Background: Implantable cardioverter-defibrillators (ICDs) can provide life-saving therapies for ventricular arrhythmias. Arrhythmia induction and defibrillation threshold testing is often performed at implantation and postoperatively during long-term follow-up to ensure proper device function.
Methods: We sought to evaluate the prevalence and predictors of occult device malfunction at follow-up defibrillation testing in asymptomatic individuals. A cohort of 853 patients underwent 1,578 defibrillation tests during the 13-year study period. Defibrillation efficacy was evaluated primarily by the two-shock (2S) method, with an adequate safety margin ≥10 joules (J) less than the maximum energy delivered by the ICD.
Results: A total of 38 testing failures requiring intervention were discovered during testing (2.4% of all tests). There were 11 ICD system failures resulting in failure to defibrillate, six with underdetection of ventricular fibrillation, and 21 clinically significant increases in defibrillation threshold. There was a higher incidence of failure in older ICD systems (1996–2002) compared to newer ICD systems (2003–2009), reaching statistical significance (3.6% vs 1.0%; P < 0.01). There were 178 subjects (20.8%) with a >20-J safety margin on previous testing, detected R waves >7.0 mV, and all system components implanted after 2003 at the time of testing who did not have any testing failures (0% vs 5.6%; P < 0.01).
Conclusion: Postoperative defibrillation testing identifies a small number of ICD malfunctions in asymptomatic individuals. ICD testing failure is seen more frequently in older systems and in those with borderline results from prior interrogation or testing. These findings suggest that serial postoperative defibrillation testing is not indicated in asymptomatic patients without suspicion for specific problems. (PACE 2011; 34:186–192)