The early repolarization pattern on the electrocardiogram was long considered a benign variant. Recent evidence suggests a subset of patients in whom it signifies an increased risk of sudden cardiac death. I blogged on that topic here and here.
A recent study addressed electrocardiographic distinctions:
Conclusions—ST-segment morphology variants associated with ER separates subjects with and without an increased risk of arrhythmic death in middle-aged subjects. Rapidly ascending ST segments after the J-point, the dominant ST pattern in healthy athletes, seems to be a benign variant of ER.
On the other hand, horizontal or descending ST segments signify an increased risk of death.