As already discussed in part, this syndrome is characterized by a great variability in the electrocardiographic pattern. The electrocardiogram may be completely abnormal at times, but completely normal at others . This variability has many causes and several explanations. Autonomic changes and body temperature influence the electrocardiogram. So do spontaneous or induced changes in heart rate. An artificial increase in heart rate (by atrial pacing) decreases ST segment elevation, while a decrease in heart rate increases it. These data are again in agreement with the loss of the dome of the action potential at epicardial level as the cause of ST segment elevation. Ito becomes more prominent at slow rates increasing heterogeneity and ST segment elevation. These data are also in agreement with the clinical observations documenting a bradycardia -dependency and a higher incidence of sudden death during sleep in patients with this syndrome.

Normalization of the ST segment during exercise is the most common finding in patients with this syndrome. These are logical findings because both an increase in heart rate and adrenergic stimulation decrease ST segment elevation.