Nonadequate
arrhythmia detection and delivery of electrical
therapy is still a main problem in current
implantable cardioverter defibrillator therapy. Besides supraventricular arrhythmias extra-cardiac biosignals also can cause inadequate
shock delivery. The present study focuses on nonadequate
arrhythmia detection due to oversensing of diaphragmatic myopotentials. Their clinical characteristics, incidence and management are presented. Three-hundred-eighty-four recipients of a transvenous cardioverter-
defibrillator who were implanted and followed-up at our institution between October 1991 and June 1999 were enrolled. During a mean follow-up of 32+/-25 months a total number of 139 nonadequate episodes of
arrhythmia detection due to oversensing of diaphragmatic myopotentials were observed in 33 patients (8.6%). In 11 patients a total of 32 high energy
shock deliveries occurred. Oversensing of diaphragmatic myopotentials was primarily observed in patients implanted with
defibrillator leads providing "integrated bipolar" sensing. The vast majority of nonadequate
arrhythmia detection were observed during intrinsic
bradycardia heart rate and/or antibradycardia pacing. Electrical lead failure was ruled out in every patient. In 90% of the patients with a cardioverter-
defibrillator providing programmable maximal sensitivity (n=16), the reduction of maximum sensitivity was effective in preventing further episodes of nonadequate
arrhythmia detection. In 48% of the patients with devices without programmable maximal sensitivity (n=17),
surgery revision was necessary to solve the problem.