Prevalence of sensing abnormalities in dual chamber implantable cardioverter defibrillators

Background: The clinical efficacy of ICD therapy depends on accurate sensing of intracardiac signals and sensing algorithms. We investigated the occurrence of sensing abnormalities in patients with dual chamber ICDs. Methods: The study group consisted of all patients with dual chamber ICDs enrolled in the LESS trial and patients implanted with dual chamber ICDs at a single center between January 1997 and July 2000. Electrograms of spontaneous ventricular arrhythmias requiring device intervention were analyzed. Results: A total of 48 patients met the criteria for enrollment. Among the 244 episodes, 215 (88%) were due to ventricular tachycardia and 29 (12%) were due to ventricular fibrillation. Overall undersensing was infrequent with 12 (20%) patients exhibiting on average 2.2 undersensed beats during 26 episodes of ventricular arrhythmias. There was no delay in therapy due to undersensing. Oversensing occurred in 5 (10%) patients resulting in 13 (2.7%) episodes of inappropriate therapy. None of the patients had any lead abnormal ities and oversensing resolved after device reprogramming in 4 patients while 1 patient required a separate rate sensing lead. Among patients with oversensing, 4 out of 5 were pacing before the index event while among patients with no oversensing only 5 out of 42 were pacing (P < 0.001). Conclusions: Dual chamber ICDs demonstrate outstanding accuracy of sensing. However, because of the selection of patient population requiring more frequent pacing, oversensing occurs with a significant frequency. Meticulous evaluation in such patients is necessary to minimize the likelihood of oversensing and inappropriate shocks.