Variability of atrial sensing during exercise in a patient with a dual chamber ICD caused inappropriate ICD discharges

We present the case of a patient with a dual chamber implantable cardiovert er defibrillator (ICD) who experienced inappropriate ICD discharges during exercise. Interrogation of the ICD revealed intermittent atrial undersensin g during exercise that was responsible for the erroneous classification by the ICD of sinus tachycardia as ventricular tachycardia. Monitoring of the intracardiac electrograms and Marker Channels during an exercise test confi rmed a marked decrease in P wave amplitude during exercise. By increasing t he atrial sensitivity setting the problem wets resolved.