Limitation of programmed alerts to predict ICD lead failures.

A 75-year-old man with a Sprint Fidelis ICD lead (Medtronic Inc., Minneapolis, MN, USA) experienced inappropriate shocks after sudden failure of the right ventricular (RV) pace-sense connector resulting in noise. Interrogation of the implantable cardioverter-defibrillator pulse generator revealed that the 3 AM daily measurement of RV pacing impedance was slightly higher (750 Omega) than the baseline (approximately 450-550 Omega)(although below the recommended alert level of 1,000 Omega) and markedly higher at 4 AM (1,552 Omega) when therapies were delivered. The event occurred before the patient could be alerted by the audible tones. Thus, the manufacturer's recommended impedance monitoring alert parameters will not predict all lead failures.