The atrial lead impedance was normal and the capture threshold was satisfactory. Therefore, the lead was not revised. Oversensing at the level of the atrial lead can, as in this case, cause an inappropriate automatic mode switch because of erroneous diagnosis of atrial arrhythmia. In a defibrillator, it can also interfere with discrimination based on the counts of atrial and ventricular electrograms during tachycardia. This dysfunction, if frequent, must be eliminated in a defibrillator recipient:

• By decreasing the maximum atrial sensitivity without compromising the detection of sinus rhythm, and of true atrial arrhythmias. This is generally ineffective because the amplitude of noisy signals from fractured leads or other types of interference is often large;
• By applying a discrimination scheme applicable in single chamber devices;