Noise, artifact, and oversensing related inappropriate ICD shock evaluation: ALTITUDE noise study

Approximately 12-21% of implantable cardioverter defibrillator (ICD) patients receive inappropriate shocks. We sought to determine the incidence and causes of noise/artifact and oversensing (NAO) resulting in ICD shocks.

A random sample of 2,000 patients who received ICD and cardiac resynchronization therapy defibrillator shocks and were followed by a remote monitoring system was included. Seven electrophysiologists analyzed stored electrograms from the 5,279 shock episodes. Episodes were adjudicated as appropriate or inappropriate shocks.

Of the 5,248 shock episodes with complete adjudication, 1,570 (30%) were judged to be inappropriate shocks. Of these 1,570, 134 (8.5%) were a result of NAO. The 134 NAO episodes were determined to be due to external noise in 76 (57%), lead connector-related in 37 (28%), muscle noise in 11 (8%), oversensing of atrium in seven (5%), T-wave oversensing in two (2%), and other noise in one (1%). The ICD shock itself resulted in a marked decrease in the level of noise in 60 of 134 (45%) NAO episodes, and the magnitude of this effect varied with the type of NAO (58% for external noise, 35% for muscle, 27% for lead/connector, and 0% for oversensing; P = 0.03). There was no significant difference in NAO likelihood based on type of lead (integrated bipolar 89/1,802 vs dedicated bipolar 9/140, P = 0.67).

External noise and lead/connector noise were the primary causes, while T-wave oversensing was the least common cause of NAO resulting in ICD shock. Noise/artifact decreased immediately after a shock in nearly half of episodes. The specific ICD lead type did not impact the likelihood of NAO.