Effects of Cardiac Resynchronization Therapy on the Arrhythmic Substrate in a Patient with Long QT and Torsades de pointes

We describe a patient with torsades de pointes (TdP) who was implanted with cardiac resynchronization therapy defibrillator (CRT-D). At the time of CRT-D implantation, left ventricular (LV) epicardial pacing exacerbated TdPs and developed into electrical storm, which was triggered even by biventricular pacing. We needed to inactivate the LV lead for 2 weeks. At the next device check testing of LV pacing still induced TdPs, whe reas biventricular pacing did not. After starting the continuous biventricular pacing no ventricular arrhythmias happened, and furthermore the QT intervals prolonged by LV pacing were obviously shortened only after 2 weeks as ventricular systolic function recovered. Then even continuous LV alone pacing induced no TdP. These findings indicate novel electrical effects of cardiac resynchronization therapy.