Inappropriate shocks from implanted cardioverter defibrillators caused by sensing of diaphragmatic myopotentials

Inappropriate shocks remain one of the major problems associated with the u se of implantable cardioverter defibrillators (ICD). We describe 3 patients who had inappropriate shocks due to oversensing of diaphragmatic myopotent ials. In all 3, oversensing could be demonstrated during deep inspiration o r Valsalva maneuver. The problem was remedied in one by insertion of a sepa rate rate sensing lead in the right ventricular outflow tract, in the secon d by decreasing the rate of antibradycardia pacing of the ICD, and in the t hird by decreasing the sensitivity of the ICD. We conclude that the possibi lity of sensed diaphragmatic myopotentials should be considered at the time of ICD implant so that appropriate preventive measures can be taken.