ECG predictors of T wave oversensing in subcutaneous implantable cardioverter defibrillators

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Abstract

Background

T wave oversensing (TWOS) is the commonest cause of inappropriate shocks in subcutaneous implantable cardioverter defibrillators (S-ICDs). We hypothesise that predictors of TWOS can be derived from surface ECG parameters.

Methods

In a cohort of SICD recipients in two UK centres, all patients who had TWOS (study group) were compared to all those who had not (control group). The pre-implant screen was scanned and the R wave, T wave amplitudes, QRS interval, time to peak T wave, QT interval and R:T ratio was measured using digital callipers. Logistic regression was performed to identify ECG predictors of TWOS.

Results

One hundred one patients were studied. Six (5.9%) had TWOS. The mean age of the population was 58.6 ± 18 years and the median follow-up was 19.5 months. By univariate analysis, the predictors of TWOS are QRS duration (140.7 ± 28.7 vs. 105.9 ± 24.6, P = 0.007), time to peak T wave (corrected for heart rate, pTc) (403.9 ± 22.6 vs. 347.8 ± 41.4, P = 0.006), QTc interval (500.4 ± 41.2 vs. 446.8 ± 49.7, P = 0.021), and R:T ratio (3.5 ± 1.1 vs. 9.5 ± 13.2, P = 0.034). By multivariate analysis, time to pTc is the most predictive of TWOS. A time to pTc of 390 ms cut-off point provided a sensitivity 38.5%, a specificity of 98.9%, a positive predictive value for TWOS of 83.3%, and a negative predictive value of 91.6% (AUC = 0.687).

Conclusion

In this study, time to pTc is the most powerful ECG predictor of TWOS.

Introduction

The S-ICD has a proven track record in delivering lifesaving and effective shock therapy for patients with lethal arrhythmias [1]. The S-ICD performs well in a head-to-comparison with transvenous implantable cardioverter defibrillators in discriminating supraventricular tachyarrhythmias from ventricular tachyarrhythmias [2], though results of a randomised trial comparing S-ICD to transvenous ICDs have yet to be published. Clinical experience has demonstrated that the S-ICD has limited sensing specificity due to failure to appropriately discriminate/sense electrical signals unrelated to supraventricular tachycardia [1], [3]. Indeed, registry data have reported rates of inappropriate therapy of approximately 7% per annum, mostly due to T wave oversensing and undersensing of the cardiac signal [2], [3], [4]. This rate is considerably higher than rates of inappropriate shocks reported in contemporary TV-ICD device [5].

The pre-implant ECG screen is an integral part of selecting potential S-ICD recipients and excluding patients whose QRS-T wave morphology does not satisfy the screening tool. As the S-ICD employs an ECG morphology-based sensing algorithm, we hypothesise that ECG markers may prove be useful predictors of T wave oversensing.

Section snippets

Methods

Patients who had successfully passed the pre-implant ECG screen and had an S-ICD implanted at two UK centres were studied. The study group comprised patients who had experienced TWOS and had received an inappropriate shock due to TWOS. Patients with oversensing of the cardiac signal were excluded if they had experienced oversensing due to noise, a change in QRS morphology (e.g. monomorphic ventricular tachycardia or aberrantly conducted beats). Patients who had not received an inappropriate

Results

Complete datasets could be recorded in 101 patients, 10 (9.9%) of whom were not enrolled in the EFFORTLESS registry. The mean age of the population was 58.6 ± 18 years and the S-ICD was implanted for a primary prevention indication in 75 (75%). Mean follow-up was 19.5 months. In total, 93% had dual zone programming, the most frequent setting being conditional zone 200 bpm and shock zone of 220 bpm in 54/94 (57.4%). The primary vector was programmed in 49 (48.5%), the secondary vector in 44 (43.6%)

Discussion

In this study, 5.9% of patients experienced TWOS over a median follow up of 19.5 months with a mean of 1.8 shocks per patient with TWOS. This incidence is similar to that for inappropriate shocks reported in the Effortless registry [1], [3], [4], [6]. Patients who experienced TWOS had significantly broader QRS complexes, lower R:T ratios, and greater time to peak T wave amplitude and QTc. On analysis using a univariate statistical model, all these parameters were predictive of TWOS. With

Conclusion

In this study, the ECG parameters that predict TWOS are QRS duration, time to peak T wave, QT interval and R:T ratio with time to pTc being the most powerful predictor of TWOS on multivariate analysis. These findings need to be validated in a larger cohort of S-ICD patients.

Author contributions

DW: Concept and study design, data collection, data analysis and data interpretation, drafting article, statistics, and approval of article.

GL: Data collection, critical revision of article and approval of article.

CB: Funding secured by CB, critical revision of article and approval of article.

JMM: Drafting article critical revision of article and approval of article.

Funding source

DGW was supported by an educational grant from Medtronic, Inc. Funding for the study was provided by the Russells Hall Cardiac Rhythm Management Research Fund.

Conflicts of interest

DW has received an educational grant from Medtronic UK.

JM has received Honoraria and research grants from Medtronic, St Jude, Sorin, and Boston Scientific.

JM is now the senior medical director for Boston Scientific.

Acknowledgments

The National Research Ethics Service committee for the East of England approved the study (14/EE/0197) and the study has therefore been performed with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.

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This author takes responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation.

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