Objective: The decision of whether and when to replace a device in response to an "advisory" letter requires careful consideration, because device replacement carries related risks and is influenced by the clinical characteristics of the patient.

Results: The risk/benefit of device replacement depends on four parameters: expected annual sudden cardiac death rate; residual device life; difference in failure rate between the device listed on the advisory letter and the replacement device; and the replacement procedure mortality risk. Using these four factors, we have developed an equation that provides the "number needed to replace" (NNR) to save one life. Per our model, patients implanted with a device with a failure rate approaching 1% and a probability of requiring device intervention >or=25% per year-in particular, pacemaker-dependent patients-have an NNR <250. Pacemaker-dependent patients, with devices having three or more years longevity, but with device failure rates >or=0.5%, have an NNR <100. Patients with arrhythmic risk

Conclusions: Pacemaker-dependent patients and those with high arrhythmic risk (>or=25% annually) when having "advisory" devices with high failure rate (>or=1%) have an NNR <250 and, hence, could be considered for device replacement. Conversely, patients with arrhythmic risk