The importance of the BER pattern is found not in its presence—it does not indicate underlying cardiac disease. Rather, the emergency physician must recognize this pattern in the chest pain patient as BER and not mistake it for acute MI. BER is described as a normal variant pattern. Its presence, like the normal or nondiagnostic 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 upon the individual patient.

References

1. Shipley RA, Hallaran WR. The four-lead electrocardiogram in two hundred normal men and women. Am Heart J 1936;11:325-345.

2. Mehta MC, Jain AC. Early repolarization on scalar electrocardiogram. Am J Med Sci 1995;309:305-311.

3. Parisi A, et al. The spectrum of ST segment elevation in the electrocardiograms of healthy adult men. J Electrocardiography 1971;4:136-144.

4. Golderger AL. Myocardial infarction: Electrocardiographic differential diagnosis, 4th ed. Mosby; St. Louis, 1991:100-126.

5. Aufderheide TP, Brady WJ. Electrocardiography in the patient with myocardial ischemia or infarction. In: Gibler WB, Aufderheide TP, eds. Emergency Cardiac Care, 1st ed. Mosby; St. Louis 1994:169-216.

6. Spodick DH. Differential diagnosis of the electrocardiogram in early repolarization and acute pericarditis. N Engl J Med 1976;295:523-526.

7. Glinzton LE, Laks MM. The differential diagnosis of acute pericarditis from the normal variant: New electrocardiographic criteria. Circulation 1982;65:1004-1009.