When Is it Safe not to Replace an Implantable Cardioverter Defibrillator Generator?

In most reports on patients receiving implantable cardioverter defibrillators. shocks were received mainly during the first 2 to 3 years. Thus, the question had been raised as to the need for device replacement after 3 or 4 years if no shocks had been received. In order to answer this question, shock experience in 184 putients receiving the implantable cardioverter defibrillator was analyzed. Patients were followed for a mean of 24 ± 18.7 months. A patient's shock was judged to be appropriate if there was electrocardio-graphic documentation of sustained ventricular tachyarrhythmia at the time of shock or if it was preceded by sudden onset of presyncopal or syncopal symptoms. The majority of patients had coronary artery disease. In approximately two-thirds of patients, left ventricular ejection fraction was below 40%. One hundred fourteen patients had inducible sustained monomorphic ventricular tachycardia. On follow-up, there were 29 deaths, five of which were sudden. Sixty-eight patients received an appropriate shock during follow-up (37%). Over 90% of these 68 received their first shock within the 2 years after implant. The actuarial risk of receiving an appropriate shock by the fifth year after implant was 69%. Conversely, 31% of patients who survived 5 years had not received an appropriate shock. Hazard analysis indicates that there is a high incidence of first appropriate shock during the year following implant. Subsequently, the incidence dropped to a relatively steady rate with a rise in this rate during the fifth year. This analysis suggested a bimodal distribution of appropriate shocks. The results indicate that implantable cardioverter defibrillator generators should be replaced even up to the fifth year despite the fact that a patient had not received an appropriate shock.