QT Prolongation After His Bundle Pacing: What Is the Mechanism?

An 82-year-old woman with nonischemic cardiomyopathy underwent cardiac resynchronization therapy by the use of His bundle pacing. After the procedure, the patient had repolarization abnormality with severely prolonged QTc and anterior inferior T-wave inversions, likely resulting from memory T waves associated with the correction of long-standing left bundle branch block. These changes could be potentially arrhythmogenic. (Level of Difficulty: Intermediate.).