Puzzling pacing threshold in a patient with cardiac resynchronization therapy device.

CASE A man in his sixties with dilated cardiomyopathy was admitted to our hospital for the replacement of his cardiac resynchronization therapy （CRT） device. Although his condition had been initially improved after CRT implantation and he had taken an optimized medication regimen and undergone regular device follow-up, echocardiography showed progressive dyspnea and edema with decreased left ventricular ejection fraction （LVEF）. During the procedure,his CRT was disconnected and tested using an analyzer module 2290 of the Medtronic 2090 programmer （Medtronic Inc., USA）, and a temporary pacemaker （Model 5318;Medtronic Inc., USA） and high pacing thresholds （＞5 V/0.5ms） were noted for both ventricles （Figures 1 A and B）.