Prevalence of sensing abnormalities in dual chamber implantable cardioverter defibrillators

Abstract

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 abnormalities 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.

Figure 1

Intracardiac electrogram from a patient with a dual chamber ICD showing the atrial, ventricular sense, and ventricular shock electrograms. Baseline rhythm is sinus with atrial sensing and ventricular pacing. “Noise” on the ventricular sensing channel leads to inhibition of pacing, spurious VF detection and inappropriate shock.

Figure 2

Intracardiac electrogram of a VF episode in a patient with dual chamber ICD. During initial detection of VF, two beats are undersensed (solid arrows). Both the undersensed beats are small in amplitude and immediately follow large amplitude beats. There are no channel markers corresponding to the undersensed beats and the next beat in each case falls out of VF zone (open arrows). There is no delay in detection. The device charges and delivers an 11 J shock that is unsuccessful, but the arrhythmia terminates spontaneously.