Mechanistic heterogeneity of junctional ectopic tachycardia in adults

Spontaneous junctional ectopic tachycardia (JET) in adults is rare, and the electrophysiologic mechanism has not been definitively established. Two patients who presented with JET, not associated with cardiac surgery, were evaluated and studied in the electrophysiology laboratory, and electrophysiologic and pharmacologic maneuvers were performed to assess the mechanisms of tachycardia. The junctional tachycardia in Patient 1 manifested characteristics consistent with a triggered mechanism, and was sensitive to adenosine. The junctional tachycardia in Patient 2 manifested characteristics consistent with abnormal automaticity, and was insensitive to adenosine. This is a rare clinical example of abnormal automaticity. These two cases demonstrate that JET may be due to multiple mechanisms, with data consistent with triggered activity and abnormal automaticity.